Influence of capping agents on morphology and photocatalytic response of ZnS nanostructures towards crystal violet degradation under UV and sunlight

Photo-responsive ZnS nanostructures (ZnSM1 and ZnSM2) were synthesized using 3-mercaptopropionic acid (MPA) and polyvinylpyrrolidone (PVP) capping agents respectively via reflux method. Capped photocatalysts hold unique optical properties such as absorption in visible region, multi band gap values and surface defects. Interestingly, structural analysis revealed that nanorods and nanospheres were formed with MPA and PVP whereas randomly arranged particles were formed without using any capping agent (ZnSUC). The successful passivation of -COOH (1549 cm(-1) and 1357 cm(-1)) in case of ZnSM1 whereas -CH2 (1284 cm(-1)) and C-N stretching (1429 cm(-1)) for ZnSM2 was determined by FT-IR studies. Owing to effective charge separation, 1D structure, suitable band gap energies and higher surface area (252 m(2) g(-1)), ZnSM1 exhibited enhanced photocatalytic activity towards crystal violet degradation (CV, 93%) under UV light which was about two folds higher than standard ZnS. Under sunlight, uncapped ZnS nanoparticles (ZnSUC and std. ZnS) showed minor activity in comparison to capped ZnSM1 (88%) and ZnSM2 (77%). Moreover, 83% degradation of 2-nitrophenol (NP) was obtained using ZnSM1 without using any other reducing agent under solar irradiations. Thus, present work provides more insights to understand the outstanding activity of ZnS nanomaterials towards organic pollutants beyond UV region without metal deposition.