Synthesis and characterization of hybrid MCM-41 materials for heavy metal adsorption

A small dithiocarbamate molecule, N-(2-Aminoethyl)dithiocarbamate, was synthesized, characterized and afterwards used to modify and activate the surfaces of MCM-41 materials. The structure and the surface charge properties of the starting and the novel organic–inorganic hybrid mesoporous materials were studied by means of powder X-ray diffraction, Fourier transform infrared spectroscopy, DTA/TG thermal analyses, surface area measurements and potentiometric acid–base titrations. The hybrid materials retained the regular hexagonal arrangement of cylindrical pores which is the characteristic of the MCM-41 solids, while a high content (2.57 mmol/g) of the organic molecules in the final products was achieved. Despite the high concentration of the dithiocarbamate molecules in the pores of the hybrid MCM-41 materials, final solids retained high specific surface areas (632 m2/g) indicating a homogenous incorporation of the small organic molecules in the pores. A surface complexation model was developed to explain the results of the potentiometric titrations and to describe the surface charge and H-binding properties of the starting and final hybrid materials. These materials are promising heavy metal adsorbents due to the presence of the effective dithiocarbamate groups and the low pH value (3.2) of the point of zero charge.