Co-thermochemical conversion of coffee grounds and nano Fe(III) oxides to fabricate metal-biochar for the simultaneous removal of Sb(V), Cd(II), and Ni(II) from water

Nano Fe(III) oxide (FO) was employed as an additive material for CO₂-aided pyrolysis of spent coffee grounds (SCG) and its impacts on the syngas (H₂ & CO) generation and biochar adsorption characteristics were examined. Amendment of FO led to 153 and 682% increase of H₂ and CO in pyrolytic process of SCG, respectively, which is deemed to arise from enhanced thermal cracking of hydrocarbons and oxygen transfer reaction mediated by FO. Incorporation of FO successfully created porous structure in the produced biochar. The adsorption tests revealed that the biochar exhibited bi-functional capability to remove both positively charged Cd(II) and Ni(II), and negatively charged Sb(V). The adsorption of Cd(II) and Ni(II) was hardly deteriorated in the multiple adsorption cycles, and the adsorption of Sb(V) was further enhanced through formation of surface ternary complexes. The overall results demonstrated nano Fe(III) oxide is a promising amendment material in CO₂-aided pyrolysis of lignocellulosic biomass for enhancing syngas generation and producing functional biochar.