Mangifera indica stone-assisted layered double hydroxide biocomposites: efficient contenders for reactive dye adsorption from aqueous sources

Abstract

Herein, magnesium–aluminum layered double hydroxides (Mg–Al-LDH) were synthesized by an environmentally friendly and economically promising hydrothermal technique for the adsorption of the dye reactive green 5 (RG5). To further enhance the RG5 dye adsorption capability of Mg–Al-LDH, their composites were designed by using low-cost Mangifera indica stone biomass (MISB). From their physiochemical properties evaluated by scanning electron microscopy and Fourier transform infrared spectroscopy, they were found to display an irregular morphology along with the existence of various functional groups (including OH, CO, and C–H) on surfaces, enabling prepared biosorbents to be excellent candidates for adsorption. Batch adsorption trials were conducted to determine the comparative RG5 dye adsorption efficiencies of MISB, Mg–Al-LDH and the Mg–Al-LDH@MISB composite in an aqueous medium. The highest RG5 dye adsorption capacities recorded under optimized conditions (contact time: 90 min, pH: 3, adsorbent dosage: 0.05 g, initial RG5 dye concentration: 80 mg L⁻¹ and temperature: 30 °C) for MISB, Mg–Al-LDH and the Mg–Al-LDH@MISB composite were 55.9 mg g⁻¹, 68.4 mg g⁻¹ and 73.5 mg g⁻¹, respectively. The kinetic and isothermal study showed the best fit of the pseudo 2nd order and Freundlich models. Thermodynamic parameters illustrated the spontaneity of the process. In addition, the adsorbents as designed also possessed regeneration capability as evidenced by their RG5 dye desorption potential. Therefore, this research opens up new doors for the development of environmentally friendly Mg–Al-LDH by developing composites with economically feasible biomass for industrial wastewater treatment.