Síntese de nanopartículas de prata mediadas por extratos vegetais de Astrocaryum aculeatum

Abstract

Considering the different methods of preparation of silver nanoparticles (AgNPs), the biological route is an interesting alternative due to its low environmental impact and the use of renewable raw materials in the process. Plant extracts have shown promising results in the production of AgNPs, in addition, there is a great diversity of plants in the Amazon region whose extracts (stem, fruit, seed and leaf) can be used as bioreducing agents in alternative synthetic routes. The present study investigated the formation of AgNPs through synthesis mediated by aqueous extracts of tucumã pulp (Astrocaryum aculeatum) under different conditions, evaluating the impact of changes in experimental conditions on the resulting aqueous dispersions of the nanostructures. Low concentrations of tucumã extract (2 g of pulp in 200 mL of water) in the reaction medium were not sufficient to reduce all silver ions present during the investigated time period. Meanwhile, high concentrations of phytochemicals (4 g of pulp in 200 mL of water) generated a competition between the bioreduction processes and the complexation of silver cations. The conditions in alkaline medium exhibited bands related to the formation of AgNPs in a shorter time, formed more nitid signals, with greater intensity and at shorter wavelengths, according to the UV-Vis spectroscopic technique, indicating the occurrence of smaller and more uniform nanostructures acid media. The DLS results also showed a similar trend, indicating a smaller average size of AgNPs in alkaline medium in relation to the samples obtained in acidic media. For the temperature variation, an increase in this parameter resulted on an intensification of the signal related to the SPR band. However, the results of DLS suggest that the increase in temperature favors the polydispersivity of AgNPs, decreasing the metastability of the produced colloids. Antimicrobial activity was detected for the sample with intermediate concentration of plant extract (3 g of pulp in 200 mL of water), alkaline medium at 40 ºC temperature against E. coli. The results suggest that the formation of AgNPs is influenced by the experimental parameters concentration of plant extract, pH and temperature. The sample obtained using intermediate concentration of plant extract, at pH 9 and at a temperature of 40 ºC is the most appropriate condition to meet the microbicidal objective proposed in this study.