Molecularly imprinted phenyl-functionalized silica aerogels: Selective adsorbents for methylxanthines and PAHs

Molecular imprinting of highly porous silica aerogels is reported for the first time and the selective adsorption of methylxanthines and polycyclic aromatic hydrocarbons (PAHs) has been investigated. The adsorption onto surface-functionalized caffeine-imprinted silica aerogels showed the phenyl-functionalized materials to have a higher adsorption capacity than others. The characterization of imprinted and non-imprinted materials confirmed the removal of the template molecules. The specific surface area and porosity of imprinted silica aerogels were found greater than those of their non-imprinted peers. The caffeine-to-silicon and water-to-silicon molar ratios exhibited a noticeable effect on the behavior of the molecularly imprinted aerogels. The optimal synthesis conditions were applied in the competitive adsorption between caffeine and theophylline performed with caffeine-imprinted phenyl-furictionalized silica aerogels, where higher affinity towards caffeine was seen. The competitive adsorption of various PAHs onto 2-naphthol-imprinted phenyl-functionalized silica aerogels showed also a similar behavior towards 2-naphthol. Comparing the adsorption capacity of molecularly imprinted aerogels to their non-imprinted peers highlights the undeniable influence of imprinting the material on its behavior towards target molecules.