Biosynthesis of conductive and paramagnetic value-added rare earth graphitic materials

Abstract

Sustainable circularity of rare earth elements (REEs) can be achieved by phytoextraction of REEs from waste and remanufacturing them as value-added products. We have demonstrated erbium, europium, gadolinium, neodymium, and yttrium uptake using Eleocharis acicularis. The highest accumulation was observed for neodymium and gadolinium (56 and 55 mg/g dry weight), whereas yttrium (39 mg/g dw) had the lowest bioaccumulation from a feed solution of 300 mg/L over 10 days. The REE-accumulated biomass was used as raw material for graphitization at 1200°C. A higher degree of graphitization was observed in REE-graphitic material (GM) (0.91–0.97) and the lowest was observed in the non-exposed control biomass-GM (0.81), indicating the catalytic action of the REEs. XRD and SAED diffractograms showed the multilayer polycrystalline nature of the GMs, and Raman spectra demonstrated the presence of sp2 hybridization. Furthermore, Gd-GM had higher conductivity (1.09 × 104 S/m) than the commercial graphite (8.21 × 103 S/m) at 30 MPa applied pressure. The REE-GMs showed high capacitance (measured at 20–300 kHz) and an optical band gap of less than 1.11 eV. Additionally, Gd-GM showed significant paramagnetic properties, making it a potential precursor for sustainable MRI contrast agent synthesis.