Adsorption efficiency, thermodynamics, and kinetics of amino-functionalized mesoporous calcium silicate for the removal of heavy metal ions.

Amino-functionalized mesoporous calcium silicate (MCS-NH₂ ) 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-NH₂ were characterized, and the adsorption performance and thermodynamic and kinetic characteristics of MCS-NH₂ were investigated using Pb²⁺, Cd²⁺, Cr³⁺, and Cu²⁺. MCS-NH₂ maintained its mesoporous slit-pore structure with a specific surface area of 114.32 m² /g, and pore size was mainly within 4.5–49 nm in the modification. The amount of –NH2 grafted to MCS-NH₂ was 1.6106 mmol/g. The equilibrium data of Pb²⁺, Cd²⁺, Cr³⁺, and Cu²⁺ adsorbed by MCS-NH₂ 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 Pb²⁺, Cd²⁺, Cu²⁺, and Cr³⁺, respectively. The adsorption processes were endothermic, entropy increasing, and spontaneous. The adsorption of Pb²⁺, Cd²⁺, Cr³⁺, and Cu²⁺ by MCS-NH₂ 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-NH₂ can be used as an effective sorbent for removing Pb²⁺, Cd²⁺, Cr³⁺, and Cu²⁺ and other related hazardous metal ions from wastewater. [ABSTRACT FROM AUTHOR]