Intercalation processes of n-alkyl monoamines in γ-zirconium phosphate

A detailed study of the intercalation of n-alkylamines (n(c) ranging from 3 to 18) in gamma-layered zirconium phosphate is reported. The main driving force for the intercalation of short amines was found to be the protonation of their -NH2 terminal groups. The intercalation was therefore pH dependent, and two or more intercalation steps were observed before all the available acid groups of the host were utilized for the protonation. As the number of carbon atoms increases, hydrophobic forces become more and more important, and intercalation can take place even at very low pH values of the external solutions. Furthermore, only one intercalation step, with formation of a monolayer of alkylamines in the interlayer region, was observed. It was also found that when the temperature was increased above 50 degrees C, there was a consistent increment of the interlayer space, especially for long alkyl chains. The reversible increment/decrement of the interlayer space with the change of temperature was attributed to a change of the alkyl chain conformation in the interlayer region. It was also found that gamma-ZrP, fully or partially intercalated with long alkylamines, can easily insert considerable amounts of alcohols with long chains, even from very dilute solution. In this case, the main driving force was the interaction between the alkyl chains of the already intercalated amines and the alkyl chains of the alcohols. This additional uptake was possible because the maximum amount of alkyl chains that can be intercalated as a perpendicular double film in the gamma-interlayer region is about double the amount corresponding to the maximum intercalation by amine protonation. Therefore, intercalate compounds with long-chain amines behave as hydrophobic sponges for the insertion of hydrophobic compounds and could find practical application for the removal of many organic substances from dilute solutions.