Síntese verde de nanopartículas de prata a partir do extrato do bagaço de Vitis labrusca (cultivar Ives), caracterização e aplicação na desinfecção de efluentes industriais

Abstract

Traditional methodologies for the synthesis of metallic nanoparticles include the use of toxic chemicals that can have negative impacts on the environment and human health. Thus, a safer alternative to the production of these nanomaterials is based on the concepts of Green Chemistry, which uses less harmful reagents and from renewable sources. In this context, the goals of the present work were the green synthesis of silver nanoparticles (AgNPs) using the extract of Vitis labrusca (cultivars Ives) pomace, their characterization, and its subsequent application in the tertiary industrial wastewater treatment. The extraction conditions of bioactive compounds of grape pomace were previously optimized and, considering antioxidant activity, the system which achieved the best performance was extraction with a hydroalcoholic solution at 50% (v/v), assisted by a propeller. The main green synthesis parameters (i.e., extract concentration, silver nitrate concentration, and medium pH) were equally refined and the synthesized AgNPs were analyzed on the basis of their stability and morphology by means of several techniques including zeta potential (ZP), molecular absorption spectroscopy in the range of UV-Vis, transmission electronic microscopy (TEM), scanning electron microscopy with a field emission gun (SEM-FEG), energy dispersive spectroscopy (EDS), and Raman spectroscopy. The optimized conditions (AgNO3 solution at 2.5 mmol L-1, extract solution at 50.0 mg mL-1, and pH = 10.0) showed that the AgNPs had an average diameter of 2.9 nm and a charge density on nanoparticles higher than - 40.0 mV. From the information obtained by several characterization techniques, a mechanism for the green synthesis of AgNPs is proposed based on the gallic acid, which is the major phenolic compound of the hydroalcoholic extract. Bacterial activity of AgNPs was verified by determination of inhibitory minimum activity and by the formation of an inhibition halo in the bacteria grown by superficial diffusion assay, 11 against Gram-positive and Gram-negative bacteria. In conclusion, results obtained at the disinfection step revealed that chitosan-AgNPs pellets were effective in bacterial removal. After 1 h of contact, they promoted a reduction in the bacterial count of E. coli bacteria, thus enabling their application in tertiary industrial wastewater treatment. Finally, this work showed that is possible to perform an eco-friendly process for AgNPs synthesis using the extract of Vitis labrusca (cultivars Ives) pomace and utilize them as auxiliaries in wastewater disinfection