Activated charcoal modified Ag and Cu-anatase TiO2 for superior photocatalytic degradation of doxycycline under visible-solar light irradiation

Abstract

Doxycycline, a frequently used tetracycline antibiotic, remains in the environment due to its widespread use, long-term biological stability, and toxicity even at low concentrations. In this regard, this paper addresses the synthesis, characterisation, and modification of anatase TiO₂ for doxycycline degradation under visible and solar light. The 2 wt% Ag and Cu–TiO₂ was prepared via a hydrothermal reaction followed by photodeposition. To improve the adsorption capacity, the composites underwent additional modification with activated charcoal via ultrasonication. Their physicochemical properties were analyzed using XRD, FE-SEM, HR-TEM, XPS, BET, PL, TRPL, and UV-DRS techniques. The results demonstrate that the incorporation of Ag and Cu and activated charcoal into anatase TiO₂ led to enhanced crystallinity, a mesoporous structure, improved light absorption, and an increased surface area. Among modified composites, the AC (1 wt%)–Cu (2 wt%)–TiO₂ composite showed the highest adsorption and photocatalytic activity, removing up to 98.5% of doxycycline under solar light and 88.8% under visible light. This outperformed AC (1 wt%)–Ag (2 wt%)–TiO₂ (92.6%) > Cu (2 wt%)–TiO₂ (89.2%) > Ag (2 wt%)–TiO₂ (83.9%) > AC (1 wt%)–TiO₂ (77.4%) > TiO₂ (68.7%). This improvement is due to the surface plasmon resonance (SPR) effect of Cu, increased electron mobility, and the larger surface area of activated charcoal. The catalyst demonstrates excellent stability and reusability. Furthermore, HR-MS analysis was used to identify the degradation pathways of doxycycline, complemented by TOC testing and the detection of active species. Due to its enhanced catalytic performance, affordability, and eco-friendliness, the reported composite is a promising option for pharmaceutical wastewater treatment.