TiO2 nanofibres decorated with green-synthesized PAu/Ag@CQDs for the efficient photocatalytic degradation of organic dyes and pharmaceutical drugs

Abstract

Organic pollutants such as dyes and pharmaceutical drugs have become an environmental menace, particularly in water bodies owing to their unregulated discharge. It is thus required to develop an economically viable and environment-friendly approach for their degradation in water bodies. In this study, for the first time, we report green route-synthesized plasmonic nanostructures (P_M-CQDs (where M: Au and Ag)) decorated onto TiO₂ nanofibers for the treatment of toxic dye- and pharmaceutical drug-based wastewater. P_M-CQDs are efficaciously synthesized using carbon quantum dots (CQDs) as the sole reducing and capping agent, wherein CQDs are derived via a green synthesis approach from Citrus limetta waste. The characteristic electron-donating property of CQDs played a key role in the reduction of Au³⁺ to Au⁰ and Ag⁺ to Ag⁰ under visible light irradiation to obtain P_Au-CQDs and P_Ag-CQDs, respectively. Thus, the obtained CQDs, P_Au-CQDs, and P_Ag-CQDs are loaded onto TiO₂ nanofibers to obtain a P_M-CQD/TiO₂ nanocomposite (NC), and are further probed via transmission electron microscopy, scanning electron microscopy and UV-visible spectrophotometry. The degradation of organic pollutants and pharmaceutical drugs using methylene blue and erythromycin as model pollutants is mapped with UV-vis and NMR spectroscopy. The results demonstrate the complete MB dye degradation in 20 minutes with 1 mg mL⁻¹ of P_Au-CQD/TiO₂ NC, which otherwise is 30 minutes for P_Ag@CQD/TiO₂ dose under visible light irradiation. Similarly, the pharmaceutical drug was found to degrade in 150 minutes with P_Au-CQD/TiO₂ photocatalysts. These findings reveal the enhanced photocatalytic performance of the green-synthesized Au decorated with TiO₂ nanofibers and are attributed to the boosted SPR effect and aqueous-phase stability of Au nanostructures. This study opens a new domain of utilizing waste-derived and green-synthesized plasmonic nanostructures for the degradation of toxic/hazardous dyes and pharmaceutical pollutants in water.