Silica gels containing imidazole groups or hexyl groups whose compositions are well controlled have been prepared. The imidazole group in the gel was quaternized with C4H9Br, C6H13Br or C12H25Br to obtain gels that are charged and have an alkyl chain. Their binding affinities for methyl orange in water were then investigated. We aimed to clarify the relation between the structure of the gel and its binding behaviour for small molecules in water. So the binding affinities of the unquaternized and quaternized gels were compared for methyl orange in water at various temperatures and we obtained the thermodynamic parameters for this binding. It was found that in silica gel the alkyl chain that is bound chemically to the charged site is very efficient for binding the dye in water.
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