Layered double hydroxide and graphitic carbon nitride hybrid as nanoadsorbent for selected azo-dye removal from aqueous solution

Textile industry effluents contain synthetic dyes which are hazardous to the environment. Layered double hydroxide (LDH) based hybrid composites are evolving as efficient nanosized adsorbents for water treatment. In the present study, adsorbents such as Mg-Al LDH, Graphitic Carbon Nitride, g-CN, and their hybrid nanocomposites (g-C3N4: LDH, C1 = 1:1, C2 = 1:2, C3 1:5) were studied for the separation of a selected dye from aqueous media. Adsorbents and composites were prepared by hydrothermal and wet-impregnation methods and characterized by XRD and SEM-EDS. It was observed that all adsorbents showed complete dye removal within 30 min of contact time. Results indicated that all the composites were found efficient however among them C2 worked best in terms of complete dye removal. Change in the pH of the adsorption medium has no decisive effect on the removal efficiency of MO whereas room temperature, as well as lower dye concentration, favored adsorption. The composite showed good regenerative performance for up to three cycles. The kinetics for adsorption of the methyl orange (MO) on composite followed the pseudo-second-order model. The adsorption isotherms studied were Langmuir, Freundlich, and Temkin. Among all these isotherms, the Freundlich model suitably justified the experimental data. Different thermodynamics parameters, such as Delta G degrees (Gibbs free energy), Delta S degrees (change in entropy), and Delta H degrees (change in enthalpy), revealed that the adsorption of MO by g-C3N4/LDH (C2 = 1:2) composite was exothermic and spontaneous.