SYNTHESIS, CHARACTERIZATION AND APPLICATION OF TUNGSTEN TRIOXIDE-MAGNESIUM OXIDE NANOCOMPOSITE FOR THE TREATMENT OF LOCAL DYEING WASTEWATER

Abstract

ABSTRACT This study focused on the synthesis, characterization and application of tungsten trioxide/magnesium oxide (MgO/WO3) nanocomposite for the treatment of local dyeing wastewater. The individual nanoparticles (MgO and WO3) were prepared by green process and their composites, formulated by mixing the nanoparticles at different ratios using wet impregnation method. The adsorptive capacity of MgO, WO3 and MgO/WO3 nanoadsorbents were evaluated for the removal of selected heavy metals and other water quality indicator parameters from dyeing wastewater via batch adsorption mode. The synthesised nanoparticles and their nanocomposites were characterised using X-ray diffraction (XRD), High resolution electron microscopy (HRSEM), High resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDX), selected area electron diffraction (SAED) and Brunauer-Emette-Teller (BET) for their phase identification and crystallite size, morphologies, particle size distribution and dispersion, elemental composition, crystallinity and specific surface area, respectively. The XRD analysis of pure WO3 and MgO nanoparticles confirmed the formation of monoclinic phase and face centered cubic phase. The variations in the mixing ratios of MgO and WO3 nanoparticles showed the existence of chemical reaction between the nanoparticles to form magnesium tungstate (MgWO4). The EDX results showed that the synthesised nanocomposites composed of O, Mg and W which confirmed the pure formations of oxide of Mg and W. The specific surface areas of the MgO/WO3 nanocomposites at 1:1, 1:2, 2:1, 4:1 and 1:4 were 29.97, 45.28, 60.42, 104.16 and 93.58 m2/g, respectively which revealed that composite with highest surface area is MgO/WO3 (4:1) which is greater than WO3 alone with surface area (22.49 m2/g). The addition of MgO nanoparticles enhanced the surface area of WO3 nanoparticles. The adsorption studies at different contact times, adsorbent dosages and temperatures showed that adsorbent dosage and temperature are the most influential factors. The maximum removal efficiency of Cu(II), Fe(II) and Cr(VI) at optimum conditions are 98.1 %, 100 % and 100 %, respectively. The adsorption isotherms were evaluated using Langmuir, Freundlich and Elovich models and the experimental data followed Langmuir model and the adsorption kinetic conformed to the pseudo-second-order. Thermodynamic study demonstrated that the adsorption process is endothermic and spontaneous in nature. The regeneration study of the MgO, WO3 and MgO/WO3 nanoadsorbents showed that the percentage adsorption of Fe(II), Cu(II) and Cr(III) ions were high even after 4, 4 and 5 cycles, respectively. The study showed that, among the nanoadsorbents, MgO/WO3 (4:1) with highest surface area and adsorption efficiency was found most suitable for the treatment of dyeing wastewater.