Photocatalytic nitric oxide (NO) conversion technology has the characteristics of high efficiency, economy, and environment friendly to remove NO using g-C₃N₄. Introducing new adsorption sites on the surface of g-C₃N₄ through microstructure control can alter the structure-activity relationship between g-C₃N₄ and gas molecules, thereby improving photocatalytic NO conversion activity and inhibiting NO₂ generation. However, few review articles have focused on the microscopic effects of microstructural changes in g-C₃N₄ based materials on the adsorption and activation of NO and O₂. This has important guiding significance for material design work in the field of NO conversion and strategies to fundamentally improve NO conversion activity and selectivity. Therefore, our work systematically summarizes the strategy of introducing adsorption and activation sites through microstructure control, and emphasizes the role of these sites in the photocatalytic NO conversion process. The aim is to clarify the influence of adsorption and activation sites on adsorption behavior and the correlation between these sites and reaction paths. Finally, the development trend and future prospects of increasing the level of g-C₃N₄ adsorption and activation in the field of photocatalytic NO conversion are introduced, which is expected to provide an important reference for the development and practical application of g-C₃N₄-based photocatalytic materials.

Recently, the regulation of electronic spin polarization has attracted considerable interest as an effective strategy to mitigate the rapid recombination of photo-generated charges. However, current research predominantly targets individual photocatalysts, where the efficiency of charge separation still has significant room for improvement. Herein, a ZnFe_1.2Co_0.8O₄ (ZFCO) and BiVO₄ (BVO) S-scheme heterojunction was developed, which synergistically promoted charge separation through the S-scheme heterojunction and spin polarization, and further enhanced the photocatalytic performance in removing organic pollutants under an external magnetic field. Experimental results revealed that under sole light irradiation, ZB-1.5 (ZFCO : BVO = 3 : 2) demonstrated optimal performance, with a reaction rate constant (k) for tetracycline (TC) degradation of 0.0146 min⁻¹. Under light irradiation and magnetic field conditions, the reaction rate constant (k) of ZB-1.5 for TC degradation increased to 0.0175 min⁻¹, indicating enhanced photocatalytic performance. DFT calculations indicated that ZFCO exhibited the spin polarization. Photoluminescence measurements demonstrated that the S-scheme heterojunction structure improved the charge separation efficiency. In addition, possible degradation pathways and toxicity were assessed, indicating successful detoxification. This work provides some useful insights into utilizing S-scheme heterojunctions to develop photocatalysts with efficient separation of photo-generated charges.

The sluggish electron migration rate and pronounced electron-hole recombination, pose significant obstacles to achieving high photocatalytic efficiency. The utilization of multiple catalysts for the construction of heterojunctions can effectively enhance charge separation. A series of Keggin-type hollow dodecahedral polyoxometalates were prepared via hydrothermal synthesis, and their molecular orbitals were modified through the addition of metal elements. The incorporation of metal elements modulated the electronic structure of polyoxometalates, effectively enhancing the electron aggregation capability of polyoxometalates. Single-component catalysts often face serious hole-electron recombination. In order to solve this problem, the scheme of constructing heterojunction is proposed to improve the electron transport efficiency. By immobilizing ZnCdS nanoparticles onto the polyoxometalate surface, the heterojunction architecture was engineered to significantly enhance the interfacial charge transfer capability. Density Functional Theory (DFT) calculations and the experimental results indicate that the modulation of metallic components renders the polyoxometalate a more favorable energy-level orbital. The catalytic mechanism of ZnCdS and KMoP S-scheme heterojunction was also verified. The formation of S-scheme heterojunctions further improves the electron transfer efficiency compared to other traditional heterojunctions, achieving efficient utilization of photo generated electrons and holes. Additionally, the S-scheme heterojunction shifts the catalystʼs d-band center closer to the Fermi level, thereby improving electrical conductivity. This article provides a new approach for energy level regulation of polyoxometalates and the design of S-scheme heterojunctions.

Photocatalytic hydrogen peroxide (H₂O₂) production is a crucial process for clean energy conversion, involving the reduction of O₂ through two electrons. However, this process is often hampered by the sluggish water oxidation involving the photogenerated holes. To address this challenge, we have constructed a dual-functional S-scheme ZnO/CdIn₂S₄ heterojunction systerm coupling the H₂O₂ generation with a value-added benzylamine (BA) oxidation reaction. In this dual-functional photocatalytic system, photogenerated electrons in CdIn₂S₄ efficiently reduce O₂ to produce H₂O₂, while photogenerated holes in ZnO selectively oxidize BA to N-benzylidenebenzylamine. Leveraging the advantages of the S-scheme heterojunction, the optimized ZnO/CdIn₂S₄ photocatalyst displays an enhanced H₂O₂ production rate (386 μmol·L⁻¹·h⁻¹) and BA oxidation fraction (81%) than pure ZnO or CdIn₂S₄. Femtosecond transient absorption (fs-TA) spectroscopy confirm the ultrafast S-scheme electron transfer from the ZnO conduction band (CB) to the CdIn₂S₄ valence band (VB) upon photoexcitation of the ZnO/CdIn₂S₄ composite. Besides, timely depletion of VB holes in ZnO and CB electrons in CdIn₂S₄ can accelerate the interfacial electron transfer in the ZnO/CdIn₂S₄ S-scheme heterojunction. The innovative design of the ZnO/CdIn₂S₄ S-scheme photocatalyst provides new insights for developing efficient dual-functional heterojunction photocatalytic systems and introduces a novel method for studying S-scheme heterojunctions using fs-TA spectroscopy.

Improving the separation efficiency of photogenerated charge carriers to significantly enhance the redox capability of photocatalysts remains a major challenge in the field of photocatalysis. To address this issue, this study successfully synthesized a CeO₂/Bi₁₉Br₃S₂₇ S-scheme heterojunction catalyst using a hydrothermal method, aiming to enhance the photocatalytic performance of the catalyst. The synthesis of the CeO₂/Bi₁₉Br₃S₂₇ composite not only improved the separation efficiency of photogenerated charge carriers but also endowed the catalyst with stronger redox capabilities and greater driving force, significantly boosting its photocatalytic performance. Experimental results showed that the CO production rate of the CeO₂/Bi₁₉Br₃S₂₇ composite catalyst reached 13.5 μmol g⁻¹ h⁻¹, which is 5.19 times higher than that of the pure Bi₁₉Br₃S₂₇ catalyst and 2.81 times higher than that of the pure CeO₂ catalyst. This significant enhancement indicates that the CeO₂/Bi₁₉Br₃S₂₇ composite catalyst exhibited stronger catalytic performance in CO generation reactions. Furthermore, CeO₂/Bi₁₉Br₃S₂₇ catalyst achieved a CH₄ production rate of 4.3 μmol g⁻¹ h⁻¹, which is 3.1 times higher than that of the CeO₂ catalyst and 2.7 times higher than that of the Bi₁₉Br₃S₂₇ catalyst, further confirming its superior performance in CH₄ generation reactions. These results demonstrate that the CeO₂/Bi₁₉Br₃S₂₇ composite catalyst not only shows significant improvements in CO and CH₄ production rates but also exhibits excellent photocatalytic performance, highlighting its potential application in the field of photocatalysis. This study provides new insights into improving the separation efficiency of photogenerated charges and offers valuable references for the future development of highly efficient photocatalytic materials. By constructing the S-scheme heterojunction structure, the recombination of photogenerated charge carriers can be effectively suppressed, thereby enhancing the efficiency of photocatalytic reactions and providing a new solution for sustainable energy utilization.

The simultaneous enhancement of separation and utilization of bulk and surface charges is crucial for achieving efficient photocatalytic H₂ evolution reactions. In this study, NiCr₂O₄/T-CZS composites were fabricated by incorporating NiCr₂O₄ nanosheets onto the surface of twinned Cd_0.5Zn_0.5S (T-CZS) nanoparticles using a solvent evaporation strategy. After optimization, the 6% NiCr₂O₄/T-CZS exhibited an impressive hydrogen (H₂) evolution rate (r_H2) of 81.4 mmol∙h⁻¹∙g⁻¹ when employing polylactic acid (PLA) plastic as a sacrificial agent in NaOH solution. The reason behind this can be mainly attributed to the fact that T-CZS consists of wurtzite Cd_0.5Zn_0.5S (WZ-CZS) and zinc blende Cd_0.5Zn_0.5S (ZB-CZS) with slight band structure differences, thereby facilitating rapid bulk phase and interface charge separation due to the S-scheme charge transfer routes between WZ-CZS and ZB-CZS, as well as T-CZS and NiCr₂O₄. Moreover, this system can effectively retain electrons with strong reducing ability for efficient H₂ evolution reaction (HER) and generate hot electrons through the localized surface plasmon resonance (LSPR) effect of NiCr₂O₄, which enhances the absorption of UV-Vis-NIR light energy, thereby facilitating the HER process. What's more, NaOH solution can indirectly promote the HER kinetics by enhancing the oxidative driving force of holes. Additionally, other metal chromates (MCr_xO_y), such as CoCr₂O₄, AgCrO₂, Bi₆CrO₁₂, BaCrO₄, ZnCr₂O₄, CdCr₂O₄, CuCr₂O₄ etc., were employed to enhance the activity of T-CZS too. The results show that above homo-heterojunction composites can integrate waste plastic degradation and photocatalytic H₂ evolution effectively based on their S-scheme bulk phase and interface charge separation mechanisms. This work provides new insights into energy and environmental challenges.

The intrinsic surface atomic configuration of photocatalyst without unstable or difficult-to-generate atomic vacancies often limits the formation of effective interaction between metal single atom (MSA) cocatalyst and photocatalyst, thus inhibiting the stability and performance improvement of single-atom photocatalysts. In this study, we present a convenient and cost-effective photochemical oxygen reduction reaction (ORR) mechanism to prepare thermodynamically stable noble metal single-atom cocatalysts on TiO₂ photocatalyst under mild condition (only consuming water and oxygen at 101325 Pa and 25 ℃). The first-principles simulation firstly theoretically reveals that the intrinsic surface configuration of TiO₂ can only produce unstable Pt―O₂ structure. However, ORR occurring on TiO₂ can not only provide one foreign oxygen to coordinate with Pt single atom (PtSA), but also induce one surface lattice oxygen to move toward PtSA, promoting the formation of one thermodynamically stable Pt―O₄ species, demonstrated by the experimental synthesis of PtSA on TiO₂ in oxygen atmosphere instead of inert atmosphere. The obtained stable PtSA-TiO₂ photocatalysts exhibit a photocatalytic rate of 320.4 mmol·g⁻¹·h⁻¹ for the coproduction of high-purity hydrogen and value-added acetaldehyde with a selectivity of 99.65%, three-fold higher than the activity of Pt nanoparticles-loaded TiO₂. This strategy is further extended to other noble metals, such as Rh and Pd.

Photocatalysis technology, utilizing solar-driven reactions, is poised to emerge as a reliable strategy to alleviate environmental and energy pressures. Thus, whether the photocatalytic performance is excellent depends on the reasonable design of photocatalysts. By considering factors such as morphology engineering, band gap engineering, co-catalyst modification, and heterojunction construction, the photocatalysts with superior performance can be developed. Inspired by this unique characteristic, photocatalysts with a hollow structure endow numerous advantages in photocatalyst design, including enhanced multiple refraction and reflection of light, reduced transport distance of photo-induced carriers, and provided plentiful surface reaction sites. Herein, we systematically review the latest progress of hollow structured photocatalysts and summarize the diversity from geometric morphology, internal structure, and chemical composition. Specifically, the synthetic strategies of hollow structured photocatalysts are highlighted, including hard template, soft template, and template free methods. Furthermore, a series of hollow structured photocatalysts have also been described in detail, such as metal oxide, metal sulfide, metal-organic framework, and covalent organic framework. Subsequently, we present the potential applications of hollow structured photocatalysts in photocatalytic pollutant degradation, H₂ production, H₂O₂ production, CO₂ reduction, and N₂ fixation. Simultaneously, the relevant relationship between hollow structure and photocatalytic performance is deeply discussed. Toward the end of the review, we introduce the challenges and prospects in the future development direction of hollow structured photocatalysts. The review can provide inspiration for better designing hollow structured photocatalysts to meet the needs of environmental remediation and energy conversion.

Photocatalytic reduction of carbon dioxide (CO₂) has emerged as an effective technology to transform CO₂ into valuable chemicals. Metal-organic frameworks (MOFs) show great promise due to their adjustable structures, huge specific surface areas, excellent catalytic properties, and remarkable photo responsiveness. Herein, the MOF material NNU-55(Fe) was employed for the photocatalytic transformation of CO₂ into carbon monoxide (CO). Through electronic modulation of the active metal center (Fe-N4) via inorganic anionic ligand tuning, the photocatalytic performance of NNU-55(Fe) MOFs can be easily regulated. Notably, NO₃⁻-coordinated NNU-55(Fe) demonstrated superior catalytic performance compared to SO₄²⁻- and Cl⁻-coordinated catalysts, achieving a CO production of 124 μmol∙g⁻¹ within 3 h. The stronger electron donation capacity of NO₃⁻ leads to an improved electron density of Fe centers, which lowers the Fe d-band center and enhances the bonding orbital occupancy in the adsorption system, thereby increasing the adsorption strength of CO₂ and reduction activity. This study highlights a simple strategy for altering the catalytic activity and electrical structure of MOFs by altering the coordinated inorganic ligands of metal sites, offering a novel approach to developing efficient photocatalytic materials.

Photocatalytic hydrogen (H₂) production is a clean energy technology, with great potential for addressing the global energy crisis and related environmental problems. However, single-component photocatalysts often suffer from low efficiency primarily due to fast charge carrier recombination and the tradeoff between light-absorbing capacity and redox capabilities. Constructing heterojunctions provides a promising strategy to overcome these drawbacks, and S-scheme heterojunctions have recently stood out, demonstrating the capability to efficiently facilitate electron/hole separation, while maximizing the redox capability. Among them, polymer-based S-scheme photocatalysts are emerging, though the charge carrier dynamics in inorganic-organic S-scheme heterojunctions remain to be elucidated. Herein, we fabricated an S-scheme heterojunction comprised of the conjugated polymer dibenzothiophene-S, S-dioxide-alt-benzodithiophene (DBTSO-BDTO) and cadmium sulfide (CdS) for photocatalytic H₂ production. The S-scheme mechanism was verified using in situ irradiated X-ray photoelectron spectroscopy, and the charge carrier transfer dynamics were analyzed in depth using femtosecond transient absorption spectroscopy, which revealed that a considerable fraction of electrons undergo interfacial charge transfer in the CdS/DBTSO-BDTO composite. Owing to the improved charge separation efficiency and redox capability, the performance of the composite surpassed that of DBTSO-BDTO and CdS, and the H₂ evolution rate of the optimized CdS/DBTSO-BDTO material reached 3313 μmol·h⁻¹·g⁻¹, three times that of pure CdS. The findings provide new insights into the electron transfer mechanisms of S-scheme heterojunctions, and can guide the design of polymer-based photocatalysts for solar fuel production.

Platinum (Pt) is an excellent oxygen reduction cocatalyst with great potential for the photocatalytic production of H₂O₂. However, its catalytic efficiency is limited by the strong adsorption of O₂, which facilitates O―O bond cleavage and reduces selectivity for the 2-electron oxygen reduction reaction (ORR). Fortunately, the strength of the Pt―O bond can be weakened by adjusting the structure of the cocatalyst to modify the electronic structure of Pt. In this paper, Pt and Ag cocatalysts are successively modified on the (010) facet of BiVO₄ through a two-step photodeposition method. Due to the occurrence of a displacement reaction during the process, a synergistic catalyst with a hollow AgPt alloy core and an electron-rich Pt^δ− shell (AgPt@Pt) structure is ultimately synthesized. Photocatalytic experiments demonstrated that the H₂O₂ production from BiVO₄ modified with hollow AgPt@Pt reached an impressive 1021.5 μmol∙L⁻¹. This corresponds to an AQE of 5.1%, which is 28.6 times higher than that of the Pt/BiVO₄ photocatalyst with only 35.7 μmol∙L⁻¹. Furthermore, research results show that AgPt can transfer electrons to the Pt shell to generate electron-rich Pt^δ− active sites, thus increasing the antibonding orbital occupancy of Pt―O_ads in AgPt@Pt catalysts. This electron redistribution weakens the adsorption strength of O₂ on Pt, promoting the 2-electron ORR and facilitating the efficient generation of H₂O₂. This synthesis strategy offers a versatile approach for preparing other Pt-based nano-alloy cocatalysts with improved activity for the selective reduction of O₂ to H₂O₂.

Designing heterojunctions based on carbon nitride offers a promising pathway for enhancing photocatalytic efficiency. This study develops an all-organic S-scheme metal-free heterojunction uniquely composed of carbon nitride nanosheets (GCNNS) and a donor-acceptor conjugated polymer, poly p-aminobenzylidene-so-aniline (PASO), synthesized through a simple yet effective ball-milling technique. This heterojunction demonstrates excellent photocatalytic efficiency for hydrogen (H₂) evolution. The optimized GCNNS/PASO-10 sample attains an H₂ evolution rate of 10.12 mmol·g⁻¹·h⁻¹, which is about 5.9 times and 19.5 times greater than those of pure GCNNS and PASO, respectively. This improvement is due to the unique interfacial bonding, increased visible-light absorption, and efficient charge carrier separation facilitated by a strong internal electric field within the S-scheme. Theoretical calculations and characterization reveal that this heterojunction's S-scheme mechanism optimally aligns energy bands and promotes spatial charge separation, driving superior photocatalytic activity. This work presents the unique advantage of all-organic materials for heterojunction construction and provides insights into designing advanced S-scheme systems for sustainable energy conversion.

Green photocatalytic synthesis of hydrogen peroxide (H₂O₂) represents a promising alternative to the energy-intensive anthraquinone process, yet it is hindered by rapid carrier recombination and insufficient redox capacity in sacrificial-agent-free systems. This work reports a melamine foam (MF)-supported sulfur (S)-doped carbon nitride (SCN)/S vacancy-modified Cd_0.5Zn_0.5In₂S₄ (CZIS) S-scheme heterojunction (CZIS/SCN/MF) via an in situ chemical bath-hydrothermal method for sacrificial-agent-free H₂O₂ photosynthesis. The S-scheme charge transfer mechanism was confirmed by in situ irradiated X-ray photoelectron spectroscopy, free-radical trapping electron paramagnetic resonance, femtosecond transient absorption spectra and theoretical calculations. Specifically, the sulfur doping could modulate the local charge distribution of the carbon nitride framework to reinforce the interfacial built-in electric field for the CZIS/SCN S-scheme heterojunction. Meanwhile, the calcination-induced S-vacancies in CZIS could serve as photoelectron traps, promoting charge separation, and reserving photoinduced holes for H₂O oxidation, thereby achieving sacrificial-agent-free H₂O₂ synthesis. Coupled with the photothermal effect of MF's three-dimensional porous framework, the CZIS/SCN/MF catalyst with optimized S-doping density and SCN dosage delivers an H₂O₂ production rate of 3.46 mmol·g⁻¹·h⁻¹ in pure water, surpassing most of the sacrificial-agent-free systems. This study proposes a novel strategy for synergistic interfacial charge regulation and energy conversion enhancement in sacrificial-agent-free photocatalytic systems.

With the rapid development of new energy industries, the utilization of waste batteries has attracted the attention of researchers. Developing a hydrogen peroxide photosynthesis system with battery recycling materials as photocatalysts presents a significant challenge. In this study, an ultrasonic self-assembly technique is employed to integrate LiFePO₄ (LFPO) nanoparticles, derived from spent batteries, with g-C₃N₄ (CN) nanosheets, thereby creating an inorganic/organic S-scheme photocatalyst for the production of H₂O₂. In situ analyses using X-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM) demonstrate that the interaction between LFPO and CN facilitates the development of an internal electric field (IEF), which in turn gives rise to a distinctive S-scheme charge transfer mechanism. Combining electron spin resonance spectroscopy, radical-trapping experiments, and in situ DRIFTS spectra, three pathways for H₂O₂ formation are identified. Benefited from enhanced carrier separation, strong redox power, and multichannel H₂O₂ formation, the optimal composite shows an impressive H₂O₂-production rate of 3.22 mol∙g⁻¹∙h⁻¹ under simulated solar irradiation. This research provides a potential method to investigate a sustainable H₂O₂ photosynthesis pathway by designing S-scheme heterojunctions from spent battery materials.

Complete mineralization of persistent organic pollutants in wastewater remains a formidable challenge. Here, we report the rational design of a ZIF-8-derived ZnO/polyaniline (PANI) S-scheme heterojunction synthesized via in situ oxidative polymerization. Advanced characterizations confirm the S-scheme charge transfer mechanism within the ZnO/PANI heterojunction. The optimized composite achieves complete phenol mineralization within 60 min while concurrently generating H₂O₂ at a rate of 0.75 mmol∙L⁻¹·h^–1 under simulated solar irradiation. Mechanistic studies verify that the S-scheme heterojunction retains strong redox potentials, driving the formation of reactive oxygen species for H₂O₂ production and phenol degradation. This work establishes a universal design paradigm for MOF-derived inorganic/organic S-scheme heterojunctions, effectively coupling solar-driven energy conversion with environmental remediation.

S-scheme heterojunctions have garnered significant interest in photocatalytic CO₂ conversion to valuable products (e.g., CH₄) due to their enhanced charge separation and robust redox capabilities. Carbon dots (CDs), with their tunable band structures and light absorption ranges, show particular promise in constructing efficient S-scheme photocatalytic systems. Nevertheless, the critical roles of CDs' band alignment and surface adsorption properties in determining heterojunction configuration, charge carrier kinetics, and ultimately CO₂ activation/product selectivity distribution remain insufficiently explored. Herein, we construct four CDs/TiO₂ heterojunctions using CDs synthesized from varied carbon sources, in which S-scheme heterojunctions were successfully constructed based on cost-effective coal pitch (C-GQDs, 1.75 nm), glucose (G-CQDs, 1.84 nm), and acetone (CQDs-X, 1.82 nm) carbon sources, whereas Type-Ⅰ heterojunctions were formed by carbon black based CDs (GQDs-A, 1.92 nm). Systematic investigations reveal that both the band structure and adsorption characteristics of CDs play important roles in the charge transfer path and separation efficiency, CO₂ adsorption and activation capacities, and product selectivity in photocatalytic CO₂ reduction. Remarkably, the introduction of CDs significantly broadens the photo-response range compared to fresh TiO₂, and in particular, the C-GQDs/TiO₂ exhibits exceptional performance with a CH₄ production rate of 32.7 μmol·g⁻¹·h⁻¹, surpassing TiO₂ by 6.3-fold and outperforming GQDs-A/TiO₂, CQDs-X/TiO₂, and G-CQDs/TiO₂ by factors of 3.8, 2.7, and 2.3, respectively. This heterojunction simultaneously achieves 72.6% CH₄ selectivity and 98.1% hydrocarbons selectivity (encompassing CH₄, C₂H₆, C₂H₄, and C₃H₈). In contrast, composites incorporating GQDs-A, CQDs-X, or G-CQDs exhibit substantially diminished CH₄ selectivity (< 40.0%). The high CH₄ production rate and selectivity of C-GQDs/TiO₂ can be attributed to its unique S-scheme heterojunction structure, higher reduction potential, and well-matched CO₂ and H₂O adsorption and activation capabilities. This study provides unique insights into the efficient photoreduction of CO₂ to CH₄ driven by the S-scheme heterojunction electron transfer pathway in CDs/TiO₂ photocatalysts.