Kinetics and thermodynamics of reactive and vat dyes adsorption on MgO nanoparticles

Abstract In the present study, magnesium oxide (MgO) nanoparticles have been synthesized and their adsorption behavior was tested for the removal of dyes found in textile wastewater. Levafix Fast Red CA (LFR) and Indanthren Blue BC (IB) were chosen as models for reactive and vat dyes respectively. The prepared MgO was highly crystalline with a crystallite size in the range of 25–30 nm. The effect of parameters like pH, contact time and temperature on the adsorption process was studied. Equilibrium experiments showed that MgO nanoparticles are more selective towards LFR than IB which may be related to the more number of reactive groups found in LFR. Langmuir adsorption isotherm fitted well into the experimental data with high correlation coefficients. Kinetic modeling suggested that pseudo-second-order model can better describe the adsorption of dyes onto nanomagnesia and film diffusion was the rate limiting step. The heat of adsorption (Δ H °) indicated the exothermic nature of the process and negative values of free energy ( Δ G °) indicated that the adsorption is spontaneous.