Effect of the surface chemical groups of activated carbons on their surface adsorptivity to aromatic adsorbates based on π-π interactions

• A graphitic AC was provided with π-donor or π-withdrawing surface chemical functions.
• The nature of the surface functions influences the basicity of graphite sheets.
• Highly polar pyrimidine ligands are adsorbed on the AC through π-π interactions.
• Adsorption of pyrimidine ligands do not relate with the amount of surface functions.
• Adsorption of pyrimidine ligands is affected by the basicity of the graphite sheets.

Three activated carbons with different surface chemical groups were used to analyse the influence of these groups on their adsorption capacities towards aromatic-type molecules whose adsorption is based on π-π interactions with surface arene centres. The three activated carbons studied were a low-functionalized carbon (Merck), an oxygen-rich carbon obtained by HNO3 oxidation of Merck, and a nitrogen-rich carbon also prepared from Merck by mild HNO3 oxidation followed by treatment with a dicyanodiamide/dimethyl formamide mixture at 300 °C. The nature of the surface chemical groups of the three activated carbons was investigated by both physical and chemical techniques (TPD, XPS, Boehm analysis and pH potentiometric titration). A systematic study of the adsorptions of a series of analogous aromatic adsorbates on the three activated carbons was carried out to study the adsorption mechanisms. In all cases the adsorption mechanism is based on π-π interactions between the aromatic moiety of the adsorbates and the arene centres of the graphite sheets. The differences in the normalized adsorption capacities of the adsorbents for a set of adsorbates indicate that the π-donor or π-withdrawing character of the functional groups have a clear influence on the basicity of the arene centres.

Figure optionsDownload as PowerPoint slide