Functionalized carbon spheres for extraction of nanoparticles and catalyst support in water

Increased use of nanomaterials in commercial products will lead to environmental contamination in the near future. So far, limited adsorbents are available for the removal of such emerging pollutants from water. The objective of this work was to synthesize functionalized carbon nanospheres (C-spheres) for the removal of emerging nanopollutants from water and to study the mechanisms involved. C-spheres were prepared using hydrothermal carbonization of glucose. Post-modification with polyethylenimine (PEI) generated amine-coated C-spheres, followed by protonation using diluted acid solution. The surface functional groups and morphologies of the Cspheres were characterized using infrared spectroscopy and field emission scanning electron microscopy, respectively. The C-spheres were used for the extraction of citrate-capped gold and silver nanoparticles from water. The equilibrium adsorption data was interpreted using Langmuir and Freundlich isotherms, and the adsorption mechanism was investigated using kinetic studies. Our data suggest that the adsorption of nanoparticles on modified C-spheres followed pseudo-second-order kinetics, and adsorption can be best explained by the Langmuir adsorption model. The observed results suggest that the developed material shows enhanced extraction capacities (102 mg/g for AuNPs and 135 mg/g for AgNPs). Further, the NP-adsorbed C-spheres were evaluated for the catalytic reduction of p-nitrophenol to demonstrate the activity of adsorbed NPs.