Nonhydrolytic sol-gel in-situ synthesis of high performance MgAl2O4/C adsorbent materials

Abstract

MgAl2O4/C composite was prepared via a facile low-temperature non-hydrolytic sol-gel (NHSG) route, using Mg powder, Al wire and isopropanol as raw materials. The influence of types of magnesium source and heat treatment temperature on the synthesis and adsorption properties were investigated, and the adsorption mechanism was also studied. The results showed that the amorphous MgAl2O4 formed at < 600 °C, and it crystallized at 700 °C. No impurity phase appeared in the samples calcined at 700–1300 °C, which was attributed to MgAl2O4 crystallized directly from Mg(Al(OiPr)4)2. The uniform-doped carbon in MgAl2O4/C composites came in-situ from the organic groups in Mg(Al(OiPr)4)2. MgAl2O4/C showed a superior adsorption capacity for Congo red (CR). The bimetallic alkoxides structure was favorable for high adsorption property, and the adsorption property of amorphous MgAl2O4/C was significantly superior to that of its crystalline counterpart. The adsorption kinetics data was fitted with the pseudo-second-order model, while the Langmuir isotherm model could well descript the adsorption isotherm behavior, and the maximum adsorption capacity for CR was 5690 mg/g. The high adsorption capacity was attributed to the Lewis acid-base reaction and the electrostatic interactions between the anionic dye CR and MgAl2O4/C surface as well as the in-situ carbon, and amorphous state.