Application, exploration, and improvement of electrochemical processes for the degradation of selected contaminants in water
Date
2022
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
The field of environmental engineering stands out as one of the few disciplines that is defined by its goals as opposed to being defined by its means. One of the advantages of being a goal-oriented discipline is that the use of different techniques is not only allowed but encouraged when treating environmental problems. For instance, while the fields of physics, chemistry and biology can tackle different environmental issues directly, many solutions to specific challenges can arise from multiple disciplines simultaneously. Among the problem-solving tools that environmental engineers utilize, electrochemistry shows great promise. Through the study of this discipline, it is possible to expand the pathways for contaminant remediation by driving specific reactions with the use of long-lasting catalysts and energy from renewable sources during low consumption hours. ☐ The present study expands on the contaminant remediation field through electrochemical methods by exploring the technique in two different directions. Firstly, both collaborative sides of an electrochemical reaction were studied; oxidation was demonstrated through the degradation of hydrogen peroxide to oxygen gas and protons, while reduction was employed to transform nitrate to nitrogen gas and water. Secondly, a new application of electrochemical methods was demonstrated through the recovery of sulfuric acid from its mixture with hydrogen peroxide, called piranha solution. Thirdly, process improvement was explored by the further modification of the initial electrode used for piranha solution recycling as well as the study of factors affecting the reduction of nitrate using a Cu:Pd metallic catalyst alloy as the cathode. ☐ The oxidation of H2O2 was first demonstrated by the use of a ruthenium dioxide anode on a titanium substrate that obtained its full decomposition after 5 hours at 0.32A/cm2. The electrode was later improved by the addition of iridium dioxide catalyst, achieving a further increase from 17.5% to 35% in H2O2 degradation efficiency. Results in the first two chapters show the utilization potential of electrochemical methods from a chemical, environmental and economic perspective. On the reduction front, a Cu75Pd25 cathode was shown to be the most efficient electrode for the selective reduction of nitrate to inert nitrogen gas. Further improvements driven by pH, electrode catalyst loading, and initial nitrate concentration were also explored with an accomplished product selectivity of 84%. In addition, a heating process, combined with a cooling speed exploration on the catalytic effects of the electrode, showed that 12 hours of heat application at 200oC along with rapid cooling by quenching on an electrode with low catalyst loading obtained the highest improvement in nitrogen gas selectivity with a 12% increase. Finally, the improvements were enhanced through the use of multiple quenching cycles to a nitrogen gas selectivity increase of an additional 8%. Such improvements were partially attributed to a new micro sheet crystalline structure of the alloy. ☐ This dissertation demonstrates the potential applicability of electrochemistry in existing environmental problems, allowing for new, more economical contaminant remediation pathways as demonstrated in the recovery of sulfuric acid from piranha solution. In addition, an improved method for nitrate degradation to nitrogen gas is demonstrated as well as the influence of heating temperatures and cooling speed on electrode catalytic activity.
Description
Keywords
Catalysis, Electrochemistry, Contaminant remediation, Nitrate degradation, Piranha solution, Electrochemical reaction, Water contamination