Novel biosynthetic AuNPs as the efficient catalyst for organic contaminants degradation: one-step preparation, degradation kinetics and mechanism

Metallic nanoparticles derived from biosynthesis are both cost-effective and biocompatible. In the present work, Aspergillus niger cell-free filtrate was used to biosynthesize gold nanoparticles (AuNPs) in one step, which served as the catalyst in the removal of multiple contaminants. The reaction solution was visually observed to be purple and had an UV–vis characteristic absorption peak near 540 nm, which supported the biosynthesis of AuNPs. To better understand biosynthesis, the influences of key factors such as precursor concentration, biomass amount, pH and temperature were examined. The biosynthetic AuNPs were subjected by DLS, zeta potential, XRD, TGA, XPS, TEM and FTIR measurements, respectively. The extracellular proteins from the cell-free filtrate were responsible for the reduction and stabilization of AuNPs. In particular, the catalytic mechanism and the reaction kinetics of novel AuNPs in degrading different types of contaminants were investigated. The moderate AuNPs could catalyze the complete degradation of nitro-aromatics and several dyes within 20 min. Especially to remove methyl orange and Congo red, biosynthetic AuNPs showed overwhelming catalytic performance with the rate constants of 0.283 min −1 and 0.516 min −1 . As a result, the nanoparticles synthesized by this facile and sustainable approach have considerable potential for pollution treatment.