Determination Of Harmful Vapors Utilizing Cataluminescence On Nanosized Materials Prepared In Supercritical Fluid

Cataluminescence (CTL) sensors based on nano-materials are of great potential and development value. It has advantages of no material loss, no need of light source, high sensitivity, fast analysis, wide linear range, simple equipment, and easy to realize automation. However, the CTL gas sensor suffers from the fact that few systems have been applied in practical use due to the insufficient sensitivity and selectivity. The sensitivity of the sensors is closely related to the catalytic activity of nanomaterials. Therefore, the paper is aim to 1) prepare higher catalytic activity nanomaterials with good dispersion, small particle size and high specific surface area by supercritical fluids (SCFs) technology; 2) improve the sensitivity and selectivity of the CTL gas sensor and expand its scope of application.In the paper, we prepared MgO and Y₂O₃ nanoparticles with high catalytic activity by supercritical fluid drying (SCFD) method, according to their higher sensitivity and excellent selectivity to detect specific organic harmful gases, a CTL sensor based on MgO-SCFD was developed for the detection of vinyl acetate vapor; By using carbon nanotubes (CNTs) as templates, SiO₂ nanotubes have been successfully synthesized in SCFs. As the CTL intensities of all the vapors on the surface of SiO₂ nanotubes were higher in comparison with that of SiO₂ nanoparticles, using the SiO₂ nanotubes as sensing material, a new CTL sensor for ethyl acetate vapor has been developed. The results included as follows:1. The CTL gas sensor of vinyl acetate based on MgO nanoparticles has been studied. In this section, we prepared MgO and Y₂O₃ nanoparticles by SCFD methodin comparison with MgO and Y₂O₃ nanoparticles prepared by common drying method (CD), and it was found that the CTL intensities of some harmful gases on MgO-SCFD and Y₂O₃-SCFD nanoparticles were much higher than that of MgO-CD and Y₂O₃-CD. A cataluminescence (CTL) sensor using MgO-SCFD as the sensing material was developed for the detection of vinyl acetate vapor. The proposed sensor showed high sensitivity and selectivity to vinyl acetate at optimized conditions. The linear range of CTL intensity versus concentrations of vinyl acetate vapor was 1.8mg/m3～1800mg/m3, with detection limits of 0.7 mg/m3 . None or only very low levels of significant interference were observed while the foreign substances such as acetone, acetaldehyde, ethyl acetate, acetic acid, formaldehyde, ammonia, ethanol, benzene and methanol were passing through the sensor. This method allows rapid determination of vinyl acetate in air at workshop.2. The CTL gas sensor of ethyl acetate based on SiO₂ nanotubes has been studied. In this section, two morphologies of SiO₂ nanomaterials (SiO₂ nanotubes and nanoparticles) have been successfully synthesized in SCFs. The CTL features of the two SiO₂ nanomaterials to some common harmful gases were compared, and the results showed that SiO₂ nanotubes have better CTL sensing characteristic to some common harmful gases. The SiO₂ nanotubes not only have uniform size and shape with a high specific surface area, but also exhibit superior sensitivity and selectivity to ethyl acetate vapor. Using the SiO₂ nanotubes as sensing material, a CTL sensor for ethyl acetate vapor was developed. The proposed sensor showed high sensitivity and specificity to ethyl acetate at optimized conditions. With detection limits of 0.85 ppm, the linear range of CTL intensity versus concentrations of ethyl acetate vapor was 2.0 to 2000 ppm. None or only very low levels of interference were observed while the foreign substances such as acetone, acetaldehyde, acetic acid, formaldehyde, ammonia, ethanol, benzene and methanol were passing through the sensor. This method allows rapid determination of ethyl acetate in air at workshop.