Optimization of biosynthesis of stabilized silver nanoparticles using bitter orange peel by-products and glycerol

Abstract

Nowadays, the biosynthesis of metal nanoparticles (NPs) through eco-friendly, cost-effective, and sustainable methods has drawn considerable attention. In this study, the green synthesis of silver NPs using AgNO3 salt and the peel extract of bitter orange (Citrus aurantium) as a reducing agent was modeled and optimized by central composite design (CCD). Accordingly, the process parameters including pH (7–11), time (0–4 h), and the ratio of extract/salt solution (0:100–20:80 v/v) were considered to model the responses including the spectrophotometric wavelength of maximum absorbance (λmax) and the maximum absorbance value at λmax (Amax), which represented the size and concentration of Ag NPs, respectively. Additionally, the stabilizing effect of glycerol (ratio of glycerol to salt 0–10 g/g) on the optimum treatment was studied using spectrophotometric and SEM analyses. The results showed that the quadratic and linear models were acceptably fitted to the experimental responses of Amax and λmax, respectively. The optimization results demonstrated that the optimal reaction parameters to achieve the maximum Amax were pH = 10.92, time = 3.5 h and ratio of extract/salt = 17.94:82.06 (v/v). Furthermore, glycerol could favorably play a stabilizer role in the optimum biosynthesized Ag NPs during the reaction and 14 days of storage at room temperature. The ICP-OES and TEM analyses of the stabilized Ag NPs (with 2.5 g/g glycerol) showed the presence of Ag element as nanospheres with ∼20 nm in size. The Ag NPs had great antibacterial properties against Staphylococcus aureus and Escherichia coli. Therefore, the bitter orange peel extract and glycerol could be promisingly used as novel reducing and stabilizing agents, respectively, to synthesize nanosilver via an eco-friendly and economical green approach.