High selectivity for metal ion adsorption: from mesoporous phosphonated titanias to meso-/macroporous titanium phosphonates

A family of hybrid surface-phosphonated titania, titania–phosphonate, and titanium phosphonate porous materials with different organic groups in the network was synthesized by utilizing a series of organophosphonic acids as the coupling molecules. The crystalline degree of the obtained hybrids decreased by increasing the original added coupling molecule amount, with the structural phase transformed from phosphonated titania to titanium phosphonate, and simultaneously the nanoarchitecture changed from mesoporous to hierarchically meso-/macroporous structure. The whole synthesis process was performed under a very wide pH range by a template-free strategy. The samples were characterized by XRD, N2 sorption, SEM, TEM, FT-IR, MAS NMR, XPS, and TG-DSC analysis. It is revealed that the integrity of organic groups remained inside the framework of the synthesized hybrids. All the synthesized adsorbents exhibited large capacity of heavy metal ion adsorption with a definite selectivity, which depended on the nature and positions of organically functional groups.