Study On Humidity Sensors Based On Zeolite/Polyaniline Composite Film

In recent years, Polyaniline (PANI) has become one of the most popular polymer materials, which has excellent performance such as high sensitivity, fast response speed, low cost and high stability at room temperature. The volume of PANI will change when absorbing water and the conductivity of PANI varies under the different humidity environment. With these features, PANI can be applied to the field of humidity sensors. Zeolites have a large specific surface area and strong ion exchange capacity. It also can preferentially absorb some polar gases such as:NH3, H2O and H2S. Therefore, zeolites can be used as a composite material to improve the properties of the humidity sensors. In summary, zeolites mixed with PANI in proportion can prepare a good sensor.In this paper, the synthesis of zeolites, humidity sensing properties of the composite films are studied systematically. We also analyze the mechanism that zeolites improve the performance of the sensors. The main contents are as follows:We study several existing methods of synthesizing zeolites and compare their advantages and disadvantages. Then we analysis the factors affecting the synthesis of zeolites such as the ratio of reactants, the composition, the amount of structure-directing agent, the ratio of Si and Al, pH, crystallization temperature and crystallization time. We synthesize A-type zeolites with the addition of the structure-directing agent using hydrothermal method.We prepare the different proportion of PANI/zeolites composite films sensors and pure PANI thin film sensors on the electrode. By measuring the output-humidity curves of each group of sensors, we find that composite films sensors have a better sensitivity and linearity compared with the pure PANI thin film sensors. When the ratio of PANI/zeolites is 15:1, the sensor shows the best humidity sensing performance. Then we measure hysteresis property, response and recovery property, stability and repeatability of composite films sensors. The sensor has good repeatability and short-term stability. The response time is 8s, the recovery time is 22s, the hysteresis is 5% RH.The sensitive thin film existing on the surface of interdigital electrode humidity sensor has the electrode reaction, which lead to the poor stability of sensor. The silicon bridge sensors have high linearity, repeatability, long-term stability and low power. Therefore, we prepare the different proportion of PANI/zeolites composite films sensors and pure PANI thin film sensors on silicon bridge. We measure and study the humidity properties of silicon bridge sensors. Comparing the output-humidity curves, we find that the best doping ratio is 10:1. The silicon bridge humidity sensors have good linearity, repeatability and long-term stability. The hysteresis is 3% RH, the response time is 17s, and the recovery time is 45s.Finally, we discussed and analyzed the mechanism that zeolites improve the performance of the sensors.