Flow rate 1.6µL/s

In this experiment, we wanted to see formation of cyclohexane at 1.6µL/s.There is a difference only m/z 56(main peak of cyclohexane) due to the delay time of low flow rate and due to the good complete mixing into the DEMS cell.

Also we calculated Z and current efficiency of CO₂ for this flow rate. At 2.5 V z of acetaldehyde equals 2.4 per C₆H₁₂, current efficiency of CO₂ equals %13.

Cyclohexane produce to CO₂ with 6 electron but in this result 2.4 number of electron are consumed and nearly 0.8 electron used for CO₂ ( 0.13 x 6 ). May be there were some other product but for this result we can not say any name of product because we checked cyclohexanol , cyclohexanon and benzene but there were not any effect of this molecules.

We did this experiment because we did not see any effect of cyclohexanon in figure 5.12 and we tried it in this flow rate but we did not see any effect of it too. The other masses and CV approximately same the other result.

6.2.3 Flow rate : 10 µl/s

The shoulder in I₅₆ (1.6V-1.9V) correspond to a small shoulder in the faradic current, which becomes visible at a higher current resolution.

7. CONCLUSION

DEMS measurements performed on a BDD electrode indicate that the direct oxidation of ethanol and Cyclohexane. DEMS was used to identify products and intermediates of the reaction, monitored online during the potential sweep. The measurements showed that the main product of ethanol oxidation is CO₂, acetaldehyde and cyclohexane oxidation is CO₂. The indirect mechanism of electrooxidation of ethanol and cyclohexane, mediated by quasi free hydroxyl radicals, is assumed. It has been shown that oxidation of both ethanol and cyclohexane is a fast reaction, whereas the rate determining step is the water discharge to hydroxyl radicals. In this work potential range is used between -0.7 V to 2.8 V because the major advantage of BDD electrodes is their wide electrochemical window which allows oxidation of organic compounds in aqueous electrolytes. At high electrode potentials hydroxyl radicals (OH•) are produced at the surface.

Highly boron-doped conductive diamond electrodes are shown here to exhibit excellent performance for the electrochemical oxidation of ethanol and cyclohexane.

Well-defined sweep rate- dependent cyclic voltammograms and mass spectroscopies were obtained. Consider a simplified mechanism of oxygen evolution on BDD electrodes, in which the first step is the discharge of water leading to formation of quasi free hydroxyl radicals.

H₂O → OH• + H⁺ + e

-These hydroxyl radicals are further discharged to oxygen, probably via formation of hydrogen peroxide, according to the global reaction.

2OH• → O2 + 2H⁺ + 2e

The indirect oxidation of organic compounds R mediated by quasi free hydroxyl radicals on BDD surface can be expressed as:

R + OH• → RO + H⁺ + e

During oxidation of ethanol and cyclohexane on BDD electrodes, in addition to CO₂ and O₂ evolution, acetaldehyde (m/z=29) and acetic acid were detected as intermediates.

we obtained 12-24% CO2 and 30-40% acetaldehyde (depends on flow rate and potential ) as main product during ethanol oxidation. For cyclohexane oxidation, we obtained 10-15% CO2 (depend on flow rate) as a main product.

Table 7.1. Number of electron (Z), the current efficiencies for CO2 and acetaldehyde in 1.10^-3 M ethanol + 0.5 M H₂SO₄ and number of electron and current efficiencies for CO2 in 1.10^-4 M Cyclohexane + 0.5M H2SO4 at 2.5 V and different flow rate.

Ethanol Cyclohexane

FlowRate (µL/s)

Z CO2 % Acetaldehyde % Z CO2 %

1.6 2.4 24 40 2.7 11

5 3.2 20 30 2.4 13

8. SUMMARY

The first extensive study of use of diamond electrodes in electrochemistry was done by Pleskov in 1987. Since than, the synthetic BDD thin films have attracted attention of researchers resulting in a rapid increase in the number of publications (Fig. 8.1) and patents. Until now, the main electrochemical applications of diamond electrodes are in the domains of: electrosynthesis, electrochemical treatment of organic pollutants electroanalysis, preparation of strong oxidants and recovery of heavy metals (Pleskov,1987), (A. Morao, 2004).

Figure 8.1. Yearly research publications on diamond electrochemistry (Agnieszka Kapalka 2008).

Conductive boron-doped chemical vapor-deposited diamond thin films have emerged as unique electrode materials in electrochemistry due to their attractive properties, including very low background current, a wide electrochemical potential window in aqueous media, high resistance to corrosion, mechanical stability and

conventional carbon-based electrodes such as glassy carbon (GC) and highly oriented pyrolytic graphite (HOPG) in some electroanalytical applications. First, the wide electrochemical potential window of the diamond electrode allows the sensitive electroanalytical detection of chemical species that react at relatively high potentials.

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İlköğretim Okulu’ and I continued intermediate school in ‘ DSİ Baraj İlköğretim Okulu’ After that I finished to high school in ATO Anatolian high school in 2002 and continued my study in chemistry in University of Çukurova a BSc in chemistry in 2003 and I started to master in Institute of Naturel and Applied Sciences University of Çukurova in 2007. Last year I studied in Bonn üniversity for second year of my master via erasmus program.