In our paper we propose to use the liquid crystal host doped by nanoscale magnetite dopants for detecting toxic influence of carbon monoxide. We use the cholesteric liquid crystal material host doped by nanoscale magnetite dopants as material for primary transducer of optical sensor of carbon monoxide.

Gas sensors by using of optical methods have as usually, straightforward design and possess higher sensitivity, selectivity and stability than non-optical methods with much longer lifetime. Spectroscopy is mostly used as one of the gas sensing optical methods. There are several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy.

Toxic effect of carbon monoxide causes severe poisoning. This toxic effect is deadly dangerous to human life and health. The carbon monoxide detection is complicated, because this gas has no odor or color and does not absorb well known sorbents (eg. conventional masks). It is impossible to sense this gas in the environment without special means. At the breathing this highly toxic gas gets into the blood and binds to hemoglobin in 200–500 times faster than oxygen.

Liquid crystals are perspective materials for the detection of hazardous gases, due to high sensitivity to change of their molecular ordering under the external influence. Such changes can be easily detected optically, because liquid crystals possess large optical anisotropy.

The magnetite sensitivity to carbon monoxide was used to design high selectivity gas sensor. Such high sensitivity is explained by the presence of iron atoms in the oxidation state +2 and +3, as in case of the hemoglobin molecule. The principle of sensor operation is based on determination of changes in the selective reflection spectrum of the cholesteric liquid crystal doped by nanoscale magnetite dopants, and all registration is done in the visible region of the spectrum. The concentration of carbon monoxide in air is proportional to the minimum amount of shifted of the minimum of selective reflection wavelength of the cholesteric liquid crystal doped nanoscale magnetite. At the carbon monoxide influence on cholesteric liquid crystal doped by nanoscale magnetite, the shift of the minimum selective reflection wavelength toward higher wavelengths occurs.

Spectral studies of cholesteric liquid crystal doped with magnetite nanoparticles are carried out in 200–900 nm wavelength range, at 293–326 K temperature range and with carbon monoxide concentrations from 0 to 50 mg/m3. When carbon monoxide concentration is increased, the significant changes in position of transmittance minimum wavelength are observed. With the aim to increase the efficiency of the carbon monoxide sensor operation we propose to the use the nanoscale magnetite with higher oxidation state, +3 (Fe3O4).

These changes can be explained by the interaction between magnetite nanoparticles and carbon monoxide molecules. At the same time, the shape and symmetry of nanoparticles can affect on their electronic properties and corresponding on the mechanism of interaction with carbon monoxide. It can be assumed that the CO molecules, competing with the liquid crystal molecules by adsorption on the surface of magnetite nanoparticles, can form relatively stable coordination bonds with the surface of magnetite as well as with functional groups of the LC. This leads to violation of ordering cholesteric crystal, leading to change in the transmission spectrum of the composite LC – magnetite more noticeable the higher the concentration of CO is.

Ключові слова: carbon monoxide, liquid crystal, nanoscale dopants, optical sensor

Повний текст: PDF (Ukr)