S⁺I^- Ionic Formation Mechanism to New Mesoporous Aluminum Phosphonates and Diphosphonates

Pure mesoporous aluminum phosphonates and diphosphonates have been synthesized through an S + I - surfactant-assisted cooperative mechanism by means of a one-pot preparative procedure from aqueous solution and starting from aluminum atrane complexes and phosphonic and/or diphosphonic acids. A soft chemical extraction procedure allows opening the pore system of the parent mesostructured materials by exchanging the surfactant without mesostructure collapse. The hybrid nature of the pore wall can be modulated continuously from organic-free mesoporous aluminum phosphates (ALPOs) up to total incorporation of organophosphorus entities (mesoporous phosphonates and diphosphonates). The organic functional groups become basically attached to the pore surface or inserted into the ALPO framework (homogeneously distributed along the surface and inner pore walls) depending on the use of phosphonic or diphosphonic acids, respectively. X-ray powder diffraction, transmission electron microscopy, and surface analysis techniques show that these new hybrid materials present regular unimodal pore systems whose order decreases as the organophosphorus moiety content increases. NMR spectroscopic results not only confirm the incorporation of organophosphorus entities into the framework of these materials but also provide us useful information to elucidate the mechanism through which they are formed.