Doctoral Dissertations

Date of Award

12-2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Sandeep Agnihotri

Committee Members

Chris Cox, Terry L. Miller, David J. Keffer

Abstract

The adsorption of water in nanoporous materials becomes an important issue in the environmental fate and applications when one considers the practical use of these materials as adsorbents for hazardous organic compounds in the diverse environments.

In this study, the complexity of water-SWNTs interaction was investigated by morphological and chemical characterization techniques, by gravimetric adsorption measurement and by interpretation of experimental adsorption isotherms by fitting to several existing semi-empirical water adsorption models. Commercially available SWNTs samples were measured for chemical and physical characterization such as O% by x-ray photoelectron spectroscopy, ID/IG by Raman spectroscopy and surface and porosity by nitrogen adsorption at 77 K. Water adsorption isotherms and kinetics on SWNTs were performed by custom-built gravimetric measurement (detection limit = 0.1 μg).

Water adsorption isotherms data obtained gravimetrically from T= 5, 20, 35 ºC were consequently fitted to several semi-empirical models that were developed to interpret adsorption isotherms of water in common carbonaceous adsorbents. The applicability of these models was evaluated by high correlation coefficients and the significance of temperature sensitive water-specific sample properties such as the degree of primary sites, sizes of water clusters aggregating on primary sites and filling micropore and equilibrium constants. Those fitting parameters were evaluated by comparison to the results obtained from characterization type experiments. Conclusively, the Do & Do equation, as modified by Marban et al., is the most suitable semi-empirical equation for v predicting from experimental isotherms alone the size of molecular clusters that facilitate adsorption in SWNTs. This model can deconvoluted the experimental isotherms into two pseudo-isotherms: adsorption onto hydrophilic groups and filling of micropores, and quantifying the concentration of hydrophilic functional groups, as well as determining the micropore volume explored by water. Isosteric heat of water adsorption calculated from experimental isotherms and that for pseudo-isotherms; functional groups and micropore isotherms, on SWNTs was similar to those available in the current literature reportedly estimated by calorimetric or molecular simulation technique. This research approach may be useful in interpreting experimental water adsorption to aide purely theoretical methods of studying the behavior of water as well as to better understand the environmental fate of carbon materials.

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