Synthesis and characterization of MCM-49/MCM-41 composite molecular sieve: an effective adsorbent for chromate from water

In this work a porous material, an MCM-49/MCM-41 composite molecular sieve, was synthesized via a microwave assisted hydrothermal process and characterized to observe its optimal properties for heavy metal chromate removal. The adsorption properties of chromate onto MCM-49/MCM-41 and the factors that influence its adsorption, such as chromate concentration and contact time, were investigated. It was found that MCM-49/MCM-41 is micro/mesoporous with a surface area of 372 m(2) g(-1) and average pore size of 2.9 nm. The adsorption capacity of MCM-49/MCM-41 was as high as 4.10 mg g(-1) for chromate at a temperature of 298 K, when the initial concentration of chromate was 50 mg L-1. The adsorption isotherm data of chromate fit well with both Freundlich and Langmuir adsorption isotherm models and the adsorption kinetics was well fitted using a pseudo-second order kinetic model. Thermodynamic parameters such as the standard Gibbs free energy (Delta G), enthalpy change (Delta H) and standard entropy change (Delta S) were also evaluated. Thermodynamic analysis indicates that the adsorption of chromate onto MCM-49/MCM-41 is a spontaneous and exothermic process. These results suggest that MCM-49/MCM-41 could serve as a promising adsorbent for potential applications in the removal of chromate from wastewater.