It is a well‐known fact that the pronounced photogenerated charge recombination and poor light absorption are the main bottlenecks of photocatalysis applications. The conventional approaches to ...address these problems involve bandgap engineering and suppression of charge recombination after light irradiation, which results in an enhancement in the photocatalytic performance of the materials. However, the most essential aspect of surface modification to engineer active sites on the catalyst surface is generally not given much importance. Contrary to this, defect engineering is another approach by which the optical, charge separation, and surface properties of the photocatalytic materials can be tuned. In this review article, the effect of the introduction of vacancies on the photocatalytic properties of selected semiconductor materials, viz., metal oxides, perovskite oxides, metal sulfides, oxyhalides, and nitrides is comprehensively summarized. The engineering of vacancies in these materials not only improves their optical and charge transfer properties but also affects the surface properties, which are helpful in the adsorption of the reactants on catalyst surface. Herein, photocatalytic hydrogen evolution and nitrogen fixation applications of vacancy engineered materials are discussed in detail along with the current trends, scalability requirements, and rigorous experimental protocols.
Vacancies in materials can control their optical, charge separation, and surface properties. Herein, the recent progress in the vacancy engineered materials for photocatalytic H2 and NH3 production is reviewed along with their scalability requirements. The vacancy engineered materials provide active catalytic sites for the H2O and N2 molecules and also control their adsorption, dissociation, and subsequent reduction.
Transition metal phosphides (TMP) posses unique physiochemical, geometrical, and electronic properties, which can be exploited for different catalytic applications, such as photocatalysis, ...electrocatalysis, organic catalysis, etc. Among others, the use of TMP for organic catalysis is less explored and still facing many complex challenges, which necessitate the development of sustainable catalytic reaction protocols demonstrating high selectivity and yield of the desired molecules of high significance. In this regard, the controlled synthesis of TMP‐based catalysts and thorough investigations of underlying reaction mechanisms can provide deeper insights toward practical achievement of desired applications. This review aims at providing a comprehensive analysis on the recent advancements in the synthetic strategies for the tailored and tunable engineering of structural, geometrical, and electronic properties of TMP. In addition, their unprecedented catalytic potential toward different organic transformation reactions is succinctly summarized and critically analyzed. Finally, a rational perspective on future opportunities and challenges in the emerging field of organic catalysis is provided. On the account of the recent achievements accomplished in organic synthesis using TMP, it is highly anticipated that the use of TMP combined with advanced innovative technologies and methodologies can pave the way toward large scale realization of organic catalysis.
This review aims to draw a comprehensive picture on the recent advancements in the synthesis strategies for modulating the physiochemical, geometrical, and electronic properties of transition metal phosphides and exploration of their unprecedented catalytic potential toward different organic transformation reactions.
Maximum utilization of the full solar spectrum has been considered as a holy grail in the field of photocatalysis and has emerged important in the recent years, as the world needs to move towards ...renewable energy sources and also to maintain environmental health. In the search for a sustainable solution, we have come up with a strategic combination of materials, which can be active under all the three regions, namely ultraviolet (UV), visible and near infrared (NIR) of the sunlight. Specifically, we have developed a series of nanocomposites comprising of two dimensional nanosheets of zinc oxide (ZnO) and graphitic carbon nitride (GCN), and successfully coupled them with upconversion nanoparticles (UCNP). These nanocomposites have been successfully utilized for the photocatalytic chromium (Cr(VI)) reduction. The prepared nanocomposites exhibit an excellent photocatalytic activity toward reduction of Cr(VI) under different light region. A plausible mechanism for the photocatalytic process has been proposed based on the detailed study. This work is expected to pave way for the strategic design and development of many photocatalytic systems, which can utilize sunlight to the maximum extent.
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•ZnO-gC3N4 nanosheet heterojunctions decorated with upconversion nanoparticles.•Photocatalysts with wide solar spectrum activity all UV, visible and NIR irradiations.•Excellent photocatalytic activity toward reduction of toxic Cr(VI) to Cr(III) species.•Pave way for strategic design and development of many photocatalytic systems.
Plasmonic photocatalysis has emerged as a prominent and growing field. It enables the efficient use of sunlight as an abundant and renewable energy source to drive a myriad of chemical reactions. For ...instance, plasmonic photocatalysis in materials comprising TiO2 and plasmonic nanoparticles (NPs) enables effective charge carrier separation and the tuning of optical response to longer wavelength regions (visible and near infrared). In fact, TiO2‐based materials and plasmonic effects are at the forefront of heterogeneous photocatalysis, having applications in energy conversion, production of liquid fuels, wastewater treatment, nitrogen fixation, and organic synthesis. This review aims to comprehensively summarize the fundamentals and to provide the guidelines for future work in the field of TiO2‐based plasmonic photocatalysis comprising the above‐mentioned applications. The concepts and state‐of‐the‐art description of important parameters including the formation of Schottky junctions, hot electron generation and transfer, near field electromagnetic enhancement, plasmon resonance energy transfer, scattering, and photothermal heating effects have been covered in this review. Synthetic approaches and the effect of various physicochemical parameters in plasmon‐mediated TiO2‐based materials on performances are discussed. It is envisioned that this review may inspire and provide insights into the rational development of the next generation of TiO2‐based plasmonic photocatalysts with target performances and enhanced selectivities.
While photocatalysis has been focused on TiO2‐based materials, the harvesting of plasmonic effects has emerged as an efficient strategy to enhance photocatalytic performances. Therefore, the combination of TiO2 with plasmonic nanoparticles has attracted massive attention. This review covers the fundamentals, recent advances, and representative examples, and provides future guidelines in the field of TiO2‐based plasmonic photocatalysis toward various important molecular transformations.
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•V2CTx and E-V2CTx were prepared by chemical etching and exfoliation of V2AlC.•E-V2CTx shows selective adsorption of organic dyes.•V2AlC and V2CTx shows selectivity in degradation of ...organic dyes and pharmaceutical drugs.•Catalysts show remarkable reusability in oxidative degradation of contaminants.
The search of expeditious materials for selective removal of residual contaminants, is an imperative task to the scientific community. In this work, we report the use of vanadium carbide MXenes, for the first time in (i) selective separation of organic dyes, (ii) degradation of pharmaceutical drugs and (iii) degradation of organic dyes. In particular, the exfoliated vanadium carbide (E-V2CTx) MXene shows remarkable selective adsorption of methylene blue dye (within 20 min) in a mixture of different organic dyes. The etched vanadium carbide (V2CTx) MXene shows excellent activity in selective degradation of pharmaceutical drugs (within 2 min) whereas V2AlC MAX phase shows remarkable activity in selective degradation of organic dyes (within 8 min) through advanced oxidation processes. The material shows an adsorption capacity of 16 mg L-1 within 20 min, with an initial concentration of 20 mg L-1. The degradation pathways were analyzed for the degradation of pharmaceutical drugs as well as organic dyes. The materials show remarkable reusability for multiple cycles in oxidative degradation of contaminants. This work provides a path for the design and development of efficient vanadium carbide MXene based materials for wastewater remediation.
In the pursuit towards the use of sunlight as a sustainable source for energy generation and environmental remediation, photocatalytic water splitting and photocatalytic pollutant degradation have ...recently gained significant importance. Research in this field is aimed at solving the global energy crisis and environmental issues in an ecologically-friendly way by using two of the most abundant natural resources, namely sunlight and water. Over the past few years, carbon-based nanocomposites, particularly graphene and graphitic carbon nitride, have attracted much attention as interesting materials in this field. Due to their unique chemical and physical properties, carbon-based nanocomposites have made a substantial contribution towards the generation of clean, renewable and viable forms of energy from light-based water splitting and pollutant removal. This review article provides a comprehensive overview of the recent research progress in the field of energy generation and environmental remediation using two-dimensional carbon-based nanocomposites. It begins with a brief introduction to the field, basic principles of photocatalytic water splitting for energy generation and environmental remediation, followed by the properties of carbon-based nanocomposites. Then, the development of various graphene-based nanocomposites for the above-mentioned applications is presented, wherein graphene plays different roles, including electron acceptor/transporter, cocatalyst, photocatalyst and photosensitizer. Subsequently, the development of different graphitic carbon nitride-based nanocomposites as photocatalysts for energy and environmental applications is discussed in detail. This review concludes by highlighting the advantages and challenges involved in the use of two-dimensional carbon-based nanocomposites for photocatalysis. Finally, the future perspectives of research in this field are also briefly mentioned.
Photocatalytic materials for photocatalysis is recently proposed as a promising strategy to address environmental remediation. Metal-free graphitic carbon nitride (g-C3N4), is an emerging ...photocatalyst in sulfate radical based advanced oxidation processes. The solar-driven electronic excitations in g-C3N4 are capable of peroxo (O‒O) bond dissociation in peroxymonosulfate/peroxydisulfate (PMS/PDS) and oxidants to generate reactive free radicals, namely SO4•− and OH• in addition to O2•− radical. The synergistic mechanism of g-C3N4 mediated PMS/PDS photocatalytic activation, could ensure the generation of OH• radicals to overcome the low reductive potential of g-C3N4 and fastens the degradation reaction rate. This article reviews recent work on heterojunction formation (type-II heterojunction and direct Z-scheme) to achieve the bandgap for extended visible light absorption and improved charge carrier separation for efficient photocatalytic efficiency. Focus is placed on the fundamental mechanistic routes followed for PMS/PDS photocatalytic activation over g-C3N4-based photocatalysts. A particular emphasis is given to the factors influencing the PMS/PDS photocatalytic activation mechanism and the contribution of SO4•− and OH• radicals that are not thoroughly investigated and require further studies. Concluding perspectives on the challenges and opportunities to design highly efficient persulfate-activated g-C3N4 based photocatalysts toward environmental remediation are also intensively highlighted.
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•Advantages of peroxymonosulfate/peroxydisulfate (PMS/PDS) photocatalytic activation are mentioned.•The synergistic heterojunction effect on PMS/PDS over g-C3N4-based photocatalysts is evaluated.•The role of sulfate (SO4•−) radicals for pollutant degradation application are elaborated.•Challenges and future prospects of the photocatalytic activation PMS/PDS are proposed.
A novel graphitic carbon nitride (g-C3N4)–CaTiO3 (CTCN) organic–inorganic heterojunction photocatalyst was synthesized by a facile mixing method, resulting in the deposition of CaTiO3 (CT) nanoflakes ...onto the surface of g-C3N4 nanosheets. The photocatalytic activity of the as-synthesized heterojunction (along with the controls) was evaluated by studying the degradation of an aqueous solution of rhodamine B (RhB) under UV, visible and natural sunlight irradiation. The CTCN heterojunction with 1:1 ratio of g-C3N4/CT showed the highest photocatalytic activity under sunlight irradiation and was also demonstrated to be effective for the degradation of a colorless, non-photosensitizing pollutant, bisphenol A (BPA). The superior photocatalytic performance of the CTCN heterojunction could be attributed to the appropriate band positions, close interfacial contact between the constituents and extended light absorption (both UV and visible region), all of which greatly facilitate the transfer of photogenerated charges across the heterojunction and inhibit their fast recombination. In addition, the two-dimensional (2D) morphology of g-C3N4nanosheets and CT nanoflakes provides enough reaction sites due to their larger surface area and enhances the overall photocatalytic activity. Furthermore, the active species trapping experiments validate the major role played by superoxide radicals (O2 −•) in the degradation of pollutants. Based on scavenger studies and theoretically calculated band positions, a plausible mechanism for the photocatalytic degradation of pollutants has been proposed and discussed.
Utilizing waste lignocellulosic biomass to synthesize biofuel precursors constructs an important way to solve the current energy crisis. In this work, we have prepared a sulfonated acid catalyst from ...pine needles derived biochar using chlorosulfonic acid for conversion of fructose to levulinic acid and levulinic acid to ethyl levulinate. In the best optimized conditions, sulfonated biochar as a catalyst exhibited excellent catalytic activity for the fructose conversion to levulinic acid and its esterification to ethyl levulinate with yield 33% and 97%.
•Biochar (BC) has been prepared from pine needles biomass waste.•Sulfonation of biochar (SBC) results in Brønsted acidic sites.•SBC has been used as catalyst for the conversion of fructose to levulinic acid.•Ethyl levulinate has been synthesized from levulinic acid in 97% yield.
The sunlight driven photocatalytic activity of semiconductor based nanostructures has attracted widespread attention in recent years for environmental remediation and energy applications. Numerous ...good semiconductors, including ZnO, have wide bandgaps and are active only under ultraviolet light, which comprises only 5% of sunlight. Several strategies, such as noble metal doping, non-metal doping,
etc.
, have been adapted to make ZnO heterostructures active in the visible light region. One other strategy is to dope ZnO with narrow bandgap semiconductors like MoS
2
. In addition, co-doping with graphene as a support material can enhance pollutant adsorption and can aid in electron transport, thereby leading to pollutant degradation. In this work, we report our investigations on the synergetic role played by MoS
2
-RGO doping to enhance the photocatalytic activity of ZnO nanoparticles, and especially to utilize both the UV and visible light regions of the solar spectrum. The ZnO-MoS
2
-RGO heterostructures, having different levels of doping, were prepared by a facile hydrothermal method and were characterized thoroughly using different spectroscopy and microscopy techniques. The photocatalytic performance was evaluated by studying the degradation of methylene blue, a model dye pollutant, and carbendazim, a colorless hazardous fungicide, under natural sunlight irradiation. The results reveal that doping of ZnO nanoparticles with 1 wt% MoS
2
-RGO was optimal and possessed the highest photocatalytic activity among all the investigated samples. A possible mechanism is proposed and discussed in detail.
In this work, we report on the synergetic role played by MoS
2
-RGO doping in enhancing the photocatalytic activity of ZnO nanoparticles, especially in utilizing both the UV and the visible light regions of the solar spectrum.
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