Unconventional Strategy to Anatase TiO2 Nanocrystals with Tunable Surface Chemistry via Liquid Crystalline Polyamides as a Functional Matrix

An unconventional but robust route to synthesize anatase TiO2 colloidal nanocrystals with tunable surface chemistry and dimensions was developed via liquid crystalline polyamides (LCPAs) with pyridine rings as a functional matrix. Titanium(IV) tetraisopropoxide (TTIP), as the precursor of TiO2 nanocrystals, was selectively incorporated into the compartment containing pyridine ring units via a coordination interaction between the pyridine rings and precursors, followed by an in situ direct polycondensation reaction of two monomers with TTIP into amorphous TiO2 nanoparticles encapsulated into the LCPA matrix. The functional polyamide chains capped on the surface of the TiO2 nanoparticles can be readily carbonized at 500 °C in inert atmosphere (argon), subsequently with the carbon forming a protecting coating on the surface of TiO2 nanocrystals to prevent the nanocrystals from aggregating. In addition, the amorphous TiO2 was simultaneously transformed into anatase TiO2 after 500 °C calcination. The carbon shell on the surface of anatase TiO2 nanocrystals can be readily removed by calcination at a relatively low temperature (400 °C) in air. At last, the carboxyl-terminated polymers, such as PMMA–COOH or PEG–COOH, were chosen as functional ligands for the surface modification of anatase TiO2 nanocrystals to fabricate core@shell anatase TiO2@polymer colloidal nanocrystals. The sizes of anatase TiO2 nanocrystals can be also tuned by adjusting the molar ratio of TTIP precursors to pyridine units.