Catalytic reduction of 4-nitrophenol using gold nanoparticles biosynthesized by cell-free extracts of Aspergillus sp. WL-Au

A facile one-pot eco-friendly process for synthesis of gold nanoparticles (AuNPs) with high catalytic activity was achieved using cell-free extracts of Aspergillus sp. WL-Au as reducing, capping and stabilizing agents. The surface plasmon resonance band of UV-vis spectrum at 532 nm confirmed the presence of AuNPs. Transmission electron microscopy images showed that quite uniform spherical AuNPs were synthesized and the average size of nanoparticles increased from 4 nm to 29 nm with reaction time. X-ray diffraction analysis verified the formation of nano-crystalline gold particles. Fourier transform infrared spectra showed the presence of functional groups on the surface of biosynthesized AuNPs, such as OH, NH, CO, CH, COH and COC groups, which increased the stability of AuNPs. The biogenic AuNPs could serve as a highly efficient catalyst for 4-nitrophenol reduction. The reaction rate constant was linearly correlated with the concentration of AuNPs, which increased from 0.59 min−1 to 1.51 min−1 with the amount of AuNPs increasing form 1.46 × 10−6 to 17.47 × 10−6 mmol. Moreover, the as-synthesized AuNPs exhibited a remarkable normalized catalytic activity (4.04 × 105 min−1 mol−1), which was much higher than that observed for AuNPs synthesized by other biological and conventional chemical methods.