Synthesis of nanorod-like mesoporous γ-Al2O3 with enhanced affinity towards Congo red removal: Effects of anions and structure-directing agents

Mesoporous gamma-Al2O3 with unique nanorod-like morphology were successfully synthesized by hydrothermal treatment of the freshly precipitated amorphous alumina gel using aluminium sulfate, aluminium nitrate and aluminium chloride as aluminium sources, and Pluronic P123 and F127 as structure-directing agents (SDAs), respectively. The microstructures, morphologies and textural properties of the as-prepared materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N-2 adsorption-desorption techniques. The adsorption performance of the gamma-Al2O3 for Congo red removal becomes better in the order of anions of aluminium sources: SO42-, Cl- and NO3-, and the SDAs: F127 and P123. Especially, the gamma-Al2O3 prepared from aluminium sulfate using P123 as SDA exhibits excellent adsorption performance for Congo red compared to those of the gamma-Al2O3 prepared from the other two aluminium salts, and it only takes 2 min for it to reach the adsorption capacity of 99.2 mg g(-1). The combination effect of different aqueous ionic radius of SO42-, Cl- and NO3-, different ethylene oxide (EO)/propylene oxide (PO) ratio and different molecular weights of P123 and F127 is suggested to be responsible for their significant difference in adsorption performance towards Congo Red removal.