Self-Organized Porous Titanium-Chitosan Hybrid Materials with Tunable Functions

Multifunctional hybrid polymer-based materials are shown to self-organize into a patterned solid microstructure, specific enough to induce cooperative catalytic interactions between primary amine sites and grafted titanium (Ti) sites. We demonstrate this by a new procedure for the grafting of titanium sites onto the backbone of polyhydroxylated-amine-containing polymer (chitosan). The Ti grafting is shown to form an amorphous hybrid (Ti@CS) high surface area material (up to 130 m² g⁻¹), despite the strong thermodynamic tendency of CS to collapse into a compact structure held by hydrogen bonds. We find that the surface area of Ti@CS materials is stable even at 110 °C under high vacuum. Tuning of the grafting conditions and the post treatment conditions provide control over the functionalities of both the Ti sites and the primary amine sites. These can be tuned such that the nitro-aldol condensation (Henry), used as probe reaction, is either (i) not catalyzed, (ii) catalyzed by amines promoted by Ti presence or (iii) catalyzed cooperatively by the primary amines and the Ti sites. Critical parameters related to the microstructure and chemical interactions between the organic and inorganic components are discussed in detail and cross-referenced with catalytic results.