Synthesis, characterization and removal performance of Cr (Ⅵ) by orange peel-based activated porous biochar from water.

A novel high-active porous activated biochar (KC) has been successfully prepared through a two-step chemical activation method with KOH by using orange peel as raw materials. The KC demonstrates several remarkable advantages for Cr (VI) removal from water, including large specific surface area of 1998 m2/g, well-developed porous microstructure, rich oxygen-containing functional groups and abundant surface-active sites. With these merits, the KC exhibits an outstanding experimental absorption capacity of Cr (VI) of 285.5 mg g−1 for 2400 mins at pH 2.0. The influences of initial pH, contact time, concentration and temperature on the remediation are investigated. The adsorption behavior fit well to Elovich model, suggesting a chemical adoption process. The Langmuir model fits better than the Freundlich model in simulating the adsorption isotherm, which implies a monolayer adsorption reaction through chemical adsorption. Mechanism studies demonstrate that chemical adoption, reduction, ion exchange and complexation with the assistance of oxygen-containing functional groups and porosity are involved in removal process of Cr (VI). Our work offers a feasible approach to optimize microstructure of biochar with satisfactory adsorption performance. [Display omitted] • The biochar has been prepared via a two-step KOH-assistant activation method. • Effects of pH, contact time and concentration on removing Cr (VI) are studied. • The underlying removal mechanisms are clearly analyzed. • The experimental adsorption capacity of biochar reaches 285.5 mg g−1. [ABSTRACT FROM AUTHOR]