All-solid-stated Planar PH Sensor And Study On Its Response Characteristics

In the development of facility agricultural,the physical and chemical properties of the culture substrate affect the growth of crops directly.The pH value is one of the important parameters of the cultivation substrate,which has important influence on fertility and nutrients of substrate.Therefore,it is important to grasp the pH of cultivation substrate which provide basis for regulating the status of water and fertilizer in the cultivation process,then improve the production and quality of the facility agricultural crops.This article fully investigated and analyzed domestic and overseas research on pH sensors,then according to the special characteristics of heterogeneous measurement systems such as soil cultivation matrix,combineing electrode structure features performance,an all-solid-stated planar pH sensor was presented.Furthermore,in-situ pH measurement of cultivation substrate was carried out.The main research contents and research results are as following.(1)Theory analysis on pH sensor design and its fabrication.Analysing theory of pH sensor detection based on Nernst response,theory of metal heat treatment annealing related,electrode/solution interface double layer capacitor model,combineing magnetron sputtering coating technology,and heat treatment annealing process and spin coating method,an all-solid-stated planar pH sensor was designed and fabricated,which used Sb electrode as working electrode,Ag / AgCl electrode as reference electrode,and modified by Nafion.(2)Study on effect of heat-treated temperature on performance of pH sensor.Through metal electrode film thickness characterization,obtained the thickness of Ag film was 3.8?m and the Sb film was 200 nm.Surface morphology and spectral analysis of electrodes was carried out,which showed that after heat treatment,the surface morphology of the electrodes was improved,and the surface density of the films was increased.However,when the heat-treatded temperature was over-high,the quality of Sb film deteriorated.The electrodes heat-treated at 200°C showed better morphology,elemental composition and stronger binding forces between electrode film and substrate.Electrochemical experiments were carried out to explore the response characteristics of pH sensors in sensitivity,response time,and stability.The results showed that the heat-treated temperature had a certain effect on the performance of the pH sensor.The pH sensor heat-treated at200°C had good properties,and the sensitivity of the sensor was 74.0 mV/pH,the response time was within 3 s,the standard deviation was less than 2 mV in 700 s period.(3)Study on effect of electrodes surface area on performance of pH sensor.Through metalelectrode film thickness characterization,obtained the thickness of Ag film was 3.0?m and the Sb film was 200 nm.According to surface morphology and spectral analysis of electrodes,the observation showed that the surface of the electrode film was smooth,compact and dense,and the content of each element of the film was in an acceptable range.Response characteristics of pH sensors with different electrode surface areas was analyzed.The results showed that pH sensor with electrode surface area of 16 mm2 had ideal response characteristics.The corresponding sensitivity was 67.30 mV/pH,response time was within 3.5 s,and the test was performed continuously for 700 s,and the standard deviation was less than 2 mV in 700 s period.(4)Study on temperature and humidity double compensation and application experiment.The temperature effect on pH sensor detection was studied,then obtained the temperature compensation mathematical model of the sensor.The moisture effect on pH detection conducted in a heterogeneous system of mixed cultivation substrates,then obtained the mathematical model for moisture compensation.Furthermore,the temperature and humidity double compensation mathematical model of the developed pH sensor in mixed cultivation matrix was obtained.Application experiments was carried out in liquid environments and mixed cultivation substrates respectively.The results showed that the measurement accuracy of the pH sensor was improved obviously after temperature and humidity double compensation.The absolute error was in the range of-0.10 to-0.05 in the liquid environment,and in the mixed culture medium,the absolute error was between-0.20 and-0.13,which conforms to the actual production requirements.The all-solid-stated planar pH sensor developed in this article adopted single-planar electrode structure,which shortened the distance between two electrodes,and realized in-situ measurement of a heterogeneous system with a certain water content.