Research On Detection Technology Of Persistent Organic Pollutants Based On Terahertz Waves

Terahertz wave refers to electromagnetic waves propagating at frequencies between 300 GHz and 3THz. In wavelengths, this range corresponds to 0.1 mm to 1.0 mm. Terahertz wave has a bright future both in academic research and application because of its unique properties. At present, the application techniques of THz wave have been widely spreaded to imaging and spectrocopy. Based on existing fruits on spectrocopy, we did some experimental and theoretical work on POPs detection.Persistent Organic Pollutants (POPs) have attracted the extensive attention in recent years, as they could cause serious environmental pollution and long-term harm to the organism. Although some methords of POPS detections are already deployed, there are still limitations in the cost, quality and efficiency of testing. A practical and efficient integration of persistent organic detection technology is becoming more and more essential.Regarding to the situation above, in this paper, we are trying to carry out basic research on POPs detection with THZ wave. At the first attempt, the terahertz fingerprint spectroscopies of sulfur and chlorine compounds are analyzed with terahertz time domain spectroscopy technique and quantum chemistry theory, to explore the potential of terahertz fingerprint technique in the field of pure POPS detection. After that, the organic matter mixed with tobacco, trying to detect the sample in the mixture and trace the linear relationship between concentration and absorption coefficients with three different methods in a hierarchy way, to provide basic experiment data and prepare for futher investigation of qualitative and quantitative analyse.In this dissertation, the main tasks are:(1) We applied THz time domain spectroscopy technology to alpha-endosulfan and beta-endosulfan, that are two kinds of isomers of persistent organic endosulfan, acquired the time domain, frequency domain, absorption and refractive index spectrums in their effective range. The results showed that there are significant differences in their absorption spectrums. even between two isomers.(2) Regarding to POPS's unique characteristic, that they generally contain stable element chlorine, the chlorinated insecticide, fipronil's terahertz fingerprint is analyzed, including the diagram of the time domain, frequency domain, refractive index and absorption coefficients, outcoming also showed that the chlorine fipronil has its own unique fingerprints. The study provides an important experimental data for establishing the fingerprint spectrum of the persistent organic molecules in the THz range and in-depth analysis of organic molecules configuration and conformation.(3)We applied the terahertz spectroscopy technology to the mixture, which is the combination of persistent organic pesticides and tobacco, obtained and compared the terahertz absorption spectra of mixture with the pure substance, to detect whether it contains the substance, trying the qualitative analysis of low concentrations.(4)We ended up with quantitative analysis of solid mixture and liquid mixture, tracing the relationship between concentration and absorption coefficients mainly with two different methods:Partial Least Squares and LLE algorithma.The conclusion of the paper and the future study on persistent organic terahertz spectrum improvements are discussed.