| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 89 === It becomes more important to monitor the concentration of acetic acid in many applications such as environment protection and hospital performances. Especially, in the high-level densification and the drainage of wastewater, it had regulations for the acetic acid concentration discharged. In conventional, it is very fullblown to analyze acetic acid concentration, but it still has many disadvantages to improve the in-situ acetic acid detection. Therefore, to fabricate the acetic acid sensor by electrochemical method has advantages; such as short analyzing time, simple analyzing theorem, using convenient instruments and low cost. Besides, it is also important to minimize the sensor.
In the flowing system, the optimal sensing condition for a 1000ppm acetic acid is 0.1MKCl as carrier solution in 10mL/min flow rate and the applied potential is —0.1V (vs. Ag/AgCl), using mercury-modified carbon, as a working electrode. The results show that the response current is 4.4 times larger than that by using the bare carbon electrode. In the different concentrations of acetic acid, the recovery time increases with acetic acid concentration. In the flowing system, the equation of calibration curve is I=2.3×10-6〔HAc〕 -0.56, the sensitivity is 2.3×10-6mA/cm2/ppm and the linearity is R2=0.95.
In the batch system, the optimal sensing condition is acetonitrile as organic solvent, the lead as working electrode and 0.01M [CH3(CH2)3]4NBF4 as supporting electrolyte and at 25℃. The limiting current of acetic acid was found in the potential window in the range from —1.8 to -2.6V(vs. Ag/Ag+) in CH3CN solution with TBAT. In sensing acetic acid, the correlation equation is the curve, I= 3.15×10-3×〔HAc〕-1.1 at —2.2V(vs. Ag/Ag+ in CH3CN solution with TBAT). The correlation coefficient of R2=0.98, the sensitivity of the system is 3.15×10-3mA/cm2/ppm and response time is 100 seconds.
In water solution, we used 0.5M sulfuric acid as supporting electrolyte and the applied anodic potential at 2.5V(vs. Ag/AgCl). Besides, the materials of anode are compared. The results indicate that the platinum foil and sputtered platinum have advantages which are stable background currents, high sensitivity, shorter response time and large S/N ratio. The correlation equation using platinum foil as working electrode is I=6.85×10-3×〔HAc〕+15.85 and its R2=0.98, sensitivity is 6.85×10-3mA/cm2/ppm and response time is 21 seconds.
In potassium hydroxide alkaline solution, the limiting currents were obtained in the potential range from 1.2 to 1.75V (vs. Ag/AgCl).The acetic acid response currents, which were obtained by subtraction the background currents of the potassium hydroxide from the measured currents. The effect of potassium hydroxide concentration on the sensitivity is not obviously. Increasing potassium hydroxide concentration from 0.04 to 0.06M, the response time increases from 15 to 100 seconds. The effect of temperature on sensing is that the sensitivities increase with temperature linearly. Increasing stirred rates, the response current approaches steady state within a short time and decreases with the response times. The sensitivities do not change with the gap distances between the anode and the cathode, which indicates that solution is good conductivity. Meanwhile, comparing the sensing results at 25℃, the best sensing performance is 0.04M NaOH, 250RPM stirred rate, and 1.2V(vs. Ag/AgCl) applied potential. The correlation equation at optimum condition is I= 3.86×10-3×〔HAc〕＋0.14, linearity correlation coefficient R2=0.998. The sensitivity and the response time of the system are 3.86×10-3mA/cm2/ppm and 15 seconds, respectively.
With the platinum working electrode prepared by sputtering, the sensing correlation equation in 0.04MNaOH is I=2.93×10-4×〔HAc〕-0.007, the linearity correlation coefficient R2=0.92, and sensitivity is 2.93×10-4mA/cm2 /ppm.
In 0.04M NaOH solution, the experimental diffusivity coefficient of acetic acid is 1.76×10-11m2/s which is smaller than theoretical value 10-9m2/s. The experimental diffusion layer thickness of acetic acid is 4.28×10-5m and it is in the theoretical range between 10-6 to 10-3m.
|
|---|
