| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 88 === It is of great important to monitor the concentration of ammonia and ammonium ion in many subjects and applications such as environment protection, biochemical engineering, medical care and industrial safety control. In the previous study, Pt/NafionR electrode was reported as an effective detecting device to ammonium ion. However, the conventional impregnation-reduction (I-R) and two-side (or Takenaka-Torikai, T-T) methods, which were commonly used in preparing the Pt/NafionR electrodes, encountered considerable problems in mass transfer. Therefore, the sensitivity of the electrodes that prepared by the above two conventional methods was ill and faulty. In this research, ultrasonic irradiation was applied to both the I-R and T-T preparation process to increase the mass transfer rate of the reacting species of the chemical deposition reaction, and hence to promote the sensitivity of the Pt/NafionR electrode. After that, a Pt/NafionR electrode, which was prepared by sputtering method, was compared with that prepared by I-R method with ultrasonic irradiation in their sensitivity to ammonium ion. Also, the prepared electrodes were used to detect ammonia gas.
Both the recovery time and response current of ammonium ion sensing are significantly affected by the application of ultrasonic irradiation to prepare the Pt/NafionR electrodes. By using 0.01M Pt salt and 0.2M reducing agent solution at 45oC for 30min, the optimum condition of ultrasonic irradiation, of which Pt/NafionR electrode to be prepared with in the I-R process, was power level 8 (88.0watt) and 60% duty cycle. The prepared electrode has the maximum specific active surface area, 202.1 cm2 Pt/cm2 NafionR and the highest XRD platinum peak, 1666.83count. At the same sensing condition, the sensitivity of the electrode prepared with ultrasonic irradiation in the I-R process (18.4mA/M) is 4.5 times as large as that of the electrode prepared without ultrasonic irradiation (4.2mA/M). Comparing with the recovery time of the electrode prepared without ultrasonic irradiation (396s), the one with ultrasonic irradiation (211s) was about 50% shorter. Besides, the electrode prepared with the optimum condition of ultrasonic irradiation in the I-R process exhibited a good linear response to ammonia gas from 4% to 100%, and has a detection limit approximately to 2%. Both impregnation and reduction stages were significantly affected by ultrasonic irradiation during the preparation of Pt/NafionR electrode. The sensitivity of NH4+ detection and the specific active surface area of the electrodes prepared with ultrasonic irradiation are higher and larger then that of the electrodes prepared without ultrasonic irradiation. The ultrasonic effect in the I-R process was more significant in the reduction stage than in the impregnation stage.
In T-T preparation process, by using 0.01M Pt salt and 0.2M reducing agent solution at 45oC for 30min, the optimum condition of ultrasonic irradiation is power level 5 (55.0watt) and 60% duty cycle. The prepared electrode has the maximum specific active surface area, 229.3 cm2 Pt/cm2 NafionR and the highest XRD platinum peak, 1431.82count. At the same sensing condition, the sensitivity of the electrode prepared with ultrasonic irradiation in the T-T process (60.2mA/M) is 3.3 times as large as that of the electrode prepared without ultrasonic irradiation (18.1mA/M). Comparing with the recovery time of the electrode prepared without ultrasonic irradiation (248s), the one with ultrasonic irradiation (129s) is about 50% shorter.
The electrode prepared by sputtering method is effective in detecting ammonium ion. When the preparation conditions are 1.010-2torr, 15cm3/s and 10.0watt, the optimum operation time is 10min. At this condition, the prepared electrode has the highest sensitivity and shortest recovery time of 17.8mA/M and 422s, respectively. The above electrode has a linear response to NH3 between 3% and 100%. Its detection limit was about 2%.
At the same sensing condition, the sensitivity of the electrodes prepared by I-R and sputtering methods to ammonium ion are 18.4mA/M and 17.8mA/M, respectively. The sensitivity of the electrode prepared by sputtering method, 0.1921μA/%, is higher than that of the electrode prepared by I-R method, 0.0859μA/%.
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