Amino-functional biocarbon with CO2-responsive property for removing copper(II) ions from aqueous solutions

Abstract Amino-functional biocarbons (NH3-HTC, FA-HTC) were synthesized by one-pot hydrothermal carbonization of glucose (HTC) using ammonia (NH3) or ammonium formate (FA) additives. The as-prepared amino-functional biocarbons had specific surface areas of (5 to 8) m2/g, amino- content of (4 to 5) mmol/g, COOH content of (2 to 4) mmol/g and OH content of about 1 mmol/g. Experiments at 20 °C revealed that the as-prepared amino functional biocarbons NH3-HTC and FA-HTC, had copper (II) ion adsorption capacities of 182 mg/g and 265 mg/g over a 60 min period and approached 90% saturation within 15 min. Adsorption isotherms of NH3-HTC could be described by the Freundlich model (R2 > 0.95) and thermodynamic parameters of NH3-HTC showed that copper (II) adsorption was mainly physical adsorption. X-ray photo-electron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy of biocarbon adsorbents revealed that both amino groups and oxygen groups of the biocarbon adsorbent are involved in the copper (II) ion adsorption mechanism. Biocarbon adsorbents could be regenerated with 0.1 M nitric acid, 0.1 M organic acids (oxalic, citric), or CO2 bubbling. Amino-functional biocarbons are simple to prepare from biomass-derived compounds, they have high affinity for metal ions and they can be regenerated with environmentally-safe methods.