Facile preparation of Fe2O3 Al2O3 composite with excellent adsorption properties towards Congo red

Abstract

To remove the harmful dye Congo red (CR) from water, porous Fe2O3 Al2O3 composite was designed using a sol-gel and an organic solvent sublimation drying (OSSD) strategy. The composite contained mainly γ-Al2O3, together with various amounts of γ-Fe2O3, α-Fe2O3, and/or AlFeO3 if Fe/Al and heating strategy were properly controlled. It has high specific surface areas ranging from 126 to 210 m2/g. Its pores (10–30 nm) were formed between the homogeneously mixed Fe2O3 and Al2O3 spherical nano particles. Its CR adsorption behaviour was affected by such factors as pH, initial CR concentration and contact time, and had reached a maximum equilibrium adsorption capacity of ~941 mg/g under the neutral pH condition (~7.5) and an initial CR concentration of 100 mg/L. Such adsorption behaviour obeyed the Weber-Morris intra-particle diffusion, pseudo-second-order kinetic and Freundlich isotherm models, suggesting that the adsorption behaviour was kinetically limited by the intra-particle diffusion and chemical adsorption steps and it was likely to be multi-layer adsorption. Furthermore, it also showed a magnetization of around 3.48–5.51 emu/g under the magnetic field (3T), ensuring decent magnetic properties for recycling. This work may provide new insights for the efficient removal of organic dyes.