Recent Advancements in Photocatalysis Coupling by External Physical Fields

: Photocatalysis is one of the most promising green technologies to utilize solar energy for clean energy achievement and environmental governance, such as artiﬁcial photosynthesis, water splitting, pollutants degradation, etc. Despite decades of research, the performance of photocatalysis still falls far short of the requirement of 5% solar energy conversion efﬁciency. Combining photocatal-ysis with the other physical ﬁelds has been proven to be an efﬁcient way around this barrier which can improve the performance of photocatalysis remarkably. This review will focus on the recent advances in photocatalysis coupling by external physical ﬁelds, including Thermal-coupled photocatalysis (TCP), Mechanical-coupled photocatalysis (MCP), and Electromagnetism-coupled photocatalysis (ECP). In this paper, coupling mechanisms, materials, and applications of external physical ﬁelds are reviewed. Speciﬁcally, the promotive effect on photocatalytic activity by the external ﬁelds is highlighted. This review will provide a detailed and speciﬁc reference for photocatalysis coupling by external physical ﬁelds in a deep-going way.


Introduction
In order to achieve the carbon emission reduction target, photocatalysis has been widely considered to be a promising technology.After half a century of development, photocatalysis has tended to increasingly maturate, especially in many fields, such as pollutant degradation, water splitting, CO 2 reduction, and desulfurization [1][2][3][4][5][6][7][8][9][10][11].However, the main reason limiting photocatalytic technology from basic research to practical application is that the conversion efficiency of solar energy is still very low, which is far from meeting the requirements of commercial applications [12,13].At present, there are two main ways to break the bottleneck of the efficiency of photocatalytic energy conversion: one is to enhance the absorption rate of the solar spectrum and the other is to efficiently promote the separation of photogenerated carriers.
Techniques for modification of photocatalytic materials, such as doping, compositing other materials, cocatalyst loading, morphology controlling, etc., have been confirmed to improve light absorption and photogenerated carrier separation efficiently [14][15][16][17][18].However, the energy conversion efficiency is still very low although it has been improved to some extent by these modifications.Therefore, it is necessary to find a new way to achieve a breakthrough in photocatalytic performance.Studies have shown that photocatalytic activity can be greatly improved by adding other physical fields to the photocatalytic reaction process [19,20].Generally, the assisted external field can provide additional energy to the photocatalytic system, which will power photogenerated charge separation and thereby improve the efficiency of photocatalysis.According to the energy form, as shown in Figure 1 the assisted physical field can be divided into the thermal field, mechanical field, and, electromagnetic field.In terms of energy generation types, it can also be divided thereby improve the efficiency of photocatalysis.According to the energy form, as shown in Figure 1 the assisted physical field can be divided into the thermal field, mechanical field, and, electromagnetic field.In terms of energy generation types, it can also be divided into infrared thermal effect, microwave thermal effect, ultrasonic cavitation effect, friction electrostatic effect, external controllable electromagnetic field effect, and so on.One of the most common assisted physical fields is the thermal field.For example, in the photocatalytic reaction, most of the infrared light in the sunlight cannot be effectively used, which will dissipate into heat.Since infrared light and heat are inseparable, the infrared absorbing material can be composited into the photocatalytic material to collect the infrared band energy promoting the separation of photogenerated carriers.In addition, other non-contact external fields, such as the electric field, magnetic field, microwave field, and ultrasound field, can significantly improve the efficiency of the photocatalytic system, which have different mechanisms and respective advantages.Therefore, we will provide a detailed and specific reference for photocatalysis coupling by external physical fields, including thermal-coupled photocatalysis (TCP), mechanical-coupled photocatalysis (MCP), and electromagnetism-coupled photocatalysis (ECP).This paper will mainly focus on coupling mechanisms, materials, and applications of external physical fields.Specifically, the promotive effect on photocatalytic activity by the external fields will be highlighted.

Thermal-Coupled Photocatalysis (TCP)
To break through the existing bottleneck of photocatalytic activity, thermal energy has been introduced into photocatalysis systems.Generally, traditional photothermal catalysis can be divided into three types [19,[21][22][23][24][25][26][27]: (1) thermal-coupled photocatalysis (TCP); (2) photo-coupled thermocatalysis (PCT); and (3) photothermal co-catalysis (PTC).As for PCT, light is not the main driving force of the reaction, which is used only to provide heat and promote the thermocatalytic process.Therefore, we will focus on the TCP and PTC, where light is the main driving force for the reaction.Compared with conventional photocatalysis, TCP can combine the advantages of thermal and light energy, thereby greatly improving photocatalytic activity.The mechanism of efficiently photocatalytic activity for TCP can be summarized as follows: (1) thermal energy may help generate electron-hole pairs; (2) thermal energy can re-emit the trapped electrons and drive them rapidly for transfer to the surface of the photocatalyst; (3) thermal energy can increase the collision rate with more efficient collisions of molecules; and (4) the high surface temperature of photocatalyst will promote the dissociative adsorption of reactant molecules.Here, we will try to summarize the current research progress of TCP including the primary source of thermal energy, materials for TCP and, the main applications of TCP.Therefore, we will provide a detailed and specific reference for photocatalysis coupling by external physical fields, including thermal-coupled photocatalysis (TCP), mechanicalcoupled photocatalysis (MCP), and electromagnetism-coupled photocatalysis (ECP).This paper will mainly focus on coupling mechanisms, materials, and applications of external physical fields.Specifically, the promotive effect on photocatalytic activity by the external fields will be highlighted.

Thermal-Coupled Photocatalysis (TCP)
To break through the existing bottleneck of photocatalytic activity, thermal energy has been introduced into photocatalysis systems.Generally, traditional photothermal catalysis can be divided into three types [19,[21][22][23][24][25][26][27]: (1) thermal-coupled photocatalysis (TCP); (2) photo-coupled thermocatalysis (PCT); and (3) photothermal co-catalysis (PTC).As for PCT, light is not the main driving force of the reaction, which is used only to provide heat and promote the thermocatalytic process.Therefore, we will focus on the TCP and PTC, where light is the main driving force for the reaction.Compared with conventional photocatalysis, TCP can combine the advantages of thermal and light energy, thereby greatly improving photocatalytic activity.The mechanism of efficiently photocatalytic activity for TCP can be summarized as follows: (1) thermal energy may help generate electron-hole pairs; (2) thermal energy can re-emit the trapped electrons and drive them rapidly for transfer to the surface of the photocatalyst; (3) thermal energy can increase the collision rate with more efficient collisions of molecules; and (4) the high surface temperature of photocatalyst will promote the dissociative adsorption of reactant molecules.Here, we will try to summarize the current research progress of TCP including the primary source of thermal energy, materials for TCP and, the main applications of TCP.

The Primary Source of Thermal Energy 2.1.1. External Direct Heating
The simplest method to realize TCP is to introduce an external heating process through traditional heat convection, heat conduction, and heat radiation.Increasing the external temperature can inhibit the recombination of photogenerated carriers and reduce the charge transfer resistance, thereby increasing the photocatalytic reaction rate.Huang et al. synthesized Co 0.85 Se/Mn 0.3 Cd 0.7 S nanorods for photocatalytic H 2 production [28].As shown in Figure 2a, the catalyst itself has no thermal catalytic activity.The H 2 production was improved with the increase in temperature.Jing et al. reported a Cu 2 O-rGO/TiO 2 photocatalyst whose H 2 evolution rate (17,800 µmol g −1 h −1 ) under the photothermal condition (90 • C) is 4.7 times higher than that under only photocatalytic condition (25 • C), as shown in Figure 2b [29].The photothermal effect facilitates the separation of photogenerated electron-hole pairs and simultaneously accelerates the reaction rate on the catalyst surface during H 2 evolution.Li et al. synthesized a low-cost Cu 2 O/g-C 3 N 4 heterojunction by a simple hydrothermal method and realized efficient photothermal conversion of CO 2 into ethanol [30].As shown in Figure 2c, under photothermal catalysis, the rate of ethanol is 1.89 times that of photocatalysis and 7.05 times that of thermocatalysis at 100 • C. The temperature enhanced the thermal motion of the radical, which promotes the formation of ethanol through the CH 3 dimerization.

External Direct Heating
The simplest method to realize TCP is to introduce an external heating process through traditional heat convection, heat conduction, and heat radiation.Increasing the external temperature can inhibit the recombination of photogenerated carriers and reduce the charge transfer resistance, thereby increasing the photocatalytic reaction rate.Huang et al. synthesized Co0.85Se/Mn0.3Cd0.7Snanorods for photocatalytic H2 production [28].As shown in Figure 2a, the catalyst itself has no thermal catalytic activity.The H2 production was improved with the increase in temperature.Jing et al. reported a Cu2O-rGO/TiO2 photocatalyst whose H2 evolution rate (17,800 μmol g −1 h −1 ) under the photothermal condition (90 °C) is 4.7 times higher than that under only photocatalytic condition (25 °C), as shown in Figure 2b [29].The photothermal effect facilitates the separation of photogenerated electron-hole pairs and simultaneously accelerates the reaction rate on the catalyst surface during H2 evolution.Li et al. synthesized a low-cost Cu2O/g-C3N4 heterojunction by a simple hydrothermal method and realized efficient photothermal conversion of CO2 into ethanol [30].As shown in Figure 2c, under photothermal catalysis, the rate of ethanol is 1.89 times that of photocatalysis and 7.05 times that of thermocatalysis at 100 °C.The temperature enhanced the thermal motion of the radical, which promotes the formation of ethanol through the CH3 dimerization.(a) H2-evolution rate of 7 wt% Co0.85Se/Mn0.3Cd0.7S at various reaction temperatures (5-25 °C) under visible light for 1 h (Reprinted/adapted with permission from Ref. [28].Copyright 2021, copyright Elsevier).(b) H2 production rates under light, thermal, and photothermal conditions (10 mg of 1.0%Cu2O-rGO/TiO2 was used.)(Reprinted/adapted with permission from Ref. [29].Copyright 2022, copyright Elsevier).(c) The achieved product yield of C2H6O over Cu2O/g-C3N4 at different temperatures (Reprinted/adapted with permission from Ref. [30].Copyright 2021, copyright Elsevier).

Near-Infrared Indirect Heating
Near-infrared indirect heating produces the photothermal effect by photothermal materials.Under near-infrared light irradiation, the absorbed photons could excite the electrons, which would migrate until they recombine with the holes.Therefore, there is an essential distinction between TCP via external direct heating and near-infrared indirect heating in terms of the way to enhance the photocatalytic activity.The photothermal effect can increase the temperature in a local area to induce a collective effect of multistage processes, which include charge excitation, charge carrier mobility, and reaction barriers.Photothermal material SnSe nanoparticles that serve as "hot islands" on ZnIn2S4 monolayer were proposed as an ideal model for investigating the role of the photothermal contribution in photocatalysis [31].The energetic photoexcited electrons of nanoparticle SnSe interact with the lattice to transfer their energy to phonons for photothermal conversion.Therefore, SnSe acts as a "hot island" to release thermal energy, which increases the temperature around it.Then, the increased temperature in the local area that is caused by the photothermal effect can induce a collective effect to accelerate the photocatalytic reaction of ZnIn2S4 to enhance the photocatalytic performance, as shown in Figure 3.The core-shell structured WO3/CdS photocatalyst has been reported for full-spectrum solar energy

Near-Infrared Indirect Heating
Near-infrared indirect heating produces the photothermal effect by photothermal materials.Under near-infrared light irradiation, the absorbed photons could excite the electrons, which would migrate until they recombine with the holes.Therefore, there is an essential distinction between TCP via external direct heating and near-infrared indirect heating in terms of the way to enhance the photocatalytic activity.The photothermal effect can increase the temperature in a local area to induce a collective effect of multistage processes, which include charge excitation, charge carrier mobility, and reaction barriers.Photothermal material SnSe nanoparticles that serve as "hot islands" on ZnIn 2 S 4 monolayer were proposed as an ideal model for investigating the role of the photothermal contribution in photocatalysis [31].The energetic photoexcited electrons of nanoparticle SnSe interact with the lattice to transfer their energy to phonons for photothermal conversion.Therefore, SnSe acts as a "hot island" to release thermal energy, which increases the temperature around it.Then, the increased temperature in the local area that is caused by the photothermal effect can induce a collective effect to accelerate the photocatalytic reaction of ZnIn 2 S 4 to enhance the photocatalytic performance, as shown in Figure 3.The core-shell structured WO 3 /CdS photocatalyst has been reported for full-spectrum solar energy conversion.The wrapped WO 3 with abundant oxygen vacancy can store electrons activated by UV-visible light, which can then be released by NIR light.The solar-to-hydrogen conversion efficiency under simulated solar light irradiation reaches as high as 3.00% [32].Non-precious metal co-catalysts S vacancies 1T-WS 2 , CuS, and plasmonic nanoparticles could also facilitate the driving of the photothermal effect [33,34].
Catalysts 2022, 12, x FOR PEER REVIEW conversion.The wrapped WO3 with abundant oxygen vacancy can store electron vated by UV-visible light, which can then be released by NIR light.The solar-to-hyd conversion efficiency under simulated solar light irradiation reaches as high as 3.00 Non-precious metal co-catalysts S vacancies 1T-WS2, CuS, and plasmonic nanopa could also facilitate the driving of the photothermal effect [33,34].

Microwave Indirect Heating
The effect of microwave irradiation is a combination of thermal effects and no mal microwave effects, arising from the heating rate, super-heating or ''hot spots the selective absorption of radiation by polar substances [35,36].Therefore, it is o practical significance to use the coupling of microwave and UV light to improve th ciency of photocatalytic activity.The special thermal effect generated by microwav is different from external direct heating and near-infrared indirect heating, which quickly increase temperature and more uniform temperature in solution.Ling et a successfully prepared uniformly Ag-loaded TiO2 for photocatalytic degradation o and MO coupling by microwave irradiation [37].The improved photocatalytic de tion activity of Ag/TiO2 was due to the thermal effect and non-thermal effect.Und crowave irradiation, silver nanoparticles can not only promote the charge separatio cess but also enhance the adsorption of organic pollutants on the surface of TiO2, as in Figure 4. Wang et al. reported a novel Z-scheme SrTiO3/MnFe2O4 nanocompos tetracycline (TC) degradation under MW-UV exposure [38].It has been found th combination of MW catalytic and UV photocatalytic oxidation technologies achiev perior SrTiO3/MnFe2O4 catalytic performance.The Z-scheme SrTiO3/MnFe2O4 syste plays high catalytic activity under MW-UV.Particularly, the generated MW plasma erates electron transfer and separation of e − -h + pair, which promotes the enhancem redox capacity and the oxidation of organics.Gayathri et al. found that the simulta irradiation by MW and UV is more efficient and synergistic for the mineralization dye compared to the respective individual energy sources [39].The synergistic en ment in the photocatalytic (UV/ZnO) degradation, as well as mineralization of rhod B (RhB) by MW, is attributed to the increased formation of reactive oxygen species and the formation of surface defects in ZnO, which inhibits the recombination of generated electrons and holes.MW can also enhance the photocatalytic degradatio mineralization of RhB even in systems with less dissolved oxygen because of the ef transference of oxygen from the bulk of the catalyst to the surface.

Microwave Indirect Heating
The effect of microwave irradiation is a combination of thermal effects and nonthermal microwave effects, arising from the heating rate, super-heating or "hot spots", and the selective absorption of radiation by polar substances [35,36].Therefore, it is of great practical significance to use the coupling of microwave and UV light to improve the efficiency of photocatalytic activity.The special thermal effect generated by microwave field is different from external direct heating and near-infrared indirect heating, which shows quickly increase temperature and more uniform temperature in solution.Ling et al. have successfully prepared uniformly Ag-loaded TiO 2 for photocatalytic degradation of 4-CP and MO coupling by microwave irradiation [37].The improved photocatalytic degradation activity of Ag/TiO 2 was due to the thermal effect and non-thermal effect.Under microwave irradiation, silver nanoparticles can not only promote the charge separation process but also enhance the adsorption of organic pollutants on the surface of TiO 2 , as shown in Figure 4. Wang et al. reported a novel Z-scheme SrTiO 3 /MnFe 2 O 4 nanocomposite for tetracycline (TC) degradation under MW-UV exposure [38].It has been found that the combination of MW catalytic and UV photocatalytic oxidation technologies achieves superior SrTiO 3 /MnFe 2 O 4 catalytic performance.The Z-scheme SrTiO 3 /MnFe 2 O 4 system displays high catalytic activity under MW-UV.Particularly, the generated MW plasma accelerates electron transfer and separation of e − -h + pair, which promotes the enhancement of redox capacity and the oxidation of organics.Gayathri et al. found that the simultaneous irradiation by MW and UV is more efficient and synergistic for the mineralization of the dye compared to the respective individual energy sources [39].The synergistic enhancement in the photocatalytic (UV/ZnO) degradation, as well as mineralization of rhodamine B (RhB) by MW, is attributed to the increased formation of reactive oxygen species (ROS) and the formation of surface defects in ZnO, which inhibits the recombination of photogenerated electrons and holes.MW can also enhance the photocatalytic degradation and mineralization of RhB even in systems with less dissolved oxygen because of the efficient transference of oxygen from the bulk of the catalyst to the surface.

Materials of Thermal-Coupled Photocatalysis
In thermal-coupled photocatalysis, there are three primary sources of thermal energy: external direct heating, near-infrared indirect heating, and microwave indirect heating.Generally, external direct heating and microwave indirect heating have nothing special requests for the materials.Here, we will focus on the near-infrared indirect heating materials which show a photothermal effect irradiated by near-infrared light.The surface temperature of materials will increase locally by converting solar energy into heat energy [22-24,

Metallic Materials with Localized Surface Plasmon Effect
Under illumination, when the frequency of the light matches the resonant frequency of conduction-band electrons, electromagnetic waves can induce collective oscillations of electrons at the interface between a conducting material and a dielectric medium, such as air or water.Because it is very localized, this phenomenon is called localized surface plasmon resonance (LSPR) [41][42][43].LSPR excitation can lead to a significant enhancement of the local electric field and a high concentration of energetic (hot) electrons on the surface of the plasmonic structure, a process that leads to a rapid increase in the local surface temperature of the materials.The excited hot carriers then distribute the thermal charge through electron-electron or electron-phonon scattering.Therefore, LSPR involves three distinct processes: enhancement of the local electric field, generation of hot electrons, and photothermal conversion.

Materials of Thermal-Coupled Photocatalysis
In thermal-coupled photocatalysis, there are three primary sources of thermal energy: external direct heating, near-infrared indirect heating, and microwave indirect heating.Generally, external direct heating and microwave indirect heating have nothing special requests for the materials.Here, we will focus on the near-infrared indirect heating materials which show a photothermal effect irradiated by near-infrared light.The surface temperature of materials will increase locally by converting solar energy into heat energy [22][23][24]40].According to different photothermal conversion mechanisms (as shown in Figure 5), near-infrared light can be converted to heat by three categories of materials: (1) Metallic materials with localized surface plasmon effect; (2) Narrow-band semiconductors with non-radiative relaxation; and (3) Carbon-based materials with thermal vibration.Therefore, TCP can be realized by near-infrared indirect heating through the composite material of photocatalysts and near-infrared absorption materials.

Materials of Thermal-Coupled Photocatalysis
In thermal-coupled photocatalysis, there are three primary sources of thermal en ergy: external direct heating, near-infrared indirect heating, and microwave indirect heat ing.Generally, external direct heating and microwave indirect heating have nothing spe cial requests for the materials.Here, we will focus on the near-infrared indirect heating materials which show a photothermal effect irradiated by near-infrared light.The surface temperature of materials will increase locally by converting solar energy into heat energy [22][23][24]40].According to different photothermal conversion mechanisms (as shown in Fig ure 5), near-infrared light can be converted to heat by three categories of materials: (1 Metallic materials with localized surface plasmon effect; (2) Narrow-band semiconductors with non-radiative relaxation; and (3) Carbon-based materials with thermal vibration Therefore, TCP can be realized by near-infrared indirect heating through the composite material of photocatalysts and near-infrared absorption materials.

Metallic Materials with Localized Surface Plasmon Effect
Under illumination, when the frequency of the light matches the resonant frequency of conduction-band electrons, electromagnetic waves can induce collective oscillations o electrons at the interface between a conducting material and a dielectric medium, such as air or water.Because it is very localized, this phenomenon is called localized surface plas mon resonance (LSPR) [41][42][43].LSPR excitation can lead to a significant enhancement o the local electric field and a high concentration of energetic (hot) electrons on the surface of the plasmonic structure, a process that leads to a rapid increase in the local surface temperature of the materials.The excited hot carriers then distribute the thermal charge through electron-electron or electron-phonon scattering.Therefore, LSPR involves three distinct processes: enhancement of the local electric field, generation of hot electrons, and photothermal conversion.

Metallic Materials with Localized Surface Plasmon Effect
Under illumination, when the frequency of the light matches the resonant frequency of conduction-band electrons, electromagnetic waves can induce collective oscillations of electrons at the interface between a conducting material and a dielectric medium, such as air or water.Because it is very localized, this phenomenon is called localized surface plasmon resonance (LSPR) [41][42][43].LSPR excitation can lead to a significant enhancement of the local electric field and a high concentration of energetic (hot) electrons on the surface of the plasmonic structure, a process that leads to a rapid increase in the local surface temperature of the materials.The excited hot carriers then distribute the thermal charge through electron-electron or electron-phonon scattering.Therefore, LSPR involves three distinct processes: enhancement of the local electric field, generation of hot electrons, and photothermal conversion.
The LSPR effect has been observed in many metal nanoparticles (NPs) and their alloys, such as Au, Ag, Cu, AuCu, and AuAl, etc. [44][45][46][47][48][49][50][51][52].Schatz et al. investigated the localized surface plasmon resonance (LSPR) of Cu NPs [44].It was found that Cu shows strong and narrow LSPR peaks comparable to Ag and Au.Yan et al. reported using plasmonic Au−Pd nanostructures to directly capture visible to near-infrared light for chemical reactions [45].The Au NPs are tightly bound to the Pd NPs for efficient light harvesting.Under plasmonic excitation, catalytic reactions are induced and accelerated through plasmonic photocatalysis and photothermal conversion.Under 809 nm laser irradiation at 1.68 W, the yield of the Suzuki coupling reaction was two times higher than when thermally heated to the same temperature.Liu et al. developed embedded coupled metal nanostructures, which proved to be an effective strategy to improve the utilization of LSPR effects (as shown in Figure 6) [46].Compared with traditionally isolated Au nanoparticles, the contribution of Au nano chains to the enhanced light conversion rate is increased by a factor of 3.5.Ma et al. developed a series of Au-Al intermetallic compounds with a high LSPR effect [47].The results show that the hot carrier generation rate of AuAl 2 and AuAl is higher than that of Au, and the energy rate of the resulting hot carriers is higher than that of Au.At the same time, the transport performance of hot carriers in AuAl 2 and AuAl is also better than that of Au.
Catalysts 2022, 12, x FOR PEER REVIEW 6 of 37 strong and narrow LSPR peaks comparable to Ag and Au.Yan et al. reported using plasmonic Au−Pd nanostructures to directly capture visible to near-infrared light for chemical reactions [45].The Au NPs are tightly bound to the Pd NPs for efficient light harvesting.Under plasmonic excitation, catalytic reactions are induced and accelerated through plasmonic photocatalysis and photothermal conversion.Under 809 nm laser irradiation at 1.68 W, the yield of the Suzuki coupling reaction was two times higher than when thermally heated to the same temperature.Liu et al. developed embedded coupled metal nanostructures, which proved to be an effective strategy to improve the utilization of LSPR effects (as shown in Figure 6) [46].Compared with traditionally isolated Au nanoparticles, the contribution of Au nano chains to the enhanced light conversion rate is increased by a factor of 3.5.Ma et al. developed a series of Au-Al intermetallic compounds with a high LSPR effect [47].The results show that the hot carrier generation rate of AuAl2 and AuAl is higher than that of Au, and the energy rate of the resulting hot carriers is higher than that of Au.At the same time, the transport performance of hot carriers in AuAl2 and AuAl is also better than that of Au.Besides metal nanoparticles, some semiconductor materials with metallic phases are also candidates for LSPR, such as CuS, Ti3C2, TiN, WO3-x, etc. [42,[53][54][55][56][57][58][59][60].Dai et al. demonstrated the reversible displacement of surface-dependent localized surface plasmon resonances (LSPR) in CuS nanodisks [53].As shown in Figure 7, LSPR curves (curves 1-4) shift with increasing surface-treatment cycles.Tian et al. prepared unique Cu7S4-Cu9S8 heterostructured hollow cubes with remarkable photothermal effects [55].It is shown that the strong near-infrared plasmonic absorption of Cu7S4-Cu9S8 promotes the hot carrier transport between Cu7S4 and Cu9S8, thereby promoting the catalytic reaction.Shi et al. successfully synthesized biocompatible Ti3C2 nanosheets (MXenes) for cancer therapy [56].Due to the LSPR effect of the semi-metallic Ti3C2 nanosheets, the ultrathin Ti3C2 nanosheets have strong absorption and conversion efficiency for NIR laser irradiation (808 nm).Naik et al. demonstrated that TiN is a plasmonic material in visible and near-infrared regions [57].The research results show that TiN has comparable performance to Au in plasmonic applications, and is significantly better than gold and silver in conversion optics and other aspects.Manthiram et al. demonstrated that the metallic phase of WO3-x nanoparticles possesses strong and tunable localized surface plasmon resonance [42].Xue et al. prepared Pd-loaded plasmonic WO3-x nanowires and demonstrated that the plasmon excitation of WO3-x nanowires by long wavelength irradiation can greatly promote Suzuki coupling reactions catalyzed by the attached Pd nanoparticles [58].Besides metal nanoparticles, some semiconductor materials with metallic phases are also candidates for LSPR, such as CuS, Ti 3 C 2 , TiN, WO 3-x , etc. [42,[53][54][55][56][57][58][59][60].Dai et al. demonstrated the reversible displacement of surface-dependent localized surface plasmon resonances (LSPR) in CuS nanodisks [53].As shown in Figure 7, LSPR curves (curves 1-4) shift with increasing surface-treatment cycles.Tian et al. prepared unique Cu 7 S 4 -Cu 9 S 8 heterostructured hollow cubes with remarkable photothermal effects [55].It is shown that the strong near-infrared plasmonic absorption of Cu 7 S 4 -Cu 9 S 8 promotes the hot carrier transport between Cu 7 S 4 and Cu 9 S 8 , thereby promoting the catalytic reaction.Shi et al. successfully synthesized biocompatible Ti 3 C 2 nanosheets (MXenes) for cancer therapy [56].Due to the LSPR effect of the semi-metallic Ti 3 C 2 nanosheets, the ultrathin Ti 3 C 2 nanosheets have strong absorption and conversion efficiency for NIR laser irradiation (808 nm).Naik et al. demonstrated that TiN is a plasmonic material in visible and near-infrared regions [57].The research results show that TiN has comparable performance to Au in plasmonic applications, and is significantly better than gold and silver in conversion optics and other aspects.Manthiram et al. demonstrated that the metallic phase of WO 3-x nanoparticles possesses strong and tunable localized surface plasmon resonance [42].Xue et al. prepared Pd-loaded plasmonic WO 3-x nanowires and demonstrated that the plasmon excitation of WO 3-x nanowires by long wavelength irradiation can greatly promote Suzuki coupling reactions catalyzed by the attached Pd nanoparticles [58].

Narrow-Band Semiconductors with Non-Radiative Relaxation
Unlike plasmonic materials, some narrow-band semiconductors generate heat through the nonradiative relaxation of electron-hole pairs.Under illumination, when the semiconductor receives energy greater than or equal to its forbidden bandwidth, electronhole pairs are generated inside the semiconductor.Afterwards, the excited electrons and holes can relax to lower energy levels and release energy in the form of photons.Phonon relaxation leads to localized heating of the lattice and constitutes a temperature distribution that depends on its optical absorption [22,40,61].
TiO2 is a typical representative of this photothermal conversion mechanism.Huang et al. report a large-scale production method for the synthesis of black TiO2 by aluminum reduction, and the obtained samples have a unique crystalline core-amorphous shell structure (TiO2@TiO2-x) [62].Under the illumination of the AM1.5GXe lamp solar simulator, the temperature of TiO2@TiO2-x increases, which leads to more electronic excitation and relaxation and enhanced thermal emission.Black TiO2 absorbs approximately 65% of the total solar energy through improved visible and infrared absorption.Ozin et al. synthesized black TiOx (x < 2) by reducing white P25 TiO2 nanocrystals with magnesium (Mg) [63], as shown in Figure 8a.The research results show that under the simulated illumination of 1 solar intensity, black TiOx can effectively generate water vapor, and its photothermal conversion efficiency is as high as 50%.Yu et al. showed a slow photon effect in TiO2 photonic crystals (TiO2 PCs) with extraordinary photothermal effects that outperform commercial TiO2 and TiO2 nanotube arrays for photocatalytic methane production, as shown in Figure 8b [64].Liu et al. proposed a novel diatom-like photothermal material using TiO2 thin-film bilayer melamine foam (TiO2-PANi@MF) for solar-driven clean water production [65].The material can achieve full-spectrum light absorption and photothermal conversion.The evaporation rate of 2.12 kg m −2 h −1 was achieved under 1 sun irradiation, and the solar steam conversion efficiency was as high as 88.9%.

Narrow-Band Semiconductors with Non-Radiative Relaxation
Unlike plasmonic materials, some narrow-band semiconductors generate heat through the nonradiative relaxation of electron-hole pairs.Under illumination, when the semiconductor receives energy greater than or equal to its forbidden bandwidth, electron-hole pairs are generated inside the semiconductor.Afterwards, the excited electrons and holes can relax to lower energy levels and release energy in the form of photons.Phonon relaxation leads to localized heating of the lattice and constitutes a temperature distribution that depends on its optical absorption [22,40,61].TiO 2 is a typical representative of this photothermal conversion mechanism.Huang et al. report a large-scale production method for the synthesis of black TiO 2 by aluminum reduction, and the obtained samples have a unique crystalline core-amorphous shell structure (TiO 2 @TiO 2-x ) [62].Under the illumination of the AM1.5GXe lamp solar simulator, the temperature of TiO 2 @TiO 2-x increases, which leads to more electronic excitation and relaxation and enhanced thermal emission.Black TiO 2 absorbs approximately 65% of the total solar energy through improved visible and infrared absorption.Ozin et al. synthesized black TiO x (x < 2) by reducing white P25 TiO 2 nanocrystals with magnesium (Mg) [63], as shown in Figure 8a.The research results show that under the simulated illumination of 1 solar intensity, black TiO x can effectively generate water vapor, and its photothermal conversion efficiency is as high as 50%.Yu et al. showed a slow photon effect in TiO 2 photonic crystals (TiO 2 PCs) with extraordinary photothermal effects that outperform commercial TiO 2 and TiO 2 nanotube arrays for photocatalytic methane production, as shown in Figure 8b [64].Liu et al. proposed a novel diatom-like photothermal material using TiO 2 thin-film bilayer melamine foam (TiO 2 -PANi@MF) for solar-driven clean water production [65].The material can achieve full-spectrum light absorption and photothermal conversion.The evaporation rate of 2.12 kg m −2 h −1 was achieved under 1 sun irradiation, and the solar steam conversion efficiency was as high as 88.9%.
In addition to TiO 2 , some semiconductor materials with defects also have near-infrared light-to-heat conversion properties.Chou et al. reported the NIR-photothermal properties of chemically exfoliated MoS 2 (ceMoS 2 ) [66].The absorbance of ceMoS 2 in NIR is approximately 7.8 times higher than that of graphene oxide (GO).Its extinction coefficient at 800 nm is 29.2 L g −1 cm −1 , which is higher than that of gold nanorods.Jun et al. have demonstrated for the first time that chemically exfoliated MoS 2 can be an efficient photothermal material for the creation of fresh water in solar evaporators [67].Due to the efficient photothermal conversion of ce-MoS 2 nanosheets, the solar evaporation efficiency can reach 76% under the light intensity of 0.76 kW/m 2 .Guo et al. proposed oxygen-deficient molybdenum oxide quantum dots (MoO 3-x QDs), which have an absorption spectrum matching that of sunlight in both the visible and near-infrared regions, resulting in a good interfacial heating effect on water evaporation [68].As shown in Figure 9a, theoretical models suggest that the unique photothermal properties of MoO 3-x QDs are caused by the oxygen defect level rather than the LSPR effect.Qi et al. proposed a new route to activate inert In(OH) 3 into 2D black In 2 O 3-x nanosheets via photoinduced defect engineering, as shown in Figure 9b [69].Due to a large number of oxygen vacancies on the layers, the black In 2 O 3-x nanosheets have a strong photothermal conversion ability.In the photothermal catalytic water gas shift experiment (RWGS), the CO production rate is as high as 103.21 mmol g −1 h −1 .
and relaxation and enhanced thermal emission.Black TiO2 absorbs approximately 65% of the total solar energy through improved visible and infrared absorption.Ozin et al. synthesized black TiOx (x < 2) by reducing white P25 TiO2 nanocrystals with magnesium (Mg) [63], as shown in Figure 8a.The research results show that under the simulated illumination of 1 solar intensity, black TiOx can effectively generate water vapor, and its photothermal conversion efficiency is as high as 50%.Yu et al. showed a slow photon effect in TiO2 photonic crystals (TiO2 PCs) with extraordinary photothermal effects that outperform commercial TiO2 and TiO2 nanotube arrays for photocatalytic methane production, as shown in Figure 8b [64].Liu et al. proposed a novel diatom-like photothermal material using TiO2 thin-film bilayer melamine foam (TiO2-PANi@MF) for solar-driven clean water production [65].The material can achieve full-spectrum light absorption and photothermal conversion.The evaporation rate of 2.12 kg m −2 h −1 was achieved under 1 sun irradiation, and the solar steam conversion efficiency was as high as 88.9%.In addition to TiO2, some semiconductor materials with defects also have near-infrared light-to-heat conversion properties.Chou et al. reported the NIR-photothermal properties of chemically exfoliated MoS2 (ceMoS2) [66].The absorbance of ceMoS2 in NIR is approximately 7.8 times higher than that of graphene oxide (GO).Its extinction coefficient at 800 nm is 29.2 L g −1 cm −1 , which is higher than that of gold nanorods.Jun et al. have demonstrated for the first time that chemically exfoliated MoS2 can be an efficient photothermal material for the creation of fresh water in solar evaporators [67].Due to the efficient photothermal conversion of ce-MoS2 nanosheets, the solar evaporation efficiency can reach 76% under the light intensity of 0.76 kW/m 2 .Guo et al. proposed oxygen-deficient molybdenum oxide quantum dots (MoO3-x QDs), which have an absorption spectrum matching that of sunlight in both the visible and near-infrared regions, resulting in a good interfacial heating effect on water evaporation [68].As shown in Figure 9a, theoretical models suggest that the unique photothermal properties of MoO3-x QDs are caused by the oxygen defect level rather than the LSPR effect.Qi et al. proposed a new route to activate inert In(OH)3 into 2D black In2O3-x nanosheets via photoinduced defect engineering, as shown in Figure 9b [69].Due to a large number of oxygen vacancies on the layers, the black In2O3-x nanosheets have a strong photothermal conversion ability.In the photothermal catalytic water gas shift experiment (RWGS), the CO production rate is as high as 103.21 mmol g −1 h −1 .

Carbon-Based Materials with Thermal Vibration
Carbon-based materials have always been a research hotspot in the field of catalysis due to their excellent chemical stability and high light absorption [70,71].Carbon-based materials possess abundant conjugated π-bonds and thus can convert solar energy into thermal energy through thermal vibration mechanisms.Under sunlight illumination, a large number of conjugated π bonds require only a small amount of energy to excite loosely held electrons, followed by electron relaxation via electron-electron and electronphonon scattering.This causes the molecules to generate heat, which in turn causes the macroscopic heating of the material [72][73][74].
Carbon nanotubes (CNTs) are a classic carbon-based photothermal material.Using carbon nanotubes (CNTs) to modify flexible wood films (F-Wood/CNTs), Hu et al. created an efficient solar steam generation device [75].Benefiting from the excellent light absorption of the black CNT coating, as shown in Figure 10a, its solar steam power generation device exhibits a high efficiency of 81% at 10 kW cm −2 .An all-carbon nanotube (CNT) hybrid film was prepared by Jia et al.The hybrid film has ultra-high solar absorbance, low

Carbon-Based Materials with Thermal Vibration
Carbon-based materials have always been a research hotspot in the field of catalysis due to their excellent chemical stability and high light absorption [70,71].Carbon-based materials possess abundant conjugated π-bonds and thus can convert solar energy into thermal energy through thermal vibration mechanisms.Under sunlight illumination, a large number of conjugated π bonds require only a small amount of energy to excite loosely held electrons, followed by electron relaxation via electron-electron and electron-phonon scattering.This causes the molecules to generate heat, which in turn causes the macroscopic heating of the material [72][73][74].
Carbon nanotubes (CNTs) are a classic carbon-based photothermal material.Using carbon nanotubes (CNTs) to modify flexible wood films (F-Wood/CNTs), Hu et al. created an efficient solar steam generation device [75].Benefiting from the excellent light absorption of the black CNT coating, as shown in Figure 10a, its solar steam power generation device exhibits a high efficiency of 81% at 10 kW cm −2 .An all-carbon nanotube (CNT) hybrid film was prepared by Jia et al.The hybrid film has ultra-high solar absorbance, low thermal conductivity, and excellent light-to-heat conversion capability [76].The photothermal conversion efficiency of a single hybrid film is 87.4% under 1 sun illumination.Zhang et al. used SiO 2 nanoparticles to graft carbon nanotubes (CNTs) to prepare CNTs-SiO 2 superhydrophobic coatings [77].Due to the superhydrophobicity of the coating surface and the remarkable photothermal conversion ability of CNTs, the CNTs-SiO 2 coating can significantly delay the water freezing time and effectively melt the ice layer within seconds under laser irradiation.
Graphene, including graphene oxide (GO) and reduced graphene oxide (rGO), has long been known for its powerful photothermal conversion capabilities.Dai et al. developed nanosheets of reduced graphene oxide (nano-rGO) with high near-infrared (NIR) absorbance, as shown in Figure 10b [78].The single-layered nano-rGO sheets have an average lateral dimension of ∼20 nm, and their NIR absorption is six times higher than that of non-reduced covalent PEGylated nano-GO.Jiang et al. synthesized two-dimensional rGO and one-dimensional multi-walled CNTs (MWCNTs) as rGO-MWCNT-based films to enhance photothermal performance [79].The surface of the rGO-MWCNT-based film is rough, thereby reducing the reflection of light and thereby realizing almost all light trapping.Under 1 sun illumination, the surface temperature is as high as 78 • C, which is 10 • C higher than the result of pure rGO film.The solar thermal conversion efficiency can reach 80.4%.Qiu et al. prepared a reduced graphene oxide-based (rGO-based) covalent organic framework hydrogel (KTG) with a three-dimensional porous structure as a platform for enhanced uranium capture via photothermal desalination [80].KTG can obtain a special uranium capture capacity (521.6 mg g −1 ) under one sunlight exposure, which is 42.4% higher than that under dark conditions.
Catalysts 2022, 12, x FOR PEER REVIEW 9 of 37 thermal conductivity, and excellent light-to-heat conversion capability [76].The photothermal conversion efficiency of a single hybrid film is 87.4% under 1 sun illumination.Zhang et al. used SiO2 nanoparticles to graft carbon nanotubes (CNTs) to prepare CNTs-SiO2 superhydrophobic coatings [77].Due to the superhydrophobicity of the coating surface and the remarkable photothermal conversion ability of CNTs, the CNTs-SiO2 coating can significantly delay the water freezing time and effectively melt the ice layer within seconds under laser irradiation.Graphene, including graphene oxide (GO) and reduced graphene oxide (rGO), has long been known for its powerful photothermal conversion capabilities.Dai et al. developed nanosheets of reduced graphene oxide (nano-rGO) with high near-infrared (NIR) absorbance, as shown in Figure 10b [78].The single-layered nano-rGO sheets have an average lateral dimension of ∼20 nm, and their NIR absorption is six times higher than that of non-reduced covalent PEGylated nano-GO.Jiang et al. synthesized two-dimensional rGO and one-dimensional multi-walled CNTs (MWCNTs) as rGO-MWCNT-based films to enhance photothermal performance [79].The surface of the rGO-MWCNT-based film is rough, thereby reducing the reflection of light and thereby realizing almost all light trapping.Under 1 sun illumination, the surface temperature is as high as 78 °C, which is 10 °C higher than the result of pure rGO film.The solar thermal conversion efficiency can reach 80.4%.Qiu et al. prepared a reduced graphene oxide-based (rGO-based) covalent organic framework hydrogel (KTG) with a three-dimensional porous structure as a platform for enhanced uranium capture via photothermal desalination [80].KTG can obtain a special uranium capture capacity (521.6 mg g −1 ) under one sunlight exposure, which is 42.4% higher than that under dark conditions.Polymers, such as polypyrrole (PPy), and polydopamine (PDA), are also very powerful in photothermal conversion.Dai et al. constructed uniform PPy nanoparticles [81].As shown in Figure 10c, the PPy nanoparticles have good colloidal stability and strong NIR absorption, and their photothermal conversion efficiency is better than that of the well-known Au nanorods.Jun et al. demonstrated a polydopamine (PDA)-coated polyvinylidene fluoride (PVDF) photothermal membrane for solar-driven membrane distillation [82].The film has remarkable light absorption and excellent light-to-heat conversion performance.Under the irradiation of 0.75 kW/m 2 , its distillation performance efficiency is 45%.Xu et al. improved light-harvesting efficiency over a wide spectral and angular range by exploiting self-organized surface structures on large-area multilayer polypyrrole (PPy) nanosheets [83].The solar heat conversion efficiency is as high as 95.33%.In addition, when used for solar steam power generation, the measurement efficiency can reach 92% under 1 sun illumination.Chen et al. developed a porous framework photothermal Polymers, such as polypyrrole (PPy), and polydopamine (PDA), are also very powerful in photothermal conversion.Dai et al. constructed uniform PPy nanoparticles [81].As shown in Figure 10c, the PPy nanoparticles have good colloidal stability and strong NIR absorption, and their photothermal conversion efficiency is better than that of the well-known Au nanorods.Jun et al. demonstrated a polydopamine (PDA)-coated polyvinylidene fluoride (PVDF) photothermal membrane for solar-driven membrane distillation [82].The film has remarkable light absorption and excellent light-to-heat conversion performance.Under the irradiation of 0.75 kW/m 2 , its distillation performance efficiency is 45%.Xu et al. improved light-harvesting efficiency over a wide spectral and angular range by exploiting self-organized surface structures on large-area multilayer polypyrrole (PPy) nanosheets [83].The solar heat conversion efficiency is as high as 95.33%.In addition, when used for solar steam power generation, the measurement efficiency can reach 92% under 1 sun illumination.Chen et al. developed a porous framework photothermal microgroove-structured aerogel (PDA/PEI/PPy@PI-MS MGA, pppMGA) [84].Combin-ing the porous micro-grooved structure of the pppMGA evaporation interface with the light absorption ability of PPy, the light absorption rate (98%) was effectively improved.Under 1 sun illumination, the pppMGA evaporator can achieve a high evaporation rate (∼1.38 kg m −2 h −1 ) and a high photothermal conversion efficiency (∼93.04%).

Applications of Thermal-Coupled Photocatalysis
Thermal-coupled photocatalysis has applications in many fields, including artificial photosynthesis, water splitting, pollutant degradation, etc.The thermal-coupled photocatalysis achievements in recent years are summarized and listed in Table 1.

Artificial Photosynthesis
Photosynthesis is one of the most important reactions on Earth.Artificial photosynthesis attempts to replicate natural photosynthesis, thereby achieving the goal of reducing CO 2 .Artificial photosynthesis can simply be defined as the process of converting CO 2 and water into carbon-based fuels under sunlight [141][142][143].Products from CO 2 reduction include CH 4 , CO, methanol, methane, etc.However, the single photocatalytic method suffers from disadvantages, such as low charge separation efficiency, poor light-harvesting ability, and less reduction selectivity.In contrast, thermal-coupled photocatalysis couples solar and thermal energy, providing a more reliable solution.
Combining the photocatalytic properties of TiO 2 with the thermocatalytic properties of CeO 2 , Fiorenza et al. synthesized TiO 2 -CeO 2 -based catalysts for artificial photosynthesis [89].Furthermore, the addition of Co-Cu oxide increases the number of oxygen vacancies, which facilitates the separation of carriers.As shown in Figure 11, under the combined action of thermal energy and solar energy, the CO and CH 4 yields can reach 12 µmol g −1 h −1 and 1.84 µmol g −1 h −1 , respectively.Xuan et al. designed SrTiO 3 /Cu@Ni/TiN catalysts for CO 2 reduction to ethanol [85].Non-noble metallic materi-als, such as Cu, Ni, and TiN were used to enhance the plasmonic effect for efficiently capturing solar full-spectrum energy.The optimal ethanol evolution rate is 21.3 µmol g −1 h −1 , and the ethanol selectivity is 79%.Lou et al. constructed a plasmonic semiconductor heterostructure photocatalyst with pyroelectric black phosphorus (BP) and plasmonic tungsten oxide (WO) for artificial photosynthesis [86].Under the irradiation of visible light and NIR light, the plasmonic thermal effect of WO can increase the local temperature to 86 • C, triggering the pyroelectric effect of BP, generating pyroelectric carriers, and enhancing the electron transfer from BP to WO.Thus, the photothermal catalytic performance is enhanced.Its CO generation reaches 26.1 µmol g −1 h −1 , which is 7 times and 17 times that of plasma WO and pyroelectric BP, respectively.Xu et al. developed a novel lead-free perovskite Cs 3 Sb 2 I 9 photocatalyst to efficiently reduce CO 2 to CO and methane via photothermal co-catalysis [92].Its optimal production rate is 95.7 µmol g −1 h −1 , which is 87 times and 5.2 times higher than that of pure photocatalysis and pure thermal catalysis, respectively.The study found that the defective active sites generated by thermal excitation of Cs 3 Sb 2 I 9 photocatalysts can adsorb and activate CO 2 , while the large number of electrons excited by light can provide CO 2 reduction ability, and their synergistic effect enhances the catalytic activity.Cui et al. reported ultrathin porous g-C 3 N 4 nanosheets decorated with AuCu alloy NPs for photothermal catalytic CO 2 reduction to ethanol [49].The strong interaction between metal and g-C 3 N 4 accelerates the transfer of photogenerated charges.In addition, the increase in temperature leads to enhanced thermal motion of molecules, leading to a synergistic effect of photocatalysis and thermocatalysis.At 120 • C, the yield and selectivity of ethanol is 0.89 mmol g −1 h −1 , which is 4.2 times higher than that of photocatalysis and 7.6 times higher than that of thermal catalysis.
Catalysts 2022, 12, x FOR PEER REVIEW 14 of 37 pure photocatalysis and pure thermal catalysis, respectively.The study found that the defective active sites generated by thermal excitation of Cs3Sb2I9 photocatalysts can adsorb and activate CO2, while the large number of electrons excited by light can provide CO2 reduction ability, and their synergistic effect enhances the catalytic activity.Cui et al. reported ultrathin porous g-C3N4 nanosheets decorated with AuCu alloy NPs for photothermal catalytic CO2 reduction to ethanol [49].The strong interaction between metal and g-C3N4 accelerates the transfer of photogenerated charges.In addition, the increase in temperature leads to enhanced thermal motion of molecules, leading to a synergistic effect of photocatalysis and thermocatalysis.At 120 °C, the yield and selectivity of ethanol is 0.89 mmol g −1 h −1 , which is 4.2 times higher than that of photocatalysis and 7.6 times higher than that of thermal catalysis.

Water Splitting
To effectively solve the consumption of fossil fuels and the serious environmental problems that accompany combustion, modern society has been looking for a clean, renewable, and cheap energy production method.Solar-driven photocatalytic water splitting for H2 production is a potentially effective solution to the energy crisis, especially with few environmental concerns [144][145][146].However, there are widespread problems in photocatalytic water splitting for H2 production, including low solar energy utilization efficiency, poor response to visible and infrared light, and rapid recombination of photogenerated electrons and holes.To improve these problems, introducing thermal energy into a photocatalytic H2 production system has become a research hotspot.
Li et al. prepared Ag-polydopamine nanoparticles co-decorated defective mesoporous carbon nitride nanosheet assemblies (Ag-PDA/DCN) [96].The photocatalytic H2 evolution rate of this material is as high as 3840 μmol g −1 h −1 , driven by visible and near-infrared light, which is seven times higher than that of PDA/DCN.This is mainly due to the rapid electron transfer achieved by Ag-PDA nanoparticles, which further expands the photoresponse of DCN, resulting in an obvious photothermal effect, which further enhances the photocatalytic activity.Yu

Water Splitting
To effectively solve the consumption of fossil fuels and the serious environmental problems that accompany combustion, modern society has been looking for a clean, renewable, and cheap energy production method.Solar-driven photocatalytic water splitting for H 2 production is a potentially effective solution to the energy crisis, especially with few environmental concerns [144][145][146].However, there are widespread problems in photocatalytic water splitting for H 2 production, including low solar energy utilization efficiency, poor response to visible and infrared light, and rapid recombination of photogenerated electrons and holes.To improve these problems, introducing thermal energy into a photocatalytic H 2 production system has become a research hotspot.
Li et al. prepared Ag-polydopamine nanoparticles co-decorated defective mesoporous carbon nitride nanosheet assemblies (Ag-PDA/DCN) [96].The photocatalytic H 2 evolution rate of this material is as high as 3840 µmol g −1 h −1 , driven by visible and near-infrared light, which is seven times higher than that of PDA/DCN.This is mainly due to the rapid electron transfer achieved by Ag-PDA nanoparticles, which further expands the photoresponse of DCN, resulting in an obvious photothermal effect, which further enhances the photocatalytic activity.Yu et al. used an S-vacancy 1T-WS 2 (Vs-1T-WS 2 ) as a photothermal co-catalyst and complexed it with CdS to promote photocatalytic H 2 evolution [33].The catalyst can achieve H 2 evolution performance of 70.9 mmol g −1 h −1 at 500 nm with an apparent quantum yield (AQY) of 39.1%.The introduction of Vs-1T-WS 2 not only expanded the light absorption range but also accelerated the directional migration of electrons from CdS to S vacancies through the induced photothermal effect.Guo et al. proposed an efficient two-phase photocatalytic H 2 production system [103].The system uses a charred wood substrate to convert liquid water into water vapor and split the water vapor into H 2 in the presence of light without additional energy.The particle photocatalytic system based on the wood/CoO system achieved H 2 production rate as high as 220.74 µmol h −1 cm −2 , indicating that the photothermal-photocatalytic biphasic system is cost-effective and beneficial for practical applications.Ho et al. have successfully synthesized Ag@SiO 2 @TiO 2 /Au catalysts with dual effects of enhanced charge transfer and photothermal heating for photo-splitting water for H 2 production (as shown in Figure 12) [104].The catalyst has an extremely high H 2 generation rate of 30.2 mmol g −1 h −1 .Ag@SiO 2 absorbs visible light for efficient photothermal conversion, thereby promoting the increase in the number of active sites for photocatalytic reactions.The Au Nps reduced the charge recombination in TiO 2 and further enhanced the photocatalytic performance.Jiang et al. reported the incorporation of single-atom silver into g-C 3 N 4 (SAAg-g-CN) as a low-cost and efficient photocatalyst [101].The unique coordination of SAAg-g-CN can shorten the electron transfer pathway and facilitate H 2 desorption, thereby advancing the photocatalytic H 2 production process.Furthermore, the strong N-Ag covalent bond masks the weakness of the metal NP cocatalyst in terms of growth and agglomeration under high-temperature reactions, ensuring the remarkable performance of SAAg-g-CN in thermal-assisted photocatalytic H 2 production.The average H 2 evolution rate (75 µmol g −1 h −1 ) of this catalyst is nine times that of g-C 3 N 4 .
Catalysts 2022, 12, x FOR PEER REVIEW 15 of 37 μmol h −1 cm −2 , indicating that the photothermal-photocatalytic biphasic system is cost-effective and beneficial for practical applications.Ho et al. have successfully synthesized Ag@SiO2@TiO2/Au catalysts with dual effects of enhanced charge transfer and photothermal heating for photo-splitting water for H2 production (as shown in Figure 12) [104].The catalyst has an extremely high H2 generation rate of 30.2 mmol g −1 h −1 .Ag@SiO2 absorbs visible light for efficient photothermal conversion, thereby promoting the increase in the number of active sites for photocatalytic reactions.The Au Nps reduced the charge recombination in TiO2 and further enhanced the photocatalytic performance.Jiang et al. reported the incorporation of single-atom silver into g-C3N4 (SAAg-g-CN) as a low-cost and efficient photocatalyst [101].The unique coordination of SAAg-g-CN can shorten the electron transfer pathway and facilitate H2 desorption, thereby advancing the photocatalytic H2 production process.Furthermore, the strong N-Ag covalent bond masks the weakness of the metal NP cocatalyst in terms of growth and agglomeration under high-temperature reactions, ensuring the remarkable performance of SAAg-g-CN in thermal-assisted photocatalytic H2 production.The average H2 evolution rate (75 μmol g −1 h −1 ) of this catalyst is nine times that of g-C3N4.

Pollutants Degradation
Organic dyes are the most notorious pollutants in the aquatic environment.The lowcost degradation of organic fuels is of great significance in industrial production.Thermalcoupled photocatalysis degradation of organic pollutants is low-cost and can be performed under mild conditions, so it is considered a promising technology.At present, researchers have made more research results on the degradation of common organic dyes, such as methylene blue (MB) [109][110][111][112], rhodamine B (RhB) [113][114][115][116], and methyl orange (MO) [117,118], etc. Zhou et al. prepared a polydopamine/defective ultrathin mesoporous graphitic carbon nitride (PDA/DCN) Z-scheme organic assembly [109].Under the light, the removal rate of MB was as high as 98% within 70 min.PDA extends the photoresponse to the near-infrared region and produces a pronounced photothermal effect, thereby enhancing the catalytic performance.Bao et al. fabricated CoFe2O4-modified BiOCl layered microspheres (CFO-BiOCl) [115].The CFO-BiOCl sample has obvious photothermal catalytic activity, decomposing 99% of RhB within 5 min under full-spectrum light irradiation.Its excellent photocatalytic performance can be attributed to the suitable band ar-

Pollutants Degradation
Organic dyes are the most notorious pollutants in the aquatic environment.The low-cost degradation of organic fuels is of great significance in industrial production.Thermal-coupled photocatalysis degradation of organic pollutants is low-cost and can be performed under mild conditions, so it is considered a promising technology.At present, researchers have made more research results on the degradation of common organic dyes, such as methylene blue (MB) [109][110][111][112], rhodamine B (RhB) [113][114][115][116], and methyl orange (MO) [117,118], etc. Zhou et al. prepared a polydopamine/defective ultrathin mesoporous graphitic carbon nitride (PDA/DCN) Z-scheme organic assembly [109].Under the light, the removal rate of MB was as high as 98% within 70 min.PDA extends the photore-sponse to the near-infrared region and produces a pronounced photothermal effect, thereby enhancing the catalytic performance.Bao et al. fabricated CoFe 2 O 4 -modified BiOCl layered microspheres (CFO-BiOCl) [115].The CFO-BiOCl sample has obvious photothermal catalytic activity, decomposing 99% of RhB within 5 min under full-spectrum light irradiation.Its excellent photocatalytic performance can be attributed to the suitable band arrangement of CoFe 2 O 4 and BiOCl as well as the photothermal effect, which elevates the organic pollutant molecules to a more active state (as shown in Figure 13).Tian et al. integrated porous Au/TiO 2 with butterfly P. paris's wings (PW) as an Au/TiO 2 _PW photocatalyst [117].The Au NPs enhanced the photothermal effect of the catalyst, and the PW could adjust the temperature, thus avoiding overheating and reducing the catalytic activity.The material exhibits excellent MO degradation performance due to the synergistic effect between photothermal and photocatalysis.Due to the synergistic effect of photothermal and photocatalysis, the degradation rate of MO was 74.2% within 30 min, which was 3.4 times that of TiO 2 .
Catalysts 2022, 12, x FOR PEER REVIEW 16 of 37 photothermal and photocatalysis, the degradation rate of MO was 74.2% within 30 min, which was 3.4 times that of TiO2.Volatile organic compounds (VOCs) are the main air pollutants on the earth, which have great harm to human health and the environment.At present, the thermal-coupled photocatalysis degradation of VOCs has made great progress.Common VOCs, including toluene [120][121][122][123][124], benzene [136], phenol [132,133], and 2,4-dichlorophenol [125][126][127][128], be efficiently degraded under thermal-coupled photocatalysis.Jiang et al. investigated the performance of Pt−Cu/TiO2 nanocatalysts for photo−thermal catalytic degradation of toluene [120].The photothermal effect of PtCu alloy nanoparticles and the photocatalysis of TiO2 induced a synergistic effect (as shown in Figure 14), which resulted in a higher efficiency of toluene degradation than the thermocatalytic or photocatalytic process.At 110 °C, the toluene degradation rate is close to 100%.Li et al. prepared Z-scheme Ag/Ag3PO4/CeO2 heterojunction photothermal catalysts for gaseous benzene degradation [136].At the initial benzene concentration of 600 ppm, the removal rate after 3 h was 90.18%.Ag3PO4 has better solar light absorption ability and CeO2 has a good thermal conductivity at lower temperatures.Under illumination, the photothermal effect promotes the efficient separation of photoexcited electrons and holes.Zhu et al. successfully prepared a photothermal catalyst Bi12CoO20 with wide spectrum adsorption (up to 1000 nm) [133].The photothermal effect leads to the conversion of Co 3+ and Bi 3+ to Co 2+ and Bi 5+ at the octahedral site, which promotes charge separation.The catalyst has a high photothermal activity for the degradation of phenols, which is 2-8 times higher than the reported Bi25CoO40, P25-TiO2, g-C3N4, and Bi2WO6.A layered heterojunction photocatalyst Cu/TiO2-x/CoP was prepared by Xing et al. [125].The LSPR effect of Cu NPs enables the catalyst to have a significant photothermal effect, thus exhibiting good photothermal-photocatalytic performance.It has a high photocatalytic degradation rate for 2,4-dichlorophenol (99.2%), which is 7.6 times that of the initial TiO2.Volatile organic compounds (VOCs) are the main air pollutants on the earth, which have great harm to human health and the environment.At present, the thermal-coupled photocatalysis degradation of VOCs has made great progress.Common VOCs, including toluene [120][121][122][123][124], benzene [136], phenol [132,133], and 2,4-dichlorophenol [125][126][127][128], be efficiently degraded under thermal-coupled photocatalysis.Jiang et al. investigated the performance of Pt−Cu/TiO 2 nanocatalysts for photo−thermal catalytic degradation of toluene [120].The photothermal effect of PtCu alloy nanoparticles and the photocatalysis of TiO 2 induced a synergistic effect (as shown in Figure 14), which resulted in a higher efficiency of toluene degradation than the thermocatalytic or photocatalytic process.At 110 • C, the toluene degradation rate is close to 100%.Li et al. prepared Z-scheme Ag/Ag 3 PO 4 /CeO 2 heterojunction photothermal catalysts for gaseous benzene degradation [136].At the initial benzene concentration of 600 ppm, the removal rate after 3 h was 90.18%.Ag 3 PO 4 has better solar light absorption ability and CeO 2 has a good thermal conductivity at lower temperatures.Under illumination, the photothermal effect promotes the efficient separation of photoexcited electrons and holes.Zhu et al. successfully prepared a photothermal catalyst Bi 12 CoO 20 with wide spectrum adsorption (up to 1000 nm) [133].The photothermal effect leads to the conversion of Co 3+ and Bi 3+ to Co 2+ and Bi 5+ at the octahedral site, which promotes charge separation.The catalyst has a high photothermal activity for the degradation of phenols, which is 2-8 times higher than the reported Bi 25 CoO 40 , P25-TiO 2 , g-C 3 N 4 , and Bi 2 WO 6 .A layered heterojunction photocatalyst Cu/TiO 2-x /CoP was prepared by Xing et al. [125].The LSPR effect of Cu NPs enables the catalyst to have a significant photothermal effect, thus exhibiting good photothermal-photocatalytic performance.It has a high photocatalytic degradation rate for 2,4-dichlorophenol (99.2%), which is 7.6 times that of the initial TiO 2 .
the octahedral site, which promotes charge separation.The catalyst has a high photothermal activity for the degradation of phenols, which is 2-8 times higher than the reported Bi25CoO40, P25-TiO2, g-C3N4, and Bi2WO6.A layered heterojunction photocatalyst Cu/TiO2-x/CoP was prepared by Xing et al. [125].The LSPR effect of Cu NPs enables the catalyst to have a significant photothermal effect, thus exhibiting good photothermal-photocatalytic performance.It has a high photocatalytic degradation rate for 2,4-dichlorophenol (99.2%), which is 7.6 times that of the initial TiO2.In addition to the above organic pollutants, thermal-coupled photocatalysis can also be used for the degradation of bisphenol A (BPA), formaldehyde, etc. Xing et al. fabricated flower-like hollow W 18 O 49 @ZnIn 2 S 4 core-shell Z-type heterojunctions on carbon fiber cloth (CC) [130].The catalyst showed good photocatalytic degradation performance for the degradation of bisphenol A (BPA) under simulated sunlight, and the removal rate of bisphenol A (BPA) was 95%.α-MnO 2 /graphene oxide nanohybrid was prepared by Rong et al. [137].The catalyst can decompose 100% of formaldehyde at room temperature.On the one hand, the addition of graphene oxide is beneficial to improving the light absorption capacity and photothermal conversion efficiency; on the other hand, it is beneficial to electron transfer and separation of electrons and holes.These synergistic effects significantly enhance the catalytic activity of α-MnO 2 /graphene oxide nanohybrid.

Mechanical-Coupled Photocatalysis (MCP)
Noncentrosymmetric materials with spontaneous polarization, ferroelectric polarization, or piezoelectric polarization can be used to utilize mechanical energy.For example, when a piezoelectric material is subjected to compressive stress or tensile stress, the material will deform and a built-in electric field with different directions will be generated.This piezoelectric effect has been utilized in the field of photocatalysis to further improve photocatalytic efficiency.Generally, external forces are applied by ultrasound, stirring, and so on.Here, we will try to summarize the current research progress of MCP including the primary source of mechanical energy and materials for MCP.In addition, we also list the application results of mechanical-coupled photocatalysis in recent years in Table 2.  Ultrasound is currently the most important source of mechanical energy in mechanicalcoupled photocatalysis [19,20,[188][189][190][191].The photocatalytic reaction is carried out in a custom-made glass vessel exposed to the light and equipped with an ultrasonic generator machine.Ultrasonic waves will produce a cavitation effect in a liquid medium, which can generate microbubbles with a series of dynamic processes, such as contraction, expansion, oscillation, and implosion.After the microbubbles burst, the resulting local hot spot temperature can reach 5000 K, and the pressure can reach 500 atm.Therefore, as for MCP, the ultrasound is always coupled with a cooling system to remove the temperature effect caused by ultrasonic waves [192].
Zeng et al. studied the piezoelectric photocatalytic properties of Au-modified BiOBr, and the reaction setup is shown in Figure 15 [179].Under the action of ultrasound, the removal rate of carbamazepine (CBZ) reached 95.8% within 30 min, and its rate constant was 1.73 times higher than the sum of the individual piezoelectric and photocatalytic properties.Zhai et al. synthesized BiOX/BaTiO 3 (X = Cl, Br, Cl 0.166 Br 0.834 ) composites for MO degradation [168].Under the assistance of ultrasound, the piezoelectric photocatalytic performance (k = 0.15824 min −1 ) of the material far exceeds the sum of photocatalysis alone (k = 0.01159 min −1 ) and piezoelectric catalysis (k = 0.01208 min −1 ).This can be attributed to the synergistic effect of its chemical potential difference and piezoelectric potential difference to stop the recombination of photogenerated carriers.Wang et al. prepared oxygen vacancies (OVs)-dominated SrBi 4 Ti 4 O 15 nanosheets for tetracycline degradation [173].Under the synergistic effect of visible light and ultrasound, the degradation efficiency was greatly improved, and the oxidation rate constant reached 0.058 min −1 , which was 2.15 times and 14.5 times higher than those under only visible light irradiation and only ultrasound, respectively.Xue et al. synthesized a core/shell BaTio 3 /TiO 2 nanocomposite [160].Under the co-excitation of ultrasound and UV irradiation, the oxidation rate constant of BaTiO 3 /TiO 2 nanofibers in RhB dye can reach 0.0967 min −1 , which is 3.22 times higher than that under UV irradiation alone.
Catalysts 2022, 12, x FOR PEER REVIEW 20 of 37 degradation [168].Under the assistance of ultrasound, the piezoelectric photocatalytic performance (k = 0.15824 min −1 ) of the material far exceeds the sum of photocatalysis alone (k = 0.01159 min −1 ) and piezoelectric catalysis (k = 0.01208 min −1 ).This can be attributed to the synergistic effect of its chemical potential difference and piezoelectric potential difference to stop the recombination of photogenerated carriers.Wang et al. prepared oxygen vacancies (OVs)-dominated SrBi4Ti4O15 nanosheets for tetracycline degradation [173].Under the synergistic effect of visible light and ultrasound, the degradation efficiency was greatly improved, and the oxidation rate constant reached 0.058 min −1 , which was 2.15 times and 14.5 times higher than those under only visible light irradiation and only ultrasound, respectively.Xue et al. synthesized a core/shell BaTio3/TiO2 nanocomposite [160].Under the co-excitation of ultrasound and UV irradiation, the oxidation rate constant of BaTiO3/TiO2 nanofibers in RhB dye can reach 0.0967 min −1 , which is 3.22 times higher than that under UV irradiation alone.

Stir
The actuation of most piezoelectric materials requires an ultrasound, which undoubtedly greatly limits their applications.Therefore, researchers began to look for simpler driving methods, such as stirring.A new material design was proposed by Zhang et al.By combining semiconductors with a self-driven energy pad, they achieved piezo-photocatalysis under mild mechanical perturbation (stirring) without external energy input [171].As shown in Figure 16, the energy pad consists of a porous composite graphenepiezoelectric polymer film that combines piezoelectric and dielectric power generation and stores electricity in situ.This energy buffering results in a large and prolonged electric field in response to mild mechanical perturbations.The experimental results show that the electric field enhances the photocatalytic performance of TiO2, BiOI, and CdS by 300%, 21%, and 400%, respectively.Bian et al. prepared core-shell lead zirconate titanate (PZT)/TiO2 catalysts [178].By harvesting the mechanical energy of the water, an internal

Stir
The actuation of most piezoelectric materials requires an ultrasound, which undoubtedly greatly limits their applications.Therefore, researchers began to look for simpler driving methods, such as stirring.A new material design was proposed by Zhang et al.By combining semiconductors with a self-driven energy pad, they achieved piezo-photocatalysis under mild mechanical perturbation (stirring) without external energy input [171].As shown in Figure 16, the energy pad consists of a porous composite graphene-piezoelectric polymer film that combines piezoelectric and dielectric power generation and stores electricity in situ.This energy buffering results in a large and prolonged electric field in response to mild mechanical perturbations.The experimental results show that the electric field enhances the photocatalytic performance of TiO 2 , BiOI, and CdS by 300%, 21%, and 400%, respectively.Bian et al. prepared core-shell lead zirconate titanate (PZT)/TiO 2 catalysts [178].By harvesting the mechanical energy of the water, an internal piezoelectric field is induced.Under stirring at 800 rpm, the transient photocurrent of this catalyst was approximately 1.7 times that at 400 rpm.The experimental results show that the photocatalytic degradation rates of RhB, bisphenol A and phenol are greatly improved.This indicates the facilitation of the stirring-induced piezoelectric field.Xue et al. synthesized ZnO/MoS 2 nanoarrays on Ni foam [170].The porous structure of the Ni substrate can effectively induce the applied deformation on the nanorod array and generate a built-in piezoelectric field by stirring the water flow, thereby enhancing the photocatalytic performance.Under illumination, the degradation rate of MO increased with the increase of stirring speed, and its highest degradation efficiency reached 92.7%.Fu et al. synthesized ternary ZnO/ZnS/MoS 2 nanocomposites and realized piezoelectric photocatalytic performance [166].Under illumination, the photocatalytic degradation efficiency of the catalyst for MB was 36.15%, and under the combined action of stirring and illumination, the degradation efficiency was increased to 87.14%.This excellent catalytic performance can be attributed to the stirring-induced piezoelectric field, which enhances charge separation.
Catalysts 2022, 12, x FOR PEER REVIEW 21 of 37 illumination, the degradation efficiency was increased to 87.14%.This excellent catalytic performance can be attributed to the stirring-induced piezoelectric field, which enhances charge separation.

Titanate-Based Materials
Titanate-based materials are widely used in mechanical-coupled photocatalysis, such as BaTiO3 [147,168,174,180,[193][194][195], SrTiO3 [155,182,196], and PbTiO3 [153,183].Wang et al. synthesized Ag2O−BaTiO3 hybrid photocatalysts [193].Under periodic ultrasonic excitation, the spontaneous polarization potential of BaTiO3 nanocrystals to ultrasonic waves can be used as an alternating built-in electric field to continuously separate photo-induced carriers, which significantly improves the photocatalytic activity and cycling performance of the Ag2O−BaTiO3 hybrid structure.Li et al. prepared a cyclic Ti32-oxo cluster (CTOC)/BaTiO3/CuS three-layer heterojunction material for tetracycline degradation [174].As shown in Figure 17, under the combined action of visible light irradiation and ultrasonic vibration, the catalyst reached 100% decomposition efficiency within 60 min.Under ultrasonic vibration, BaTiO3 generates a polarized electric field, which inhibits the recombination of photogenerated carriers and improves photocatalytic performance.Zhang et al. synthesized a BaTiO3/SrTiO3 nanocomposite [155].The degradation rate of BaTiO3/SrTiO3 nanofibers to RhB within 30 min under the combined action of ultrasound and ultraviolet rays was 97.4%, which was 2.2 times that of pure SrTiO3 nanofibers.Cao et al. synthesized OH-modified SrTiO3 and used it as a catalyst for piezoelectric photocatalytic H2 production [182].Because the catalyst has super-hydrophilic molecular contacts, as well as more oxygen vacancies, the carrier separation is effectively promoted.Under the action of ultrasound, the optimal piezoelectric-photocatalytic H2 evolution rate (701.2μmol g −1 h −1 ) was 5.3 times that of the ordinary SrTiO3 photocatalytic H2 evolution rate.Jiang et al. studied the piezoelectric effect on the heterogeneous photocatalytic H2 production of SrTiO3 (STO) [196].The piezoelectric effect led by the ultrasonic cavitation had a different influence on heterogeneous photocatalytic H2 production with or without

Titanate-Based Materials
Titanate-based materials are widely used in mechanical-coupled photocatalysis, such as BaTiO 3 [147,168,174,180,[193][194][195], SrTiO 3 [155,182,196], and PbTiO 3 [153,183].Wang et al. synthesized Ag 2 O−BaTiO 3 hybrid photocatalysts [193].Under periodic ultrasonic excitation, the spontaneous polarization potential of BaTiO 3 nanocrystals to ultrasonic waves can be used as an alternating built-in electric field to continuously separate photoinduced carriers, which significantly improves the photocatalytic activity and cycling performance of the Ag 2 O−BaTiO 3 hybrid structure.Li et al. prepared a cyclic Ti 32 -oxo cluster (CTOC)/BaTiO 3 /CuS three-layer heterojunction material for tetracycline degradation [174].As shown in Figure 17, under the combined action of visible light irradiation and ultrasonic vibration, the catalyst reached 100% decomposition efficiency within 60 min.Under ultrasonic vibration, BaTiO 3 generates a polarized electric field, which inhibits the recombination of photogenerated carriers and improves photocatalytic performance.Zhang et al. synthesized a BaTiO 3 /SrTiO 3 nanocomposite [155].The degradation rate of BaTiO 3 /SrTiO 3 nanofibers to RhB within 30 min under the combined action of ultrasound and ultraviolet rays was 97.4%, which was 2.2 times that of pure SrTiO 3 nanofibers.Cao et al. synthesized OH-modified SrTiO 3 and used it as a catalyst for piezoelectric photocatalytic H 2 production [182].Because the catalyst has super-hydrophilic molecular contacts, as well as more oxygen vacancies, the carrier separation is effectively promoted.Under the action of ultrasound, the optimal piezoelectric-photocatalytic H 2 evolution rate (701.2µmol g −1 h −1 ) was 5.3 times that of the ordinary SrTiO 3 photocatalytic H 2 evolution rate.Jiang et al. studied the piezoelectric effect on the heterogeneous photocatalytic H 2 production of SrTiO 3 (STO) [196].The piezoelectric effect led by the ultrasonic cavitation had a different influence on heterogeneous photocatalytic H 2 production with or without sacrificial agents.The sacrificial agents with different viscosity and positions of the ultrasonic vibrators also affected the photocatalytic H 2 production of STO.Through in situ photocatalysis and sonophotocatalysis deposition of Pt nanoparticles, it was found that Pt nanoparticles preferred to aggregate on the local surface of STO nanoparticles by ultrasonic cavitation.It was explained that a piezoelectric potential on the local surface of STO would be built by ultrasonic cavitation.Xu et al. combined PbTiO 3 with g-C 3 N 4 to construct a PbTiO 3 /g-C 3 N 4 heterostructured photocatalyst with close contact [153].By applying ultrasonic-induced mechanical waves, its built-in piezoelectric field was enhanced, which significantly facilitated charge separation.Under ultrasonic conditions, its photocatalytic performance was enhanced by 30%.

Sulfide-Based Materials
In mechanical-coupled photocatalysis, sulfide materials, such as CdS [176,183,197,198], MoS2 [158,174,175], and ZnS [162,187], have also received much attention.Liu et al. synthesized a novel PbTiO3/CdS hybrid material for photocatalytic H2 production [183].The piezo-photocatalysis activity of PbTiO3/CdS (849.0 μmol g −1 h −1 ) was much higher than that of the photocatalysis alone (98.9 μmol g −1 h −1 ), after the alternating piezoelectric potential was introduced by ultrasonic waves.Specifically, as shown in Figure 18, when the direction of the applied periodic force is changed, the direction of the chemical potential difference is also changed and superimposed on the built-in piezoelectric field, thereby accelerating the carrier separation.Zhao et al. prepared CdS nanoparticles with a phase junction by controlling the hydrothermal temperature [197].Under ultrasonic vibration, a dynamic piezoelectric field is excited inside the CdS nanoparticles.The presence of the piezoelectric field eliminates the shielding effect of carriers in the built-in electric field of the phase junction, enabling the continuous separation of photogenerated carriers, and thereby enhancing the photocatalytic efficiency of CdS.Cui et al. synthesized a MoS2@Ag2O heterostructured photocatalyst for efficient all-solar photocatalysis [199].Under full sunlight and ultrasonic excitation, its MO degradation rate exceeds 95%.During this process, the spontaneous polarization potential of MoS2 forms a built-in electric field, and the ultrasonic wave as the driving force can continuously change the potential generated by the piezoelectric effect.Therefore, under ultrasonic excitation, the piezoelectric effect enhances the carrier separation, thereby enhancing the photocatalytic performance.Lin

Sulfide-Based Materials
In mechanical-coupled photocatalysis, sulfide materials, such as CdS [176,183,197,198], MoS 2 [158,174,175], and ZnS [162,187], have also received much attention.Liu et al. synthesized a novel PbTiO 3 /CdS hybrid material for photocatalytic H 2 production [183].The piezo-photocatalysis activity of PbTiO 3 /CdS (849.0 µmol g −1 h −1 ) was much higher than that of the photocatalysis alone (98.9 µmol g −1 h −1 ), after the alternating piezoelectric potential was introduced by ultrasonic waves.Specifically, as shown in Figure 18, when the direction of the applied periodic force is changed, the direction of the chemical potential difference is also changed and superimposed on the built-in piezoelectric field, thereby accelerating the carrier separation.Zhao et al. prepared CdS nanoparticles with a phase junction by controlling the hydrothermal temperature [197].Under ultrasonic vibration, a dynamic piezoelectric field is excited inside the CdS nanoparticles.The presence of the piezoelectric field eliminates the shielding effect of carriers in the built-in electric field of the phase junction, enabling the continuous separation of photogenerated carriers, and thereby enhancing the photocatalytic efficiency of CdS.Cui et al. synthesized a MoS 2 @Ag 2 O heterostructured photocatalyst for efficient all-solar photocatalysis [199].Under full sunlight and ultrasonic excitation, its MO degradation rate exceeds 95%.During this process, the spontaneous polarization potential of MoS 2 forms a built-in electric field, and the ultrasonic wave as the driving force can continuously change the potential generated by the piezoelectric effect.Therefore, under ultrasonic excitation, the piezoelectric effect enhances the carrier separation, thereby enhancing the photocatalytic performance.Lin et al. developed a monolayer and few-layer MoS 2 nanosheets (NSs) for bacterial inactivation [200].After 60 min of mechanical vibration or visible light irradiation, MoS 2 NSs can reduce Escherichia coli (E.

Polyvinylidene Fluoride
As a common piezoelectric material, polyvinylidene fluoride (PVDF) has great application potential in mechanical-coupled photocatalysis [161,169,171,181,185,201,202].Sun et al. successfully synthesized a ZnS/Bi2S3-PVDF thin film photocatalyst containing S vacancies (ZnS-VS/Bi2S3-PVDF) [181].As shown in Figure 19, the synergistic effect of the PVDF polarization electric field induced by ultrasonic cavitation and the built-in electric field formed between the ZnS-VS/Bi2S3 dissimilar junction structure is beneficial to suppressing the recombination of carriers.Its H2 evolution rate reaches 10.07 mmol g −1 h −1 .Zhang et al. prepared a PVDF/MoS2 cavity/Au heterostructured photocatalyst for MB degradation [202].The synergistic effect of the MoS2 cavity and PVDF fibers not only enhances the intrinsic piezoelectric activity of PVDF but also increases the catalytically active centers and free carrier density.The degradation efficiency was as high as 99.9% within 45 min.Lu et al. combined ZnO with PVDF thin films to obtain a bi-piezoelectric integration effect, resulting in enhanced photocatalytic performance [161].In addition, the piezoelectric potential and photocatalytic activity of the as-prepared ZnO nanorods increased with the increase of the (100) crystal face ratio.Under flowing water conditions, its optimal photocatalytic activity is 10 times that of a single photocatalytic activity.Wang et al. synthesized a bi-piezoelectric ZnO nanorod (NR)/PVDF-HFP sponge-like film [169].Under water flow, the catalyst can generate an integrated piezoelectric field that greatly drives the separation of photogenerated charge carriers.The results showed that the reaction rate constant for the degradation of MO increased three-fold when the flow rate was increased from 200 rpm to 1000 rpm.

Polyvinylidene Fluoride
As a common piezoelectric material, polyvinylidene fluoride (PVDF) has great application potential in mechanical-coupled photocatalysis [161,169,171,181,185,201,202].Sun et al. successfully synthesized a ZnS/Bi 2 S 3 -PVDF thin film photocatalyst containing S vacancies (ZnS-VS/Bi 2 S 3 -PVDF) [181].As shown in Figure 19, the synergistic effect of the PVDF polarization electric field induced by ultrasonic cavitation and the built-in electric field formed between the ZnS-VS/Bi 2 S 3 dissimilar junction structure is beneficial to suppressing the recombination of carriers.Its H 2 evolution rate reaches 10.07 mmol g −1 h −1 .Zhang et al. prepared a PVDF/MoS 2 cavity/Au heterostructured photocatalyst for MB degradation [202].The synergistic effect of the MoS 2 cavity and PVDF fibers not only enhances the intrinsic piezoelectric activity of PVDF but also increases the catalytically active centers and free carrier density.The degradation efficiency was as high as 99.9% within 45 min.Lu et al. combined ZnO with PVDF thin films to obtain a bi-piezoelectric integration effect, resulting in enhanced photocatalytic performance [161].In addition, the piezoelectric potential and photocatalytic activity of the as-prepared ZnO nanorods increased with the increase of the (100) crystal face ratio.Under flowing water conditions, its optimal photocatalytic activity is 10 times that of a single photocatalytic activity.Wang et al. synthesized a bi-piezoelectric ZnO nanorod (NR)/PVDF-HFP sponge-like film [169].Under water flow, the catalyst can generate an integrated piezoelectric field that greatly drives the separation of photogenerated charge carriers.The results showed that the reaction rate constant for the degradation of MO increased three-fold when the flow rate was increased from 200 rpm to 1000 rpm.

Electromagnetism-Coupled Photocatalysis (ECP)
The electromagnetism-coupled photocatalysis is divided into two parts to review.They are electro-coupled photocatalysis and magnetism-coupled photocatalysis, respectively.In addition, Table 3 summarizes the application results of electromagnetism-coupled photocatalysis in recent years.

Electromagnetism-Coupled Photocatalysis (ECP)
The electromagnetism-coupled photocatalysis is divided into two parts to review.They are electro-coupled photocatalysis and magnetism-coupled photocatalysis, respectively.In addition, Table 3 summarizes the application results of electromagnetism-coupled photocatalysis in recent years.

Electro-Coupled Photocatalysis
Adding an external electric field to the photocatalytic system can effectively promote the separation and migration of photogenerated carriers.At present, there are two main ways for researchers to add an electric field: one is to directly connect to an external power source during the photocatalytic process, and the other is to polarize the catalyst in the electric field and then perform photocatalytic experiments.
Directly adding an external electric field during the photocatalytic process is a common utilization method in electro-coupled photocatalysis.Li et al. synthesized rutile TiO 2 nanograss on titanium mesh [222].By connecting the titanium mesh to a power source, the photocatalytic removal capacity of rutile TiO 2 nanograss for Cr(VI) ions in wastewater can reach 143.8 mg/g under an external electric field and sunlight.Studies have shown that electrons provided by an external electric field can effectively inhibit the recombination of photogenerated carriers, thereby enhancing the catalytic activity.Pan et al. synthesized layered TiO 2 microspheres for the removal of tributyltin (TBT) in electro-coupled photocatalysis, and the reaction setup is shown in Figure 20 [214].The bias potential provided by the applied electric field greatly facilitates the separation of photogenerated carriers.The results show that the removal reaction rate constant (k = 0.0488 min −1 ) under electro-coupled photocatalysis is nearly times higher than that under photocatalysis (k = 0.0052 min −1 ).Zhang et al. developed a new electro-assisted photocatalytic technology for liquid and gas phase reactions (such as water splitting and CO 2 reduction) [220].They applied a lower external voltage on the self-doped TiO 2 nanotube films.With electrical assistance, the recombination of photogenerated carriers is greatly suppressed, and photoexcited electrons are ejected from the catalyst, enabling spatial separation of carriers.It is worth mentioning that the photocatalytic redox reaction is integrated on a thin film in this system, rather than taking place on traditional separate electrodes.
is worth mentioning that the photocatalytic redox reaction is integrated on a thin film in this system, rather than taking place on traditional separate electrodes.In addition to directly adding an external electric field, the researchers also developed another way of electrically coupled photocatalysis.They put the ferroelectric material into an external electric field for polarization before conducting the photocatalytic experiments.The strong ferroelectric field formed by the polarized material can effectively promote charge separation and improve photocatalytic efficiency.Nam et al. prepared polarized K0.5Na0.5NbO3powder by a corona polarization method for H2 production [221].The enlarged positively charged surface of the catalyst promotes the photocatalytic activity.Under optimal conditions, its photocatalytic activity was increased by 7.4 times.Yun et al. prepared well-polarized BiFeO3 nanoparticles by a simple electrical polarization method [210].The photocatalytic degradation rate of RhB by the polarized BiFeO3 nanoparticles was increased by two times compared with the unpolarized.Its excellent photocatalytic performance can be attributed to the improved carrier separation by ferroelectric polarization.Tian et al. prepared ultrathin Bi2MoO6 nanosheets with strong ferroelectricity by a corona polarization method for photocatalytic CO2 reduction [223].Its CO generation rate is 14.38 μmol g −1 h −1 , which is more than 10 times higher than that of bulk Bi2MoO6.As shown in Figure 21, this combined strategy significantly promotes the separation of photogenerated electrons and holes, enriches the reaction sites for CO2 adsorption, and jointly improves the photocatalytic CO2 reduction performance.In addition to directly adding an external electric field, the researchers also developed another way of electrically coupled photocatalysis.They put the ferroelectric material into an external electric field for polarization before conducting the photocatalytic experiments.The strong ferroelectric field formed by the polarized material can effectively promote charge separation and improve photocatalytic efficiency.Nam et al. prepared polarized K 0.5 Na 0.5 NbO 3 powder by a corona polarization method for H 2 production [221].The enlarged positively charged surface of the catalyst promotes the photocatalytic activity.Under optimal conditions, its photocatalytic activity was increased by 7.4 times.Yun et al. prepared well-polarized BiFeO 3 nanoparticles by a simple electrical polarization method [210].The photocatalytic degradation rate of RhB by the polarized BiFeO 3 nanoparticles was increased by two times compared with the unpolarized.Its excellent photocatalytic performance can be attributed to the improved carrier separation by ferroelectric polarization.Tian et al. prepared ultrathin Bi 2 MoO 6 nanosheets with strong ferroelectricity by a corona polarization method for photocatalytic CO 2 reduction [223].Its CO generation rate is 14.38 µmol g −1 h −1 , which is more than 10 times higher than that of bulk Bi 2 MoO 6 .As shown in Figure 21, this combined strategy significantly promotes the separation of photogenerated electrons and holes, enriches the reaction sites for CO 2 adsorption, and jointly improves the photocatalytic CO 2 reduction performance.is worth mentioning that the photocatalytic redox reaction is integrated on a thin film in this system, rather than taking place on traditional separate electrodes.In addition to directly adding an external electric field, the researchers also developed another way of electrically coupled photocatalysis.They put the ferroelectric material into an external electric field for polarization before conducting the photocatalytic experiments.The strong ferroelectric field formed by the polarized material can effectively promote charge separation and improve photocatalytic efficiency.Nam et al. prepared polarized K0.5Na0.5NbO3powder by a corona polarization method for H2 production [221].The enlarged positively charged surface of the catalyst promotes the photocatalytic activity.Under optimal conditions, its photocatalytic activity was increased by 7.4 times.Yun et al. prepared well-polarized BiFeO3 nanoparticles by a simple electrical polarization method [210].The photocatalytic degradation rate of RhB by the polarized BiFeO3 nanoparticles was increased by two times compared with the unpolarized.Its excellent photocatalytic performance can be attributed to the improved carrier separation by ferroelectric polarization.Tian et al. prepared ultrathin Bi2MoO6 nanosheets with strong ferroelectricity by a corona polarization method for photocatalytic CO2 reduction [223].Its CO generation rate is 14.38 μmol g −1 h −1 , which is more than 10 times higher than that of bulk Bi2MoO6.As shown in Figure 21, this combined strategy significantly promotes the separation of photogenerated electrons and holes, enriches the reaction sites for CO2 adsorption, and jointly improves the photocatalytic CO2 reduction performance.

Magnetism-Coupled Photocatalysis
In recent years, more and more attention has been paid to the promotion of magnetic fields on photocatalytic performance.In a magnetism-coupled photocatalytic system, the magnetic-field-induced Lorentz force diverts the charge from its original recombination path, leading to more carriers participating in the reaction, thereby enhancing the photocatalytic activity [206,213,216,225,226].In addition, for materials with electron spin properties, the magnetic field can also enhance the electron-spin parallel alignment, which also has a positive effect on photocatalytic performance [209,217,227].
Gao et al. reported a Lorentz force-enhanced photogenerated carrier separation strategy using highly crystalline TiO 2 nanosheets with few defects as photocatalysts [225].Studies have shown that the Lorentz force suppresses photogenerated carrier recombination, making more carriers available for transport in photocatalysts.The results showed that the photocatalytic degradation rate of MO was increased by 26% only by placing permanent magnets under the photocatalytic reactor.Nan et al. synthesized a 3D/2D Mn 2 O 3 /g-C 3 N 4 photocatalyst for simultaneous removal of nitrate and ammonia from polluted water and developed a magnetic field-enhanced photocatalytic system [226].Under the action of an external magnetic field, the removal efficiencies of nitrate and ammonia were 94.5% and 97.4%, respectively.The external magnetic field promotes the separation of carriers by generating the Lorentz force.Tsang et al. reported a photocatalytic water splitting system based on Fe 3 O 4 /N-TiO 2 magnetic photocatalyst assisted by the local magnetic field effect [217].At a magnetic field strength of 180 mT and 270 • C, the quantum efficiency at 437 nm reaches 88.7%.As shown in Figure 22, the synergistic effect of the Lorentz force and spin polarization greatly facilitates the charge separation process, thereby enhancing the photocatalytic efficiency.Sang et al. prepared a CdS/MoS 2 /Mo hybrid structured photocatalyst and studied the effect of magnetic field on photocatalytic activity [218].The relative motion between the metal molybdenum sheet and the rotating magnetic field forms a kinematic electromotive force.This electromotive force significantly inhibits the photoinduced carrier recombination of CdS.Under the synergistic effect of MoS 2 co-catalyst, its photocatalytic H 2 production performance is improved by approximately 89% compared with single photocatalysis.Chen et al. synthesized a Mn 3 O 4 /γ-MnOOH photocatalyst for norfloxacin (NOR) degradation [215].Under the action of magnetic field-assisted visible light, the degradation rate of NOR was 98.8% within 60 min.In neutral media, positively charged NOR and negatively charged catalysts align in the presence of a magnetic field, thereby enhancing the reactivity.Furthermore, the opposing Lorentz force contributed to the mutual attraction between NOR and catalyst, which accelerated NOR degradation.

Magnetism-Coupled Photocatalysis
In recent years, more and more attention has been paid to the promotion of magnetic fields on photocatalytic performance.In a magnetism-coupled photocatalytic system, the magnetic-field-induced Lorentz force diverts the charge from its original recombination path, leading to more carriers participating in the reaction, thereby enhancing the photocatalytic activity [206,213,216,225,226].In addition, for materials with electron spin properties, the magnetic field can also enhance the electron-spin parallel alignment, which also has a positive effect on photocatalytic performance [209,217,227].
Gao et al. reported a Lorentz force-enhanced photogenerated carrier separation strategy using highly crystalline TiO2 nanosheets with few defects as photocatalysts [225].Studies have shown that the Lorentz force suppresses photogenerated carrier recombination, making more carriers available for transport in photocatalysts.The results showed that the photocatalytic degradation rate of MO was increased by 26% only by placing permanent magnets under the photocatalytic reactor.Nan et al. synthesized a 3D/2D Mn2O3/g-C3N4 photocatalyst for simultaneous removal of nitrate and ammonia from polluted water and developed a magnetic field-enhanced photocatalytic system [226].Under the action of an external magnetic field, the removal efficiencies of nitrate and ammonia were 94.5% and 97.4%, respectively.The external magnetic field promotes the separation of carriers by generating the Lorentz force.Tsang et al. reported a photocatalytic water splitting system based on Fe3O4/N-TiO2 magnetic photocatalyst assisted by the local magnetic field effect [217].At a magnetic field strength of 180 mT and 270 °C, the quantum efficiency at 437 nm reaches 88.7%.As shown in Figure 22, the synergistic effect of the Lorentz force and spin polarization greatly facilitates the charge separation process, thereby enhancing the photocatalytic efficiency.Sang et al. prepared a CdS/MoS2/Mo hybrid structured photocatalyst and studied the effect of magnetic field on photocatalytic activity [218].The relative motion between the metal molybdenum sheet and the rotating magnetic field forms a kinematic electromotive force.This electromotive force significantly inhibits the photo-induced carrier recombination of CdS.Under the synergistic effect of MoS2 co-catalyst, its photocatalytic H2 production performance is improved by approximately 89% compared with single photocatalysis.Chen et al. synthesized a Mn3O4/γ-MnOOH photocatalyst for norfloxacin (NOR) degradation [215].Under the action of magnetic field-assisted visible light, the degradation rate of NOR was 98.8% within 60 min.In neutral media, positively charged NOR and negatively charged catalysts align in the presence of a magnetic field, thereby enhancing the reactivity.Furthermore, the opposing Lorentz force contributed to the mutual attraction between NOR and catalyst, which accelerated NOR degradation.

Conclusions
In this review, we summarized the current research progress of thermal-coupled Photocatalysis (TCP), Mechanical-coupled Photocatalysis (MCP), and Electromagnetismcoupled Photocatalysis (ECP), including the primary sources of external energy, the related materials, and the main applications.These external physical fields can significantly improve the efficiency of the photocatalytic system, which have different mechanisms and respective advantages.In summary, the common feature of these external physical fields coupling to photocatalysis is that external physical fields can re-emit the trapped electrons and drive them rapidly to transfer to the surface of the photocatalyst.Though assisted external physical fields can overcome the inherent weakness of the photocatalytic reaction process, there are still some fundamental issues and challenges to be explored.
(i) Evaluation of energy conversion efficiency.When external physical fields are applied to the photocatalytic reaction process, additional energy will inevitably be input into the system.Therefore, the solar energy conversion efficiency cannot only be considered when calculating energy conversion efficiency.The extra energy generated by external physical fields should be taken into account.(ii) Ubiquitous thermal effect.Thermal energy is low-quality energy.The external physical fields will eventually dissipate into heat energy.The special thermal effects can be generated by microwaves, ultrasonic waves, and electromagnetism waves.Thus, it is important to distinguish thermal effects and non-thermal effects on photocatalysis coupling by external physical fields.(iii) A single material response for multiple-physical fields.To realize photocatalysis coupling by external physical fields, composite materials combining photocatalysts and external field absorption materials are usually used.However, the composite materials are complicated both in the synthesis and photocatalytic reaction process.So, it is interesting to explore a single material that can respond to multiple-physical fields.For example, the spontaneous symmetry-breaking semiconductors can absorb multiple-physical fields at the same time, which might be used in photocatalysis coupling by external physical fields.(iv) Mechanisms for potential barrier formation by external physical fields.When external physical fields are applied to photocatalysts, a built-in electric field with different directions will be generated to separate the photogenerated carriers.However, mechanisms for potential barrier formation by external physical fields need to be uncovered.Thus, this built-in electric field can be controlled and optimized in favor of photocatalysis coupling by external physical fields.(v) Reactor design for photocatalysis coupling by external physical fields.The traditional photocatalytic reactor is not satisfied with photocatalysis coupling by external physical fields.The design principles of the reactor must be high-efficiency and well-adapted for different external physical fields.(vi) Horizontal comparison is neglected in the study of photocatalysis coupling by external physical fields.Different external physical fields should make different contributions to photocatalysis.Keeping a balance between photocatalytic efficiency and economic efficiency, the best assisted physical field for photocatalysis needs to be further studied.

Figure 1 .
Figure 1.Schematic diagram of three types of external field-assisted photocatalysis.

Figure 1 .
Figure 1.Schematic diagram of three types of external field-assisted photocatalysis.
40].According to different photothermal conversion mechanisms (as shown in Figure 5), near-infrared light can be converted to heat by three categories of materials: (1) Metallic materials with localized surface plasmon effect; (2) Narrow-band semiconductors with non-radiative relaxation; and (3) Carbon-based materials with thermal vibration Therefore, TCP can be realized by near-infrared indirect heating through the composite material of photocatalysts and near-infrared absorption materials.

Figure 6 .
Figure 6.(a) Photocatalytic H 2 evolution activity of pure Zn 0.67 Cd 0.33 S and Zn 0.67 Cd 0.33 S supported by Au nanoparticles with different spatial arrangements (Au@Zn 0.67 Cd 0.33 S) under visible light irradiation (≥420 nm); blue columns represent the enhancement promoted by plasmonic-Au nanostructures.(b) Illustration for the proximity of semiconductors to the electromagnetic fields of plasmonic Au nanoparticles [46].

Figure 10 .
Figure 10.(a) Light absorption spectra for the F-Wood and F-Wood/CNTs membranes (Reprinted/adapted with permission from Ref. [75].Copyright 2017, copyright Wiley-VCH).(b) UV-vis absorption curves of nano-GO and nano-rGO, respectively.The inset shows a zoom-in view of the curves in the 800 nm region (Reprinted/adapted with permission from Ref. [78].Copyright 2011, copyright American Chemical Society).(c) UV-vis-NIR extinction spectra were recorded for 25 μg mL −1 PVA stabilized PPy nanoparticles dispersed in water and stored at 4 °C for six months.The inset shows the prepared sample (Reprinted/adapted with permission from Ref. [81].Copyright 2013, copyright Wiley-VCH).

Figure 10 .
Figure 10.(a) Light absorption spectra for the F-Wood and F-Wood/CNTs membranes (Reprinted/adapted with permission from Ref. [75].Copyright 2017, copyright Wiley-VCH).(b) UVvis absorption curves of nano-GO and nano-rGO, respectively.The inset shows a zoom-in view of the curves in the 800 nm region (Reprinted/adapted with permission from Ref. [78].Copyright 2011, copyright American Chemical Society).(c) UV-vis-NIR extinction spectra were recorded for 25 µg mL −1 PVA stabilized PPy nanoparticles dispersed in water and stored at 4 • C for six months.The inset shows the prepared sample (Reprinted/adapted with permission from Ref. [81].Copyright 2013, copyright Wiley-VCH).

Figure 12 .
Figure 12.The schematic diagram illustrates the mechanism for enhanced photocatalytic H2 generation due to photothermal and photochemical effects (Reprinted/adapted with permission from Ref. [104].Copyright 2021, copyright Wiley-VCH).

Figure 12 .
Figure 12.The schematic diagram illustrates the mechanism for enhanced photocatalytic H 2 generation due to photothermal and photochemical effects (Reprinted/adapted with permission from Ref. [104].Copyright 2021, copyright Wiley-VCH).

Figure 14 .
Figure 14.Mechanistic diagram of the photo−thermal catalytic degradation of the toluene reaction on Pt−Cu/TiO 2 catalysts (Reprinted/adapted with permission from Ref. [120].Copyright 2022, copyright American Chemical Society).
et al. developed a monolayer and few-layer MoS2 nanosheets (NSs) for bacterial inactivation [200].After 60 min of mechanical vibration or visible light irradiation, MoS2 NSs can reduce Escherichia coli (E.coli) by 99.999%.After the deposition of Au nanoparticles (NPs) on MoS2 NSs, the time was shortened to 45 min.Furthermore, after synergizing mechanical vibration and near-infrared (NIR) light irradiation, Au-MoS2 eliminated E. coli in only 15 min.Zhai et al. modified In2S3 nanosheets with ZnS and Ba-

Table 1 .
Summary of thermal-coupled photocatalysis in recent years.

Table 2 .
Summary of mechanical-coupled photocatalysis in recent years.

Table 3 .
Summary of electromagnetism-coupled photocatalysis in recent years.

Table 3 .
Summary of electromagnetism-coupled photocatalysis in recent years.