Organic compounds for improving quantification of environmental trace elements and to study CO2 conversion via combination of analytical and electrochemical techniques

• Main Author: Budanovic, Maja
• Other Authors: Richard D. Webster
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Science::Chemistry::Organic chemistry
• Online Access: https://hdl.handle.net/10356/136762
• Institution: Nanyang Technological University

Air pollution has been recognized as the world’s leading environmental health risk and has risen in parallel with the atmospheric concentration of carbon dioxide and increasing anthropogenic emissions which include toxic heavy metals. Consequently, research pertaining to this area is highly relevant to broad societal aims of achieving environmental sustainability. In this study analytical and electrochemical approaches have been applied with the aim of providing new insights and techniques that will help better detect toxic heavy metals in the air and reduce societal reliance on CO2 emitting fossil fuels. The latter can be accomplished by manufacturing hydrocarbons from readily available carbon dioxide, whereas air quality can be more carefully monitored utilizing inductively coupled plasma - mass spectrometry (ICP-MS) analysis of highly toxic mercury (Hg) along with other pollutants. The current issue with using ICP-MS in Hg determination is the questionable accuracy and precision of the chemical analysis. Hence, an improved ICP-MS method for simultaneous analysis of Hg together with other trace metals has been developed. The method used addition of lithium tetrathiafulvalene carboxylate (LiCTTF) as a preservation additive and resulted in an enhanced stability of Hg in standard solution, improved ICP-MS measurements of air samples and sample preparation. The ability of LiCTTF to act as stabilizing agent has been assessed electrochemically. As a result, the complexation reaction between mercury and sulfur atoms in tetrathiafulvalene has been verified through potential shifts recorded with square-wave and cyclic voltammetry. The development of efficient and stable electrocatalysts that are highly product selective and can operate at minimal overpotentials to achieve high faradaic yields is important to produce economically viable systems. An electrochemical study reduced CO2 into methanol and determined influencing parameters using pyridine as well as nicotinic acid, nicotinamide, and riboflavin members of the vitamin B family to establish their catalytic abilities. Parameters found to influence CO2 reduction include impurities present in reagents, resin and blank electrolysis samples resulting in a positive bias. On the other hand, higher catalyst concentration and reaction temperature, increased electrode surface and pH as well as the use of a carefully designed electrolytical cell resulted in improved methanol yields. A gas chromatography – mass spectrometry method was efficiently developed for quantification of very low product levels that could be present as liquid phase after electrolysis, and that cannot be detected using nuclear magnetic resonance (NMR). In all cases, methanol was detected in limited yields and it is believed to be hindered by the hydrogen evolution reaction (HER), a major competing side reaction. Also, methanol losses have been detected through bubbling gas processes attributed to electrode surface and solution disruptions. Finally, a series of synthesized corannulene derivatives have been electrochemically characterized and have been shown to possess enhanced electron affinities that were applied for the purpose of CO2 trapping in organic solvents. In their reduced states they can undergo reactions with CO2 and could be further applied to produce useful chemicals.