Synthesis characterization and ion exchange properties of aluminum phosphonates

Three aluminum organophosphonate compounds; aluminum phenylphosphonate, aluminum octylphosphonate, and aluminum octadecylphosphonate, have been synthesized by refluxing aluminum nitrate with an excess of the appropriate organophosphonic acid in aqueous, methanol, or butanol solvents respectively. Each of these compounds was found to have pillared layered structures and ligand to metal ratios of 2:1. Additionally, these compounds were shown to exhibit cation exchange properties. In contrast to that observed for conventional cation-exchange resins, the exchange capacities of these compounds are larger for small cations, such as Li+ and Na+, than for larger ions such as Na+ and K+. The results indicate a size selectivity which is directly related to the accessibility of these ions to the exchangeable sites of these compounds.