Preparation And Performance Of Titanium Dioxide Electrode PH Sensor For Cultivation Substrate

In facility agriculture,pH value of cultivated substrate is an important factor affecting crop growth.Accurate online pH value detection of cultivated substrate is of great significance to promote automatic intelligent production of facility agriculture.When pH value is detected online,the cultivated substrate around the electrode is often in ionic unsaturated solution state.Moreover,repeated use of the electrode in the cultivated substrate will cause wear on the electrode itself,leading to the increase of the error of online detection of cultivated substrate pH value.Aiming at the above problems,this paper developed a titanium dioxide（TiO₂）electrode with super hydrophilic,wear-resistant and hydrogen ion sensitive characteristics.The influence of annealing treatment on various properties of TiO₂ electrode was analyzed experimentally.Based on the TiO₂ electrode,A pH sensor based on extended gate field effect transistor（EGFET）was designed and tested,and the pH value of cultivated substrate was tested online with temperature compensation formula in actual cultivation substrate.The main research contents and results are as follows:（1）The detection theory of metal/metal oxide electrode pH sensor was analyzed,combined with the actual application of online pH detection of cultivated substrate,the effect of the hydrophilicity of electrode surface on online pH detection of cultivated substrate was analyzed,and higher requirements were put forward for the wear resistance of electrode surface.The beneficial effect of annealing treatment on TiO₂electrode surface was analyzed,and the annealing process was determined to improve the hardness of electrode surface,so as to improve the wear resistance.The detection principle of EGFET sensor was analyzed to provide theoretical basis for designing EGFET pH sensor based on TiO₂ electrode.（2）TiO₂ electrode was prepared by chemical corrosion method,and the electrode surface was treated by annealing process.X-ray diffraction（XRD）test showed that all the annealed electrodes were amorphous,and X-ray photoelectron spectroscopy（XPS）test showed that TiO₂ content on the surface of the annealed electrode at 200℃was the highest.Annealing treatment does not change the surface morphology of the electrode,and the hardness of the electrode increases with the increase of annealing temperature.The smaller the electrode wear,the smaller the hydrophilic attenuation.The pH response sensitivity of the electrode annealed at 200℃was the best,reaching-52.07 m V/pH.When the electrode was used in the cultivation substrate for many times,it still maintained good pH response performance.（3）EGFET pH sensor based on TiO₂ electrode is designed.The sensitivity of EGFET pH sensor is 0.05063 V/pH and-0.97863（μA）^0.5/pH under linear state and saturated state,and the linearity is 0.9977 and 0.9992,respectively.The maximum response time was 18s in different pH buffers.In the repeatability test,the difference of I_DS before and after the buffer at pH 4.03 and 7.95 was 0.20%and-0.15%.In the stability test at pH 4.03,6.86 and 9.04,the coefficient of variation of I_DS was small.0.0019,0.0027 and 0.0057,respectively,and the stability is optimal in acidic solution.The test results show that the EGFET pH sensor based on TiO₂ electrode has good pH response sensitivity,linearity,response time,repeatability and stability,and these characteristics are conducive to the application of pH sensor in the online pH detection of cultivated substrate.The temperature compensation test of EGFET pH sensor was carried out under different ambient temperatures,and the temperature compensation algorithm was established.（4）Application test of pH sensor in cultivated substrate.When the sensor is used to detect pH value in the cultivated substrate at different temperatures,the absolute value of the error reaches the maximum of 0.78 at the ambient temperature of 288 K.After temperature compensation,the error is reduced by 0.61 and the absolute value of the error is only 0.15,which proves that the temperature compensation formula is feasible.The pH sensor has good accuracy in different temperatures,different water contents and different kinds of cultivation substrates,and the absolute values of the errors after temperature compensation are all within 0.30.After the sensor was inserted into the culture substrate for 10 times,the contact Angle of the electrode surface remained good,the maximum was 15.15°,which proved that the sensor electrode had good durability.The application of the research results is conducive to realizing the accurate online pH detection of cultivation substrate and promoting the automatic intelligent production of facility agriculture.