A Study on Preparation of Nano Iron Oxides-Based Metal Biochar Using Co-Pyrolysis in a CO2 Environment and Adsorption of Cr(VI)

This study explored the effects of blending nano iron (III) oxides (NIO) with coffee grounds (CG) in a pyrolytic process under a CO 2 environment on the generation of syngas (H 2 and CO) and biochar properties regarding the removal of Cr(VI) from aqueous solutions. CG and NIO were physically mixed; CG was mass maintained at 1 g while NIO was added. Based on the mass ratio, the resulting solution was named NICG1(NIO/CG ratio=1:1). Compared with the generation amounts of syngas (0.37 mole% H 2 & 0.28 mole% CO) at 650°C from single pyrolysis of CG, co-pyrolysis with NIO-based additives resulted in increased production of syngas, with the measured concentrations of H 2 and CO reaching 0.99 mole% and 0.86 mole% at the same temperature, respectively. During the pH effect experiments, NICG1 demonstrated the highest removal efficiency under acidic conditions with pH = 2. Adsorption kinetic experiments demonstrated that the pseudo-second-order rate model was suitable for assessing the removal of Cr(VI) by NICG1. Furthermore, the removal of Cr(VI) using NICG1 fitted well with the Freundlich isothernm adsorption model (R 2 = 0.9807). In conclusion, co-pyrolysis of blending nano iron(III) oxide and coffee grounds can be considered an efficient resource for simultaneously producing syngas (H 2 and CO) as a fuel (energy resource) and metal-biochar as an adsorbent.