Carbonized lignosulfonate-based porous nanocomposites for adsorption of environmental contaminants

Abstract

Carbon-based adsorbents possess exceptional adsorption capability, making them an ideal platform for the remediation of environmental contaminants. Here, we demonstrate carbonized lignosulfonate (LS)-based porous nanocomposites with excellent adsorption performance towards heavy metal ions and cationic dye pollutants. Through microwave-assisted hydrothermal carbonization, a green approach was employed to carbonize lignosulfonate to carbon spheres. The LS-derived carbon spheres were then oxidized into nanographene oxide (nGO) carbon dots. A facile two-step procedure that involved the self-assembly of nGO and gelatin into a hydrogel precursor coupled with freeze-drying enabled the construction of three-dimensional (3D) free-standing porous composites without the use of organic solvents or chemical crosslinking agents. The favorable pore structure and abundance of surface functional groups on the nGO/gelatin porous composite proved to substantially facilitate the adsorption of Cu(II) in comparison to conventionally-used activated carbon. Further enhancement of adsorption performance was achieved by introducing additional surface functional groups through a non-covalent functionalization of the porous composite with lignosulfonate. The presence of negatively-charged sulfonate groups increased the Cu(II) equilibrium adsorption capacity (66 mg/g) by 24% in comparison to the non-functionalized nGO/gelatin counterpart. Both functionalized and non-functionalized composites exhibited significantly faster adsorption rates (40 min) compared to many graphene- or GO-based adsorbents reported in literature. In addition to the adsorption of heavy metal ions, the composites also demonstrated good adsorption capacity towards cationic dyes such as methylene blue. This paves the way for a high value-added application of lignin in environmental remediation and opens up new possibilities for the development of sustainable materials for adsorption and water purification.