Adsorptive properties of MgO/WO3 nanoadsorbent for selected heavy metals removal from indigenous dyeing wastewater

Abstract

The magnesium oxide/tungsten trioxide (MgO/WO3) nanocomposites were prepared at different mixing ratios using a combination of green and wet impregnation methods and subsequently utilized as nanoadsorbent for the removal of selected heavy metals from Indigenous dyeing wastewater. The synthesized nanomaterials were characterized using High-resolution electron microscopy (HRSEM), High-resolution transmission electron microscopy (HRTEM), Energy Dispersive Spectroscopy (EDS), Selective Area Diffraction (SAED), X-ray diffraction (XRD) and Brunauer Emmett-Teller (BET) N2 Adsorption-desorption method. HRSEM/HRTEM analysis demonstrated the formation of a distinct spherical shape irrespective of the mixing ratio of MgO on WO3 nanoparticles. XRD analysis confirmed the existence of a monoclinic phase and face centred cubic phase for WO3 and MgO nanoparticles and strong interaction between the nanoparticles leading to the formation of magnesium tungstate (MgWO4). The BET analysis revealed a higher surface area (104.2 m2/g) for mesoporous MgO/WO3 nanocomposite with a mixing ratio (4:1) than WO3 alone with a surface area (22.5 m2/g). The maximum removal efficiency of Cu(II) (98.1%), Fe(II) (100%) and Cr (VI) (100%) was achieved at an optimum contact time of 12, 12 and 14 min respectively. The adsorption data evaluated using Langmuir, Freundlich and Temkin models showed that experimental data best fitted the Langmuir model while the fitness of adsorption data to different kinetic models followed pseudo-second- order. The adsorption of the selected metal ion using MgO/WO3 nanoadsorbent was based on electrostatic attraction, ion exchange, and pore diffusion mechanism. The thermodynamic study demonstrated the endothermic and spontaneous nature of the metal sorption process. MgO/WO3 nanoadsorbent with a mixing ratio (4:1) exhibited greater adsorption efficiency than other nanoadsorbents and has excellent regeneration potentials after 5 cycles.