Preparation of Negatively Charged Hybrid Adsorbents and Their Applications for Pb2+ Removal

A novel approach to the negatively charged hybrid adsorbents was proposed. These hybrid adsorbents were prepared via the ring opening of pyromellitic acid dianhydride (PMDA) and N-[3-(trimethoxysilyl)propyl]ethylenediamine and a subsequent sol gel process. Fourier transform infrared spectra confirmed the step products. Their adsorption kinetics, isotherm, and thermodynamic parameters Delta G, Delta H, and Delta S for Pb2+ removal from aqueous solution were examined. Differential scanning calorimetry and thermogravimetric analysis thermal amylases showed that these samples had high thermal stability and the crystallization temperature increased with an increase in the PMDA content because of cross-linking between organic and inorganic moieties and the further formation of a hybrid matrix. Adsorption experiments indicated that Pb2+ adsorption on these hybrid adsorbents followed the Lagergren second-order kinetic and Langmuir isotherm models. The negative values of Delta G and the positive values of Delta H showed that Pb2+ adsorption on these hybrid adsorbents was spontaneous and an endothermic process in nature. Scanning electron microscopy and energy-dispersive spectrometry images further confirmed Pb2+ ions on the surfaces of samples A-D. Moreover, a desorption experiment indicated that they can be regenerated. These findings suggest that the prepared hybrid adsorbents are promising in the separation and recovery of Pb2+ ions from contaminated water.