Photocatalytic and antibacterial potential of silver nanoparticles derived from pineapple waste: process optimization and modeling kinetics for dye removal

Green chemistry offers several benefits over other synthesis routes of nanoparticles due to their eco-friendly attributes during their formulation as well as application stages. In the present study, an aqueous extract of Ananas comosus (Pineapple) peel waste was successfully exploited for the synthesis of ultra small (average size 14-20nm) silver nanoparticles (AgNPs) without adding any reducing or stabilizing agents. Two major factors, i.e., concentration ratio between silver ion precursor versus peel extract and synthesis pH were found to be influential for achieving monodispersed and stable AgNPs. Biogenic AgNPs adorned with natural moieties demonstrated good photocatalytic activity against methylene blue (MB) dye under sunlight illumination for various conditions. The process variable, e.g., solution pH, initial MB concentration and contact time were optimized using response surface methodology (RSM) based on three levels Box-Behnken design. A maximum MB removal of 98.04% was achieved at optimized values of 9.96 pH, 40ppm initial dye concentration and 173min of contact time. The kinetics of MB removal was best fitted to its first order kinetic model (R-2=0.996) in concurrence with intraparticle diffusion-mediated adsorption. AgNPs were also found to be effective to kill pathogenic bacterial strains, Pseudomonas aeruginosa and Bacillus subtilis as characterized from zone of inhibition (ZoI) and viability tests. Undergoing photochemical reactions, the generation of reactive oxygen species (ROS) was elucidated as the major mechanism of AgNPs' toxicity modulating membrane permeability. This strategy is not only economically viable and environmentally benign, synthesized AgNPs were capable to remove methylene blue dye almost completely under ambient conditions through solar energy.