Valorisation of sugar cane bagasse using hydrothermal carbonisation in the preparation of magnetic carbon nanocomposite in a single-step synthesis applied to chromium adsorption

BACKGROUND: Sugar cane bagasse (SB) is a by-product of the sugar cane industry, and is obtained on a large scale. In this paper, SB was used as a source of carbon for preparing a magnetic carbon nanocomposite (MCN-SB) through one-step hydrothermal carbonisation (HTC), in the presence of iron (III) nitrate. By way of comparison, SB was replaced by glucose in HTC (MCN-GLU), and a thermal treatment of this material was then performed under an N2 atmosphere (MCN-GLU-HT). The physical and chemical properties of the nanocomposites were assessed, and the magnetic samples were applied as adsorbents. RESULTS: MCN-SB and MCN-GLU are composed of iron oxide nanoparticles embedded in carbonaceous matrix which also contain oxygenated groups. The MCN-SB sample was already magnetic after HTC, showing a magnetization saturation (Ms) of 5.0 emu g−1, due to the presence of magnetite, whereas MCN-GLU consisted of hematite and required additional thermal treatment (HT) to acquire magnetic properties, with MCN-GLU-HT showing an Ms of 30.5 emu g−1. In turn, the mesoporous structure and higher specific surface area (SSA) of MCN-GLU-HT (SSA 90 m2 g−1) than MCN-SB (SSA 53 m2 g−1) was a causative factor for its higher capacity of hexavalent chromium [Cr (VI)] removal (939 μg g−1), when compared to MCN-SB (768 μg g−1), which has a nonporous structure. CONCLUSION: The results suggest that SB can be reused, by means of HTC, for the preparation of a magnetically recoverable adsorbent, showing good adsorption properties. © 2022 Society of Chemical Industry (SCI).