Carbon-Dot-Decorated Silver and Gold Nanocomposites for Antibacterial Activity and Degradation of Organic Dyes

A hydrothermal process has been used to prepare highly fluorescent green-emitting crystalline carbon dots (CDs) at 200 °C using Bismarck brown dye. The HR-TEM image shows the clear lattice fringes with d-spacing values of 0.23 and 0.33 nm corresponding to the (100) and (002) planes, respectively, indicating the crystalline nature of carbon dots. These as-synthesized carbon dots have been successfully used to make two different nanocomposite systems, consisting of silver and gold nanoparticles with carbon dots. Here carbon dots act as a reducing agent in the presence of UV light/blue LED light to synthesize silver and gold nanoparticles from their respective metal salts. In the presence of silver and gold nanoparticles, the fluorescence of carbon dots was almost quenched in their respective nanocomposite systems. These carbon dots and carbon-dot-decorated silver/gold nanocomposite systems have been well characterized by various analytical techniques including UV–vis spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transformed infrared spectroscopy (FT-IR), and X-ray diffraction spectroscopic (XRD) study. Interestingly, carbon-dot-containing silver nanoparticles (CD-AgNP) exhibit a potential antibacterial activity against Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. The CD-AgNP shows a maximum inhibition zone diameter of 20, 15, 14, and 20 mm and having a minimum inhibitory concentration (MIC) of 12–16, 12–16, 16–25, and 16–25 μg/mL for S. Aureus, E. coli, B. subtilis, and P. aeruginosa, respectively, while the gold nanocomposite (CD-AuNP) has been utilized for the degradation of hazardous organic dyes including methyl orange (MO), Congo red (CR), and Evan's blue (EB) within 10–12 min.