Electroflotation and electrooxidation are the two attractive processes in wastewater treatment. However, the lack of ideal electrodes has long been a problem. This dissertation reports two types of high-performance electrodes, Ti/lrO₂-Sb₂O₅-SnO₂ and Ti/B-doped diamond (Ti/BDD), for electroflotation and electrooxidation, respectively. _{2 2 5 2 2 2 2 5 2 2 2 2 5 2}...[ Read more ]

Electroflotation and electrooxidation are the two attractive processes in wastewater treatment. However, the lack of ideal electrodes has long been a problem. This dissertation reports two types of high-performance electrodes, Ti/lrO₂-Sb₂O₅-SnO₂ and Ti/B-doped diamond (Ti/BDD), for electroflotation and electrooxidation, respectively.

The Ti/lrO₂-Sb₂O₅-SnO₂ electrode developed in the present study was much more stable than the conventional Ti/lrO₂ electrode with 97.5 percent of the precious Ir saved. The high stability of Ti/lrO₂-Sb₂O₅-SnO₂ with a low Ir content is attributed to the usage of conductive Sb-doped SnO₂ as a dispersing agent, the formation of a metastable solid solution, the interfacial bonding improvement, and the compact structure of the lrO₂-Sb₂O₅-SnO₂ film. An electrode system consisting of a fork-like Ti/lrO₂-Sb₂O₅-SnO₂ anode and a Ti cathode with a similar shape has been successfully applied to electroflotation to separate oil, suspended solids, fluorides, and Cr(lV) for over one year. The Ti/lrO₂-Sb₂O₅-SnO₂ electrode still performs well for O₂ evolution without any noticeable deterioration in activity.

Deposition of stable BDD films on titanium substrates is generally believed to be very difficult. In the present study, the durability of Ti/BDD electrodes has been improved significantly by optimizing the BDD film depositing conditions and using a proper organic additive. Different additives were investigated, and CH₂(OCH₃)₂ was found to be the best one. The improved stability is attributed to the enhanced diamond nucleation and growth rates. In comparison with Ti/Sb₂O₅ electrodes, the generally believed very active ones, the Ti/BDD electrodes obtained have 2-3 times higher current efficiencies in oxidizing various pollutants such as acetic acid, maleic acid, phenol, and dyes. A Ti/BDD electrode prepared from the H₂ + CH₄ + CH₂(OCH₃)₂ gas mixture has been used for over 300 hours, and the superior activity remains. The successful development of the stable and active Ti/BDD electrodes significantly increases the feasibility of industrial application of electrooxidation to wastewater treatment.