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Separation and Enrichment of Environmental Pollutants Using Nanometer Materials as Sorbents

Author: LiuGuoHong
Tutor: ZhangXinRong；ZhuYongFa
School: Tsinghua University
Course: Chemistry
Keywords: nanometer materials separation and enrichment chemiluminescence destructive adsorption environmental analysis
CLC: X506
Type: PhD thesis
Year: 2004
Downloads: 982
Quote: 3
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Abstract


Separation and enrichment of environmental pollutants using nanometer materials as sorbents were performed in this dissertation. The main research contents are listed as follows:1. A novel method, based on a phenomenon that chlorinated volatile organic compounds (CVOCs) were decomposed over nanometer TiO2 and their decomposed products were selectively enriched on nanometer TiO2, has been developed for determination of CVOCs using chemiluminescence (CL). The factors such as temperature and flow rate during enrichment, temperature and flow rate during desorption and concentrations of NaOH and luminol affecting CL intensities were studied. The calibration of CL emission intensity versus CCl4 concentration under the optimal conditions was linear in the range from 0.1 ppm to 380 ppm. The detection limit for CCl4 was 0.04 ppm (signal / noise was 3). The effect of determination of other CVOCs under the same conditions was investigated. The results showed that CL intensities increased with the order CH2Cl2 < CHCl3 < CCl4. This method could be potentially applied to the analysis of total chlorinated compounds in air, since this method provided the best of reactivity and surface effect of nanometer materials and offered high sensitivity of CL.2. The mechanism of the enrichment of CVOCs over nanometer TiO2 was investigated from the aspects including solid products, gas products and intermediate products by using CCl4 as a model compoud. The results showed that titanium oxychloride was formed during the reaction between CCl4 and TiO2 so that chlorine was enriched over TiO2. Cl2 was released from nanometer TiO2 due to the exchange of chlorine with oxygen in the carrier gas at relatively high temperature. Therefore, the method was applied to both the determination of chlorinated organic compounds and the destructive <WP=6>adsorption of them in air. TiO2 was regenerated through the exchange of chlorine with oxygen during desorption, therefore, the reactor packed with nanometer TiO2 had the reversibility, which could overcome the shortage of irreversibility of the reactors during destructive adsorption of chlorinated organic compounds as reported in the literatures.3. A trace enrichment method based on the application of multiwalled carbon nanotubes (MWNTs) as a solid-phase extraction (SPE) sorbent for chlorobenzenes was developed. The SPE conditions affecting extraction recoveries, including the sample volume, the kinds of eluents, the volume and the flow rate of eluent, were optimized. The adsorption characteristics were compared between MWNTs and current SPE sorbents including C18 silica and activated carbon. The results showed that the adsorption capacities of MWNTs, C18 bonded silica, activated carbon for 1,2-Dichlorobenzene at an equilibrium concentration of 90 μg/mL were 236.6, 188.8 and 150.2 mg/g, respectively. The results also showed that MWNTs had higher extraction recoveries for chlorobenzenes. This method would be applied to the determination of chlorobenzenes in natural and polluted waters.

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CLC: > Environmental science, safety science > Environmental pollution and its prevention > General issues > Control of environmental pollution and its exclusion
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