In this work, we present preparation and stabilization methods for highly crystalline TiO2 nanoparticle suspensions for the successful deposition of transparent, photocatalytically active TiO2 thin films toward the degradation of organic pollutants by a low temperature deposition method. A proof-of-concept is provided wherein stable, aqueous TiO2 suspensions are deposited on glass substrates. Even if the processing temperature is lowered to 150-200 °C, the subsequent heat treatment provides transparent and photocatalytically active titania thin layers. Because all precursor solutions are water-based, this method provides an energy-efficient, sustainable, and environmentally friendly synthesis route. The high load in crystalline titania particles obtained after microwave heating opens up the possibility to produce thin coatings by low temperature processing, as a conventional crystallization procedure is in this case superfluous. The impact of the precursor chemistry in Ti(4+)-peroxo solutions, containing imino-diacetic acid as a complexing ligand and different bases to promote complexation was studied as a function of pH, reaction time and temperature. The nanocrystal formation was followed in terms of colloidal stability, crystallinity and particle size. Combined data from Raman and infrared spectroscopy, confirmed that stable titanium precursors could be obtained at pH levels ranging from 2 to 11. A maximum amount of 50.7% crystallinity was achieved, which is one of the highest reported amounts of anatase nanoparticles that are suspendable in stable aqueous titania suspensions. Decoloring of methylene blue solutions by precipitated nanosized powders from the TiO2 suspensions proves their photocatalytic properties toward degradation of organic materials, a key requisite for further processing. This synthesis method proves that the deposition of highly crystalline anatase suspensions is a valid route for the production of photocatalytically active, transparent films on heat-sensitive substrates such as polymers.

Abbreviations 1 1 PA 6: polyamide 6, MB: Methylene Blue, IL: inline, DC: dip-coating, H: hydrophilic 2 ABSTRACT Titania has already proven its added value for air and water treatment. The higher the surface-to-volume area, the better the performance of the TiO2 photocatalyst. These nanoparticles are typically applied in a slurry form. The use of titania nanoparticles in suspension has, however, multiple disadvantages such as a high turbidity and complex recovery of the photocatalyst after use. Therefore, immobilization of titania nanoparticles on a porous support such as a nanofibrous membrane, can be highly valuable for water treatment. These TiO2 functionalized nanofibrous membranes may be used not only in a membrane separation reactor, but also in a contact reactor. In this study, TiO2 nanoparticles were immobilized on both polymer (polyamide 6) and ceramic (silica) nanofibrous membranes. Polymer nanofibers are chosen as they are the state-of-the-art material, silica nanofibers on the contrary are less studied but show additional advantages due their excellent chemical and thermal stability and can thus offer a clear benefit for a wider range of applications. Two immobilization techniques were used, namely inline functionalization and dip-coating. Inline functionalization showed to be the preferred method for polyamide 6 nanofibrous membranes, dip-coating for silica nanofibrous membranes. Complete degradation of isoproturon, an actual concern in water treatment, is shown. Even the widely available commercial TiO2 nanoparticles allowed for a complete isoproturon removal as the result of a correct immobilization process on nanofibrous materials. This clearly opens up the high value of TiO2 functionalized nanofibrous membranes for organic (micro)pollutants removal.

In this paper, we report on the synthesis of BaZrO3 nanostructures by novel bottom-up synthesis methods. Nanocrystals with diameters ranging from 5 to 10 nm are prepared from aqueous or multiple phase precursor solutions. In order to transform the precursor solutions into nanocrystal containing suspensions, both conventional and microwave-assisted solvothermal treatments are used. An additional heat treatment was necessary to obtain crystalline particles starting from the aqueous precursor, while crystalline particles are directly obtained after solvothermal treatment of the multiple phase precursor. The crystallinity and size of the obtained nanoparticles are investigated by means of dynamic light scattering, X-ray diffraction and transmission electron microscopy. We found that the nature of the bases used in the multiple phase precursor have an effect on the particle morphology. In general, the microwave-assisted solvothermal synthesis renders the best prospects towards small particle sizes between 3 and 5 nm in diameter with a narrow size distribution. In addition, the process exhibits higher energy efficiency, resulting in lower reaction times (5 min-2 h) in comparison with the conventional solvothermal treatment (4-24 h)

No abstract

Although already some mesoporous (2 -50 nm) sol-gel TiO2 synthesis strategies exist, no pore size control beyond the 12 nm range is possible without using specialized organic structure directing agents synthetized via controlled anionic/radical polymerizations. Here we present the use of reversible addition-fragmentation chain transfer (RAFT) polymerization as a straightforward and industrial applicable alternative to the existing controlled polymerization methods for structure directing agent synthesis. Poly(N,N-dimethylacrylamide)-blockpolystyrene (PDMA-b-PS) block copolymer, synthesized via RAFT, was chosen as structure directing agent for the formation of the mesoporous TiO2. Crack-free thin layers TiO2 with tunable pores from 8 to 45 nm, could be acquired. For the first time, in a detailed and systematic approach, the influence of the block size and dispersity of the block copolymer is experimentally screened for their influence on the final meso-TiO2 layers. As expected, the mesoporous TiO2 pore sizes showed a clear correlation to the polystyrene block size and the dispersity of the PDMA-b-PS block copolymer. Surprisingly the dispersity of the polymer was shown not to be affecting the standard deviation of the pores. As a consequence RAFT could be seen as a viable alternative to the aforementioned controlled polymerization reactions for the 2 synthesis of structure directing agents enabling the formation of mesoporous pore-size controlled TiO2. To examine the photocatalytic activity of the mesoporous TiO2 thin layers the degradation of acetaldehyde, a known indoor pollutant, was studied. Even after three years of aging, the TiO2 thin layer retained most of its activity.