Effective removal of methylene blue with zero-valent iron/tea residual biochar composite: Performance and mechanism

[Display omitted] •Zero-valent iron-biochar (BFN) was obtained via pyrolysis and alkali fusion at 600 °C.•BFN has a specific surface area of 382.66 m2·g−1 and pore volume of 0.2300 cm3·g−1.•BFN exhibited a adsorption capacity (452.5 mg·g−1) for MB (150 mg·g−1) at pH 7.•MB removal via BFN is a process of chemical adsorption, reduction and oxidation. Zero-valent iron (Fe0)-modified biochar (BFN) was prepared via low-temperature pyrolysis of tea residue (TR) and ferric nitrate hexahydrate (FN) coupled with NaOH activation for the removal of methylene blue (MB). BFN exhibited a specific surface area of 382.66 m2·g−1, an average pore diameter of 4.97 nm and an equilibrium adsorption capacity as high as 452.5 mg·g−1 of 0.33 g·L−1 toward 150 mg·L−1 MB within 60 min at 30 °C and pH 7.0. The recovered MB is far below of the removal rate in each of adsorption–desorption cycle because the removal mechanism is that MB molecular was firstly chemically adsorbed, then it was reduced and mineralized by BFN with the formation of nitrate, sulfate, CO2 and H2O.