Biochar: Preserving the long-term catalytic activity of biosynthesized PdNPs/AuNPs in Cr(VI) reduction

Palladium nanoparticles (PdNPs) and gold nanoparticles (AuNPs) synthesized within yeast biomass can be effectively preserved in yeast biochar while maintaining their catalytic activity. Herein, we observe well-preserved PdNPs/AuNPs within yeast biochars, alongside the retention of cell morphology. Notably, the crystal structures of AuNPs within biochars exhibit similarity to that of uncarbonized samples, suggesting minimal influence of carbonization on nanoparticle structure. XPS analysis reveals the transformation of organic bacterial cells into heterocyclic aromatic-carbon material during pyrolytic carbonization. Chemical states analysis indicates the prevalence of metallic Pd(0)/Au(0) with limited PdO_x/AuO_x content in yeast biochars. FTIR analysis highlights increased aromaticity of biochars with typical bands for aromatic ring, and new bands appeared in Pd/Au-loaded biochars possibly attribute to PdO_x/AuO_x. Moreover, yeast biochars exhibit significantly improved Cr(VI) removal capacities compared to yeast biomass. Specifically, we detect complete removal within 18 h for CYPd and CYPdG biochars, contrasting with less than 65 % removal efficiency in yeast biomass. These findings underscore the potential of carbonization in enhancing the long-term catalytic activity of biosynthesized PdNPs/AuNPs for efficient Cr(VI) reduction, offering promising avenues for environmental remediation strategies.