Alkyl modified MCM-41 for the sorption of alizarin and limonene from liquid and gas phase

To increase the affinity to hydrophobic molecules, mesoporous hydrophilic material MCM-41 was functionalized by alkyls of various chain lengths, namely ethyl-, isobutyl-, octyl-, and octadecyl-. The performed characterization methods (EA, XRD, DVS, nitrogen sorption, TGA, benzene TPD) demonstrated the successful modification of mesoporous sieve, the preservation of the supports structure, and especially the increase in its lipophilic character in the modification row: none < ethyl- < isobutyl- < octyl- < octadecyl-. Two hydrophobic molecules, alizarin (from the liquid phase) and limonene (from the liquid and gas phases), were chosen as the model substances for adsorption tests. In the liquid phase, higher amounts of alizarin were adsorbed on the materials with higher lipophilicity, however, the adsorption of limonene displayed distinct behavior. In this case, the specific surface area was more important than lipophilicity. Despite this tendency, a higher amount of the probe was adsorbed in the case of limonene (12.5 mg/g(MCM-41)) in comparison to alizarin (5.8 mg/(goctadecyl modified MCM-41)). The opposite trend was seen in the adsorption of limonene from the gas phase because, as would be predicted, the adsorbed amount increased with the increasing lipophilicity. The findings of our study proved that the functionalization of MCM-41 with lipophilic chains can boost its affinity towards lipophilic compounds (alizarin, limonene) demonstrating their potential application, for example, as adsorbents for colorants or terpenes.