Citrus limetta Risso peel mediated green synthesis of gold nanoparticles and its antioxidant and catalytic activity

Green synthesis of noble metal nanoparticles is now receiving great attention because of their numerous applications such as optics, catalysis, and biomedicine. In this work, gold nanoparticles were synthesized from peel extract of sweet lime (Citrus limetta Risso), which is usually discarded as a bio-waste. Bioactive components present in the fruit peel extract act as reducing and capping agents for the synthesis of gold nanoparticles from chloroauric acid (HAuCl4). The visual color change from light yellow to ruby red suggested the formation of gold nanoparticles, which was further confirmed by the maximum absorption peak at 530 nm of colloidal suspension measured by UV–vis spectroscopy. XRD spectra indicated the crystalline nature of prepared gold nanoparticles. The average crystallite size of gold nanoparticles measured from prominent peaks of XRD was found to be around 64 nm (size range: 50–80 nm), which was further supported by FESEM analysis. The components responsible for the reduction of chloroauric acid into gold nanoparticles were analyzed by FTIR, which suggested the presence of several phytochemicals e.g. phenol, carboxylic acid, amines, and alkynes in the fruit peel extract. Green prepared gold nanoparticle was further evaluated for its antioxidant and catalytic activity. Green gold nanoparticles exhibited excellent antioxidant activity evident by scavenging/inhibition of free oxygen/nitrogen radical generation. Furthermore, green gold nanoparticles demonstrated excellent catalytic activity indicated by the reduction of 4-nitrophenol into 4-aminophenol. This study highlights the significance of bio-waste for the production of nanostructure of noble metals for numerous applications.