Adsorption of eriochrome black T from aqueous phase on MgAl-, CoAl- and NiFe- calcined layered double hydroxides: Kinetic, equilibrium and thermodynamic studies

Abstract

Abstract This work reports the synthesis of MgAl-, CoAl- and NiFe-layered double hydroxides (LDH) with mole ratio of 3:1 via co-precipitation method and calcination at 350 °C under nitrogen for 2 h. The resultant calcined LDHs (CLDHs) were used for the adsorption of Eriochrome black T (EBT) dye from aqueous phase. The influence of pH, contact time, initial EBT concentration, and temperature on the EBT adsorption capacity, kinetics and mechanisms was investigated at bench scale. The optimum pH for the removal of EBT on all the three CLDHs was 2 and the equilibrium adsorption time was 60 min, 30 min and 60 min for CoAl-, MgAl- and NiFe- CLDHs, respectively. Isotherm study showed that adsorption of EBT on all the three CLDHs was best described by Langmuir isotherm model indicating monolayer adsorption behavior. The maximum adsorption capacity was found to be 419.87 mg/g, 540.91 mg/g and 132.49 mg/g for CoAl-, MgAl and NiFe- CLDHs, respectively. The results of kinetic study indicated rapid adsorption behavior for all the three compounds which well fitted pseudo-second order model. The obtained thermodynamic data suggests that the adsorption on CoAl- and MgAl- CLDHs was exothermic in nature, while that of NiFe-CLDH was endothermic in nature. The structure and morphology results obtained after EBT dye adsorption suggest that the adsorption mechanism is associated with electrostatic attraction and hydrogen/or chemical bonding between EBT dye and CLDHs surface functional groups. The high removal efficiency of EBT obtained from this study demonstrated the potential of calcined LDHs as effective adsorbents for the reclamation of wastewater contaminated with toxic pollutants.