Synthesis and adsorption performance of Mg(OH)₂ hexagonal nanosheet–graphene oxide composites

A series of Mg(OH)₂ hexagonal nanosheet–graphene oxide (GO) composites were synthesized through a simple hydrothermal method using magnesium nitrate and GO as precursors, sodium nitrate and sodium oxalate as additives, and sodium hydroxide and ammonia as precipitants. The as-prepared samples were characterized by X-ray diffraction, nitrogen adsorption–desorption isotherms, Raman spectroscopy, zeta potential analysis, and scanning electron microscopy (SEM). The adsorption affinity of the as-prepared samples toward congo red (CR) in water was analyzed and investigated. Results indicated that GO addition influenced the thickness, morphology, and adsorption performance of Mg(OH)₂ hexagonal nanosheets. As GO concentration increased, the thickness decreased. Especially at high GO concentration (1 wt%), Mg(OH)₂ hexagonal nanosheets changed into aggregated flower-like spheres. Addition of small amounts of GO also increased the adsorption capacity of Mg(OH)₂. The equilibrium adsorption data of CR on the composite were further investigated by Langmuir and Freundlich models, indicating that the Langmuir model was much more suitable for the experimental data. The sample prepared with 0.5 wt% GO showed the highest adsorption capacity with 118 mg g⁻¹. The experimental data were then fitted using pseudo-second order kinetics, suggesting that pseudo-second order kinetics could well describe the adsorption of CR on composites. Adsorption thermodynamics analysis showed that the adsorption activation energy was 29.2 kJ mol⁻¹, suggesting that the adsorption of CR onto the samples was physical adsorption. Adsorption between the samples and CR was mainly due to the strong electrostatic attraction between them because they had opposite charges. These findings indicated that Mg(OH)₂–GO composite was an effective adsorbent for the removal of CR in water. Copyright © 2015 Elsevier B.V.