Recent advances in low-temperature deposition methods of transparent, photocatalytic TiO2 coatings on polymers

In this paper, we present an overview as well as current advances in the low-temperature deposition of highly crystalline suspensions of titania nanoparticles on polymers for photocatalytic applications. The presence of preformed titania nanoparticles yields the possibility of producing photocatalytically active coatings at reduced temperatures. Transparent and photocatalytically active TiO2 coatings that degrade organic matter, have been widely applied to bestow self-cleaning properties onto surfaces. This low-temperature deposition method and its transition to polymers would open an entire array of possible self-cleaning applications. During this research, incorporation of a silica buffer layer was applied to improve the compatibility of the inorganic coating on a substrate, such as polymethylmethacrylate (PMMA) and polyphenylsulphone (PPSU). The photocatalytic activity of the obtained coating was analyzed for its photocatalytic abilities by evaluating the color removal of a dye solution (methylene blue, MB) under UV irradiation and compared with commercial Pilkington Activ (R) self-cleaning glass. Our results indicate that the titania-coated silica-polymer systems yield a higher photocatalytic activity towards the degradation of organic pollutants. This method proves that the deposition of highly crystalline anatase suspensions on silica buffer layers is a viable method to produce photocatalytic coatings on heat-sensitive substrates

Monometallic cerium layered double hydroxide supported Pd-Ni nanoparticles as high performance catalysts for lignin hydrogenolysis

Monometallic cerium layered double hydroxides (Ce-LDH) supports were successfully synthesized by a homogeneous alkalization route driven by hexamethylenetetramine (HMT). The formation of the Ce-LDH was confirmed and its structural and compositional properties studied by XRD, SEM, XPS, iodometric analyses and TGA. HT-XRD, N-2-sorption and XRF analyses revealed that by increasing the calcination temperature from 200 to 800 degrees C, the Ce-LDH material transforms to ceria (CeO2) in four distinct phases, i.e., the loss of intramolecular water, dehydroxylation, removal of nitrate groups and removal of sulfate groups. When loaded with 2.5 wt% palladium (Pd) and 2.5 wt% nickel (Ni) and calcined at 500 degrees C, the PdNi-Ce-LDH-derived catalysts strongly outperform the PdNi-CeO2 benchmark catalyst in terms of conversion as well as selectivity for the hydrogenolysis of benzyl phenyl ether (BPE), a model compound for the alpha-O-4 ether linkage in lignin. The PdNi-Ce-LDH catalysts showed full selectivity towards phenol and toluene while the PdNi-CeO2 catalysts showed additional oxidation of toluene to benzoic acid. The highest BPE conversion was observed with the PdNi-Ce-LDH catalyst calcined at 600 degrees C, which could be related to an optimum in morphological and compositional characteristics of the support

Microwave-Assisted Synthesis of Nanoscale VO2 Structures

Nanoscaled VO2 structures were made using a fast microwave-assisted synthesis method in acetophenone as solvent, starting from vanadium pentoxide V2O5. Insights in the reaction and purification process were elaborated by attenuated total reflection infrared and nuclear magnetic resonance spectroscopy, which validated the choice of oleyl amine as ligand and acetophenone as solvent. A straightforward heat treatment in inert atmosphere was used to convert the mixture of VOx (M) and VOOH phases to thermochromically active monoclinic VO2 (M) nanomaterials. This conversion process was monitored via in-situ X-ray diffraction and gave insight in the influence of ethanol and tert-butyl hydroperoxide on the crystal structure and morphology, monitored via bright-field transmission electron microscopy. The thermochromic switching was investigated with differential scanning calorimetry showing a latent heat up to 43.34 ​J/g

Thickness characterization toolbox for transparent protective coatings on polymer substrates

The thickness characterization of transparent protective coatings on functional, transparent materials is often problematic. In this paper, a toolbox to determine the thicknesses of a transparent coating on functional window films is presented. The toolbox consists of a combination of secondary ion mass spectrometry and profilometry and can be transferred to other transparent polymeric materials. A coating was deposited on designed model samples, which were characterized with cross-sectional views in transmission and in scanning/transmission electron microscopy and ellipsometry. The toolbox was then used to assess the thicknesses of the protective coatings on the pilot-scale window films. This coating was synthesized using straightforward sol-gel alkoxide chemistry. The kinetics of the condensation are studied in order to obtain a precursor that allows fast drying and complete condensation after simple heat treatment. The shelf life of this precursor solution was investigated in order to verify its accordance to industrial requirements. Deposition was performed successfully at low temperatures below 100 °C, which makes deposition on polymeric foils possible. By using roll-to-roll coating, the findings of this paper are easily transferrable to industrial scale. The coating was tested for scratch resistance and adhesion. Values for the emissivity (ε) of the films were recorded to justify the use of the films obtained as infrared reflective window films. In this work, it is shown that the toolbox measures similar thicknesses to those measured by electron microscopy and can be used to set a required thickness for protective coatings

Pair distribution function analysis of ZrO2 nanocrystals and insights in the formation of ZrO2-YBa2Cu3O7 nanocomposites

The formation of superconducting nanocomposites from preformed nanocrystals is still not well understood. Here, we examine the case of ZrO2 nanocrystals in a YBa2Cu3O7-x matrix. First we analyzed the preformed ZrO2 nanocrystals via atomic pair distribution function analysis and found that the nanocrystals have a distorted tetragonal crystal structure. Second, we investigated the influence of various surface ligands attached to the ZrO2 nanocrystals on the distribution of metal ions in the pyrolyzed matrix via secondary ion mass spectroscopy technique. The choice of stabilizing ligand is crucial in order to obtain good superconducting nanocomposite films with vortex pinning. Short, carboxylate based ligands lead to poor superconducting properties due to the inhomogeneity of metal content in the pyrolyzed matrix. Counter-intuitively, a phosphonate ligand with long chains does not disturb the growth of YBa2Cu3O7-x. Even more surprisingly, bisphosphonate polymeric ligands provide good colloidal stability in solution but do not prevent coagulation in the final film, resulting in poor pinning. These results thus shed light on the various stages of the superconducting nanocomposite formation

Synthesis methods for thermochromically active VO2 nanoparticles

In recent years, the need for smart window materials that lower the energy consumption for heating, venting and air-conditioning of buildings has grown immensely. These smart materials undergo a reversible change in physical properties depending on various conditions. A material that fits this description is vanadium dioxide, a thermochromic material that changes from a monoclinic to a rutile phase when heated above a critical temperature. This metal-insulator transition (MIT) leads to the absorption of infrared radiation. By absorbing this, a lower amount of heating-up occurs inside buildings and less cooling is needed. During this work, the main focus is the development of novel and easy methods to synthesize thermochromically active vanadium dioxide nanoparticles. Solvothermal and microwave syntheses were performed and optimized. The influence of various reaction parameters on the morphology, crystal structure and thermochromic properties of the nanosized materials was studied

Synthesis methods for thermochromically active VO2 nanoparticles

In recent years, the need for smart window materials that lower the energy consumption for heating, venting and air-conditioning of buildings has grown immensely. These smart materials undergo a reversible change in physical properties depending on various conditions. A material that fits this description is vanadium dioxide, a thermochromic material that changes from a monoclinic to a rutile phase when heated above a critical temperature. This metal-insulator transition (MIT) leads to the absorption of infrared radiation. By absorbing this, a lower amount of heating-up occurs inside buildings and less cooling is needed. During this work, the main focus is the development of novel and easy methods to synthesize thermochromically active vanadium dioxide nanoparticles. Solvothermal and microwave syntheses were performed and optimized. The influence of various reaction parameters on the morphology, crystal structure and thermochromic properties of the nanosized materials was studied