Chemistry Nexus

by WebElements: the periodic table on the web

The Science Blog reports that researchers at Penn State in the USA are developing self-cleaning titania nanotube hydrogen sensors. The hydrogen sensors are titania nanotubes coated with a discontinuous layer of palladium. Hydrogen sensors are widely used in the chemical, petroleum and semiconductor industries. They are also used as diagnostic tools to monitor certain types of bacterial infections.

“The photocatalytic properties of titania nanotubes are so large – a factor of 100 times greater than any other form of titania – that sensor contaminants are efficiently removed with exposure to ultraviolet light, so that the sensors effectively recover or retain their original hydrogen sensitivity in real world application”

“By doping the titania nanotubes with trace amounts of different metals such as tin, gold, silver, copper, niobium and others, a wide variety of chemical sensors can be made. This doping does not alter the photocatalytic properties of the titania nanotubes” says Dr. Craig A. Grimes, associate professor of Electrical Engineering and Materials Science and Engineering.1

Abstract described is a room-temperature hydrogen sensor comprised of a TiO2-nanotube array able to recover substantially from sensor poisoning through ultraviolet (UV) photocatalytic oxidation of the contaminating agent; in this case, various grades of motor oil. The TiO2 nanotubes comprising the sensor are a mixture of both anatase and rutile phases, having nominal dimensions of 22-nm inner diameter, 13.5-nm wall thickness, and 400-nm length, coated with a 10-nm-thick noncontinuous palladium layer. At 24°C, in response to 1000 ppm of hydrogen, the sensors show a fully reversible change in electrical resistance of approximately 175,000%. Cyclic voltammograms using a 1 N KOH electrolyte under 170 mW/cm2 UV illumination show, for both a clean and an oil-contaminated sensor, anodic current densities of approximately 28 mA/cm2 at 2.5 V. The open circuit oxidation potential shows a shift from 0.5 V to –0.97 V upon UV illumination.

References

1. Mor, Gopal K., Maria A. Carvalho, Ooman K. Varghese, Michael V. Pishko, and Craig A. Grimes, “A room-temperature TiO2-nanotube hydrogen sensor able to self-clean photoactively from environmental contamination“, Journal of Materials Research, 2004, 19, 628-634, http://dx.doi.org/10.1557/jmr.2004.19.2.628.

December 9th, 2009

Posted In: Chemistry

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