Titanium dioxide (TiO₂) is a commonly used wide bandgap semiconductor material for energy and environmental applications. Although it is a promising candidate for photovoltaic and photocatalytic applications, its overall performance is still limited due to low mobility of porous TiO₂ and its limited spectral response. This limitation can be overcome by several ways, one of which is doping that could be used to improve the light harvesting properties of TiO₂ by tuning its bandgap. TiO₂ doped with elements, such as alkali-earth metals, transition metals, rare-earth elements, and nonmetals, were found to improve its performance in the photovoltaic and photocatalytic applications. Among the doped TiO₂ nanomaterials, transition metal doped TiO₂ nanomaterials perform efficiently by suppressing the relaxation and recombination of charge carriers and improving the absorption of light in the visible region. This work reports the possibility of enhancing the performance of TiO₂ towards Dye Sensitised Solar Cells (DSSCs) and photocatalytic degradation of methylene blue (MB) by employing Zn doping on TiO₂ nanomaterials. Zn doping was carried out by varying the mole percentage of Zn on TiO₂ by a facile solvothermal method and the synthesized nanomaterials were characterised. The XRD (X-Ray Diffraction) studies confirmed the presence of anatase phase of TiO₂ in the synthesized nanomaterials, unaffected by Zn doping. The UV-Visible spectrum of Zn-doped TiO₂ showed a red shift which could be attributed to the reduced bandgap resulted by Zn doping. Significant enhancement in Power Conversion Efficiency (PCE) was observed with 1.0 mol% Zn-doped TiO₂ based DSSC, which was 35% greater than that of the control device. In addition, it showed complete degradation of MB within 3 h of light illumination and rate constant of $1.5466\times {10}^{-4}{s}^{-1}$ resembling zeroth order reaction. These improvements are attributed to the reduced bandgap energy and the reduced charge recombination by Zn doping on TiO₂.

Earth–abundant transition metal chalcogenide materials are of great research interest for energy production and environmental remediation, as they exhibit better photocatalytic activity due to their suitable electronic and optical properties. This study focuses on the photocatalytic activity of flower-like SnS₂ nanoparticles (composed of nanosheet subunits) embedded in TiO₂ synthesized by a facile hydrothermal method. The materials were characterized using different techniques, and their photocatalytic activity was assessed for hydrogen evolution reaction and the degradation of methylene blue. Among the catalysts studied, 10 wt. % of SnS₂ loaded TiO₂ nanocomposite shows an optimum hydrogen evolution rate of 195.55 µmolg⁻¹, whereas 15 wt. % loading of SnS₂ on TiO₂ exhibits better performance against the degradation of methylene blue (MB) with the rate constant of 4.415 × 10⁻⁴ s⁻¹ under solar simulated irradiation. The improved performance of these materials can be attributed to the effective photo-induced charge transfer and reduced recombination, which make these nanocomposite materials promising candidates for the development of high-performance next-generation photocatalyst materials. Further, scavenging experiments were carried out to confirm the reactive oxygen species (ROS) involved in the photocatalytic degradation. It can be observed that there was a 78% reduction in the rate of degradation when IPA was used as the scavenger, whereas around 95% reduction was attained while N₂ was used as the scavenger. Notably, very low degradation (<5%) was attained when the dye alone was directly under solar irradiation. These results further validate that the •OH radical and the superoxide radicals can be acknowledged for the degradation mechanism of MB, and the enhancement of degradation efficiency may be due to the combined effect of in situ dye sensitization during the catalysis and the impregnation of low bandgap materials on TiO₂.

Transition metal chalcogenides have intensively focused on photocatalytic hydrogen production for a decade due to their stronger edge and the quantum confinement effect. This work mainly focuses on synthesis and hydrogen production efficiencies of cobalt disulfide (CoS₂)-embedded TiO₂ nanocomposites. Materials are synthesized by using a hydrothermal approach and the hydrogen production efficiencies of pristine CoS₂, TiO₂ nanoparticles and CoS₂/TiO₂ nanocomposites are compared under UV irradiation. A higher amount of hydrogen production (2.55 mmol g⁻¹) is obtained with 10 wt.% CoS₂/TiO₂ nanocomposite than pristineTiO₂ nanoparticles, whereas no hydrogen production was observed with pristine CoS₂ nanoparticles. This result unveils that the metal dichalcogenide–CoS₂ acts as an effective co-catalyst and nanocrystalline TiO₂ serves as an active site by effectively separating the photogenerated electron–hole pair. This study lays down a new approach for developing transition metal dichalcogenide materials with significant bandgaps that can effectively harness solar energy for hydrogen production.

Demand for environmental protection is gaining more public attention and legislative support. The development in industrial and technological sectors results in severe environmental issues, such as environmental contamination and energy shortage. Therefore, the development of new nanocomposites that can effectively act toward environmental remediation is necessary to overcome the detrimental environmental impacts. Transition metal chalcogenides (TMC) have gained worldwide attention in recent decades and are being researched for use in different applications due to their indirect bandgaps, optoelectronic behavior, and their stability that can enable the catalysts to absorb visible light that is abundant in solar radiation. In this chapter, synthesis, characterization, and application of TMCs, such as MSx and MSex, toward environmental remediation application are reviewed. Efficiency of different TMC materials and different experimental conditions is also elaborated.

Development of efficient and affordable photocatalysts is of great significance for energy production and environmental sustainability. Transition metal chalcogenides (TMCs) with particle sizes in the 1–100 nm have been used for various applications such as photocatalysis, photovoltaic, and energy storage due to their quantum confinement effect, optoelectronic behavior, and their stability. In particular, TMCs and their heterostructures have great potential as an emerging inexpensive and sustainable alternative to metal-based catalysts for hydrogen evolution. Herein, the methods used for the fabrication of TMCs, characterization techniques employed, and the different methods of solar hydrogen production by using different TMCs as photocatalyst are reviewed. This review provides a summary of TMC photocatalysts for hydrogen production.