NMR studies of gas and water adsorption in carbon based materials Public Deposited

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  • March 21, 2019
  • Mao, Shenghua
    • Affiliation: College of Arts and Sciences, Department of Applied Physical Sciences, Materials Science Graduate Program
  • In this dissertation, we used 1H NMR to study the gas and water adsorption in carbon based materials. The NMR studies indicated that at room temperature, the interior of cap-opened Single Wall Nanotubes (SWNTs) becomes available for methane and ethane adsorption. The endohedral adsorption is the dominant mechanism when pressure is lower than 1Mpa. The adsorptions follow Langmuir adsorption isotherm with related adsorption energy of 22.7 KJ/mol for methane and 29.2 KJ/mol for ethane. The average exchange time between molecules adsorbed inside SWNTs and free gas molecules outside is on the order of 80ms. It is shown that exposure to oxygen has no effect on methane and ethane endohedral adsorption, which suggests smaller adsorption energy of oxygen compared to that of methane and ethane. In the study of the water adsorption in SWNTs at room temperature, the adsorption isotherm from 1H NMR spectrum indicated clear hysteresis loop. Quantitative analysis gave the adsorption amount of 3 mmol/g in SWNTs at saturated vapor, which was considerably lower compared to 14 mmol/g of bulk liquid water. Combined with T2 analysis, we believed that the state of adsorped water in SWNTs is in between vapor and bulk liquid. The primary adsorption sites are associated with tube ends and defects, which have strong effects on water adsorption. The study of adsorption of hydrogen in Boron doped graphite and Boron doped SWNTs proved considerable increment of adsorption energy at moderately high pressure and room temperature, which may lead to a new method for improving hydrogen storage at room temperature.
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  • Wu, Yue
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  • University of North Carolina at Chapel Hill
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