Yasuko Yamada Maruo

Coloration reactions between NO2 and organic compounds in porous glass for cumulative gas sensor

Abstract Coloration reactions between nitrogen dioxide (NO 2 ) and organic compounds, such as diazocoupling reactions, were demonstrated to occur in pores by exposing organically impregnated porous glass chips to NO 2 . An NO 2 concentration of under 1 ppm can be estimated from the absorbance changes after the coloration reactions. Good linear relationships were obtained between the absorbance changes and exposure time at 200 ppb, indicating the possibility of environmental-level analysis by accumulation. Application to an actual analysis showed that this method can give the variations in NO 2 concentrations at the environmental level.

A ppb-level NO2 gas sensor using coloration reactions in porous glass

Abstract Coloration reactions for NO 2 detection were demonstrated to occur in the pores of porous glass. Porous glass chips impregnated with a new combination of coupling reagents (sulfanilamide as a diazotizing reagent and N , N -dimethyl-1-naphthylamine as a coupling reagent) showed large absorbance changes after exposure to NO 2 in both artificial and actual environments, indicating their applicability to ppb-level NO 2 detection. A simple sensor device, consisting of this doped porous glass, a light-emitting diode as a light source, and a photodiode as a detector, can detect hourly changes in ppb-level NO 2 concentrations, which has previously been possible only by using large analytical instruments.

A ppb-level NO2 detection system using coloration reactions in porous glass and its humidity dependence

Coloration reactions between nitrogen dioxides (NO2) and diazo-coupling reagents have been shown to occur in the nano-pores of porous glass. We introduced sulfanilamide and N,N-dimethyl-1-naphthylamine as diazo-coupling reagents into porous glass. This organically doped porous glass sensor had one specific peak near 525 nm in the visible region and showed large changes in absorbance after exposure to NO2. We investigated the humidity dependence of its sensitivity during exposure to NO2 in an artificial environment. The sensitivity was almost constant from 35% to 70% RH. Thus, our simple NO2 detection system using the porous glass sensor, a light-emitting diode, and a photodiode was able to determine the hourly variations in NO2 concentration at the ppb level in an actual environment without being seriously affected by humidity in the range between 35% and 70% RH.

Fluorescence-intensity changes in organic dyes impregnated in porous glass on exposure to NO2

Abstract To develop an NO2 sensor that can measure the NO2 concentration in the atmosphere, we studied changes in fluorescence intensities of dyes impregnated in porous glass when exposed to NO2 in N2 as the first step. The NO2 sensing materials were Squarylium dye 1, Squarylium dye 2, and Rhodamine B. We found that fluorescence quenching by NO2 occurred even in porous glass. The fluorescence quenching (F0/F) increased as the NO2 concentration increased in the range of 0.2–12.3 ppm, with an almost linear relationship. The minimum detectable concentration of NO2 was 0.2 ppm.

System for detecting environmental ppb-level nitrogen dioxide I

Abstract Coloration reactions have been found between nitrogen dioxide (NO 2 ) and organic compounds, such as aromatic amine derivatives, impregnated in porous glass. A single absorption peak in the visible region was detected after the reactions for all compounds. Linear relationships were obtained between environmental NO 2 concentrations and absorbance changes at peak wavelength for some compounds. A system is proposed for detecting low-levels of NO 2 using these coloration reaction in porous glass. Our designed system is composed of an organically-impregnated porous glass sensor and a simple absorbance meter having a single-wavelength light source. It was clarified that environmental ppb-levels of NO 2 could be detected using our system and that values for hourly average concentrations of NO 2 obtained by our system agreed well with those obtained using commercial analytical instruments. A coloration reaction mechanisms are also proposed based on the experimental results obtained.

Effect of TiO 2 crystal structure on CO 2 photoreduction using Au nanoparticles on TiO 2 catalyst

Two types of gold-supported TiO₂ catalysts (anatase and rutile) were prepared using a deposition precipitation method, and their photocatalytic activity towards CO₂ reduction was tested in the gas phase using H₂O as an electron donor and a xenon lamp as the energy sources. The crystal structures were verified using a scanning electron microscope (SEM) and the loaded Au nano-particles (NPs) had no effect on the surface structure. Fourier transform infrared spectroscopy (FTIR) was used to evaluate the photoreduction products. CO and CH₄ were the major products detected in the bare rutile and anatase TiO₂, respectively. It was observed that the deposition of Au NPs on the TiO₂ catalyst surface (anatase and rutile) quantitatively enhances the reduction of CO₂ to methane (major product). Relative CH₄ production efficiencies following 2-5 h of irradiation were 5.2 for Au/TiO₂ anatase, 5.0 for Au/TiO₂ rutile, 1.7 for TiO₂ anatase and 1.0 for TiO₂ rutile. The CH₄/CO production ratios following 2-5 h of irradiation were 18.7 for Au/TiO₂ anatase, 3.8 for Au/TiO₂ rutile, 6.0 for TiO₂ anatase and 1.1 for TiO₂ rutile. Based on these results, it can be inferred that CH₄ production was enhanced by Au loading independent of the crystal structure of TiO₂, and the CH₄ production ratio was dependent on the crystal structure of TiO₂.

Development of nitrogen monoxide sensing element using 2-Phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl impregnated porous glass

Nitrogen monoxide (NO) is an important bio-regulatory molecule, and high concentrations of NO are observed in the air exhaled by patients with asthma. Therefore, chemical sensors that can detect NO via a simple method are required. We focused on 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PTIO) as a detection reagent. PTIO oxidizes NO to form nitrogen dioxide (NO2) and is used in passive samplers to measure atmospheric nitrogen oxide (NOx) concentrations. We used a porous glass as a substrate and impregnated PTIO into the pores, and evaluated the performance of the sensor element. The sensor showed absorption peaks at 567, 343, and 238 nm. Although the sensor element was stable in a nitrogen atmosphere and in air, it was not stable for light. Moreover, we performed a NO exposure experiment of the sensor element in dark conditions. We observed that the absorbance decreased when the sensor element was exposed to NO gas and that there was a linear relationship between the NO exposure time and the absorbance changes observed at both the 567 and 343 nm absorption peaks. Our results suggest that the sensor element may play both high selectivity and high sensitivity measurement of NO.