The energy from fossil fuels has been recognized as a main factor of global warming and environmental pollution. Therefore, there is an urgent need to replace fossil fuels with clean, cost-effective, long-lasting, and environmentally friendly fuel to solve the future energy crisis of the world. Therefore, the development of clean, sustainable, and renewable energy sources is a prime concern. In this regard, solar energy-driven hydrogen production is considered as an overriding opening for renewable and green energy by virtue of its high energy efficiency, high energy density, and non-toxicity along with zero emissions. Water splitting is a promising technology for producing hydrogen, which represents a potentially and environmentally clean fuel. Water splitting is a widely known process for hydrogen production using different techniques and materials. Among different techniques of water splitting, electrocatalytic and photocatalytic water splitting using semiconductor materials have been considered as the most scalable and cost-effective approaches for the commercial production of sustainable hydrogen. In order to achieve a high yield of hydrogen from these processes, obtaining a suitable, efficient, and stable catalyst is a significant factor. Among the different types of semiconductor catalysts, tungsten disulfide (WS2) has been widely utilized as a catalytic active material for the water-splitting process, owing to its layered 2D structure and its interesting chemical, physical, and structural properties. However, WS2 suffers from some disadvantages that limit its performance in catalytic water splitting. Among the various techniques and strategies that have been constructed to overcome the limitations of WS2 is heterostructure construction. In this process, WS2 is coupled with another semiconducting material in order to facilitate the charge transfer and prevent the charge recombination, which will enhance the catalytic performance. This review aims to summarize the recent studies and findings on WS2 and its heterostructures as a catalyst in the electrocatalytic and photocatalytic water-splitting processes.

Water pollution is one of the most serious environmental issues globally due to its harmful consequences on the ecosystem and public health. Various technologies have been developed for water treatment such as photocatalysis, which has recently drawn scientists’ attention. Photocatalytic techniques using semiconductors have shown an efficient removal of various water contaminants during water treatment as well as cost effectivity and low energy consumption. Tungsten disulfide (WS2) is among the promising Transition Metal Dichalcogenides (TMDs) photocatalysts, as it has an exceptional nanostructure and special properties including high surface area and high carrier mobility. It is usually synthesized via hydrothermal technique, chemical vapor deposition (CVD), and liquid-phase exfoliation (LPE) to obtain a wide variety of nanostructures such as nanosheets and nanorods. Most common examples of water pollutants that can be removed efficiently by WS2-based nanomaterials through semiconductor photocatalytic techniques are organic contaminants, pharmaceuticals, heavy metals, and infectious microorganisms. This review summarizes the most recent work on employing WS2-based nanomaterials for different photocatalytic water treatment processes.

In this study, the effect of KBr salt on the growth of TiO2 nanorods (NRs) was systematically studied. The addition of KBr with different concentrations provides a controllable growth of TiO2 NRs using hydrothermal method. The results revealed that the presence of KBr molecules affects the growth rate by suppressing the growth in the lateral direction and allowing for axial growth. This results in affecting the morphology by decreasing the diameter of the nanorods, and increasing the free space between them. Enhancing the free spaces between the adjacent nanorods gives rise to remarkable increase in the internal surface area, with more exposure side surface. To obtain benefit from the enlargement in the inner surface area, TiO2 NRs were used for the preparation of MoS2/TiO2 heterostructures. To study the influence of the morphology on their activity, TiO2 NRs samples with different KBr concentrations as well as the MoS2/TiO2 heterostructures were evaluated towards the photocatalytic degradation of Rhodamine B dyes.

Chemical vapor deposition (CVD) is one of the successful techniques for the synthesis of two-dimensional transition metal dichalcogenides (TMDCs) with different morphologies, sizes, and crystal qualities, which are beneficial for different research fields and applications. However, a controllable growth of 2D tungsten disulfide (WS 2 ) with different orientations and sizes is still a challenging issue. In this study, we demonstrate a controllable synthesis of WS 2 flakes by optimizing the CVD growth conditions. The results revealed that tuning the growth pressure successfully provides control over the orientation of the grown flakes. This monitoring allows for achieving vertically standing WS 2 nanoflakes, with maximum exposure to the edge active sites. Aiming for enhanced photocatalytic activity, the construction of vertical WS 2 nanoflake/TiO 2 nanorod heterostructure was obtained by optimizing the height between the precursor and the substrate, which provides control over the size of the flakes. In addition, the achieved WS 2 /TiO 2 heterostructures were evaluated as a photocatalyst for Rhodamine B degradation and photoelectrochemical activity (PEC).