Flower-like biogenic gold nanostructures for improved catalytic reduction of 4-nitrophenol

In this study, novel flower-like biogenic gold nanostructures were prepared using gallnut extract and HAuCl4. Gallnut extract is a rich source of phytochemicals such as tannic acid, gallic acid, and polyphenol antioxidants. The process involves the reduction of gold ions in the presence of gallnut main constituents that act as a reducing and shape directing agent for Au. The formation of gold nanoflowers (AuNFs) was confirmed by UV–visible spectroscopy at 629 nm. The absorbance broadened over time, confirming that the size of the nanoparticles increased, resulting in a flower-like framework. Transmission electron microscope analysis showed that gold nanoparticles (AuNPs) with an average size of 8.02 nm self-assemble and grow into nanoflowers with an average diameter of 60.6 nm. In addition, the catalytic behavior of AuNPs and AuNFs was compared for the reduction of 4-nitrophenol to 4-aminophenol. AuNFs showed up to 1.57 times higher catalytic activity towards 4-nitrophenol than AuNPs. The conversion yield of 4-nitrophenol to 4-aminophenol for AuNFs was determined to be 98.1% using high performance liquid chromatography. AuNFs synthesized using green process can be applied in catalysts, wastewater treatment, and sensors.