Metal-enhanced S-scheme heterojunction for the efficient degradation of triclosan and tetracycline in aqueous solutions: insights into the degradation mechanism.

This study presents a sustainable strategy for the synthesis, characterization, and assessment of the photocatalytic efficiency of an S-scheme heterojunction (TiO2/CuO/Ag0) in the degradation of two micropollutants, namely tetracycline (TC) and triclosan (TCS), under UV-A/LED light conditions. The heterojunction was fabricated using Mangifera indica extract as an eco-friendly reducing and capping agent. Various structural studies demonstrated the formation of a TiO2-CuO heterojunction decorated with Ag0 nanoparticles (NPs), thereby improving light absorption, reducing the band gap, and enhancing charge separation. EIS and Mott-Schottky results verified improved charge separation and reduced interfacial resistance, consistent with the S-scheme mechanism. Process optimization via Response Surface Methodology with Central Composite Design (RSM-CCD) identified pollutant concentration, catalyst dosage, pH, and reaction time as key parameters, achieving over 99% and 94% for TC removal and 77% and 71% for TCS removal under UV-A and visible light, respectively, at optimized conditions. Radical scavenging identified that superoxide radicals (O2˙-) and photogenerated holes (h+) were the primary oxidative species. DFT calculations and LC-MS analyses provided insights into molecular degradation pathways, while ECOSAR toxicity assessment confirmed reduced toxicity of the intermediates. The catalyst demonstrated excellent recyclability and stability, highlighting its potential for sustainable wastewater purification.