Photocatalytic hydrogen evolution by heterojunction photocatalysts is considered an effective way to address environmental and energy crises. In this work, a novel ZnCoP/CdLa₂S₄ Schottky heterojunction was prepared via a physical mixing method assisted by water bath heating and used to enhance the efficiency of photocatalytic hydrogen production. Owing to the higher work function and metallic conductivity of ZnCoP, the photoinduced electrons can transfer from CdLa₂S₄ to ZnCoP through the ZnCoP/CdLa₂S₄ interface, which suppresses the recombination of photoinduced electrons and holes. Moreover, the Schottky heterojunction formed at the interface between ZnCoP and CdLa₂S₄ inhibits electron backflow from ZnCoP to CdLa₂S₄, which further promotes the separation of electron-hole pairs. Meanwhile, the ZnCoP/CdLa₂S₄ heterojunction exhibited enhanced visible light absorption compared to CdLa₂S₄. In addition, ZnCoP acts as an electron acceptor and hydrogen evolution active site. The synergistic effect of the tight ZnCoP/CdLa₂S₄ interface, the higher work function and metallic conductivity of ZnCoP, and the formation of Schottky junctions significantly enhance the photocatalytic hydrogen production evolution performance of CdLa₂S₄. When the amount of ZnCoP was 30 wt% (wt%, mass fraction), the 30ZCP/CLS composite showed the highest photocatalytic performance, and the hydrogen production rate reached 10.26 mmol·g^-1·h^-1 under visible light irradiation and with Na₂S and Na₂SO₃ as sacrificial agents, which was 7.7 times that of CdLa₂S₄. Combined with the activity data and characterization results, a potential mechanism for photocatalytic hydrogen production over ZnCoP/CdLa₂S₄ Schottky heterojunctions was proposed.

Photocatalytic water splitting (PWS) provides an optimal approach for the sustainable production of green hydrogen. NH₂-modified covalent triazine frameworks (CTFs-NH₂) hold potential in PWS due to robust light uptake, optimal charge separation, and considerable redox potential. However, the high surface reaction barriers hinder the efficiency of PWS owing to the conversion difficulty of intermediate products. Modulating the Lewis basicity of NH₂ on CTFs offers a feasible route for addressing this challenge. In this work, electron-donating ethyl (C₂H₅) and electron-withdrawing 5-fluoroethyl groups (C₂F₅) are introduced at the para position of amine groups, producing C₂H₅-CTF-NH₂ and C₂F₅-CTF-NH₂, to adjust the Lewis basicity of CTF-NH₂. Through DFT calculations, the optical properties, excited states, electronic structures, dipole moments, and surface reaction processes of the CTF-NH₂, C₂H₅-CTF-NH₂ and C₂F₅-CTF-NH₂ are simulated. The results indicate that the electron-withdrawing C₂F₅ group can decrease the electron density and Lewis basicity on NH₂, thereby lowering the energy barriers for hydrogen and oxygen evolution reactions, effectively ameliorating the PWS efficiency of CTF-NH₂. This work unveils an innovative approach for donor-acceptor-regulated CTFs for the application of PWS.

Designing heterojunctions using two semiconductors with aligned band structures is a promising strategy for solar energy-driven photocatalytic hydrogen production. Particularly, S-scheme heterojunctions exhibit significant promise for accelerating spatial separation and migration of photoexcited charge carriers while maintaining strong redox capacity. Herein, a hierarchical S-scheme composite of red phosphorus (RP) nanoparticles decorated flower-like CeO₂ (CeO₂/RP) was synthesized via the chemical vapor deposition process. Under simulated solar light irradiation, the optimized CeO₂/RP S-scheme heterojunction exhibited a highly efficient photocatalytic hydrogen production rate of 297.8 μmol·h^-1·g^-1, which is approximately 8.8 and 5.7 times greater than that of pure CeO₂ and RP, respectively. After decoration with RP, the optical absorption of CeO₂/RP is greatly expanded to the visible light region. The effective photocatalytic performance can be primarily attributed to the presence of interfacial P-O-Ce bonds providing charge transfer pathways, as well as the development of a built-in electric field between CeO₂ and RP at the intimate interface. The photogenerated electrons follow an S-scheme mechanism, the electric field drives directional charge transfer from the conduction band (CB) of CeO₂ to the valence band (VB) of RP upon exposure to light, thus enabling the retention of photoexcited electrons and holes with higher redox potential at the CB of RP and the VB of CeO₂, respectively. This work provides a novel vision in the fabrication of S-scheme photocatalytic heterojunction systems with great photocatalytic hydrogen production performance.

Semiconductor photocatalysis makes full use of solar energy, serving as a potent tactic to solve the worldwide energy deficit and safeguard the environment. Bismuth-based photocatalysts stand out among various photocatalysts as a significant area, due to their unique crystal structure, favorable mixed electron band structure, diverse composition, and huge potential for solar catalytic conversion. This document reviews the rational design of Bi-based photocatalysts for solar energy. Recent advancements in diverse Bi-based photocatalysts such as Layered Bi, Bismuth element, BiVO₄, Bi₂S₂, and Bi₂O₃ are highlighted. Secondly, the synthesis strategies of Bi-based catalysts, including hydrothermal/solvothermal, chemical precipitation, and solid-state reaction, are summarized. Third, various structural regulation methods to improve the photocatalytic performance, including defect regulation, heteroatom doping, morphology, SPR effect utilization, and heterojunction construction, are systematically introduced. Additionally, a focus is given to the exclusive applications of Bi-based photocatalysts, including CO₂ reduction, water decomposition, N₂ fixation, NO_x removal, H₂O₂ production, and selective organic synthesis, followed by an introduction of advanced in situ characterization techniques of the Bi-based photocatalysts. Ultimately, the forthcoming obstacles are underscored, and a future outlook for Bi-based photocatalysts is anticipated. This review aims to offer detailed instructions for comprehensively understanding and logically crafting effective bismuth-based photocatalysts, while also encouraging novel ideas and advances in energy and environmental fields, contributing to the goals of green chemistry and sustainable development.

Photocatalytic technology harnesses clean, non-polluting solar energy to synthesize hydrogen peroxide (H₂O₂). In this study, ZnO/PBD S-scheme heterojunction composites, featuring ZnO nanoparticles on a donor-acceptor conjugated polymer substrate (PBD), were synthesized via the Suzuki-Miyaura reaction and hydrothermal method. The optimal ZnO/PBD composite achieved an H₂O₂ production efficiency of 4.07 mmol·g^-1·h^-1, which is 5.4 times higher than that of pristine ZnO. This significant enhancement is attributed to the formation of S-scheme heterojunctions. The successful construction of S-scheme heterojunctions was confirmed through UV-visible absorption spectroscopy and in situ irradiated X-ray photoelectron spectroscopy. Steady-state photoluminescence and femtosecond transient absorption (fs-TA) spectroscopies identified and verified the presence of defect states in ZnO. These defect states trap photogenerated electrons, adversely affecting the photocatalytic reaction. However, the S-scheme heterojunction effectively promotes the separation and transfer of electrons, mitigating this issue. The measured lifetimes of photogenerated electrons in these defect states, as determined by fitted fs-TA decay kinetics, provided further evidence of the carrier transfer mechanism in S-scheme heterojunctions. This work introduces a novel approach for studying organic/inorganic S-scheme heterojunctions using fs-TA spectroscopy.

Graphitic carbon nitride (g-C₃N₄) has gained growing attention in hydrogen peroxide (H₂O₂) photosynthesis, but the low activity of two-electron oxygen reduction reaction (2e^--ORR) still restricts its photocatalytic H₂O₂-generation performance. Herein, traditional g-C₃N₄ photocatalysts are recrystallized on KI crystal surfaces by a secondary calcination route to synthesize K incorporated highly-crystalline g-C₃N₄ photocatalysts. The synthesized CN-K photocatalyst exhibits improved inter-plane crystallization, narrowed bandgap structure, and smaller particle size from 20 to 50 nm. Moreover, the incorporated K atoms, as excellent catalytic sites, can enhance O₂ adsorption and stabilize the *OOH intermediates, thus improving the 2e^--ORR activity of the K incorporated high-crystallization g-C₃N₄ photocatalysts. Consequently, the optimized CN-K(1:6) photocatalyst exhibits a remarkably improved H₂O₂-generation rate of 7.8 mmol·L^-1·h^-1 with an AQE value of 5.17% at 420 nm, outperforming the traditional g-C₃N₄ sample by a factor of 220. This work uncovers the roles of heteroatoms in promoting the 2e^--ORR selectivity of the g-C₃N₄ photocatalyst, and offers novel insights to construct highly-active g-C₃N₄-based materials for H₂O₂ photosynthesis.

The generation of hydrogen peroxide (H₂O₂) from water and oxygen redox reaction by photocatalysis has acquired increasing attention owing to its green and clean properties. Aiming at the low intrinsic photocatalytic activity of carbon nitride (g-C₃N₄), here, an ultrathin g-C₃N₄ nanosheet photocatalyst with a large surface area and enhanced crystallinity was fabricated by a two-step thermal polymerization technique. The calcination parameters showed a significant impact on the structural properties and catalytic performance of g-C₃N₄. The remarkable H₂O₂ yield (3177.0 µmol·g^-1·h^-1) of CN-T-1 (by two-step calcination, 1 ℃·min^-1 optimal heating rate) was 3.7 times that (858.6 µmol·g^-1·h^-1) of CN-O-1 (by one-step calcination, 1 ℃·min^-1 heating rate) and higher than those of pure g-C₃N₄ in literature. Most of the H₂O₂ yield for CN-T-1 remained after five cycles, showing good stability. The enhanced catalytic performance of CN-T-1 than CN-O-1 is owing to its larger specific surface area, enhanced crystallinity, higher oxygen adsorption ability and photogenerated carrier separation efficiency, longer lifetime of carriers, and slightly larger bandgap (3.07 eV, +0.26 eV bigger than CN-O-1) with more positive valence band position owing to ultrathin layers. The •O₂^- radicals were verified to be the primary active species. A two-step single electron ORR pathway (O₂ + e^- → •O₂^- → H₂O₂) was confirmed for H₂O₂ production over CN-T-1.

To eliminate the additional assistance of previously reported strategies for the synthesis of g-C₃N₄ nanosheets such as templates, strong acids and alkalis, in this study, an innovative pattern for transportation of molten g-C₃N₄ intermediates, without any additional substance assistance, has been resoundingly established to produce amino-rich g-C₃N₄ nanosheets. The innovative pattern concretely contains the preliminary placement of melamine onto the top platform of an inverted crucible and their subsequent one-step calcination. During the calcination process, melamine and its subsequently formed g-C₃N₄ intermediate can transform into a molten state and gradually stream down along the outer surface of inverted crucible. This molten intermediate transportation pattern contributes to remarkably resist severe aggregation, resulting in the final polymerization into amino-rich g-C₃N₄ nanosheets in sequence. Moreover, the resultant amino-rich g-C₃N₄ nanosheets exhibit an evidently enhanced photocatalytic H₂O₂-production rate of ca. 85.8 μmol·L^–1·h^–1, over 2 times superior to bulk g-C₃N₄, mainly due to the fact that in addition to their nanosheet structures with enhanced specific surface areas, their amino-rich structures can efficiently reinforce the adsorption of O₂ and *OOH intermediates to accelerate their effective transformation into H₂O₂. This work delivers an innovative pattern to synthesize amino-rich g-C₃N₄ nanosheets with an insight into the photocatalytic mechanism.

Photocatalytic hydrogen production is one of the effective ways to address environmental pollution and energy crises. Herein, Ni_x-MoS₂/ZnIn₂S₄ heterojunctions were constructed to improve the separation efficiency of photogenerated electrons and holes and increase the number of active sites for hydrogen evolution. According to the catalyst characterization and theoretical calculations, the Ni at the interface between Ni_x-MoS₂ and ZnIn₂S₄ can act as a bridge for charge transfer, the Ni―S bond is the active site for H₂O dissociation, and the S site near the S vacancy on the Ni_x-MoS₂ surface enhances the hydrogen evolution reaction. Benefiting from the synergistic effect of the S vacancy and the Ni-doped MoS₂ cocatalyst, the optimal Ni_0.08-MoS₂/ZnIn₂S₄ exhibited the best hydrogen production rate of 7.13 mmol∙h⁻¹∙g⁻¹, which is 12.08 times than that of ZnIn₂S₄. This work provides a new strategy for enhancing photocatalytic efficiency through the synergistic effect of surface vacancies and doping and the optimization of heterojunctions.

Covalent organic framework (COF) materials are promising photocatalysts because of their fantastic structural and physicochemical features. To enhance photocatalytic performance, numerous metal single atoms (MSA) are loaded on COF to improve molecule adsorption. However, the inherent mechanisms and dominant factors of the heightened adsorption property are not deeply unveiled. Herein, four MSA-COF systems were constructed by severally introducing Fe, Co, Ni, and Cu single atoms in monolayer TpBpy-COF. The effect of various metal atoms modification on the electronic property and O₂ adsorption of COF was investigated using density functional theory calculations. The results show that the metal atoms are bonded to the pyridinic N atoms, forming stable MSA-COF configurations. The anchoring of metal atoms reduces the band gap and raises the Fermi level of COF. Moreover, as the atomic number of the metals increases, the d orbitals of the metal atoms gradually move to lower energy levels, manifesting a negative shift of the d-band centers. After metal atoms loading, the weak physical adsorption of O₂ on pristine COF is converted to robust chemisorption with the formation of M―O_ads bonds and intense electron transfer. Intriguingly, the adsorption energy presents a strong correlation with the d-band centers of the metal atoms. This finding is comprehended from the perspective of electron occupancy in antibonding orbitals in the adsorption systems. This work provides a feasible approach for modifying molecule adsorption on MSA-COF by regulating the d-band centers of metal atoms.

This work illustrates the novelty of double S-scheme ZnS/ZnO/CdS ternary heterojunction photocatalyst with efficient photocatalytic activity. The sample with optimal CdS content, ZnS/ZnO/CdS-14% (ZZC14%), displayed the maximum H₂ evolution rate of 4.1 mmol·g^‒1·h^‒1. The maximum photocatalytic performance was approximately 2 and 13 times higher than their corresponding counterparts, ZnS/CdS and ZnO/ZnS, respectively. A high AQE of 19.8% under 420 nm was obtained. Additionally, the slight changes in H₂ evolution activities and retentions of crystal structures after six successive cycles indicate the stability of the photocatalyst. In accordance with the theoretical calculations and experimental results, the remarkable enhancement in photocatalytic activity is attributed to fast electron transfer and separation as well as the intimate contact due to mutual interaction between S-scheme. This work highlights an innovative approach to constructing a dual S-scheme photocatalytic system with high separation and fast migration capabilities of photogenerated charge carriers for splitting water to produce hydrogen.

S-scheme heterojunction system represents a highly efficient strategy for photocatalytic applications as it can simultaneously facilitate photogenerated charge carrier separation and enhance the reduction-oxidation potentials of the photocatalyst. Despite its gigantic potential, the photocatalytic CO₂ conversion efficiency of the S-scheme heterojunction remains limited mainly attributed to the sluggish interfacial charge carrier migration and poor light utilization efficiency. Herein, we prepare an InOOH/ZnIn₂S₄ hollow sphere S-scheme heterojunction with 0D/2D contact interface for enhancing photocatalytic CO₂ conversion performance. Specifically, the hollow sphere morphology can cause the multireflection of incident light within the photocatalyst leading to enhanced light absorption of the photocatalyst. In addition, the 0D/2D contact interface can facilitate the photogenerated charge carrier migration transfer over the InOOH/ZnIn₂S₄ S-scheme heterojunction. Furthermore, combining in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) characterization and radicals trapping test, it is affirmed the accumulation of photogenerated holes and electrons respectively on InOOH and ZnIn₂S₄, which is beneficial for the effective utilization of photogenerated charge carriers. As a result, the photocatalytic CO₂ conversion performance of the optimized InOOH/ZnIn₂S₄ is ca. 25.8 times higher than that of pristine ZnIn₂S₄. Our reported results demonstrate a facile yet effective strategy for enhancing the interfacial photogenerated charge carrier migration and light utilization efficiency of S-scheme heterojunction.

Electrochemical oxygen reduction reaction via the two-electron pathway (2e-ORR) is becoming a promising and sustainable approach to producing hydrogen peroxide (H₂O₂) without significant carbon footprints. To achieve better performance, most of the recent progress and investigations have focused on developing novel carbon-based electrocatalysts. Nevertheless, the sophisticated preparations, decreased selectivity and undefined active sites of carbon-based catalysts have been generally acknowledged and criticized. To this end, transition metal oxides and chalcogenides have increasingly emerged for 2e-ORR, due to their catalytic stability and tunable microstructure. Here, the development of metal oxides and chalcogenides for O₂-to-H₂O₂ conversion is prospectively reviewed. By summarizing previous theoretical and experimental efforts, their diversity and outstanding catalytic activity are firstly provided. Meanwhile, the topological and chemical factors influencing 2e-ORR selectivity of the metal oxides/chalcogenides are systematically elucidated, including morphology, phase structures, doping and defects engineering. Thus, emphasizing the influence on the binding of ORR intermediates, the active sites and the underlying mechanism is highlighted. Finally, future opportunities and challenges in designing metal oxides/chalcogenides-based catalysts for H₂O₂ electro-synthesis are outlined. The present review provides insights and fundamentals of metal oxides/chalcogenides as 2e-ORR catalysts, promoting their practical application in the energy-related industry.

Photocatalytic hydrogen generation through water splitting driven by solar energy is regarded as a highly promising strategy to tackle the challenges of the energy crisis and environmental contamination. Tuning the electronic properties and band structures of photocatalysts is critical to improving the efficiency of charge separation and the activity of hydrogen production. Herein, donor-acceptor modified polymeric carbon nitride (CN)-based copolymers are synthesized via the introduction of 4-amino-1H-imidazole-5-carbonitrile (AICN) into the molecular skeleton of CN. The incorporation of electron donor AICN units can broaden the π-conjugated system and promote the spatial charge separation in the catalysts, thus resulting in enhanced light utilization and improved intramolecular charge carrier transfer rate. As a consequence, the AICN modified CN samples exhibit an increased photocatalytic hydrogen evolution rate, and the optimal photocatalytic activity can reach 3204 μmol·h⁻¹·g⁻¹. This molecular engineering strategy provides an effective avenue to develop high-performance CN-based photocatalysts for hydrogen evolution.

Utilizing sunlight as a renewable energy source, photocatalysis offers a potential solution to global warming and energy shortages by converting CO₂ into useful solar fuels, including CO, CH₄, CH₃OH, and C₂H₅OH. Among the various formulations investigated, copper-based photocatalysts stand out as particularly appealing for CO₂ conversion due to their cost-effectiveness and higher abundance in comparison to catalysts based on precious metals. This literature review provides a thorough summary of the latest developments in copper-based photocatalysts used for CO₂ reduction reactions, including metallic copper, copper oxide, and cuprous oxide photocatalysts. The review also provides a categorical summary of the CO₂ reduction products and a detailed categorical discussion of the means of modulation and modification of each copper-based catalyst. Finally, this review highlights the existing challenges and proposes future research directions in the development of copper-based photocatalysts for CO₂ reduction, focusing on boosting energy utilization and improving product formation rates.

Solar photocatalysis is a green, economical, and sustainable method for H₂O₂ synthesis, which has been regarded as the most promising alternative to the traditional anthraquinone oxidation method. However, single-component photocatalyst exhibits moderate activity owing to the limited light-harvesting range, fast charge recombination and inadequate redox capacity. Moreover, the addition of sacrificial agents is required in the reaction system. Herein, we present the development of an S-scheme heterojunction, achieved through photodepositing Bi₂O₃ nanoparticles (BO) on ionic covalent organic framework nanofiber (iCOF). The optimized photocatalyst iCOF/BO10 shows the highest H₂O₂ production performance in pure water, achieving an H₂O₂ yield of 9.76 mmol·g⁻¹·h⁻¹ with an apparent quantum yield (AQY) of 5.5% at 420 nm. This photocatalytic performance is approximately 2.2 and 5.6 times as high as that of pristine iCOF and BO, respectively. In-depth characterizations including in situ irradiated XPS, DFT-calculations, active species trapping experiments and in situ DRIFTS, reveal that the obtained sample not only facilitates charge carrier separation and enhances light absorption capability, but also maximizes the redox ability to concurrently achieve indirect 2e⁻ ORR and 4e⁻ WOR for H₂O₂ production. Additionally, the generated O₂ from the 4e⁻ WOR is capable of accelerating the reaction kinetics for H₂O₂ formation via the indirect 2e⁻ ORR pathway, enabling overall photocatalytic H₂O₂ synthesis. This work provides a new insight into creating innovative catalysts for achieving high-efficiency photosynthesis of H₂O₂.

S-scheme heterojunctions can preserve strong redox capacity on the basis of achieving spatial separation of photogenerated carriers. Therefore, a deep comprehension of the photoinduced charge transfer dynamics in S-scheme heterostructures is vital to enhancing photocatalytic properties. Herein, SnO₂/BiOBr S-scheme heterojunctions with tight contact are fabricated with in situ hydrothermal method. The optimal SnO₂/BiOBr exhibits excellent photocatalytic performance for CO₂ reduction, with yields of CO and CH₄ of 345.7 and 6.7 μmol∙g^–1∙h^–1, which are 5.6 and 3.7 times higher than those of the original BiOBr. The photoinduced charge transfer mechanism and dynamics of SnO₂/BiOBr S-scheme heterostructure are characterized by in situ X-ray photoelectron spectrum (XPS) and femtosecond transient absorption spectroscopy (fs-TA). A new fitted lifetime of photogenerated carriers are observed, which could be attributed to interfacial electron transfer of S-scheme heterojunction, further illustrating an ultrafast transfer channel for photoelectrons from SnO₂ conduction band to BiOBr valence band. As a result, the powerful reduced electrons in BiOBr conduction band and the powerful oxidation holes in SnO₂ valence band are retained. This work provides profound comprehension of photoinduced charge transfer mechanism of S-scheme heterojunction.

Reforming CO₂ into storable solar fuels via semiconductor photocatalysis is considered an effective strategy to solve the greenhouse effect and resource shortage. Unfortunately, the problem of rapid photogenerated carriers severely limits the CO₂ reduction capability of one-component catalysts. The fabrication of S-scheme heterojunctions with defects can result in efficient spatial separation of photo-generated charge carriers and increase adsorption and activation of nonpolar molecules. Herein, ZnWO₄/g-C₃N₄ S-scheme heterojunctions with defects are constructed through in situ growth method. The experiments show that the generation rate of CO from CO₂ reduction is up to 232.4 μmol∙g⁻¹∙h⁻¹ with a selectivity close to 100%, which is 11.6 and 8.5 times higher than those of pristine ZnWO₄ and g-C₃N₄, respectively. In situ XPS and work function analyses demonstrate the S-scheme charge transport pathway, which facilitates the spatial segregation of photogenerated carriers and promotes CO₂ reduction. In situ ESR illustrates that CO₂ molecules are adsorbed by nitrogen vacancies, which act as photoelectron acceptors during the photocatalytic reaction and are favorable for charge trapping and separation. The S-scheme charge transport mode and nitrogen vacancy work together to stimulate the efficient conversion of CO₂ to CO. This work presents significant insights to the cooperative influence of the S-scheme charge transport mode and defects in regulating CO₂ reduction activity.