Reference data for the adsorption of methanol on carbon materials

Specific and non-specific interactions on non-porous carbon black surfaces

“…We note that the overall linearity of the plots is variable and the E DRK values are given only for comparative purposes and do not relate directly to those derived using the classical form of the equation for micropore filling. For methanol on the base N330 material the non-linearity of the data is consistent with the relatively weak non-specific interaction of the alkyl group coupled with the low level of surface oxygen and hence specific interactions with the polar -OH group of the methanol as described by Carrott [8]. Hence, the isotherm is effectively type III in character but with a slight positive inflexion in the P/P 0 region 0.4-0.5 as the adsorbate-adsorbate hydrogen bonding becomes significant.…”

“…Turning to the surface areas S BET and S DRK ( Table 2) we see that, as previously observed [8] for both methods the alcohol values are lower than those derived using the nitrogen data. For methanol, S BET is always higher than S DRK but the latter increases markedly as a function of surface oxygen i.e.…”

“…For ethanol and propanol the values for S BET are lower than those for S DRK but the differences are less Table 2 Surface area (BET and DRK), characteristic energy E DRK and enthalpy parameters from alcohol data Carbon Methanol Ethanol Propanol and the S DRK values are, within error, constant for each adsorptive and are not influenced by the surface chemistry changes of the carbon showing the influence of non-specific interactions of the alkyl chains on the adsorption process. The work of Carrott [8] indicates that the adsorption of methanol onto carbon blacks at low pressures is significantly influenced by hydrogen bonds which form with polar groups on the carbon surface and that when the levels of surface oxygen are low the adsorption of methanol is limited. Our results confirm this in that firstly the methanol adsorption we observe on untreated N330, which has 1.7 at.% oxygen, yields an isotherm which is effectively Type III in character whilst the adsorption of methanol onto the N234G graphitized carbon black, which has 0.5 at.% oxygen but is of course structurally distinct from the N330, adsorbs even less methanol at low pressures and hence behaves in a similar way to the Sterling FT graphitized black reported in [8].…”

“…The work of Carrott [8] indicates that the adsorption of methanol onto carbon blacks at low pressures is significantly influenced by hydrogen bonds which form with polar groups on the carbon surface and that when the levels of surface oxygen are low the adsorption of methanol is limited. Our results confirm this in that firstly the methanol adsorption we observe on untreated N330, which has 1.7 at.% oxygen, yields an isotherm which is effectively Type III in character whilst the adsorption of methanol onto the N234G graphitized carbon black, which has 0.5 at.% oxygen but is of course structurally distinct from the N330, adsorbs even less methanol at low pressures and hence behaves in a similar way to the Sterling FT graphitized black reported in [8]. Secondly, our results show clearly that as the surface oxygen concentrations of the carbon black increase then the methanol isotherms are displaced to higher adsorption values such that their initial, submonolayer, regions become concave toward to pressure axis, they become type II in character and are differentiated according to the oxygen level of the carbon surface.…”

“…The latter are usually oxygen-containing surface groups located mainly on the edges of the graphene layer-planes of the carbon structure. This is the case for water and to some extent for alcohols, as discussed by a number of workers [1][2][3][4][5][6][7][8][9]. In the case of non-porous carbons, direct evidence of this is provided by the change in the specific enthalpy of immersion Àh i (water) (mJ m À2 ), which increases linearly with the surface oxygen content from the lower limit of approximately 35 mJ m À2 which defines the non-specific (dispersion) interaction of an oxygen free carbon.…”