posted on 2017-04-06, 00:00authored byFlorian Metzelder, Torsten C. Schmidt
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.