Structural and Optical Properties of PVP-Modified ZnS Nanoparticles for Photocatalytic Dye Degradation
Pristine and PVP-modified ZnS nanoparticles were investigated to examine how PVP addition affects structural, surface, optical, and methylene blue (MB) decolorization properties. X-ray diffraction confirmed cubic zinc-blende ZnS in all samples, with apparent Scherrer coherent-domain sizes of 3.10-3.31 nm. Electron microscopy revealed agglomeration, while HRTEM and electron diffraction confirmed locally crystalline regions in S1 and S4. The estimated direct Tauc gap decreased from 3.69 eV for S1 to 3.58 eV for S4. Between 100 and 300 K, the principal TO-like Raman band softened on heating, while visible photoluminescence changed predominantly within the overlapping green-yellow region. After 210 min under 254 nm irradiation, MB-band losses near 664 nm reached 19.33%, 58.18%, 70.00%, and 94.42% for S1-S4, compared with 6.58% for the catalyst-free control. PVP modification therefore alters optical and dye-decolorization responses while preserving the principal ZnS phase; however, dye-band attenuation alone does not establish complete mineralization.