The Library
New approaches for the study of the kinetics of reactions at immiscible liquid/liquid and air/liquid interfaces
Tools
Slevin, Christopher John (1999) New approaches for the study of the kinetics of reactions at immiscible liquid/liquid and air/liquid interfaces. PhD thesis, University of Warwick.
|
Text
WRAP_thesis_Slevin_1999.pdf - Submitted Version Download (26Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b1370627~S1
Abstract
This thesis describes the development of new techniques and new approaches
for studying the kinetics and mechanisms of reactions which occur at the interface
between two immiscible liquids. New approaches for studying the kinetics of
transfer processes at the air/water interface are also described.
Scanning electrochemical microscopy (SECM) is employed in the
equilibrium perturbation (BP) mode for studying reversible transfer processes at
liquid/liquid and air/water interfaces. In this application, an ultramicroelectrode
(UME) located in an aqueous phase, at micro metre distances from the interface of
interest, is employed to drive a transfer process, initially at equilibrium, in the
direction of the aqueous phase by depleting the local aqueous concentration of a
target species by electrolysis. The UME current flow depends on the transfer
kinetics at the interface. The development of a submarine UME allows SECM to be
conducted at the air/water interface, or at a liquid/liquid interface with the electrode
in the more dense phase. The kinetics of the extraction/stripping reactions of
aqueous copper (II) with an oxime ligand (Acorga PSO) in 1,2-dichloroethane (DCE)
and heptane are first investigated. Subsequently, measurements of the kinetics of
oxygen transfer across a condensed monolayer of l-octadecanol, as a function of
surface area, demonstrate that the accessible free area of the interface primarily
governs the rate of oxygen transfer.
SECM double potential step chronoamperometry is developed to study
irreversible transfer processes at interfaces. Theoretical modelling is applied and
tested through experimental measurements on model interfaces. Subsequently, the
rate of transfer of bromine from aqueous solutions to DCE and to air is shown to be
above the upper limit measurable by the technique, however, a lower limit on the
first order transfer rate constant ofO.S cm S-l is assigned.
A new technique, termed microelectrochemical measurements at expanding
droplets (MEMED) is developed for studying spontaneous reactions at liquid/liquid
interfaces. In MEMED, the two liquids are contacted by flowing one (feeder)
through a capillary submerged in the second (receptor), resulting in the growth of
drops at the capillary tip. The interfacial reaction generates a product or reactant
concentration profile, which extends into the receptor phase. This is probed directly
using a UME positioned opposite the capillary in the solution, operated in either a
potentiometric or an amperometric mode, as a local concentration probe. A
numerical model for mass transport in this configuration is developed, and the
technique and model are assessed by measuring both bromine transfer from aqueous
sulfuric acid solutions to drops of DCE, and bimolecular electron transfer between
iridium (IV) chloride in the aqueous solution and ferrocene in the organic phase,
which exhibit transport-controlled transfer rates under the conditions employed. The
MEMED technique is applied to measure the kinetics of the hydrolysis of
triphenylmethyl chloride (TPMCl), at the DCE/water interface, through
potentiometric measurement of the chloride ion concentration profile. The reaction
is shown to be first-order in TPMCI, occurring interfacially, with a rate constant of
6.5 x 10-5 cm s". Subsequently, the oxidation of methylanisole (MA) (feeder) by
aqueous solutions of cerium (IV) (Ce(IV» (receptor), is probed. Under the
conditions of this study, the reaction at the interface dominates, with a negligible
contribution from the aqueous phase reaction between dissolved MA and Ce(IV).
Item Type: | Thesis (PhD) |
---|---|
Subjects: | Q Science > QD Chemistry |
Library of Congress Subject Headings (LCSH): | Chemical kinetics, Scanning electrochemical microscopy, Ultramicroelectrodes, Liquids |
Official Date: | March 1999 |
Institution: | University of Warwick |
Theses Department: | Department of Chemistry |
Thesis Type: | PhD |
Publication Status: | Unpublished |
Supervisor(s)/Advisor: | Unwin, Patrick R. ; Macpherson, Julie ; Atherton, John ; Umbers, John |
Sponsors: | Engineering and Physical Sciences Research Council ; Zeneca Group PLC |
Extent: | [xiv], 298 leaves |
Language: | eng |
Request changes or add full text files to a record
Repository staff actions (login required)
View Item |
Downloads
Downloads per month over past year