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Development of Photocatalytic Active TiO 2 Surfaces by Thermal Spraying of Nanopowders

Development of Photocatalytic Active TiO 2 Surfaces by Thermal Spraying of Nanopowders. Authors: Filofteia-Laura Toma, Ghislaine Bertrand, Didier Klein, Cathy Meunier, and Sylvie Begin [1] Presented by: Gregory D. Holland October 19, 2010 Oklahoma City Community College.

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Development of Photocatalytic Active TiO 2 Surfaces by Thermal Spraying of Nanopowders

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  1. Development of Photocatalytic Active TiO2 Surfaces by Thermal Spraying of Nanopowders Authors: Filofteia-Laura Toma, Ghislaine Bertrand, Didier Klein, Cathy Meunier, and Sylvie Begin [1] Presented by: Gregory D. Holland October 19, 2010 Oklahoma City Community College

  2. Outline of Presentation • The Problem: NOx • Titanium dioxide • Sources • Uses • Experimental method • Spraying methods • Feedstock materials • Experimental results • Characterization • Conclusions Photo: http://www.germes-online.com

  3. The Problem • Nearly 15 million people in the U.S. have asthma.[2] • Concentrations of NOx as low as 0.1 ppm cause lung irritation and a measurable decrease in the lung function of asthmatics.[3] • Many major cities in the U.S. average more than 100 days a year when ambient NOx levels exceed 0.1 ppm for at least an hour (e.g. Denver, Detroit, El Paso, Phoenix, St. Louis).[4]

  4. TiO2 Photocatalysis Image: http://www.noodor.net/

  5. Titanium Dioxide Sources • Naturally occurring minerals: • Rutile - purified using a chloride process • Anatase • Brookite • Synthesized from other naturally occurring minerals: • Ilmenite (FeTiO3) - Iron removed using a sulfuric acid process Photo: http://www.hummingbirdminerals.com Naturally occurring, acicular crystals of rutile.

  6. Titanium Dioxide Uses • Primarily used as white pigment in: • Toothpaste • Paint • Sunscreen • Cosmetics • Foods • Paper • And more! Photo: http://pamdora.com Photo: http://www.enviroblog.org/ http://www.jwodcatalog.com

  7. Experimental Purpose • Evaluate TiO2 Photocatalytic degradation of gaseous nitrogen oxide pollutants (NO, NOx) • Compare different spraying methods • Compare different feed materials • Characterize coating microstructure to help explain difference in effectiveness: • Scanning electron microscopy (SEM) • X-ray diffraction (XRD)

  8. Plasma Spraying Setup

  9. Experimental Method Three different thermal spraying techniques compared: • Atmospheric plasma spraying (APS) Sulzer-Metco PTF4 plasma gun • Primary gas: Argon • Secondary gases: H2 and He • Suspension plasma spray (SPS) Custom design with peristaltic pump • Primary gas: Argon • Solvents: Distilled water (WSC) or ethanol (ASC) • High-velocity oxygen fuel (HVOF) Sulzer-Metco CDS 100 gun • Fuel gas: Methane with oxygen

  10. Experimental Method Three commercial feed stocks compared: • TiO2–ST01: 100% anatase (7 nm crystals), forming spherical particle agglomerates (10 – 50 μm) • TiO2–PC105: 100% anatase (23 nm crystals) • TiO2–P25: 80% anatase (25 nm crystals) and 20% rutile (50 nm) crystals

  11. Degradation Tests • Custom-built chamber • 0.4 grams of powder covering 54 cm2 surface • 15-W daylight lamp with 30% UVA and 4% UVB • NO and NOx concentrations measured continuously • Performances evaluated by: • Note: Initial concentrations not specified

  12. Degradation Results

  13. Characterization Results

  14. Characterization Results

  15. Characterization Results • Original feedstock compositions for comparison: • TiO2–ST01: 100% anatase (7 nm crystals), forming spherical particle agglomerates (10 – 50 μm) • TiO2–PC105: 100% anatase (23 nm crystals) • TiO2–P25: 80% anatase (25 nm crystals) and 20% rutile (50 nm) crystals

  16. Conclusions Based on Results • Aqueous suspension sprays (WSC) outperformed APS and HVOF methods, probably due to lower process temperatures • Higher anatase composition • Smaller crystallite size • Aqueous suspensions of ST01 and P25 outperformed the raw powders • Not explained by anatase composition • May be due to higher hydroxylation of the surfaces

  17. The Bottom Line • Initial studies suggest aqueous suspension plasma spraying may be an appropriate technique for producing active titania surfaces for the photocatalytic reduction of reactive gaseous pollutants such as nitrogen oxides. • Additional questions related to cost, durability, and fouling of the coatings still need to be addressed.

  18. References [1] Filofteia-Laura Toma, Ghislaine Bertrand, Didier Klein, Cathy Meunier, and Sylvie Begin, “Development of Photocatalytic Active TiO2 Surfaces by Thermal Spraying of Nanopowders,” Journal of Nanomaterials, vol. 2008, Article ID 384171, 8 pages, (2008). doi:10.1155/2008/384171 [2] Stephen Redd, “Asthma in the United Stated: Burden and Current Theories,” Environmental Health Perspectives, vol. 110, supp. 4, pp. 557-560, (2008). [3] Wisconsin Department of Natural Resources, “Nitrogen Oxide Sources and Health Effects,” http://dnr.wi.gov/air/aq/pollutant/oxides.htm, (March 23, 2010). [4] United States Environmental Protection Agency, “Risk and Exposure Assessment to Support the Review of the NO2 Primary National Ambient Air Quality Standard,” EPA document # EPA-452/R-08-008a, November 2008. Questions?

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