Highly Active, Superstable, and Biocompatible Ag/Polydopamine/g-C3N4 Bactericidal Photocatalyst: Synthesis, Characterization, and Mechanism

The goal of this paper is to develop a bactericidal photocatalyst silver/polydopamine/graphitic carbon nitride (Ag/PDA/g-C3N4) as a new type of antibacterial material with high activity, superstability, and excellent biocompatibility. Small Ag NPs (3.6–10.5 nm) disperse uniformly on the PDA-modified g-C3N4 sheets. This biophotocatalyst has excellent antibacterial activity against Escherichia coli, including low MIC100%Ag of 9.5 ppm and MBC100%Ag of 6.3 ppm but also a low cytotoxicity for human umbilical vein endothelial cells (HUVECs) because of biocompatible PDA. After 30 days in an air environment, only 0.18% of Ag+ was detected, which indicated the superstability of this biophotocatalyst compared with the state-of the-art antibacterial materials. The possible bactericidal mechanism is the synergistic effect between photocatalytic PDA-modified g-C3N4 and active Ag NPs. The Ag NPs themselves have strong antibacterial activity due to their small sizes. Importantly, under light irradiation, the surface plasmonic effect of Ag NPs and the incorporation of PDA enhance the photocatalytic activity of g-C3N4 significantly by increasing its light absorption, improving photoconductivity for photogenerated electrons and holes, and inhibiting their recombination. As a result, the sufficient radicals such as •OH and O2•– radicals can be formed. The radicals, particularly •OH, together with holes, can accelerate the death of bacteria through the destruction of biomolecules.