Adsorption efficiency, thermodynamics, and kinetics of amino-functionalized mesoporous calcium silicate for the removal of heavy metal ions
ABSTRACT Amino-functionalized mesoporous calcium silicate (MCS-NH 2 ) was synthesized by past-grafting with calcium nitrate tetrahydrate and sodium metasilicate nonahydrate as raw materials, cetyl trimethyl ammonium bromide as the template, and 3-aminopropyltriethoxysilane as the modifying agent. The structure and composition of MCS-NH 2 were characterized, and the adsorption performance and thermodynamic and kinetic characteristics of MCS-NH 2 were investigated using Pb 2+ , Cd 2+ , Cr 3+ , and Cu 2+ . MCS-NH 2 maintained its mesoporous slit-pore structure with a specific surface area of 114.32 m 2 /g, and pore size was mainly within 4.5–49 nm in the modification. The amount of –NH 2 grafted to MCS-NH 2 was 1.6106 mmol/g. The equilibrium data of Pb 2+ , Cd 2+ , Cr 3+ , and Cu 2+ adsorbed by MCS-NH 2 fitted the Langmuir and Redlich–Peterson models well but were more suitable for the latter. The maximum adsorption capacities deduced from the Langmuir model were 717.97, 631.43, 628.61, and 366.88 mg/g for Pb 2+ , Cd 2+ , Cu 2+ , and Cr 3+ , respectively. The adsorption processes were endothermic, entropy increasing, and spontaneous. The adsorption of Pb 2+ , Cd 2+ , Cr 3+ , and Cu 2+ by MCS-NH 2 was rapid and reached equilibrium within 60 min. The adsorption kinetics fitted the pseudo second-order model well, and the adsorption activation energy was 21.0187, 18.1051, 25.9062, and 16.8084 kJ/mol, respectively. The adsorption mechanisms included physical adsorption, chemical adsorption (especially surface complexing adsorption), and ion exchange, among which chemical adsorption was the dominant mechanism. The findings suggest that MCS-NH 2 can be used as an effective sorbent for removing Pb 2+ , Cd 2+ , Cr 3+ , and Cu 2+ and other related hazardous metal ions from wastewater.
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