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

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 degrees 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 Escherichia coli 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.

Automated summary

In this study, silver phosphate nanocomposites were synthesized using brewery wastes at different temperatures and times to obtain varying component ratios. It was found that BW7 nanocomposites exhibited higher antibacterial activity due to a larger silver phosphate content and a thinner organic overlayer compared to BW5 nanocomposites. The presence of Ag-met in the structure adversely affected the antimicrobial property of the nanocomposites.