Enhanced photodegradation of organic contaminants using V-ZnS_QDs@TiO₂ photocatalyst in an aqueous medium

Vanadium-doped zinc sulfide quantum dots complexed with TiO₂ have been designed using the sol-gel technique and characterized using analytical techniques, such as X-ray diffraction analysis (XRD), UV-Vis diffuse reflectance spectra (DRS), Fourier transforms Infra Red (FTIR), Brunauer-Emmett-Teller analysis (BET), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and transmission electron microscopy (TEM). The X-ray diffraction analysis of the composite material showed sharp peaks corresponding to both TiO₂ and ZnS_QDs. The FTIR analysis exhibits a strong and broad absorption at 807 cm^-1 indicating the assimilation of vanadium metal in the ZnS_QDs lattice. The DRS spectra showed a bathochromic shift of 25 nm in the synthesized V-ZnS_QDs@TiO₂ composite compared with the pure sample. The photocatalytic performance of the synthesized composite was tested by studying the degradation of two different chromophoric organic dyes, rhodamine B (RhB), methylene blue (MB) and a drug derivative paracetamol (PCM) in aqueous suspension under UV-light illumination. Among the synthesized materials, the composite (V-ZnS_QDs@TiO₂) was established to be more active than the pure ZnS_QDs, TiO₂, and V-ZnS_QDs for the degradation of compounds under investigation. The activity of the synthesized catalyst was also tested for the mineralization of all compounds by measuring the depletion in total organic carbon (TOC) at different irradiation times. The results showed that the catalyst degrades the compounds and mineralizes them efficiently. The primary reactive species involved in the photodegradation reaction were determined by quenching studies, terephthalic acid, and NBT probe methods. A probable mechanistic pathway for the decomposition of compounds has been proposed.