Sunlight-Assisted Photodegradation of Tetracycline Using ZnS-Melamine-Formaldehyde Nanocomposites

The degradation of colorless tetracycline hydrochloride (TCH), a widely used antibiotic, is a significant environmental concern due to its persistence in aquatic systems. The zinc sulfide (ZnS) nanoparticle fabricated melamine-formaldehyde polymer (MFP)-based nanocomposite (ZnS-MFP) was prepared via a hydrothermal polymerization method, followed by surface modification through a simple precipitation route. The degradation of TCH through photocatalysis adheres to pseudo-first-order kinetics with a significantly faster rate under natural sunlight than under artificial bulb light. It is observed that a maximum 90% of 100 mg L^-1 TCH is degraded within 120 min in the presence of ZnS-MFP, with more than two times higher degradation efficiency than under artificial bulb light. The comparative ¹H NMR and UV-vis spectroscopic analysis of the TCH molecule and degraded products confirmed the degradation of TCH in the presence of the catalyst. Moreover, high-resolution mass spectrometry (HR-MS) was used to identify the intermediates that were formed during degradation. Radical scavenging experiments revealed the significant involvement of holes (h⁺), which further produce hydroxyl radicals (•OH) during photodegradation and are responsible for the degradation of TCH molecules. The efficacy of ZnS-MFP was further validated in real wastewater samples, where significant TCH removal was observed. Additionally, the composite retained considerable activity over five photocatalytic cycles. These results establish ZnS-MFP as a promising, recyclable photocatalyst for the sunlight-driven treatment of antibiotic-contaminated water.