Preparation of nano-magnetic activated biochar from Vicia faba Peel: application for Eriochrome Black T and Cr(Ⅵ) removal from aqueous phases

Magnetic-activated biochar nanocomposite (MABN) was synthesized for the first time from a novel precursor viz. Vicia faba Peel (VFP) via a one-pot ZnCl₂/FeCl₃ activation route. The preparation conditions, including the amount of the activator (1:1 -3:1 ZnCl₂/FeCl₃: VFP), activation temperature (400-800 °C), and time of activation (30-120 min), were optimized. The outcomes disclosed that an impregnation ratio of 1:1 activator: VFP, 600 °C, and 60 min, were the typical conditions to synthesize the best MABN. Identifying the MABN by several techniques, including FTIR spectroscopy, VSM, XRD, FESEM, EDX, TEM, and specific surface area, was accomplished. The findings disclosed that this MABN had a specific surface area of 449.72 m²/g, a mesoporous structure, and a saturation magnetization of 11.11 emu/g. After trying MABN in eliminating Eriochrome Black T dye (EBT) and Cr (VI) from their aqueous phases, the maximum elimination of EBT from 200 mg/L initial concentration was 97.10% using 0.20 of MABN at a pH= 2. 0 for 120 min at 30 °C. The highest removal of Cr (VI) from a solution containing 100 mg/L amounted to 99.55 %, employing 0.20 g of MABN at 30 °C for 90 min and a pH of 2.0. Adsorption data were fitted correctly to the Langmuir isotherm and the pseudo-2nd-order kinetic model. Moreover, the maximum adsorption capacity (Q_m, mg/g) for EBT and Cr (VI) using the resulting MABN were 102.58 mg/g and 95.16 mg/g, respectively. The MABN could be recycled and reused with an adsorptive performance of over 80 % for EBT and above 90 % for Cr (VI) in the 4^th reuse cycle. In conclusion, utilizing VFP as a precursor for producing MABN via a single-step preparation route employing ZnCl₂/FeCl₃ as an activator and magnetizing agent is feasible to create an adsorbent with an effective adsorptive performance to various pollutants from wastewaters.