An efficient and comparative adsorption of Congo red and Trypan blue dyes on MgO nanoparticles: Kinetics, thermodynamics and isotherm studies

Abstract

Cubic phase of MgO nanoparticles were prepared by microwave-assisted combustion synthesis and investigated for the removal of toxic dyes like Congo Red (CR) and Trypan blue (TB). The crystallite size of the MgO nanoparticle was calculated to be 18 nm from XRD pattern. The sample was further characterized by FTIR, TGA and FESEM techniques. The dyes were subjected to prototypical batch adsorption process, including investigation of different parameters like MgO dosage, dye concentration, solution pH, agitation speed and temperature. It was found that, 0.2 g of MgO NPs showed maximum removal efficiency for both the dyes (more than 98%), having 25 ppm of dye concentration at an acidic pH (3–4). The maximum loading capacity of MgO NPs was obtained to be 136 mg/g and 132 mg/g for CR and TB, respectively. Different thermodynamic parameters like ΔG0, ΔH0 and ΔS0 were measured. The negative ΔH0 and the positive ΔS0 values for both the dyes correspond to an exothermic process and an increase in randomness of the adsorbent and dye. The isotherm analysis exhibited that the Freundlich model fits better to the experimental equilibrium data, suggesting heterogeneous surface of the nanoparticles. Whereas, the kinetic data revealed a pseudo 2nd order rate for adsorption process.