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    Methylene blue removal from aqueous solutions using a biochar/gellan gum hydrogel composite: Effect of agitation mode on sorption kinetics

    Year: 2023

    Journal: International Journal of Biological Macromolecules, Volume 232, 2023-03-31, page 123355

    Authors: Elgarahy, Ahmed M.; Mostafa, Hamida Y.; Zaki, Elsayed G.; ElSaeed, Shymaa M.; Elwakeel, Khalid Z.; Akhdhar, Abdullah; Guibal, Eric

    Keywords: Mesoporous gellan gum (GG)/PVA-biochar composite; Methylene blue sorption from alkaline solutions; Sonication effects on kinetics; Sorption/desorption kinetics

    Hydrogel membranes are prepared by casting a mixture of gellan gum (associated with PVA) and biochar produced from a local Egyptian plant. The mesoporous material is characterized by a specific surface area close to 134 m2 g−1, a residue of 28 % (at 800 °C), and a pHPZC close to 6.43. After grinding, the material is tested for Methylene Blue sorption at pH 10.5: sorption capacity reaches 1.70 mmol MB g−1 (synergistic effect of the precursors). The sorption isotherms are fitted by both Langmuir and Sips eqs. MB sorption increases with temperature: the sorption is endothermic (∆H°: 12.9 kJ mol−1), with positive entropy (∆S°: 125 J mol−1 K−1). Uptake kinetics are controlled by agitation speed (optimum ≈200 rpm) and resistance to intraparticle diffusion. The profiles are strongly affected by the mode of agitation: the equilibrium time (≈180 min) is reduced to 20–30 min under sonication (especially at frequency: 80 kHz). The mode of agitation controls the best fitting equation: pseudo-first order rate agitation for mechanical agitation contrary to pseudo-second order rate under sonication. The sorption of MB is poorly affected by ionic strength (loss <6 % in 45 g L−1 NaCl solution). Desorption (faster than sorption) is completely achieved using 0.7 M HCl solution. At the sixth recycling, the loss in sorption is close to 5 % (≈ decrease in desorption efficiency). The process is successfully applied for the treatment of MB-spiked industrial solution: the color index decreases by >97 % with a sorbent dose close to 1 g L−1; a higher dose is required for maximum reduction of the COD (60 % at 3 g L−1).
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