Simultaneous Electrochemical Oxidation of Methylene Blue and Reduction of CO 2 1 using CNTs/CF electrodes

10 Simultaneous degradation of methylene blue (MB) and reduction of CO 2 by electrochemical 11 process using CNTs/CF electrodes have been performed in various supporting electrolytes and 12 applied current conditions in this study. The CNTs/CF electrodes have been successfully 13 synthesized by chemical vapor deposition (CVD) method and employed as both cathode and anode 14 in a two-compartment electrochemical cell. The synthesized electrodes were characterized by 15 SEM and FTIR. The electrochemical oxidation efficiency of CNTs/CF electrodes in the anodic 16 cell was evaluated using MB as model compound under electrolytes of H 2 SO 4 and KHCO 3 and 17 applied currents of 10, 50 and 100 mA. The electrochemical reduction activity of CNTs/CF 18 electrodes in the cathodic cell was assessed by the conversion of CO 2 into CO and oxalic acid, and 19 the generation of H 2 under electrolytes of Na 2 SO 4 and KHCO 3 and a fixed applied current of 50 20 mA. The degradation kinetics of MB followed the pseudo-first-order model and the degradation 21 efficiency was significantly affected by applied current rather than the sort of electrolyte under 22 optimum condition. The optimal applied current can promote the high enough production of 23 oxidant but also avoid electrode damage. The synthesized electrode of CNTs/CF combined with the electrochemical systems developed in this study provide a good solution for the simultaneous 25 electrochemical oxidation of organic pollutants and reduction of CO 2 to CO to yield H 2 and CO, 26 in which reaches the dual benefits of reduction of environmental hazards and production of green 27 energy.


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Wastewater arisen from the textile and dye industries typically possessed color, which the 31 conventional wastewater treatment processes usually ineffectively deal with due to the complex 32 structures [1]. Dye molecules are normally composed of aromatic rings compounds and even 33 metals, which resulted in less biodegradation. The ordinary treatments such as adsorption and 34 coagulation are not commonly sustainable because they are chemical intensive and produce 35 hazardous sludge, respectively [2,3]. Although chemical oxidation with ozone, Fenton's reagent 36 [4] and other advanced oxidation processes have highly efficient, they still contain some 37 disadvantages relating to the high cost and operational problems [5].

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In recent decades, new advanced oxidation processes relied on the electrochemical technology 39 have been proposed as effective solutions to deal with refractory organic compounds [6,7]. These electrochemical oxidation is also considered as an economical, safe and environmentally friendly 43 technology for the wastewater treatment due to it generates highly reactive species from only 44 electrical current without using other hazardous chemicals to produce the strong oxidants.

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Electrochemical processes applied in water treatments to oxidize organic pollutants have been 46 demonstrated in many researches indicating that this approach may be feasible for large groups of 47 dye widely used in textile industry [3,[11][12][13]. 48 On the other hand, electrochemical reduction of CO2 into valuable chemicals has attracted the 49 attention as an innovative approach which utilizes renewable energy to help address the problem 50 of greenhouse gas emissions [14,15]. There are a variety of target products may be produced by 51 4 CO2 reduction, depending on the electron transfer mechanism and operation conditions. In general, 52 the main products generated during CO2 reduction process are C1 compounds (e. Then, CF coated with Ti and Ni was cut into 30 mm × 10 mm size as one piece and then placed in was conducted at high current densities using glassy carbon electrode, the surface of electrode was 212 blocked by the coverage of insoluble polymeric products which were relatively slow to oxidize or 213 desorb.

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The experimental data within reaction time of two hours were collected to calculate the rate 215 constants, as illustrated in Table 1

CO2 reduction and production of by-products 242
The production of by-products during CO2 reduction in the cathodic cell occurred at the The chemicals investigated in this study included formic acid, oxalic acid, methanol, and ethanol, 280 in which only the oxalic acid was determined, as illustrated in Figure 10. The oxalic acid was 281 generated and increased with reaction time in both Na2SO4 and KHCO3 supporting electrolytes.

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As the KHCO3 was adopted as supporting electrolytes, the production of oxalic acid dramatically

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The carbon nanotubes have been successfully grown on carbon fiber by chemical vapor deposition 296 method and used as anode and cathode for MB degradation and CO2 reduction. FTIR spectra 297 indicated that CxHy functional groups on the CNTs/CF move towards strong stretching vibration 298 as compared with pristine CF. The magnitude of the applied current possessed a greater impact 299 than the type of electrolyte for the degradation of MB in the anodic cell. The maximum 300 degradation efficiency was obtained at optimum applied current of 50 mA, which can promote the 301 high enough production of oxidant but also avoid electrode damage. In the cathodic cell for CO2 302 reduction, CO and H2 were the main gaseous products while oxalic acid was the liquid product.

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Hydrogen evolution reaction is predominant at the initial stage of the reaction while CO formation 304 increased significantly at the later stage. KHCO3 supporting electrolyte was recorded to be 305 favorable to both CO formation and hydrogen generation. Furthermore, the sorts of electrodes and 306 16 electrolytes were demonstrated to have significant effects on products generated. The developed 307 electrode combined with the electrochemical systems is the priming candidate for the simultaneous 308 electrochemical oxidation of MB and reduction of CO2 to yield clean energy of H2 and CO. The authors declare that we have no competing interests.