Green synthesis of biogenic silver particles, process parameter optimization and application as photocatalyst in dye degradation

A stable dispersion of nano-structured silver particles (AgNPs) was synthesized using an aqueous extract of Citrus sinensis (orange) peel extract. Formation of AgNPs was confirmed using UV–visible spectroscopy. In the process, orange peel was used as both reducing agent and stabilizing agent. In the presence of extract, nanoparticles remained stable even after a time span of 20 days of their synthesis. Different physical parameters such as concentration of reducing agent, temperature, pH and time were being optimized for determination of optimal condition for synthesis of stable dispersion of nanoparticles. The AgNPs were further characterized using various techniques such as X-ray diffraction, dynamic light scattering, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy for getting information about their formation, composition, hydrodynamic diameter and size. The stability of the colloidal dispersion of nanoparticles over a wide range of temperatures and pHs was evaluated. The AgNPs were found to be stable over a pH range of 2–10 and temperatures ranging 25–75 °C. Later, these synthesized AgNPs were evaluated for their potentiality in antimicrobial activity. It was found that the nanoparticles showed significant bactericidal as well as fungicidal activity depending on the size of nanoparticles. In addition to this, AgNPs were evaluated for photocatalytic degradation of an azo dye, Congo red. Kinetic study of degradation has also been carried out and was found that the reaction followed pseudo-first-order kinetics.