Catalytic Conversion of CO₂to Formate Promoted by a Biochar-Supported Nickel Catalyst Sourced from Nickel Phytoextraction Using Cyanogen-Rich Cassava

In this work, we have demonstrated for the first time that a cyanogen-glucoside-rich cassava plant (Manihot esculenta) is highly efficient in phytoextraction (up to 88%) of nickel to obtain a type of bio-ore comprising Ni nanoparticles (NPs) supported on the recovered plant material. Up to 1251 ppm was extracted from low Ni concentration soil by the cassava plant, as was measured by flame atomic absorption spectrometry. The bio-ore was used as a resource for preparing a heterogeneous catalyst (Ni@CassCat), in which Ni NPs are supported on mesoporous biochar following a calcination step. Ni@CassCat was characterized using high-resolution transmission electron microscopy with energy-dispersive X-ray, scanning electron microscopy with energy-dispersive X-ray, powder X-ray diffraction, N2-sorption techniques, and ultraviolet-visible spectrometry. Subsequently, Ni@CassCat was used as a heterogeneous catalyst to hydrogenate carbon dioxide (CO2) to formate with a turnover number of 485. Furthermore, the recyclability of Ni@CassCat was demonstrated. This work demonstrates a two-pronged approach to sustainability, transforming two waste streams (mine tailings and CO2) to value.