Effective removal of Cr(VI) from aqueous solution by diamino-functionalised mesoporous MCM-48 and selective oxidation of cyclohexene and ethylbenzene over the Cr containing spent adsorbent.

Adsorptive removal of Cr(VI) by N -3-trimethoxysilylpropylethylenediamine (AEAPTMS) functionalised MCM-48 prepared via grafting method was investigated with respect to contact time, adsorbent dose, initial metal ion concentration, pH, amine loading and temperature. The synthesized samples were characterized by X-ray diffraction (XRD), fourier transform infrared (FTIR) spectrocopy, scanning electron microscopy (SEM), N 2 adsorption-desorption isotherm and thermogravimetric analysis (TGA). 1.5 mmol AEAPTMS functionalised MCM-48 sample showed highest adsorption among the modified samples under similar conditions. Adsorption kinetics was successfully fitted by pseudo second-order kinetic model. The experimental data fitted well to the Langmuir adsorption isotherm model with a calculated maximum adsorption capacity of 166.67 mg/g. The overall adsorption was a spontaneous and endothermic process as signified by the thermodynamic parameters. Another aspect of the work was the high catalytic efficiency of chromium containing spent adsorbent obtained by adsorption of Cr(VI) from the aqueous solution. The catalytic activity of the obtained catalyst was found to depend on the amount of adsorbed chromium. The spent adsorbents behaved as efficient catalysts for oxidation of cyclohexene (81.0% conversion) and ethylbenzene (94.6% conversion) with 96.7% and 100% selectivity towards desired product when 70% tert-Butyl hydroperoxide (TBHP) was used as oxidant. [ABSTRACT FROM AUTHOR]