Green and scalable synthesis of nanosilver loaded silica microparticles by spray-drying: application as antibacterial agent, catalyst and SERS substrate

Silver nanoparticles (Ag NPs) have found wide-spread applications as antibacterial agents, catalysts and in chemical detection via surface-enhanced Raman spectroscopy (SERS). To avoid agglomeration and unwanted release to the environment, Ag NPs are usually loaded onto various substrates. However, simple procedures for large-scale synthesis of this important material are still lacking. Here, we demonstrate a facile, green and scalable synthesis of Ag NPs loaded to ceramic substrates. Environment-friendly biopolymer (gum arabic) and ceramic (silica) nanoparticles were spray-dried to obtain surface-functionalized mesoporous silica substrate. Thereafter, the silver precursor was reduced in situ to obtain Ag NPs attached to the silica substrate. Gum arabic played a crucial role in reducing and attaching Ag NPs to the substrate. The resulting composite material was characterized using X-ray diffraction, high-resolution transmission electron microscopy, field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The antimicrobial efficacy of the synthesized composite was evaluated against a gram-negative bacterium, Escherichia coli and a gram-positive bacterium, Staphylococcus aureus. Complete bactericidal effect was observed for composite harboring silver concentration as low as 19 µg ml−1 and 76 µg ml−1 for Escherichia coli and Staphylococcus aureus, respectively. Furthermore, the composite was used as a catalyst in the reduction reaction of 4-nitrophenol and rhodamine B by sodium borohydride. The rate constant for 4-nitrophenol reduction was found to be 1750 s−1 g−1. The composite demonstrated its applicability as a substrate for surface-enhanced Raman spectroscopy (SERS) wherein very dilute concentration (10−9 M) of crystal violet and rhodamine 6G could be easily detected.