Band Gap Engineered MoS₂ Nanosheets-Anchored ZIF-8 Composite Towards Degradation and Reduction of Crystal Violet and Picric Acid in Wastewater

Environmental restoration because of the occurrence of harmful organic substances in our environment has received widespread attention amongst the researchers. Wastewater containing nitro-aromatic compounds and organic dyes are recently recognized as a new danger due to their toxicity towards all forms of living organisms. It is urgently needed to remove organic dye from our water systems in an efficacious manner for the purpose of both drinking and wastewater management. Binary MoS₂ nanosheets@ZIF-8 nanocomposite was synthesized by hydrothermal method. The characterization techniques such as PXRD, XPS, EDS, FE-SEM, TEM, UV-DRS and PL were performed to investigate the structure, composition, morphology and optical properties of the synthesized nanocomposite. The catalytic activity of MoS₂ nanosheets@ZIF-8 was tested by reduction of Picric acid (PA) in presence of NaBH₄ and the photocatalytic degradation of Crystal Violet (CV) under visible-light which is not reported in any literature till date, to check the application of the synthesized nanocomposite for wastewater remediation. Original ZIF-8 had a band gap of 5.2 eV, however incorporation of MoS₂ nanosheets on the ZIF-8 phase narrowed down the band gap of the MoS₂ nanosheets@ZIF-8 composite to 3.2 eV. MoS₂ nanosheets@ZIF-8 composite showed significantly high degradation of CV ~ 96% under visible light at optimum conditions of catalyst amount = 16 mg, dye concentration = 25 ppm and pH = 10. The degradation of CV followed first order kinetics with a first order rate constant of 0.0947 min⁻¹. The as-synthesized catalyst showed good recyclability by showing a degradation efficiency of 85% till the fifth cycle. In addition to the photocatalytic degradation of CV, the MoS₂ nanosheets@ZIF-8 displayed significantly high catalytic activity for the reduction of PA in presence of NaBH₄ with a reduction efficiency of 96.26% and an apparent rate constant value of 2.7 × 10^–3 s⁻¹ in 20 min. The MoS₂ nanosheets@ZIF-8 nanocomposite emerged as promising material with high catalytic activity in applications involving wastewater management.