BIOGENIC SILVER NANOPARTICLES AS SUSTAINABLE CATALYSTS FOR THE DEGRADATION OF ORGANIC POLLUTANTS IN WASTEWATER

Abstract

The release of organic contaminants such as synthetic dyes, nitro aromatics, pesticides, and traces of pharmaceuticals into aquatic environments is one of the biggest environmental challenges of industrialized countries. Most of the conventional treatment technologies have a high energy demand, create secondary sludge, or cannot break down recalcitrant molecules. In this context, nanocatalysis is deemed a viable approach to the efficient degradation of such pollutants and, in particular, silver nanoparticles (AgNPs) possess a high surface-to-volume ratio, tunable surface Plasmon resonance, and high redox activity. In this research paper, both plant extracts (organic compounds) and the bacterial, fungal, and algal metabolites mediate the reduction, capping, and stabilization of AgNPs, acting as both reductants and surfactants, without the need for the toxic reductants and surfactants of traditional colloidal chemistry. The mechanisms of the biogenic synthesis, the physicochemical parameters that affect the particle size and shape of the product, and the analytical methods developed to characterize the product are discussed. Next, the catalytic activity of the biogenic AgNPs was evaluated on two representative reaction classes, namely borohydride-assisted reduction of nitro aromatics, according to the electron-relay theory of Langmuir–Hinshelwood, and photocatalytic mineralization of dyes in the presence of light and reactive oxygen species. A collection of representative literature values for degradation efficiency and apparent rate constants is presented, and the factors that affect activity, such as size, shape, dose, pH, and nature of the bimolecular capping layer, are assessed. Finally, the reusability, real-effluent applicability, green-chemistry aspects, and the major challenge to large-scale deployment are considered. Biogenic AgNPs constitute a technically viable and environmentally protective catalytic platform with respect to wastewater treatment, the focus of which needs to be statistically ensured and standardized, as well as methodologically addressed through a growing body of nanotoxicological research.

Keywords : biogenic silver nanoparticles; green synthesis; catalytic degradation; organic pollutants; wastewater treatment; photo catalysis; environmental.