Adsorption of Aqueous Metal Ions on Oxygen and Nitrogen Functionalized Nanoporous Activated Carbons

• Published in: Langmuir Vol. 21; no. 9; pp. 3892 - 3902
• Main Authors: Xiao, B, Thomas, K. M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 26.04.2005
• Subjects: Adsorbents; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Porous materials; Surface physical chemistry; Amphoteric; Oxygen; Metal ion; Zero charge point; Nitrogen; Carbon; Complexes; Porous material; Displacement; Mechanism; Hydrolysis; Infrared spectrometry; Acrylonitrile polymer; Adsorption; Activated carbon; Proton; Ion exchange; Structure; Acid base titration; Functional group
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la047135t

In this study, the adsorption characteristics of two series of oxygen and nitrogen functionalized activated carbons were investigated. These series were a low nitrogen content (∼1 wt % daf) carbon series derived from coconut shell and a high nitrogen content (∼8 wt % daf) carbon series derived from polyacrylonitrile. In both series, the oxygen contents were varied over the range ∼2−22 wt % daf. The porous structures of the functionalized activated carbons were characterized using N2 (77 K) and CO2 (273 K) adsorption. Only minor changes in the porous structure were observed in both series. This allowed the effect of changes in functional group concentrations on metal ion adsorption to be studied without major influences due to differences in porous structure characteristics. The surface group characteristics were examined by Fourier transform infrared (FTIR) spectroscopy, acid/base titrations, and measurement of the point of zero charge (pHPZC). The adsorption of aqueous metal ion species, M2+(aq), on acidic oxygen functional group sites mainly involves an ion exchange mechanism. The ratios of protons displaced to the amount of M2+(aq) metal species adsorbed have a linear relationship for the carbons with pHPZC ≤ 4.15. Hydrolysis of metal species in solution may affect the adsorption of metal ion species and displacement of protons. In the case of basic carbons, both protons and metal ions are adsorbed on the carbons. The complex nature of competitive adsorption between the proton and metal ion species and the amphoteric character of carbon surfaces are discussed in relation to the mechanism of adsorption.