Generation of supported silver nanoparticles by reduction of silver-exchanged LTA zeolite

G. MACHADO; M. R. GONZALEZ; E.I. BASALDELLA; A. M. PEREYRA

Santa Fe

Congreso; VI San Luis Conference I; 2018

UNL-INTEC.CONICET

Supported nanoparticles remain a subject of intense studies because of their countless applications in many technological areas such as catalysis, sensor design, electronics, medicine, etc. Recent developments are based on the control of properties in the nanometer range in order to obtain suitable materials for particular applications. In case of Ag nano species, the specific properties arise from variations in the chemical states and positions of silver entities dispersed in the matrix. Different meso- or microporous materials are being used as support in order to precipitate silver nanoparticles on their external and internal surfaces, such as mesoporous silica MCM-41, SBA-15, faujasites, NaA. Besides, several advantages are offered by using microporous materials as supports because they allow the synthesis of particles with narrow size distributions and homogeneously dispersed in their internal surfaces.In this work, silver nanoparticles dispersed in a solid matrix consisting of micrometer-sized crystals of zeolite NaA were obtained. The reduction method for getting the metallic nanoparticles, as well as the presence of silver in the exchange sites of the zeolite, were varied in order to establish their influence on the generation of supported, individual, not segregated silver nanoparticles. Two procedures for obtaining silver nanoparticles were applied: (1) thermal treatment in O2 atmosphere and (2) chemical reduction using sodium citrate. Transmission electron microscopy (TEM) and UV-vis spectroscopy (UV-vis) analyses confirmed the presence of rounded crystalline silver nanoparticles, homogeneously dispersed on the outer surface of the zeolite crystals. Silver nanoparticles coexist with non-crystalline clusters and silver cations hosted inside the porous structure. The existence of Ag0 and Ag2O nanoparticles was confirmed by X-ray diffraction (XRD). The chemical treatment mostly led to the formation of Ag2O nanoparticles. According to the reduction treatment, the size of synthesized nanoparticles can oscillate from 2 up to 34 nm, exceeding the pore diameter of the three-dimensional matrix network. This fact suggests that the Ag ordering starts inside the matrix cavities with cluster formation and posterior occurrence of cluster linking and growth on the external zeolite surface.