Titania mesoporous layer

The dye-sensitized solar cell (DSC), often called the Gratzel cell, is constructed as follows. A layer of titania paste consisting of anatase nanoparticles is spread onto a glass plate that is coated with a thin conducting layer of fluorine-doped Sn02. The paste contains organic binders that are removed when the film is calcined in air (typically at 450-500 °C), leaving a mesoporous titania film (ca. 10 pm thick) with a porosity of around 50 %. The titania film is immersed in... 

Because the currently used y-alumina is not stable in all acid and basic environments used in industry [2], the development of mesoporous layers other than y-alumina deserves attention as well. Most common materials that can be used for the mesoporous layer are zirconia and ti-tania [3,4], but recently also the preparation of mesoporous hafnia is described [5], Hafnia seems to be a very interesting membrane material, because it can, unlike zirconia and titania, be fired up to 1850°C without a phase transformation of its monoclinic form. Hafnia also has a high chemical resistance toward acid and basic media. Another interesting material, currently under investigation by the group of Brinker is mesoporous silica [6,7], This material is especially interesting because a tailor made morphology and pore-size is possible. 

Since then, other colloidal oxide systems have been investigated in order to prepare ceramic mesoporous membranes designed for ultrafiltration. The preparation of an electronically conductive membrane from a Ru02 Ti02 mixed oxides sol and the application to an electro-ultrafiltration process [25,26], as well as the preparation of titania and zirconia ultrafiltration membranes [27], have been described following a colloidal process in which a partial destabilization of a metal oxide colloidal suspension is used to produce top layers with different pore size and pore volume in the mesoporous range. In agreement... 

Amorphous silica has also been mentioned as a starting metal oxide material for the preparation of particulate mesoporous membranes. These membranes were prepared from commercial sols, Ludox (DuPont) or Cecasol (Sobret), and coated on a macroporous a-alumina support [35]. In contrast to crystalline membrane materials such as alumina, titania or zirconia, the evolution of pore size with temperature of amorphous silica membranes was revealed to be more sensitive to drying conditions than to firing temperature (Table 7.1). When heat-treated for several hours at 800°C the silica top layer transformed from an amorphous state to cristobalite. 

Mesoporous y-alumina and titania supporting layers were severely attacked by the precursor solution (with high alkalinity) and could not be used. Macro-porous a-alumina supports (pore diameter 0.16 pm, porosity = 46%) could however be successfully applied. 

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