Adsorbent Properties of Porous Boron Nitride and Activated Carbon: A Comparative Study

Porous boron nitrides
possess beneficial properties such as high
thermal and chemical stability which are critical for applications
in adsorption processes. In order to assess possible fields of applications,
trace-level adsorption isotherms of different hydrocarbons on two
synthesized porous boron nitrides and two commercial activated carbons
are compared. By normalizing the adsorptive loadings on the micropore
surface area, superior adsorption performances of the BN materials
on polar and aromatic adsorptives with up to 50% higher loadings compared
to the activated carbons can be shown. Nonpolar adsorptives, on the
other hand, feature higher specific loadings on the activated carbon.
Consequently, the size of the micropore surface appears to be decisive
for nonpolar adsorptives, while the higher polarity of the boron nitrides
is the dominant influencing factor for the adsorption of polar and
aromatic components. For an energetic study of the adsorbents, calorimetric
experiments were performed to identify and discuss adsorbent-adsorptive
interactions. While the initial heat of adsorption of the nonpolar n-hexane is lower on the boron nitride than on the activated
carbon due to a less favorable spatial arrangement, toluene shows
comparable values on both adsorbent classes and the polar acetone
shows higher values on the polar boron nitride. Considering technical
applications in adsorption technology, the thermal stability of the
boron nitrides is investigated using spontaneous ignition temperatures
and points of initial oxidation. Here, the porous boron nitrides with
oxidation temperatures above 900 °C show about 400 °C higher
values and thus a significantly higher thermal stability.