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
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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. Image: http://www.noodor.net/
TiO2 Photocatalysis
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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:
Naturally occurring, acicular crystals of rutile.

6. Titanium Dioxide Uses Primarily used as white pigment in: Toothpaste
Paint
Sunscreen
Cosmetics
Foods
Paper
And more!
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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
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 , 8 pages, (2008). doi: /2008/ [2] Stephen Redd, “Asthma in the United Stated: Burden and Current Theories,” Environmental Health Perspectives, vol. 110, supp. 4, pp , (2008). [3] Wisconsin Department of Natural Resources, “Nitrogen Oxide Sources and Health Effects,” (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 a, November 2008.
Questions?