| 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. |
- Nilsson, Erik, 1980, et al.
(författare)
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Low-Temperature Synthesis and HRTEM Analysis of Ordered Mesoporous Anatase with Tunable Crystallite Size and Pore Shape
- 2011
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 23:11, s. 2781-2785
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Tidskriftsartikel (refereegranskat)abstract
- A new direct synthesis methodology for the preparation of mesoporous titania with hexagonal mesostructure and with walls of tunable crystallinity and crystallite size has been developed. As the crystallites grow they eventually reach a point where they are too big to fit within the pore walls, the mesoorder becomes distorted and is finally lost. It is run at an unprecedented low temperature of 40 degrees C without the need for an autoclave or high-temperature post-treatment procedures and is thus compatible with low temperature stable substrates. High-resolution transmission electron microscopy and electron diffraction reveal that the pore walls of the mesoordered material consists of anatase TiO2 nanoparticles. The method allows for a wide choice of synthesis time during which the anatase crystallites grow slowly within the range of 2-5 nm in size but needs to be kept such that the crystallites have not yet grown too large for them to be coassembled into an ordered mesostructure.
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| 3. |
- Nilsson, Erik, 1980, et al.
(författare)
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Synthesis of nanoparticulate anatase and rutile crystallites at low = mperatures in the Pluronic F127 microemulsion system
- 2011
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Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 26:2, s. 288-295
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Forskningsöversikt (refereegranskat)abstract
- A low-temperature synthesis method for preparing nanosized TiO(2) crystallites has been developed based on a Pluronic F127 microemulsion system. Both anatase and rutile polymorphs can be prepared, and there exists a temperature window between 40 and 50 degrees C where the formation of rutile is favored over anatase. At 60 degrees C and above, anatase is kinetically favored and only very slowly transforms to rutile at 60 degrees C. The results differ from previous observations regarding formation kinetics and temperature range for rutile formation as well as in the microscopic aggregation of the formed nanoparticles. This development of a low-temperature synthesis of crystalline titania nanoparticles within the Pluronic block copolymer system is an important and enabling step toward devising a direct synthesis route for the formation of ordered mesoporous and crystalline titania.
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| 4. |
- Nordström, Jonas, 1980, et al.
(författare)
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Concentration- and pH-dependence of highly alkaline sodium silicate solutions
- 2011
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 356:1, s. 37-45
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Tidskriftsartikel (refereegranskat)abstract
- In this study two routes for the gelation of water glass have been investigated; the destabilization by a change in pH and by an increase in concentration through evaporation. Both methods produce optically transparent, highly viscous, homogeneous solutions. The structure and dynamics of the solutions along the two routes have been investigated with Dynamic Light Scattering, 29Si-Nuclear Magnetic Resonance spectroscopy, viscosity measurements and infrared spectroscopy. We find that the two routes are fundamentally different. Increasing the concentration of the sodium silicate system leaves the silica speciation apparently unchanged. Lowering the pH leads to condensation reactions, thus a change in the silica speciation.
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