Influência do ácido glicólico na síntese de nanopartículas de prata por método alcoólico

Abstract

Metal nanoparticles have gained significant scientific interest due to their physicochemical properties, such as high conductivity and catalytic activity, improved optical properties and biocidal activity against pathogenic microorganisms. In particular, silver nanoparticles have potential activity against bacteria, fungi and viruses. In the present study, the objective was to synthesize and characterize silver nanoparticles prepared by the alcoholic method. The method consists of the chemical reduction of silver using ethanol with the addition of polyvinylpyrrolidone (PVP), without and with the presence of glycolic acid (GA), in proportions 1:1; 1:5 and 1:10 (AgNO3/PVP:GA). The reaction system was kept under reflux and under constant stirring for 4 h at 80°C. The samples were characterized regarding their optical, structural, morphological properties and size estimation. Confirmation of the formation of silver nanoparticles was performed using the spectroscopy technique in the UV-Vis region. The formation of the characteristic plasmonic band of AgNPs was observed around 420nm without and with the presence of glycolic acid, thus confirming the formation of AgNPs. The identification of the functional groups present in the samples was evaluated by the technique of vibrational absorption spectroscopy in the infrared region (FTIR). The AgNPs samples, for being constituted mostly of ethanol, showed the characteristic vibrational modes of this. The nanoparticles showed positive charges and zeta potential values ​​of 16.8 ± 0.485mV; 12.7mV; 3.37mV and 3.04mV, for AgNPs and AgNPs-GA (1:1; 1:5 and 1:10), respectively. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) indicated that the materials presented nanometric dimensions, almost spherical shape with an average diameter of 8.70nm, 7.7nm, 8.6nm and 11.5nm (MET); 10.1 ± 2.50nm, 140 ± 59.7nm, 188 ± 83.2nm and 247 ± 68.1nm (DLS), for syntheses performed without and with the presence of glycolic acid (1:1; 1:5 and 1:10), respectively. In the results obtained by SAED, the AgNPs presented a face-centered cubic crystal structure (CFC) characteristic of Ag, in which the results corroborate the crystallographic record JCPDS 04-0783. It is concluded that the synthesis of AgNPs only in the presence of PVP resulted in stable alcoholic colloidal suspensions. As GA was added in the aforementioned proportions, a decrease in colloidal stability and consequent aggregation of the particles was observed. Larger dimensions and different shapes of silver nanoparticles were observed as the GA concentration in the reactions increased. In the results obtained by SAED, the AgNPs showed a face-centered cubic crystal structure (CFC) characteristic of Ag, in which the results corroborate the diffraction data JCPDS 04-0783. It was concluded that the synthesis of AgNPs only in the presence of PVP resulted in alcoholic colloidal suspensions, yellow in color, considered stable. As GA was added in the aforementioned proportions, a possible reduction in colloidal stability, change in viscosity and widening of plamonic bands was observed. Larger dimensions and different shapes of AgNPs were observed as the concentration of GA increased.