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Article

Construction of Novel Z-Scheme g-C3N4/AgBr-Ag Composite for Efficient Photocatalytic Degradation of Organic Pollutants under Visible Light

by
Xuefeng Hu
*,
Ting Luo
,
Yuhan Lin
and
Mina Yang
*
School of Environmental Science and Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China
*
Authors to whom correspondence should be addressed.
Catalysts 2022, 12(11), 1309; https://doi.org/10.3390/catal12111309
Submission received: 28 September 2022 / Revised: 17 October 2022 / Accepted: 20 October 2022 / Published: 25 October 2022
(This article belongs to the Special Issue Advances in Heterojunction Photocatalysts)
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Abstract

As a green and sustainable technology to relieve environmental pollution issues, semiconductor photocatalysis attracted great attention. However, most single-component semiconductors suffer from high carrier recombination rate and low reaction efficiency. Here, we constructed a novel visible-light-driven Z-scheme g-C3N4/AgBr-Ag photocatalyst (noted as CN-AA-0.05) using a hydrothermal method with KBr as the bromine source. The CN-AA-0.05 photocatalyst shows an excellent photocatalytic degradation performance, and a rhodamine B (RhB) degradation ratio of 96.3% in 40 min, and 2-mercaptobenzothiazole (MBT) degradation ratio of 99.2% in 18 min are achieved. Mechanistic studies show that the remarkable performance of CN-AA-0.05 is not only attributed to the enhanced light absorption caused by the Ag SPR effect, but also the efficient charge transfer and separation with Ag nanoparticles as the bridge. Our work provides a reference for the design and construction of efficient visible-light-responsive Z-scheme photocatalysts, and an in-depth understanding into the mechanism of Z-scheme photocatalysts.

1. Introduction

Organic pollutants in environmental water bodies such as dyes and pesticides seriously endanger the ecological environment and human health [1]. Due to the requirements of green and low carbon, the greatest expectation for the treatment of organic pollutants in water is semiconductor photocatalytic degradation [2,3,4]. However, single-component semiconductors are commonly confronted with low efficiency due to the poor charge transfer and separation [5,6,7,8]. The construction of Z-scheme photocatalytic systems that mimic natural photosynthesis is a promising strategy to improve the photocatalytic efficiency of semiconductor photocatalysts [9,10,11]. A Z-scheme photocatalytic system generally consists of an oxidation reaction catalyst (PS II), a reduction reaction catalyst (PS I), and an electron mediator [5,6]. Under irradiation, both PS II and PS I catalysts of the Z-scheme system generate photo-generated charges [5,6]. The photo-generated electrons of PS II migrate to the electron mediator and recombine with the photo-generated holes of PS II, then the photo-generated electrons in PS I induce a reduction reaction while the photo-generated holes in PS II induce an oxidation reaction [5,6]. Since the reduction reaction and oxidation reaction occur at different sites, the Z-scheme system not only reduces the thermodynamic requirements of the photocatalytic reaction, providing a large space for the selection and design of photocatalytic materials, but also promotes the separation and transport of photo-generated carriers, greatly inhibiting the recombination of carriers [5,6].
Graphitic carbon nitride (g-C3N4) is a unique two-dimensional semiconductor photocatalyst without metal elements. It is regarded as one of the most likely semiconductors for large-scale applications in the future because of low cost, high stability, and visible-light-responsive activity [12,13]. Z-scheme systems based on g-C3N4, such as WO3/g-C3N4 [14,15,16], Ag3PO4/g-C3N4 [17,18], TiO2/g-C3N4 [19,20,21], and AgX/g-C3N4 [22], were reported to be widely used in various environmental remediation reactions. To further improve the performance of g-C3N4-based Z-scheme photocatalysts, researchers also tried to introduce a third component such as noble metal nanoparticles into the system [23,24,25]. On one hand, noble metal nanoparticles can act as electron acceptors to further promote the interfacial charge transfer and separation. On the one hand, noble metal nanoparticles can induce a surface plasmon resonance (SPR) effect and, effectively enhance the light absorption ability. For example, Shen [23] et al. constructed g-C3N4/Ag/Ag3PO4 composites by a simple in-situ deposition method. The g-C3N4/Ag/Ag3PO4 shows a phenol degradation kinetic constant of 1.13 min−1, almost 60 and 2.5 times higher than that of pure g-C3N4 and Ag/Ag3PO4, respectively. In addition, the CdS/Ag/g-C3N4 Z-scheme photocatalyst reported by Qian [24] et al. has a high H2 evolution rate of 1376.0 μmol h−1∙g−1 in lactic acid scavenger solution, which is 3.12 and 1.76 times that of CdS and CdS/g-C3N4, respectively.
In this work, we prepared a series of novel visible-light-driven Z-scheme g-C3N4/AgBr-Ag photocatalysts with different component ratios, through a hydrothermal method with KBr as the bromine source. Different from other methods [26,27,28] that use CTAB as the bromine source, our method with KBr as the bromine source avoids the surfactant contamination of water body. In addition, compared with the method of combining g-C3N4 and AgBr by direct physical means, our method of compounding different components by a hydrothermal process led to the formation of a new component metallic Ag. The g-C3N4/AgBr-Ag Z-scheme photocatalyst showed excellent photocatalytic degradation activities of RhB and MBT under visible light irradiation. Moreover, the stability and the possible photocatalytic mechanism of the g-C3N4/AgBr-Ag Z-scheme photocatalyst were also investigated in detail.

2. Results and Discussion

Figure 1a shows the XRD patterns of the CN, Ag/AgBr, and CN-AA-X catalysts (X = 0.03, 0.05, or 0.07), and CN-AA-0.05-D. The characteristic peaks at 13.1° and 27.5° for CN sample are clearly observed, which are attributed to the (1 0 0) in-plane of tris-triazine units and the (0 0 2) diffraction planes of g-C3N4, respectively [29]. The diffraction peaks at 26.8°, 31.0°, 44.4°, 55.1°, 64.6°, 73.3°, and 81.8° for the Ag/AgBr sample are assigned to the (1 1 1), (2 0 0), (2 2 0), (2 2 2), (4 0 0), (4 2 0), and (4 2 2) planes of AgBr crystal (JCPDS 06-0438), respectively [30], and the faint diffraction peak at 38.1° for Ag/AgBr sample corresponds to the metallic Ag. For all the CN-AA-X catalysts, the characteristic peaks present the coexistence of Ag, AgBr, and g-C3N4 phases, although the characteristic peaks ascribed to the metallic Ag are much weaker due to the low content. For the CN-AA-0.05-D catalyst, the characteristic peaks are similar to those of CN-AA-X catalysts, except that no peak ascribed to the metallic Ag is observed.
The microstructures and morphologies of prepared CN, CN-AA-0.05, and CN-AA-0.05-D catalysts are revealed by SEM, TEM, and HRTEM observations (Figure 1b–f). It can be seen that the pure g-C3N4 presents a compact lamellar structure with a rough surface (Figure 1b). Some slit-shaped pores appear in the CN-AA-0.05 sample due to the introduction of Ag/AgBr (Figure 1c). The CN-AA-0.05-D shows a microstructure similar to that of pure g-C3N4, but some irregular particles deposition is observed on the surface (Figure 1e). Figure 1d is the TEM of CN-AA-0.05, in which the Ag/AgBr nanoparticle is anchored on the surface of g-C3N4. The Ag/AgBr nanoparticle is confirmed by HRTEM image, as shown in Figure 1f, and the particle displays three distinct areas with different lattice fringes. The lattice with d spacing of 0.24 nm corresponds to the (1 1 1) plane of metallic Ag, while those of 0.28 and 0.33 nm can be indexed to the (2 0 0) plane and the (1 1 1) plane of AgBr, respectively. This undoubtedly shows the effectiveness of hydrothermal treatment to partially reduce Ag+ to Ag0. All of these confirm the formation of the contact interface between AgBr, g-C3N4, and metallic Ag.
The elemental composition and chemical valence state of as-prepared CN, CN-AA-0.05, and CN-AA-0.05-D catalysts were investigated by XPS (Figure 2). It is clearly shown in Figure 2a that CN consists of C, N, and small amounts of adsorbed O elements, while both the CN-AA-0.05 and CN-AA-0.05-D samples consist of Ag, Br, C, N, and O elements. Figure 2b shows the C 1s XPS spectra of CN, CN-AA-0.05, and CN-AA-0.05-D samples. For all the three samples, the peaks at 284.62, 285.93, and 287.81 eV correspond to the surface adventitious carbon, sp2 C atoms bonded to N in an aromatic ring (N-C=N), and sp3 hybridized C atoms [C-(N)3], respectively [31]. According to the N 1s XPS spectra of the CN, CN-AA-0.05, and CN-AA-0.05-D samples (Figure 2c), the peaks at 398.31, 398.93, 400.60, and 404.42 eV are attributed to the signals of sp2 hybridized aromatic N atoms bonded to carbon atoms (C-N=C), tertiary N bonded to C atoms in the form of N-(C)3, N–H structure, and charging effect, respectively [32]. Figure 2d displays the Ag 3d XPS spectra of the CN-AA-0.05 and CN-AA-0.05-D samples. For the CN-AA-0.05 sample, the two peaks corresponding to the Ag 3d5/2 and Ag 3d3/2, respectively, can be fitted to four peaks. The Ag+ in AgBr is responsible for the peaks at 367.08 eV and 373.18 eV, while metallic Ag is responsible for the peaks at 367.80 eV and 374.36 eV [30,33]. For the CN-AA-0.05-D sample, only peaks ascribed to the Ag+ can be observed, which is consistent with the XRD result. It implies that the hydrothermal treatment plays a key role in the formation of metallic Ag. For both the CN-AA-0.05 and CN-AA-0.05-D samples, the two peaks at 67.68 and 68.77 eV in Figure 2e are attributed to the Br 3d5/2 and Br 3d3/2, respectively [30].
The optical property of CN, AgBr, CN-AA-X (X = 0.03, 0.05 or 0.07), and CN-AA-0.05-D were determined by UV–vis DRS test (Figure 3a). CN shows an absorption edge of about 460 nm, while AgBr exhibits an absorption edge of about 480 nm. For the CN-AA-X sample, the absorption intensity enhances compared with that of CN, and the absorption intensity increases with the increasing X value (the Ag/AgBr content), mainly due to the surface plasmon absorption of Ag and the interaction between Ag and AgBr. The estimated bandgaps of CN, AgBr, CN-AA-0.03, CN-AA-0.05, CN-AA-0.07, and CN-AA-0.05-D are 2.48, 2.36, 2.43, 2.38, 2.39, and 2.40 eV, respectively (Figure 3b) [34,35].
PL spectra (Figure 3c) and time-resolved fluorescence decay spectra (Figure 3d) were measured to study the transfer and annihilation processes of photo-generated carriers of CN-AA-0.05 and other comparative catalysts. As shown in Figure 3c, the PL intensity of CN is the highest, and the PL intensity decreases significantly after the introduction of Ag/AgBr. For CN-AA-0.05, the PL intensity is the lowest. These results indicate that an appropriate amount of Ag/AgBr introduction can effectively suppress the recombination of photo-generated carriers, thereby enhancing the catalytic performance. According to Figure 3d, the carrier lifetime of the CN-AA-0.05 catalyst is much shorter than that of CN, which indicates the efficient charge transfer among the components of the Z-scheme system.
Figure 3e shows the FTIR spectra of the pure g-C3N4 and CN-AA-X catalysts. The broadband at 3000–3400 cm−1 corresponds to the stretching modes of terminal NH2 or NH groups. The absorption peaks at 1641 and 1567 cm−1 are attributed to C=N stretching, and 1406, 1330, and 1241 cm−1 are assigned to the aromatic C-N stretching [36,37]. Additionally, the sharp characteristic ring breath peak of the triazine units is found at 808 cm−1 [36,37]. It is noticed that the introduction of Ag/AgBr does not obviously affect the FTIR of g-C3N4.
The photocatalytic activities of CN, AgBr, CN-AA-X (X = 0.03, 0.05 or 0.07), and CN-AA-0.05-D materials were firstly evaluated by the degradation of dye RhB under visible light. As shown in Figure 4a, CN shows a photocatalytic degradation rate of 41.2% within 50 min, while AgBr or CN-AA-0.05-D exhibit a slightly better photocatalytic degradation performance than CN. For all CN-AA-X catalysts, the activities increase significantly compared with pure CN or AgBr, demonstrating the importance of the construction of g-C3N4/AgBr-Ag heterojunction photocatalysts for enhancing the photocatalytic performance. CN-AA-0.05 exhibits the best photocatalytic degradation performance of RhB among all CN-AA-X catalysts, with a degradation rate of 96.3% within 40 min, which indicates that there is an optimal Ag/AgBr introduction amount for the enhancement of photocatalytic degradation performance. Finally, after the first-order kinetic curve fitting, the calculated degradation rate constants are 0.008 min−1 for CN, 0.014 min−1 for AgBr, 0.030 min−1 for CN-AA-0.03, 0.061 min−1 for CN-AA-0.05, 0.032 min−1 for CN-AA-0.07, and 0.017 min−1 for CN-AA-0.05-D (Figure 4b). Subsequently, the activities of photocatalytic degradation MBT under visible light by these materials were further investigated. As shown in Figure 4c, CN-AA-0.05 exhibits the best photocatalytic degradation performance of MBT, with a degradation rate of 99.2% within 18 min. The activity trend of CN, AgBr, CN-AA-0.03, CN-AA-0.05, CN-AA-0.07, and CN-AA-0.05-D for photocatalytic degradation of MBT is the same as that of RhB, and the calculated degradation rate constants are 0.0234, 0.040, 0.128, 0.197, 0.157, and 0.049 min−1, respectively (Figure 4d). The slope values of the linear fit corresponding to CN-AA-0.03, CN-AA-0.05, and CN-AA-0.07 seem to be affected especially by the very last irradiation point (i.e., 40 min) in Figure 4b. This may be due to degradation characterization of RhB. Degradation of RhB is accompanied by the blue shift of the absorption maximum due to the N-deethylation reaction, as we reported before [38], but the recorded value is still the maximum absorption position of RhB (553 nm), resulting in a deviation from first-order linear fitting.
In conclusion, the CN-AA-0.05 composite material prepared by hydrothermal method with the AgNO3 addition amount of 0.05 g shows the best degradation performance, with the RhB degradation rate of 96.3% in 40 min and the MBT degradation rate of 99.2% in 18 min. As shown in Figure 5, the MBT degradation rate of CN-AA-0.05 remains above 90% after five cycles of 20 min per cycle, which demonstrates the excellent stability of the CN-AA-0.05 catalyst.
The reactive species that may be involved in a photocatalytic process mainly include ·OH, ·O2−, h+, and e−. To accurately infer the mechanism of a photocatalytic reaction, it is first necessary to determine the type of active species that plays the most critical role in the photocatalytic process. Here, the essential active species during the MBT degradation process were investigated by quenching experiments [39]. EA (10 mmol/L), BQ (12 mmol/L), EDTA-2Na (12 mmol/L), and Cr(VI) (0.05 mmol/L) were applied to quench ·OH, ·O2−, h+, and e−, respectively. As shown in Figure 6a, the addition of BQ and EDTA-2Na greatly reduces the photocatalytic degradation performance of MBT, which indicates the important roles of ·O2− and h+ in the photocatalytic degradation process. The addition of EA has little effect on MBT degradation, suggesting a negligible contribution of ·OH. Furthermore, the addition of Cr(VI) enhances the activity of photocatalytic degradation of MBT, which is attributed to the fact that more h+ can react with MBT rather than recombine with electrons due to the quenching of electrons by Cr(VI). In detail, under visible light irradiation, CN-AA-0.05 can be photo-excited to yield electron (e–) and hole (h+). On one hand, organic pollutants that react irreversibly with photo-generated h+ can enhance the photocatalytic electron–hole separation, which results in more CB electrons for Cr(VI) reduction. On the other hand, photoelectrons transfer to the conduction band and are captured by oxygen to form O2●−, or by Cr(VI) to form lower valent state chromium, which results in more holes for organic pollutants oxidation. The synergistic effect of Cr(VI) reduction and organic pollutants degradation over semiconductor photocatalysis was reported previously [40,41,42].
To identify the carrier transfer mechanism in the photocatalytic degradation process over CN-AA-0.05, radical spin-trapping experiments were further carried out. For the O2●− spin-trapping test, there is no signal in dark, however, characteristic peaks of DMPO-OOH adduct (pointing to superoxide radical) emerge under visible light (Figure 6b). This result is coherent with the scavenging investigation, where O2●− seems to have an important contribution to MBT degradation. For the ·OH spin-trapping test, the quartet ascribed to DMPO-OH spin-adduct (hydroxyl radical EPR fingerprint) is also observed under visible light (Figure 6c), but the signal disappears in an oxygen-free condition. It is very well-known that in aqueous solution, the DMPO-OOH spin-adduct has a lifetime of ca. 30 s that rapidly evolves into DMPO-OH spin-adduct [43]. This indicates that the observed DMPO-OH signal should be the transformation product of DMPO-OOH, which verifies the negligible contribution of ·OH to MBT degradation.
Based on the above results and the related literature [44,45,46,47], the possible photocatalytic mechanism of CN-AA-0.05 was proposed (Figure 7). Under visible light, both g-C3N4 and AgBr are excited to generate eCB− and hVB+. The eCB− of AgBr are quickly transferred to metallic Ag through the Schottky barrier, and, subsequently, the electrons in Ag are transferred to the VB of g-C3N4 and recombine with the hVB+ of g-C3N4. That is, Ag acts as an electron transfer bridge. Therefore, the eCB− of g-C3N4 with strong reduction capability and hVB+ of AgBr with strong oxidation capability remain, enabling the Z-scheme mechanism. The eCB− of g-C3N4 can further react with O2 to form crucial active species O2·−, which, together with hVB+ of AgBr, can oxidize and degrade organic pollutants.

3. Experimental Section

3.1. Catalyst Preparation

The g-C3N4 powders were synthesized by heating melamine in a muffle furnace. In a typical process, 10 g melamine was placed in a crucible with a cover. The crucible was heated to 550 °C at a heating rate of 5 °C/min and then kept for 3 h. After cooling to the room temperature, the yellow product g-C3N4 was obtained and noted as CN.
The g-C3N4/AgBr-Ag was synthesized as follows: X g of AgNO3 (X = 0.03, 0.05, or 0.07) and 0.5 g of g-C3N4 were added to 80 mL of ethylene glycol, and the mixture was stirred at room temperature for 1 h. Then, 0.7X g KBr was added, and the mixture was stirred for another 6 h. Subsequently, the obtained mixture was transferred to an autoclave for the hydrothermal reaction at 180 °C for 10 h. Finally, the product was washed with deionized water 5 times, washed with ethanol once, and dried in an oven at 50 °C. The obtained sample was noted as CN-AA-X (X is the added mass of AgNO3). For comparison, g-C3N4/AgBr-Ag without hydrothermal treatment was also prepared by the same method, which was marked as CN-AA-X-D.

3.2. Catalyst Characterization

The crystal structures of the samples were investigated on a Bruker D8 Advance X-ray diffractometer (XRD) using Cu Kα radiation source. The morphologies and microstructures of catalysts were observed by scanning electron microscopy (SEM) and transmission electron microscopy (HRTEM) on a Zeiss Sigma500 (Oberkochen, Baden-Württemberg, Germany) and a JEOL JEM 2100F electron microscope (Tokyo, Japan), respectively. X-ray photoelectron spectroscopy (XPS) was performed on a Kratos AXIS SUPRA spectrometer (Manchester, UK). The UV–vis diffuse reflectance spectra (DRS) were obtained by a Cary 5000 spectrophotometer (Santa Clara, CA, USA) using BaSO4 as the reflectance standard. Photoluminescence (PL) spectra and time-resolved fluorescence emission decay spectra were recorded on an Edinburgh FS5 fluorescence spectrometer (Edinburgh, UK) with the excitation wavelength of 350 nm. Fourier-transform infrared (FTIR) spectra of synthesized samples were obtained on a spectrophotometer (Vertex70, Bruker, Saarbrucken, Germany) using the standard KBr disk method. Electron paramagnetic resonance (EPR) analyses were performed on a Bruker E500 spectrometer (Karlsruhe, Germany). Reactive radicals with short lifetimes are difficult to study directly by EPR spectroscopy. The spin-trapping approach allows us to identify the radical by causing them to react with trap molecules chosen so as to obtain relatively stable radical adducts [48]. DMPO (5,5-Dimethyl-1-pyrroline N-oxide) was used as spin-trap agent, ·OH was detected in deionized water, but ·O2− was detected in methyl sulfoxide (DMSO) solution in the present study. EPR tests were performed as follows: reaction solutions in 1 mm quartz capillary inside a 4 mm quartz tube were introduced into EPR cavity and tested before/after visible light irradiation. Oxygen-free spin-trapping investigation was performed through nitrogen bubbling of the solutions prior to the experiment. Sweep width of 100 G, microwave power of 0.2 mW, sweep time 5.24 s, microwave frequency of 9.41 GHz, and microwave attenuation of 30 dB were used during test.

3.3. Photocatalytic Tests

The photocatalytic activities of prepared photocatalysts were evaluated by the degradation of rhodamine B (RhB) and 2-mercaptobenzothiazole (MBT) under visible light. The light source used in the tests was a xenon lamp (300 W) with a 420 nm cut filter, and the distance between the reactor and the light source was 5 cm. For all photocatalysis experiments, 15 mg of photocatalyst was dispersed in MBT (30 mL, 20 mg/L) or RhB (30 mL, 50 mg/L) aqueous solution, and the suspension was stirred in the dark for 1 h. Then, the lamp was turned on to initiate the photocatalytic reaction. A total of 3 mL of suspension was taken at given time intervals, followed by centrifugation to remove the photocatalyst completely. The concentrations of RhB and MBT in the degradation process were determined by a UV–vis spectrometer (UV-2600) at wavelengths of 553 nm and 312 nm, respectively. Similar to aforementioned catalytic removal processes in the presence of sample CN-AA-0.05, EA (10 mmol/L), BQ (12 mmol/L), EDTA-2Na (12 mmol/L), and Cr(VI) (0.05 mmol/L) were added into reaction system to quench ·OH, ·O2−, h+, and e−, respectively. Each experiment was conducted three times.
MBT was selected as the target for the stability test experiment. The number of cycles was 5, and the reaction time for each cycle was 20 min.

4. Conclusions

Here, a novel visible-light-driven Z-scheme g-C3N4/AgBr-Ag photocatalyst was fabricated by a simple hydrothermal method with KBr as the bromine source. Compared with pure g-C3N4 or AgBr, the photocatalytic degradation activity of organic pollutants over g-C3N4/AgBr-Ag is significantly enhanced. Hydrothermal treatment is believed to transforms part of AgBr into metallic Ag. Metallic Ag initiates the SPR effect and acts as an electron transfer bridge, which finally improves the visible light absorption capacity and carrier separation efficiency of Z-scheme g-C3N4/AgBr-Ag. Our work not only provides an experimental basis for the design and construction of efficient visible-light-responsive Z-scheme photocatalysts, but also provides an in-depth understanding into the mechanism of Z-scheme photocatalytic degradation of organic pollutants.

Author Contributions

Conceptualization, X.H. and M.Y.; methodology, X.H., T.L. and M.Y.; investigation, T.L. and X.H.; writing—original draft preparation, Y.L.; writing—review and editing, X.H. and M.Y.; supervision, X.H. and M.Y.; project administration, X.H. and M.Y.; funding acquisition, X.H. and M.Y. All authors have read and agreed to the published version of the manuscript.

Funding

National Natural Science Foundation of China (no. 22176120, 22206118) and Shaanxi Thousand Talents Plan-Youth Program Scholars.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Alharbi, O.M.L.; Basheer, A.A.; Khattab, R.A.; Ali, I. Health and environmental effects of persistent organic pollutan. J. Mol. Liq. 2018, 263, 442–453. [Google Scholar] [CrossRef]
  2. Chen, D.; Cheng, Y.; Zhou, N.; Chen, P.; Wang, Y.; Li, K.; Huo, S.; Cheng, P.; Peng, P.; Zhang, R.; et al. Photocatalytic degradation of organic pollutants using TiO2-based photocatalysts: A review. J. Clean. Prod. 2020, 268, 121725. [Google Scholar] [CrossRef]
  3. Zhao, Y.; Li, Y.; Sun, L. Recent advances in photocatalytic decomposition of water and pollutants for sustainable application. Chemosphere 2021, 276, 130201. [Google Scholar] [CrossRef] [PubMed]
  4. Hassan, J.Z.; Raza, A.; Qumar, U.; Li, G. Recent advances in engineering strategies of Bi-based photocatalysts for environmental remediation. Sustain. Mater. Technol. 2022, 33, e00478. [Google Scholar] [CrossRef]
  5. Li, H.; Tu, W.; Zhou, Y.; Zou, Z. Z-Scheme photocatalytic systems for promoting photocatalytic performance: Recent progress and future challenges. Adv. Sci. 2016, 3, 1500389. [Google Scholar] [CrossRef]
  6. Xu, Q.; Zhang, L.; Yu, J.; Wageh, S.; Al-Ghamdi, A.A.; Jaroniec, M. Direct Z-scheme photocatalysts: Principles, synthesis, and applications. Mater. Today 2018, 21, 1042–1063. [Google Scholar] [CrossRef]
  7. Li, S.; Cai, M.; Liu, Y.; Wang, C.; Lv, K.; Chen, X. S-scheme photocatalyst TaON/Bi2WO6 nanofibers with oxygen vacancies for efficient abatement of antibiotics and Cr (VI): Intermediate eco-toxicity analysis and mechanistic insights. Chin. J. Catal. 2022, 43, 2652–2664. [Google Scholar] [CrossRef]
  8. Shi, Q.; Raza, A.; Xu, L.; Li, G. Bismuth oxyhalide quantum dots modified sodium titanate necklaces with exceptional population of oxygen vacancies and photocatalytic activity. J. Colloid Interf. Sci. 2022, 625, 750–760. [Google Scholar] [CrossRef]
  9. Zhou, P.; Yu, J.; Jaroniec, M. All-solid-state Z-scheme photocatalytic systems. Adv. Mater. 2014, 26, 4920–4935. [Google Scholar] [CrossRef]
  10. Zhang, W.; Mohamed, A.R.; Ong, W.-J. Z-Scheme photocatalytic systems for carbon dioxide reduction: Where are we now? Angew. Chem. Int. Ed. 2020, 59, 22894–22915. [Google Scholar] [CrossRef]
  11. Huang, D.; Chen, S.; Zeng, G.; Gong, X.; Zhou, C.; Cheng, M.; Xue, W.; Yan, X.; Li, J. Artificial Z-scheme photocatalytic system: What have been done and where to go? Coord. Chem. Rev. 2019, 385, 44–80. [Google Scholar] [CrossRef]
  12. Shi, Q.; Zhang, X.; Liu, X.; Xu, L.; Liu, B.; Zhang, J.; Xu, H.; Han, Z.; Li, G. n-situ exfoliation and assembly of 2D/2D g-C3N4/TiO2 (B) hierarchical microflower: Enhanced photo-oxidation of benzyl alcohol under visible light. Carbon 2022, 196, 401–409. [Google Scholar] [CrossRef]
  13. Ong, W.-J.; Tan, L.-L.; Ng, Y.H.; Yong, S.-T.; Chai, S.-P. Graphitic carbon nitride (g-C3N4)-based photocatalysts for artificial photosynthesis and environmental remediation: Are we a step closer to achieving sustainability? Chem. Rev. 2016, 116, 7159–7329. [Google Scholar] [CrossRef]
  14. Cadan, F.M.; Ribeiro, C.; Azevedo, E.B. Improving g-C3N4: WO3 Z-scheme photocatalytic performance under visible light by multivariate optimization of g-C3N4 synthesis. Appl. Surf. Sci. 2021, 537, 147904. [Google Scholar] [CrossRef]
  15. Zhou, S.; Wang, Y.; Zhou, K.; Ba, D.; Ao, Y.; Wang, P. In-situ construction of Z-scheme g-C3N4/WO3 composite with enhanced visible-light responsive performance for nitenpyram degradation. Chin. Chem. Lett. 2021, 32, 2179–2182. [Google Scholar] [CrossRef]
  16. Jing, H.; Ou, R.; Yu, H.; Zhao, Y.; Lu, Y.; Huo, M.; Huo, H.; Wang, X. Engineering of g-C3N4 nanoparticles/WO3 hollow microspheres photocatalyst with Z-scheme heterostructure for boosting tetracycline hydrochloride degradation. Sep. Purif. Technol. 2021, 255, 117646. [Google Scholar] [CrossRef]
  17. Du, J.; Xu, Z.; Li, H.; Yang, H.; Xu, S.; Wang, J.; Jia, Y.; Ma, S.; Zhan, S. Ag3PO4/g-C3N4 Z-scheme composites with enhanced visible-light-driven disinfection and organic pollutants degradation: Uncovering the mechanism. Appl. Surf. Sci. 2021, 541, 148487. [Google Scholar] [CrossRef]
  18. Cheng, R.; Wen, J.; Xia, J.; Shen, L.; Kang, M.; Shi, L.; Zheng, X. Photo-catalytic oxidation of gaseous toluene by Z-scheme Ag3PO4-g-C3N4 composites under visible light: Removal performance and mechanisms. Catal. Today 2022, 388–389, 26–35. [Google Scholar] [CrossRef]
  19. Xu, C.; Li, D.; Liu, X.; Ma, R.; Sakai, N.; Yang, Y.; Lin, S.; Yang, J.; Pan, H.; Huang, J.; et al. Direct Z-scheme construction of g-C3N4 quantum dots/TiO2 nanoflakes for efficient photocatalysis. Chem. Eng. J. 2022, 430, 132861. [Google Scholar] [CrossRef]
  20. Bi, X.; Yu, S.; Liu, E.; Liu, L.; Zhang, K.; Zang, J.; Zhao, Y. Construction of g-C3N4/TiO2 nanotube arrays Z-scheme heterojunction to improve visible light catalytic activity. Colloids Surf. A 2020, 603, 125193. [Google Scholar] [CrossRef]
  21. Hu, K.; Li, R.; Ye, C.; Wang, A.; Wei, W.; Hu, D.; Qiu, R.; Yan, K. Facile synthesis of Z-scheme composite of TiO2 nanorod/g-C3N4 nanosheet efficient for photocatalytic degradation of ciprofloxacin. J. Clean. Prod. 2020, 253, 120055. [Google Scholar] [CrossRef]
  22. Murugesan, P.; Narayanan, S.; Manickam, M.; Murugesan, P.K.; Subbiah, R. A direct Z-scheme plasmonic AgCl@g-C3N4 heterojunction photocatalyst with superior visible light CO2 reduction in aqueous medium. Appl. Surf. Sci. 2018, 450, 516–526. [Google Scholar] [CrossRef]
  23. Shen, Y.; Zhu, Z.; Wang, X.; khan, A.; Gong, J.; Zhang, Y. Synthesis of Z-scheme g-C3N4/Ag/Ag3PO4 composite for enhanced photocatalytic degradation of phenol and selective oxidation of gaseous isopropanol. Mater. Res. Bull. 2018, 107, 407–415. [Google Scholar] [CrossRef]
  24. Qian, L.; Hou, Y.; Yu, Z.; Li, M.; Li, F.; Sun, L.; Luo, W.; Pan, G. Metal-induced Z-scheme CdS/Ag/g-C3N4 photocatalyst for enhanced hydrogen evolution under visible light: The synergy of MIP effect and electron mediator of A. Mol. Catal. 2018, 458, 43–51. [Google Scholar] [CrossRef]
  25. Bao, Y.; Chen, K. AgCl/Ag/g-C3N4 hybrid composites: Preparation, visible light-driven photocatalytic activity and mechanism. Nano-Micro Lett. 2016, 8, 182–192. [Google Scholar] [CrossRef]
  26. Yang, Y.; Guo, W.; Guo, Y.; Zhao, Y.; Yuan, X.; Guo, Y. Fabrication of Z-scheme plasmonic photocatalyst Ag@ AgBr/g-C3N4 with enhanced visible-light photocatalytic activity. J. Hazard. Mater. 2014, 271, 150–159. [Google Scholar] [CrossRef]
  27. Li, Y.; Zhao, Y.; Fang, L.; Jin, R.; Yang, Y.; Xing, Y. Highly efficient composite visible light-driven Ag–AgBr/g-C3N4 plasmonic photocatalyst for degrading organic pollutants. Mater. Lett. 2014, 126, 5–8. [Google Scholar] [CrossRef]
  28. Xu, Y.; Xu, H.; Yan, J.; Li, H.; Huang, L.; Xia, J.; Yin, S.; Shu, H. A plasmonic photocatalyst of Ag/AgBr nanoparticles coupled with g-C3N4 with enhanced visible-light photocatalytic ability. Colloids Surf. A 2013, 436, 474–483. [Google Scholar] [CrossRef]
  29. Dong, F.; Wu, L.; Sun, Y.; Fu, M.; Wu, Z.; Lee, S.C. Efficient synthesis of polymeric gC 3 N 4 layered materials as novel efficient visible light driven photocatalysts. J. Mater. Chem. 2011, 21, 15171–15174. [Google Scholar] [CrossRef]
  30. An, C.; Wang, J.; Jiang, W.; Zhang, M.; Ming, X.; Wang, S.; Zhang, Q. Strongly visible-light responsive plasmonic shaped AgX: Ag (X = Cl, Br) nanoparticles for reduction of CO2 to methanol. Nanoscale 2012, 4, 5646–5650. [Google Scholar] [CrossRef]
  31. Chai, B.; Peng, T.; Mao, J.; Li, K.; Zan, L. Graphitic carbon nitride (gC3N4)–Pt-TiO2 nanocomposite as an efficient photocatalyst for hydrogen production under visible light irradiation. Phys. Chem. Chem. Phys. 2012, 14, 16745–16752. [Google Scholar] [CrossRef] [PubMed]
  32. Ge, L.; Han, C. Synthesis of MWNTs/g-C3N4 composite photocatalysts with efficient visible light photocatalytic hydrogen evolution activity. Appl. Catal. B 2012, 117–118, 268–274. [Google Scholar] [CrossRef]
  33. Luo, T.; Hu, X.; She, Z.; Wei, J.; Feng, X.; Chang, F. Synergistic effects of Ag-doped and morphology regulation of graphitic carbon nitride nanosheets for enhanced photocatalytic performance. J. Mol. Liq. 2021, 324, 114772. [Google Scholar] [CrossRef]
  34. Li, S.; Cai, M.; Liu, Y.; Wang, C.; Yan, R.; Chen, X. Constructing Cd0. 5Zn0. 5S/Bi2WO6 S-scheme heterojunction for boosted photocatalytic antibiotic oxidation and Cr (VI) reduction. Adv. Powder Mater. 2023, 2, 100073. [Google Scholar] [CrossRef]
  35. Li, S.; Cai, M.; Wang, C.; Liu, Y.; Li, N.; Zhang, P.; Li, X. Rationally designed Ta3N5/BiOCl S-scheme heterojunction with oxygen vacancies for elimination of tetracycline antibiotic and Cr(VI): Performance, toxicity evaluation and mechanism insight. J. Mater. Sci. Technol. 2022, 123, 177–190. [Google Scholar] [CrossRef]
  36. Ji, H.; Chang, F.; Hu, X.; Qin, W.; Shen, J. Photocatalytic degradation of 2,4,6-trichlorophenol over g-C3N4 under visible light irradiation. Chem. Eng. J. 2013, 218, 183–190. [Google Scholar] [CrossRef]
  37. Li, W.; Ma, Q.; Wang, X.; He, S.; Li, M.; Ren, L. Hydrogen evolution by catalyzing water splitting on two-dimensional g-C3N4-Ag/AgBr heterostructure. Appl. Surf. Sci. 2019, 494, 275–284. [Google Scholar] [CrossRef]
  38. Hu, X.; Mohamood, T.; Ma, W.; Chen, C.; Zhao, J. Oxidative decomposition of rhodamine B dye in the presence of VO2+ and/or Pt (IV) under visible light irradiation: N-deethylation, chromophore cleavage, and mineralizatio. J. Phys. Chem. B. 2006, 110, 26012–26018. [Google Scholar] [CrossRef]
  39. Pan, C.; Zhu, Y. New type of BiPO4 oxy-acid salt photocatalyst with high photocatalytic activity on degradation of dye. Environ. Sci. Technol. 2010, 44, 5570–5574. [Google Scholar] [CrossRef]
  40. Hu, X.; Ji, H.; Chang, F.; Luo, Y. Simultaneous photocatalytic Cr (VI) reduction and 2,4,6-TCP oxidation over g-C3N4 under visible light irradiation. Catal. Today 2014, 224, 34–40. [Google Scholar] [CrossRef]
  41. Wang, C.; Li, S.; Cai, M.; Yan, R.; Dong, K.; Zhang, J.; Liu, Y. Rationally designed tetra (4-carboxyphenyl) porphyrin/graphene quantum dots/bismuth molybdate Z-scheme heterojunction for tetracycline degradation and Cr (VI) reduction: Performance, mechanism, intermediate toxicity appraisement. J. Colloid Interface Sci. 2022, 619, 307–321. [Google Scholar] [CrossRef] [PubMed]
  42. Li, S.; Wang, C.; Cai, M.; Liu, Y.; Dong, K.; Zhang, J. Designing oxygen vacancy mediated bismuth molybdate (Bi2MoO6)/N-rich carbon nitride (C3N5) S-scheme heterojunctions for boosted photocatalytic removal of tetracycline antibiotic and Cr (VI): Intermediate toxicity and mechanism insight. J. Colloid Interface Sci. 2022, 624, 219–232. [Google Scholar] [CrossRef] [PubMed]
  43. Finkelstein, E.; Rosen, G.M.; Rauchman, E.J.; Paxton, J. Spin trapping of superoxide. Mol. Pharmacol. 1979, 16, 676–685. [Google Scholar] [PubMed]
  44. Wang, P.; Huang, B.; Dai, Y.; Whangbo, M.-H. Plasmonic photocatalysts: Harvesting visible light with noble metal nanoparticles. Phys. Chem. Chem. Phys. 2012, 14, 9813–9825. [Google Scholar] [CrossRef]
  45. Chen, D.; Li, T.; Chen, Q.; Gao, J.; Fan, B.; Li, J.; Li, X.; Zhang, R.; Sun, J.; Gao, L. Hierarchically plasmonic photocatalysts of Ag/AgCl nanocrystals coupled with single-crystalline WO3 nanoplates. Nanoscale 2012, 4, 5431–5439. [Google Scholar] [CrossRef]
  46. Ye, L.; Liu, J.; Gong, C.; Tian, L.; Peng, T.; Zan, L. Two different roles of metallic Ag on Ag/AgX/BiOX (X = Cl, Br) visible light photocatalysts: Surface plasmon resonance and Z-scheme bridge. ACS Catal. 2012, 2, 1677–1683. [Google Scholar] [CrossRef]
  47. Jiang, J.; Li, H.; Zhang, L. New insight into daylight photocatalysis of AgBr@ Ag: Synergistic effect between semiconductor photocatalysis and plasmonic photocatalysis. Chem. Eur. J. 2012, 18, 6360–6369. [Google Scholar] [CrossRef]
  48. Lauricella, R.; Tuccio, B. Detection and characterisation of free radicals after spin trapping. In Electron Paramagnetic Resonance Spectroscopy; Springer: Cham, Switzerland, 2020; pp. 51–82. [Google Scholar]
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Figure 1. (a) XRD patterns of CN, Ag/AgBr, CN-AA-X(X = 0.03, 0.05 or 0.07), CN-AA-0.05-D. (b) The SEM image of CN. (c) SEM images of CN-AA-0.05 and (d) TEM images of CN-AA-0.05. (e) The SEM image of CN-AA-0.05-D. (f) The HRTEM image of CN-AA-0.05.
Figure 1. (a) XRD patterns of CN, Ag/AgBr, CN-AA-X(X = 0.03, 0.05 or 0.07), CN-AA-0.05-D. (b) The SEM image of CN. (c) SEM images of CN-AA-0.05 and (d) TEM images of CN-AA-0.05. (e) The SEM image of CN-AA-0.05-D. (f) The HRTEM image of CN-AA-0.05.
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Figure 2. Full (a), C 1s (b), N 1s (c) XPS spectra of CN, CN-AA-0.05 and CN-AA-0.05-D; Ag 3d (d), Br 3d (e) XPS spectra of CN-AA-0.05 and CN-AA-0.05-D.
Figure 2. Full (a), C 1s (b), N 1s (c) XPS spectra of CN, CN-AA-0.05 and CN-AA-0.05-D; Ag 3d (d), Br 3d (e) XPS spectra of CN-AA-0.05 and CN-AA-0.05-D.
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Figure 3. (a) UV–vis DRS and (b) plots of (ahν)1/2 versus energy (hν) of CN, AgBr, CN-AA-X (X = 0.03, 0.05, 0.07), and CN-AA-0.05-D. (c) The PL spectra of CN and CN-AA-X (X = 0.03, 0.05, 0.07). (d) The time-resolved fluorescence decay spectra of CN and CN-AA-0.05. (e) The FTIR spectra of CN and CN-AA-X (X = 0.03, 0.05, 0.07).
Figure 3. (a) UV–vis DRS and (b) plots of (ahν)1/2 versus energy (hν) of CN, AgBr, CN-AA-X (X = 0.03, 0.05, 0.07), and CN-AA-0.05-D. (c) The PL spectra of CN and CN-AA-X (X = 0.03, 0.05, 0.07). (d) The time-resolved fluorescence decay spectra of CN and CN-AA-0.05. (e) The FTIR spectra of CN and CN-AA-X (X = 0.03, 0.05, 0.07).
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Figure 4. Photocatalytic (a) RhB and (c) MBT degradation activities of CN, AgBr, CN-AA-X (X = 0.03, 0.05, 0.07), and CN-AA-0.05-D. Kinetic curves of photocatalytic degradation of (b) RhB and (d) MBT by CN, AgBr, CN-AA-X (X = 0.03, 0.05, 0.07), and CN-AA-0.05-D.
Figure 4. Photocatalytic (a) RhB and (c) MBT degradation activities of CN, AgBr, CN-AA-X (X = 0.03, 0.05, 0.07), and CN-AA-0.05-D. Kinetic curves of photocatalytic degradation of (b) RhB and (d) MBT by CN, AgBr, CN-AA-X (X = 0.03, 0.05, 0.07), and CN-AA-0.05-D.
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Figure 5. The cycling experiments of photocatalytic degradation of MBT by CN-AA-0.05 catalyst.
Figure 5. The cycling experiments of photocatalytic degradation of MBT by CN-AA-0.05 catalyst.
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Figure 6. (a) Effects of different scavengers on photocatalytic degradation of MBT over CN-AA-0.05. (b) EPR spectra of CN-AA-0.05 in DMSO with DMPO as the capture agent. (c) EPR spectra of CN-AA-0.05 in deionized water with DMPO as the capture agent.
Figure 6. (a) Effects of different scavengers on photocatalytic degradation of MBT over CN-AA-0.05. (b) EPR spectra of CN-AA-0.05 in DMSO with DMPO as the capture agent. (c) EPR spectra of CN-AA-0.05 in deionized water with DMPO as the capture agent.
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Figure 7. Schematic illustration of proposed photocatalysis mechanism of g-C3N4/AgBr-Ag composites under visible light irradiation.
Figure 7. Schematic illustration of proposed photocatalysis mechanism of g-C3N4/AgBr-Ag composites under visible light irradiation.
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Hu, X.; Luo, T.; Lin, Y.; Yang, M. Construction of Novel Z-Scheme g-C3N4/AgBr-Ag Composite for Efficient Photocatalytic Degradation of Organic Pollutants under Visible Light. Catalysts 2022, 12, 1309. https://doi.org/10.3390/catal12111309

AMA Style

Hu X, Luo T, Lin Y, Yang M. Construction of Novel Z-Scheme g-C3N4/AgBr-Ag Composite for Efficient Photocatalytic Degradation of Organic Pollutants under Visible Light. Catalysts. 2022; 12(11):1309. https://doi.org/10.3390/catal12111309

Chicago/Turabian Style

Hu, Xuefeng, Ting Luo, Yuhan Lin, and Mina Yang. 2022. "Construction of Novel Z-Scheme g-C3N4/AgBr-Ag Composite for Efficient Photocatalytic Degradation of Organic Pollutants under Visible Light" Catalysts 12, no. 11: 1309. https://doi.org/10.3390/catal12111309

APA Style

Hu, X., Luo, T., Lin, Y., & Yang, M. (2022). Construction of Novel Z-Scheme g-C3N4/AgBr-Ag Composite for Efficient Photocatalytic Degradation of Organic Pollutants under Visible Light. Catalysts, 12(11), 1309. https://doi.org/10.3390/catal12111309

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