Freezing-Induced Loading of TiO into Porous Vaterite Microparticles: Preparation of CaCO/TiO 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/TiO composite template cores. The preparation of CaCO/TiO composite particles is challenging because of the poor compatibility of TiO and CaCO in an aqueous medium. To prepare stable CaCO/TiO composites, TiO nanoparticles were loaded into mesoporous CaCO microparticles with a freezing-induced loading technique. The inclusion of TiO nanoparticles into CaCO 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 matrix was dissolved, resulting in microreactor capsules loaded with TiO 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 and magnetite FeO nanoparticles into CaCO templates.