| Metal salts have a variety of different hydrates,which are also a form of heavy metal presence.Heavy metal salt hydrates containing different crystalline waters affect to some extent the stability of drugs or the effectiveness of chemical processes.Therefore,in order to effectively identify metal hydrates,this paper is the first to make use of terahertz spectroscopy to effectively characterise different hydrates of transition metal sulphates with the help of metal salt hydrates exhibiting different absorption properties in the terahertz band.Based on terahertz time-domain spectroscopy as a detection tool,this thesis investigates the pre-treatment of test samples and characterises a variety of metal salt hydrates and their pyrolysis products.The main contents of the thesis are as follows.In Chapter 1,the background and significance of the research on terahertz wave techniques and terahertz time-domain spectroscopy are described in detail.The progress of domestic and international research in the characterisation of heavy metals,such as traditional spectroscopy and new detection techniques,is described in an overview.The challenges and difficulties of traditional material detection techniques at the present stage are clearly pointed out,and the necessity and urgency of developing a simple and rapid characterisation method based on the terahertz time-domain spectroscopy technique are described.In Chapter 2,the method of acquiring terahertz characteristic parameters of metal salt hydrates is described in detail.Detailed performance parameters of the terahertz systems used are given,the challenges and difficulties at this stage of terahertz time-domain spectroscopy detection technology are pointed out,and corresponding solutions are given.The principles and processes of terahertz signal processing methods are discussed in detail,i.e.the conversion of time domain signals into important information such as frequency spectrum,refractive index and absorption spectra,which can then be applied as analytical tools for the characterisation of metal salt hydrates.In Chapter 3,terahertz spectroscopy is applied to the characterisation of magnesium sulphate and its hydrates.An overview of the properties,applications and chemistry of magnesium sulphate hydrate is given;the sample pre-treatment methods are investigated,analysed and optimised for problems arising from the preparation of samples;and characteristic terahertz spectra of magnesium sulphate hydrate and its pyrolysis products are collected.In Chapter 4,terahertz spectroscopy is applied to characterise zinc sulphate and its hydrate.An overview of the properties,applications and chemistry of zinc sulphate hydrate is given;the characteristic terahertz spectra of zinc sulphate hydrate and its pyrolysis products are acquired using the sample pre-treatment method summarised in the previous chapter.In Chapter 5,terahertz spectroscopy is used to investigate whether characteristic absorption spectra exist for all the major forms of heavy metals present in nature.The terahertz absorption spectra of various heavy metals and their compounds were collected by adjusting and optimising the sample pre-treatment methods for different heavy metals and their compounds to provide a reference for further studies on the absorption properties of heavy metals in the terahertz band.The paper focuses on the characterisation of magnesium sulphate,zinc sulphate and their hydrates using a terahertz time-domain spectroscopy system.By drying the samples at constant temperature after a simple and rapid pretreatment,different pyrolysis products were obtained and their terahertz absorption spectra were investigated,and the experimental results showed that the different hydrates exhibited significantly different terahertz absorption properties.This provides an important reference for a variety of applications and detection tools for metal salt hydrates,as well as a simple,fast and effective characterisation tool for the detection of transition metal sulphates and their hydrates. |
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