The quest for a clean, renewable and sustainable energy future has been highly sought for by the scientific community over the last four decades. Photocatalytic water splitting is a very promising technology to proffer a solution to present day environmental pollution and energy crises by generating hydrogen fuel through a “green route” without environmental pollution. Transition metal dichalcogenides (TMDCs) have outstanding properties which make them show great potential as effective co-catalysts with photocatalytic materials such as TiO2, ZnO and CdS for photocatalytic water splitting. Integration of TMDCs with a photocatalyst such as TiO2 provides novel nanohybrid composite materials with outstanding characteristics. In this review, we present the current state of research in the application of TMDCs in photocatalytic water splitting. Three main aspects which consider their properties, advances in the synthesis routes of layered TMDCs and their composites as well as their photocatalytic performances in the water splitting reaction are discussed. Finally, we raise some challenges and perspectives in their future application as materials for water-splitting photocatalysts.

A one-step colloidal synthesis of hierarchical nanoflowers of WS2 is reported. The nanoflowers were used to fabricate a chemical sensor for the detection of ammonia vapors at room temperature. The gas sensing performance of the WS2 nanoflowers was measured using an in-house custom-made gas chamber. SEM analysis revealed that the nanoflowers were made up of petals and that the nanoflowers self-assembled to form hierarchical structures. Meanwhile, TEM showed the exposed edges of the petals that make up the nanoflower. A band gap of 1.98 eV confirmed a transition from indirect-to-direct band gap as well as a reduction in the number of layers of the WS2 nanoflowers. The formation of WS2 was confirmed by XPS and XRD with traces of the oxide phase, WO3. XPS analysis also confirmed the successful capping of the nanoflowers. The WS2 nanoflowers exhibited a good response and selectivity for ammonia.

The need to exploit the exotic properties of ZrS2 synthesized via colloidal means is imperative. For almost a decade now there has been no literature on the colloidal synthesis of ZrS2 nanomaterials. Meanwhile, several publications are available on other methods of synthesis mostly chemical vapour transport (CVT) and chemical vapour deposition (CVD). The synthesized bulk material from the CVT method is further subjected to exfoliation (mechanical or liquid) to obtain mono or few‐layers of ZrS2. With the colloidal method, there is a possibility of the oxide being formed during the synthesis of ZrS2 and likely destabilization of the nanomaterial after synthesis on exposure to ambient environment. In this study, both the heat up and hot injection methods were employed to fabricate various morphologies of ZrS2 nanomaterials. The metal and sulphur precursors were dissolved in a mixture of octadecene (ODE) and oleic acid (OA); and refluxed at a temperature of 290 °C in the presence of nitrogen gas. ODE served the role of non‐coordinating solvent, while OA served as the capping agent. Nanorods, nanospheres and nanosheets were obtained from the heat up method. Meanwhile, the hot injection approach produced nanosheets and nanospheres with well noticeable hollow centres. Powder X‐ray diffractometer (PXRD) validated the formation of the ZrS2 hexagonal phase with traces of oxides of zirconium, ZrO2. The peak of S2p was conspicuously absent while the Zr3d peak was well noticeable in the XPS spectra. XPS and EDS measurements confirmed the replacement of the sulphur atom by the O atom on the surface of the nanomaterials. Only one exciton peak was observed for the absorption spectra from both the heat up and hot injection methods; and thermal thermogravimetry analysis (TGA) revealed three plateaux of decomposition of the nanomaterials.

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