Unveiling the photocatalytic and antimicrobial activities of star-shaped gold nanoparticles under visible spectrum.

This study reports on the facile development of star-shaped gold nanoparticles via seed-mediated growth protocol. Gold nanostars (AuNSTs) demonstrated average particle size of 48 nm using transmission electron microscopy (TEM). Chemical composition of AuNSTs was verifired using energy dispersive X-ray spectroscopy (EDX) mapping. AuNSTs demonstrated high optical response under visible spectrum, with maximum absorption at 685 nm, using UV-Vis spectroscopy. Therefore AuNSTs could be involoved into photocatalytic reaction under visible spectrum. AuNSTs demonstrated superior performance in degradation of rhodamine B dye (RB), and disinfection of some pathogenic bacteria. AuNSTs offered enhanced removal efficiency against rhodamine B dye (82.0 ± 0.35% in 135 min) under visible irradiation. Remarkably, under proper conditions of pH = 9, approximately 94 ± 0.55% of a 10 ppm RB solution was effectively photodegraded after 135 min; this could be ascribed to the strong electrostatic attraction between negatively charged AuNSTs surface and positive RB contaminant. This superior photocatalytic activity of AuNSTs could be correlated to high interfacial charge transfer efficiency for Au, and enhanced charge pair separation under visible spectrum. Additionally, AuNSTs exhibited potential antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). AuNSTs demonstrated substantial antibacterial activity via disk diffusion and microbroth dilution tests with zones of inhibition and minimum inhibitory concentrations (MIC) for E. coli (20.0 ± 0.54 mm, 1.25 µg/ml) and S. aureus (23.0 ± 0.35 mm, 0.625 µg/ml), respectively. In conclusion, AuNSTs demonstrated efficient dye removal capabilities along with significant antimicrobial activity against gram-positive and gram-negative bacterial strains.