Design of Molecular Recognition and Adsorbents for Harmful Molecules in Water using Nanospace-Organic-Inorganic Triple Nano-structure

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Molecular selective adsorption of alkylphenols and alkylanilines are studied for n-alkyl grafted MCM-41 with different alkyl-chain lengths and Al contents. Octyl groups gave better performance of the adsorbents than pentyl and dodecyl groups. Nitrogen and water adsorption isotherms revealed that the octyl-grafted sample has a large volume of strongly hydrophobic nanospaces between the grafted alkyl chains. Octyl-grafted MCM-41 adsorbed alkylphenols from aqueous solutions with high molecular selectivity : Nonylphenol, an endocrine disrupter, is efficiently removed by adsorption into n-octyl grafted MCM-41, while adsorption of t-amylphenol is small and that of phenol is undetectable. Comparison of molecular selectivities for alkylphenols and alkylanilines reveals that hydrophilic and hydrophobic groups on molecules independently affect the selectivity. Infrared spectra of n-heptylaniline captured in the adsorbent show that the amino groups are strongly hydrogen-bonded onto the inorganic pore walls : The molecules fit the organic-inorganic nanostructure, interacting with the inorganic walls as well as the organic moiety. Since the molecules were adsorbed with much larger amounts than that of Al atoms doped in MCM-41, the effect of the acid sites produced by Al doping on the adsorption was not large in the present case. It was concluded that large volume of highly hydrophobic nanospaces that were walled by the ionic inorganic surfaces was important for efficient adsorption of these molecules