Antibacterial activity of SnO2 in visible light enhanced by erbium–cobalt co-doping

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In this work, a series of SnO2 samples with systematically varied doping amounts of Er and Co were prepared via a precipitation–hydrothermal method. The results show that after Er doping, the 4I15/2 ground state of Er3+ jumps to the 4H11/2 higher-energy level, and the Er-doped SnO2 samples can efficiently convert low-energy light into high-energy light. Thus, Er doping is beneficial for improving the visible and near-infrared light response of SnO2 and thus enhances its photocatalytic performance. Furthermore, doping SnO2 with Co leads to a distortion of the SnO2 lattice. A proportion of the SnO2 lattice is replaced by Co atoms, which can effectively lower the bandgap of SnO2, widen its optical response range, and enhance its sunlight absorption efficiency. The photocatalytic antibacterial activities of pure SnO2, as well as SnO2 co-doped with Er and Co in visible light, were investigated under visible light using Escherichia coli. SnO2 shows the best antibacterial activity and electron–hole separation efficiency when co-doped with 1.5 mol. % Er and 1.5 mol. % Co (Er1.5Co1.5-SnO2). Gradient experiments reveal that mainly the reactive oxygen species affect the antibacterial activity of pure SnO2. The improved antibacterial performance of Er1.5Co1.5-SnO2 is attributed to the increased generation of·O2− and·OH. In addition, scavenger experiments reveal that·O2− is the key contributor to the enhanced antibacterial activity of SnO2.