Plasmonic Au–TiO2 Nanowire/Nanotube Heterostructures for Multifunctional Photocatalysis: Dye and Pesticide Degradation, Water Splitting, and Antibacterial Activity

Abstract

Methylene blue (MB) and pesticide residues in wastewater pose serious environmental and health concerns. In this study, TiO₂ nanowires grown on nanotube arrays (TNWs/TNAs) and their Au nanoparticle-decorated counterparts (Au–TNWs/TNAs) were fabricated for multifunctional applications, including photocatalytic degradation, photoelectrochemical (PEC) water splitting, and antibacterial activity. TNWs/TNAs were synthesized via anodization, followed by the deposition of ~19.5 nm Au nanoparticles (6.8–8.7 at.%) using Turkevich synthesis and immersion methods. Both films exhibited uniform morphology with anatase-phase TiO₂. Photocatalytic performance was evaluated under UV–Vis light (100 mW/cm²) by monitoring the degradation kinetics of MB and four common pesticides—dimethoate (DMT), methiocarb (MTC), carbofuran (CBF), and carbaryl (CBR)—using LC-MS/MS. Au–TNWs/TNAs demonstrated significantly enhanced degradation rate constants (k): 10.41 × 10⁻³ min⁻¹ for MB, and 19.8, 18.8, 83.0, and 8.73 × 10⁻² min⁻¹ for DMT, CBF, MTC, and CBR, respectively, representing 1.2–1.46× improvements over pristine TNWs/TNAs. These enhancements are attributed to the localized surface plasmon resonance (LSPR) effect of Au, which improves visible-light absorption and charge separation. For PEC performance, Au-TNWs/TNAs achieved a high and stable photocurrent density of 0.51 mA/cm² under UV-Vis illumination (100 mW/cm²), representing a ~70% enhancement compared to the pristine TNWs/TNAs. Additionally, the Au-TNWs/TNAs demonstrated strong antibacterial activity, achieving an E. coli inhibition rate of 61.6% under dim laboratory light and up to 99.9% under low-intensity UV-Vis irradiation (6.3 mW/cm²). These findings highlight the potential of plasmon-enhanced Au–TiO₂ nanowire/nanotube heterostructures as versatile nanomaterials for integrated applications in dye and pesticide photodegradation, PEC water splitting and antimicrobial control.