The Study On Ammonia Sensor Based On Zeolites

Recently,zeolite has received an increasing attention in the field of gas sensing.There are many unique properties for zeolite,which will improve the sensitivity and selectivity of the gas sensors.In this paper,we attempted to explore the gas sensing properties of the zeolite as the functional material of the ammonia sensor.Firstly,hydrothermal method is applied for the synthesis of A type and Y type zeolite powder,then Y zeolite powder was sintered in different temperature,according to the XRD patterns,the optimum sintering temperature of Y type zeolite powder is 600 ?.Secondly,Y zeolite powder is applied to the solid electrolyte and silver is applied to the electrode,the capacity structure of ammonia sensor was made by screen printing process.In order to achieve the maximize response,the Na-Y zeolite based sensor with different excitation frequency is tested for 100 ppm NH3.The results showed that the sensor has the best response to ammonia,with the excitation frequency at 3 kHz.Therefore,in the following experiments,3 kHz is the optimum excitation frequency of sensor.Furthermore,at 150~250 ?,under the certain conditions,testing the sensor's response to ammonia,the tests show that the response value to 100 ppm NH3 is 36.2%,and the optimal working temperature was 200 ?.Thirdly,we exchanged Na-Y to the proton H+,alkali metal element Li+,rare earth elements La3+,noble metal Pd2+ and Ag+,of which salt solution was adopted for each element by the method of liquid phase ion exchange in this thesis.In addition,different ions were exchanged and made into the sensor.The above tests were carried out under the same conditions,and compared with the properties of the Na-Y type sensor.The results showed that the average response properties of Y type zeolite increased with ion exchange to Ni,Ag and La,the responseof Y zeolite with H and Pd were less than that of Na-Y type zeolite based sensor.Also,the selective test about Ag-Y has inactivity to O2,theresults indicate the sensor has good selectivity for CO2 and CO,and the different volume fraction O2 had no effect on the sensor,but the C3H6 and NO had a weak effect on the sensor.Fourthly,in order to investigated the capacity of the sensor to ammonia,the thickness of the sensor was changed and different thickness was designed.Under the same testing conditions,above-mentioned properties of the Ag-Y type zeolite based sensors with different thickness were tested.The results showed that the sensor's response to ammonia improved with the increase of the thickness of the zeolite based sensor.Finally,this paper attempted to replace the Y type zeolite with the zeolite A and zeolite ZSM-5,we prepared the capacitance type zeolite based sensors with the same structure,and by exchanging the cation of zeolite A and zeolite ZSM-5,preparing Ag-A zeolite and Ag-ZSM-5 zeolite based sensor with AgNO3 solution of the same concentration,we discussed the improved sensor's response characteristic to NH3.The results showed that the Na-A type and Ag-A type zeolite based sensors did not respond to ammonia,but the H-ZSM-5 type and Ag-ZSM-5 type zeolite based sensors had a certain response to NH3,and the former had greater response than the latter.In conclusion,we systematically studied some properties of the zeolite based sensor for the detection of ammonia this thesis.The performance of Y zeolite based ammonia sensor was mainly discussed.The experimental results showed that the use of Ag-Y zeolite sensor had a good effect on detecting ammonia.