Efficient removal of Congo red and Alkali Blue 6b using biochar derived from wheat bran:kinetics, isotherms, and mechanism

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Abstract

The biochar with rich functional groups and well-developed pore structure was obtained from wheat bran (WB) via immersing and non-immersing (BC-NaK and BC-NaK-n) followed by mixed molten salt template for activation. The specific surface areas (S BET ) of BC-NaK and BC-NaK-n were 851.59 m 2 g − 1 and 564.22 m 2 g − 1 , respectively, which were used as adsorbents for the removal of anionic dyes Congo red (CR) and Alkali Blue 6b (AB6b) from aqueous solution. The results of adsorption experiments showed that BC-NaK had better adsorptive capacities than BC-NaK-n for CR and AB6b. The adsorption behaviors of CR and AB6b onto BC-NaK were better in accordance with pseudo-second-order kinetic model and Langmuir, Sips and Koble-Corrigan isotherm models. The maximum monolayer adsorptive capacities of CR and AB6b on BC-NaK reached 1150.11 mg g − 1 and 622.28 mg g − 1 at 298K, respectively. In addition, the thermodynamic parameters indicated that the adsorption processes of CR and AB6b were spontaneous and endothermic. The adsorption mechanism of CR and AB6b on BC-NaK mainly included hydrogen bonding, electrostatic interactions, π-π interactions and hydrophobic interactions. Overall, the biochar prepared from WB had superior adsorption capacities for the anionic dyes CR and AB6b, which could be promising adsorbent for organic dye wastewater.

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