Simultaneous magnetization and activation as a facile way to improve the adsorption capacity of walnut shell biochars for anionic azo dyes

초록

This study investigated the effects of magnetization and simultaneous magnetization and activation (SMA) on the adsorption of the azo dyes (i.e., Congo red (CR) and amaranth (AM)) by walnut shell biochars (WSB). SMAmodified walnut shell biochar (WSBSMA) has a larger specific surface area (626.2 m2/g) than that of WSB (9.4 m2/g) and magnetized WSB (WSBM; 482.6 m2/g) because ZnCl2 inhibited tar formation during pyrolysis. Consequently, WSBSMA showed superior adsorption capacities (Qmax = 8.13-13.25 mg/g) compared to WSB (Qmax = 0.44-1.65 mg/g) and WSBM (Qmax = 7.70-12.95 mg/g). The pseudo-second-order and Langmuir models better described the adsorption kinetics and isotherm, suggesting that chemisorption primarily governs the adsorption process. The EDS and XPS analyses revealed that CR and AM adsorption onto WSB, WSBM, and WSBSMA was mainly governed by it-it electron-donor-acceptor interaction. In the case of WSBM and WSBSMA, electrostatic interaction was additionally involved in the adsorption of CR and AM due to the presence of iron oxides, resulting in higher removal efficiencies compared to WSB. Furthermore, WSBSMA maintained excellent reusability (reuse efficiencies >= 60 %) after six adsorption-desorption cycles. Therefore, SMA is considered a viable approach to enhance the adsorption capacity of CR and AM onto WSB.

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