Date of Award

2013

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Chemistry and Biochemistry

Keywords

Pure sciences, Bromate, Hydroquinone sensors, Chemical oscillatots, Palladium nanoparticle synthesis, Pattern formation

Supervisor

Jichang Wang

Supervisor

Todd Loughead

Rights

info:eu-repo/semantics/openAccess

Abstract

Autocatalytic reactions are a kind of fascinating reactions in nonlinear chemical and biochemical systems because of their unique features. The auto-catalyst can multiply itself leading to the spontaneous generation of order. Coupled autocatalytic reactions, providing a positive/negative feedback to control the multiplication of the auto-catalyst, can give rise to extraordinary complex behavior such as sequential oscillations. A new bromate-based oscillator was successfully designed that employs metol as its organic substrate. Complex reaction behaviors were observed when the system was subjected to bromine removal and oxygen exposure. Transitions from simple to sequential oscillations took place as a function of the age of the metol stock solution, in which an important intermediate is 1,4-hydroquinone and the main final products are 1,4-benzoquinone and bromobenzoquinones. Various analytical techniques were applied such as TOF-MS, GC/MS, NMR, UV, etc. Since bromobenzoquinones are parts of the major products in metol-bromate-ferroin system, a new type of minimal bromate oscillator is found based on the bromination of 1,4-benzoquinone. The oscillator contains a reagent benzoquinone, which does not react with metal catalyst ferroin/ferriin, but modulates the evolution of bromide ions through the reaction between 1,4-benzoquinone and bromine. It could exhibit spontaneous oscillations in a closed reactor. Due to the role of the organic substrate is only the bromine removal, we define this system as a batch minimal bromate oscillator. We further investigated the photochemical behavior of the minimal bromate oscillator, in which the reduction of ferriin/Cerium (IV) was dominated by bromide ions rather than by organic substrates as known in most of bromate oscillators. The chemical oscillations exhibited ultrasensitive response to illumination, and the influence of light evolved from constructive to inhibitory. In order to determine the dynamic of organic intermediates, such as 1,4-hydroquinone, which is involved in metol-bromate-ferroin and 1,4-cyclohexanedione (CHD)-bromate-metal catalyst systems, a new type of modified carbon electrode was developed to simultaneously determine 1,4-hydroquinone and pyrocatechol with differential pulse voltammetry. By applying it into the test of dynamics of 1,4-hydroquinone in the CHD-bromate uncatalyzed system, we successfully monitored the concentration change of 1,4-hydroquinone during the oscillations.

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