AuGa2-based plasmonic nanocomposite with engineered d-band for enhanced photocatalytic and antibacterial activities

Ga is a liquid metal above 29.8 °C that alloys easily with numerous metals and has potential to support the facile synthesis of multifunctional plasmonic materials. Herein, we prepared the AuGa2-based plasmonic nanocomposite using liquid Ga and investigated its photocatalytic and bacterial activities. Our method involved ultrasonicating the liquid Ga in the chloroauric acid solution, followed by annealing at 500 °C for 2 h to convert the in-situ mixture formed into the plasmonic nanocomposite containing AuGa2 nanoparticles (NPs), α-phase gallium oxide (α-Ga2O3) nanorods, and Au NPs. Characterization analyses were conducted using the X-ray diffractometer, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscope, and UV–Vis spectrophotometer. The AuGa2 NPs engineered a unique d-band center and profile distinct from those of the Au, and exhibited enhanced dual-band optical absorptions at approximately 520 and 740 nm. The full-potential density function theory calculation via the WIEN2k software revealed that the dual-band absorptions arose from interband transitions and surface plasmon resonance. Photocatalytic activity was analyzed via the decomposition of Rhodamine B (RhB) under the ultraviolet (UV) lamp, Xe lamp, 532 nm laser, and 808 nm laser; and bacterial activity was analyzed against the Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacterial suspensions. The AuGa2-based plasmonic nanocomposite showed exceptional performance for the photocatalytic degradation of RhB under UV, visible, near-infrared (NIR) illumination, as well as excellent antibacterial activities against the S. aureus and E. coli under NIR illumination. The discussion of the results was on the basis of the d-band model being empowered by the alloying and plasmonic effects. This study can be extended to the exploration of other liquid-metal-based nanocomposites with great prospects for the scaling up their syntheses and analyzing their unprecedented properties.