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

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

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]

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

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.

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

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)

Plasma Spraying Setup

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 Solvents: Distilled water (WSC) or ethanol (ASC) High-velocity oxygen fuel (HVOF) Sulzer-Metco CDS 100 gun Fuel gas: Methane with oxygen

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

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

Degradation Results

Characterization Results

Characterization Results

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

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

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.

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?