Study On PH Sensor Based On Magnetron Sputtering TiO₂ Electrode And Its Online Detection And Compensation For PH Value Of Cultivation Substrate

The pH value of cultivation substrate is an important production process information of plant cultivation,which directly affects the existence,transformation and availability of substrate nutrients.Accurate on-line detection of pH value of cultivation substrate is the key and foundation to realize digitalization and intelligence of facility agriculture.Aiming at the problems of many influencing factors and poor accuracy in on-line detection of pH value of cultivation substrate,this paper comprehensively analyzes the related research of pH sensor at home and abroad,and studies the response mechanism of TiO₂ sensitive electrode to hydrogen ion concentration and the migration mechanism of hydrogen ions in micro-solution of cultivation substrate by combining the characteristics of on-line detection of cultivation substrate and its pH value.TiO₂ sensitive electrode and Ag/Ag Cl reference electrode are prepared by magnetron sputtering,and the pH sensor is constructed.The influence of the thickness and area of the sensitive membrane on the output potential performance of the sensor is studied and analyzed,and the double compensation model of water content and K⁺ion concentration for on-line detection of pH value of cultivation substrate is established to improve the accuracy of on-line detection of pH value of cultivation substrate.The main research contents and results are as follows:（1）Study on the response mechanism of TiO₂ sensitive electrode to hydrogen ion concentration.The principle of detecting hydrogen ion concentration with TiO₂ as a sensitive material is analyzed,and the electrode/solution electric double layer model is established.Combined with the"Oxygen Nesting"model,the main influencing factors and laws of the performance of the sensitive electrode are analyzed.The results show that with the increase of the specific surface area of the transition layer between TiO₂ electrode and the culture medium micro-solution,the number of reaction binding points per unit surface area is more,and the response performance of TiO₂ sensitive electrode to the pH value of the culture medium micro-solution will be greatly enhanced.（2）Study on the generation and migration mechanism of hydrogen ions in micro-solution of culture medium.Combined with the theory of soil colloid electric double layer,it is analyzed that the generation of H⁺in the micro-solution of cultivation matrix mainly comes from the dissociation of matrix particles H⁺,the displacement in matrix colloid and the hydrolysis of Al³⁺.The migration process of hydrogen ions is mainly influenced by the water content of the culture medium.By analyzing the process that the contact state and contact form between the sensitive electrode and the culture medium change with the water content,the migration behavior of hydrogen ions to the electrode surface in the micro solution of the culture medium is obtained.（3）Preparation and surface characterization of pH sensor based on magnetron sputtering TiO₂electrode.TiO₂ sensitive electrode and Ag/Ag Cl reference electrode were prepared by magnetron sputtering technology,and the pH sensor was constructed.By XRD,XPS and SEM,the surface morphology of the electrode was observed and its physical and chemical characteristics were analyzed.It was found that the films prepared by magnetron sputtering were amorphous TiO₂crystal,and the surface roughness and porosity of the electrode began to increase with the increase of thickness.（4）Experimental study on the influence of the thickness and area of electrode sensitive film on the output performance of pH sensor.By testing the sensitive electrode in different pH buffers,it is concluded that the increase of electrode thickness will reduce the sensitivity,hysteresis,response time and drift rate of the sensor,and the increase of area will increase the stability of the sensor response,reaching the upper limit at 15 mm×15 mm;It is optimized that when the TiO₂thin film is sputtered by magnetron sputtering at 15 mm×15 mm×200 nm,the pH response of the sensor is good,with sensitivity of 51.17 m V/pH,response time of 10 s,lag of 3-6 m V,drift rate of about 6 m V/h and good ion selectivity.（5）On-line detection and compensation of pH sensor and its application.Through the experiment of online detection of pH value of peat substrate by direct measurement（DSM）,the compensation model of online detection error moisture content is established,and it is found that the concentration of K⁺ions will affect the compensation effect of online detection error moisture content of pH value.On-line pH detection test of mixed culture substrates with different proportions of peat and vermiculite showed that the pH value of culture substrates with high peat content in organic substrates was more easily affected by K⁺ion concentration.Through the combined test of water content and K⁺ion concentration,and the fitting of three-dimensional space plane,the error compensation model of online detection of pH value by two parameters of cultivation substrate water content and K⁺ion concentration was established.Finally,the application experiment of on-line detection of pH value of cultivation substrate was carried out.The results showed that the absolute error of on-line detection of pH value of cultivation substrate was reduced from 0.63-unit pH value to 0.12 after error compensation,which met the actual production requirements.The research work is helpful to realize more rapid and accurate on-line detection of pH value of cultivation substrates,and has very important theoretical significance and application value for promoting agricultural intelligent modernization.