Electrochemical wastewater treatment at nanostructured anodes. (2019)
Type of ContentElectronic Thesis or Dissertation
Thesis DisciplineChemical Engineering
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
AuthorsKariman, Asadollahshow all
Water pollution is one of the greatest challenges of the twenty-first century; therefore, there has been a high demand to find a suitable eco-friendly technology to treat wastewater. Advanced oxidation processes (AOPs) are an effective solution for treating various organic pollutants. Among AOPs, electrochemical oxidation is a promising way to treat a wide range of organic compounds with high chemical toxicity and non-biodegradability.
The main objectives of this thesis work were: 1) to understand the mechanism of electrochemical organic oxidation, 2) to investigate the possibility of anode properties improvement for the organic oxidation by addition of nanoparticles into the oxide layer of anode, 3) to study the effect of pulsed and constant electrolysis on the current efficiency of the organic oxidation using numerical simulation.
The IrO₂-Sb₂O₅-SnO₂/Ti anode was prepared via standard thermal decomposition method and 4-nitrophenol (4-NP) chosen as the model organic compound. It is confirmed that this anode does follow the “active” anode mechanism, with the rate of 4-NP oxidation being dependent on the coverage adsorbed oxygen on the surface of the anode. This surface coverage is estimated by fitting steady-state polarisation curves with a micro-kinetic model describing the oxygen evolution behaviour of the anode. The rate of oxidation is dependent on the surface coverage at relatively low overpotentials where mass transport limitation is avoided, and this rate is controlled by mass transport of 4-NP to the anode surface at high overpotential. It is also shown that the assumption in the literature that the rate of organic oxidation is much larger than the oxygen evolution reaction is not valid at all the times provided that mass transfer does not limit the process.
The incorporation of nanoparticles into a thermally prepared IrO₂ anode as a way of improving its service lifetime was investigated. The results show that incorporation of up to 25 wt% antinomy-doped tin oxide nanoparticles into the coating formed crack-free structure during the thermal decomposition process and thus enhanced the service lifetime of modified electrode dramatically by up to 10x compared to the pure IrO₂ anode. Importantly, these nanoparticle additions have minimal effect on the performance of the anode towards the oxygen evolution reaction. It is proposed that adding the right quantity of nanoparticles into the IrO₂ layer improved the anodes lifetime by minimising electrolyte penetration to the substrate while increasing the mechanical strength of the layer.
The incorporation effect of antimony-doped tin oxide (ATO) nanoparticles on DSA electrode and oxidation pathway of 4-NP was investigated. Due to high energy consumption of “non- active” anode such as BDD, combinition of anode material with high activity towards organic oxidation and low activity towards OER at low potentials is chosen. The result indicates that an increase in nanoparticles weight percentage leads to increase in the electrochemical active surface area (EASA), in which anode with 5 wt% ATO nanoparticles has the highest electrochemical active surface area. The complete oxidation of intermediate and products occurs at anodes with the incorporation of ATO nanoparticles, while partial oxidisation of 4- NP occurs at pure IrO₂ anode with high accumulation of 2-hydroxy-benzoquinone (HBQ).
The electrochemical oxidation of organic species using pulsed and constant potential electrolysis is investigated through numerical simulations on “non-active” anode. By comparing the pulsed potential organic oxidation with constant potential organic oxidation over a range of electrolysis, it can be concluded that the current efficiency of pulse potential organic oxidation is improved over a range of potentials compare to constant potential electrolysis. Both models validated by comparing the simulation against the experimental data recorded at the pulsed and constant potential at BDD electrode.