Photocatalytic nitrate reduction to ammonia has attracted increasing attention as a sustainable strategy for simultaneous ammonia synthesis and nitrate pollutant remediation under mild conditions. Compared with conventional nitrogen fixation routes, nitrate reduction possesses higher reactant solubility and lower activation barriers, making it more favorable for solar-driven nitrogen upcycling. Nevertheless, the reaction involves complicated multistep proton-coupled electron transfer processes and suffers from sluggish kinetics, charge recombination, and competing side reactions, which severely limit ammonia selectivity and efficiency. This review systematically summarizes recent advances in photocatalytic nitrate-to-ammonia conversion from both mechanistic and catalyst-design perspectives. Fundamental thermodynamics, reaction pathways, intermediate evolution, and rate-determining steps are first discussed, followed by recent progress in electronic structure regulation, defect and active-site engineering, heterostructure construction, interfacial polarization modulation, reaction pathway control, and microenvironment engineering. Particular attention is given to the intrinsic correlation among charge dynamics, intermediate stabilization, and reaction selectivity. Emerging insights from operando characterization and theoretical calculations are also highlighted to bridge experimental observations with mechanistic understanding. Finally, current challenges involving ammonia quantification, selectivity regulation, mechanistic ambiguity, and practical scalability are critically discussed, together with future opportunities in mechanism-oriented catalyst design and data-driven catalyst discovery.

Photocatalysis is one of the most promising technologies for solving environmental and energy problems, but current photocatalysts still suffer from low visible light utilization and insufficient photogenerated charge separation efficiency. Therefore, in this work, D-A tubular materials with tubular carbon nitride (TCN) as electron donor (D) and 2-mercaptobenzothiazole (BZ) as electron acceptor (A) were constructed by molecular doping and modulation of the carbon nitride geometry. It was shown that the introduction of BZ could modulate the electronic structure of the catalyst, promote electron migration from TCN to BZ, and inhibit the recombination of photogenerated electrons and holes. Meanwhile, the ultra-thin tubular structure could expose more active sites. In addition, the adsorption of protons by BZ-TCN was further improved due to the modulation of the charge distribution between the components by the introduction of small molecules. Among them, the photocatalytic hydrogen production rate of BZ0.1-TCN was twice that of TCN. The in-depth discussion of the components through theoretical calculations and characterization tests contributes to the understanding of the mechanism of photocatalytic hydrogen production.

The photocatalytic performance is fundamentally reliant on the efficient separation and utilization of charge carriers generated by light. Here, a carbon nitride-based homojunction photocatalyst, integrating pristine 2D carbon nitride (PCN) with cyano-rich boron-doped carbon nitride (CBCN) via electrostatic self-assembly. The incorporation of boron and cyano groups induces a positive band structure shift in CBCN and reducing of work function, which helps the forming a Type II homojunction after combing with PCN. Due to advanced 2D/2D interfacial architecture the optimized PCN/CBCN-25 sample achieved a H-2 evolution rate of 2173 mu mol g(-1) h(-1) in photocatalytic H-2 production coupled with selective benzyl alcohol oxidation, 2.6 times higher than PCN, while maintaining 95.9 % benzaldehyde selectivity. This work underscores the importance of band structure engineering and interfacial design in advancing carbon nitride-based homojunction catalysts.

Biochar is a porous carbonaceous material synthesized through the pyrolysis of diverse biomass resources, including agricultural and forestry residues as well as livestock manure. It possesses superior characteristics such as a large specific surface area, adjustable pore architecture, abundant surface functional groups, and favorable electrical conductivity. With the increasingly severe global energy shortage and environmental pollution problems in recent years, biochar has emerged as a green, low-cost functional material with distinct application superiority in multiple key research directions, including energy storage and conversion, chemical catalysis, environmental restoration, and signal sensing and detection. This study comprehensively summarizes the latest research advances of biochar in the aforementioned application fields, focusing on innovative achievements in photocatalytic and electrocatalytic hydrogen generation, supercapacitors and electrochemical energy storage systems, persulfate activation technology, carbon dioxide capture, remediation of heavy metal and organic contaminants, volatile organic compound (VOC) adsorption, as well as electrochemical sensing devices. Existing research results demonstrate that modification strategies including metal and non-metal doping, surface oxidation treatment, and compounding with semiconductors or metal oxide materials can effectively improve the catalytic activity and functional performance of biochar. Furthermore, this paper prospects the future interdisciplinary development trends of biochar, analyzes the existing research gaps in mechanism exploration, structural optimization design, and industrial large-scale preparation, and provides theoretical and practical references for the further popularization and application of biochar in sustainable energy development and environmental governance fields.

Efficient charge separation and durable cocatalyst interfaces are critical for advancing visible-light photocatalytic hydrogen production. Here, we develop an in situ selenization strategy that anchors defect-rich Co0.85Se quantum dots onto CdS nanorods while simultaneously forming a Se-doped CdS surface layer, yielding a tightly coupled QDs-shell-core heterostructure. This construction establishes a spatial dual built-in electric field arising from Se-doping-induced band modulation and the Co0.85Se/CdS interfacial junction, which strongly promotes directional electron transfer. Experimental characterizations and DFT calculations jointly reveal that the defect-rich Co0.85Se QDs act as efficient electron sinks, accelerating H2 evolution. Consequently, the optimized photocatalyst delivers a hydrogen evolution rate of 61.66 mmol g-1 h-1 with only 0.7 wt% Co0.85Se loading, which is far exceeding pristine CdS and outperforming Pt/CdS and presents markedly enhanced photostability. This study offers a practical pathway for designing low-loading, non-noble-metal cocatalyst systems for high-performance solar hydrogen production.

Solar-driven photocatalytic H2 evolution is often limited by the mismatch between bulk charge transport and interfacial proton reduction kinetics. Although defect engineering and cocatalyst loading are widely employed to enhance photocatalytic activity, the respective roles of bulk crystallinity and interfacial coupling remain insufficiently distinguished. In this work, two structurally well-defined CdS model systems were constructed, including highly crystalline {100}-faceted nanorods (CdSR) and defect-rich {001}-faceted nanosheets (CdSS), and subsequently coupled with MoSe2 as a cocatalyst. MoSe2/CdSR exhibits a high H2 evolution rate of 35.2 mmol center dot g-1 center dot h-1, corresponding to a 5.8-fold enhancement relative to pristine CdSR, which is mainly attributed to efficient long-range charge transport in the highly crystalline bulk. In contrast, MoSe2/CdSS shows a much larger relative activity enhancement (22.1-fold), arising from strengthened interfacial electronic coupling and abundant anchoring sites for MoSe2. Despite the pronounced relative improvement, the absolute H2 evolution rate of MoSe2/CdSS remains significantly lower than that of MoSe2/CdSR, highlighting that bulk crystallinity fundamentally governs the efficiency ceiling of photocatalytic performance. This study clarifies the distinct yet complementary roles of bulk charge transport and interfacial charge extraction, and provides a rational design principle for high-efficiency composite photocatalysts.

Photocatalysis has emerged as a promising solar-driven strategy for sustainable energy conversion and chemical production. In particular, coupling photocatalytic H2 evolution with the selective oxidation of biomass-derived substrates offers a dual pathway for green H2 evolution and high-value chemical upgrading. Among various photocatalysts, ternary sulfide ZnIn2S4 has attracted increasing attention owing to its tunable band structure, visible-light responsiveness, and structural versatility. This review critically summarizes recent advances in ZnIn2S4-based photocatalysts for the synergistic valorization of biomass-derived compounds and H2 evolution. Emphasis is placed on understanding how structural engineering strategies, including elemental doping, defect modulation, heterojunction construction, and surface active-site regulation, govern interfacial charge dynamics, band alignment, and reaction selectivity. These modifications not only promote efficient separation and migration of photogenerated carriers but also enable selective activation of C-H and C-O bonds in biomass molecules, thereby facilitating targeted oxidation pathways. Furthermore, current challenges related to product selectivity, reaction mechanism elucidation, and long-term system stability are systematically discussed. By correlating catalyst structure with redox coupling behavior, this review provides mechanistic insights and design principles for ZnIn2S4-based photocatalysts, aiming to guide future development of efficient and robust solar-driven biomass conversion systems coupled with H2 evolution.

The insufficient photogenerated charge separation efficiency and low light absorption capacity of carbon nitride (CN) limit the production efficiency of hydrogen. Grafting organic small molecules onto CN to construct a donor-acceptor (D-A) system is an effective strategy for enhancing the photocatalytic performance. This work constructed a fully organic D-A material by grafting 2-benzothiazolamine (BZM) onto tubular CN (TCN) to alter the band structure of TCN. The all-organic D-A system disrupts the structural symmetry of CN and forms new charge transfer pathways, thereby accelerating intermolecular electron separation and transfer. The results of the photocatalytic hydrogen production experiment show that the photocatalytic hydrogen production rate of TCN-BZM0.3 reaches 4.11 mmol g-1 h-1 and exhibits good photocatalytic stability. This work investigates the facilitating effect of D-A structures on charge transfer and elucidates the corresponding photocatalytic mechanism, thereby providing valuable insights into the rational design of highly efficient organic photocatalysts.

The photocatalytic production of hydrogen peroxide (H2O2) utilizing graphitic carbon nitride (g-C3N4) offers a sustainable alternative to the conventional, energy-intensive anthraquinone method. Nevertheless, the practical deployment of pristine g-C3N4 is constrained by its limited absorption of visible light, rapid recombination of photogenerated charge carriers, and low surface catalytic activity. This review critically examines various modification strategies aimed at enhancing the H2O2 generation efficiency of g-C3N4-based photocatalysts. Prominent approaches encompass elemental doping, defect modification, and the junction engineering. These modifications synergistically enhance light absorption, facilitate charge separation, and accelerate oxygen reduction reaction kinetics. Consequently, such engineered photocatalysts have achieved H2O2 production rates reaching millimolar concentrations per hour under visible-light irradiation, alongside marked improvements in selectivity and apparent quantum efficiency. Despite these significant advancements, challenges persist in realizing broad-spectrum solar energy utilization, ensuring long-term operational stability, and developing scalable synthesis methods for catalyst fabrication. This review delineates prospective research directions aimed at advancing efficient and practical photocatalytic systems for sustainable hydrogen peroxide synthesis.

The effective S-scheme homojunction relies on the precise regulation of band structure and construction of advantaged charge migration interfaces. Here, the electronic structural properties of g-C 3 N 4 were modulated through meticulous polymerization of self-assembled supramolecular precursors. Experimental and DFT results indicate that both the intrinsic bandgap and surface electronic characteristics were adjusted, leading to the formation of an in-situ reconstructed homojunction interface facilitated by intrinsic van der Waals forces. The homojunction catalyst, composed of g-C 3 N 4 nanodots and ultra-thin g-C 3 N 4 nanoflakes, exhibited a significant S-scheme carrier separation mechanism, which enhances the utilization of electrons and holes. Consequently, under AM 1.5 light irradiation (~100 mW/cm 2 ), the g-C 3 N 4 homojunction photocatalyst achieved a remarkable hydrogen evolution rate of 580 μmol h −1 . Furthermore, a reversed CH 4 selectivity in CO 2 reduction was observed, yielding 80.30 μmol g −1  h −1 with a selectivity of 96.86 %, in contrast to the performance of bulk g-C 3 N 4 , which produced only 2.22 μmol g −1  h −1 with the 15.69 % CH 4 selectivity. These findings not only highlight the significant potential of the g-C 3 N 4 homojunction photocatalyst for hydrogen production and CO 2 reduction but also propose a superior and effective strategy for optimizing the structural properties of g-C 3 N 4 , which are crucial for the design of photocatalytic reactions.

The “Solar Sabatier” reaction has emerged as a promising sustainable method for the CO 2 hydrogenation. The development of advanced metal‐support catalysts based on Strong Metal‐Support Interaction (SMSI) offers significant advantages in the activation of CO 2 and the regulation of selectivity. Herein, a novel composite Ni/CaTiO 3 catalyst consisting of Ni and Ni‐doped CaTiO 3 is synthesized and utilized in the CO 2 methanation. A noteworthy finding is that the incorporation of Ni into the CaTiO 3 matrix is instrumental in the formation of oxygen vacancies and the establishment of SMSI between Ni and CaTiO 3 . The enhanced SMSI resulting from the surface‐doped Ni atoms not only facilitated effective interface contact between metallic Ni and the CaTiO 3 surface but also significantly improved the migration efficiency of hydrogen atoms reduced the reaction barrier for CO 2 methanation and optimized the rate‐limiting step, all of which are advantageous for the CO 2 methanation. Consequently, the optimized catalysts exhibited extraordinary performance, achieving a CO 2 conversion rate of 87.77%, CH 4 generation rate of 3.12 mol g Ni −1 h −1 , and ≈100% CH 4 selectivity under ambient pressure conditions. This investigation lays the groundwork for the design of highly active “Solar Sabatier” catalysts and offers a novel understanding of the mechanisms underlying effective SMSI.

The photocatalytic hydrogen (H2) evolution reaction driven by solar energy is one of the most promising methods to alleviate energy and environmental problems. Regrettably, the rapid recombination of photogenerated electrons and hole pairs in semiconductor catalysts leads to low solar energy conversion efficiency. To address this problem, we chose the method of co-catalyst loading. This study uses an in-situ self-assembly growth strategy to load high-valent cobalt sulfide (CoS) onto bulk carbon nitride (BCN) for photocatalytic H2 evolution. The results show that the photocatalytic H2 evolution performance of the optimal ratio of CoS and BCN composite (CoS-BCN(15%)) is 156 times that of BCN. The main reason for the performance improvement is that CoS nanoparticles act as co-catalysts to increase the carrier migration rate. Moreover, CoS nanoparticles contain mixed-valence Co3+/Co2+. During the reaction, high-valence cobalt ions become electron transfer stations, reacting with additional electrons to generate low-valence ions, reducing the recombination of carriers. Additionally, combined experiments and theoretical calculations show that the CoS surface is more conducive to the precipitation of H2 than BCN. This study provides a reference for further exploring the mechanism of action of co-catalysts.

The recycling of plastic waste presents a viable solution to the pressing issue of resource scarcity, while simultaneously enhancing ecosystem health and mitigating potential risks to human well-being. Photocatalytic reforming of plastics is a promising green method for the conversion of plastics into valuable organic matter and H-2. In this study, we reported a CoP-anchored Schottky junction catalyst on Zn0.5Cd0.5S, which facilitates the organic reforming of microplastics in conjunction with hydrogen production under light irradiation. The composites demonstrated exceptional photocatalytic efficiency, allowing for the effective separation and transfer of photogenerated charge carriers between CoP and Zn0.5Cd0.5S. Among them, the Zn0.5Cd0.5S/CoP-3 sample exhibits the highest hydrogen precipitation rate (similar to 9.26 mmol h(-1) g(-1) ), which is 5.7 times higher than that of pristine Zn0.5Cd0.5S. The oxidation products of PET were also analyzed by H-1 NMR, which showed that PET was effectively degraded to molecular compounds such as formate and acetate. This research presents a cost-effective, sustainable, and environmentally friendly photocatalytic system for the reforming of plastics and the generation of green hydrogen.

This review delves into the burgeoning field of graphitic carbon nitride (g-C3N4) photocatalysis, offering a comprehensive synthesis of recent advancements. It first examines the structural and electronic properties of g-C3N4, and further explores how these intrinsic characteristics regulate its performance in light-driven reactions. Despite its potential, g-C3N4 faces hurdles such as restricted visible-light absorption and suboptimal charge carrier dynamics. To this end, the review outlines innovative strategies to enhance its light-harvesting and charge-transport capabilities, including defect engineering, bandgap modulation, and the design of nanostructured architectures. Moreover, it highlights the critical importance of developing scalable synthesis protocols that strike a balance between efficiency and cost-effectiveness. Finally, future research perspectives are presented, with a specific emphasis on unlocking the full application potential of g-C3N4 in sustainable energy production and environmental remediation.

Given the depletion of fossil fuels, photocatalytic hydrogen production shows great promise for renewable energy. The manganese cadmium sulfide (MCS) photocatalyst has great potential in the photocatalytic preparation of solar fuels. However, the photocatalytic performance of MCS is limited by sluggish reaction kinetics and rapid recombination of photoinduced charge carriers. Therefore, in this study, a nanorod-shaped CeO2@MCS S-Scheme heterojunction photocatalyst was synthesized via a two-stage hydrothermal process and utilized for photocatalytic hydrogen production. It has been confirmed that the carrier migration in the CeO2@MCS photocatalyst follows the classic S-Scheme heterojunction mechanism, which efficiently preserves highly reactive photoexcited electrons, enhancing charge carrier migration efficiency. Moreover, the variable valence property of Ce can regulate the local band bending and optimize the built-in electric field at the heterojunction interface, thereby inhibiting the recombination of charge carrier-hole pairs in the S-Scheme heterojunction. Compared with pure CeO2 and MCS, the construction of the CeO2@MCS S-Scheme heterojunction exhibits higher charge separation efficiency and more active sites available for redox reactions. This study emphasizes the importance of the S-Scheme heterojunction as an effective strategy to improve photocatalytic activity, the carrier recombination probability can be effectively reduced by valence change.

Photocatalytic seawater hydrogen evolution performance of graphitic carbon nitride (g-C3N4) is limited by rapid charge recombination and insufficient active sites. A Pt/Co0.85Se/g-C3N4 heterostructure with dual-channel electron transfer mitigates this. The work function difference induces an interfacial built-in field, enhancing electron migration. Co0.85Se acts as a cocatalyst/electron sink and an activity promoter for Pt, boosting proton reduction efficiency. This yields an exceptional H2 evolution rate of 10772 mu mol g-1 h-1 in seawater, surpassing Co0.85Se/g-C3N4 and Pt/g-C3N4 controls by 8.0 and 2.2 times respectively. Experimental and computational results confirm suppressed recombination and facilitated interfacial charge transfer, establishing a design basis for efficient photocatalytic seawater hydrogen production.

The inadequate charge separation and suboptimal water oxidation performance significantly hinder photocatalytic hydrogen production, particularly in the context of overall water splitting efficiency. In this study, the electronic structure of g-C3N4 is modified through the incorporation of localized graphitization sites. Both theoretical and experimental findings indicate that the enhanced conjugation properties of these new sites facilitate the establishment of a built-in electric field within the material, thereby promoting rapid charge carrier separation. Furthermore, the synthesized ribbon-like g-C3N4 catalyst demonstrates improved water oxidation performance, attributed to an increased light absorption capacity and a positive shift in the valence band resulting from structural modifications. Due to the enhanced carrier utilization efficiency and improved oxygen generation capability, the optimized ribbon-like g-C3N4 sample achieves an overall water splitting performance characterized by a hydrogen evolution rate of 33.3 mu mol g-1 h-1 and an oxygen evolution rate of 16.4 mu mol g-1 h-1. This research highlights the critical role of built-in electric fields and water oxidation capacity in photocatalytic water splitting reactions, serving as a significant reference for the development of high-performance g-C3N4 catalysts.

The rational construction of heterojunction interfaces plays a critical role in enhancing the carrier separation efficiency for photocatalytic hydrogen evolution. In this study, a ZnIn2S4/H2WO4 S-scheme heterojunction was successfully synthesized via a self-assembly strategy. Compared with conventional WO3, the H2WO4 component exhibits a lower work function, which significantly promotes surface electron overflow and establishes an optimized S-scheme charge transfer pathway. Structural characterization reveals that the intimate integration of H2WO4 nanosheets within ZnIn2S4 nanoflowers provides enhanced interfacial contact, thereby facilitating efficient charge separation and migration. As a result, the optimized ZnIn2S4/H2WO4 composite demonstrates a hydrogen evolution rate of 138 mmol/g/h, achieving a 4.7-fold enhancement over pristine ZnIn2S4 and a 1.9-fold improvement compared to the ZnIn2S4/WO3. This work highlights the dual requirements for oxidation photocatalysts in S-scheme systems: precise band gap alignment and favorable surface electronic properties, both essential for enabling efficient electron overflow and ensuring effective S-scheme charge migration channels.

Graphitic carbon nitride (g-C3N4) is an organic semiconductor material that contains only the elements carbon (C) and nitrogen (N). It has attracted great interest in many fields, including photocatalysis, solar cells, electrochemistry, and gas sensing, due to its suitable band position, easy structural adjustment, inexpensive and abundant raw materials, simple preparation, and high thermal, mechanical, and chemical stability. In the above-mentioned fields, photocatalytic hydrogen production is the best green and sustainable method, which can directly convert low energy density solar energy into high calorific value hydrogen energy, and is regarded as an emerging technology with huge development potential. However, traditional thermal shrinkage techniques used for producing bulk g-C3N4 have disadvantages such as easy exciton recombination, low conductivity, limited specific surface area, and narrow light absorption range. These limitations ultimately led to suboptimal photo-catalytic hydrogen production results, making g-C3N4 unsuitable for large-scale commercial hydrogen production. In view of this, researchers have studied a series of strategies to improve the photocatalytic hydrogen production capability of g-C3N4. This article provides a systematic and critical overview of the recent research progress of graphitic carbon nitride (g-C3N4) in photocatalytic hydrogen evolution, with emphasis on synthesis methods, structural characterization techniques, and modification strategies. The review distills the breakthrough achievements of the past five years and further establishes a theoretical framework for designing efficient and stable g-C3N4-based photocatalysts, thereby offering guidance for overcoming current limitations and promoting future large-scale, commercial hydrogen production technologies.

The efficient and sustaining activation of Fe sites is of great importance for the heterogeneous photo-Fenton system. Here, through a simple doping strategy, the active Fe centers have been introduced into oxygen vacancy-rich WO3 nanoplates. The Fe sites were activated by the electron transferring from W atom to Fe sites because of oxygen vacancies association between W and Fe in the photo-excitation process. The directional transport of electrons not only promoted the regeneration of Fe2+ to continuously activate the photo-Fenton system, but also promoted the transfer of the photogenerated charge carriers. In addition, the results of the DFT calculations prove that the doping of Fe in turn helps the stability of the oxygen vacancy. As a result, the optimized Fe-WO3-0.75 sample exhibited a kinetic rate of 0.0424 min-1 in the degradation of tetracycline hydrochloride. This rate is more than three times higher than that of WO3 (0.0137 min-1). The Fe-WO3 catalyst exhibited a good stability and a wide range of adaptability of pH values by taking advantage of the synergy of Fe sites and oxygen vacancy, which indicates the practical potentials for environmental applications.