Silver Nanoparticle Films as Sulfide Gas Sensors in Oddy Tests
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1047-Y04-04
Silver Nanoparticle Films as Sulfide Gas Sensors in Oddy Tests Rui Chen1, Laura Moussa2, Hannah R. Morris1, and Paul M. Whitmore1 1 Art Conservation Research Center, Carnegie Mellon University, 700 Technology Drive, Pittsburgh, PA, 15219 2 Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, PA, 15213
ABSTRACT The preparation and performance of a silver nanoparticle-based sensor for use in Oddy tests are reported. A suspension of spherical silver nanoparticles (Ag NPs) (mean diameter of 30 nm, absorption of surface plasmon resonance (SPR) at 428 nm) in methanol was synthesized and the Ag NPs were assembled into monolayer films on glass slides, using polyethylenimine as a linking agent. UV-Vis spectrophotometry was employed to measure the SPR intensity of the Ag NP films in order to evaluate the extent of reaction. It was observed that the Ag NP films were quite stable under Oddy test conditions in a blank test, after a brief alteration of the spectrum due to particle dispersal, with no significant decrease in the SPR intensity after 1.5 months at 60°C and 100% RH. The sensitivity of Ag NP films to sulfide gases emitted from a test wool fabric in the Oddy test was investigated. UV-Vis spectra taken after the Oddy tests showed the disappearance of the Ag NP SPR peak and the growth of the UV absorption due to Ag2S. Elemental analysis with energy dispersive x-ray spectroscopy confirmed that sulfur had been incorporated into the Ag NP film. Ag NP assemblies of lower NP density were created that indicated the presence of sulfide gases prior to significant tarnishing of a Ag foil. The results demonstrate that the Ag NP films can be used as sensitive, quantitative optical sensors to replace Ag foils in the Oddy test system. INTRODUCTION Air pollutants in a museum environment and gases emitted from storage and display materials can cause or accelerate the degradation of materials, particularly metals, used in works of art. For example, reduced sulfur gases such as hydrogen sulfide (H2S) are known to be quite harmful to some artifacts because it creates tarnish on the surface of silver, black sulfides on copper alloy objects, and blackens white lead pigments [1]. A general and practical method widely applied in museums to evaluate the safety of storage and display materials is the Oddy test, which was first proposed by Andrew Oddy at the British Museum in 1973. The Oddy test is performed by enclosing a sample of the material of interest along with metal coupons (usually silver, copper, and lead) in a 100% RH environment. The test system is incubated at 60°C for 28 days, after which the coupons are visually examined for evidence of corrosion due to off-gassing emissions from the test material. The original Oddy test has undergone modification over the years. In order to decrease the variation between laboratories of assessments on identical materials and to reduce the test preparation time, standard procedures were devised and the experimental setup was simplified to the 3-in-1 tes
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