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Water Res ; 203: 117547, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34412015


In flow anode systems, surface-bound hydroxyl radicals (*OH) are generated at the solid-liquid interface of suspended particulate charge carriers at potentials well below that required for oxygen evolution as a result of water splitting. While these surface-bound radicals are powerful indiscriminant oxidants that often lead to complete mineralization of organic pollutants, the more selective process of direct electron transfer (DET) may also occur at the particle electrode interfaces and play a critical role in the degradation of some contaminants. In this study, we investigated DET processes in a flow anode system in which carbon black was utilized as the flow anode material and Pt, Ti, IrRu and IrTa meshes were used as the current collectors. The results indicate that the use of a carbon black flow anode enhanced the DET rate by 20 times at 1.0 V vs Ag/AgCl compared to the control experiment with no carbon black particles present. Low solution conductivity had a more obvious negative effect on the DET process (compared to *OH mediated oxidation) due to the high potential drop and inhibition of mass transfer processes at the solid-liquid interfaces of the anode particles. The DET rates were dependent on the particular anode current collector used (i.e., Ti, IrRu, IrTa or Pt mesh) with differences in rates ascribed to the electron transfer resistance of the current collectors in the flow anode system. Detailed investigation of the degradation of phenol in a flow anode system revealed that this widely studied contaminant could be degraded with an energy consumption of 3.08 kWh m-3, a value substantially lower than that required with other techniques. Results of this study provide a better understanding of the DET mechanism at the solid-solid and solid-liquid interfaces with these insights expected to benefit the design of flow anode materials and current collectors and lead to the improvement in performance of flow anode systems.

Fenol , Poluentes Químicos da Água , Eletrodos , Elétrons , Oxirredução , Fenóis , Poluentes Químicos da Água/análise
Water Res ; 200: 117259, 2021 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-34058481


Electrochemical advanced oxidation processes (EAOPs) have emerged as a promising water treatment alternative but major breakthroughs are still needed in order for EAOPs to be competitive with traditional treatment technologies in terms of energy cost. Most existing studies have been conducted at high potentials to generate the powerful hydroxyl radical oxidant (aqueous •OH). While adsorbed hydroxyl radicals (OH*) may form at a much lower energy cost, their possible utilization is limited due to the poor mass transfer of this highly reactive species on solid electrodes. In this report, we describe a novel flow anode system using 4-16 µm Magnéli phase titanium suboxide particles as the anode material which enables the generation of a high steady state •OH concentration (5.4 × 10-12 mol m-2) at only 1.5 V (vs SHE) in a dilute electrolyte (5 mM KH2PO4). The energy cost of removal per order of selected water contaminants (tetracycline and orange II in this study) using the flow anode is 1.5--6.7 Wh m-3, which is 1 - 4 orders of magnitude lower than that of existing techniques. The anode material used demonstrates great stability with the configuration readily scaled up. The results of this study provide new insight into a high efficiency, low cost water treatment technology for organic contaminant degradation.

Poluentes Químicos da Água , Purificação da Água , Eletrodos , Radical Hidroxila , Oxirredução , Água
Environ Sci Technol ; 54(8): 5227-5236, 2020 04 21.
Artigo em Inglês | MEDLINE | ID: mdl-32202775


Magnéli phase titanium suboxide, Ti4O7, has attracted increasing attention as a potential electrode material in anodic oxidation as a result of its high efficiency and (electro)chemical stability. Although carbon materials have been amended to Ti4O7 electrodes to enhance the electrochemical performance or are present as an unwanted residual during the electrode fabrication, there has been no comprehensive investigation of how these carbon materials affect the electrochemical performance of the resultant Ti4O7 electrodes. As such, we investigated the electrochemical properties of Ti4O7 electrodes impregnated with carbon materials at different contents (and chemical states). Results of this study showed that while pure Ti4O7 electrodes exhibited an extremely low rate of interfacial electron transfer, the introduction of minor amounts of carbon materials (at values as low as 0.1 wt %) significantly facilitated the electron transfer process and decreased the oxygen evolution reaction potential. The oxygen-containing functional groups have been shown to play an important role in interfacial electron transfer with moderate oxidation of the carbon groups aiding electron uptake at the electrode surface (and consequently organic oxidation) while the generation of carboxyl groups-a process that is likely to occur in long-term operation-increased the interfacial resistance and thus retarded the oxidation process. Results of this study provide a better understanding of the relationship between the nature of the electrode surface and anodic oxidation performance with these insights likely to facilitate improved electrode design and optimization of operation of anodic oxidation reactors.

Titânio , Poluentes Químicos da Água , Carbono , Eletrodos , Oxirredução