Properties and Mechanisms of Volatile Organic Vapors Adsorption on Multiple Wall Carbon Nanotubes

• Main Authors: Mei-syue Li, 李美雪
• Other Authors: 施養信
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/09311508145669742562

碩士 === 國立中興大學 === 土壤環境科學系所 === 94 === Abstract Two multiwall carbon nanotubes (MWNTs), CNT1 and CNT2, with the nanostructures and the uniform properties that may provide novel and excellent absorption properties of gases were studied. A diverse volatile organic compounds (VOCs) was used as chemical probes to investigate the adsorption mechanisms of MWNTs at room temperature (303K). The adsorption experiments of a variety of VOCs on MWNTs under various relative humidity were performed to get better understanding of the effect of humidity on sorption processes. The photographs of SEM (scanning electron microscopy) and TEM (transmission electron microscopy) showed that both MWNTs were aggregated and had no metal catalysts on the surface. The spectroscopic analysis of these two MWNTs mostly indicated they were similar. CNT2 had a little more diamond-like carbon than CNT1 examined with Raman spectra. 13C NMR (13C nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy) measurements detected CNT1 having a tiny more C=C than CNT2. However, the amorphous carbon on the exterior layers of CNT2 was observed by electron microscopies. The adsorption coefficients of VOCs on CNT2 were larger than those on CNT1. It may result from that the impurity of MWNTs provided more sorption capacity to organic chemicals. Under two different humid conditions (55 % and 90 %), adsorption equilibrium coefficients of VOCs on the MWNTs decreased with the increasing of water content. Some adsorption sites for VOCs previously on the MWNTs were occupied by water molecules under humid conditions. The adsorption equilibrium coefficients of trichloroethylene, benzene, n-hexane, and acetone decreased with increasing temperature between 303 K and 363 K. It is an exothermic process. The adsorption heats (ΔH) of trichloroethylene, benzene, and n-hexane on the MWNTs were smaller than 40 kJ/mol. Consequently, the VOCs molecules performed physicosorption on the MWNTs surface. Adsorption equilibrium coefficients of n-alkanes and alcohols on the MWNTs became larger with more carbon atoms on the molecular structures of n-alkane and alcohol and larger with more chloro atoms on the chlorinated compounds. Several LSER (linear solvation energy relationship) equations were obtained by the regression of the sorption coefficients of VOCs on MWNTs. The analysis of the interactions based on these LSERs indicated that the London dispersion force was the major adsorption interaction in the adsorption process on MWNTs. LSERs of MWNTs at high and ambient relative humid were large different at abilities of hydrogen bond donor and acceptor. The ability of hydrogen bond donor was decreased with humidities but the ability of hydrogen bond acceptor was increased with humidity. Several LSERs equations were developed to facilitate the prediction of different organic chemicals on MWNTs which could be potential adsorbents for organic traps, chemical sensors, and gas treatment.