Development of a UPLC-MS/MS method for pesticide analysis in paddy water and evaluation of anodic TiO₂ nanostructured films for pesticide photodegradation and antimicrobial applications

Pesticide contamination in agricultural water poses serious environmental and public health risks, particularly due to the accumulation of harmful residues that threaten aquatic ecosystems and human health. This study investigated the levels of five pesticides-carbaryl (CBR), methiocarb (MTC), diazinon (DZN), chlorpyrifos (CLO), and cypermethrin (CYPER)-in agricultural water samples from Can Tho City and Hau Giang Province, Vietnam. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was employed for their detection and quantification. Chlorpyrifos was the most frequently detected pesticide (32.5%), with concentrations ranging from 1.7 to 10.9 ng mL^-1. The concentrations of cypermethrin, carbaryl, methiocarb, and diazinon were 2.6-9.4 ng mL^-1, 1.3-14.3 ng mL^-1, 4.1-7.7 ng mL^-1, and 2.8-10.5 ng mL^-1, respectively. The persistence of pesticide residues in the water samples highlights the significant contamination concerns in the region. To address this issue, two types of TiO₂ nanophotocatalysts-TiO₂ nanotube arrays (TNAs) and TiO₂ nanowires on nanotube arrays (TNWs/TNAs)-were synthesized for the photocatalytic degradation of the identified pesticides. Under UV-vis irradiation (∼96 mW cm^-2), both nanostructures achieved rapid pesticide degradation, with removal efficiencies of up to 99% within 25 minutes. TNWs/TNAs exhibited superior photocatalytic performance, attributed to their increased surface area compared to TNAs. In addition to pesticide degradation, their antibacterial activity was assessed. Under weak UV-vis light (6.3 mW cm^-2), both TNAs and TNWs/TNAs achieved 100% antibacterial efficacy against <i>Escherichia coli</i>, significantly higher than the 68% efficacy of UV light treatment alone. Even under dark conditions, TNWs/TNAs demonstrated enhanced antibacterial activity, achieving 63% efficacy compared to 12% for TNAs. These results underscore the dual functionality of TNWs/TNAs as effective photocatalysts for both pesticide degradation and bacterial inactivation, presenting a promising approach for agricultural water treatment.