title: Environmental Conditions Influencing Sorption of Inorganic Anions to Multiwalled Carbon Nanotubes Studied by Column Chromatography.
abstract: Sorption to carbon-based nanomaterials is typically studied in batch experiments. An alternative method offering advantages to study sorption is column chromatography. Sorbent packed columns are used and sorption data are determined by relating sorbate retention to that of a nonretarded tracer. We have now for the first time applied this technique to study the influence of environmental conditions on sorption of inorganic anions (bromide, nitrite, nitrate, and iodide) to multiwalled carbon nanotubes. Deuterium oxide was used as nonretarded tracer. Sorption isotherms were best described by the Freundlich model. Sorption increased in the order bromide < nitrite < nitrate < iodide. Increasing ionic strength from 1 mM to 100 mM sodium chloride significantly reduced or completely suppressed sorption (bromide, nitrite) due to competition with chloride. pH strongly affected sorption as negatively charged analytes were attracted by the positively charged surface at pH 3. At pH > 4.5 the surface charge was negative, but sorption was still detectable at pH 6 and 9. Consequently, other forces than electrostatic attraction contributed to sorption. These forces may include H-bonding as indicated by sorption enthalpy determined by variation of column temperature. Overall, column chromatography represents a promising alternative in sorption studies to reveal sorbent properties.
authors.affiliation: Instrumental Analytical Chemistry, University of Duisburg-Essen , Universitätsstrasse 5, 45141 Essen, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Metzelder
authors.affiliation: Instrumental Analytical Chemistry, University of Duisburg-Essen , Universitätsstrasse 5, 45141 Essen, Germany.|Centre for Water and Environmental Research (ZWU), University of Duisburg-Essen , Universitätsstrasse 2, 45141 Essen, Germany.|IWW Water Centre, Moritzstraße 26, 45476 Mülheim an der Ruhr, Germany.
authors.forename: Torsten C
authors.identifier: http://orcid.org/0000-0003-1107-4403
authors.initials: TC
authors.lastname: Schmidt
mesh_terms: D000327:Adsorption; D001965:Bromides; D002845:Chromatography; D006863:Hydrogen-Ion Concentration; D037742:Nanotubes, Carbon; D009994:Osmolar Concentration; D013696:Temperature
chemical_list: D001965:Bromides; D037742:Nanotubes, Carbon