Tohru Tanaka

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.