Graphene/ternary layered double hydroxide composites: Efficient removal of anionic dye from aqueous phase

Ternary layered double hydroxide, MgCoAl (MCA) and its graphene-based composite (G/MCA) were fabricated via a simple co-precipitation technique. The composites along with their calcined products (MCA-C) and (G/MCA-C) were used as adsorbents for the removal of an anionic dye, methyl orange (MO), from aqueous phase. The characterization results (scanning electron microscopy and transmission electron microscopy) revealed homogeneous dispersion of graphene onto the MCA. Calcination of G/MCA resulted in a rough and heterogeneous surface with significant improvement in oxygen functionalities and surface area, which plays a crucial role in improved dye adsorption performance. Adsorptive equilibrium was established at 240 min for MCA and G/MCA and 180 min for MCA-C and G/MCA-C respectively at pH 3 and optimum dosage of 10 mg. The Redlich-Peterson and Langmuir isotherm models closely describe the adsorption process with maximum adsorption capacities of 357.14, 384.62, 400.12 and 434.78 mg/g for MCA, G/MCA, MCA-C, and G/MCA-C respectively. Kinetics modeling indicates the adequacy and fitness of the pseudo-second-order model. A thermodynamics evaluation substantiates the exothermic nature of the adsorption processes. The MO-graphene ternary LDH composite adsorption process is controlled by several mechanisms including hydrogen bonding, surface adsorption, chemical and electrostatic interactions with surface reconstruction. The high removal efficiency of the MO coupled with high recovery and reusability of these nanomaterials showcases their potential for deployment in wastewater treatment.