Long-lasting CaO/ZnO composite antimicrobial material: Antimicrobial mechanism and water disinfection performance

In this study, hexagonal prismatic CaO/ZnO composites were successfully synthesised and exhibited efficient, long-lasting antimicrobial activity against Escherichia coli ( E. coli ). Density functional theory calculations, combined with photoelectrochemical and optical property analyses, demonstrated that the CaO/ZnO heterojunction significantly enhanced electron–hole separation efficiency compared with pure CaO and ZnO. Scavenger experiments revealed a time-dependent shift in the dominant antimicrobial mechanism. In the short term (Day 1, high alkaline environment), the ionic (alkaline) bactericidal mechanism (76.9%) was dominant, while reactive oxygen species (ROS)-mediated killing (14.2%) acted synergistically. In the long term (Day 15, near-neutral environment), the ROS-mediated bactericidal mechanism became dominant (45.3%), working synergistically with the sustained ionic bactericidal effect (41.3%). Lipid peroxidation and bacterial respiratory chain dehydrogenase activity assays confirmed that ROS generated by the CaO/ZnO composites caused severe damage to both the outer membrane and intracellular physiological functions of E. coli . Long-term antimicrobial tests, continuous pH monitoring and time-dependent scavenger experiments were conducted to elucidate the prolonged antimicrobial mechanism. As the alkaline effect of CaO gradually diminished, the contribution of ROS-mediated bactericidal activity in the CaO/ZnO composite increased significantly compared with pure CaO and ZnO, thereby maintaining stable antimicrobial activity. Three antimicrobial sponges were fabricated using CaO/ZnO as the active agent, all of which exhibited excellent antimicrobial performance. Among them, only CaO/ZnO@PU demonstrated optimal cyclic stability, maintaining 100% antimicrobial efficiency over five consecutive cycles, and achieved complete bacterial inactivation within 30 min in dynamic water filtration experiments. This study presents a promising antimicrobial material and provides clear insights its time-dependent antimicrobial mechanism.