GIS zeolite obtained by the microwave-hydrothermal method: Synthesis and evaluation of its adsorptive capacity

Abstract

Developing synthetic routes that lead to the formation of zeolites with small porous systems, such as GIS zeolites, has attracted great interest since these structures have unique properties in catalysis and adsorption, but are still underused. In this study, GIS type zeolite nanoparticles were synthesized by the microwave-assisted hydrothermal method. Two synthesis routes were evaluated using two different silica precursor sources. Silicon dioxide was used in crystalline and amorphous forms. The material was characterized by X-ray diffraction (XRD), nitrogen physisorption, zeta potential (ZP), high-resolution scanning electron microscopy (SEM-FEG), high-resolution transmission electron microscopy (HRTEM) and by energy dispersive X-ray spectroscopy (EDS). The obtained crystalline phase was the Na–P1 type zeolite (GIS structure). The BET surface area of the particles was 17 m2/g and the average pore size was 4 nm. These zeolites were used for Mn(II) ions adsorption in aqueous medium. Considering the studied adsorption conditions, adsorption was higher at pH 8, using an adsorbent concentration of 1 g/L and with 30 min of contact time. The kinetic model that best described the process was the pseudo-second order model and the isotherm model that best fitted to the experimental data was the Langmuir model, which indicates adsorption in monolayers and high affinity between the adsorbate and the adsorbent. The maximum adsorption capacity was 44.05 mg/g.