Carbon quantum dot-decorated TiO2 for fast and sustainable antibacterial properties under visible-light

This work demonstrates that the effective use of antimicrobial agents (CQDs-TiO2: carbon quantum dot-decorated titanium dioxide) and natural resources, such as sunlight, is able to improve the ability of sustainable degradation of bacteria. The CQDs-TiO2 nanomaterials, prepared using the hydrothermal method, were characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM) and Transmission electron microscope (TEM). The CQDs-TiO2 properties and their antimicrobial activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were systematically evaluated. The antibacterial efficiency reached 90.9% and 92.8% toward E. coli and S. aureus, respectively, with 1 μg/mL CQDs-TiO2 under visible light for 24 h. Under visible light irradiation, CQDs-TiO2 greatly improved absorption of visible light and increased the content of free radicals. These free radicals directly attack the bacterial cells, degrade organic matter within the cells and finally break down bacteria. Seven cycles of antimicrobial experiments using recycled materials demonstrated that the ability of CQDs-TiO2 to sustainably degrade bacteria was stronger than pure titanium dioxide (TiO2). It is noteworthy that carbon quantum dots (CQDs) not only prevent TiO2 from agglomerating, but also attract bacteria and carry TiO2 to the cell. In addition, CQDs-TiO2 showed very low cytotoxicity and can be applied to medical and human health fields.