Preparation and characterization of nanoporous resin for heavy metal removal from aqueous solution

New nanoporous resin (NPR), based on organic xerogel compounds, was prepared at 150 °C by sol–gel method from pyrogallol and formaldehyde mixtures in water using perchloric acid as catalyst. NPR was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and nitrogen porosimetry. The metal uptake characteristics were explored using well-established and effective parameters including pH, contact time, initial metal ion concentration and temperature. Optimum adsorptions of Cr(VI) and Cd(II) were observed at pH 3 and 4, respectively. Langmuir model gave the better fit for Cd(II) whereas for Cr(VI), Freundlich model was better than the other models to fit the experimental data. Kinetic studies revealed that the adsorption of Cd(II) was very fast compared to Cr(VI), and its data are well fitted by the pseudo-second-order kinetic model. The thermodynamic properties, i.e. ΔG°, ΔH° and ΔS°, showed that adsorption of Cr(VI) and Cd(II) onto NPR was endothermic, spontaneous and feasible in the temperature range of 27–55 °C.