Functionalized Linear Conjugated Polymer/TiO2 Heterojunctions for Significantly Enhancing Photocatalytic H2 Evolution

Conjugated polymers (CPs) have attracted much attention in recent years due to their structural abundance and tunable energy bands. Compared with CP-based materials, the inorganic semiconductor TiO2 has the advantages of low cost, non-toxicity and high photocatalytic hydrogen production (PHP) performance. However, studies on polymeric-inorganic heterojunctions, composed of D-A type CPs and TiO2, for boosting the PHP efficiency are still rare. Herein, an elucidation that the photocatalytic hydrogen evolution activity can actually be improved by forming polymeric-inorganic heterojunctions TFl@TiO2, TS@TiO2 and TSO2@TiO2, facilely synthesized through efficient in situ direct C–H arylation polymerization, is given. The compatible energy levels between virgin TiO2 and polymeric semiconductors enable the resulting functionalized CP@TiO2 heterojunctions to exhibit a considerable photocatalytic hydrogen evolution rate (HER). Especially, the HER of TSO2@TiO2 heterojunction reaches up to 11,220 μmol g−1 h−1, approximately 5.47 and 1260 times higher than that of pristine TSO2 and TiO2 photocatalysts. The intrinsic merits of a donor-acceptor conjugated polymer and the interfacial interaction between CP and TiO2 account for the excellent PHP activity, facilitating the separation of photo-generated excitons. Considering the outstanding PHP behavior, our work discloses that the coupling of inorganic semiconductors and suitable D-A conjugated CPs would play significant roles in the photocatalysis community.


Introduction
The efficient use of solar energy by conserving it in the form of chemical bonds is considered to be one of the most effective ways to build sustainable society.Hydrogen energy, featured by high energy density, high calorific value and zero pollution, has been widely regarded as a clean secondary energy [1][2][3][4].Solar-driven hydrogen evolution has been developed as a promising means for obtaining renewable energy; meanwhile, the seek for highly active photocatalysts that are capable of efficiently absorbing sunlight to drive the hydrogen evolution reaction (HER) has aroused tremendous interest from scientists.From this perspective, the first discovery of titanium dioxide (TiO 2 ) as an inorganic semiconductor photocatalyst, dating back to 1972, reported by Fujishima and Honda [5], laid the foundations and brings infinite opportunities in the field of photocatalysis.Benefiting from the advantages of low cost, non-toxicity, high stability, n-type semiconducting properties, and strong oxidizing ability under light irradiation, TiO 2 has been considered as the most representative semiconductor photocatalyst and has been widely used in molecular photocatalysis [5] and photocatalyzed hydrogen production (PHP) [6][7][8].However, the intrinsic narrow photo-response range of TiO 2 severely limits the light-harvesting ability and causes the rapid recombination of photogenerated electron-hole (e − -h + ) pairs, which has greatly hindered the development of titanium dioxide-based photovoltaic conversion technologies.In order to overcome the abovementioned drawbacks, organic semiconductors have gradually emerged as promising candidates for photocatalysis [9][10][11][12].Among these, conjugated polymers (CPs), including the g-C 3 N 4 derivatives [13][14][15], conjugated microporous polymers (CMP) [16][17][18][19][20][21], frameworks of covalent triazines (CTFs) [22][23][24], covalent organic frameworks (COF) [25][26][27][28], and linear conjugated polymers (LCPs) [29][30][31][32], are showcasing the enormous potentials for PHP.
The broad designability of CPs at the molecular-level allows the regulation of structural and electronic properties, which results in narrower bandgap (E g ) and wider absorption range compared to TiO 2 [33,34].However, the CP-based photocatalysts still suffer from lower charge carrier mobility because of their shorter exciton diffusion length.In order to settle shortcomings of the single-component photocatalysts, the reasonable exploitation of heterojunctions between CPs and TiO 2 is desired to be explored, wherein the formed CP@TiO 2 heterojunctions might take the advantages of CPs and TiO 2 [35].As a result, an extended visible-light responsive and the enhanced photoexcited e − -h + pairs separation would be expected for the CP@TiO 2 heterojunctions, thus accelerating the migration of photogenerated charge carriers between CPs and TiO 2 .Such CP@TiO 2 heterojunctions, in which CPs are mainly g-C 3 N 4 , CMP and COF structures [36][37][38][39][40][41][42][43][44][45][46][47], have showed great potentials in PHP fields.
Donor-acceptor (D-A) conjugated polymers with alternating structures have emerged as promising photocatalysts for hydrogen generation [48][49][50], owing to the intramolecular pull-push effect of D-A structure that would promote electron (e − )/hole (h + ) separation in the presence of light irradiation [51][52][53].To our knowledge, organic-inorganic heterojunctions composed of D-A type CPs and TiO 2 have rarely been investigated to date.For example, Chen and Xiang et al. reported that CMP@TiO 2 heterojunction with D-A motif, in which 1,3,5-triethynylbenzene and thiadiazole derivatives act as D and A unit, respectively, exhibited dramatically increased PHP performance with Pt-cocatalyst [46].Lately, the same group designed a series of linear conjugated poly(benzothiadiazole) and incorporated onto the surface of TiO 2 in a similar in situ polycondensation strategy, the resulting heterojunctions consisting of electron-donor and electron-acceptor units embodied superior PHP activity in the absence of a Pt-cocatalyst [54].In 2019, Xiang and Huang et al. introduced benzene (D) and 2-fluorobenzene(A) to prepare a library of functionalized D-A type heterojunctions in the presence of TiO 2 ; the results showed that the HER of functionalized 4% BFBA-TiO 2 was up to 228.2 µmol h −1 [55].Therefore, it is still challenge to build CP@TiO 2 heterojunctions involving D-A architecture whilst little progress has been made.Recently, Wang and Zhang et al. described the fabrication of homopolymer poly (dibenzothiophene-S, S-dioxide) (PDBTSO)/TiO 2 composite composed of A-A structure, exhibiting considerable HER [47].These meaningful achievements inspired us to explore whether the strategy of introduction D-A conjugated polymers to form TiO 2 -based heterojunction is applicable for improving the PHP performance or not.
Given our consideration in this work, LCPs TFl, TS and TSO 2 were employed as the polymeric "partner" to couple with pristine TiO 2 , and the resulting CP@TiO 2 heterojunctions TFl@TiO 2 , TS@TiO 2 and TSO 2 @TiO 2 were prepared with in situ direct C-H arylation polymerization processes.The structural information, opt-electronic and the photocatalytic H 2 production were investigated.Benefiting from the D-A merits, TSO 2 @TiO 2 heterojunction exhibited broader light responsiveness and more efficient photo-excited charge separation and transfer.HER of TSO 2 @TiO 2 heterojunction reaches 11,220 µmol h −1 g −1 under full arc light irradiation, which is 5.47 and 1260 times higher than that of pure polymeric TSO 2 and TiO 2 , respectively.Our findings offer an alternative way to fabricate a polymeric heterojunction photocatalyst consisting of a D-A building block for boosting PHP performance.
X-ray photoelectron spectroscopy (XPS) measurement was performed to analyze the elemental composition and chemical state of pristine TiO 2 and the obtained TSO 2 and TSO 2 @TiO 2 (Figure 2 and Figure S1).The XPS survey spectrum illustrated in Figure 2a elucidated the existence of Ti, O, C, and S elements in the chemical composition of TSO 2 @TiO 2 , suggesting the successful construction of the expected heterojunction.Meanwhile, the corresponding high resolution XPS (HR-XPS) spectra of Ti 2p shown in Figure 2b indicate two similar peaks, which are ascribed to Ti 2p 1/2 and Ti 2p 3/2 , respectively, for pure TSO 2 and TSO 2 @TiO 2 .Simultaneously, the HR-XPS spectra of O 1s demonstrates the characteristic peaks for OH and Ti-O-Ti on the surface of TiO 2 with a slight energy shift for TSO 2 @TiO 2 compared to those of TSO 2 and TiO 2 (Figure 2c).Similarly, the HR-XPS C 1s spectra of TSO 2 @TiO 2 shows a slightly up-shifted binding energy compared with the polymeric TSO 2 (Figure 2d).The change in binding energy indicates the involvement of an interfacial interaction between the TSO 2 and TiO 2 , which could accelerate the charge transfer.To further investigate the heterojunction morphology of CP@TiO2, transmission electron microscopy (TEM) and EDS measurements were carried out next (Figures 3, S2 and  S3).Typically, pure TiO2 is in the shape of microspheres; however, when composites are formed by coupling with the conjugated polymers, small particles and many folds are observed on the surface (Figure 3a-c).In addition, a high-resolution TEM was carried out on TSO2@TiO2 and it was evident that the la ice striations were anatase (101) with a crystalline surface spacing of 0.35 nm (Figure 3d).The EDS elemental analysis of the TSO2@TiO2 composite shows the existence of Ti, S, C and O atoms (Figures S2 and S3).Therefore, both high-resolution TEM and EDS clearly prove the successful formation of the TSO2@TiO2 heterojunction.To further investigate the heterojunction morphology of CP@TiO 2 , transmission electron microscopy (TEM) and EDS measurements were carried out next (Figure 3, Figures S2 and S3).Typically, pure TiO 2 is in the shape of microspheres; however, when composites are formed by coupling with the conjugated polymers, small particles and many folds are observed on the surface (Figure 3a-c).In addition, a high-resolution TEM was carried out on TSO 2 @TiO 2 and it was evident that the lattice striations were anatase (101) with a crystalline surface spacing of 0.35 nm (Figure 3d).The EDS elemental analysis of the TSO 2 @TiO 2 composite shows the existence of Ti, S, C and O atoms (Figures S2 and S3).Therefore, both high-resolution TEM and EDS clearly prove the successful formation of the TSO 2 @TiO 2 heterojunction.
To further investigate the heterojunction morphology of CP@TiO2, transmission electron microscopy (TEM) and EDS measurements were carried out next (Figures 3, S2 and  S3).Typically, pure TiO2 is in the shape of microspheres; however, when composites are formed by coupling with the conjugated polymers, small particles and many folds are observed on the surface (Figure 3a-c).In addition, a high-resolution TEM was carried out on TSO2@TiO2 and it was evident that the la ice striations were anatase (101) with a crystalline surface spacing of 0.35 nm (Figure 3d).The EDS elemental analysis of the TSO2@TiO2 composite shows the existence of Ti, S, C and O atoms (Figures S2 and S3).Therefore, both high-resolution TEM and EDS clearly prove the successful formation of the TSO2@TiO2 heterojunction.The specific Brunauer-Emmett-Teller (BET) surface area of LCPs, CP@TiO 2 heterojunctions and TiO 2 was obtained by nitrogen adsorption-desorption isotherms methods (Figure 4), which indicates a descending order in a sequence of TSO 2 @TiO 2 > TS@TiO 2 > TFl@TiO 2 .The relatively high surface area of TS@TiO 2 , about six times than of pristine TiO 2 , is favorable for the adsorption of reactant molecules and provides a wider range of sites for photocatalytic reactions.The specific Brunauer-Emme -Teller (BET) surface area of LCPs, CP@TiO2 heterojunctions and TiO2 was obtained by nitrogen adsorption-desorption isotherms methods (Figure 4), which indicates a descending order in a sequence of TSO2@TiO2 > TS@TiO2 > TFl@TiO2.The relatively high surface area of TS@TiO2, about six times than of pristine TiO2, is favorable for the adsorption of reactant molecules and provides a wider range of sites for photocatalytic reactions.TFl@TiO2, TS@TiO2, TSO2@TiO2, and TiO2.

Opt-Electronic Properties
The optical properties of TiO2, LCPs and CP@TiO2 heterojunctions were first characterized by UV-vis diffuse reflectance spectroscopy (DRS) (Figure 5a), which reveals that both LCPs and CPs@TiO2 heterojunctions have wide and strong light absorption, located in the range of 300 to 600 nm, compared to pristine TiO2, enabling them to act as suitable light-harvesting materials.To our delight, TSO2 exhibits a redshift phenomenon compared to those of TFl and TS among the three LCPs, which is probably due to the fact that TSO2 has an intramolecular donor-acceptor (D-A) interaction induced by the D-A structure.In contrast, TFl and TS contain D-D structures, thus proving the push-pull electron effect of the D-A interaction is of great significance for broadening the light-absorption.Particularly, the TSO2@TiO2 heterojunction possesses the most red-shifted absorption between 300-600 nm, with an extended absorption peak at ~700 nm compared to those of TFl@TiO2 and TS@TiO2, could be a ributable to the tighter connection of the polymer TSO2 to TiO2.As can be seen in Figure 5b, the optical band gaps (Eg) of TFl, TS and TSO2 are, as calculated by Tauc plots, 2.2, 2.19 and 2.18 eV, respectively.In addition, the Eg values of TiO2 and the CP@TiO2 heterojunctions are 3.2 (TiO2), 2.25 (TFl@TiO2), 2.28 (TS@TiO2) and 2.17 eV (TSO2@TiO2), among which the narrowest Eg of TSO2@TiO2 is consistent with the wide light absorption property.

Opt-Electronic Properties
The optical properties of TiO 2 , LCPs and CP@TiO 2 heterojunctions were first characterized by UV-vis diffuse reflectance spectroscopy (DRS) (Figure 5a), which reveals that both LCPs and CPs@TiO 2 heterojunctions have wide and strong light absorption, located in the range of 300 to 600 nm, compared to pristine TiO 2 , enabling them to act as suitable light-harvesting materials.To our delight, TSO 2 exhibits a redshift phenomenon compared to those of TFl and TS among the three LCPs, which is probably due to the fact that TSO 2 has an intramolecular donor-acceptor (D-A) interaction induced by the D-A structure.In contrast, TFl and TS contain D-D structures, thus proving the push-pull electron effect of the D-A interaction is of great significance for broadening the light-absorption.Particularly, the TSO 2 @TiO 2 heterojunction possesses the most red-shifted absorption between 300-600 nm, with an extended absorption peak at ~700 nm compared to those of TFl@TiO 2 and TS@TiO 2 , could be attributable to the tighter connection of the polymer TSO 2 to TiO 2 .As can be seen in Figure 5b, the optical band gaps (Eg) of TFl, TS and TSO 2 are, as calculated by Tauc plots, 2.2, 2.19 and 2.18 eV, respectively.In addition, the Eg values of TiO 2 and the CP@TiO 2 heterojunctions are 3.2 (TiO 2 ), 2.25 (TFl@TiO 2 ), 2.28 (TS@TiO 2 ) and 2.17 eV (TSO 2 @TiO 2 ), among which the narrowest Eg of TSO 2 @TiO 2 is consistent with the wide light absorption property.To evaluate the abilities of photogenerated carrier migration and separation for the obtained LCPs and CP@TiO2 heterojunctions, we then carried out the steady-state PL (Figure 5c), TPR (Figure 5d) and EIS (Figure 5e) measurements.The PL intensities for D-A type TSO2 and TSO2@TiO2 heterojunction are comparative and relatively lower than those of the remaining four samples, indicating an immense tendency for photo-to-current conversion, thereby resulting in superior separation of the e − /h + pairs.In addition, the PL intensities of TFl@TiO2 and TS@TiO2 heterojunctions are significantly lower than the behaviors of their parent conjugated polymers, which are in accordance with the DRS results.Furthermore, the TPR curves showcase that the instantaneous photocurrent-time response of three heterojunctions is in a sequence of TSO2@TiO2 > TS@TiO2 > TFl@TiO2, To evaluate the abilities of photogenerated carrier migration and separation for the obtained LCPs and CP@TiO 2 heterojunctions, we then carried out the steady-state PL (Figure 5c), TPR (Figure 5d) and EIS (Figure 5e) measurements.The PL intensities for D-A type TSO 2 and TSO 2 @TiO 2 heterojunction are comparative and relatively lower than those of the remaining four samples, indicating an immense tendency for photo-to-current conversion, thereby resulting in superior separation of the e − /h + pairs.In addition, the PL intensities of TFl@TiO 2 and TS@TiO 2 heterojunctions are significantly lower than the behaviors of their parent conjugated polymers, which are in accordance with the DRS results.Furthermore, the TPR curves showcase that the instantaneous photocurrent-time response of three heterojunctions is in a sequence of TSO 2 @TiO 2 > TS@TiO 2 > TFl@TiO 2 , implying that more light-induced excitons can be generated for the D-A motif containing TSO 2 @TiO 2 heterojunction [58,59].Consistent with the PL and TPR results, the EIS experiments demonstrate that the order of the Nyquist circle radius is TSO 2 @TiO 2 < TS@TiO 2 < TFl@TiO 2 .Therefore, the smallest arc radius of the Nyquist plot for TSO 2 @TiO 2 means it has lower interfacial resistance and excellent charge mobility characters [60][61][62].

Photocatalytic Hydrogen Production Performances
Based on the opt-electronic properties of LCPs and CP@TiO 2 heterojunctions, the PHP performances were spontaneously tested under visible or full-arc light irradiation by utilizing the relevant photocatalysts (10 mg) dispersed in N-methyl pyrrolidone (NMP)/H 2 O (30 mL) aqueous solutions, together with the ascorbic acid (AA) as a sacrificial electron donor (SED) [20,32].As shown in Figure 5a, apparent differences are observed for the normalized hydrogen evolution rates (HERs) of three LCPs under full-arc light irradiation, among which the polymeric TSO 2 photocatalyst exhibits the highest PHP activity with HER of 2050 µmol/g −1 h −1 due to the introduction of the D-A structure.However, the raw material TiO 2 only shows weak PHP capacity (8.9 µmol/g −1 h −1 ).Impressively, enormous improvements in HERs are found when TiO 2 is coupled with LCPs for CP@TiO 2 heterojunctions compared to those of TiO 2 and their parent LCPs (Figure 6b).Specifically, the HERs in the full-arc band are 1430 (TFl@TiO 2 ), 2000 (TS@TiO 2 ) and 11,220 µmol/g −1 h −1 (TSO 2 @TiO 2 ), respectively, which indicates that the formation of heterojunction would improve the performance of polymeric photocatalysts because of the charge transfer between the polymer and TiO 2 .In comparison, we also test the PHP activities of CP@TiO 2 heterojunctions under the irradiation of visible light (λ > 420 nm) for their intense absorption in this range.As displayed in Figure 6b, the HERs of TFl@TiO 2 , TS@TiO 2 and TSO 2 @TiO 2 are still far exceeded by the corresponding LCPs and TiO 2 , albeit with inferior performance compared with the full-arc band irradiation, proving that the combination of conjugated polymer and TiO 2 can significantly extend the visible light response.Notably, the HERs of TSO 2 @TiO 2 heterojunction are 1260 and 5.47 times higher than those of pristine TiO 2 and the linear polymeric photocatalyst TSO 2 , respectively, which suggests that building D-A architecture-type polymeric and forming organic polymer@TiO 2 heterojunctions is an effective strategy for improving the performance of PHP for the reason that the interaction between the D-A motif and TiO 2 could synergistically facilitate exciton diffusion and enhance charge separation for proton reduction.
To explore the effect of different SEDs on the PHP activities, as illustrated in Figure 6c, TEOA, TEA and Na 2 S/Na 2 SO 3 were used instead of AA.As a result, a better performance was achieved when AA was employed as the SED.With the optimized condition in hand, the cycling experiments were studied to assess the long-term stability of TSO 2 @TiO 2 heterojunction toward the PHP reaction.As depicted in Figure 6d, steady photocatalytic dihydrogen gas generation could be observed through 20 h cycling test with four successive cy-cles, implying the photochemical stability of the TSO 2 @TiO 2 heterojunction.Meanwhile, the TSO 2 @TiO 2 was recovered for structural investigation, and no discernible differences were observed from both the UV-vis and FT-IR spectra compared to the as-prepared one (Figure 7a,b), demonstrating the long-term photo-stability of the TSO 2 @TiO 2 during the PHP process.To explore the effect of different SEDs on the PHP activities, as illustrated in Figure 6c, TEOA, TEA and Na2S/Na2SO3 were used instead of AA.As a result, a be er performance was achieved when AA was employed as the SED.With the optimized condition in hand, the cycling experiments were studied to assess the long-term stability of TSO2@TiO2 heterojunction toward the PHP reaction.As depicted in Figure 6d, steady photocatalytic dihydrogen gas generation could be observed through 20 h cycling test with four successive cycles, implying the photochemical stability of the TSO2@TiO2 heterojunction.Meanwhile, the TSO2@TiO2 was recovered for structural investigation, and no discernible differences were observed from both the UV-vis and FT-IR spectra compared to the as-prepared one (Figure 7a,b), demonstrating the long-term photo-stability of the TSO2@TiO2 during the PHP process.To explore the effect of different SEDs on the PHP activities, as illustrated in Figure 6c, TEOA, TEA and Na2S/Na2SO3 were used instead of AA.As a result, a be er perfor mance was achieved when AA was employed as the SED.With the optimized condition in hand, the cycling experiments were studied to assess the long-term stability o TSO2@TiO2 heterojunction toward the PHP reaction.As depicted in Figure 6d, steady photocatalytic dihydrogen gas generation could be observed through 20 h cycling tes with four successive cycles, implying the photochemical stability of the TSO2@TiO2 het erojunction.Meanwhile, the TSO2@TiO2 was recovered for structural investigation, and no discernible differences were observed from both the UV-vis and FT-IR spectra com pared to the as-prepared one (Figure 7a,b), demonstrating the long-term photo-stability of the TSO2@TiO2 during the PHP process.According to the above experimental results, the plausible mechanism for the increased photocatalytic H 2 evolution of TSO 2 @TiO 2 heterojunction is proposed in Figure 8.Since the pure polymeric D-A type TSO 2 exhibits more negative LUMO value and less positive value than those of pristine TiO 2 (Figure 5f), TSO 2 rather than TiO 2 is photo-activated under the illumination of full-arc or visible light (λ > 420 nm).As a result, hole-electron pairs were generated from the TSO 2 phase.Meanwhile, some of the photo-generated electrons were inclined to jump from the LUMO energy level of TSO 2 to the conduction band of TiO 2 , driven by the built-in electric field, via the interfacial heterojunction, thus subsequently reacting with the protons derived from water to produce H 2 .
Besides, the photo-generated holes can easily transfer from the valence band of TiO 2 to the HOMO energy level of TSO 2 , which in turn contributes to oxidizing the AA to AA + .Therefore, the effective photo-excited e − -h + separation of TSO 2 @TiO 2 heterojunction results in enhanced photocatalytic H 2 generation.
8. Since the pure polymeric D-A type TSO2 exhibits more negative LUMO value and less positive value than those of pristine TiO2 (Figure 5f), TSO2 rather than TiO2 is photo-activated under the illumination of full-arc or visible light (λ > 420 nm).As a result, holeelectron pairs were generated from the TSO2 phase.Meanwhile, some of the photo-generated electrons were inclined to jump from the LUMO energy level of TSO2 to the conduction band of TiO2, driven by the built-in electric field, via the interfacial heterojunction, thus subsequently reacting with the protons derived from water to produce H2.Besides, the photo-generated holes can easily transfer from the valence band of TiO2 to the HOMO energy level of TSO2, which in turn contributes to oxidizing the AA to AA + .Therefore, the effective photo-excited e − -h + separation of TSO2@TiO2 heterojunction results in enhanced photocatalytic H2 generation.

Materials and Methods
All of the starting materials and reagents were purchased from commercial suppliers and used directly without further purification.Anhydrous toluene was pretreated with calcium hydride (CaH2) and freshly distilled.
FT-IR spectra were collected on a FT-IR spectrometer (Bruker ALPHA) and the KBr was mixed with the sample for sample preparation.The morphology of heterojunction photocatalysts was obtained by scanning electron microscopy (SEM, MLA650F, Hillsboro, OR, USA) and transmission electron microscopy (TEM, FEI Tecnai G2 F20, Thermo Fisher Scientific, Waltham, MA, USA).We recorded polymer photoluminescence (PL) conductivity by employing a HORIBA FL-1000 fluorescence spectrometer for solid powders.EDS uses TESCAN MIRA LMS + Quantax 200 X Flash 6|60.X-ray diffraction (XRD) was measured by the Thermo Fisher NexsaI instrument.X-ray photoelectron spectroscopy (XPS) was measured by the Thermo Fisher NexsaI instrument.The solid UV-visible absorption spectra of the synthesized polymers were detected by a UV-2600 spectrophotometer using BaSO4 as a substrate reference.The water contact angle was measured using a JCY type contact angle measuring instrument.Transient photo-response tests were performed using a three-electrode configuration electrochemical workstation (CHI650E/700E, Huachen Co., Ltd., Shanghai, China) to measure transient photocurrents using a Pt electrode as the auxiliary electrode and an Ag/AgCl electrode containing a saturated KCl solution as the reference electrode.The polymer was ultrasonically dispersed with ethanol to form a

Materials and Methods
All of the starting materials and reagents were purchased from commercial suppliers and used directly without further purification.Anhydrous toluene was pretreated with calcium hydride (CaH 2 ) and freshly distilled.
FT-IR spectra were collected on a FT-IR spectrometer (Bruker ALPHA, Billerica, MA, USA) and the KBr was mixed with the sample for sample preparation.The morphology of heterojunction photocatalysts was obtained by scanning electron microscopy (SEM, MLA650F, Hillsboro, OR, USA) and transmission electron microscopy (TEM, FEI Tecnai G2 F20, Thermo Fisher Scientific, Waltham, MA, USA).We recorded polymer photoluminescence (PL) conductivity by employing a HORIBA FL-1000 fluorescence spectrometer for solid powders.EDS uses TESCAN MIRA LMS + Quantax 200 X Flash 6|60.X-ray diffraction (XRD) was measured by the Thermo Fisher NexsaI instrument.X-ray photoelectron spectroscopy (XPS) was measured by the Thermo Fisher NexsaI instrument.The solid UV-visible absorption spectra of the synthesized polymers were detected by a UV-2600 spectrophotometer using BaSO 4 as a substrate reference.The water contact angle was measured using a JCY type contact angle measuring instrument.Transient photo-response tests were performed using a three-electrode configuration electrochemical workstation (CHI650E/700E, Huachen Co., Ltd., Shanghai, China) to measure transient photocurrents using a Pt electrode as the auxiliary electrode and an Ag/AgCl electrode containing a saturated KCl solution as the reference electrode.The polymer was ultrasonically dispersed with ethanol to form a suspension, which was then dripped onto ITO conductive glass to form a sample with an effective area of 0.6 cm × 0.6 cm, and tested in a 0.1 M aqueous sodium sulfate solution as the electrolyte.Cyclic voltammetry tests were carried out with cyclic voltammetry using an electrochemical workstation (CHI650E/700E, Huachen Co., Ltd., Shanghai, China) with a three-electrode system using a glassy carbon electrode as the working electrode, an Ag/AgCl electrode as the reference electrode, and a Pt electrode as the auxiliary electrode, and an electrolyte was prepared by dissolving the TBAPF6 in acetonitrile solution, and the electrolyte was then used as an electrophoretic solution according to the equation: E HOMO = −(E OX + 4.8 eV(νs Ag/Ag + ) − E OX Fc/Fc+ ), E HOMO was calculated from the curve.The volume of nitrogen adsorption was recorded over a relative pressure range between 0.01 and 0.99 points in the relative pressure range of 0.05-0.2were used for the calculation of the surface area according to the Brunauer-Emmet-Teller (BET) theory.

Synthesis of 3,7-Dibromodibenzothiophene-S,S-dioxide [63]
NBS (2.47 g, 13.87 mmol) was added into this solution of dibenzothiophene-S, S-dioxide (1.5 g, 6.94 mmol) in concentrated H 2 SO 4 (90 mL) in several portions, and the resulting mixture was stirred at 0-5 • C for 24 h.The mixture was carefully poured into ice/water.The off-white solid was filtered off, washed with 20% aqueous sodium hydrogen carbonate, water and dried to an afford white solid.The product was further recrystallized from chloroform to gain a white crystal with a 60% yield. 1
• C under vacuum conditions for 24 h.