Microfluidic Production of Poly(1,6-hexanediol diacrylate)-Based Polymer Microspheres and Bifunctional Microcapsules with Embedded TiO₂ Nanoparticles

Application of TiO₂ as a photocatalyst and UV protector is restricted by the difficulties in the recovery of TiO₂ nanoparticles after water treatment. In this work, TiO₂ nanoparticles (Degussa P25) were immobilised within easily recoverable poly­(1,6-hexanediol diacrylate) poly­(HDDA)-based polymer microspheres produced by on-the-fly photopolymerization of microfluidically generated droplets. Because of fast polymerization reaction, TiO₂ was uniformly distributed within the polymer network. The transformation of double bonds in terminal vinyl groups of HDDA monomer into single bonds during photopolymerization was confirmed by Fourier transform infrared spectroscopy. The microspheres containing 0.5 wt % TiO₂ embedded in a poly­(HDDA) matrix degraded 80% of methylene blue from 1 ppm aqueous solution in 9 h under UV light irradiation of 0.9 mW/cm² at 365 nm. The microspheres could easily be separated from water and used in repeated cycles without any loss in photocatalytic activity. The inclusion of TiO₂ within a polymer matrix increased the thermal degradation temperature of the material from 364 to 389 °C. Bifunctional microcapsules consisting of aqueous or liquid paraffin core enclosed within a TiO₂/poly­(HDDA) composite polymer shell were also prepared. The fluorescent dye calcein was encapsulated in the core with 100% efficiency.