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

Porous boron nitrides\npossess beneficial properties such as high\nthermal and chemical stability which are critical for applications\nin adsorption processes. In order to assess possible fields of applications,\ntrace-level adsorption isotherms of different hydrocarbons on two\nsynthesized porous boron nitrides and two commercial activated carbons\nare compared. By normalizing the adsorptive loadings on the micropore\nsurface area, superior adsorption performances of the BN materials\non polar and aromatic adsorptives with up to 50% higher loadings compared\nto the activated carbons can be shown. Nonpolar adsorptives, on the\nother hand, feature higher specific loadings on the activated carbon.\nConsequently, the size of the micropore surface appears to be decisive\nfor nonpolar adsorptives, while the higher polarity of the boron nitrides\nis the dominant influencing factor for the adsorption of polar and\naromatic components. For an energetic study of the adsorbents, calorimetric\nexperiments were performed to identify and discuss adsorbent-adsorptive\ninteractions. While the initial heat of adsorption of the nonpolar <i>n</i>-hexane is lower on the boron nitride than on the activated\ncarbon due to a less favorable spatial arrangement, toluene shows\ncomparable values on both adsorbent classes and the polar acetone\nshows higher values on the polar boron nitride. Considering technical\napplications in adsorption technology, the thermal stability of the\nboron nitrides is investigated using spontaneous ignition temperatures\nand points of initial oxidation. Here, the porous boron nitrides with\noxidation temperatures above 900 °C show about 400 °C higher\nvalues and thus a significantly higher thermal stability.