Potassium-assisted synthesis of SUZ-4 zeolite as an efficient adsorbent for Pb2+ removal from wastewater

Abstract

With the assistance of K+, the amount of organic template (TEAOH) in the synthesis was enormously reduced to only 3% of that in the traditional synthesis for the SUZ-4 zeolite. Characterizations such as XRD, SEM, XRF, N2 adsorption/desorption, and 27Al MAS NMR were carried out to determine the physicochemicalproperties of SUZ-4 zeolites (T1 and T13) synthesized with different TEAOH amount. The specific role of the additional K+ in the synthesis was determined by the combination of experimental data and density functional theory (DFT) calculations. It showed that K+ co-caged with TEA+ preferentially locate in the cages containing 8-MR, and the role of the co-caging K+ ions is to arrange the formed composition building units (CBU) into the SUZ-4 framework. The SUZ-4 zeolite exhibited a fast adsorptive equilibrium of 5 min and high selectivity for Pb2+ in wastewater. The effects of temperature, contact time, adsorbent dosage, pH and initial concentration of Pb2+ solution on adsorption capacity were studied to optimize process conditions. The adsorption kinetics and isotherms suggested that the adsorption rate is determined by the chemical adsorption on the adsorbent surface, and the adsorption ability is related to the physisorption sites in the pores. The adsorption process was composed of two steps and was the comprehensive contribution of ion exchange and chemical adsorption of PbO formation. There was no downtrend in the adsorption of SUZ-4 for Pb2+ after ten adsorption-desorption cycles, demonstrating the excellent application prospects of SUZ-4 in removing Pb2+ in wastewater.