This study investigates the use of manganese oxide-biochar-nanocomposites synthesized from coffee husk (CH) and khat leftover (KL) for Cr(VI) removal from water. Two pristine biochars of CH and KL were separately synthesized by pyrolyzing their biomasses at 300 ℃ for 1 h. Similarly, biochar-based nanocomposites were synthesized by pretreating 25 g of each biomass with 12.5 mmol of KMnO4 and pyrolyzing at 300 ℃ for 1 h. The pristine biochars, synthesized by pyrolysis of CH and KL, removed 74.98% and 84.78% of Cr(VI) from aqueous solutions containing 20 mg L-1, respectively. However, the resulting nanocomposites exhibited a maximum removal efficiency of 99.63% with manganese oxide-coffee husk biochar nanocomposite (MnOX-CHBNC) and 99.84% with manganese oxide-khat leftover biochar nanocomposite (MnOX-KLBNC) of the Cr(VI). The adsorption isotherm fitted well with the Langmuir isotherm, indicating favorable monolayer adsorption. The kinetics of adsorption followed the pseudo-first-order model. The MnOX-CHBNC and MnOX-KLBNC demonstrated satisfactory removal efficiencies even up to six cycles, indicating their potential effectiveness for large-scale use in removing Cr (VI) from wastewater.

KEY WORDS: Adsorption, Biochar-nanocomposite, Coffee husk, Cr(VI) removal, Khat leftovers

Bull. Chem. Soc. Ethiop. 2024, 38(5), 1225-1240.                                                       

DOI: https://dx.doi.org/10.4314/bcse.v38i5.3