Activating Oxygen and Degrading the Water Treatment Industry’s Most Challenging Micropollutant with TAML Activators and Oxidants
Creators: name: Tang, Liang
Publisher: name: Carnegie Mellon University
Year: 2016
Subjects: subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences

description: The immense industrial development and large population of our time demands the development of innovative, cost-effective, and universal water treatment processes to remove anthropogenic contaminants and pathogens and provide sufficient clean potable water. TAML activators are a family of green oxidation catalysts that deliver superior catalysis for the oxidation of hazardous environmental pollutants at environmentally relevant concentrations. This is translating into advanced water treatment processes that are more effective than existing processes. In this thesis, TAML catalysis has been studied in the decomposition of the extremely persistent micropollutant, metaldehyde, under laboratory conditions to guide development of a better real world option. TAML/H<sub>2</sub>O<sub>2</sub> slowly degrades metaldehyde to acetaldehyde and acetic acid via a process that was monitored by nuclear magnetic resonance spectroscopy (1H NMR). Further study found that substituting NaClO forH<sub>2</sub>O<sub>2 </sub>in the TAML system increased the turnover number of one 0.4 μM aliquot of catalyst to 106 from 32 under laboratory conditions in pH 7 (0.01 M phosphate, D<sub>2</sub>O) at 25 °C. This showed that oxidant substitution results in a ~3-fold higher catalyst efficiency without altering the reaction rate, identifying oxidant choice as a significant design tool for TAML processes. The observation of metaldehyde decomposition under mild conditions provides a further indication that TAML catalysis holds immense promise for advancing water treatment to add to the conclusions of Brunel University UK collaborative studies on London wastewater. A detailed kinetic study of catalyst activation is presented delivering advanced understanding of the catalyst activation process which is rate determining in most TAML applications. Finally, the potential applications of TAML catalysis are extended through a study of the reactivity of less reactive TAML/O2 systems in reverse micelles of Aerosol OT (AOT) in n-octane. n-Octane serves as a proximate reservoir supplying O2 to result in partial oxidation of FeIII- to FeIVcontaining species, mostly the FeIIIFeIV (major) and FeIVFeIV (minor) dimers which coexist with the FeIII-TAML monomeric species. The speciation depends on the pH and the degree of hydration w0, viz. the amount of water in the reverse micelles. Reactive electron donors such as NADH, Pinacyanol chloride (PNC) and hydroquinone undergo the TAMLcatalyzed oxidation by O<sub>2</sub>. Kinetic evidence is presented for the existence of unusual second-order catalytic pathways in the oxidation of NADH to NAD+ and in the bleaching of PNC. Depending on the substrate and reaction conditions, a second-order pathway in catalyst either dominates or proceeds in obvious combination with a first-order pathway in catalyst. Despite the limitation of low reactivity, the new systems highlight an encouraging step in replacing TAML peroxidase-like chemistry with more attractive dioxygenactivation chemistry.