Highly-ordered layered organo-mineral materials prepared via reactions of n-alkylphosphonic acids with apatite

This work describes a novel class of layered organo-mineral materials manufactured via a single-step solution-phase reaction of n-alkylphosphonic acids (C_nH_2n+1P(O)(OH)₂) with calcium hydroxyapatite mineral (CaHAP). TEM, SAXS, WAXS, FTIR, and Vapor Phase Adsorption data suggest that these alkyl-CaHAP materials present a surface-modified CaHAP matrix coated with ordered layers of calcium alkylphosphonates that are strongly adhered to the surface. Interlayer spacing increases from 1.47 (C₃-CaHAP) to 4.77 nm (C₁₈-CaHAP). According to FTIR, ordering of alkyl chains improves with the alkyl chain length. The organic loads in these alkyl-CaHAP can be controlled over a wide range (up to ∼60%) by varying alkyl chain and the concentration of alkylphosphonic acids in the solution.