Trimetallic CdTiZr oxide photocatalysts anchored on rGO: heterojunction-driven charge separation for improved photocatalytic and antibacterial efficacy

Abstract

The efficient mineralisation of dye pollutants remains a challenge due to the rapid charge carrier recombination and limited light absorption in metal oxide catalysts. Despite extensive investigation conducted on the photocatalytic properties of rGO/metal oxide composites, trimetallic heterojunction systems that can facilitate directional charge carriers are still underdeveloped. In this study, a trimetallic CdO–TiO₂–ZrO₂ oxide (CTZ) photocatalyst supported on rGO, denoted as CTZ/rGO, was successfully synthesised via a sol–gel method, which facilitated interfacial charge separation. This enhanced the photocatalytic and antibacterial performance. The CTZ/rGO composite showed better degradation efficiency than the pure CTZ system, i.e. 87.08% for Alizarin red and 86.96% for Nile blue, with 60 minutes of exposure time under UV light illumination. The apparent rate constant increased up to 0.0338 and 0.0337 min⁻¹, respectively, indicating enhanced reaction kinetics. The reduction of the band gap to 2.11 eV and the enhancement of the electron transport across the interface indicated that the charge transport mediated by rGO supresses electron–hole recombination. It also retained ∼80% degradation efficiency after five cycles. It exhibited significant antibacterial activity towards both Gram-positive and Gram-negative bacteria. These results demonstrate the impact of heterojunction engineering and the integration of charge carriers with a conductive carbon substrate. The results also demonstrate the feasibility of a multifunctional material for environmental remediation on a large scale.