Synthesis and characterization of montmorillonite – Mixed metal oxide composite and its adsorption performance for anionic and cationic dyes removal

Abstract

Composite material based on montmorillonite – mixed metal oxides (MMT_MMO) derived from ZnAl layered double hydroxides was successfully synthesized by facile co-precipitation method under the presence of montmorillonite suspension followed by calcination at 400 °C. The as-synthesized material was characterized by several characterization techniques, including XRD, FTIR, SEM, TEM, TGA, and BET, then tested as an adsorbent for removal of both methylene blue (MB) as a cationic dye and congo red (CR) as the anionic dye from aqueous solution under different contact time, dye concentration, temperature, and pH. The as-synthesized MMT_MMO exhibited the hybrid characteristic of MMT and nano-sized mixed metal oxides. Nano-sized mixed metal oxides were successfully distributed on the surface of MMT, which brings advantages to improving the adsorption capacity of the material for anionic-based dye removal. Moreover, the average pore diameter of synthesized MMT_MMO composite was not significantly different (3.69 nm) compared to the original MMT (3.70 nm). The adsorption kinetics of MB and CR onto MMT_MMO was best fitted by the pseudo-second-order model, which indicated that the rate-limiting step was chemisorption. The equilibrium adsorption isotherm modeling to the experimental data revealed that the adsorption equilibrium data were best fitted by the Langmuir model, with maximum adsorption capacity reached 40 mg/g, which indicated that the sorption process occurred chemically in a monolayer of a homogenous surface. The calculation of the adsorption thermodynamic parameters exhibited that the adsorption process was conducted spontaneously under endothermic nature. This work provides a facile method for producing bifunctional material for the adsorption of both anionic and cationic dyes, which exhibited potential for total dyes removal from industrial wastewater.