The alternative material of the metal oxide H + selective electrode as a glass electrode has caused extensive attention. Most of the metal oxide pH electrochemical sensors reported is based on precious metal oxide electrodes, and the preparation cost is more expensive, but W and its oxide. The price is relatively low. At present, the preparation method of WO3 electrodes has electrochemical cycle voltammetry, chemical oxidation and ion sputtering deposition, these methods have problems with complex process, oxide pollution environment, not easy to control chemical components, and H + response performance is also Room for improvement. Sol-Gel Technology has a simple preparation process, and does not require expensive equipment, it is easy to control the morphology and ingredients of the membrane, and a wide range of applications in the field of numerous functional surface membranes. This paper attempts to prepare WO3, H + selective electrodes using Sol-Gel method, discusses the influence of heat treatment temperature on response performance, and research on the response speed, response range, response sensitivity, temperature effect, and anti-ion interference in electrochemical sensors. .
2 experiment and preparation process, detection method
2.1 Preparation of WO3 Electrochemical Sensor
The Na2WO4 solution was treated with a cation exchange resin (0017, Nankai University) to obtain a light yellow colloid solution, and then H2O2, C2H5OH was added as a stabilizer to improve sol stability. The Sol coating was applied in the surface of the metal W (Zhuzhou Cemented Carbide Products) to prepare a WO3 coating by a heat treatment temperature of 100 to 400 ° C. One end of the WO3 coating electrode is ground, and then weld from the Cu wire spot and is blocked with an insulating gel, and the oxide H +-sensitive film is exposed, and WO3 working electrodes are prepared. WO3 working electrode and saturated tract chemical test system (AUTEST) constitute an electrochemical sensor.
2.2 Opening Potential Monitoring
0.01 mol / l CH3COOH / HBO3 / H3PO4 / KCl buffer solution, 0.1 mol / l NaOH or 0.1 mol / LHCl regulated pH is adjusted, and an electrochemical test such as open circuit potential monitoring is performed in a buffer solution.
3 results and discussion
3.1 Factors of WO3 Electrochemical Sensor H + Response Sensitivity
Studies have found that the H + response range of the WO3 electrochemical sensor prepared by different heat treatment temperatures is a pH of 2 to 11, and there is a good linear relationship in this pH range. The heat treatment process of the WO3 working electrode has an effect on the sensitivity of the sensor, corresponding to the heat treatment temperature of 100, 200, 300, 400 ° C, the response sensitivity is 46.8, 52.6, 39.1, 37.4 mV / pH, respectively, as shown in Figure 1 (a) Indicated. The response sensitivity of the WO3 electrochemical sensor is also related to the temperature of the test solution, and the response sensitivity increases with the temperature rise of the test environment. At 25, 35, 45, 55 ° C, the response sensitivity is 52.56, 54.85, 57.56, 59.45 mV / pH, but there is still a certain gap with the E-pH slope of the ideal in different temperatures.
3.2 Factors of H + response speed of WO3 electrochemical sensors
The heat treatment temperature of the WO3 working electrode has an effect on the response speed of the sensor. In the pH of 4.01, 6.85, 9.14 test solution, the response time prepared at different temperatures, found that the sensor preparation of 200 ° C is the fastest, and the response time is at 1 min In addition, the heat treatment temperature increases, resulting in a decrease in the response speed, such as 300 ° C, 400 ° C treatment, within 1 to 4 minutes, as shown in FIG. 1 (b). Figs. 2 (a), (b) respectively correspond to the potential response curve of the electrode in the pH of 100, 200 ° C in a pH of 9.14 buffer solution, and the response time is 90, 50 s, respectively.
The pH of the solution also affects the response speed of the sensor, and Figures 2 (c) and (b) are the potential response curve of 200 ° C in a pH of 4.01 and 9.14 buffer solution, and the response time in the pH is 4.01 solution is About 30 s, the pH is about 9.14 solution is about 50 s, indicating that the electrode response is faster in a solution having a high H + concentration. In order to study the effect of solution temperature on the potential response speed, the potential response time at different temperatures was tested in the same pH solution. Studies have shown that the rise in solution temperature increases the response speed of the electrode. 2 (b) and (d) are the potential response curve at 25, 50 ° C in the pH of 9.14, and the response time is 50, 20 s, respectively, indicating that the temperature rise will accelerate the response speed of the electrode.
3.3 WO3 electrochemical sensor H + response ion interference factors
The anti-interference resistance of the W / WO3 electrode was studied by ion interference. 0.1 mol / l Na +, K +, F-, NO3-, I-interference ions were added to the buffer solution. The E-pH relationships under interference ions were: F (157.6) -PH (52.3), R = -0.999; E (166.8) -PH (52.2), R = -0.999; E (174.8) -ph (53.7) ), R = -0.998; E (198.2) -PH (55.5), r = -0.997; E (120.3) -PH (49.2), R = -0.994; no interfering ion's E-pH relationship is: E ( 165.8) -PH (52.6), r = -0.997. The selective coefficient of mixing ion interference was found to be found, Na +, K + 10-10, F- was 10-6, oxidative NO3- and reductive I- were 10-4. It can be seen that Na +, K +, and F-on the sensor's response behavior has little effect, oxidative NO3- and reductive I-I-sensor's H + response has an impact.
4 Conclusion
The WO3 pH electrochemical sensor prepared by Sol-Gel method has better H + response performance, and the H + response range pH is 2 to 11. The heat treatment system has an effect on the sensitivity of the sensor, and the electrodes prepared at 200 ° C heat treatment temperatures have the best response sensitivity 52.6 mV / pH. The response speed is related to the heat treatment temperature of the electrode, the test temperature, and the solution pH is related. The sensor has a good H + ion selectivity, +1 and -1 price common ions and F - H + response linear relationship to the sensor is small, but the oxidative substance such as I-, NO-3 H + response is interference .
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