Insight into enhanced adsorption of Congo red by petal-like MgAl2O4: effect of dehydroxylation

Abstract

This paper reports a facile treatment to enhance the capacity of petal-like MgAl2O4 for Congo red (CR) adsorption. The influence of dehydroxylation treatment on the adsorption performance of petal-like MgAl2O4is investigated. FT-IR, XPS, TG, XRD and FE-SEM are employed to analyze the differences between samples without and with dehydroxylation. Mechanism on the adsorption capacity improvement of CR by MgAl2O4 after dehydroxylation is investigated systematically. Results show that the adsorption process conforms well to the pseudo-second-order kinetic model and Langmuir isotherm model. The adsorption mechanism study shows that the adsorption of CR on petal-like MgAl2O4is mainly due to chemisorption including Lewis acid-base interaction and electrostatic attraction. It is observed that the maximum adsorption capacity of petal-like MgAl2O4after dehydroxylation reaches 3264.54 mg/g, much higher than sample without dehydroxylation (591.72 mg/g). Most Lewis acid sites of petal-like MgAl2O4 (Mg2+ and Al3+) without dehydroxylation process are occupied by hydroxyl groups. It is not conductive to combine with NH2- and -SO32- in CR molecular, resulting in the deterioration of adsorption performance. The activity of Mg2+ and Al3+ in MgAl2O4 can be recovered greatly after the removal of hydroxyl groups, and it is favorable to the adsorption between MgAl2O4 and CR.