produktblattalliance 01 englisch...sol-gel processing offers many possibilities of adjusting and...
TRANSCRIPT
Initial situation
Processing techniques for TiO2 thin filmshave been developed at Fraunhofer ISCfor optical applications. Starting frommetal alkoxides large areas of glass canbe coated with high optical qualities atmoderate investment costs. Problemsarising during this sol-gel procedureregarding the reproducibility and thestability of coating solutions have beenovercome by using amorphous solubleprecursor powders.
Development of highly activephotocatalytic coatings
The structural features of TiO2 surfacesare very important for the performanceof the material. Sol-gel processing offersmany possibilities of adjusting andoptimizing the microstructure of thinfilms. For optical applications dense TiO2
films with smooth surfaces were re-quired, whereas for photocatalytic appli-cations TiO2 films with rough and highsurface areas may be advantageous.
To evaluate the specific activity ofdifferent materials, a reactor forphotochemical degradation reactionswas fabricated at Fraunhofer ISC(Figure 1). The oxidation ofdichloroacetic acid (a) to carbondioxide and hydrogen chloride orthe oxidation of methanol (b) to form-aldehyde in the presence of photo-catalytic TiO2 coatings can be measuredas a function of irradiation time:
a) Cl2CH-COOH + O2 → 2 CO2 + 2 HCl
b) 2 CH3-OH + O2 → 2 CH2O + 2 H2O.
Fraunhofer Photocatalysis Network
www.photokatalyse.fraunhofer.de
c/o Fraunhofer ISTBienroder Weg 54E38108 Braunschweig, Germany
MarketingDr. Simone KondruweitPhone +49(0)531/2155-535Fax +49(0)531/2155-900E-Mail [email protected]
Fraunhofer Institute for Silicate Research
Prof. Gerd MüllerNeunerplatz 297082 Würzburg, Germanywww.isc.fraunhofer.de
Your contact:
Dr. Frank HutterPhone +49(0)931/4100-402E-Mail [email protected]
Bettina HerbigPhone +49(0)931/4100-403E-Mail [email protected]
Photocatalytic Coatings
AllianzPhotokatalyse
FraunhoferFhG
Figure 1: Scheme of the cylindrical reactorat Fraunhofer ISC for measurements ofphotocatalytic activity of TiO2-coated glasssubstrates.
Figure 2: Photocatalytic activity of acommercial, architectural glass (TiO2-coated) vs. a dense and a porous TiO2 sol-gel thin film.
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The photocatalytic degradation ofdichloroacetic acid can easily bemonitored by measuring the amountof chloride ions formed during thephotocatalytic experiments, whereasformaldehyde is detected by a specificcolor reaction and subsequentphotometric measurements.
In figure 2 the photocatalytic activity ofdense TiO2 thin films prepared by thesol-gel processing is compared toa commercially available productdeveloped for architectural applications.The degradation rates of both samplesare similar indicating that already thedense TiO2 films developed for opticalapplications can well compete with thecommercial product manufacturedby an APCVD (Atmospheric PressureChemical Vapour Deposition) method.
The addition of specific organicmolecules to the coating solutions andthe burn-out of these substances in afinal curing step, thereby generatinga defined porosity, increase thephotocatalytic activity of the porousTiO2 film (Figure 2). The electron andthe atomic force micrograph (SEM,AFM) in figure 3 shows that the accessof organic pollutants to lower parts ofthe TiO2 film is facilitated by pores,which thereby enlarge the TiO2surface for photocatalytic reactions.The embossing of sol-gel films witha stamper, thus forming a periodicpattern, is another method of changingthe microstructure of these inorganicsurfaces. Such a periodic pattern ofa TiO2 thin film on glass is displayedin an atomic force microscopy profile(AFM) in figure 4.
Thin film analysisand perspectives
For the characterization anddevelopment of photocatalyticcoatings there are, besides SEMand AFM, many analytical methodsavailable at Fraunhofer ISC, e.g. FTIR,Raman, UV/VIS and fluorescencespectroscopy as well as TEM, XPS andXRD. Besides the two constitutingeffects (photocatalytic activity,photoinduced hydrophilicity) ofphotocatalytic coatings, there are manyother properties required for differentapplications: e.g. hardness, scratchresistance, transparency, weatheringand long-term stability. These qualitiescan also be tested by diverse methods(taber abraser, sun and xeno test, QUV(abbreviation for Q Panel CompanyUltraviolett) weathering).
The comparison of the photocatalyticperformance of TiO2 coatings by theevaluation of further test methods andthe development of coatings that areactive over a long period of time andactivated in the visible light range(λ > 400 nm) is the key part of ourongoing research and developmentproject in co-operation with otherFraunhofer institutes (IST, IFAM, FEP,ISE, IGB, IME). In this projectphotocatalytic coatings are preparedby various methods (e.g. sol-gel,magnetron sputtering, atmosphericplasma processing etc.). Additionally,analytical testing methods and deviceswill be developed, and biological andenvironmental aspects of photocatalysiswill be investigated.
Figure 3: Scanning electron (SEM) and atomicforce (AFM) micrograph of a porous TiO2sol-gel thin film.
Figure 4: Atomic force micrograph (AFM) ofan embossed TiO2 sol-gel thin film.
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