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Desulphurization of fossil fuels is a critical process in reducing the sulphur content from environment, which is a major contributor to atmospheric pollution. Traditional desulphurization techniques, while effective, often involve high energy consumption and the use of harsh chemicals. Recently, photocatalytic desulphurization has emerged as a promising, eco-friendly alternative, leveraging the potential of photocatalysts especially semiconductor heterojunctions to enhance photocatalytic efficiency. This review comprehensively discusses the significance and mechanism of photocatalytic desulphurization reactions, designing of various heterojunctions such as conventional, p-n, Z-scheme and S-scheme, their charge transfer mechanism and properties and their contribution to the photocatalytic desulphurization activity. Heterojunctions, formed by combining different semiconductor materials, facilitate efficient charge separation and broaden the light absorption range, thereby improving the photocatalytic performance under visible light. Furthermore, the recent advancements in the heterojunction systems in the field of photocatalytic desulphurization activity have been discussed in detail and summarized. The current limitations and challenges in this particular field are also explored. The paper concludes with an outlook on future research directions and the potential industrial applications of heterojunction-powered photocatalytic desulphurization, emphasizing its role in achieving cleaner energy production and environmental sustainability. [Display omitted] • Mechanisms elaboration from perspective of photocatalysts and desulphurization. • Systematic overview on photocatalytic heterojunctions: Issues and innovations. • Investigation on recent advances in photocatalytic desulphurization by heterojunctions. • Evaluation of effectiveness and stability. • Discussion on the development prospects and challenges. [ABSTRACT FROM AUTHOR]

[Display omitted] • MIL-88B(Fe)/Cu 7 S 4 S-scheme heterojunctions with S-vacancies have been developed. • MIL-88B(Fe)/Cu 7 S 4 exhibit superior photocatalytic activity toward tetracycline degradation. • The heterojunction provides rapid charge transfer and diminished recombination. • S-scheme mechanism was verified by in situ XPS, UPS and energy band structure. In order to meliorate the photocatalytic performance of materials, semiconductor heterojunction construction and engineering of vacancies/defects has been a successful strategy for advanced wastewater treatment. Herein, a sulfur vacancies rich S-scheme heterojunction was constructed by incorporating MIL-88B(Fe) and Cu 7 S 4 was constructed by in-situ hydrothermal method. The optimized MIL-88B(Fe)(20 wt%)/Cu 7 S 4 (20MCS) heterojunction exhibited superior photocatalytic activity with 94.3 % TC (20 mg L−1) removal within 90 min. The S-scheme heterojunction facilitates efficient charge carriers' separation, interfacial charge transfer facilitated by sulfur vacancies with high photo-redox capability as determined by EIS, TPCR band analysis and PL experiments. The in-situ XPS findings and UPS (work function determination) were used as direct experimental evidence for the S-scheme route and the existence of sulfur defects was confirmed by electron paramagnetic resonance (EPR). The prepared heterojunction photocatalyst demonstrates excellent efficiency, stability, and adaptability to practical environmental conditions as tested in real water samples. The scavenging and ESR experiments disclosed that O 2 – and OH radicals were generated. The mechanism for TC degradation by 20MCS was also proposed based on analysis of degradation intermediates. This novel hybrid S-scheme heterojunction photocatalyst system is quite promising for high performance environmental remediation exhibiting both stability and remarkable activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • AgFeO 2 -Bi 5 O 7 I S-type heterojunctions developed by facile route. • AgFeO 2 -Bi 5 O 7 I exhibit superior 98.2 % norfloxacin degradation in120 min. • Rapid charge transfer and minimum recombination via S-scheme mechanism and oxygen-vacancies. • ●OH and ●O 2 – radicals as major reactive species- ESR findings. • Superior performance in solar light as well in different water matrices. Developing highly efficient heterojunction photocatalysts for high performance antibiotic removal is of immense importance but still remains a challenge. Herein, AgFeO 2 -Bi 5 O 7 I (AF-BI), a promising oxygen vacancies rich binary S-scheme heterojunction photocatalyst was synthseized via co-precipitation and hydrothermal treatment. The spherical AgFeO 2 spheres were uniformly affixed on the nanorods of Bi 5 O 7 I via an intimate contact, as verified through electron microscopy. The photodegradation efficiency of optimized 15 %AgFeO 2 -Bi 5 O 7 I (15AF-BI) for norfloxacin (NFX) was 98.2 % (120 min) with apparent rate constant 0.022 min−1 which was 4 times pure AgFeO 2. In municipal water, removal efficiency reached 90.4 % and a high 76.1 % and 65.2 % total organic carbon removal in 3 h in visible light and solar light respectively was achieved. The coupling of AgFeO 2 and Bi 5 O 7 I triggers electron transfer, forming an internal electric field (leading to a directional charge transfer efficient separation of the photo-induced carriers as confirmed by PL, EIS, TPCR results. The validation of existence of S-scheme mechanism and oxygen vacancies was achieved by in-situ X-ray photoelectron spectroscopy (XPS) and EPR analysis. The free radical scavenging experiments and electron spin resonance (ESR) spectroscopy revealed ●OH and ●O 2 – radicals were the major reactive species involved in the photodegradation process. The heterojunction is magnetic and can be separated under guidance of magnetic field which makes reusability and separation easy. Based on ESR findings, band structure analysis and mass spectrometry NFX degradation route was predicted. This work provides effective potential solution for preparing new magnetic S-scheme heterojunctions for effective antibiotics degradation and further will expand to realm of clean energy storage and conversion. [ABSTRACT FROM AUTHOR]

The reasonable designing, interfacial tuning and construction of S-scheme heterostructures offering high performance water pollutants treatment and energy production still remains challenging. Following the structure, band structure and interface function perspective, we prepared Fe 7 S 8 /CuIn 5 S 8 heterostructures photocatalysts with sulfur vacancies for superior norfloxacin (NOR) degradation and hydrogen production under visible light. In particular, for optimal 30FS/CIS (30%Fe 7 S 8 /CuIn 5 S 8), the H 2 evolution was up to 35.6 mmol g−1 h−1 which was 11.5 times than pristine Fe 7 S 8 with TEOA as sacrificial agent. The heterojunction could also show 98.7% degradation of NOR in 90 min under visible light. Interestingly, using NOR pollutant as sacrificial agent under synergistic conditions, 22.7 mmol g−1 h−1 H 2 evolution and 98.9% degradation of NOR (in 45 min) was achieved. The significantly boosted photocatalytic pollutant degradation and hydrogen generation performance over Fe 7 S 8 /CuIn 5 S 8 hybrids is ascribed to the efficient S-scheme charge transfer and active sites provided by sulfur vacancies (V s). The deep electron transfer mechanism and the charge transfer efficiency were supported by in-situ XPS, UPS, electrochemical experiments and photoluminescence. Experimental results including scavenging tests and ESR findings provided the direct evidence of photogenerated holes and ●OH radicals for pollutant degradation and electrons in hydrogen generation. This work contributes to effective designing and developing high-activity visible light/solar light assisted heterojunction photocatalysts for realizing superior clean energy generation and pollutant degradation. [Display omitted] • Novel S-scheme Fe 7 S 8 /CuIn 5 S 8 heterostructures successfully constructed. • Synchronous norfloxacin degradation and hydrogen evolution are realized. • The sulfur vacancies promote separation and light absorption. • The photogenerated holes/●OH and electrons are utilized for pollutant degradation and H 2 production. • The photocatalytic mechanism of H 2 evolution and NOR degradation were proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Overview of fundamentals of Nb 2 O 5 as photocatalyst-structure and properties. • Heterojunction photocatalysts -Z and S scheme- charge transfer routes. • Recent advances in Nb 2 O 5 based heterojunctions for photocatalytic applications. • Strategies for improving the photocatalytic performance Nb 2 O 5 based heterojunctions. Significant advancements in the field of photocatalysis in recent years have highlighted the heterojunctions based on Nb 2 O 5 as a focal point of research. This comprehensive review diligently analyses the progress in Nb 2 O 5 -based heterojunctions for their application in photocatalysis, focusing on synthesis, characteristics and their pivotal role in addressing crucial energy and environmental challenges. The review emphasizes the fundamental principles of photocatalysis in pollutant removal and H 2 generation, elucidating key processes such as light absorption, charge generation and surface reactions. The different types of heterojunctions, their basic principles and role in enhancing the charge separation and overall photocatlytic performance have been discussed. The recent advances in Nb 2 O 5 -based heterojunctions are extensively discussed for the photocatalytic applications such as pollutants removal and H 2 evolution. Furthermore, the review delves into strategies employed to enhance the photocatalytic activity of Nb 2 O 5 -based heterojunctions such as doping, oxygen vacancies modification, morphological engineering and atomic control, as well as loading with support materials. Each strategy is explained, emphasizing its impact on charge separation and overall efficiency. The review concludes by highlighting existing challenges and providing insights into potential future directions that integrates synthetic processes, novel methods for photoelectric characterization, and an in-depth understanding of the local structure of Nb 2 O 5. This review serves as a valuable resource for researchers in the field, offering a comprehensive overview of the state-of-the-art in Nb 2 O 5 -based heterojunctions for advanced photocatalytic applications. [ABSTRACT FROM AUTHOR]

Photocatalysis has established itself as a fascinating topic, giving promise for effective processing of greenhouse gases and contaminants into useful products, in the search for renewable energy sources and atmospheric rehabilitation. This review study provides a thorough examination of S-scheme heterojunction photocatalysts with an emphasis on their uses in the photocatalytic reduction of CO 2 , N 2 fixation and NO x degradation processes. The review explains various environment-related issues, the basic ideas of photocatalysis and heterojunctions, emphasizing the benefits of S-scheme topologies in increasing interfacial transmission of charges and lowering electron-hole recombination. The fundamentals and issues of photocatalytic CO 2 reduction, nitrogen fixation and NO x degradation, outlining the mechanics involved in employing S-scheme heterojunctions have been discussed. The recent advancements of S-scheme photocatalysts for a variety of applications are highlighted in this review. The future prospects of such assemblies are also critically evaluated, highlighting the importance of full use of solar spectrum, wide scale preparation of photocatalysts, maintaining the redox capability and mechanism elucidation to prepare superior S-scheme heterojunctions to resolve the important energy and environmental issues. [Display omitted] • S-scheme heterojunctions as efficient photocatalysts –Fundamentals and advantages. • Mechanisms of photocatalytic CO 2 reduction, N 2 fixation and NO x degradation. • Designing and synthesis of S-scheme heterojunction photocatalysts. • Applications for reducing CO 2 into fuels, fixation of N 2 into NH 3 and degrading NO x. [ABSTRACT FROM AUTHOR]

A binary S-scheme heterojunction photocatalyst, ZIF-67/Ag 3 VO 4 (ZAV), was successfully synthesized using a hydrothermal technique. The optimal ZAV-30 (ZIF-67/30 wt%Ag 3 VO 4) demonstrated excellent performance by degrading 98.5% of Venlafaxine (VEN) within 60 min under visible light. Extensive investigations were carried out regarding the crystal structure, morphology, composition, specific surface area, optical characteristics and electrochemical impedance. The ZAV-30 heterojunction photocatalyst outperformed bare ZIF-67 and Ag 3 VO 4 photocatalysts, primarily due to enhanced photon absorption and improved charge carriers' separation via S-scheme transfer, redox capability and high charge transfer capacity supported by electrochemical experiments and photoluminescence. The S-scheme transfer was validated by in-situ XPS measurements after light exposure. Scavenger experiments indicated that both •OH and •O 2 − played crucial roles as active species in the photocatalytic process. Mass spectrometry (MS) analysis of intermediates facilitated the proposal of a probable photocatalytic degradation pathway for VEN. The photoactivity of the heterojunction was influenced by a range of factors including the pH of the VEN solution, initial VEN concentration, ZAV photocatalyst dosage, and ion effects. Interestingly the ZAV-30 heterojunction exhibited superior performance in lake water, tap water and river water too. Importantly, the ZAV-30 heterojunction exhibited excellent stability and reusability, making it a promising photocatalyst. [Display omitted] • ZIF-67/Ag 3 VO 4 S-scheme heterojunction synthesized by hydrothermal technique. • ZAV-30 demonstrated 98.5% degradation of Venlafaxine within 60 min under visible light. • The S-scheme transfer accelerates charge transfer, separation and strong redox capability. • •OH and •O 2 − as main active species for photocatalytic degradation • High mineralization, reusability and durability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fundamentals of S-scheme and dual S-scheme have been discussed. • Types of heterojunctions are elaborated with mechanism comparisons. • Recent developments in synthetic methods and different morphology of S-scheme and dual S- schemes. • S-scheme and dual S-scheme for photocatalytic environmental remediation and energy production. • Bottlenecks, conclusion and future prospects discussed. Discovering alternative materials and technologies that provide the meaningful potential to environmental and energy-related challenges in critical to the long-term viability of industrial activity and the evolution of society. Photocatalysts are undeniably important, and scientists are working hard to improve their photocatalytic performance. The high recombination rates of photogenerated electron-hole pairs as well as poor redox capability are addressed via heterojunction modification. In this direction, oxidation type and reduction type photocatalysts based S-scheme heterojunctions are highly promising owing to highly diminished recombination facilitated by internal electric field. This review has focused on the shift from Z-scheme to new revolutionary S-scheme based photocatalytic materials with high performance applications in the field of energy and environment. It can be concluded that controllable built-in electric field intensity and stable interfacial carrier transport process make S-scheme heterostrctures ideal. However their application is mainly limited to powder photocatalysts, don't apply to photo-chemistry and solar cells with external circuit, reaction thermodynamics and dynamics management in S-scheme photocatalysts is not adequate. To some extent, dual S-schemes address to these limitations and further research is to be carried out to fight the bottlenecks. Several perspectives on the future of S-scheme and dual S-scheme heterostructure were also provided based on rigorous review of the reported results. A discussion on the previously reported different types of heterojunctions and S-schemes is presented in this review along with plausible charge transfer mechanisms. The synthetic routes to S-scheme heterojunctions are also provided along with modifications and combinations. The current designing and perspective applications in numerous pollutant degradation, hydrogen production and CO 2 conversion is selectively highlighted. The transition of mechanism elucidation from Z-scheme to S-scheme has been discussed with suitable case studies. However, S-scheme heterojunctions designing and fabrication is still new commercially and so present readiness and bottlenecks have been discussed. Hence it is quite imperative for a future roadmap to be laid to design and develop economically viable high performance S-scheme heterojunctions. [ABSTRACT FROM AUTHOR]

The step-scheme (S-scheme) heterojunctions with superior redox capability have recently emerged as one of the most promising materials for cleaning up of contaminated environments. Herein, we synthesized g-C 3 N 4 /NiFe 2 O 4 (NFC) heterojunction photocatalyst via a hydrothermal route for the degradation of Cephalexin (CPX). The integration of g-C 3 N 4 and NiFe 2 O 4 into heterojunction with an effective S-scheme transfer which prevents the recombination of essential photoexcited electron-hole pairs leads to excellent 99.3% of photocatalytic degradation of CPX within 60 min under visible light. The scavenging experiments suggested •OH and •O 2 - radicals generated on high potential bands of S-Scheme g-C 3 N 4 /NiFe 2 O 4 as active species responsible for high performance CPX removal. The degradation intermediates were examined by Liquid Chromatography mass spectroscopy (LC-MS) and a probable pathway of CPX degradation was proposed accordingly. The inherent work function between g-C 3 N 4 and NiFe 2 O 4 leads to bending of conduction and valence bands which subsequently forms an built-in electric field across the interface facilitating the superior separation of photogenerated electrons and holes. The five subsequent recycling tests demonstrated the catalyst's strong photocatalytic stability and the easy recovery process because of its magnetic characteristic. This research may bring fresh insights for constructing magnetic photocatalysts based on g-C 3 N 4 , which are both highly effective and stable. Additionally, it also paves a path for the designing of S-scheme heterojunctions with great performance for environmental remediation applications. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni 5 P 4 /g-C 3 N 4 S-scheme dual-function heterojunction photocatalyst was prepared. • 25NP/CN junction shows 40.1 mmol g-1h-1H 2 evolution and 94.4 % CBZ removal in a coupled process. • Holes and OH radicals for CBZ degradation and electrons for H 2 generation via e-/H 2 O and 2e-/2H+. • Intermolecular H+ transfer via cyclic intermediate between Ni and degradation products. • Junction works in oxic/anoxic mediums- detailed mechanisms analysed. With a goal of waste-to-energy conversion, herein we report synchronous hydrogen evolution and pollutant degradation via photocatalysis utilizing novel Ni 5 P 4 /g-C 3 N 4 S-scheme (Step scheme) heterojunction. The 25 %Ni 5 P 4 /g-C 3 N 4 (25NP/CN) sample generates 40.1 mmol g-1h-1hydrogen evolution and 94.4 % carbamazepine degradation simultaneously under visible light and anaerobic conditions. Furthermore, the hydrogen evolution with carbamazepine, bisphenol A, sulfamethoxazole and rhodamine B is manifolds higher than in water. From The in-situ XPS results confirm the S-scheme transfer between Ni 5 P 4 and g-C 3 N 4. The presence of Ni0@Ni 5 P 4 where strong covalent interactions between Ni0 and Ni-P single layers on Ni 5 -P 4 not only enhanced the visible absorption, charge transfer but also leads to hydrogen formation by H+ transfer via a cyclic intermediate in a co-ordinate complex of degradation intermediates with Ni. This route is in addition to obvious e-/H+. The CBZ degradation and hydrogen evolution in aerobic/oxic conditions was also studied and 25NP/CN performs well under this atmosphere, inferring that oxidised intermediates act as electron donors and maintains the H 2 evolution in longer run too. The photogenerated holes directly oxidized the pollutant in addition to OH radicals in anoxic medium and separated/accumulated electrons leads to hydrogen evolution. The scavenging experiments reveal that photogenerated holes directly oxidized the pollutant in addition to OH radicals in anoxic medium and separated/accumulated high potential electrons (via S-scheme transfer) leads to hydrogen evolution. The clean energy production and pollutant mineralization are synchronously achieved. Henceforth, a waste-to-energy route is proposed by coupling photocatalytic hydrogen evolution to environmental restoration. [ABSTRACT FROM AUTHOR]

Significant ecosystem damage and severe environmental issues have surfaced due to unplanned exploitation of resources and industrial expansion. The water bodies are continuously polluted by numerous organic dyes released from industrial effluents. In this work, we report construction of new g-C 3 N 5 /Bi 24 O 31 Br 10 S-scheme heterojunction for UV–visible light driven superior organic dye degradation. The integrated heterojunction with high interfacial charge transfer exhibited excellent 99.08% (∼100%) within 60 min exposure which is manifolds higher than bare g-C 3 N 5 and Bi 24 O 31 Br 10. The mechanistic investigations showed that the key active radicals in photocatalytic CV degradation are the •O 2 - and h+. Building an S-scheme model with favourable energy band structure encourages efficient separation of charges while maintaining the inherent redox capacity of the g-C 3 N 5 /Bi 24 O 31 Br 10 catalyst, which is highly beneficial for superior photocatalytic performance. This work offers a fresh viewpoint for creating organic-inorganic hybrid new S-scheme heterojunctions for high performance photocatalytic waste-water treatment. • High efficiency 2D–2D g-C 3 N 5 /Bi 24 O 31 Br 10 S-scheme heterojunction was designed. • Catalyst exhibit excellent degradation efficiency of 99.08% for CV removal. • PL suggests the efficient charge separation of the carriers. • ·O 2 - and h+ are responsible for CV degradation. [ABSTRACT FROM AUTHOR]

Designing and fabrication of smart hybrid multifunctional materials for energy/fuel production and environmental detoxification is indeed of great significance for sustainable development. Herein, we synthesized a new well-structured S-scheme heterostructure Fe@TiO 2 /Boron Carbon nitride (FT/BCN) with high performance tetracycline degradation and selective CO 2 photo-reduction to CH 4. Under visible light irradiation, 96.3% tetracycline was degraded in 60 min using best performing FT30/BCN sample with a high 83.2% total organic carbon removal in 2 h. The tetracycline degradation rate for FT30/BCN composite catalyst was ∼7 times than bare boron carbon nitride (BCN). The impact of reaction parameters as pH, presence of interfering electrolytes, light source and water matrix was also investigated. The FT30/BCN photocatalyst shows dramatic improvement in CO 2 photoreduction as exhibited in 24.7 μmol g−1 h−1 CH 4 and 2.4 μmol g−1 h−1 CO evolutions with optimal 91.1% CH 4 selectivity. Pure BCN shows a poor 39.1% selectivity. Further, effect of alkali activation, CO 2 /H 2 O feed ratio, reducing agent and light source onto CH 4 production and selectivity was also investigated. The CH 4 evolution and selectivity was improved because of enhanced visible light absorption, high adsorption potential, charge carrier separation and high reducing power of photogenerated electrons induced by an effective S-scheme heterojunction between Fe@TiO 2 and boron carbon nitride. An S-scheme (step-scheme) charge transfer mechanism is here operative both during tetracycline removal and CO 2 reduction. The drug degradation route and photocatalytic mechanism for antibiotic removal and CO 2 reduction was also predicted. [Display omitted] • Fe@TiO 2 /Boron carbon nitride heterojunction fabricated by hydrothermal route. • High performance antibiotic removal under visible and solar light. • Photo-induced CO 2 reduction with H 2 O for highly selective CH 4 production. • Efficient S-scheme charge transfer mechanism observed between Fe@TiO 2 and BCN. • Antibiotic degradation and selective CH 4 production detailed mechanism elucidated. [ABSTRACT FROM AUTHOR]