Titanium dioxide is a semiconductor oxide photocatalyst, which is chemically and biologically inert but exhibits excellent photocatalytic activity in the ultraviolet (UV) region. In addition, since it is available at a low cost, it is the material of choice for hydrophilic self-cleaning surfaces. Titania thin films are conventionally produced by sol-gel route and possess good photo catalytic efficiency. The photo catalytic efficiency is directly related to the high-surface area, crystalline structure of the titania films and on the type of substrate used. In titania films formed on soda lime substrates it has been studied that the sodium ions underneath navigate into the thin film and cause detrimental effects to the photo catalytic properties. Hence there is a need to prevent these detrimental effects using a barrier layer on top of the substrate and protect the photo catalytic activity.

A research team headed by Urska Stangar at the Laboratory for Environmental Research, Nova Gorica Polytechnic, Slovenia have developed titania thin films, which are deposited on soda lime glass plates protected by a thin silicon dioxide layer (it prevents diffusion of alkali ions impurities from the glass substrate in the active titania film during its heat treatment). Thin films were prepared by the sol-gel processing and dip-coating deposition technique. Titania sols and coatings were made from a modified titanium iso-propoxide precursor with ethyl acetoacetate and a solvent 2-methoxyethanol, in the presence or absence of nonionic surfactant. Films were deposited by a dip-coating technique on soda-lime glass plates with a barrier (protecting) silica layer and then heat-treated at 500 degrees C for 30 min. Thin films were made by the simple sol-gel route at ambient conditions and characterised. Their thickness and granular nanostructure were controlled by the addition of templating agents (nonionic surfactants). The thickness of the films formed without the surfactant was 300 nm and with surfactant was 1200 nm.

"The significance is that we have tested the films in a specially designed bigger reactor for water purification and they perform very well. Immobilised films on glass plates are placed on the rotating holder in the core of the reactor. Pesticides in water are photocatalytically decomposed by the simultaneous action of UV light and TiO2 thin film catalyst," Stangar tells Technical Insights.

Specific potential applications of this work are in the fields of water and air purification. Namely, the property of this material is that it is photo catalytically active that is, under solar irradiation (UV part) it is activated and acts as a catalyst for the degradation of various organic pollutants in water and air. It has so called self-cleaning and antibacterial properties (under solar light the impurities or bacteria on such a surface are decomposed due to the photocatalytic ability of a semiconductor titanium dioxide coating).

Stangar adds, "The next step in the development would be further simplification of the processing and preparation conditions in order to have higher application value. One of such parameter is a decrease in the calcination temperature, which would allow the deposition of films on temperature sensitive substrates, such as plastic, and even on the already installed objects in a building construction."

The research group collaborates with others on the development of this work. The partners are: a Slovene company, Nova Gorica Polytechnic, and three academic institutions from Italy, Austria, and Greece. Patents have been filed for this technology in Japan.
 

Details:

Urska Lavrencic Stangar

Laboratory for Environmental Research

Nova Gorica Polytechnic

Vipavska 13, Rozna Dolina SI-5000

Nova Gorica Slovenia

Phone: +386-5-3315-241, +386-31-702324

E-mail: urska.lavrencic@p-ng.si

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