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

Abstract

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.

Which Biopolymers Are Better for the Fabrication of Multilayer Capsules? A Comparative Study Using Vaterite CaCO3 as Templates

“…In the past decades, a number of novel drug formulation strategies have emerged to enhance the therapeutic efficiency of the drugs. , Among others, polymer nano- and microcapsules are highlighted as especially promising candidates for this purpose. The advantages of polymer capsules comprise not only efficient drug entrapment − but also controlled drug release in response to physical–chemical triggers, which can be provided either by external stimuli − or by the internal microenvironment of the living tissue itself ( e.g. , pH and temperature). , Besides this, diverse modifications of the capsule surface allow targeting toward specific cells .…”

Mesoporous One-Component Gold Microshells as 3D SERS Substrates

“…This Au coating is robust enough to keep the integrity of the Au microparticles formed after the dissolution of the CaCO 3 template (Figure 2g,f). Previous studies already demonstrated complete elimination of the template by the addition of EDTA, even in the presence of polymer multilayers [32] and TiO 2 NPs [33], which, together with no steric limitations expected for the release of the products of CaCO 3 dissolution (free ions and Ca-EDTA complex) from the mesopores, suggests the fabrication of one-component Au microparticles. These Au microshells maintain a porous structure on their surface representing a kind of thick porous shell that collapsed (spherical shape lost but integrity kept) during the sample drying as a required step for SEM imaging.…”

Biopolymer-Based Multilayer Capsules and Beads Made via Templating: Advantages, Hurdles and Perspectives

“…Moreover, due to the variety of loading mechanisms, one is able to tailor the loading technique to the biomaterial of interest; for instance, certain macromolecules or nanoparticles may be sensitive to salt solutions forming the crystal template and, hence, adsorption may be preferred. In addition, freezing-induced loading was recently demonstrated with the loading of TiO 2 nanoparticles [130].…”