Reusable photocatalytic film for efficient water disinfection under low light intensity

Access to microbiologically safe water remains a pressing global issue, especially in resource-limited and disaster-affected regions. This study introduces a self-floating photocatalytic film that achieves >4.3-log bacterial inactivation in 10 litres of highly contaminated water within 40 min under low natural sunlight intensity (13–18 mW cm−2), where conventional photocatalysts (for example, TiO2, g-C3N4 and so on) are nearly ineffective. The remarkable performance is attributed to reactive oxygen species, especially oxygen-centred organic radicals, an unconventional active species with ultralong lifetimes—several orders of magnitude longer than typical reactive oxygen species. Their persistence allows accumulation under weak illumination, sustaining disinfection efficiency despite limited photon input. Moreover, oxygen-centred organic radicals can avoid attacking the catalyst, conferring excellent film stability (reusable ≥50 times), thereby ensuring cost-effectiveness and sustainability. With low energy demand, high robustness and operational simplicity, this photocatalytic film is particularly suitable for resource-limited regions and is promising for real-world applications in global water safety. A self-floating photocatalytic film enables rapid bacterial inactivation under weak natural sunlight.