Hierarchically meso-/macroporous titanium tetraphosphonate materials: Synthesis, photocatalytic activity and heavy metal ion adsorption

Hierarchically meso-/macroporous titanium tetraphosphonate materials with intraframework ethylenediamine groups were synthesized by a simple surfactant-free process with the use of sodium salt of ethylene diamine tetra(methylene phosphonic acid) and titanium tetrabutoxide precursors under a very wide pH range from pH = 3–13. Besides the macroporous structure of 100–300 nm in size, a wormhole-like mesostructure was in the macropore surface layers of the framework and a mesocellular foam structure in the core part of the macroporous walls, rendering an unusual hierarchical structure of titanium phosphonates, which was supported by the electron microscopic observation and nitrogen adsorption analysis. Characterization by FT-IR, NMR and XPS indicated the integrity of the organophosphonate groups in the macro-/mesoporous solid. The synthesized materials exhibited not only high photocatalytic activity under UV-light irradiation, but also large capacity for heavy metal ion adsorption with a preference sequence of Cd2+ < Cu2+ < Pb2+ and effective regeneration ability, suggesting very promising photocatalysts for organic waste degradation and adsorbents for metal ion recovery and wastewater cleanup.