Although already some mesoporous (2–50 nm) sol–gel TiO 2 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)- block -polystyrene (PDMA- b -PS) block copolymer, synthesized via RAFT, was chosen as structure-directing agent for the formation of the mesoporous TiO 2 . Crack-free thin layers TiO 2 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-TiO 2 layers. As expected, the mesoporous TiO 2 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 synthesis of structure-directing agents enabling the formation of mesoporous pore size-controlled TiO 2 . To examine the photocatalytic activity of the mesoporous TiO 2 thin layers, the degradation of acetaldehyde, a known indoor pollutant, was studied. Even after 3 years of aging, the TiO 2 thin layer retained most of its activity.

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. (C) 2017 Elsevier B.V. All rights reserved.

Titanium dioxide, TiO2, is a very versatile and cheap material that can be used in a lot of different applications like (photo)catalysis, sensing and self cleaning coatings.1 Many of these applications take advantage of a high specific surface area and a high degree of crystallinity. As there is always the trade-off between these two parameters, obtaining both in the same material is not straightforward. By using microwave irradiation we were able to achieve this goal. A highly mesoporous titania material with a specific surface area above 330 m²/g,which is among the highest numbers presented in literature, was obtained by adding an additional microwave irradiation step during a normal evaporation-induced self-assembly (EISA) synthesis. The degree of crystallinity which is often neglected in literature, was determined using Rietveld refinement and an increased degree of crystallinity with more than 10 % was achieved. The isoelectric point, particle size and surface groups remained the same after the addition of a microwave irradiation step to the synthesis, thus retaining the material properties that are crucial for applications. One step further in obtaining outstanding materials is the addition of noble metal nanoparticles on mesoporous titania. This kind of materials has a lot of applications in the (photo)catalyst sector. Many synthesis routes are already developped to prepare these kind of materials, but little is known about the oxidation state of the metal ions present in these materials even though it can be an important factor when one studies the reaction mechanisms of a reaction. Therefore we performed a study of the oxidation state of gold atoms of Au/TiO2 materials reduced in four different ways, using X-ray adsorption spectroscopy (XAS).2 We found that different particle sizes, oxidation states and interactions of the gold with the titania support are obtained when one uses different reduction methods. When one uses these composite materials in photocatalytic remediation reactions or alcohol oxidation reactions, one can observe differeneces between these samples even though the gold loading stays the same. REFERENCES 1. M. Arin, P. Lommens, et al., J. Eur. Ceram. Soc., 2011, 31, 1067-1074. 2. M. Meire, P. Tack, et al., Spectrochim. Acta B, 2015, 110, 45-50.

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.

Mesoporous titanium dioxide is a material finding its use in a wide range of applications. For many of these, it is important to achieve a high degree of crystallinity in the material. It is generally accepted that the use of the soft templating approach to synthesize mesoporous titania, results in a compromise between crystallinity and specific surface area due to thermal instability of the used templates. In this paper, we explore how the use of microwave irradiation can influence the crystallinity, specific surface area, and the electronic properties of mesoporous titania. Therefore, we combined microwave radiation with an evaporation-induced self-assembly (EISA) synthesis. We show that additional microwave treatment at carefully chosen synthesis steps can enhance the crystallinity with 20 % without causing significant loss of surface area (>360 m2/g). Surface photovoltage measurements were used to investigate the electronic properties. The photocatalytic activity of the samples was evaluated in aqueous media by following the degradation of an industrial dye, methylene blue, and the herbicide isoproturon under UV irradiation and in gaseous media looking at the degradation of acetaldehyde, a common indoor pollutant under UVA irradiation. In all cases, the microwave treatment results in more active materials.

Combining photocatalytic properties with a high specific surface area, mesoporous titania can be used in a wide range of applications such as water treatment, air purification and water splitting. Conventionally, soft template synthesis routes comparable to silica syntheses (EISA, hydrothermal syntheses, etc.) are used. These syntheses are time consuming processes, including long aging times and inefficient heating procedures while still only moderate degrees of crystallinity are obtained. [1] Obtaining a material with both a high porosity and a high crystallinity poses a challenge as crystal growth leads to collapsing of the pores. Microwave irradiation can be the solution for these problems. Microwaves directly couple to the solvent molecules used during synthesis, making it possible to create very fast heating, avoiding slow heat transfer through different materials (air-metal-solution) typical for hydrothermal routes. In TiO2 nanoparticle synthesis, replacing a hydrothermal synthesis by microwave irradiation not only reduced the synthesis time but also an increase in crystallinity was observed [2], therefore it is also possible that microwave irradiation improves the degree of crystallinity in mesoporous titania, solving both problems of conventional solution syntheses. We found that the use of microwave irradiation makes it indeed possible to enhance the degree of crystallinity of mesoporous titania, while avoiding the loss of specific surface area. Other properties like particle size, band gap energy and isoelectric point also remained unaffected by the microwave treatment. Against expectations the photocatalytic activity of the microwave irradiated samples, exhibiting an increased crystallinity, was lower compared to the non treated samples. We are investigating this reduction using EPR and other techniques to understand the underlying effects of microwave irradiation. REFERENCES [1] Ismail, A. A. and Bahnemann, D. W., J. Mater.Chem. 32 (2011) 11686. [2] Dufour, F., Cassaignon, S., Durupthy, O., Colbeau-Justin, C. and Chaneac, C., Eur. J. Inorg. Chem. 16 (2012) 2707.

XPS was used as an evalution tool for nanoparticles in HTSC thin films. Ar-sputtering was used for depthprofiling and as such it was shown that this is a useful tool to evaluate the distribution of the nanoparticles within the thin film.

The functionalization of titania based materials with noble metal cocatalysts such as gold or platinum is a well known procedure to improve the catalytic activity of these materials in for example the degradation of organic pollutants or CO conversion. Parameters such as cocatalyst load, noble metal particle size and oxidation state influence the efficiency of these materials. We have impregnated a mesoporous titania powder with a gold salt and used different synthesis routes to reduce the gold ions. A structural analysis was performed using electron microscopy and nitrogen sorption. An X-ray absorption near edge structure spectroscopy study, in both high and low resolution, was performed to investigate the influence of the different reduction methods on the oxidation state of the gold atoms. This technique can also provide information on the local environment of the gold atoms and their interaction with the titanium dioxide host. We found that varying the reduction method has a significant impact on the oxidation state of the gold cocatalysts. This lead to varying interactions with the titania support and charging of the gold nanoparticles.

Mesoporous materials, exhibiting high specific surface areas and narrow pore size distributions are very attractive for applications such as adsorption and catalysis. At the same time, titania is an interesting material because of its photocatalytic properties under UV radiation. Mesoporous titania can show a strongly enhanced photocatalytic activitiy compared to its non porous variants. Reports on the synthesis of mesoporous titania discuss mainly results obtained from conventional soft-templating, blockcopolymer based synthesis routes like EISA or hydrothermal synthesis. Yet, hydrothermal heating is a time consuming process. Therefore our work focuses on the use of microwave assisted methods for the synthesis of mesoporous titania. Microwaves can directly couple to the solvent molecules used during a synthesis, leading to efficient heating, as slow heat transfer through different materials (air-metal-solution) is avoided. Rietveld analysis is used to determine the crystallinity of the samples. We were able to show that using microwave based syntheses, mesoporous titania with increased crystallinity and a high specific surface area can be obtained. We have evaluated mesoporous titania in water purification applications. The photocatalytic activity of the different mesoporous TiO2 samples is tested by following the degradation of methylene blue under UV illumination. Some first results on the degradation of some highly mobile pesticides present in surface waters will also be shown.

Titania is the most widely studied and applied material for photocatalytic applications. Enhancing the surface area of a titania catalyst could significantly increase its activity as photocatalytic reactions typically proceed on or near the surface of the material. In this report, mesoporous titania is used in water purification applications. The photocatalytic activity of different mesoporous TiO2 samples obtained from various synthesis approaches is tested by following the degradation of methylene blue and some highly mobile pesticides present in surface waters under UV illumination. Not only the specific surface area of the samples determines their efficiency, also the crystallinity and chemical nature of their surface are crucial. Therefore, we use Rietveld analysis to determine the crystallinity of the samples. IR spectroscopy reveals that titanol groups present on the surface play an important role in the activity of the material. This means that to further enhance the activity of the material, a lot of attention needs to be paid to the surface of TiO2 and the interactions of the organic pollutants and the surface of mesoporous titania. In the case of the degradation of the pesticides, the intermediate species are determined to make sure no toxic species are obtained.

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).

Introduction: Titania is the most widely studied and applied material for photocatalytic applications. Enhancing the surface area of a titania catalyst could significantly increase its activity as photocatalytic reactions typically proceed on or near the surface of the material. Conventional soft template synthesis routes like EISA or hydrothermal syntheses are time consuming processes, including long aging times and inefficient heating procedures. [1] Our work focuses on the use of microwave assisted methods for the synthesis of mesoporous titania. Microwaves can directly couple to the solvent molecules used during synthesis, making it possible to create very fast heating, avoiding slow heat transfer through different materials (air-metal-solution) typical for hydrothermal routes. In order to achieve the highest increase in photocatalytic activity, the material needs to be highly crystalline. In case of titania nanoparticles synthesized through hydrothermal methods, it has been shown before that microwave irradiation improves the crystallinity of the nanoparticles and allows reducing synthesis temperature and time [2], therefore it is also possible that microwave irradiation improves the degree of crystallinity in mesoporous titania. Results and Discussion: Mesoporous titania samples are prepared using an EISA and a hydrothermal route, with and without microwave irradiation. Rietveld analysis was used to determine that microwave irradiation was indeed able to enhance the degree of crystallinity in mesoporous titania. Other characteristics like specific surface area, particle size and band gap energy of the materials, were not affected by the microwave treatment. The different synthesis routes lead to materials with a different surface chemistry. This could be revealed by using FTIR to determine the surface groups. The isoelectric points of the materials were also investigated and are depended on the synthesis route. Conclusions: Using microwave irradiation it is possible to enhance the degree of crystalline material in mesoporous titania without a negative effect on other characteristics of the material. Different synthesis routes lead to materials with different surface properties which is important for specific applications of the materials. References [1] A. A. Ismail and. D. W. Bahnemann, J. Mater.Chem. 2011, 32, 11686-11707. [2] F. Dufour, S. Cassaignon, O. Durupthy, C. Colbeau-Justin and C. Chaneac, Eur. J. Inorg. Chem. 2012, 16, 2707-2715.