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In pursuit of advancing photocatalysts for superior performance in water treatment and clean energy generation, researchers are increasingly focusing on layered double hydroxides (LDHs) which have garnered significant attention due to their customizable properties, morphologies, distinctive 2D layered structure and flexible options for modifying anions and cations. No review has previously delved specifically into ZnCr and NiCr LDH-based photocatalysts and therefore, this review highlights the recent surge in ZnCr and NiCr-based LDHs as potential photocatalysts for their applications in water purification and renewable energy generation. The structural and fundamental characteristics of layered double hydroxides and especially ZnCr-LDHs and NiCr-LDHs are outlined. Further, the various synthesis techniques for the preparation of ZnCr-LDHs, NiCr-LDHs and their composite and heterostructure materials have been briefly discussed. The applicability of ZnCr-LDH and NiCr-LDH based photocatalysts in tackling significant issues in water treatment and sustainable energy generation is the main emphasis of this review. It focuses on photocatalytic degradation of organic pollutants in wastewater, elucidating the principles and advancements for enhancing the efficiency of these materials. It also explores their role in H 2 production through water splitting, conversion of CO 2 into valuable fuels and NH 3 synthesis from N 2 , shedding light on their potential for clean energy solutions. The insights presented herein offer valuable guidance for researchers working towards sustainable solutions for environmental remediation and renewable energy generation. [Display omitted] • Fundamentals and properties of Layered Double Hydroxides (LDHs). • ZnCr and NiCr LDHs as photocatalysts-Properties and Performance. • Water treatment and clean energy production-Mechanism and issues. • ZnCr and NiCr LDH based water treatment & clean energy production. • The challenges and future development direction for sustainable use are discussed. [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]

[Display omitted] • Oxygen vacancies fundamentals and importance in photocatalysis. • Oxygen vacancies rich heterojunction-Synthetic strategies. • OVs rich Z-scheme and S-scheme heterojunctions- Photocatalytic mechanism. • Applications for Hydrogen production and water treatment. • The existing challenges and future perspectives. Photocatalytic removal of pollutants and energy production is a green, low cost and environment friendly technology for addressing the mounting pressure of energy crisis and environmental deterioration. Developing efficient photocatalysts is still a big challenge for accelerating the photocatalytic hydrogen production and pollutant degradation especially utilizing solar light. Therefore, constructing oxygen vacancies rich Z-scheme and S-scheme semiconductor heterojunctions emerged as a promising approach to enhance the light harvesting and increasing the redox capability of photocatalysts. This review comprehensively summarises the state of art focus on oxygen vacancy's role in photocatalysts especially in Z-scheme and S-scheme heterojunctions including synthesis process and modifications. In particular, the functions of oxygen vacancy in supporting the main processes in photocatalytic energy production and pollutant removal, such as light absorption, charge separation and conversion are highlighted in this review. The current issues and future prospective in oxygen vacancies rich heterojunctions for efficient photocatalytic removal of pollutant and energy production are also addressed. Finally, a brief discussion on challenges and future prospects is demonstrated. [ABSTRACT FROM AUTHOR]

The population explosion and rapid economic development has led to tremendous increase in the per capita use of fossil fuel energy resulting in major environmental consequences. To tackle these significant energy and environmental concerns, semiconductor photocatalysis is viewed as a promising environmentally friendly and sustainable solution. The photocatalytic hydrogen evolution utilizes solar energy into clean hydrogen energy which makes it green, environmentally friendly and effective technique to meet energy demands. This process requires workable catalysts to reach a significant reaction rate because of their multiple electrons and multiple proton nature. Among various visible light active photocatalytic materials, metal molybdates have been reported as emerging class of materials owing to their outstanding features as stable crystal structure, photo-corrosion inhibition, high redox efficiency, low cost and toxicity and suitable band structure. The present research provides an extensive review of the most recent advances and new insights into the utilization of metal molybdates in photocatalytic clean energy production and environment challenges. This review article summarizes the recent progresses in advanced strategies applied in metal molybdate based photocatalysts to enhance the photocatalytic performance. The advanced strategies are categorized as control over morphology and surface modification, doping of heteroatom, co-catalyst loading, noble metal deposition and construction of heterojunction, which are devoted to photocatalytic H 2 production and CO 2 reduction and to overcome the fast recombination of charge carriers and increasing the light absorption capacity. The fabrication strategies of metal molybdates and based materials are discussed in detail, as well as their usage as catalysts for H 2 evolution and CO 2 reduction have been analysed. Metal molybdates are promising photocatalysts for addressing present environmental issues, and this work paves the way for future photocatalytic research and development, which may assist in the development of highly effective photocatalysts for sustainable energy needs. [Display omitted] • Metal molybdates as photocatalysts-Structure and properties. • Introduced the synthetic routes: Effect on properties and photocatalytic performance. • Discussed strategies to improve the photocatalytic potential of metal molybdates. • Application for superior hydrogen evolution and CO 2 conversion-Recent advances. • Fundamentals and bottlenecks along with future prospects are discussed. [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]

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]

In the contemporary era marked by pressing environmental and energy challenges, there is a growing imperative to create effective and eco-friendly approaches to combat pollution and promote the generation of clean and green energy. One such strategy that has attracted much interest recently is the photocatalytic generation of green energy and pollutant removal. Numerous photocatalysts have been created to treat water and generate clean energy. Zn-Ti LDH materials are two-dimensional materials that have unique physical and chemical properties, making them promising photocatalysts. Zn-Ti LDHs have a distinctive layered structure that makes them extremely adaptable for photocatalytic applications. This structure also provides large surface areas, customisable compositions, and abundant active sites. However, Zn–Ti LDH has a low solar energy efficiency because it is primarily triggered by ultraviolet light, which makes up around 5% of sunshine. Therefore, this investigation aims to provide a thorough summary of the latest advancements in the modification of the materials based on Zinc-Titanium Layered Double Hydroxides (Zn-Ti LDHs) for a broad spectrum of photocatalytic uses. This study also covers the fabrication methods for Zn-Ti LDHs and the creation of heterojunctions and composites based on Zn-Ti LDHs. Additionally, it delves into the mechanisms underlying the degradation of pollutants and the generation of clean energy. We have highlighted the potential for new prospects, existing challenges, and progress in this context. [Display omitted] • Fabrication and photocatalytic mechanisms of Zn-Ti LDH based materials for environmental solutions. • Latest advancements in heterojunctions and composites utilizing Zn-Ti LDH for applications in photocatalysis. • Various approaches for enhancing the photocatalytic capabilities of Zn-Ti LDH are explored. • The summary, challenges, and future outlook are all addressed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ag@BiPO 4 /BiOBr/BiFeO 3 heterojunction prepared by a simple route. • Wide spectrum response- High performance in UV, Vis, NIR and Solar light. • A dual Z-scheme mechanism predicted-SPR effect of Ag. • High degradation of Norfloxacin-Degradation pathway predicted. • Elucidating mechanism for binary, PBF and APBF under UV & visible-Scavenging & ESR. Abstract Metallic Ag deposited BiPO 4 /BiOBr/BiFeO 3 ternary nano-hetero-structures were rationally designed and synthesized by a simple precipitation-wet impregnation-photo deposition method. The plasmonic junction possesses an excellent wide spectrum photo-response and makes best use of BiPO 4 which is otherwise a poor photocatalyst. Ag@BiPO 4 /BiOBr/BiFeO 3 showed superior photocatalytic activity for degradation of norfloxacin (NFN) under visible, ultra-violet, near-infra-red and natural solar light. Especially catalyst APBF-3 (0.3 wt% Ag@BiPO 4 /BiOBr/BiFeO 3) shows 98.1% degradation of NFN (20 mg/L) in 90 min under visible light and 99.1% in less than 45 min under UV exposure. Free radical scavenging experiments and electron spin resonance (ESR) results has been used for explanation of charge transfer, photocatalytic mechanism and role of radicals for binary, ternary and Ag deposited ternary junctions for UV and visible exposure. Metallic Ag in addition to its surface plasmon resonance helps in protection of high conduction band and valence band in the three semiconductors. A dual Z-scheme mechanism has been predicted by comparing with possibilities of double charge and vectorial charge transfer. [ABSTRACT FROM AUTHOR]

• g-C 3 N 4 and MOFs based heterojunctions –synthesis routes and advantages. • Types of g-C 3 N 4 and MOFs heterojunctions were discussed-modification strategies. • g-C 3 N 4 and MOFs based heterojunctions for photocatalytic environmental remediation and energy production. • Conclusion and future research prospects on g-C 3 N 4 and MOFs based on heterojunctions. Photocatalytic technology has emerged as a promising solution for environmental remediation and energy production, and the development of efficient and stable photocatalysts is of great importance. Recent advances in g-C 3 N 4 /Metal Organic Frameworks (MOFs) heterojunctions have shown excellent potential in achieving high-performance photocatalytic environmental remediation and energy production. In this review, we have summarized the recent advances in the design and synthesis of g-C 3 N 4 /MOFs heterojunctions and their application in photocatalytic environmental remediation and energy production. We have discussed the advantages and challenges of g-C 3 N 4 /MOFs heterojunctions, such as enhanced light absorption, increased surface area, and improved electron-hole separation, and their effects on photocatalytic performance. We also highlight the recent research progress in the utilization of g-C 3 N 4 /MOFs heterojunctions for various environmental remediation applications, including the degradation of organic pollutants and the removal of heavy metals, as well as for energy production applications such as hydrogen evolution and CO 2 reduction. Furthermore, we provide an overview of the latest theoretical and experimental investigations into the mechanisms of photocatalysis in g-C 3 N 4 /MOFs heterojunctions, which can help to guide the rational design of high-performance photocatalysts. Our analysis of the literature reveals that g-C 3 N 4 /MOF heterojunctions have demonstrated excellent photocatalytic activity for the degradation of various pollutants, such as methyl orange, rhodamine B, and bisphenol A. For instance, a g-C 3 N 4 /ZIF-8 heterojunction achieved a photocatalytic degradation rate of 99.9% for methyl orange under visible light irradiation within 60 min. Moreover, the g-C 3 N 4 /MOF heterojunctions have also been found to be efficient in water splitting for hydrogen production. For instance, a g-C 3 N 4 /UiO-66 heterojunction achieved a hydrogen production rate of 1260 μmol h−1g−1 under visible light irradiation. The recent data on the advances in g-C 3 N 4 /MOFs heterojunctions demonstrate their enormous potential for practical applications in photocatalytic environmental remediation and energy production. [ABSTRACT FROM AUTHOR]

In this research work we report synthesis of g-C 3 N 4 /FeVO 4 (CI) and g-C 3 N 4 /FeVO 4 /Fe@NH 2 -Biochar (CIB) nano-hetero assemblies for removal of methyl paraben (MeP) and 2-cholrophenol (2-CP) via adsorption, photocatalysis and photo-ozonation. CI and CIB have been characterized by FT-IR, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV–Vis spectroscopy, photoluminescence (PL), vibrating sample magnetometry (VSM), Brauner-Emmet Teller surface area analyzer (BET). CIB shows good photocatalytic activity owing to higher specific area, nanosheet porous structure, stability, broader solar spectrum response and reduced charge carriers recombination. Fe@NH 2 -biochar facilitates the degradation via high adsorption capability due to reduced recombination, better charge separation, adsorption and acting of biochar as sink of electrons. The CIB photocatalytic system was tested under three experimental conditions for photodegradation of MeP and 2-CP; adsorption followed by photo-degradation (AP); simultaneous adsorption and photocatalysis (SAP); SAP + O 3 . An apparent synergism between adsorption, photocatalysis and photo-ozonation brings out excellent and promising results. 98.4% of MeP and 90.7% of CP degradation was achieved under simultaneous adsorption and photocatalysis in presence of CIB. The results were analyzed in terms of reaction kinetics, adsorption isotherms, scavenger effect, liquid chromatography-mass spectrometry (LC-MS), Total Organic Carbon (TOC) analysis and cytotoxicity analysis of treated water. An efficient TOC removal 74.2 & 73.9% for MeP and 2-CP were respectively achieved under SAP + O 3 +CIB photocatalysis system. Degradation pathways have been proposed for degradation of MeP and CP thorough photo-degradation and photo-ozonation. The cyto-toxicity studies on Human peripheral blood lymphocytes provide a reference for removal of noxious pollutants in real systems. This experimental work paves a way to design tuneable simple junctions for photocatalytic applications by utilizing various experimental protocols. [ABSTRACT FROM AUTHOR]

In this research work we report Gum-ghatti supported ZnSe-WO 3 nano-hetero-assembly for solar powered degradation of endocrine disruptor Bisphenol S (BPA). The photocatalyst was characterized by Scanning electron microscopy (SEM), High resolution transmission electron microscopy (HRTEM), Small area electron diffraction (SAED), X-Ray diffraction (XRD), Fourier transform infra red spectroscopy (FTIR), Photoluminescence (PL), Energy dispersive X-ray (EDX), UV–vis spectrophotometry and Brauner Emmet Teller surface area analyzer (BET). We achieve a Z-scheme photocatalyst (ZnSe-WO 3 ) with a higher charge flow and visible absorption. Gum ghatti acts as a superadsorbent and a sink for charge carriers. The removal of BPA has been studied under three experimental protocols where 99.5% removal was achieved by symbiose of photocatalysis-adsorption-ozonation in just 45 min hetero-assembly has a high surface area, stability and reduced carrier recombination. The results have been analyzed by scavenger effect, mass spectrometry, kinetics and total organic carbon (TOC) analysis. 49.4% of TOC was removed and COD was reduced to 16.7% after 2 h in symbiotic condition. From the band edges and scavenger effect it was inferred that superoxide radical anions are major attacking species. The work paves way for designing of novel photocatalysts with increasing biogenic quotient and higher efficiency. [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]

Extensive research is being done to develop multifunctional advanced new materials for high performance photocatalytic applications in the field of energy production and environmental detoxification, MXenes have emerged as promising materials for enhancing photocatalytic performance owing to their excellent mechanical properties, appropriate Fermi levels, and adjustability of chemical composition. Numerous experimental and theoretical research works implied that the dimensions of MXenes have a significant impact on their performance. For photocatalysis to thrive in the future, we must understand the current state of the art for MXene in different dimensions. Using MXene co-catalysts in widely used in photocatalytic applications such as CO 2 reduction, hydrogen production and organic pollutant oxidation, this study focuses on the most recent developments in MXenes based materials, structural modifications, innovations in reaction and material engineering. It has been reported that using 5 mg of CdS–MoS 2 -MXene researchers were able to generate as high as 9679 μmol/g/h hydrogen under visible light. The MXenes based heterojunction photocatalyst Co 3 O 4 /MXene was utilized to degrade 95% bisphenol A micro-pollutant in just 7 min. Numerous novel materials, their preparations and performances have been discussed. Depending upon the nature of MXene-based materials, the synthesis techniques and photocatalytic mechanism of MXenes as co-catalyst are also summarized. Finally, some final thoughts and prospects for developing highly efficient MXene-based photocatalysts are provided which will indeed motivate researchers to design novel hybrid materials based on MXenes for sustainable solutions to energy and pollution issues. [Display omitted] • MXenes as new interesting class of photocatalysts. • Composites and heterojunctions with 0D, 1D, 2D, 3D MXenes. • Variable and tunable optical band gaps. • Suitable for energy production and pollution mitigation. [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]

[Display omitted] • Novel Z-scheme Bi 7 O 9 I 3 /B 4 C heterojunction synthesized by hydrothermal route. • Antibiotic as sacrificial agent- H 2 evolution and antibiotic removal simultaneously. • Antibiotic degradation route and photocatalytic mechanism probed. • Waste to clean energy concept. The dual-function photocatalytic systems with a promising capability for hydrogen evolution and simultaneous pollutant degradation are surely a significant step towards waste-to-energy conversion goals. However, the performance of such photocatalysts is often limited by poor visible-light activity, charge separation and surface reverse reaction involving photogenerated electrons and radicals/intermediates. In this work, we report hydrothermal synthesis of novel Bi 7 O 9 I 3 /B 4 C (BIBC) heterojunction photocatalyst for advanced Norfloxacin antibiotic degradation with simultaneous hydrogen evolution under visible light. In particular, BIBC-30 heterojunction shows H 2 evolution rate of 812 μmol g−1h−1 with simultaneous 94.2% NFN removal which are much higher than bare B 4 C (∼6 times) and Bi 7 O 9 I 3 (∼4 times). Under oxic/aerobic conditions too, a high 456.3 μmol g−1h−1H 2 evolution with nearly complete norfloxacin degradation was achieved. The low band gap of Bi 7 O 9 I 3 and presence of metallic Bio extends the absorbance to NIR region and B 4 C enlarges the surface area of junction along with suppression of the back reaction. It was observed that BIBC heterojunction exhibits manifolds H 2 evolution rate with NFN as sacrificial agent (18.3% apparent quantum efficiency) is manifolds higher than pure water, methanol, triethanolamine and rhodamine B. An effective Z-scheme charge transfer facilitated by Bio is active in the intimately coupled heterojunction with suitably placed energy bands. This work shows that waste to energy conversion can be promisingly achieved by performing H 2 evolution and pollutant removal simultaneously. [ABSTRACT FROM AUTHOR]

• Novel Fe 3 O 4 -BiVO 4 /Cr 2 V 4 O 13 heterojunction fabricated. • High charge separation and interfacial charge transfer. • High performance removal of fluoxetine under visible light. • ●OH as active species -high potential band protection. • Fe 3 O 4 and Cr redox mediated Z-scheme mechanism. Hybrid heterojunction photocatalysts dramatically improve the pharmaceutical wastewater treatment potential. In this work, we report construction of novel Fe 3 O 4 -BiVO 4 /Cr 2 V 4 O 13 (FBC) with high interfacial transfer for visible and solar photo-degradation of fluoxetine (FX). Within 60 min of visible exposure, FBC removes 99.2% of FX and rate is ~ 8 times BiVO 4. The strongly coupled heterojunction leads high charge separation, interfacial charge transfer which attributes to the exceptional performance. Scavenging experiments and electron spin Resonance (ESR) probe suggest ●OH and ●O 2 – radicals as dominant species. The band structure and other experiments reveal a Z-scheme effective charge transfer is in action mediated by Fe 3 O 4. [ABSTRACT FROM AUTHOR]

In this work, a carbon quantum dots (CQDs) decorated dual Z-scheme CeO 2 /g-C 3 N 4 /V 2 O 5 heterojunction (CCGV) was rationally synthesized by simple hydrothermal method. The crystal structure, morphology, and optical properties of the photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectroscopy. CCGV catalyst shows high visible absorption, including near infra-red region and solar light via two-channel charge transfer (dual Z-scheme), reduced recombination, and up-conversion effect of CQDs. The heterojunction was used for visible assisted photo-reduction of carcinogenic hexavalent chromium ions (Cr(VI)) with a 99% reduction in 100 min without any sacrificial agent or hole scavenger. The reaction becomes more rapid with tartaric acid as a scavenger with a complete reduction in just 30 min under visible light. Photogenerated electrons are the dominant active species, followed by ●O 2 −, as revealed by the scavenging experiments. The use of sacrificial agents and scavengers suggests that photogenerated electrons were the dominant active species followed by ●O 2 − radicals. The electrochemical impedance spectroscopy and photoluminescence results confirm highly reduced recombination, high charge separation, and charge transfer capacity in the dual Z-scheme heterojunction. The conduction band edges of CeO 2 and V 2 O 5 (which are protected by the dual charge transfer) have an appropriate potential for the rapid reduction of hexavalent chromium. The XPS scan of the catalyst after separation shows the presence of Cr in the +3 oxidation state, suggesting complete photo-reduction. This study is promising for developing wide spectrum active simple heterojunction photocatalysts for pollutant removal with high efficiency. Image 1 • Dual Z-scheme CQDs @ CeO 2 /g-C 3 N 4 /V 2 O 5 heterojunction (CCGV) was successfully prepared. • CCGV junction shows efficient photoreduction of carcinogenic hexavalent chromium. • Visible, NIR and solar activity with high visible capture. • Mechanistic approach-Scavenging and Sacrificial agents. • Comparison between conventional and dual Z-scheme-high potential bands. [ABSTRACT FROM AUTHOR]

• Bio-inspired hybrid materials as photocatalysts. • Biopolymers as templates, supports, immobilisation substrates for photocatalysts. • Enzymes, peptides, proteins based materials-coupling biodegradation. • Greener synthesis of metal based photocatalysts-opportunities and developments. • Photocatalytic degradation of various pollutants by biomaterials-based catalysts. New materials tend to revolutionize scientific community and human race on a larger level. Scientists worldwide have not just been working on some wondrous materials with superior properties but have progressively focused on greener bio-inspired or bio-compatible materials for sustainable development. An increasing number of researchers have been working on using biomaterials as a part of photocatalysts for stability, bio-compatibility, generation of more reactive oxygen species and enhancement of optical absorption. In this review we have focussed on photocatalysts based on biopolymers, biochar, carbons, enzymes and proteins. This review presents various types of bio-inspired nanomaterials and their use as sustainable photocatalysts for degrading various venomous pollutants. The effect of pyrolysis temperature, temperature gradient, feedstock and synthetic route of biochar and carbon on the properties and final performance of derived photocatalysts has also been discussed. The increase in surface area, active adsorption sites, electron shuttling & reservoir properties, high visible absorption, charge separation and biocompatibility have also been elaborated. As far as photocatalytic performance is considered such bio-based photocatalysts are often questioned for their stability under such conditions and poor activity as compared to pure metal-based catalysts. These limitations can be overcome by choice of materials, modifications, new designing routes and coupling of biological methods and photocatalysis for removal of pollutants even from water from waste water treatment plants. Suitable modification to biomolecules as functionalisation has been reported for better adsorption of pollutants. The role of biomaterials in generation of reactive oxygen species, recombination suppression, interactions with pollutants, optical absorption, separation of charge carriers, shuttling and electron flow has also been elaborately explained. The concerns, challenges and future opportunities are also included in this review. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ti3+ self-doped Ti-Bi 2 WO 6 @ACB exhibits oxygen vacancies, OFGs, and defects. • Ti-Bi 2 WO 6 @ACB efficiently degraded high concentrations of CAP and disinfection. • Ultrasound enhances photocatalytic activity related to synergistic sonocatalysis. • The Ti-doping can generate more ROS, and ACB prevents TiO 2 /Bi 2 WO 6 agglomeration. • The degradation process of CAP is recorded, and six degradation paths are possible. A novel engineered biochar (ACB)-based Ti-doped Bi 2 WO 6 composite (Ti-Bi 2 WO 6 @ACB) was synthesized via a one-step hydrothermal reaction for the efficient degradation of chloramphenicol (CAP) and extensive environmental applications. Multiple characterization techniques, CAP degradation effects, total organic carbon (TOC) removal, effects of environmental factors, recycling tests, actual wastewater treatment, enhancement strategies, and disinfection effects were systematically evaluated. It was found that Ti-Bi 2 WO 6 @ACB is a Ti3+ self-doped TiO 2 /Bi 2 WO 6 /ACB ternary heterogeneous photocatalyst. The introduction of ACB and Ti doping enhanced the elemental composition, oxygen-containing functional groups, defect structure (oxygen vacancies), visible-light absorption, and active sites. Moreover, Ti-Bi 2 WO 6 @ACB effectively inhibited the recombination of photogenerated carriers. The removal efficiency of Ti-Bi 2 WO 6 @ACB for 50 mg⋅L−1 CAP was 92.44 % at 120 min of irradiation, and the TOC removal rate was 67.72 %, which was significantly higher than that of the control treatment. Ti-Bi 2 WO 6 @ACB is reusable and photostable, with approximately 99 % sterilization of Staphylococcus aureus and Escherichia coli within 10 min of light irradiation and 48 h of cultivation. The addition of H 2 O 2 , ultrasonication, heating, and blowing air in the system improved the photocatalytic efficiency. The ultrasound enhancement mechanisms are related to the effects of cavitation, microjets, and photocatalysis coupled with sonocatalysis. CAP degradation was dominated by OH, O 2 −, and h+. The doping of Ti3+/TiO 2 generated more defects and O 2 −, and the ACB acted as a carrier to prevent the agglomeration of TiO 2 and Bi 2 WO 6. Further, the degradation process of CAP was documented and the degradation pathways may include hydroxylation addition, methanol denaturation, substitution, C–N bond breaking, oxidation, hydrolysis, and decarboxylation reactions. The research presents fresh insights into the development of high-performance engineered biochar-based composite for environmental detoxification. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni 1-x Zn x Fe 2 O 4 inverse spinel ferrite photocatalyst prepared by combustion route. • Dopant determined CB shifting-higher thermodynamic O 2 − generation potential. • Superior photo-degradation of levofloxacin under visible and solar light. • Higher charge separation and transfer capacity-metal redox. • Suitable degradation pathway for levofloxacin proposed. Spinel ferrites with a compatible electronic band structure are always excellent candidates for photo-catalytic environmental detoxification employing visible light and solar energy. However, the potential is not harnessed to its fullest owing to unnerving charge carrier recombination. In this work, we report the synthesis of Ni 1-x Zn x Fe 2 O 4 (x = 0, 0.1, 0.3, & 0.5) mixed spinel ferrites via combustion route. As prepared samples were characterized for phase identification using X-ray diffraction (XRD) and Reitveld refined pattern confirms the formation of single phased cubic structure with a nano-metric crystallite size. The homogeneous distribution of grains and particles is evidenced by shape and size morphological studies. Raman spectroscopy reveals the presence of motion of oxygen in tetrahedral and octahedral voids. The dc electrical resistivity measured using the two probe method is found to be in the range of 107 to 108 Ω-cm. The optical band gap measured for all photo-catalysts resides at 2.11–2.53 eV. The ferrite photocatalyst exhibits high visible absorption, superior charge transfer capacity, and highly suppressed recombination as suggested by electrochemical impedance spectroscopy and photoluminescence results. The change in band structure with variable Zn content was monitored by shifting of conduction and valence bands. The photo-catalyst Ni 0.7 Zn 0.3 Fe 2 O 4 (N2) exhibited 96.8% levofloxacin (LEV) degradation in 90 min of visible light exposure. The effect of parameters such as pH, catalyst dosage, electrolytes and water matrix was analysed in detail. The photo-catalytic degradation rate was enhanced in the presence of persulfate and H 2 O 2. Furthermore, the high magnetic character of the catalysts aids in their retrieval post utilization in catalysis. In terms of band structure analysis, role of dopants, metal redox, and scavenging studies, a suitable photo-catalytic process was proposed. Degradation intermediates discovered by liquid chromatography–mass spectrometry analysis were also recommended as a pathway of degradation. These findings open up exciting possibilities for developing novel solar active photo-catalytic systems based on spinel ferrites for efficient environmental cleanup. [ABSTRACT FROM AUTHOR]

In recent times cost-effective advanced materials with dual applications in photocatalytic water treatment and electrochemical sensing have been explored and developed. Herein we report facile solution combustion synthesis of ZnO/Fe 2 O 3 (ZF) type-II heterojunction for electrochemical sensing of dopamine and visible assisted photocatalytic reduction of carcinogenic Cr(VI) into Cr(III). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to evaluate the compatibility of the electrodes for DA sensing. Furthermore, DPV curves revealed that ZF2 (ZnO: Fe 2 O 3 - 3:0.5) modified GCEs possessed 0.27 μM and 0.7 μM of LOD and LOQ with good linear range from 3 μM to 30 μM. Overall, reproducibility and interference studies confirm the efficient use of material for DA sensing. The junction ZF2 shows best performance with 88% Cr(VI) photo-reduction under visible light in 90 min and 100% reduction with tartaric acid as sacrificial agent (utilizing holes) in just 45 min. The effect of sacrificial agents and scavengers suggest the photogenerated electrons were major active species followed by ●O 2 −. The CB edges have enough potential for rapid reduction of hexavalent chromium under visible light and solar light. The photoluminescence and electrochemical impedance suggest lowered recombination, high charge separation and charge transfer capacity in the heterojunction. The transfer of electrons from conduction band of Fe 2 O 3 to that of ZnO having high enough negative potential to reduce Cr(VI), thus utilizing the CB potential of wide band gap ZnO for rapid visible photocatalysis. In addition shortcomings as low conductivity Fe 2 O 3 and high band gap of ZnO are both minimized in the junction. This study confirmed that popular semiconductors as ZnO and Fe 2 O 3 have enough potential in dual role as electrochemical sensors and visible photocatalysts with best performance by optimizing the conditions and ratios. Image 1 [ABSTRACT FROM AUTHOR]

The worldwide energy demand is steadily increasing and estimated to be doubled by the year 2050 due to a continuous hike in economies and population. A large part of the global energy requirement procures using traditional energy sources such as fossil fuels, which are non-renewable. Also, their excessive consumption imparts negative impacts on the environment by CO 2 , and CO emissions, which constantly increase the average global temperature. Therefore, the need for a more reliable, sustainable, inexpensive, renewable and environmentally-friendly form of energy is imperative. From these perspectives, hydrogen energy is emerging as one of the most promising alternatives to overcome rising energy demand with a zero-carbon footprint. Herein, various layered double hydroxides (LDH) nanocomposite owing to their attractive physicochemical properties and synergistic effect with other materials in the field of hydrogen production are reviewed. Why the class of LDHs materials is critical and their ideographic properties which make them promising materials in the field of water splitting via photocatalysis and electrocatalysis are also discussed. The synthetic methods of LDHs based nanocomposites fabrication are summarized. Various challenges and strategies from the viewpoint of a different method of hydrogen production through LDHs are reported. Additionally, multiple techniques like surface plasmon resonance (SPR), heterojunction formation, and doping with co-catalyst to increase the efficiency for photocatalytic hydrogen production are also presented. Hopefully, this review will help the readers explore highly efficient, inexpensive and stable LDH catalysts toward photocatalytic water splitting. • Current issues related with energy requirements and green energy sources. • Recent advancements in LDH based electrocatalysts and photocatalysts for water splitting. • Challenges in conventional photocatalysts based water splitting. • Strategies to enhance photocatalytic hydrogen evolution and oxygen evolution reactions. [ABSTRACT FROM AUTHOR]

In precedent work, nano-ZnO was supported on activated carbon or brick grain particles using simple co-precipitation method. Successful formation of ZnO-activated carbon (ZnO-AC) and ZnO-brick grain particle (ZnO-BGP) nanocomposites was ascertained by various spectral techniques. Scanning electron microscope (SEM) images revealed that ZnO particles were highly dispersed in activated carbon/brick grain particles. The size of ZnO-AC and ZnO-BGP was found to be 70 and 80 nm, respectively. Both ZnO-AC and ZnO-BGP exhibited excellent adsorption and photocatalytic activity for malachite green (MG) and congo red dye (CR) degradation. The adsorption data for MG and CR removal followed pseudo second order kinetic model. The adsorption capacity followed the order: ZnO-AC > ZnO-BGP > ZnO. The effect of adsorption on photocatalysis was explored under different reaction conditions. Simultaneous adsorption and photocatalysis (A + P) exhibited promoting effect on dye degradation. While adsorption followed by photocatalysis (A − P) had retarding effect on dye removal. ZnO-AC/A + P system emerged as highly efficient for MG and CR degradation. The rate of photodegradation followed pseudo first order kinetics. Using ZnO-AC/A + P system, 99 and 92% of COD removal was attainted for MG and CR degradation, respectively. The oxidative degradation mainly occurred through hydroxyl radicals. The prepared nanocomposites possessed higher recyclability and could be easily separated from solution by sedimentation. [ABSTRACT FROM AUTHOR]

• Novel Mg 0.5-x Cu x Zn 0.5 Fe 2 O 4 spinel ferrite prepared. • Dopant induced shifts in conduction bands-high potential. • High performance removal of carbamazepine under visible light. • ●O 2 – as active species. • High charge separation via metal redox cycle and dopants. Environmental friendly and robust Mg 0.5-x Cu x Zn 0.5 Fe 2 O 4 (x = 0, 0.01 & 0.02) nano-photocatalyst was prepared by facile solution combustion method for high performance photocatalytic removal of carbamazepine (CBZ). Mg 0.3 Cu 0.2 Zn 0.5 Fe 2 O 4 catalyst shows 94.3% degradation in 90 min visible exposure and 78.2% total organic carbon (TOC) removal. The Cu dopant driven conduction band shifting to more negative side leads to improved ●O 2 – formation supported by electron spin resonance (ESR) probe. The dopants and metal redox cycles lead to higher visible absorption and reduced recombination boosting the CBZ removal. The degradation pathway and photocatalytic mechanism is also predicted. [ABSTRACT FROM AUTHOR]

Fabricating magnetically recoverable solar-active photocatalysts with high performance capabilities for removal of recalcitrant and emerging pollutants has gained worldwide attention. Especially pharmaceutical pollutants as sulfonamides drugs which are now frequently detected in water systems are hard to remove because of their resistance to microbial and biological oxidation. This laboratory scale experiment presents synthesis of Mg substituted Zn nano-ferrite (Zn 1-x Mg x Fe 2 O 4) (x = 0, 0.2, 0.4) by facile modified sol-gel technique for sulfadiazine (SDZ) degradation. Effect of Mg doping on the zinc ferrite were investigated in this work which was analyzed by Transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction. The UV-diffuse reflectance spectroscopy studies reveal higher visible absorption extending to longer wavelengths. The VB of the ferrite catalyst shifts to 2.30 eV in substituted ferrite M2Z8 (x = 0.2) capable of hydroxyl radicals generation from H 2 O, which is difficult in parent ferrite without any Mg substitution. The electrochemical impedance spectroscopy and photo-current response analysis also reveal low impedance, higher charge flow and separation in case of M2Z8 catalyst which is reflected in the 99.1% SDZ degradation in 90 min with 73.2% total organic carbon removal in 120 min. Scavenging experiments confirm that hydroxyl radicals are main active species involved in degradation with Mg2+ and Fe3+ catalyzing the generation of hydroxyl radicals by undergoing redox process. LC-MS and TOC analysis confirm the drug mineralization. The work aims at fabricating solar active tunable photocatalysts for photo-degradation and mineralization of pharmaceutical pollutants using cost-effective approach. Unlabelled Image • Magnetic solar active nano-Zn 1-x Mg x Fe 2 O 4 photocatalyst-facile synthesis • Mg enhances the degradation rate and radical generation. • Shifting of CB and VB-Changed dynamics of radical generation • High performance degradation of sulfadiazine drug-visible and solar light • Mechanism elucidation, high mineralization and magnetic recovery [ABSTRACT FROM AUTHOR]

Herein we report a greener microwave method for fabrication of La/Cu/Zr/carbon quantum dots trimetallic nanocomposites(La/Cu/Zr/CQDs TNCs). The structural aspects and chemical nature of the TNCs were considered using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical band property of the trimetallic nanocomposites was examined using UV–vis spectroscopy. The adsorptional versus photocatalytic activity of the La/Cu/Zr/CQDs TNCs was investigated for the removal of a persistent organic pollutant i.e., malachite green dye and ampicillin antibiotic, under visible light irradiation. Overall, the current approach relates to green chemistry principles for fabrication La/Cu/Zr/CQDs trimetallic nanocomposites which hold promise for the development of surprisingly proficient adsorptional-photocatalytic systems. It has been observed that 96% ampicillin antibiotic and 86% of malachite green were degraded in 4 h of photoirridation under adsorption in dark followed by photocatalysis and coupled adsorptional/photocatalysis process. [ABSTRACT FROM AUTHOR]

The photocatalytic degradation of methyl orange (MO) and congo red (CR) dyes from aqueous solution have been attempted using chitosan-g-poly(acrylamide)/ZnS (ChPA/ZS) nanocomposite materials. Nanocomposites were successfully prepared in the aqueous solution through microwave radiations. Band gap property of composite was studied using UV–vis spectrophotometer. The ChPA/ZS nanocomposite was characterized by various techniques. The photocatalytic activity of ChPA/ZS was evaluated for methyl orange and congo red dyes degradation in aqueous solution under simulated solar irradiation. The degradation of dyes was recorded higher for ChPA/ZS nanocomposite. After 2 h of irradiation, 75% of congo red dye was degraded and 69% of methyl orange was degraded after 4 h of simulated solar irradiation. ChPA/ZS composite showed a higher rate of dye degradation owing to outstanding adsorbing properties of cross linked polyacrylamide. [ABSTRACT FROM AUTHOR]