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The activation of the chemically inert basal plane of 2H-MoS2 can be achieved by inducing pores and generating vacancies by several other techniques toward enhanced electrocatalytic HER activity.

Enhanced photocatalytic hydrogen evolution on 30-1T/2H-MoS2 with a higher concentration of the 1T phase was achieved due to the higher availability of electrons and dense active sites after the incorporation of the 1T phase in 2H-MoS2.

Fossil fuels as a double-edged sword are essential to daily life. However, the depletion of fossil fuel reservoirs has increased the search for alternative renewable energy sources to procure a more sustainable society. Accordingly, energy production through water splitting, CO2 reduction and N2 reduction via photocatalytic and electrocatalytic pathways is being contemplated as a greener methodology with zero environmental pollution. Owing to their atomic-level thickness, two-dimensional (2D) semiconductor catalysts have triggered the reawakening of interest in the field of energy and environmental applications. Among them, following the unconventional properties of graphene, 2D MoS2 has been widely investigated due to its outstanding optical and electronic properties. However, the photo/electrocatalytic performance of 2D-MoS2 is still unsatisfactory due to its low charge carrier density. Recently, the development of 2D/2D heterojunctions has evoked interdisciplinary research fascination in the scientific community, which can mitigate the shortcomings associated with 2D-MoS2. Following the recent research trends, the present review covers the recent findings and key aspects on the synthetic methods, fundamental properties and practical applications of semiconducting 2D-MoS2 and its heterostructures with other 2D materials such as g-C3N4, graphene, CdS, TiO2, MXene, black phosphorous, and boron nitride. Besides, this review details the viable application of these materials in the area of hydrogen energy production via the H2O splitting reaction, N2 fixation to NH3 formation and CO2 reduction to different value-added hydrocarbons and alcohol products through both photocatalysis and electrocatalysis. The crucial role of the interface together with the charge separation principle between two individual 2D structures towards achieving satisfactory activity for various applications is presented. Overall, the current studies provide a snapshot of the recent breakthroughs in the development of various 2D/2D-based catalysts in the field of energy production, delivering opportunities for future research.

Nowadays the blossoming interest has been paid for efficient hydrogen production which is promising candidates towards clean energy and a sustainable environment. With regards visible light photocatalysis system satisfying the realms of energy demands which has witnessed an environmental impact. On behalf of this, the choice of a suitable photocatalytic system becoming an urgent issue. Inspired by the advantages of p-n heterojunction photocatalytic system over the above obstacles, herein we have demonstrated MoS2/ZnIn2S4 system as the p-n heterojunction composite photocatalyst by adopting a one-step simple hydrothermal method. The products obtained were summarized through various physicochemical as well as electrochemical characterizations. From the Mott-Schottky analysis, the p and n characteristics of MoS2 and ZnIn2S4 have been proved. The photocatalytic activity of the as-obtained photocatalysts has been tested towards H2 evolution under visible light irradiation. From the experiment, it has been revealed that with only 1% MoS2 content, MoS2/ZnIn2S4 heterojunction photocatalysts exhibited a hydrogen evolution rate of 320.2 μmol/h which is 10 times higher than the neat ZnIn2S4 (32 μmol/h) respectively. The enhanced photocatalytic activity is due to the formation of a space charge region between the interfacial region of two components via the hydrothermal technique, which leads to an enhancement in the charge separation through the p–n heterojunction and thus modulating the photocatalytic activity.

The development of effective and low cost-efficient strategies for energy storage and conversions as well as an eco-friendly environment to sustain is an important current issue. Over past few years, the concept of graphene has triggered research on various 2D materials, especially single as well as few-layered transition metal dichalcogenides. Owing to its extraordinary physicochemical properties and outstanding electronic features, MoS2 is a promising and benchmark material. In comparison to semiconducting 2H-MoS2 exhibiting active sites only on edges, the metallic 1T MoS2 possesses more electrochemically active sites (both on edges and basal surfaces), enlarged interlayer distance, high electronic conductivity, and chemical activity but has stabilization issues. In the 1T/2H-MoS2 mixed-phase heterostructure, where partial transformation occurs from the 2H to 1T phase, the kinetic barrier decreases and more electron transfer occurs, providing an increased number of active sites. In this case, the metastable 1T phase is stabilized due to the interaction of the 2H phase, thereby greatly boosting its catalytic activity. This review gives a comprehensive overview on the structure and various approaches for the fabrication of 1T/2H-MoS2. It also summarizes applications for energy conversion, storage, and pollutant abatement including hydrogen evolution via electro/photocatalysis, supercapacitors, lithium-ion batteries, lithium–sulfur batteries, as well as organic and inorganic pollutant degradation.

Hydrogen evolution from water splitting by means of a photocatalytic approach is an ideal future energy source and free of fossil reserves, in contrary photocatalytic O2 evolution remains a bottleneck due to high over potential and low efficiency. For reasonable use of solar light, photocatalysts must be sufficiently stable and efficient toward harvesting of sunlight from both theoretical and practical viewpoints. In this regard, here we have prepared MoS2-modified UiO-66-NH2 MOF through a facile hydrothermal technique and evaluated its efficiency toward photocatalytic H2 and O2 evolution by water splitting in the presence of sacrificial agents. A couple of similar type of analyses have been studied previously; however, this analysis represents a diverse scientific approach on the basis of interfacial contact toward reveal the actual potential of nanoflakes MoS2 as well as UiO-66-NH2. In this regard the as-synthesized photocatalyst was well-characterized by XRD, FTIR, UV-vis diffuse reflectance spectra, FESEM, HRTEM, XPS, and BET analysis techniques, which provide sufficient evidence toward successful synthesis of the pristine materials and efficacious anchorage of MoS2 on the active surface of UiO-66-NH2 by the ionic interaction between Zr-O and S/Mo. Among the synthesized photocatalysts (3 wt %) MoS2/UiO-66-NH2 shows the optimum outcome toward H2 and O2 evolution, i.e., 512.9 μmol/h (4.37 times greater than bare UiO-66-NH2) and 263.6 μmol/h (4.25 and 11.32 times greater than bare UiO-66-NH2 and MoS2, respectively). The superior performance obtained by the composite is due to the synergistic effect of pristine UiO-66-NH2 and MoS2 which proceeds through a type-II interband alignment for the facile channelization of excitons. This investigation will bestow a beneficial blue-print to construct challenging photocatalysts and to find out the paramount performance toward photocatalytic water redox reaction.

Perovskite type materials have high potential photocatalytic application towards both hydrogen energy generation and organic dye degradation due to their high stability and good reusability. Here, it is the first analysis of photocatalytic degradation of RhB and hydrogen energy evolution under visible light over MoS2/LaFeO3 nanocomposite. The physicochemical properties of the materials were characterized using a range of techniques such as XRD, TEM, XPS, FTIR, PL, photocurrent, etc. The optical properties of the nanocomposite show good absorption in UV-Vis spectra as compared to the bare LaFeO3. In this study, MoS2/LaFeO3 nanocomposite was synthesized through single step in situ hydrothermal processes with a narrow bandgap, enhanced photocatalytic application under visible light. This novel MoS2/LaFeO3 nanocomposite is an efficient and promising photocatalyst for both hydrogen energy evolution and organic dye degradation.

Developing effective and simple one-pot synthetic strategies regarding the formation of heterojunction photocatalytic semiconductors remains an intense challenge in research pursuits. Further scheming of the p-n heterojunction has sustained renewed interest in catalysis, photocatalysis, energy storage, and conversion because they easily accelerate the bulk charge separation efficiency. Thus we have successfully designed a Au-MoS2/ZnIn2S4 heterojunction photocatalyst for the first time by adopting a simple one-pot hydrothermal technique, followed by a deposition-precipitation method. By adjusting the mole ratio of Mo with that of Zn and In precursors, we have fabricated a MoS2/ZnIn2S4 p-n heterojunction photocatalyst, and the established p-n heterojunction between MoS2 and ZnIn2S4 is demonstrated by various physicochemical and morphological characterizations. An interfacial junction is created between MoS2 and ZnIn2S4 at the depletion region via an in situ formation mechanism, leading to the enhancement of the charge separation through the p-n heterojunction and thus improving the photocatalytic activity. Moreover, the photocatalytic activity is projected to further improve by the incorporation of Au nanodots on the surface of MoS2/ZnIn2S4 photocatalysts. The increase in activity is due to the generation and participation of a large number of direct-electron-transfer-induced hot electrons in the photochemical reaction. From the experimental results, Au-MoS2/ZnIn2S4 heterojunction photocatalysts with only 1% MoS2 and 1% Au loading content displayed a 561.25 μmol/h H2 evolution rate and 84% degradation of phenol, which are nearly 15 and 6 times higher than those neat ZnIn2S4. In addition Au-MoS2/ZnIn2S4 photocatalysts exhibit a photocurrent density of ∼2.56 mAcm-2, which is nearly 2.4 times higher than that of the MoS2/ZnIn2S4 heterojunction photocatalyst. This exertion represents the synergetic enhancement of photocatalytic activity through the p-n heterojunction as well as the hot-electron participation by the metal nanocatalyst, which is an inspiration for developing efficient photocatalysts.

Designing of an efficient heterostructure photocatalyst for photocatalytic organic pollutant removal and H2 production has been a subject of rigorous research intended to solve the related environmental aggravation and enormous energy crises. Z-scheme-based charge-transfer dynamics in a p-n heterostructure could significantly replicate the inherent power of natural photosynthesis, which is the key point to affect the transportation of photoinduced exciton pairs. In this finding, a series of p-type MoS2 loaded with n-type NiFe-layered double hydroxide (LDH) forming a heterostructure MoS2/NiFe LDH were designed by electrostatic self-assembled chemistry and an in situ hydrothermal strategy for photocatalytic rhodamine B (RhB) dye degradation and H2 production. The creation of p-n heterojunctions of type-II and Z-scheme mode of charge transfer modified the optical and electronic property of the as-synthesized MSLDH3, thereafter promoting the generation, separation, and migration of photoinduced electron-hole pairs. The as-synthesized MSLDH3 showed superior photocatalytic activities in degradation of RhB with H2 evolution, which was enhanced by 3- and 4.5-fold and 10.9 and 19.2 times higher than that of NiFe LDH and MoS2, respectively. Last but not the least, heterostructure MSLDH3 possesses practical stability for its resultant enhanced photocatalytic activity with recyclability for everyday life.

The abolition of environmental pollutants and production of hydrogen (H2) from water using a heterogeneous photocatalyst is a demanding science of the current scenario to solve the increasing environmental pollution and worldwide energy catastrophe in modern life. To validate this purpose, the design of low-cost and durable semiconductor-based photocatalysts with great light absorption capacity becomes the most challenging issue for researchers. Regarding this, herein the phosphotungstic acid (HPW)-anchored Zr6O4(OH)4(BDC)6 (UiO-66) metal-organic framework (MOF), i.e., HPW@UiO-66, has been prepared by a hydrothermal method and is efficient, stable, and capable of harvesting solar energy toward the degradation of tetracycline hydrochloride (TCH) and H2 production in the presence of a sacrificial donor. The ionic interaction between HPW and UiO-66 plays a key role toward the photostability and charge-transfer mechanism of the composite and is well characterized with X-ray diffraction, UV diffuse-reflectance spectroscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. A total of 30 wt % HPW@UiO-66 shows a maximum degradation of about 87.24% of a 20 ppm TCH solution in 60 min of solar-light irradiation and about 353.89 μmol/h of H2 production. The conduction- and valence-band potentials are well characterized with Mott-Schottky measurement and a delay charge recombination process through electrochemical impedance spectroscopy. The proposed mediator-free Z-scheme-oriented electron-hole migration route is well supported by photoluminescence, and the scavenger test well explains the better charge-carrier separation and high catalytic performance of the prepared composite. This research will bestow an advantageous blueprint to fabricate novel and challenging photocatalysts toward the photocatalytic treatment of environmental pollutants and H2 evolution.

Due to the enormous demand for effective conversion of solar energy and large-scale hydrogen production, cost-effective and long-lasting photocatalysts are believed to be necessary for global produ...

Herein, a novel Cu-MoO3/g-C3N4 hybrid nanocomposite was successfully synthesized by a two-step strategy of one-pot pyrolysis followed by the impregnation method. The structure, phase, morphology and electronic environment of MoO3, g-C3N4 and Cu in the composite were determined by various characterization methods. The oxygen vacancies of MoO3 were ascertained by UV-DRS, Raman, and XPS analysis. The formation of the heterostructure was characterised by electrochemical measurements. The photocatalytic performance of the composite was investigated by the water reduction reaction and the reduction of an important inorganic pollutant, Cr(vi). In the presence of Cu NPs, the H2 evolution of the MoO3/g-C3N4 hybrid was found to be 652 μmol h-1 with an apparent energy conversion efficiency of 13.46%, and up to 95% of Cr(vi) was reduced using citric acid as a hole scavenger. The remarkably enhanced photocatalytic performance was attributed to the combined effect of the double Z-scheme mechanism and defective MoO3. The in situ formation process of the MoO3/g-C3N4 hybrid followed a direct Z-scheme charge transfer by generating a great number of defects at the solid-solid interface, similar to that of a conductor, and offered low electrical resistance, whereas loading of Cu NPs built up an indirect Z-scheme charge transfer to establish the double Z-scheme charge transfer mechanism. This hybrid material produces a photocurrent density of 12.1 mA cm-2, in good agreement with the photocatalytic activity. This study highlights the facilitation effect of MoO3 due to oxygen vacancies and charge transfer through the double Z-scheme mechanism to open up a new window in the field of 2D nanostructured photocatalytic materials.

In terms of solar hydrogen production, semiconductor-based photocatalysts via p–n heterojunctions play a key role in enhancing future hydrogen reservoir. The present work focuses on the successful synthesis and characterization of a novel p-MoS2/n-CeO2 heterojunction photocatalyst for excellent performance toward solar hydrogen production. The synthesis involves a simple in situ hydrothermal process by varying the wt % of MoS2. The various characterization techniques support the uniform distribution of CeO2 on the surface of crumpled MoS2 nanosheets, and the formation of p–n heterojunction is further confirmed by transmission electron microscopy and Mott–Schottky analysis. Throughout the experiment, it is demonstrated that 2 wt % MoS2 in the MoS2/CeO2 heterojunction photocatalyst exhibits the highest rate of hydrogen evolution with a photocurrent density of 721 μA cm–2. The enhanced photocatalytic activity is ascribed to the formation of the p–n heterojunction that provides an internal electric field to facilitate the photogenerated charge separation and transfer.

Among various renewable energy projects, harvestation of clean solar energy through semiconductor-based photocatalysis is now emerging as a feasible technology and has gained considerable interdisciplinary attention for its diversified potential in energy and environmental applications. Until now, although a good number of photocatalytic materials were reported, g-C3N4 is found to be a promising material in a variety of applications. To introduce desirable electronic properties and more number of surface active sites, designing of nanoporous g-C3N4 has been recognized as one of the most agreeable avenues to extend its potential applications. In nanoporous g-C3N4 network, the highly interconnected pores render the material with high surface area, offer numerous pathways for mass transport and multiple reflection of incident light, and favor strong adsorption at the active sites. Here, we have highlighted how further control over porosity and morphology can be achieved by using different templates during formation. Large available surface not only absorbs the organic/inorganic pollutants effectively by offering more number of active sites but also prevents aggregation of particles by accelerating diffusion kinetics. This chapter mainly focused on various types of templates used for the preparation of porous g-C3N4 and its applications in detail with special reference to dye degradation, reduction of hexavalent Cr, and reduction of CO2 and for the evolution of H2 photocatalytically.

The abolition of environmental pollutants and production of hydrogen (H

Due to the enormous demand for effective conversion of solar energy and large-scale hydrogen production, cost-effective and long-lasting photocatalysts are believed to be necessary for global production of sustainable and clean hydrogen fuel. Robust and highly efficient p-n heterojunction photocatalysts have a striking ability to enhance light-harvesting capacity and retard the recombination of photoexcitons. A series of p-MoS