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Recent Progress in π-Conjugated Polymer-Inorganic Heterostructures for Photocatalysis

Yu-Qin Xing ,  Shi-Yong Liu

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Citation:  Yu-Qin Xing, Shi-Yong Liu. Recent Progress in π-Conjugated Polymer-Inorganic Heterostructures for Photocatalysis[J]. Chinese Journal of Structural Chemistry, 2022, 41(9): 220905. doi: 10.14102/j.cnki.0254-5861.2022-0188 shu

Recent Progress in π-Conjugated Polymer-Inorganic Heterostructures for Photocatalysis

    • 作者简介: Yu-Qin Xing received her Master degree in Chemical Engineering from Jiangxi University of Science and Techno-logy in 2022. Her research interests focus on photocatalytic water splitting using heterojunctions;
    Shi-Yong Liu is a full professor at Jiangxi University of Science and Technology (JXUST). He received his B.S. degree from Nanchang University in 1999, his Master degree in 2005 from Fuzhou University, and his Ph.D. degree in 2008 from Zhejiang University (ZJU). He was postdoctoral researcher in 2010-2016 at ZJU, and a visiting professor in 2014-2015 and University of Washington, USA. He became a research scientist in 2008 at Taizhou University (Zhejiang) and joined JXUST in 2017. His research interests focus on the design and synthesis of organic semiconductor for renewable energy applications, such as photocatalysis and organic photovoltaics;
    通讯作者: , chelsy@zju.edu.cn; chelsy@jxust.edu.cn

English

  • INTRODUNTION

    The ever-increasing consumption of traditional fossil fuel has led to severe energy and environmental crisis. Carbon dioxide (CO2), sulfur dioxide (SO2) and other harmful gases released by the combustion of fossil fuels bring about the greenhouse effect, acid rain and many other environmental problems.[1-3] Thus, it is highly urgent to develop sustainable and renewable energies to solve environmental problems. Semiconductor photocatalysis technology has arisen tremendous attention because of its great potential via direct utilization of the inexhaustible and renewable solar energy to solve both energy and environmental problems. Photocatalysis can easily convert solar energy into storable chemical energy. Photocatalytic H2O splitting into H2 and O2, conversion of CO2 to hydrocarbons (e.g., CH4) and fuels (e.g., CH3OH, C2H5OH and HCOOH) and environmental remediation are three major applications (Figure 1) that have attracted extensive attention.[4, 5] Typically, photocatalytic reactions include four steps (Figure 1): (i) formation of photogenerated e- - h+ pairs upon light absorption (hv ≥ Eg); (ii) separation of electron-hole pairs; (iii) charge migration to the photocatalyst surface; and (iv) electrons/holes participating in reduction/oxidation reactions. Thereby, a rational design of photocatalysts and reaction system should simultaneously take these four factors into account.

    Figure 1

    Figure 1.  Diagram of the basic pathways of photocatalytic water splitting, pollutant degradation, and CO2 reduction.
    DownLoad: Full-Size Img PowerPoint

    Since TiO2 was discovered for the photoelectrochemical splitting water to generate hydrogen (H2) by Fujishima et al in 1972, [6] numerous inorganic semiconductor photocatalysts have been explored. According to the energy bands and redox capacities (Figure 2), inorganic photocatalysts can be typically divided into oxidation photocatalysts (TiO2, ZnO, WO3, α-Fe2O3, BiVO4 and Cu2O, etc.), reduction photocatalysts (CdS, Cu2O, C3N4, etc.) and metal sulfide photocatalysts (CdS, ZnS, MoS2, etc.). Generally speaking, oxidation and reduction semiconductors are respectively featured by lower valence band (VB) and higher conduction band (CB), which accordingly benefit photocatalytic oxidative reactions (e.g., water oxidation half reaction) and reductive reaction (e.g., water reduction half reaction), respectively. Meanwhile, metal sulfides possess VBs and CBs that fall between those of oxidation and reduction semiconductors (Figure 2). Despite remarkable progress which has been made in inorganic-based photocatalysis in the past decades, most of inorganic semiconductors are still far from practical applications owing to their limited light absorption and fast recombination of photogenerated e- - h+ pairs.

    Figure 2

    Figure 2.  VB and CB alignments of common inorganic photocatalysts.
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    As counterparts of inorganic semiconductors, organic polymer semiconductor photocatalysts featured by widely adjustable band gap, abundant structural diversity, excellent optical and electronic properties have received widespread attention. Yanagida et al. first reported the conjugated linear poly(p-phenylene) for photocatalytic hydrogen production (PHP) under ultraviolet light.[7] Besides, Wang et al. proposed the new application of polymeric graphitic carbon nitride (g-C3N4) featuring simple preparation process and high thermal stability similar to inorganic semiconductors, which shows excellent photocatalytic hydrogen evolution rate (HER) and has become a research hotspot in photocatalysis.[8] Different from rigid g-C3N4, conjugated polymers (CPs) synthesized via wet chemistry, such as C-C bond cross couplings, have attracted extensive attention due to their large delocalized π-system, widely tunable structures, excellent photoelectrochemical properties, facile optimization of bandgaps, and so on.[9-12] In many cases, they can exhibit strong absorptance in a wide range of light wavelength. However, polymeric semiconductor photocatalysts still suffer from the drawbacks of poor stability and short exciton diffusion length in tens of nanometers. The huge challenge in photocatalysis is that photogenerated electron-hole pairs thermodynamically tend to recombine at the surface/interface attributed to strong Coulombic attraction, which is unfavorable to the photocatalytic redox process. Meanwhile, it is irreconcilable for a single semiconductor photocatalyst which simultaneously possesses narrow bandgap and strong redox ability (Figure 1). Heterojunction appears at this point when simultaneously taking broad light absorption and strong redox ability into account, which can hardly be satisfied by a single semiconductor. Among varied hybridization strategies, [13-15] the most straightforward way is the construction of heterostructures that can integrate advantages of individual components while alleviate respective shortcomings. Till now, heterojunctions for photocatalysis have mainly focused on inorganic-inorganic dual semiconductors.[16, 17] Besides, many heterojunctions between g-C3N4 and metal oxide semiconductors have also been developed.[18] However, g-C3N4, as an n-type semiconductor with wide bandgap and rigid structure, still suffers from disadvantages of poor light absorptance and limited modification of chemical structures. In recent years, the heterojunctions based on inorganic semiconductors and π-conjugated soft polymers with widely tunable optical properties and tailorable structures for varied photocatalytic applications have received great attention.[19, 20] Compared to inorganic-inorganic heterojunction, the unique property of P-I heterojunction lies in that its heterojunction can be finely modulated by tunning the ratio of polymer to in-organic semiconductor. On the other hand, compared to polymer-polymer heterojunctions, the P-I soft-hard heterojunctions have the unique properties of higher stability and lower cost. Hence, P-I heterojunctions can combine the advantages of both polymer and inorganic semiconductors and meanwhile overcome their respective shortcomings.

    This minireview summarizes the latest progress of P-I soft-hard heterojunctions, including their preparation methods, mechanism study, applications and prospects. According to the pathway of charge transfer, P-I photocatalytic heterojunctions can be mainly classified as I/II type, p-n junction, Z- and S-scheme mechanisms. Meanwhile, the applications of P-I heterojunction photocatalysts mainly focus on three aspects, i.e., photocatalytic hydrogen or oxygen production, CO2 reduction and degradation of organic pollutants. Besides the previous excellent reviews on the progress of Z- or S-scheme heterojunction photocatalysts, [21, 22] a comprehensive and timely review on the P-I heterojunctions for photocatalysis should be quite instructive and necessary.

    TYPES OF P-I PHOTOCATALYTIC HETEROJUNCTIONS AND MECHANISM STUDIES

    The construction of heterojunction can facilitate the transport of charge carriers to enhance photocatalytic performance. Appropriate VB and CB are required with matching energy band levels to construct P-I heterojunctions. According to the transfer of photogenerated charge, the heterostructure photocatalysts can be generally divided into following four categories, i.e., I/II type, p-n junction, Z-scheme and S-scheme mechanisms (Figure 3).

    Figure 3

    Figure 3.  shows that type-II heterojunction with staggered band structure is fundamentally different from the type-I. The CB and VB levels of SCA are both higher than those of SCB. And the electrons and holes are not on the same semiconductor, and thus the e- - h+ recombination rate on the same semiconductor is effectively inhibited.
    DownLoad: Full-Size Img PowerPoint

    Types of P-I Heterojunctions. For type-I heterojunction (Figure 3a), the CB of semiconductor A (SCA) is higher than that of semiconductor B (SCB), while the VB of SCA is lower than that of SCB. As a result, the electrons and holes are thus accumulated on SCB and SCA, respectively.

    P-n heterojunction is proposed based on type-II heterojunctions (Figure 3c). Due to the presence of internal electric field (IEF), photogenerated electrons and holes are concentrated in the p-and n-regions, respectively. Consequently, electrons and holes are spatially separated and thus improve photocatalysis. Compared with type-I heterojunction, p-n/type-II heterojunctions can greatly enhance the charge carrier separation in space owing to the existence of IEF.[23]

    Unlike the classical heterojunctions (i.e., type-I/II, and p-n heterojunctions), the photogenerated electrons and holes of Z- and S-scheme heterojunction (Figure 3d) are accumulated at high oxidation and reduction potentials (OP and RP) and thus minimize the charge recombination, which can efficiently achieve the separation of e- - h+ pairs with simultaneously maximized reduction and oxidation capacities.[21, 22]

    Typically, the Z-scheme heterojunctions consist of two staggered semiconductors and a redox electron mediator pair, wherein a larger potential offset is needed to make electron acceptors and donators to accept and donate electrons, respectively, which may lead to the weakened reduction and oxidation capacity. On the other hand, the S-scheme heterojunction consists of both reduction and oxidation photocatalysts, wherein the three major factors including the band bending, built-in electric field, and Coulomb force have been well combined, which retains the highest reduction and oxidation capacities of two semiconductors. Because of this advantage, S-scheme heterojunctions have been intensively studied in recent years.

    Characterizations of Heterojunctions. The characterization methods for varied heterojunctions include in-situ XPS, noble metal deposition, radical capture experiments and theoretical calculations. For p-n heterojunction, the Mott-Schottky (M-S) typically shows "V" or inverted "V" shape characters owing to the presence of internal electric field.[18] The verification methods of S-scheme heterojunction have been summarized by Yu et al.[21] Direct Z-scheme heterojunction represents one of the most efficient photocatalytic protocols.[24, 25]

    In-situ XPS. The variation of binding energy can directly reflect the changes of surface electron density, and the decrease of electron density leads to the increase of binding energy. Therefore, the direction of charge can be detected by the change of binding energy. In-situ XPS measurement can detect migration direction of electrons by measuring changes in the binding energy of elements under light irradiation compared with those measured in darkness. Wang et al. reported ultrathin nanosheets polyimide (PI) formed polymer-inorganic hybrid with CdS, in which 15% CdS/PI showed the highest performance due to the direct Z-scheme formation.[24] As the XPS spectra shown in Figure 4a and b, the C 1s and N 1s signals shift to higher binding energy for CdS/PI under light irradiation compared to those tested in darkness. On contrary, the binding energies of Cd 3d and S 2p under visible-light irradiation decreased (Figures 4c-d). These in-situ XPS analyses reveal that the photoinduced electrons in PI can migrate to CdS under light irradiation, suggesting the formation of direct Z-scheme CdS/PI heterojunction.

    Figure 4

    Figure 4.  Ex-situ and in-situ XPS spectra of (a) C 1s, (b) N 1s of PI and 15% CdS/PI, (c) Cd 3d and (d) S 2p of CdS and 15% CdS/PI.[24] (e) TEM, HRTEM images, (f) Pt XPS spectrum of BE-CdS-10.0 hybrid after in-situ photodeposition of Pt from H2PtCl6, (g) Proposed photocatalytic H2 production mechanism.[20]
    DownLoad: Full-Size Img PowerPoint

    Noble Metal Deposition. Noble metals can be selectively deposited on the electron-rich region, which can reveal the region holding photogenerated electrons, thus confirming the charge carrier transfer route. Chen group reported organic/inorganic hybrid (BE/CdS) prepared from modified conjugated polybenzothiazole (B-BT-1, 4-E, noted as BE) flake and CdS nanorods.[20] In the presence of a semiconductor, Pt4+ in H2PtCl6 was reduced to Pt0 under light irradiation. TEM and corresponding HRTEM images of BE/CdS hybrids (Figure 4e) confirmed that Pt nanoparticles were loaded on BE rather than CdS. The XPS spectra of Pt showed that the binding energies of Pt 4f7/2 and 4f5/2 are 72.3 and 75.5 eV (Figure 4f), respectively, which nearly equal to the standard energy of zero Pt, implying the presence of Pt0, and the electron is migrated from CB of CdS to the VB of BE via a Z-scheme instead of type II mechanism (Figure 4g).

    Radical Capture Experiments. •OH- and •O2- are two commonly used radicals for detection experiments, which can be captured by benzoquinone (BQ) and isopropylalcohol (IPA), respectively. For instance, g-C3N4-AQ-MoO3 hybrid photocatalyst exhibits excellent photocatalytic performance by the formation of Z-scheme heterojunction.[25] The •OH and •O2- radical signals in g-C3N4, MoO3, and g-C3N4-AQ-MoO3 were studied by DMPO spin-trapping ESR spectra. Under light irradiation, g-C3N4-AQ-MoO3 hybrid possesses both DMPO-•O2- and DMPO-•OH signals, demonstrating the formation of Z-scheme heterojunction.

    PREPARATION METHODS OF P-I PHOTOCATALYTIC HETEROSTRUCTURES

    The preparation methods of P-I heterojunction photocatalysts mainly include in situ polymerization, hydrothermal and solvothermal treatment, electrostatic self-assembly, ball milling methods, etc. Table 1 summarizes the preparation methods of P-I heterojunction photocatalysts.

    Table 1

    Table 1.  Summarized Preparation Methods of P-I Heterojunction Photocatalysts
    DownLoad: CSV
    Catalysts Dosage (mg) Preparation method Ref.
    BE-CdS 30 in-situ polycondensation [20]
    DBTSO@TiO2 10 in-situ polycondensation [26]
    PyOT@TiO2 10 in-situ polymerization [27]
    BBT/TiO2 10 in-situ polymerization [28]
    BE-Au-TiO2 30 in-situ polymerization [29]
    DPP-Car/TiO2 100 in-situ polymerization [30]
    WO3@TiO2 20 in-situ chemical deposition method [31]
    CdS/PI 50 solvothermal method [24]
    g-C3N4/BiVO4 80 hydrothermal method [32]
    Fe2O3/g-C3N4 50 electrostatic self-assembly
    approach    		 [33]
    g-C3N4@BiOI 50 electrostatic self-assembly
    approach    		 [34]
    Ag3PO4/PDI 20 self-assembly approach [35]
    g-C3N4/Bi4Ti3O12 - ball milling [36]
    g-C3N4/Bi4NbO8Cl 100 ball milling [37]
    BE/black TiO2 30 ball milling [38]
    g-C3N4/MnO2 - wet-chemical method [39]
    CP/g-C3N4 50 molecular engineering strategy [40]
    P3HT/g-C3N4 10 facile rotary evaporation [41]
    CdS-DETA 50 microwave hydrothermal method [42]
    PPy/TiO2 50 reverse microemulsion polymerization [43]
    (PANI)/TiO2 - hydrothermal-chemisorption process [44]
    ZnONRs-PANI - electrophoretic deposition [45]
    WO3@Cu@PDI 5 water bath method [46]
    (TNZnPc)/TiO2 - electrospinning and solvothermal method [47]

    In-situ Polymerization. In situ polymerization, featured by simplicity and tightly bound interface, represents one of the most widely used methods for the synthesis of heterostructures.[26-31] Our previous work reported PyOT@TiO2 polymer-inorganic he-terojunctions can be smoothly constructed by an in-situ direct C-H arylation polycondensation.[27] Meanwhile, the mechanically mixed 50% PyOT-TiO2 was also prepared to make comparable study with the in-situ synthesized 50% PyOT@TiO2. After being sonicated in ethanol and standing for a few mins (Figure 5), two separated phases, i.e., reddish-brown PyOT and white TiO2, can be distinctly observed in 50% PyOT-TiO2. In sharp contrast to the mechanically mixed 50% PyOT-TiO2, a stable and uniformed single phase still retains for the in-situ prepared 50% PyOT @TiO2, showing that PyOT has been tightly bonded on the surface of TiO2 particles, and there must be a strong interaction between PyOT and TiO2.

    Figure 5

    Figure 5.  Mechanically mixed 50% PyOT-TiO2 and in situ prepared 50% PyOT@TiO2, and the images of their ultrasonic dispersions in EtOH.[27]
    DownLoad: Full-Size Img PowerPoint

    Hydrothermal and Solvothermal Methods. Typically, a hydrothermal process is carried out under high pressure as well as temperature in autoclaves, resulting in high crystallinity and narrow particle size distribution of the synthesized semiconductor nanoparticles.[24, 32] The solvothermal synthesis process is similar to the hydrothermal synthesis except for using different solvents. Organic solvents are commonly utilized in solvothermal process.

    Electrostatic Self-assembly Method. The electrostatic selfassembly method is based on the electrostatic interaction of polyelectrolyte with opposite charge. Electrostatic self-assembly does not need to form chemical bonds, which can be easily operated and has high stability.[33-35]

    Ball Milling. Ball milling is a facile, efficient and green techno-logy for the synthesis of composite photocatalysts with minimal or no involvement of solvent.[36-38] Besides the abovementioned methods, other methods including wet chemical method, [39] molecular engineering strategy, [40] facile rotary evaporation, [41] microwave hydrothermal method, [42] reverse microemulsion polymerization, [43] hydrothermal-chemisorption process, [44] electrophoretic deposition, [45] water bath method, [46] electrospinning technique and solvothermal processing[47] have also been developed for the preparation of P-I heterostructures.

    PHOTOCATALYTIC APPLICATIONS OF P-I HETEROSTRUCTURES

    Polymer-inorganic heterostructures have been widely used in photocatalytic hydrogen or oxygen evolution, CO2 reduction and environmental remediation.[48, 49]

    Photocatalytic Water Splitting. Photocatalytic hydrogen production from water splitting has been regarded as one of the most important technologies for converting renewable solar energy to clean fuels. The main obstacle of photocatalytic overall water splitting is the half-reaction of oxygen generation that involves a four-electron pathway with a slow kinetics. Thereby, in many cases, sacrificial agents are required to consume holes or electrons, which correspond to sacrificial electron donors (SED) and sacrificial electron acceptors (SEA), respectively. SED, including lactic acid (LA), ascorbic acid (AA), triethanolamine (TEOA), triethanolamine (TEA), Na2S, Na2SO3, methanol (MeOH) and ethanol (EtOH), are consumable to valence band holes, while SEA agents, such as AgNO3 and ferric chloride (FeCl3), consume conduction band electrons.

    Similar to the most widely studied inorganic TiO2-based photocatalysts, g-C3N4-based polymeric photocatalysts have also received extensive attention owing to its tunable synthetic methods, high specific surface area, low cost, high stability, and unique optical and electronic properties. Meanwhile, various inorganic photocatalysts have been integrated with g-C3N4 to build P-I heterojunctions.[18, 23, 50] Zhu et al. reported the transformation of MoS2 morphology from 0D to 2D and 3D porous structures coupling with 2D-g-C3N4 to synthesize 0D (2D, 3D)-MoS2/g-C3N4 photocatalysts for PHP application (Figure 6a-d).[18] 0D-MoS2 quantum dots and 2D-MoS2 nanosheets were first introduced onto 3D-CN to construct 0D/3D-MCN and 2D/3D-MCN through facile impregnation and in situ photo-deposition method. The effect of the MoS2-covered 2D gC3N4 morphologies on PHP was systematically investigated. Changing the morphology of g-C3N4 from 2D to 3D porous structure is beneficial to gain more surface-active sites, higher transfer efficiency and larger specific surface area. This work highlights that modulating the morphology of MoS2 can affect the charge transfer pathway of 0D/3D-MCN and 2D/3D-MCN heterostructures (Figure 6e).

    Figure 6

    Figure 6.  (a) The rate curves of samples for photocatalytic H2 production, (b) the effect of the 0D-MoS2 QDs amount, (c) HER of 2D-MoS2 nanosheets, (d) recircling test of 0D/3D-MCN-3.5%, (e) proposed photocatalytic mechanisms for the 0D/3D-MCN and 2D/3D-MCN composites.[18]
    DownLoad: Full-Size Img PowerPoint

    Besides g-C3N4, other π-conjugated polymers (CP) and inorganic semiconductors heterojunctions for photocatalytic H2 production have also been developed.[26, 27, 51-56] P-I heterojunction photocatalysts rationally combine respective advantages of polymer and inorganic semiconductors to improve the photocatalytic performance. Most of heterojunctions between the conjugated polymer materials and inorganic semiconductor are prepared by an in-situ synthetic strategy. Wang group reported poly(dibenzothiophene-S, S-dioxide)@TiO2 nanoparticles (PDBT- SO@TiO2) composite through in situ polymerization, which exhibit the highest HER up to 51.5 mmol h-1g-1.[26]

    Yu group developed an S-scheme heterojunction photocatalyst between a pyrene-based CP, i.e., pyrene-alt-triphenylamine (PT) and CdS nanocrystals (Figure 7a-e). The optimal CdS/PT hybrid, integrating 2 wt% PT with CdS and 1 wt% Pt as cocatalyst, exhibited an outstanding HER of 9.28 mmol h-1g-1 with an apparent quantum efficiency (AQE) up to 24.3%, which is about 8 times higher than that of pristine CdS. Kelvin probe force microscopy (KPFM) and in-situ XPS analyses fully demonstrate the mechanism of S-scheme charge transfer.[51] Importantly, the C 1s peaks of CP2, and the Cd 3d and S 2p peaks of CdS negatively and positively shifted under light irradiation, respectively, as compared to those in dark, proving the photoelectron transfer direction from CdS to PT.

    Figure 7

    Figure 7.  (a-c) High-resolution XPS spectra, (d) schematic illustration of photoirradiation KPFM, (e) schematic illustration of S-scheme charge transfer process.[51] (f) Normalized HERs under visible or full arc light, (g) p-n heterojunction of PyOT@TiO2.[27] (h) Schematic diagram of catalysts synthesis, (i) hydrogen production by (Pt-PPy)-TiO2, (Pt-TiO2)-PPy and Pt-(PPy-TiO2).[52]
    DownLoad: Full-Size Img PowerPoint

    Our group reported the P-I (PyOT@TiO2) heterojunctions that are built via in-situ C-H arylation polycondensation. All resultant heterostructures, including 10%, 50% and 80% PyOT @TiO2, exhibited much higher HERs compared to the pristine TiO2 and PyOT either under visible or full-arc irradiation. 50% PyOT@TiO2 dispersed in an ascorbic acid (AA) aqueous solution (pH = 4) shows the highest HER in the absence of Pt co-catalyst (Figure 7f). P-n heterojunction charge transfer that contributes to the enhanced photocatalytic performance was revealed by M-S plot and •OH detection experiments.[27]

    Remita et al. designed a P-I heterostructure (Figure 7h-i) based on ternary polypyrrole PPy-TiO2 nanocomposites with 2 nm-Pt nanoparticles, i.e., (Pt-PPy)-TiO2, (Pt-TiO2)-PPy and Pt-(PPy-TiO2). Photocatalytic hydrogen evolution tests in 25% MeOH aqueous solution reveal that Pt-(PPy-TiO2) nanostructures with co-deposition of Pt nanoparticles on TiO2 and PPy show much higher HER than(Pt-PPy)-TiO2 and (Pt-TiO2)-PPy irradiated either by UV or visible light.[52]

    Zhang et al. designed reduced graphite oxide/CdS-DETA (PRGO/CdS-DETA) porous composites with excellent PHP performance and stability.[53] Chen group synthesized CMPs with different structures by Sonogashira coupling polycondensation between 4, 7-dibromobenzo[c][1, 2, 5]thiadiazole and 1, 3, 5-triethyn-ylbenzene to construct heterojunctions with inorganic semiconductors TiO2 and CdS for both PHP and photocatalytic degradation applications.[20, 28, 54] Multifunctional π-conjugated microporous poly(benzothiadiazole)/TiO2 (BBT/TiO2) heterojunction through an in-situ polycondensation can dramatically improve the photocatalytic activity for H2 evolution and degradation of ciprofloxacin under the visible light.[28] The possible mechanisms of PHP and CIP photodegradation for BBT/TiO2 heterojunction are proposed as shown in Figure 8 (a-b). To further improve the photocatalytic performance of conjugated polymer-TiO2 composites, a linear conjugated polymer (benzothiadiazole) (B-BT-1, 4-E) was employed to form a binary composite heterojunction with TiO2 via a facile in-situ strategy (Figure 8 c).[54] As a result, B-BT-1, 4-E/TiO2 showed a wider visible light absorption and more efficient charge mobility than CMP-based BBT/TiO2. Besides, a new type of polymer/inorganic hybrid using modified conjugated polybenzothiadiazole (B-BT-1, 4-E, noted as BE) flake and CdS nanorod was also developed by the same group.[20] Based on the comprehensive photocatalytic experiments, the HER of optimal BE-CdS hybrid was 8.3 and 23.3 times higher than those of CdS and BE, respectively, attributing to broader visible/near-infrared (vis/NIR) light absorption region (400-700 nm) and rapid photogenerated e-/h+ separation owing to the formation of Z-scheme heterojunction.[20]

    Figure 8

    Figure 8.  Proposed mechanism for (a) photocatalytic H2 production, (b) photodegradation of CIP over BBT-TiO2 heterojunction.[28] (c) In situ fabrication of B-BT-1, 4-E on the surface of TiO2.[54] (d) Configuration of energy band positions and Z-scheme photogenerated charge carrier transfer in the BE-CdS hybrid photocatalyst.[20]
    DownLoad: Full-Size Img PowerPoint

    Yan et al. reported photocatalytic oxygen evolution by Fe2O3/C3N4 and Fe2O3/C-C3N4 heterojunctions, respectively, which were about 10- and 30-folds higher than that of pristine g-C3N4, showing the presence of strong interaction between amorphous carbon and Fe2O3.[56] In addition, oxygen evolution at λ = 450, 470 and 500 nm was also studied, demonstrating that heterostructures can boost the electron and hole pairs migration, separation, and thus photocatalytic reaction.

    Zhang et al. reported polymer/inorganic g-C3N4/CoN nitride heterostructure realizes more than 4-fold enhancement in catalytic activity for O2 evolution compared to the bare g-C3N4, with a highest O2 evolution rate up to 607.2 µmol g-1h-1 under visible light.[57] Cooper et al. reported a Z-scheme photocatalyst consisting of linearly conjugated polymers and BiVO4 used for overall water splitting under visible light.[58] Zhao et al. reported a C3N4 and WO3-based heterostructure photocatalyst via a facile hydrothermal strategy for mediator-free overall water splitting. And the excellent C3N4-WO3 composite has the highest H2/O2 production rate (2.84 and 1.46 µmol h-1, respectively) and the quantum yield is 0.9%.[59]

    Photocatalytic overall water splitting without sacrificial agents represents one of the most ideal protocols for solar to chemical energy conversions. Although overall water splitting seems very fascinating, it is a thermodynamically up-hill process (∆G0 = 237.13 kJ∙mol-1), which is still far from the practical applications owing to the low solar-to-hydrogen (STH) conversion efficiency. Wang et al. designed Fe2O3/reduced graphene oxide/polymer carbon nitride (Fe2O3/RGO/PCN) ternary heterojunction (RGO nanosheets as solid mediators) to accelerate carrier transfer and achieve an efficient photocatalytic performance for the overall water splitting.[60] The photocatalytic H2 and O2 production rates of PCN in the presence of Pt were, respectively, 20.9 and 9.4 μmol h-1, with a 2:1 stoichiometric ratio for H2: O2. When Fe2O3 nanoparticles were added into PCN, the water splitting activity was slightly higher than that of pure PCN. Impressively, when RGO nanosheets were used as a solid electronic medium to connect the hydrogen and oxygen evolution photocatalysts, the optimum overall water splitting activity could be further enhanced (H2: 43.6 μmol h-1 and O2: 21.2 μmol h-1). Table 2. summarizes the photocatalytic water splitting of reported P-I heterostructures.

    Table 2

    Table 2.  Summary of Reported P-I Heterostructures for Photocatalytic Water Splitting
    DownLoad: CSV
    Catalysts Cocatalyst Sacrificial reagent Activity (µmol h-1g-1) AQE (420 nm) Ref.
    MoS2/g-C3N4 - lactic acid H2: 817.1 - [18]
    BE-CdS 1.0 wt% Pt Na2S/Na2SO3 H2: 40990 7.5% [20]
    CoOx@g-C3N4 - TEA H2: 262.9 1.9% [23]
    PDBTSO@TiO2 3.0 wt% Pt TEOA H2: 51500 13% [26]
    PyOT@TiO2 - AA H2: 1200 - [27]
    BBT/TiO2 0.3 wt% Pt, TEOA H2: 6750 1.45% (450 nm) [28]
    BE-Au-TiO2 1.0 wt% Pt TEOA H2: 26040 7.8% [29]
    CdS/PI 1.0 wt% Pt lactic acid H2: 613  - [24]
    Fe2O3/g-C3N4 1.0 wt % Pt TEOA H2: 398.0 - [33]
    TiO2/C3N4 1.0 wt %Pt TEOA H2: 1540 4.94% (365 nm) [50]
    CdS/PT 1 wt% Pt lactic acid H2: 9280 24.3% (400 nm) [51]
    PPy-TiO2 1 wt% Pt CH3OH H2: 3200 - [52]
    PRGO/CdS-DETA 0.6 wt% Pt Na2S/Na2SO3 H2: 10500 29.5% [53]
    B-BT-1, 4-E/TiO2 - TEOA H2: 7346.7 1.91% [54]
    g-C3N4/CdCO3/CdS 3 wt% Pt Na2S/Na2SO3 H2: 3521 - [55]
    g-C3N4-AQ-MoO3 2 wt% Pt TEOA H2: 2999 - [25]
    Fe2O3/C-C3N4 - AgNO3 O2: 223 - [56]
    g-C3N4/CoN - AgNO3 O2: 607.2 - [57]
    P10/BiVO4 - - H2: 5.0 - [58]
    O2: 2.7
    C3N4-rGO-WO3 1.0 wt % Pt - H2: 12.4 0.9% [59]
    O2: 7.3
    Fe2O3/RGO/PCN - - H2: 1090 - [60]
    O2: 530

    CO2 Reduction. Inspired by natural photosynthesis, photocatalytic conversion of CO2 into other carbon-containing products such as hydrocarbon or alcohol chemical fuels has attracted extensive attention.[61-66] In 1979, Inoue et al. reported, for the first time, the reduction of CO2 to CO, CH4, CH3OH, HCOOH and other carbon-based fuels using semiconductor photoelectricity catalysis. Nevertheless, photocatalytic CO2 reduction is a multiple-step reaction with a large uphill thermodynamic barrier, which is still an ongoing and challenging topic.

    Ding group developed an α-Fe2O3/g-C3N4 (FCN) hybrid for photocatalytic CO2 reduction (Figure 9a).[67] The total photocatalytic CH3OH evolution rates of α-Fe2O3, g-C3N4 and FCN hybrid were compared. There is no CH3OH product for pristine α-Fe2O3, and photocatalytic activity of the pure g-C3N4 for CO2 reduction is only 1.94 μmol h-1g-1. For FCN hybrids, the effect of the varied mass ratio of α-Fe2O3 to g-C3N4 on CH3OH production was investigated. As a result, the FCN hybrid with a 40:60 ratio exhibited the highest CH3OH production rate (5.63 μmol h-1g-1), which is approximately 2.9 times higher than that of single-component g-C3N4. Mechanism study showed that the PL intensity of FCN (40:60) is much lower than that of pure g-C3N4 (Figure 9b), indicating the presence of Fe element can effectively reduce the recombination of photogenerated electron-hole pairs. Wong group reported a hierarchical direct Z-scheme system combining 3D urchin-like α-Fe2O3 and g-C3N4 photocatalysts. It provides an enhanced photocatalytic activity of reduction of CO2 to CO, yielding a CO evolution rate of 27.2 μmol h-1g-1 in the absence of cocatalyst as well as sacrifice agent (Figure 9c), [68] which is about 2.2 times higher than that of the pristine g-C3N4 (10.3 μmol h-1g-1). The wavelength dependence of quantum efficiency (QE) for α-Fe2O3/g-C3N4 hybrid achieved 0.499% and 0.963% at λ = 365 and 420 nm, respectively (Figure 9d). Wang group designed inorganic-organic hybrid photocatalysts to enhance the reduction of CO2 under visible light. A Mn complex was installed onto Bi2WO6 via bisphosphonate groups, which possess advantages of low cost and high efficiency toward CO2 reduction.[69] Li group reported a Co-MOF/Cu2O heterojunction with high selectivity for the visible light-driven reduction of CO2 to CO without using any photosensitizer and sacrificial reagents. This p-n heterojunction Co-MOF/Cu2O hybrid composite (xCMC) exhibited remarkable CO production rate of 3.83 µmol g-1h-1, which is 9.6-fold higher than that of single-component Cu2O.[70]

    Figure 9

    Figure 9.  (a) Average CH3OH production rates of g-C3N4, α-Fe2O3 and FCN hybrid, (b) PL spectra of CN and FCN (40:60).[67] (c) Average CO production rates of g-C3N4, α-Fe2O3, and α-Fe2O3/g-C3N4 hybrid, (d) wavelength dependence of QE of α-Fe2O3/g-C3N4.[68]
    DownLoad: Full-Size Img PowerPoint

    Besides the abovementioned examples, many other P-I heterojunction photocatalysts for CO2 reduction, such as g-C3N4/ SnS2, [71] g-C3N4/WO3, [72] g-C3N4/ZnO, [73] AgCl@g-C3N4, [74] NiTiO3/ g-C3N4, [75] Au@g-C3N4/SnS, [76] and p-BN@Zn/Co-ZIF, [77] carbonized polymer dots/Bi4O5Br2, [78] SnO2-x/g-C3N4, [79] FeTiO3/TiO2, [80] Ag3PO4/g- C3N4, [81] and CeO2/g-C3N4[82] have also been developed, all of which show enhanced photocatalytic activities compared to the single-component photocatalysts. Table 3 summarizes the recent reports on the P-I heterostructures for photocatalytic CO2 Reduction.

    Table 3

    Table 3.  Reaction Conditions and Photocatalytic Activities of P-I Heterojunctions for CO2 Reduction
    DownLoad: CSV
    Catalysts Mass
    (mg)    		 Products evolution
    rate (μmol h-1g-1)    		 AQY (%) Ref.
    α-Fe2O3/g-C3N4 10 CH3OH (5.63) - [67]
    α-Fe2O3/g-C3N4 25 CO (27.2) 0.499
    (365 nm)    		 [68]
    Co-MOF/Cu2O 20 CO (3.83) - [70]
    g-C3N4/SnS2 50 CH4 (0.21)
    CH3OH (0.77)    		 - [71]
    g-C3N4/WO3 3 CH3OH (1.1) - [72]
    g-C3N4/ZnO 100 CH3OH (0.6) - [73]
    AgCl@g-C3N4 300 CH4 (25.67)
    CH3COOH (1.2)
    HCOOH (0.67)    		 0.211
    (475 nm)    		 [74]
    NiTiO3/g-C3N4 10 CH3OH (13.74) - [75]
    Au@g-C3N4/SnS 50 CH4 (3.8)
    CH3OH (5.3)    		 15.3
    (525 nm)    		 [76]
    BN@Zn/Co-ZIF 20 CO (152.2) - [77]
    CPDs/Bi4O5Br2 30 CO (132.42) 0.81
    (380 nm)    		 [78]
    SnO2-x/g-C3N4 20 CH3OH (3) - [79]
    FeTiO3/TiO2 50 CH3OH (0.462) - [80]
    Ag3PO4/g-C3N4 10 CO (44)
    CH3OH (9)
    CH4 (0.2)
    C2H5OH (0.1)    		 - [81]
    CeO2/g-C3N4 50 CO (11.8)
    CH4 (9.08)    		 - [82]

    Environmental Remediation. Water pollution is mainly faced with extremely complex components with the characteristics of high concentration, difficult degradation and lasting toxicity, representing one of the most serious threats to human life. Phenols, polycyclic aromatic hydrocarbons, ammonia nitrogen, cyanide, sulfide and other harmful substances are the main sources of organic pollutants. Copious strategies to environmental remediation, including physical adsorption, chemical degradation, biodegradation, and photocatalytic degradation, have been developed.[83-86] Among which, semiconductor-mediated photocatalytic pollutant degradation, as a green and promising method, has attracted extensive attention.

    Yu group reported a direct Z-scheme photocatalyst based on 2D/2D g-C3N4/MnO2 nanocomposite for dye degradation and phenol removal with enhanced activity (Figure 10a-b).[39] The degradation rate of RhB by g-C3N4/MnO2 composites achieved as high as 91.3% after irradiation for 60 min, while those of g-C3N4 and MnO2 were only 19.6% and 22.3%, respectively. Based on the Langmuir-Hinshelwood model, their decomposition behavior is consistent with the pseudo-first-order kinetics and the apparent rate constant of the g-C3N4/MnO2 nanocomposite was 0.033 min, about ~9 and ~5 times higher than those of pristine g-C3N4 and MnO2, respectively. Moreover, the 2D/2D g-C3N4/MnO2 also exhibit dramatically enhanced activity toward phenol removal (Figure 10c-d). Finally, the improved photocatalytic activity of g-C3N4/MnO2 is mainly ascribed to the formation of Z-scheme heterojunction, as proved by Mott-Schottky measurement, electron paramagnetic resonance (EPR) and XPS spectra (Figure 10e).

    Figure 10

    Figure 10.  Photocatalytic degradation rate of (a) RhB and (c) phenol. The kinetics fitted curves and apparent reaction rates of (b) RhB and (d) phenol, (e) mechanism of the g-C3N4/MnO2 nanocomposite.[39]
    DownLoad: Full-Size Img PowerPoint

    Besides aforementioned cases, many other P-I heterojunction photocatalysts, such as CN/rGO@BPQDs, [87] CoO/g-C3N4, [88] α-Fe2O3/g-C3N4, [89] PPy/TiO2, [43] Nb2O5/g-C3N4, [90] WO3@Cu@PDI, [46] PDI/BiOCl, [91] g-C3N4/Cu2O@Cu, [92] AgBr/P-g-C3N4, [93] and DPP-Car/TiO2[30] have also been reported for organic pollutants degradation, showing enhanced photocatalytic activities for the degradation of various pollutants. Table 4 summarizes the recent reports on the P-I heterostructures for environmental remediation.

    Table 4

    Table 4.  Reaction Conditions and Photocatalytic Activities of P-I Heterojunctions for Pollutant Degradation
    DownLoad: CSV
    Catalyst Pollutant
    concentration
    (mg L-1)    		 Pollutants Rate
    constant
    (k, min-1)    		 Ref.
    MnO2/g-C3N4 50 phenol 0.0407 [39]
    CN/rGO@BPQDs 10 RhBa 0.183 [87]
    50 TCb 0.0194
    CoO/g-C3N4 10 TCb 0.0404 [88]
    α-Fe2O3/g-C3N4 - NO 0.0156 [89]
    PPy/TiO2 20 MOc 0.0089 [43]
    Nb2O5/g-C3N4 20 TCb 0.0096 [90]
    WO3@Cu@PDI 20 TCb 0.08 [46]
    PDI/BiOCl 5 phenol 0.013 [91]
    g-C3N4/Cu2O@Cu 15 BPSc 0.0062 [92]
    AgBr/P-g-C3N4 0.1 EPHd 0.0409 [93]
    Bi2Sn2O7/PDIH 10 NORe 0.4903 [94]
    DPP-Car/TiO2 10 MOf 0.0563 [30]
    a Rhodamine B (RhB); b Tetracycline (TC); c Bisphenol-S (BPS); d Ephedrine (EPH); e Norfloxacin (NOR) and f Methyl ora (MO).

    CONCLUSIONS AND OUTLOOK

    In this minireview, the synthesis, classification and applications of P-I heterojunctions are summarized and discussed. The mechanism and charge transfer pathway of P-I heterojunctions can be revealed by hydroxyl radical measurement, photocurrent measurements, in-situ XPS, M-S plot, DFT calculation, and so forth. Compared to single-component semiconductor photocatalysts, P-I heterojunction can combine the advantages of respective components, i.e., polymeric and inorganic semiconductors, to improve the photocatalytic performance. Although P-I heterojunction photocatalysis has made enormous progress in recent years, there are some key issues that still need to be addressed.

    Firstly, the preparation methods of P-I heterojunctions are relatively monotonous. In-situ polymerization is a major method for the preparation of P-I heterojunction photocatalysts. In the future, more attention should be paid to the rational design of preparation methods. Secondly, photocatalytic hydrogen or oxygen production from water splitting generally requires the addition of a hole or electron sacrificial agent. When the sacrificial agent is exhausted, the photocatalytic efficiency will be greatly reduced. Hence it is imperative to add sacrificial agent regularly, which is not conformed to the atomic economy and environmental protection that we are pursuing now. But it is still a great challenge to design superior photocatalysts without adding sacrificial agents to achieve the effect of photocatalytic water splitting. Finally, the exact photocatalytic mechanisms of P-I heterojunctions still need to be further revealed. For example, the reaction mechanism of photocatalytic CO2 reduction is still ambiguous, and the optimal reaction path and active intermediates are also controversial. And the study of heterojunction mechanism is still a great challenge.

    Although some encouraging results have been achieved so far, the stability and efficiency of P-I hybrid nanocomposites are still far from satisfying the requirements of large-scale application. There is an urgent need to develop green, atom-economic, [26, 95, 96] efficient and multifunctional P-I heterojunctions with controllable morphology, defined structure, broad light harvesting, excellent charge carrier mobility, and well-matched energy level. The P-I heterojunctions based on electron donor-acceptor (D-A) types of polymers[97] are also expected to possess synergetic effect on the enhancement of charge separation. Considering that conjugated polymers typically have high-lying conduction band with strong reductive capacity, the heterojunctions based on the combination of π-conjugated polymer with a second inorganic semiconductor that have a deep-lying valence band are expected to achieve the separation of electron hole pairs with simultaneously maximized reduction and oxidation capacities, and thus provide great opportunity for photocatalytic overall water splitting.


    ACKNOWLEDGEMENTS: The National Natural Science Foundation of China (Nos. 21374075 and 22169009), Jiangxi Provincial Natural Science Foundation (No. 20212ACB204007) and the Jiangxi Provincial Key Laboratory of Functional Molecular Materials Chemistry (20212BCD42018) are acknowledged for financial support. COMPETING INTERESTS
    The authors declare no competing interests.
    For submission: https://www.editorialmanager.com/cjschem
    Full paper can be accessed via http://manu30.magtech.com.cn/jghx/EN/10.14102/j.cnki.0254-5861.2022-0188
    ADDITIONAL INFORMATION
    1. [1]

      Wang, H.; Li, X.; Zhao, X.; Li, C.; Song, X.; Zhang, P.; Huo, P.; Li, X. A review on heterogeneous photocatalysis for environmental remediation: from semiconductors to modification strategies. Chin. J. Catal. 2022, 43, 178-214. doi: 10.1016/S1872-2067(21)63910-4

    2. [2]

      Wang, M.; Wu, X.; Wang, S.; Lu, C. A stable polyoxometalate-based coordination polymer for light driven degradation of organic dye pollutant. Chin. J. Struct. Chem. 2021, 40, 1449-1455.

    3. [3]

      Yuan, L.; Qi, M.; Tang, Z.; Xu, Y. Coupling strategy for CO2 valorization integrated with organic synthesis by heterogeneous photocatalysis. Angew. Chem. Int. Ed. 2021, 60, 21150-21172.

    4. [4]

      Su, T.; Shao, Q.; Qin, Z.; Guo, Z.; Wu, Z. Role of interfaces in two-dimensional photocatalyst for water splitting. ACS Catal. 2018, 8, 2253-2276.

    5. [5]

      Wu, H.; Miao, T.; Shi, H.; Xu, W.; Fu, X.; Qian, L. Probing photocatalytic hydrogen evolution of cobalt complexes: experimental and theoretical methods. Chin. J. Struct. Chem. 2021, 40, 1696-1709.

    6. [6]

      Fujishima, A.; Honda, K. Electrochemical photolysis of water at a semiconductor electrode. Nature 1972, 238, 37-38. doi: 10.1038/238037a0

    7. [7]

      Yanagida, S.; Kabumoto, A.; Mizumoto, K.; Pac, C.; Yoshino, K. Poly(p-phenylene)-catalysed photoreduction of water to hydrogen. J. Chem. Soc. Chem. Commun. 1985, 8, 474.

    8. [8]

      Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J.; Domen, K.; Antonietti, M. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 2009, 8, 76-80. doi: 10.1038/nmat2317

    9. [9]

      Lan, Z.; Ren, W.; Chen, X.; Zhang, Y.; Wang, X. Conjugated donor-acceptor polymer photocatalysts with electron-output "tentacles" for efficient hydrogen evolution. Appl. Catal. B Environ. 2019, 245, 596. doi: 10.1016/j.apcatb.2019.01.010

    10. [10]

      Cheng, J. -Z.; Liu, L. -L.; Liao, G.; Shen, Z. -Q.; Tan, Z.; Xing, Y.; Li, X. -X.; Yang, K.; Chen, L.; Liu, S. -Y. Achieving an unprecedented hydrogen evolution rate by solvent-exfoliated CPP-based photocatalysts. J. Mater. Chem. A 2020, 8, 5890-5899. doi: 10.1039/C9TA13514F

    11. [11]

      Lan, Z.; Zhang, G.; Chen, X.; Zhang, Y.; Zhang, K.; Wang, X. Reducing the exciton binding energy of donor-acceptor-based conjugated polymers to promote charge-induced reactions. Angew. Chem. Int. Ed. 2019, 30, 10236-10240.

    12. [12]

      Li, G.; Xie, Z.; Wang, Q.; Chen, X.; Zhang, Y.; Wang, X. Asymmetric acceptor-donor-acceptor polymers with fast charge carrier transfer for solar hydrogen production. Chem. Eur. J. 2021, 27, 939-943. doi: 10.1002/chem.202003856

    13. [13]

      Li, G.; Wang, B.; Wang, R. g-C3N4/Ag/GO composite photocatalyst with efficient photocatalytic performance: synthesis, characterization, kinetic studies, toxicity assessment and degradation mechanism. Chin. J. Struct. Chem. 2020, 39, 1675-1688.

    14. [14]

      Low, J.; Yu, J.; Jaroniec, M.; Wageh, S.; Al-Ghamdi, A. Heterojunction photocatalysts. Adv. Mater 2017, 29, 1601694. doi: 10.1002/adma.201601694

    15. [15]

      Li, H.; Li, X.; Lang, X. Extending the π-conjugated molecules on TiO2 for the selective photocatalytic aerobic oxidation of suldes triggered by visible light. Sustain. Energy Fuels 2021, 5, 2127-2135.

    16. [16]

      Xu, F.; Zhang, L.; Cheng, B.; Yu, J. Direct Z-scheme TiO2/NiS core-shell hybrid nanofibers with enhanced photocatalytic H2-production activity. ACS Sustain. Chem. Eng. 2018, 6, 12291-12298.

    17. [17]

      Zhang, J.; Liao, H.; Sun, S. Construction of 1D/1D WO3 nanorod/TiO2 nanobelt hybrid heterostructure for photocatalytic application. Chin. J. Struct. Chem. 2020, 39, 1019-1028.

    18. [18]

      Zhou, B.; Yang, B.; Waqas, M.; Xiao, K.; Zhu, C.; Wu, L. Design of a p-n heterojunction in 0D/3D MoS2/g-C3N4 composite for boosting the efficient separation of photogenerated carriers with enhanced visible-light-driven H2 evolution. RSC Adv. 2020, 10, 19169-19177.

    19. [19]

      Zhao, B.; Zhao. Y.; Liu, P.; Men, Y.; Meng, X.; Pan, Y. Progress and understanding on catalysts with well-defined interface for boosting CO2 conversion. Chin. J. Struct. Chem. 2022, 41, 41324-41333.

    20. [20]

      Zhang, X.; Xiao, J.; Hou, M.; Xiang, Y.; Chen, H. Robust visible/near-infrared light driven hydrogen generation over Z-scheme conjugated polymer/CdS hybrid. Appl. Catal. B Environ. 2018, 224, 871-876.

    21. [21]

      Xu, Q.; Zhang, L.; Cheng, B.; Fan, J.; Yu, J. S-Scheme heterojunction photocatalyst. Chem 2020, 6, 1543-1559.

    22. [22]

      Liao, G.; Li, C.; Liu, S.; Fang, B.; Yang, H. Emerging frontiers of Z-scheme photocatalytic systems. Trends Chem. 2022, 4, 111-127.

    23. [23]

      Zhu, Y.; Wan, T.; Wen, X.; Chu, D.; Jiang, Y. Tunable type I and II heterojunction of CoOx nanoparticles confined in g-C3N4 nanotubes for photocatalytic hydrogen production. Appl. Catal. B Environ. 2019, 244, 814-822.

    24. [24]

      Hu, Y.; Hao, X.; Cui, Z.; Zhou, J.; Chu, S.; Wang, Y.; Zou, Z. Enhanced photocarrier separation in conjugated polymer engineered CdS for direct Z-scheme photocatalytic hydrogen evolution. Appl. Catal. B Environ. 2020, 260, 118131.

    25. [25]

      Ma, X.; Wang, G.; Qin, L.; Liu, J.; Li, B.; Hu, Y.; Cheng, H. Z-scheme g-C3N4-AQ-MoO3 photocatalyst with unique electron transfer channel and large reduction area for enhanced sunlight photocatalytic hydrogen production. Appl. Catal. B Environ. 2021, 288, 120025.

    26. [26]

      Shu, G.; Wang, Y.; Li, Y.; Zhang, S.; Jiang, J.; Wang, F. A high performance and low cost poly (dibenzothiophene-S, S-dioxide)@TiO2 composite with hydrogen evolution rate up to 51.5 mmol h-1 g-1. J. Mater. Chem. A 2020, 8, 18292-18301.

    27. [27]

      Xing, Y. -Q.; Tan, Z.; Cheng, J.; Shen, Z.; Zhang, Y.; Chen, L.; Liu, S. -Y. In situ C-H activation-derived polymer@TiO2 p-n heterojunction for photocatalytic hydrogen evolution. Sustain. Energy Fuels 2021, 5, 5166-5174.

    28. [28]

      Hou, H.; Zhang, X.; Huang, D.; Ding, X.; Wang, S.; Yang, X.; Li, S.; Xiang, Y.; Chen, H. Conjugated microporous poly(benzothiadiazole)/TiO2 heterojunction for visible-light-driven H2 production and pollutant removal. Appl. Catal. B Environ. 2017, 203, 563-571.

    29. [29]

      Xiao, J.; Luo, Y.; Yang, Z.; Xiang, Y.; Zhang, X.; Chen, H. Synergistic design for enhancing solar-to-hydrogen conversion over TiO2 based ternary hybrid. Catal. Sci. Technol. 2018, 8, 2477-2487.

    30. [30]

      Yang, L.; Yu, Y.; Zhang, J.; Chen, F.; Meng, X.; Qiu, Y.; Dan, Y.; Jiang, L. In-situ fabrication of diketopyrrolopyrrole-carbazole-based conjugated polymer/TiO2 heterojunction for enhanced visible light photocatalysis. Appl. Surf. Sci. 2018, 434, 796-805.

    31. [31]

      Yang, X.; Fu, H.; Wang, W.; Xiong, S.; Han, D.; Deng, Z.; An, X. Enhanced solar light photocatalytic performance based on a novel Au-WO3@TiO2 ternary core-shell nanostructures. Appl. Surf. Sci. 2020, 505, 144631.

    32. [32]

      Lu, M.; Li, Q.; Zhang, C.; Fan, X.; Li, L.; Dong, Y.; Chen, G.; Shi, H. Remarkable photocatalytic activity enhancement of CO2 conversion over 2D/2D g-C3N4/BiVO4 Z-scheme heterojunction promoted by efficient interfacial charge transfer. Carbon 2020, 160, 342-352.

    33. [33]

      Xu, Q.; Zhu, B.; Jiang, C.; Cheng, B.; Yu, J. Constructing 2D/2D Fe2O3/g-C3N4 direct Z-scheme photocatalysts with enhanced H2 generation performance. Solar RRL 2018, 2, 1800006.

    34. [34]

      You, Z.; Wu, C.; Shen, Q.; Yu, Y.; Chen, H.; Su, Y.; Wang, H.; Wu, C.; Zhang, F.; Yang, H. A novel efficient g-C3N4@BiOI p-n heterojunction photocatalyst constructed through the assembly of g-C3N4 nanoparticles. Dalton Trans. 2018, 47, 7353-7361.

    35. [35]

      Cai, T.; Zeng, W.; Liu, Y.; Wang, L.; Dong, W.; Chen, H.; Xia, X. A promising inorganic-organic Z-scheme photocatalyst Ag3PO4/PDI supermolecule with enhanced photoactivity and photostability for environmental remediation. Appl. Catal. B Environ. 2020, 263, 118327.

    36. [36]

      Guo, Y.; Li, J.; Gao, Z.; Zhu, X.; Liu, Y.; Wei, Z.; Zhao, W.; Sun, C. A simple and effective method for fabricating novel p-n heterojunction photocatalyst g-C3N4/Bi4Ti3O12 and its photocatalytic performances. Appl. Catal. B Environ. 2016, 192, 57-71.

    37. [37]

      You, Y.; Wang, S.; Xiao, K.; Ma, T.; Zhang, Y.; Huang, H. Z-Scheme g-C3N4/Bi4NbO8Cl heterojunction for enhanced photocatalytic hydrogen production. ACS Sustain. Chem. Eng. 2018, 6, 16219-16227. doi: 10.1021/acssuschemeng.8b03075/suppl_file/sc8b03075_si_001.pdf

    38. [38]

      Zhang, X.; Xiao, J.; Peng, C.; Xiang, Y.; Chen, H. Enhanced photocatalytic hydrogen production over conjugated polymer/black TiO2 hybrid: the impact of constructing active defect states. Appl. Surf. Sci. 2019, 465, 288-296.

    39. [39]

      Xia, P.; Zhu, B.; Cheng, B.; Yu, J.; Xu, J. 2D/2D g-C3N4/MnO2 nanocomposite as a direct Z-scheme photocatalyst for enhanced photocatalytic activity. ACS Sustain. Chem. Eng. 2018, 6, 965-973.

    40. [40]

      Yu, F.; Wang, Z.; Zhang, S.; Ye, H.; Kong, K.; Gong, X.; Hua, J.; Tian, H. Molecular engineering of donor-acceptor conjugated polymer/g-C3N4 heterostructures for significantly enhanced hydrogen evolution under visible-light irradiation. Adv. Funct. Mater. 2018, 28, 1804512.

    41. [41]

      Zhang, X.; Peng, B.; Zhang, S.; Peng, T. Robust wide visible-light-responsive photoactivity for H2 production over a polymer/polymer heterojunction photocatalyst: the significance of sacrificial reagent. ACS Sustain. Chem. Eng. 2015, 3, 1501-1509.

    42. [42]

      Ke, X.; Dai, K.; Zhu, G.; Zhang, J.; Liang, C. In situ photochemical synthesis noble-metal-free NiS on CdS diethylenetriamine nanosheets for boosting photocatalytic H2 production activity. Appl. Surf. Sci. 2019, 481, 669-677.

    43. [43]

      Sun, L.; Shi, Y.; Li, B.; Li, X.; Wang, Y. Preparation and characterization of polypyrrole/TiO2 nanocomposites by reverse microemulsion polymerization and its photocatalytic activity for the degradation of methyl orange under natural light. Polym. Compos. 2013, 34, 1076-1080.

    44. [44]

      Jo, W.; Kang, H. (Ratios: 5, 10, 50, 100, and 200) polyaniline-TiO2 composites under visible- or UV-light irradiation for decomposition of organic vapors. Mater. Chem. Phys. 2013, 143, 247-255.

    45. [45]

      Belabed, C.; Tab, A.; Moulai, F.; Černohorský, O.; Boudiaf, S.; Benrekaa, N.; Grym, J.; Trari, M. ZnO nanorods-PANI heterojunction dielectric, electrochemical properties, and photodegradation study of organic pollutant under solar light. Int. J. Hydrogen Energy 2021, 46, 20893-20904.

    46. [46]

      Zeng, W.; Cai, T.; Liu, Y.; Wang, L.; Dong, W.; Chen, H.; Xia, X. An artificial organic-inorganic Z-scheme photocatalyst WO3@Cu@PDI supramolecular with excellent visible light absorption and photocatalytic activity. Chem. Eng. J. 2020, 381, 122691.

    47. [47]

      Zhang, Q.; Zhou, S.; Fu, S.; Wang, X. Tetranitrophthalocyanine zinc/TiO2 nanofibers organic-inorganic heterostructures with enhanced visible photocatalytic activity. Nano 2017, 12, 1750117.

    48. [48]

      Pei, K.; Zhai, T. Emerging 2D organic-inorganic heterojunctions. Cell Rep. Phys. Sci. 2020, 1, 100166.

    49. [49]

      Wang, H.; Qian, C.; Liu, J.; Zeng, Y.; Wang, D.; Zhou, W.; Gu, L.; Wu, H.; Liu, G.; Zhao, Y. Integrating suitable linkage of covalent organic frameworks into covalently bridged inorganic/organic hybrids toward efficient photocatalysis. J. Am. Chem. Soc. 2020, 142, 4862-4871.

    50. [50]

      Yan, J.; Wu, H.; Chen, H.; Zhang, Y.; Zhang, F.; Frank Liu, S. Fabrication of TiO2/C3N4 heterostructure for enhanced photocatalytic Z-scheme overall water splitting. Appl. Catal. B Environ. 2016, 191, 130-137.

    51. [51]

      Cheng, C.; He, B.; Fan, J.; Cheng, B.; Cao, S.; Yu, J. An inorganic/organic S-scheme heterojunction H2-production photocatalyst and its charge transfer mechanism. Adv. Mater. 2021, 33, 2100317.

    52. [52]

      Yuan, X.; Wang, C.; Dragoe, D.; Beaunier, P.; Colbeau-Justin, C.; Remita, H. Highly promoted photocatalytic hydrogen generation by multiple electron transfer pathways. Appl. Catal. B Environ. 2021, 281, 119457.

    53. [53]

      Dai, K.; Hu, T.; Zhang, J.; Lu, L. Carbon nanotube exfoliated porous reduced graphene oxide/CdS-diethylenetriamine heterojunction for efficient photocatalytic H2 production. Appl. Surf. Sci. 2020, 512, 144783.

    54. [54]

      Xiang, Y.; Wang, X.; Zhang, X.; Hou, H.; Dai, K.; Huang, Q.; Chen, H. Enhanced visible light photocatalytic activity of TiO2 assisted by organic semiconductors: a structure optimization strategy of conjugated polymers. J. Mater. Chem. A 2018, 6, 153-159.

    55. [55]

      Wang, J.; Fan, Y.; Pan, R.; Hao, Q.; Ye, J.; Wu, Y.; Ree, T. In situ bridging nanotwinned all-solid-state Z-scheme g-C3N4/CdCO3/CdS heterojunction photocatalyst by metal oxide for H2 evolution. Nanoscale 2022, 14, 7408-7417.

    56. [56]

      Kong, L.; Yan, J.; Li, P.; Frank Liu, S. Fe2O3/C-C3N4-based tight heterojunction for boosting visible-light-driven photocatalytic water oxidation. ACS Sustain. Chem. Eng. 2018, 6, 10436-10444.

    57. [57]

      Zhang, J.; Zhang, G.; Zhang, J. Organic/inorganic nitride heterostructure for efficient photocatalytic oxygen evolution. Appl. Surf. Sci. 2019, 475, 256-263.

    58. [58]

      Bai, Y.; Nakagawa, K.; Cowan, A.; Aitchison, C.; Yamaguchi, Y.; Zwijnenburg, M.; Kudo, A.; Sprick, R.; Cooper, A. Photocatalyst Z-scheme system composed of a linear conjugated polymer and BiVO4 for overall water splitting under visible light. J. Mater. Chem. A 2020, 8, 16283-16290.

    59. [59]

      Zhao, G.; Huang, X.; Fina, F.; Zhang, G.; Irvine, J. Facile structure design based on C3N4 for mediator-free Z-scheme water splitting under visible light. Catal. Sci. Technol. 2015, 5, 3416-3422.

    60. [60]

      Pan, Z.; Zhang, G.; Wang, X. Polymeric carbon nitride/RGO/Fe2O3: all solid state Z-scheme system for photocatalytic overall water splitting. Angew. Chem. Int. Ed. 2019, 58, 7102-7106.

    61. [61]

      Jiang, Z.; Sun, H.; Wang, T.; Wang, B.; Wei, W.; Li, H.; Yuan, S.; An, T.; Zhao, H.; Yu, J.; Wong, P. Nature-based catalyst for visible-light-driven photocatalytic CO2 reduction. Energy Environ. Sci. 2018, 11, 2382-2389.

    62. [62]

      Ran, J.; Jaroniec, M.; Qiao, S. Cocatalysts in semiconductor-based photocatalytic CO2 reduction: achievements, challenges, and opportunities. Adv. Mater 2018, 30, 1704649.

    63. [63]

      Habisreutinger, S.; Schmidt-Mende, L.; Stolarczyk, J. Photocatalytic reduction of CO2 on TiO2 and other semiconductors. Angew. Chem. Int. Ed. 2013, 52, 7372.

    64. [64]

      Chang, X.; Wang, T.; Gong, J. CO2 photo-reduction: insights into CO2 activation and reaction on surfaces of photocatalysts. Energy Environ. Sci. 2016, 9, 2177.

    65. [65]

      Izumi, Y. Recent advances in the photocatalytic conversion of carbon dioxide to fuels with water and/or hydrogen using solar energy and beyond. Coord. Chem. Rev. 2013, 257, 171.

    66. [66]

      Wang, Y.; Zhao, Z.; Sun, R.; Bian, J.; Zhang, Z.; Jing, L. TiO2-modulated tetra(4-carboxyphenyl)porphyrin/perylene diimide organic Z-scheme nano-heterojunctions for efficiently visible-light catalytic CO2 reduction. Nanoscale 2022, 14, 8041-8049.

    67. [67]

      Guo, H.; Chen, M.; Zhong, Q.; Wang, Y.; Ma, W.; Ding, J. Synthesis of Z-scheme α-Fe2O3/g-C3N4 composite with enhanced visible-light photocatalytic reduction of CO2 to CH3OH. J. CO2 Util. 2019, 33, 233-241.

    68. [68]

      Jiang, Z.; Wan, W.; Li, H.; Yuan, S.; Zhao, H.; Wong, P. A hierarchical Z-scheme α-Fe2O3/g-C3N4 hybrid for enhanced photocatalytic CO2 reduction. Adv. Mater. 2018, 30, 1706108.

    69. [69]

      Zhang, L.; Wang, W.; Wang, H.; Ma, X.; Bian, Z. Design of inorganic-organic hybrid photocatalytic systems for enhanced CO2 reduction under visible light. Chem. Eng. Sci. 2019, 207, 1246-1255.

    70. [70]

      Dong, W.; Jia, J.; Wang, Y.; An, J.; Yang, O.; Gao, X.; Liu, Y.; Zhao, J.; Li, D. Visible-light-driven solvent-free photocatalytic CO2 reduction to CO by Co-MOF/Cu2O heterojunction with superior selectivity. Chem. Eng. J. 2022, 438, 135622.

    71. [71]

      Di, T.; Zhu, B.; Cheng, B.; Yu, J.; Xu, J. A direct Z-scheme g-C3N4/SnS2 photocatalyst with superior visible-light CO2 reduction performance. J. Catal. 2017, 352, 532-541.

    72. [72]

      Ohno, T.; Murakami, N.; Koyanagi, T.; Yang, Y. Photocatalytic reduction of CO2 over a hybrid photocatalyst composed of WO3 and graphitic carbon nitride (g-C3N4) under visible light. J. CO2 Util. 2014, 6, 17-25.

    73. [73]

      Yu, W.; Xu, D.; Peng, T. Enhanced photocatalytic activity of g-C3N4 for selective CO2 reduction to CH3OH via facile coupling of ZnO: a direct Z-scheme mechanism. J. Mater. Chem. A 2015, 3, 19936-19947.

    74. [74]

      Murugesan, P.; Narayanan, S.; Manickam, M.; Murugesan, P.; 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.

    75. [75]

      Guo, H.; Wan, S.; Wang, Y.; Ma, W.; Zhong, Q.; Ding, J. Enhanced photocatalytic CO2 reduction over direct Z-scheme NiTiO3/g-C3N4 nanocomposite promoted by efficient interfacial charge transfer. Chem. Eng. J. 2021, 412, 128646.

    76. [76]

      Liang, M.; Borjigin, T.; Zhang, Y.; Liu, H.; Liu, B.; Guo, H. Z-scheme Au@void@g-C3N4/SnS yolk-shell heterostructures for superior photocatalytic CO2 reduction under visible light. ACS Appl. Mater. Interfaces 2018, 10, 34123-34131.

    77. [77]

      Wang, Y.; Hu, G.; Feng, Y.; Zhang, X.; Song, C.; Lin, J.; Huang, Y.; Zhang, Y.; Liu, Z.; Tang, C.; Yu, C. Formation of p-BN@Zn/Co-ZIF hybrid materials for improved photocatalytic CO2 reduction by H2O. Mater. Res. Bull. 2022, 152, 11186.

    78. [78]

      Wang, B.; Zhao, J.; Chen, H.; Weng, Y.; Tang, H.; Chen, Z.; Zhu, W.; She, Y.; Xia, J.; Li, H. Unique Z-scheme carbonized polymer dots/ Bi4O5Br2 hybrids for efficiently boosting photocatalytic CO2 reduction. Appl. Catal. B Environ. 2021, 293, 120182.

    79. [79]

      He, Y.; Zhang, L.; Fan, M.; Wang, X.; Walbridge, M.; Nong, Q.; Wu, Y.; Zhao, L. Z-scheme SnO2-x/g-C3N4 composite as an efficient photocatalyst for dye degradation and photocatalytic CO2 reduction. Sol. Energy Mater. Sol. Cells 2015, 137, 175-184.

    80. [80]

      Truong, Q.; Liu, J.; Chung, C.; Ling, Y. Photocatalytic reduction of CO2 on FeTiO3/TiO2 photocatalyst. Catal. Commun. 2012, 19, 85-89.

    81. [81]

      He, Y.; Zhang, L.; Teng, B.; Fan, M. New application of Z-scheme Ag3PO4/g-C3N4 composite in converting CO2 to fuel. Environ. Sci. Technol. 2015, 49, 649-656.

    82. [82]

      Li, M.; Zhang, L.; Wu, M.; Du, Y.; Fan, X.; Wang, M.; Zhang, L.; Kong, Q.; Shi, J. Mesostructured CeO2/g-C3N4 nanocomposites: remarkably enhanced photocatalytic activity for CO2 reduction by mutual component activations. Nano Energy 2016, 19, 145-155.

    83. [83]

      Chen, X.; Xu, Y.; Ma, X.; Zhu, Y. Large dipole moment induced efficient bismuth chromate photocatalysts for wide-spectrum driven water oxidation and complete mineralization of pollutants. Natl. Sci. Rev. 2020, 7, 652-659.

    84. [84]

      Zhang, Y.; Qin, H.; Hong, N.; Bao, L.; Wu, B. Syntheses, structures and photocatalytic degradation properties of two copper(II) coordination polymers with flexible bis(imidazole) ligand. Chin. J. Struct. Chem. 2021, 40, 595-602.

    85. [85]

      Gómez-Pacheco, C.; Sánchez-Polo, M.; Rivera-Utrilla, J.; López-Peñalver, J. Tetracycline removal from waters by integrated technologies based on ozonation and biodegradation. Chem. Eng. J. 2011, 178, 115- 121.

    86. [86]

      Zhu, B.; Xia, P.; Li, Y.; Ho, W.; Yu, J. Fabrication and photocatalytic activity enhanced mechanism of direct Z-scheme g-C3N4/Ag2WO4 photocatalyst. Appl. Surf. Sci. 2017, 391, 175-183.

    87. [87]

      Xiong, J.; Li, X.; Huang, J.; Gao, X.; Chen, Z.; Liu, J.; Li, H.; Kang, B.; Yao, W.; Zhu, Y. CN/rGO@BPQDs high-low junctions with stretching spatial charge separation ability for photocatalytic degradation and H2O2 production. Appl. Catal. B Environ. 2020, 5, 118602.

    88. [88]

      Guo, F.; Shi, W.; Wang, H.; Han, M.; Li, H.; Huang, H.; Liu, Y.; Kang, Z. Facile fabrication of a CoO/g-C3N4 p-n heterojunction with enhanced photocatalytic activity and stability for tetracycline degradation under visible light. Catal. Sci. & Tech. 2017, 7, 3325-3331.

    89. [89]

      Geng, Y.; Chen, D.; Li, N.; Xu, Q.; Li, H.; He, J.; Lu, J. Z-Scheme 2D/2D α-Fe2O3/g-C3N4 heterojunction for photocatalytic oxidation of nitric oxide. Appl. Catal. B Environ. 2021, 280, 119409.

    90. [90]

      Hong, Y.; Li, C.; Zhang, G.; Meng, Y.; Yin, B.; Zhao, Y.; Shi, W. Efficient and stable Nb2O5 modified g-C3N4 photocatalyst for removal of antibiotic pollutant. Chem. Eng. J. 2016, 299, 74-84.

    91. [91]

      Gao, X.; Gao, K.; Li, X.; Shang, Y.; Fu, F. Hybrid PDI/BiOCl heterojunction with enhanced interfacial charge transfer for a full-spectrum photocatalytic degradation of pollutants. Catal. Sci. Technol. 2020, 10, 372-381.

    92. [92]

      Dai, B.; Zhao, W.; Wei, W.; Cao, J.; Yang, G.; Li, S.; Sun, C.; Leung, D. Photocatalytic reduction of CO2 and degradation of bisphenol-S by g-C3N4/Cu2O@Cu S-scheme heterojunction: study on the photocatalytic performance and mechanism insight. Carbon 2022, 193, 272-284.

    93. [93]

      Chen, M.; Guo, C.; Hou, S.; Lv, J.; Zhang, Y.; Zhang, H.; Xu, J. A novel Z-scheme AgBr/P-g-C3N4 heterojunction photocatalyst: excellent photocatalytic performance and photocatalytic mechanism for ephedrine degradation. Appl. Catal. B Environ. 2020, 266, 118614.

    94. [94]

      Yin, N.; Chen, H.; Yuan, X.; Zhang, Y.; Zhang, M.; Guo, J.; Zhang, Y.; Qiao, L.; Liu, M.; Song, K. Highly efficient photocatalytic degradation of norfloxacin via Bi2Sn2O7/PDIH Z-scheme heterojunction: influence and mechanism. J. Hazard. Mater. 2022, 436, 129317.

    95. [95]

      Huang, W.; Shen, Z.; Cheng, J. -Z.; Liu, L. -L.; Yang, K.; Wen, H. -R.; Liu, S. -Y. C-H activation derived CPPs for photocatalytic hydrogen production excellently accelerated by a DMF cosolvent. J. Mater. Chem. A 2019, 7, 24222-24230.

    96. [96]

      Tan, Z. -R.; Xing, Y. -Q.; Cheng, J. -Z.; Zhang, G.; Shen, Z. -Q.; Zhang, Y. -J.; Liao, G.; Chen, L.; Liu, S. -Y. EDOT-based conjugated polymers accessed via C-H direct arylation for efficient photocatalytic hydrogen production. Chem. Sci. 2022, 13, 1725-1733.

    97. [97]

      Shen, Z. -Q.; Xing, Y. -Q.; Chen, Y.; Zhang, G.; Chen, L.; Liu, S. -Y. Nanoporous and nonporous conjugated donor-acceptor polymer semiconductors for photocatalytic hydrogen production. Beilstein J. Nanotechnol. 2021, 12, 607-623.

  • Figure 1  Diagram of the basic pathways of photocatalytic water splitting, pollutant degradation, and CO2 reduction.

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    Figure 2  VB and CB alignments of common inorganic photocatalysts.

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    Figure 3  shows that type-II heterojunction with staggered band structure is fundamentally different from the type-I. The CB and VB levels of SCA are both higher than those of SCB. And the electrons and holes are not on the same semiconductor, and thus the e- - h+ recombination rate on the same semiconductor is effectively inhibited.

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    Figure 4  Ex-situ and in-situ XPS spectra of (a) C 1s, (b) N 1s of PI and 15% CdS/PI, (c) Cd 3d and (d) S 2p of CdS and 15% CdS/PI.[24] (e) TEM, HRTEM images, (f) Pt XPS spectrum of BE-CdS-10.0 hybrid after in-situ photodeposition of Pt from H2PtCl6, (g) Proposed photocatalytic H2 production mechanism.[20]

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    Figure 5  Mechanically mixed 50% PyOT-TiO2 and in situ prepared 50% PyOT@TiO2, and the images of their ultrasonic dispersions in EtOH.[27]

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    Figure 6  (a) The rate curves of samples for photocatalytic H2 production, (b) the effect of the 0D-MoS2 QDs amount, (c) HER of 2D-MoS2 nanosheets, (d) recircling test of 0D/3D-MCN-3.5%, (e) proposed photocatalytic mechanisms for the 0D/3D-MCN and 2D/3D-MCN composites.[18]

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    Figure 7  (a-c) High-resolution XPS spectra, (d) schematic illustration of photoirradiation KPFM, (e) schematic illustration of S-scheme charge transfer process.[51] (f) Normalized HERs under visible or full arc light, (g) p-n heterojunction of PyOT@TiO2.[27] (h) Schematic diagram of catalysts synthesis, (i) hydrogen production by (Pt-PPy)-TiO2, (Pt-TiO2)-PPy and Pt-(PPy-TiO2).[52]

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    Figure 8  Proposed mechanism for (a) photocatalytic H2 production, (b) photodegradation of CIP over BBT-TiO2 heterojunction.[28] (c) In situ fabrication of B-BT-1, 4-E on the surface of TiO2.[54] (d) Configuration of energy band positions and Z-scheme photogenerated charge carrier transfer in the BE-CdS hybrid photocatalyst.[20]

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    Figure 9  (a) Average CH3OH production rates of g-C3N4, α-Fe2O3 and FCN hybrid, (b) PL spectra of CN and FCN (40:60).[67] (c) Average CO production rates of g-C3N4, α-Fe2O3, and α-Fe2O3/g-C3N4 hybrid, (d) wavelength dependence of QE of α-Fe2O3/g-C3N4.[68]

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    Figure 10  Photocatalytic degradation rate of (a) RhB and (c) phenol. The kinetics fitted curves and apparent reaction rates of (b) RhB and (d) phenol, (e) mechanism of the g-C3N4/MnO2 nanocomposite.[39]

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    Table 1.  Summarized Preparation Methods of P-I Heterojunction Photocatalysts

    Catalysts Dosage (mg) Preparation method Ref.
    BE-CdS 30 in-situ polycondensation [20]
    DBTSO@TiO2 10 in-situ polycondensation [26]
    PyOT@TiO2 10 in-situ polymerization [27]
    BBT/TiO2 10 in-situ polymerization [28]
    BE-Au-TiO2 30 in-situ polymerization [29]
    DPP-Car/TiO2 100 in-situ polymerization [30]
    WO3@TiO2 20 in-situ chemical deposition method [31]
    CdS/PI 50 solvothermal method [24]
    g-C3N4/BiVO4 80 hydrothermal method [32]
    Fe2O3/g-C3N4 50 electrostatic self-assembly
    approach    		 [33]
    g-C3N4@BiOI 50 electrostatic self-assembly
    approach    		 [34]
    Ag3PO4/PDI 20 self-assembly approach [35]
    g-C3N4/Bi4Ti3O12 - ball milling [36]
    g-C3N4/Bi4NbO8Cl 100 ball milling [37]
    BE/black TiO2 30 ball milling [38]
    g-C3N4/MnO2 - wet-chemical method [39]
    CP/g-C3N4 50 molecular engineering strategy [40]
    P3HT/g-C3N4 10 facile rotary evaporation [41]
    CdS-DETA 50 microwave hydrothermal method [42]
    PPy/TiO2 50 reverse microemulsion polymerization [43]
    (PANI)/TiO2 - hydrothermal-chemisorption process [44]
    ZnONRs-PANI - electrophoretic deposition [45]
    WO3@Cu@PDI 5 water bath method [46]
    (TNZnPc)/TiO2 - electrospinning and solvothermal method [47]
    下载: 导出CSV

    Table 2.  Summary of Reported P-I Heterostructures for Photocatalytic Water Splitting

    Catalysts Cocatalyst Sacrificial reagent Activity (µmol h-1g-1) AQE (420 nm) Ref.
    MoS2/g-C3N4 - lactic acid H2: 817.1 - [18]
    BE-CdS 1.0 wt% Pt Na2S/Na2SO3 H2: 40990 7.5% [20]
    CoOx@g-C3N4 - TEA H2: 262.9 1.9% [23]
    PDBTSO@TiO2 3.0 wt% Pt TEOA H2: 51500 13% [26]
    PyOT@TiO2 - AA H2: 1200 - [27]
    BBT/TiO2 0.3 wt% Pt, TEOA H2: 6750 1.45% (450 nm) [28]
    BE-Au-TiO2 1.0 wt% Pt TEOA H2: 26040 7.8% [29]
    CdS/PI 1.0 wt% Pt lactic acid H2: 613  - [24]
    Fe2O3/g-C3N4 1.0 wt % Pt TEOA H2: 398.0 - [33]
    TiO2/C3N4 1.0 wt %Pt TEOA H2: 1540 4.94% (365 nm) [50]
    CdS/PT 1 wt% Pt lactic acid H2: 9280 24.3% (400 nm) [51]
    PPy-TiO2 1 wt% Pt CH3OH H2: 3200 - [52]
    PRGO/CdS-DETA 0.6 wt% Pt Na2S/Na2SO3 H2: 10500 29.5% [53]
    B-BT-1, 4-E/TiO2 - TEOA H2: 7346.7 1.91% [54]
    g-C3N4/CdCO3/CdS 3 wt% Pt Na2S/Na2SO3 H2: 3521 - [55]
    g-C3N4-AQ-MoO3 2 wt% Pt TEOA H2: 2999 - [25]
    Fe2O3/C-C3N4 - AgNO3 O2: 223 - [56]
    g-C3N4/CoN - AgNO3 O2: 607.2 - [57]
    P10/BiVO4 - - H2: 5.0 - [58]
    O2: 2.7
    C3N4-rGO-WO3 1.0 wt % Pt - H2: 12.4 0.9% [59]
    O2: 7.3
    Fe2O3/RGO/PCN - - H2: 1090 - [60]
    O2: 530
    下载: 导出CSV

    Table 3.  Reaction Conditions and Photocatalytic Activities of P-I Heterojunctions for CO2 Reduction

    Catalysts Mass
    (mg)    		 Products evolution
    rate (μmol h-1g-1)    		 AQY (%) Ref.
    α-Fe2O3/g-C3N4 10 CH3OH (5.63) - [67]
    α-Fe2O3/g-C3N4 25 CO (27.2) 0.499
    (365 nm)    		 [68]
    Co-MOF/Cu2O 20 CO (3.83) - [70]
    g-C3N4/SnS2 50 CH4 (0.21)
    CH3OH (0.77)    		 - [71]
    g-C3N4/WO3 3 CH3OH (1.1) - [72]
    g-C3N4/ZnO 100 CH3OH (0.6) - [73]
    AgCl@g-C3N4 300 CH4 (25.67)
    CH3COOH (1.2)
    HCOOH (0.67)    		 0.211
    (475 nm)    		 [74]
    NiTiO3/g-C3N4 10 CH3OH (13.74) - [75]
    Au@g-C3N4/SnS 50 CH4 (3.8)
    CH3OH (5.3)    		 15.3
    (525 nm)    		 [76]
    BN@Zn/Co-ZIF 20 CO (152.2) - [77]
    CPDs/Bi4O5Br2 30 CO (132.42) 0.81
    (380 nm)    		 [78]
    SnO2-x/g-C3N4 20 CH3OH (3) - [79]
    FeTiO3/TiO2 50 CH3OH (0.462) - [80]
    Ag3PO4/g-C3N4 10 CO (44)
    CH3OH (9)
    CH4 (0.2)
    C2H5OH (0.1)    		 - [81]
    CeO2/g-C3N4 50 CO (11.8)
    CH4 (9.08)    		 - [82]
    下载: 导出CSV

    Table 4.  Reaction Conditions and Photocatalytic Activities of P-I Heterojunctions for Pollutant Degradation

    Catalyst Pollutant
    concentration
    (mg L-1)    		 Pollutants Rate
    constant
    (k, min-1)    		 Ref.
    MnO2/g-C3N4 50 phenol 0.0407 [39]
    CN/rGO@BPQDs 10 RhBa 0.183 [87]
    50 TCb 0.0194
    CoO/g-C3N4 10 TCb 0.0404 [88]
    α-Fe2O3/g-C3N4 - NO 0.0156 [89]
    PPy/TiO2 20 MOc 0.0089 [43]
    Nb2O5/g-C3N4 20 TCb 0.0096 [90]
    WO3@Cu@PDI 20 TCb 0.08 [46]
    PDI/BiOCl 5 phenol 0.013 [91]
    g-C3N4/Cu2O@Cu 15 BPSc 0.0062 [92]
    AgBr/P-g-C3N4 0.1 EPHd 0.0409 [93]
    Bi2Sn2O7/PDIH 10 NORe 0.4903 [94]
    DPP-Car/TiO2 10 MOf 0.0563 [30]
    a Rhodamine B (RhB); b Tetracycline (TC); c Bisphenol-S (BPS); d Ephedrine (EPH); e Norfloxacin (NOR) and f Methyl ora (MO).
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  • 发布日期:  2022-09-22
  • 收稿日期:  2022-08-20
  • 接受日期:  2022-09-11
  • 网络出版日期:  2022-09-20
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