Freezing-Induced Loading of TiO2 into Porous Vaterite Microparticles: Preparation of CaCO3/TiO2 Composites as Templates To Assemble UV-Responsive Microcapsules for Wastewater Treatment

The photocatalytic degradation of organic molecules is one of the effective ways for water purification. At this point, photocatalytic microreactor systems seem to be promising to enhance the versatility of the photoassisted degradation approach. Herein, we propose photoresponsive microcapsules prepared via layer-by-layer assembly of polyelectrolytes on the novel CaCO 3 /TiO 2 composite template cores. The preparation of CaCO 3 /TiO 2 composite particles is challenging because of the poor compatibility of TiO 2 and CaCO 3 in an aqueous medium. To prepare stable CaCO 3 /TiO 2 composites, TiO 2 nanoparticles were loaded into mesoporous CaCO 3 microparticles with a freezing-induced loading technique. The inclusion of TiO 2 nanoparticles into CaCO 3 templates was evaluated with scanning electron microscopy and elemental analysis with respect to their type, concentration, and number of loading iterations. Upon polyelectrolyte shell assembly, the CaCO 3 matrix was dissolved, resulting in microreactor capsules loaded with TiO 2 nanoparticles. The photoresponsive properties of the resulted capsules were tested by photoinduced degradation of the low-molecule dye rhodamine B in aqueous solution and fluorescently labeled polymer molecules absorbed on the capsule surface under UV light. The exposure of the capsules to UV light resulted in a pronounced degradation of rhodamine B in capsule microvolume and fluorescent molecules on the capsule surface. Finally, the versatility of preparation of multifunctional photocatalytic and magnetically responsive capsules was demonstrated by iterative freezing-induced loading of TiO 2 and magnetite Fe 3 O 4 nanoparticles into CaCO 3 templates.