Advancement of Microwave-Assisted Biosynthesis for Preparing Au Nanoparticles Using Extract and Evaluation of Their Catalytic Reduction of 4-Nitrophenol.

This study describes the biosynthesis of gold nanoparticles (AuNPs) using the extract of in the buffer zone of Bach Ma National Park, Vietnam, as a reducing and protecting agent using microwave-assisted synthesis. The as-synthesized AuNPs were characterized using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Compared to the conventional method, the proposed microwave-assisted method produced AuNPs having a small size of 22.07 ± 8.11 nm in a short synthesis time period. In excess NaBH, the as-prepared AuNPs demonstrated good catalytic activity for reducing 4-nitrophenol to 4-aminophenol. Furthermore, AuNPs demonstrated improved reusability after four cycles. The pseudo-first-order apparent rate constant was estimated to be 0.086 min at 303 K. Both the catalytic mechanism and reaction path of reduction were proposed. Moreover, activation energy and thermodynamic parameters, including activation enthalpy and entropy, were examined.