Superior UVA-photocatalytic antibacterial activity of a double-layer ZnO/Al2O3 thin film grown on cellulose by atomic layer deposition (ALD)

Cellulose fibers coated with a double-layer ZnO/Al2O3 thin film (cel/Al2O3/ZnO) were prepared in-situ by two successive processes of atomic layer deposition (ALD). Photoinactivation kinetics of Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria were investigated in the dark and under UVA irradiation. Compared to the initial cellulose sample (cel) and cellulose coated with an Al2O3 thin film (cel/Al2O3), superior UVA photoinhibition was achieved for both bacteria treated with cel/Al2O3/ZnO within only 30 and 45 min of UVA irradiation for E. coli and S. aureus, respectively. FE-SEM and STEM micrographs showed strongly destructive effects on the morphology of both bacterial cell walls and the cytoplasmic membrane, which were attributed to the photogenerated reactive oxygen species (ROS). The kinetic data were successfully fitted using the modified Hom model, which consists of three rate constants describing the initial shoulder, rapid log-linear, and tail regions of the curves. As our results show, this cellulose-based material, further stabilized by the ALD Al2O3 interlayer, is promising for efficient photocatalytic disinfection of water.