| Summary: | 博士 === 國立中興大學 === 環境工程學系所 === 97 === Commercially available carbon nanotubes (CNTs) were employed as adsorbents to study the adsorption of isopropyl alcohol (IPA) vapor from air stream. Adsorption of IPA vapor onto CNTs increased with decreased outer diameter (dp) of CNTs. At influent IPA concentration of 200 ppmv, the maximum adsorbed capacity of IPA onto single-walled CNTs (SWCNTs, dp<2nm, 34.58 mg/g) was higher than that onto multiwalled CNTs (dp<10 nm, 27.48 mg/g). It was indicated that SWCNTs was optimal adsorbent in all tested CNTs.
Single-walled carbon nanotubes (SWCNTs) were oxidized by HCl, HNO3 and NaOCl solutions and were selected as adsorbents to study their characterizations and adsorption properties of IPA vapor from air streams. The physicochemical properties of SWCNTs were greatly changed after oxidation by HNO3 and NaOCl solutions. These modifications include the increase in surface functional groups, which enhance the chemisorption capacity of IPA, and the decrease in pore size and the increase in surface area of micropores, which improve the physisorption capacity of IPA. The maximum IPA adsorption capacities of SWCNTs, SWCNTs(HCl), SWCNTs(HNO3) and SWCNTs(NaOCl) calculated by Langmuir model are 63.48, 54.34, 72.99 and 103.56 mg/g, respectively.
The SWCNTs(NaOCl) show the best performance of IPA removal and their adsorption mechanism appears mainly attributable to physical force with a relatively low influent IPA concentration but appears attributable to both physical and chemical forces with a relatively high influent IPA concentration.
SWCNTs(NaOCl) was employed to study adsorption kinetics, thermodynamics and desorption of IPA vapor in an air stream. The adsorption capacity of IPA decreased with temperature indicating an exothermic nature of adsorption process and slightly decreased with relative humidity showing a hydrophobic nature of adsorbent surface. The adsorption mechanism appears mainly attributable to physical force in 5-25℃ but appears primarily attributable to chemical force in 25-35℃.
A comparative study on the cyclic IPA adsorption between SWCNTs(NaOCl) and activated carbon (GAC(NaOCl)) was also conducted and the results revealed that the SWCNTs(NaOCl) show better repeated availability of IPA adsorption during 15 cycles of operation than the GAC(NaOCl). In continusely temperature swing experiment, SWCNTs(NaOCl) shows the higher removal efficiency in adsorption regin and higher concentrated rate(Ceff/C0) in desorption regine.
This suggests that the SWCNTs(NaOCl) are efficient IPA adsorbents and can be used in the prolonged cyclic adsorption/desorption operation. It also revealed that SWCNTs(NaOCl) was also more suitable for application in VOCs emitted control, extraction, and chemical sensor.
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