Nano-sized magnetic TiO2–SiO2/Fe3O4 photocatalysts and their application to photokilling of <i>Lactobacillus casei</i> and photocatalytic degradation of persistent herbicides

Abstract Nano-sized magnetic photocatalysts (nano TiO2–SiO2/Fe3O4) with a particle size of approximately 20 nm were developed for efficient water treatment. Their photocatalytic performance was comparable to those of nanoparticle photocatalysts P25. Furthermore, the photocatalysts could be conveniently separated from treated water by using a magnet. We then applied the photocatalysts to the photokilling of Lactobacillus casei and degradation of persistent herbicides (simetryn, prometryn, metolachlor, and sulfometuron methyl). L. casei, a Gram-positive bacterium lacking an outer membrane, was introduced and validated as a reliable model bacterium for photocatalytic antibacterial assessments. Complete photokilling of L. casei occurred within 50 min of ultraviolet (UV) irradiation, demonstrating simpler kinetic behavior compared with traditionally used Gram-negative model organisms. The photocatalysts also exhibited effective degradation toward 4 persistent herbicides. Their concentrations decreased from 10 ppm to below 1 ppm within 120 min.