Synthesis of graphene oxide/magnesium oxide nanocomposites with high-rate adsorption of methylene blue

A series of graphene oxide/magnesium oxide nanocomposites (GO/MgO NCs) were and applied for the removal of Methylene Blue (MB) from aqueous solutions. The prepared NCs were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The results showed that MgO particles was successfully decorated on GO. The impacts of different experimental variables on the removal of MB including GO/MgO NCs dosage, pH, contact time, and initial MB concentration were investigated. The experimental analysis of adsorption isotherms indicated that adsorption data was best fit with the Langmuir isotherm model. Among the three different synthesized weight ratios of GO/MgO (5:1, 1:1, and 1:5), 5:1 ratio showed the maximum adsorption capacity as 833 mg/g, which is higher than any previously reported GO-based composites. The synthesized GO/MgO NC is also observed to have higher adsorption capacity for MB removal, in comparison with pure GO and MgO. The kinetic adsorption data was best described by pseudo-second-order kinetic model. The pH of point of zero charge (pH(pzc)) of GO/MgO NCs was determined to be 9.7, 10.5, and 10.5 for ratios 5:1, 1:1, and 1:5, respectively. The results revealed that electrostatic attraction can be the dominant mechanism of adsorption between GO/MgO NCs and MB for pH above pH(pzc); whereas for pH below pH(pzc), other adsorption mechanisms such as hydrogen bonding and pi-pi interaction may attribute to adsorption. The high adsorption capacity of GO/MgO composites, thus makes it a promising adsorbent for water and wastewater treatment. (C) 2016 Elsevier B.V. All rights reserved