Valorization of Brewery Wastes for the Synthesis of Silver Nanocomposites Containing Orthophosphate

Abstract

Brewery wastes from stage 5 (Wort precipitate: BW5) and stage 7 (Brewer's spent yeast: BW7) were valorized for the synthesis of silver phosphate nanocomposites. Nanoparticles were synthesized by converting silver salt in the presence of brewery wastes at different temperatures (25, 50, and 80 °C) and times (10, 30, and 120 min). Unexpectedly, BW7 yielded Ag₃PO₄ nanoparticles with minor contents of AgCl and Ag metal (Ag_met). Contrastingly, BW5 produced AgCl nanoparticles with minor amounts of Ag₃PO₄ and Ag_met. Nanocomposites with different component ratios were obtained by simply varying the synthesis temperature and time. The morphology of the nanocomposites contained ball-like structures representative of Ag₃PO₄ and stacked layers and fused particles representing AgCl and Ag_met. The capping on the nanoparticles contained organic groups from the brewery by-products, and the surface overlayer had a rich chemical composition. The organic overlayers on BW7 nanocomposites were thinner than those on BW5 nanocomposites. Notably, the nanocomposites exhibited high antibacterial activity against <i>Escherichia coli</i> ATCC 25922. The antibacterial activity was higher for BW7 nanocomposites due to a larger silver phosphate content in the composition and a thin organic overlayer. The growth of Ag_met in the structure adversely affected the antimicrobial property of the nanocomposites.