Fabrication of different magnetic biochar from Citrus limetta peels for Cr (VI) adsorption: Characterisation, and performance

• Citrus Limetta peel were utilised for biochar preparation. • Chitosan modified biochar displayed highest removal efficiency (76.22%) towards Cr (VI). • Chemisorption was the main mechanism involved in adsorption. • Modified magnetic biochar could be a potential adsorbent for removal of Cr (VI) from water. Hexavalent chromium, when present in high concentrations, causes a serious threat to the ecosystem. This can lead to severe ecological damage and persistent environmental issues, making it a significant concern for long-term sustainability. Thus, there is a strong need for high-performing adsorbents to remove high concentrations of Cr (VI) from the environment. In the present study, Citrus Limetta peels were utilised to produce pristine biochar, which was treated with iron oxides to generate magnetic biochar and modified with chitosan, sodium alginate, and pectin to produce respective modified biochar. Among all five biochars, Chitosan-modified biochar (CMBC) displayed the highest removal efficiency towards Cr (VI) from water with a maximum adsorption capacity of 152.44 mg/g and a removal capacity of 76.22%. Furthermore, adsorption kinetics indicates that the adsorption process is a pseudo-second order-kinetic model with R 2 and q e of 0.99 and 99 mg/g, respectively. The Langmuir isotherm best describes the adsorption process. After five regenerative cycles, the removal efficiency was maintained at up to 71.80 %. This work highlights the remarkable potential of engineered biochar in wastewater treatment.