Synthesis and characterization of coral-like hierarchical MgO incorporated fly ash composite for the effective adsorption of azo dye from aqueous solution

Highlights: • Synthesis of coral like hierarchical MgO doped fly ash using hydrothermal process. • The effective adsorption of azo dye on MgO doped fly ash. • Adsorption equilibrium is analyzed by the Langmuir and Freundlich models. • MgFA based good adsorbent for some other anionic dyes. • XRD, FT-IR, FE-SEM and EDX studies of MgO doped fly ash. In the present work, coral like hierarchical magnesium oxide (MgO) incorporated fly ash (FA) composite (FAMgO) synthesised by sol-gel method was evaluated for the adsorption of Reactive Black 5 (RB5) azo dye from aqueous solution. Adsorbent characterization using FE–SEM, XRD and FT-IR ascertained the formation of the FAMgO composite. Batch mode sorption studies were carried out for RB5 azo dye removal as a function of pH, FAMgO dose, initial dye concentration and temperature. The compliance of Langmuir isotherm model (R² = 0.999) corroborated the homogeneous nature of sorption of RB5 dye onto FAMgO with the sorption capacity (Q_max) of 48.78 mg g⁻¹. The regression coefficient value revealed the best fit of pseudo–second–order model with the Q_e value of 29 mg g⁻¹. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° suggested the spontaneous and endothermic nature of RB5 dye sorption onto FAMgO and suitable mechanism has been proposed.