Use of nanometer mesoporous MCM-41 for the removal of Pb(II) from aqueous solution

Abstract

Mobil Composition of Matter (MCM)-41 molecular sieve was successfully synthesized. Power X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM) were used to characterize the sample. The sample showed spherical particles, and the morphology was regular. Its average particle diameter was 110 nm. TEM images showed that the sample structure presented a honeycomb pore structure and the average pore diameter was 3.5 nm. Pb2+ was adsorbed from water body by the MCM-41. The effects of acidity, contact time, temperature, adsorbent material amount and initial Pb2+ concentration on the adsorption rate were studied, and the optimum conditions of adsorption were obtained. The results show that when acidity pH value was 4.5, temperature was 25 °C, contact time was 40 min and the adsorbent material MCM-41/Pb2+ = 7.5, the adsorptive effect was the best, the adsorption rate reached 98.78% and the adsorptive capacity was 131.71 mg/g. Kinetic and thermodynamic properties of the adsorptive process were studied. Experimental results show that the adsorption of Pb2+ by MCM-41 belongs to the pseudo-second-order adsorption. According to thermodynamic equation, ΔG = ΔH − TΔS, ΔH = − 24.86 kJ/mol and ΔS = − 72.34 J/(mol K) were obtained by calculation, indicating that the adsorption was exothermic and an entropy reduction process. At the temperature of 298, 308 and 318 K, the free energy change was, respectively, ΔG1 = − 3.286 kJ/mol, ΔG2 = − 2.586 kJ/mol and ΔG3 = − 1.86 kJ/mol, illustrating that at the above temperature the reaction can be carried on spontaneously. Nitric acid, hydrochloric acid and acetic acid were, respectively, used to investigate their effect on desorption. The results show that the desorption effect using nitric acid as a desorption agent was better than those of hydrochloric acid and acetic acid. When desorption was 5 h and the nitric acid concentration was 0.5 mol/l, the desorption rate was the highest that was reached 70.01%.