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Purification Of Multi-Walled Carbon Nanotubes And Its Applications As A Sorbent In Environmental Analytical Chemistry

Posted on:2004-02-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q L LiFull Text:PDF
GTID:1101360122966850Subject:Environmental Science
Abstract/Summary:PDF Full Text Request
Since their discovery in 1991, carbon nanotubes (CNTs) have attracted great attention because of their unique properties. Nowadays, large-scale preparation of CNTs has been realized, the application of CNTs is getting more and more urgent. CNTs could be an excellent adsorbent due to their porous and graphitic structure. However, polar groups on the surface of CNTs, formed during the purification with oxidant, will result in irreversible adsorption of various compounds while CNTs are used as sorbent. Purification with reducing reagent may avoid the forming of polar groups on the surface of CNTs. It is well known that many sorbents have been widely applied in chromatographic separation and in the preconcentration of trace organic analytes in environmental samples. Tremendous effort has been made in recent years for seeking new sorbents. Therefore, the study of CNTs as a sorbent in the use of environmental analysis may bring a way out. The thesis focuses on the studies of properties and applications of CNTs. The work is summarized as follows:1. Purification of multi-walled carbon nanotubes (MWCNTs)MWCNTs, prepared by decomposition of methane with Ni-Mg-0 as the catalyst, were purified sequentially with hydrogen gas under high temperature (900 ℃) and hydrochloric acid (5 mol/L) reflux. The variations of surface area, water-absorbing capacity, amount of Ni and Mg residuals of the MWCNTs in different purification steps were investigated. The desorbing ratios of benzene, n-hexane, ethanol and acetone on the columns packed with MWCNTs in different purification steps were also investigated. The morphologies of MWCNTs in different purification steps were studied with TEM. The results suggested that the treatment of hydrogen could remove the amorphous carbon and the polar groups on MWCNTs, resulting in the decrease of surface area and water absorbing capacity and having the ends of MWCNTs cut. The water-adsorbing capacity of the purified MWCNTs (PMWCNTs) was much lower than that of activated carbon, and slightly higher than that of Carbopack B. The desorption ratios of benzene, n-hexane, ethanol, acetone on the column packed with PMWCNTs were the same as those of Carbopack B. The amounts of Ni and Mg remained on the PMWCNTs were 30 ug/g and not detected (<10 ug/g), respectively.2. Evaluation of PMWCNTs as the gas chromatographic packing materialThe PMWCNTs, graphitized carbon black (Carbopack B), activated carbon, PMWCNTs and Carbopack B modified with 5% (w/w) Carbowax 20M were used as gas chromatographic packing materials. Their characteristics for separation of some organic compounds were compared. The results showed that PMWCNTs is anexcellent packing material. Comparing to Carbopack B with the same surface area, PMWCNTs have the following characteristics: having stronger retention ability, suitable for the separation of compounds with relatively low boiling points, showing symmetric peaks for polar compounds due to its more homogeneous surface, having lower theoretical plate number. Like Carbopack B, PMWCNTs modified with 5%(w/w) Carbowax 20M can be used to separate polar compounds.3. Evaluation of PMWCNTs as a sorbent in trapping volatile organic compounds (VOCs) from environmental samplesThe evaluation was performed in terms of breakthrough volume (BTV) and recoveries of representative VOCs. Due to their hollow cavities inside, PMWCNTs were found to have much higher BTV than Carbopack B, and trap more volatile compounds. The recoveries of the tested compounds trapped with PMWCNTs were between 80%~110%, and not affected by humidity. PMWCNTs can be used as a sorbent not only in trapping VOCs from air but also in a purge-and-trap system to preconcentrate VOCs from water samples.4. Evaluation of PMWCNTs as a sorbent in solid phase extraction (SPE) to preconcentrate organophosphorous pesticides (OPPs) from water samplesOff-line SPE coupled with GC-PFPD was applied in this study. 50mg PMWCNTs were packed in an SPE cartridge for the extraction of 8 OPPs in water samples. BTVs an...
Keywords/Search Tags:carbon nanotubes, purification, sorbent, environmental sample analysis
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