Facile synthesis of MgO nanoparticles for effective degradation of organic dyes.

Abstract

In the present study, we have synthesized magnesium oxide (MgO) nanoparticles by a facile and cost-effective chemical co-precipitation method with annealing at three different temperatures (350°C, 450°C, and 550°C) for the removal of various organic dyes. X-ray diffraction studies revealed that the prepared samples are having sizes below 20 nm and with pure phase. Phase transformation of hexagonal Mg(OH)2 nanoparticles to discretely cubical structured MgO nanoparticles has been observed with increasing the annealing temperatures which is also supported by the TGA/DSC analysis. Mg-O stretching vibration peaks in the range of 400-800 cm-1 obtained by FTIR spectroscopy support the formation of MgO nanoparticles. The observed Raman active bands for the annealed sample at 550°C confirm the formation of the nanocrystalline phase since these bands are typically absent in the bulk MgO as well as in Mg(OH)2. The surface morphology of the as-prepared Mg(OH)2 are aggregated nano-petals which changed into spherical shape for MgO annealed at 550°C as studied by field emission scanning electron microscopy (FESEM). The specific surface area of MgO nanoparticles annealed at 550°C using BET isotherms is found to be 37.487 m2g-1. The optical bandgaps of the prepared samples are found to be in the range of 4.4 to 5.1 eV using the Tauc plot. Adsorption studies with a variation of initial brilliant green dye concentration and contact time are carried out along with the studies of adsorption kinetic and isotherm models. Langmuir isotherm model is the most suitable model on the basis of correlation constant with maximum BG dye adsorption capacity onto MgO@550°C which is found to be 63.9 mg/g. The adsorption kinetics followed the pseudo-second-order model. Also prepared pristine MgO nanoparticles showed significant photocatalytic performance for the degradation of various dyes; brilliant green (BG: 88.91%), methylene blue (MB: 79.05%), crystal violet (CV: 76.49%), methyl orange (MO: 68.62%), and brilliant blue (BB: 40.44%) under visible irradiation. MgO nanoparticles could be a promising adsorbent and photocatalyst that may be employed in the treatment of effluents from industries.