Colloidal systems for crystallization processes from liquid phase

Colloidal systems are involved in crystallization processes in many different ways: on one hand, colloids may be used as controlling or structure-directing agents, as nanoreactors and as scaffolds and templates for crystallization. On the other hand, it is very often desirable to obtain colloidal particles in a crystalline or nanocrystalline state. In this highlight, we cover the challenges and the recent advances on the following topics: (i) the use of polymer colloids as additives for crystallization due to their ability to control nucleation and growth and even to promote enantiomer resolution by enantioselective crystallization; (ii) state of the art in the preparation of inorganic crystalline colloids; and (iii) the application of colloidal systems (i.e., colloidal particles, droplets, micelles and vesicles) as supports, templates and nanoreactors for inorganic crystallization

Sol\u2013gel processes at the droplet interface: hydrous zirconia and hafnia nanocapsules by interfacial inorganic polycondensation

We report a simple method to prepare nanocapsules of hydrous zirconia and hafnia by interfacial precipitation in water-in-oil miniemulsions. We show that the sol\u2013gel precipitation of transition metal hydroxides, exemplified for the cases of zirconium and hafnium, can be driven to the droplet interface by addition of an organic base. The prompt addition of triethylamine generates hydroxide ions at the interface, which initiate a polycondensation of the metal hydroxo species. Electron and X-ray diffractions indicate that the resulting materials are amorphous, but can be transformed to monoclinic ZrO2 or HfO2 upon thermolytic treatment. Mixed oxides of Hf and Zr with different compositions (HfxZr1 12xO2) can also be formed by using the desired ratios of precursors. Furthermore, the ability of the hollow particles to encapsulate efficiently hydrophilic materials without leakage has been proven with the example of a water-soluble dye (fluorescein isothiocyanate)

Tin(IV) Oxide Coatings from Hybrid Organotin/Polymer Nanoparticles

Tin dioxide coatings are widely applied in glasses and ceramics to improve not only optical, but also mechanical properties. In this work, we report a new method to prepare SnO2 coatings from aqueous dispersions of polymer/organotin hybrid nanoparticles. Various liquid organotin compounds were encapsulated in polymeric nanoparticles synthesized by miniemulsion polymerization. Large amounts of tetrabutyltin and bis(tributyltin) could be successfully incorporated in cross-linked and noncross-linked polystyrene nanoparticles that served as sacrificial templates for the formation of tin oxide coatings after etching with oxygen plasma or calcination. Cross-linked polystyrene particles containing bis(tributyltin)\u2014selected for having a high boiling point\u2014were found to be especially suited for the oxide coating formation. The content of metal in the particles was up to 12 wt %, and estimations by thermogravimetrical indicated that at least 96% of the total organotin compound was converted to SnO2. The resulting coatings were mainly identified as tetragonal SnO2 (cassiterite) by X-ray diffraction, although a coexistence of this phase with orthorhombic SnO2 was observed for samples prepared with bis(tributyltin)

Dual Role of Zirconium Oxoclusters in Hybrid Nanoparticles: Cross-Linkers and Catalytic Sites

Organic\u2013inorganic hybrid nanoparticles are prepared by free-radical copolymerization of methyl methacrylate (MMA) with the structurally well-defined methacrylate-functionalized zirconium oxocluster Zr4O2(methacrylate)12. The polymerization process occurs in the confined space of miniemulsion droplets. The formation of covalent chemical bonds between the organic and the inorganic counterparts improves the distribution of the guest species (oxoclusters) in the polymer particles, overcoming problems related to migration, leaching, and stability. Because of the presence of a high number of double bonds (12 per oxocluster), the oxoclusters act as efficient cross-linking units for the resulting polymer matrix, thus ruling its swelling behavior in organic solvents. The synthesized hybrid nanostructures are applied as heterogeneous systems in the catalytic oxidation of an organic sulfide to the corresponding sulfoxide and sulfone by hydrogen peroxide, displaying quantitative sulfide conversion in 4\u201324 h, with overall turnover numbers (TON) up to 8000 after 4 cycles

Crystallization at Nanodroplet Interfaces in Emulsion Systems: A Soft-Template Strategy for Preparing Porous and Hollow Nanoparticles

A heterophase method to prepare hollow and/or porous crystalline nanoparticles of metal oxides at room temperature is presented, taking cerium(IV) oxide and \u3b3-iron(III) oxide (i.e., maghemite) as representative cases. The crystallization begins at the oil\u2013water interface in aqueous nanodroplets of the precursor in inverse (water-in-oil) miniemulsion systems, and it may continue toward the inner part of the droplets. A poly(styrene-b-acrylic acid) block copolymer is used as a structuring agent because the ability of the carboxylic groups to bind metal ions improves the inorganic shell formation. A precipitating base is added from the continuous phase, generating hydroxide species at the interface that begin the crystallization. We analyze the effects of the synthetic parameters in terms of colloidal stability and morphology of the resulting materials. In the case of maghemite samples, the prepared dispersions of hollow particles present a distinct magnetofluidic behavior