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.

Complexes of Cu(ii) with triethanolamine (TEA) are widely used in aqueous precursor solutions of Cu-based catalysts and metal oxides such as YBa2Cu3O7-δ superconductors. An outstanding question is whether such complexes are multinuclear in solution. Here, we use various spectroscopic techniques to unmistakably prove the existence of such multimers. Firstly, we introduce an original approach based on NMR spectroscopy and the Evans method that establishes the existence of multimers in aqueous solution at pH 4 and higher, and allows precise monitoring of the formation of these complexes with increasing pH. Secondly, we use extended X-ray absorption fine structure (EXAFS) spectroscopy to show that a Cu-Cu interaction exists at pH 9.5, which is not observed in acidic (pH 2) solutions. Finally, NMRD measurements reveal additional structural information regarding the multinuclear complexes. Knowledge concerning the nature of Cu(ii)-TEA complexes in solution is of great relevance in view of the design of speciation models to predict the stability of copper triethanolamine-based precursor solutions.

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.

A method to obtain photocatalytically active thin films of anatase nanocrystals on polymer substrates was explored. Anatase nanocrystals were synthesized by a fast hydrolysis synthesis in an apolar solvent and characterized with regard to their crystallinity, size, and dispersibility and the stability of the resulting suspensions. The stable titania nanocrystal suspensions were further processed for their use in polar solvents using ligand exchange. Oleic acid was exchanged for 3-aminopropyltriethoxysilane (APTES), resulting in aqueous suspensions of charge-stabilized nanocrystals. These were adapted for use as coating suspensions for surface-treated PMMA substrates in order to obtain thin films containing anatase nanocrystals covalently coupled to the surface of the PMMA substrates. Thereby, the ligand exchange was beneficial for increasing the compatibility and durability of the inorganic/organic composite, by the formation of a covalent amide bond between the silane ligands on the nanocrystals and the carboxylic acid groups on the polymer substrate. The surface morphology, transparency, and photocatalytic activity toward the degradation of organic pollutants of the coatings, obtained through dip-coating, were evaluated.

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.

In this work, ZrO2 nanocrystals (NCs) are synthesized via a solvothermal treatment in benzyl alcohol, which is an established method for the synthesis of many metal oxide nanocrystals. We found that the use of microwave heating allows for a reduction in reaction time from 2 days in the autoclave to merely 4 h in the microwave. Furthermore, we were able to tune the crystallographic phase from pure cubic to pure monoclinic zirconia by changing the reaction mechanism through the use of a different zirconium precursor. Via GC-MS measurements, we found that the release of a strong acid during synthesis controls the key mechanism behind the control over crystal phase formation. The as-synthesized ZrO2 NCs (cubic or monoclinic) are small in size (3-10 nm), yet aggregated. However, aggregate-free NCs are generated through a surface-functionalization with carboxylic acid ligands, providing stabilization in apolar solvents via steric hindrance. Solution (1)H NMR was used to study the details of this post-modification step and the surface chemistry of the resulting aggregate-free NCs. This led to the conclusion that not only a different crystal structure but also a different surface chemistry is obtained, depending on the precursor composition.

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.

This paper discusses the development of environmentally-friendly precursor inks suited for ink-jet printing of functional ceramic coatings. We synthesized superconducting materials, SrTiO3 thin films for coated conductor applications and transparent TiO2 photocatalytic coatings. Here, we discuss all aspects of ink formulation, including the stabilization of metal ions, nanoparticle inks or combination of both. This demands the investigation and determination of the inks rheological parameters. Ceramic nanoparticles are often incorporated in our inks to decrease thermal processing temperatures (e.g., TiO2 or YSZ coatings...) or enhance the properties of the functional ceramic coating (e.g., pinning centres in superconducting coatings). These ceramic nanoparticles (ZrO2, HfO2, TiO2...) are synthesized through methods based on microwave heating from aqueous and/or organic solutions. With that, we aim at developing smart and environmentally friendly processes that require lower energy input.

Nano sized luminescent materials are structures that can be used in a wide range of applications such as LED’s, computer monitors, fluorescent materials, nanocomposites, etc. The nanoparticles obtained can be deposited on a wide variety of organic or inorganic substrates by making use of wet deposition methods, which broadens the field of applications even further. As a surplus, these materials are often able to be synthesized by making use of green reaction pathways. First, the hydrothermal synthesis of lanthanum hydroxycarbonate nanoparticles in absence of extra ligands was investigated. By small changes in reaction parameters the morphology of the particles was tuned towards spherical shapes. Afterwards, the conversion of the obtained nanoparticles to lanthanum oxycarbonate and lanthanum oxide materials was followed by conducting additional heat treatments. Subsequently, the particles were tested for luminescence of the lanthanide ions. This was done by doping selected samples with Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+ and Yb3+, a wide range of trivalent lanthanide ions. A comparative study between the materials and their luminescent properties was made.

In this Article, epitaxial thin films of SrTiO3 were prepared on single crystalline (100) LaAlO3 by an aqueous chemical solution deposition method. By using different chelating agents to stabilize the metal ions in water, the impact of the precursor chemistry on the microstructural and crystalline properties of the films was studied. Thorough investigation of the precursor by means of infrared and Raman spectroscopy as well as thermogravimetric analysis revealed that stable precursors can be obtained in which strontium ions can be either free in the solution or stabilized by one of the chelating agents. This stabilization of strontium ions appeared to be essential in order to obtain single phase SrTiO3 films. Precursors in which Sr(2+) remained as free ions showed SrO microcrystal segregation. Precursors in which both metal ions were stabilized gave rise to strongly textured, dense, and terraced SrTiO3 films, allowing subsequent deposition of YBa2Cu3O7-δ with superior superconducting performances.

In this work, we focus on the outdoor testing of transparent, photocatalytically-active, TiO2 layers obtained by ink-jet printing of aqueous, nanoparticle containing sols. This approach includes a thermal treatment at strongly reduced temperatures (150 to 500°C), still resulting in coatings with photocatalytic properties comparable to, or in some cases even better than, commercially available, physical deposition based or conventional sol–gel deposited films. This type of titania coatings is being used in outdoor conditions for self-cleaning and antibacterial coatings. This means that they need to exhibit good durability and long term performance. Yet, reducing the thermal treatment temperature might have a negative effect on these parameters. This paper presents simulated artificial weathering, antibacterial and corrosion tests on the processed films, making it possible to assess their performance under real life conditions.

In this work, fully alpha-axis oriented SrTiO3 thin films were synthesized by ink-jet printing of water-based precursor inks. The developed precursor solution or 'ink' was optimized in terms of rheology, leading to the ejection of single droplets showing a maximum contact angle of 12 degrees on (100) oriented single crystal LaAlO3 substrates. By using the appropriate ink-jet deposition parameters and thermal treatment, well-textured and dense SrTiO3 films of 130 nm thickness were obtained. The biaxial texture is maintained up to the surface of the films, leading to the formation of (h00)-oriented terraces. As shown by transmission electron microscopy, excellent texture transfer was achieved from the SrTiO3 film to the YBa2Cu3O7 - delta layer deposited by pulsed laser deposition. Outstanding superconducting properties were obtained with critical current densities up to 3.6 MA cm(-2) in self-field at 77 K, demonstrating that these sustainable SrTiO3 films meet the requirements to be used as growing template for high quality superconducting coatings.

TiO2 coatings can be used to create transparent, photocatalytically active, self-cleaning surfaces and therefore have a very high industrial relevance. Functionality in this kind of TiO2 layers is only obtained after crystallization of the material at temperatures above 400 °C. This means that chemical deposition approaches do not allow deposition on heat-sensitive substrates such as polymers. Therefore, it is important to investigate innovative deposition processes that can significantly reduce the minimal temperature required for crystallization and full processing. In this work, we studied the synthesis of crystalline titania nanoparticles by microwave-assisted solvothermal methods. The use of microwaves allows to optimize the production and energy efficiency of the synthetic process. Once stable suspensions of anatase nanoparticles are obtained, these are optimized for use in ink-jet printing devices. The fact that the crystalline building blocks for the layer are now already present in the precursor inks, allows efficient deposition of transparent titania coatings at reduced temperatures. Weathering/durability tests and extensive characterization of the photocatalytic activity and hydrophilic behaviour of these layers was performed to analyze the performance and processing limits for this kind of titania coatings.

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.