| 1. |
- Esbjörnsson Elgh, Björn Neo, 1980, et al.
(författare)
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Correlating Photocatalytic Performance with Microstructure of Mesoporous Titania Influenced by Employed Synthesis Conditions
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:32, s. 16492-16499
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Tidskriftsartikel (refereegranskat)abstract
- Ordered mesoporous anatase films can be prepared at low temperature by evaporation-induced self-assembly of a microemulsion used to preform nanocrystals of titania. Here, we study the impact of storage time of the reaction solution on the structure and photocatalytic properties of such films. The formation of anatase crystallites was found to initiate and proceed during storage of the reaction solution prior to the preparation of the titania films as expected. However, in contrast to current understanding, we find that the main part of the anatase formation occurs during aging of the prepared films in a controlled relative humidity as a consequence of the rapidly increased concentration of precursor caused by the solvent evaporation during film preparation. Ordered mesoporous films were thus obtained for reaction solutions stored up to 48 h, and the crystallinity of the pore walls was found to increase with increased storage time. Interestingly, the anatase crystallite size was found to remain between 2 and 5 nm for all films prepared from reaction solutions stored up to 48 h showing that the increased crystallinity is due to an increased number density of crystallites. Films prepared from reaction solutions stored for longer times than 48 h were found to be mesoporous but with a disordered pore arrangement. These films contained crystallites with sizes up to 10 nm, apparently too large to arrange in a meso-ordered fashion in the liquid crystalline template. The photocatalytic activity of the films was evaluated for phenol degradation and found to be higher for films prepared from reaction solutions with longer storage times of the reaction solution ascribed to their larger degree of crystallinity and larger crystallite size. Interestingly, although the degree of mesoporosity is important in providing access to high specific surface area and facile transport of reactants and products to the catalyst surface, the degree of order of the mesopores was found to be of less importance for the photocatalytic performance. In addition, this work provides new generic insight into the formation mechanism of low-temperature surfactant-templated synthesis of ordered mesoporous and crystalline materials.
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| 2. |
- Bergek, Jonatan, 1984, et al.
(författare)
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Formation of titanium dioxide core-shell microcapsules through a binary-phase spray technique
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 19:35, s. 23878-23886
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Tidskriftsartikel (refereegranskat)abstract
- Core-shell microcapsules consisting of a titanium dioxide shell and a hydrophobic solvent core have been prepared with diameters of a few micrometers and a narrow size distribution using a simple and fast airbrush technique. These microcapsules were prepared at room temperature in a single-step process in which an oil with a dissolved titanium alkoxide precursor was forced together with an aqueous solution, containing a surface-active polymer, through a narrow spray nozzle using a nitrogen gas propellant. Several different parameters of chemical, physical, and processing origin were investigated to find an optimal recipe. Two different alkanes, one ketone, and four alcohols were tested and evaluated as core materials, alone or together with the antifungal biocide 2-n-octyl-4-isothiazolin-3-one (OIT). Long-chain alcohols were found suitable as core oil due to their low solubility in water and surface activity. The addition of the surface-active polymers in the water phase was important in aiding the formation and stabilization of the titanium dioxide shell. An impressive loading of 50 wt%of the semi-hydrophobic OIT was possible to encapsulate using this simple and applicable procedure.
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| 3. |
- Esbjörnsson Elgh, Björn Neo, 1980, et al.
(författare)
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A facile low-temperature synthesis of TiO2 nanoparticles with excellent polymorph control
- 2015
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Ingår i: Journal of Sol-Gel Science and Technology. - : Springer Science and Business Media LLC. - 1573-4846 .- 0928-0707. ; 76:2, s. 395-401
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Tidskriftsartikel (refereegranskat)abstract
- A facile low-temperature synthesis method of crystalline titanium dioxide nanoparticles has been developed, and the effect of temperature and acidity on polymorph selectivity has been systematically investigated. The crystal polymorph of titanium dioxide could be tuned by carefully controlling the condensation rate of titania. Conditions providing high condensation rate favoured the formation of the anatase and brookite phases, while lowering the condensation rate yielded higher rutile content. The reaction was found to proceed either in liquid state for reactions performed at low temperatures and high acidity or in a sol–gel manner for higher temperatures and lower acidity. The aggregation behaviour was found to be strongly affected by the employed synthesis conditions and by the crystal polymorph formed. The design of a facile low-temperature synthesis system with predictive control of polymorph selectivity is important for further development of titania-based materials for applications where type of polymorph is vital, such as photocatalytic and photonic.
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| 4. |
- Esbjörnsson Elgh, Björn Neo, 1980, et al.
(författare)
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Controlling anatase and rutile polymorph selectivity during low-temperature synthesis of mesoporous TiO2 films
- 2014
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 2:9, s. 3024-3030
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Tidskriftsartikel (refereegranskat)abstract
- The polymorph selectivity of a microemulsion-based synthesis solution used for evaporation-induced self-assembly preparation of ordered mesoporous titania films was studied and unexpectedly found to differ from the polymorph selectivity obtained in the films prepared from the reaction solution. While titania nanocrystallites of the rutile phase form in the reaction solution prior to film formation, crystal growth was found to continue after evaporation-induced self-assembly of titania films, resulting in a shift in polymorph selectivity to the anatase phase. Evaporation of solvent and hydrochloric acid during film formation and subsequent aging increases the concentration of the titania precursor and possibly decreases the acidity of the prepared films, both effects that increase the rate of titania condensation, thus promoting the kinetically favoured formation of anatase. The rutile content of the films can be increased by employing an extended reaction time of the synthesis solution prior to the film formation showing that preformed rutile nanocrystallites are retained and incorporated into the titania film during its formation. The crystal growth in the films could be influenced by introducing hydrochloric acid vapour during aging of the formed films, resulting in a decreased formation of anatase nanocrystallites. Such control of the polymorph selectivity in mesoporous titania films is a major advancement towards the synthesis of ordered mesoporous titania films with photocatalytically optimal anatase/rutile ratios and towards the synthesis of pure rutile mesoporous titania.
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| 5. |
- Esbjörnsson Elgh, Björn Neo, 1980, et al.
(författare)
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Controlling morphology, mesoporosity, crystallinity, and photocatalytic activity of ordered mesoporous TiO2 films prepared at low temperature
- 2014
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 2:11, s. Art. no. 113313-
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Tidskriftsartikel (refereegranskat)abstract
- Partly ordered mesoporous titania films with anatase crystallites incorporated into the pore walls were prepared at low temperature by spin-coating a microemulsion-based reaction solution. The effect of relative humidity employed during aging of the prepared films was studied using SEM, TEM, and grazing incidence small angle X-ray scattering to evaluate the mesoscopic order, porosity, and crystallinity of the films. The study shows unambiguously that crystal growth occurs mainly during storage of the films and proceeds at room temperature largely depending on relative humidity. Porosity, pore size, mesoscopic order, crystallinity, and photocatalytic activity of the films increased with relative humidity up to an optimum around 75%.
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| 6. |
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| 7. |
- Karlsson, Philip, 1977, et al.
(författare)
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Admicellar polymerization of methyl methacrylate on aluminum pigments
- 2009
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 337:2, s. 364-368
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Tidskriftsartikel (refereegranskat)abstract
- Micrometer-sized aluminum particles used as pigments in silver inks and coatings are reactive in water-based formulations. This leads to hydrogen gas evolution in the paint containers and loss of the silvery appearance of the coating. The protection of aluminum pigments from water is called inhibition and it was shown in earlier work that anionic surfactants of the phosphate ester type are effective as inhibitors, forming a protective bilayer on the aluminum pigment surface. In this work, the protection of aluminum pigments has been extended by means of an encapsulating polymer layer. A poly(methyl methacrylate) (PMMA) coating was applied on aluminum pigment particles by admicellar polymerization of methyl methacrylate. A surfactant is first adsorbed on the aluminum pigment surface and a hydrophobic monomer and initiator is subsequently solubilized inside the hydrophobic domain of the surfactant aggregates that cover the pigment. Diffuse Reflective Infrared Fourier Transform (DRIFT) spectrometry showed that PMMA was formed on the pigment particles and the amount of organic material was up to 24% of the particle weight, as measured by Thermo Gravimetric Analysis (TGA). A hydrophobic initiator, such as benzoyl peroxide, gave good results but the hydrophilic sodium persulfate resulted in poor yield of encapsulating polymer. Sodium dodecyl sulfate, which by itself is not an efficient inhibitor, was used as surfactant. Good results were obtained in terms of protection from an alkaline solution, indicating that the polymer coating per se is an efficient inhibitor. The highest amount of polymer formed on the pigment surface was obtained when the surfactant concentration was around the CIVIC.
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| 8. |
- Su, R., et al.
(författare)
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How the Anatase-to-Rutile Ratio Influences the Photoreactivity of TiO2
- 2011
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:49, s. 24287-24292
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Tidskriftsartikel (refereegranskat)abstract
- In 1991, Bickley et al. proposed a synergetic effect between anatase and rutile in Degussa P25. Since then, there has been an intensive debate about the correctness of this proposal, the origin of the synergism, and the right polymorph composition. However, a comparison of pure titanium dioxide samples with various anatase-to-rutile ratios, but otherwise identical properties, is missing. In this paper, we report about a series of utterly pure, highly porous titanium dioxide films with identical grain sizes, surface areas, and crystallinity, but varying polymorph compositions. Photocatalytic oxidation of methylene blue was utilized to investigate the influence of the anatase-to-rutile ratio on the photoreactivity. We clearly observe the synergetic effect within a well-defined range of anatase-to-rutile ratios. A film with similar to 60% anatase and similar to 40% rutile exhibits optimal performance at a 50% improved activity compared with pure anatase.
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| 9. |
- Su, R., et al.
(författare)
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Rapid Synthesis of Porous, Mixed Phase Titania Films with Tailored Orientation of Rutile for Enhanced Photocatalytic Performance
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:51, s. 27039-27046
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Tidskriftsartikel (refereegranskat)abstract
- We report on a new, one-step electrochemical oxidation method for the rapid synthesis of mixed phase, polycrystalline TiO2 porous films with oriented rutile within a few minutes. The orientation as well as the surface chemical composition of rutile nanocrystallites can readily be tuned by adjusting the additive concentrations of HCl or HF in the electrolyte during synthesis. All TiO2 films show similar large specific surface area, which is ideal for the application of photocatalysis and photoelectrocatalysis. Compared to the random-oriented TiO2 film, films with an increasing portion of exposed rutile (101) facets were found to be characterized by enhanced photocatalytic oxidation and photoelectrochemical performances. We also observed a synergistic promotion effect of the orientation and surface F impurity. Most interesting, our tailor-oriented porous TiO2 films prepared using HF as additive show an impressive photocurrent generation at zero bias, which is similar to 50 times higher compared to that of the random-oriented TiO2 film.
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| 10. |
- Örn Simonarson, Gunnar, 1986, et al.
(författare)
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Evolution of the Polymorph Selectivity of Titania Formation under Acidic and Low-Temperature Conditions
- 2019
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:3, s. 5750-5757
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Tidskriftsartikel (refereegranskat)abstract
- Evolution of the polymorph selectivity of titanium dioxide was studied under acidic and low-temperature synthesis conditions. Short synthesis times resulted in high relative amounts of the rutile phase, and long synthesis times resulted in high relative amounts of the brookite and anatase phases. The effect of titania precursor concentration was investigated and found to have a large impact on the polymorph selectivity. As the reaction proceeds with time, changes in the chemical environment, caused in particular by the gradually decreasing titania precursor concentration, are therefore likely the cause of the change in polymorph selectivity observed.
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