Adsorption removal of Congo red over flower-like porous microspheres derived from Ni/Al layered double hydroxide

Abstract

In this paper, flower-like microspheres of Ni/Al mixed oxide (Ni/Al-CLDH-H), which consist of a hollow core and mesoporous shell, were prepared with the aid of sulfonated polystyrene beads. Thanks to the unique structure, the adsorption performance of the sample toward Congo red (CR) was higher than that of the sample Ni/Al-CLDH-S consisting of a solid core and mesoporous shell, which was prepared in the absence of sulfonated polystyrene beads. The Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Redlich–Peterson and Sips isotherm models were utilized to describe the adsorption process of Ni/Al-CLDH-H; the Sips model was found to best fit the adsorption data. The adsorption kinetics of CR onto Ni/Al-CLDH-H followed the pseudo-second-order model best, compared with the use of the pseudo-first-order and Elovich models. The thermodynamic study showed that the adsorption process was endothermic and spontaneous in nature. Our newly developed material retained a superior adsorption capacity without a significant loss after a number of adsorption–desorption cycles; indicating its potential as a reusable adsorbent for efficient removal of CR in water.