Ion Interactions with Carbon Nanomaterial Surfaces in Aqueous and Non-aqueous Solutions

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In this thesis we investigated ion interactions with the surfaces of carbon nanomaterials (CNM) dispersed in different aqueous and non-aqueous solvents: aqueous dispersions, N-methyl-2-pyrrolidone dispersions, organic salt/acetonitrile dispersions and room temperature ionic liquids/acetonitrile dispersions. We used molecular dynamics simulations to understand the molecular-scale mechanisms of ion interactions with the CNM surfaces. We considered carbon nanotube and carbon "nano-onion" structures as representatives of the CNMs. Despite the high diversity of the system compositions studied in the thesis, the main features of ion interactions with CNM surfaces can be rationalized by similar mechanisms:

1) Interaction of ions with the CNM surface in dispersions are determined by the interplay of the particle-particle interactions: ion-solvent, CNM-solvent, solvent-solvent and ion-CNM interactions.

2) To make direct contacts with the carbon nanomaterial surface, ions have to become partially desolvated. The partial desolvation might be, however, energetically favorable or unfavorable depending on the strength of ion-solvent interactions. In this thesis we show that there is a strong negative correlation between the strength of ion solvation and the probability of a direct CNM-ion contact: the interfacial region becomes increasingly populated by weakly solvated ions.

3) The penalty for the partial desolvation of CNM surface adds an additional energetic "barrier" for ions to come close to the CNM surface. This can be low (like in the case of aqueous dispersions) and thus will not prevent ions to come to the surface, or it can be high (like in the case of N-methyl-2-pyrrolidone dispersions) and, thus, will prevent ions to come to the CNM surface.

In this thesis we compare the structure of the electric double layer at a CNM electrode for a neat ionic liquid (EMIm-TFSI) and its mixture with an organic solvent (acetonitrile). Mixing room temperature ionic liquids with acetonitrile decreases the ion-counterion correlations in the electric double layer. In this work we showed that one can use salt addition to alter the stability of the CNMs dispersions. Such, we predicted the "salting out" of carbon nanotubes from their stable dispersions in N-methyl-2-pyrrolidone. This effect leads to an efficient safe and inexpensive method of regulating the carbon nanotube concentration in non-aqueous dispersions.
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Dokumententyp:
Wissenschaftliche Abschlussarbeiten » Dissertation
Fakultät / Institut:
Fakultät für Chemie
iTunes U Categories:
Science » Chemistry
Dewey Dezimal-Klassifikation:
500 Naturwissenschaften und Mathematik » 540 Chemie » 540 Chemie und zugeordnete Wissenschaften
Keywords:
carbon nanomaterials, ions, dispersions, ionic liquids, solutions, computer simulation
Contributors:
Dr. Fedorov, Maxim [Reviewer]
Prof. Dr. Spohr, Eckhard [Reviewer]
Language:
Englisch
Collection / Status:
Dissertations / Document published
Date of doctoral thesis submission:
22.06.2011
Document created on:
20.10.2011
Files changed on:
20.10.2011
Date of doctoral degree:
20.09.2011
Medientyp:
Text