Direct incorporation method for the synthesis of molybdophosphate/MCM-41 silica composite: Adsorption study of heavy metals from aqueous solutions

The direct incorporation of α-Keggin structure, [PMo12O40]3−, derived from ammonium molybdophosphate into the mesopores of MCM-41 silica to synthesis MP/MCM-41 composite was carried out using soft-templating approach which based on surfactant self-assembly. The aimed composite material was characterized by XRD, FT-IR, SEM and BET techniques. Sorption properties of the synthesized composite powder were evaluated through sorption of lead, copper and cadmium ions from their multicomponent aqueous solutions. Preliminary studies of cation hydrolysis using MINTEQA2 software program was accomplished indicating that at pH of 5 the highest percent of free Pb2+, Cu2+ and Cd2+ was attained. Batch sorption tests were carried out at different initial heavy metal ion concentrations revealing that the synthesized composite has great selectivity to lead ions over copper and cadmium ions. The experimentally obtained sorption results were analyzed using pseudo-1st and -2nd order kinetic models to stand on the possible sorption mechanisms indicating the sorption behavior of the studied ions onto MP/MCM-41 composite belonged to the pseudo 2nd order kinetic model and the sorption process was a chemical process. Isotherm plots were constructed and analyzed using Langmuir and Freundlich isotherm models. Results indicated that the best fitting to the experimentally obtained data was obtained when Langmuir isotherm model was applied.