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

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 cm-2) 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 cm-2 under UV-vis illumination (100 mW cm-2), representing an ∼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 cm-2). 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.