Nickel-modified tungsten disulphide: an efficient catalyst for the reduction of nitrophenol isomers and...

Considering the extremely hazardous environmental impacts of nitrophenol isomers, this study explores an efficient and novel catalyst for their remediation via a facile reduction process. The catalyst has been optimized with varying molar ratios of nickel to tungsten disulphide in order to achieve a reduction efficiency of 99% within just 1 min for ortho-nitrophenol (ONP), while for para-nitrophenol (PNP) it required 3 min to reach the same level of reduction at the rates of 0.44 min^-1 and 0.31 min^-1 respectively. The catalyst, Ni_0.3/WS₂, with 30% nickel demonstrated the highest catalytic efficiency in the case of nitrophenol isomers as well as pharmaceutical pollutants where a 60% reduction is observed suggesting substantial transformation of the molecule without any light response. The faster reduction rate for ONP can be attributed to the favourable positioning of the nitro group, which allows closer interaction with the catalytic sites on Ni@WS₂, facilitating enhanced electron transfer and rapid hydrogenation. Conversely, the nitro group at the para position in PNP results in a slower reduction rate due to increased distance from the catalytic sites and greater steric hindrance. Furthermore, 30% Ni decoration in WS₂ was found to maximize catalytic performance by creating a balanced density of active defect sites, enhancing charge transfer via band gap reduction, and maintaining structural integrity. Higher levels of Ni concentration (60% and 100%) introduce structural distortions and reduce the active surface area, resulting in diminished catalytic efficiency. With the same catalyst, we have effectively carried out pharmaceutical pollutant remediation without any assistance of light. These observations establish the application potential of Ni_0.3WS₂ as an effective catalyst for environmental remediation and industrial applications. This study also underscores the impact of transition metal decoration on catalytic efficiency, providing valuable insights for the design of dichalcogenides and further applications.