Color Changes in Ag Nanoparticle Aggregates Placed in Various Environments: Their Application to Air Monitoring.

Koichi Ozaki,Fumitaka Nishiyama,Katsumi Takahiro

doi:10.3390/nano11030701

Abstract

Fresh Ag nanoparticles (NPs) dispersed on a transparent SiO2 exhibit an intense optical extinction band originating in localized surface plasmon resonance (LSPR) in the visible range. The intensity of the LSPR band weakened when the Ag NPs was stored in ambient air for two weeks. The rate of the weakening and the LSPR wavelength shift, corresponding to visual chromatic changes, strongly depended on the environment in which Ag NPs were set. The origin of a chromatic change was discussed along with both compositional and morphological changes. In one case, bluish coloring followed by a prompt discoloring was observed for Ag NPs placed near the ventilation fan in our laboratory, resulted from adsorption of large amounts of S and Cl on Ag NP surfaces as well as particle coarsening. Such color changes deduce the presence of significant amounts of S and Cl in the environment. In another case, a remarkable blue-shift of the LSPR band was observed for the Ag NPs stored in the desiccator made of stainless steel, originated in the formation of CN and/or HCN compounds and surface roughening. Their color changed from maroon to reddish, suggesting that such molecules were present inside the desiccator.

Highlights

IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
We propose that a silver nanoparticle (Ag NP) aggregate deposited on a transparent substrate can be candidate for long-term monitoring of the cleanliness of a living or working atmosphere
The origin of chromatic changes is examined from the viewpoints of compositional and morphological changes in Ag NPs/SiO2 stored in various environments to develop a small and cheap device for monitoring of the cleanliness of the atmosphere

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Environmental pollution has become an important problem all over the world. Nitrogen oxide (NOx ), which plays a major role in the formation of ozone and acid rain, is one of the most dangerous air pollutants. Continued exposures to NO2 cause increased incidence of acute respiratory infection [1,2]. Sulphur compounds such as sulphur oxides (SOx ) and hydrogen sulphide (H2 S) are well known to air pollutants. Even short-term exposures to SO2 are linked with respiratory effects including breathing difficulty and asthma symptoms [1,2]. The H2 S, produced by many industrial processes and decomposition of oil, is a very poisonous, corrosive, flammable and explosive gas [3]

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Discussion

Conclusion