Preparation And Characteristics Research Of Graphene-Metal Oxide Gas Sensing Materials

As a novel gas-sensing material, graphene has the advantages such as good electrical characteristics, high sensitivity and low detection limit for the gas molecules detection. However, the single graphene-based gas sensor shows the slow adsorption/ disadsorption rate and poor selectivity. The sensing properties of graphene based gas sensor could be improved by combining pure graphene and other functional gas sensing materials. In this dissertation, the micro- interdigital electrodes(IDEs) was used as the sensing device, and the resistive ammonia(NH3) gas sensor was developed with reduced graphene oxide(rGO) and metal oxide nano materials composites. The prepared composite films were characterized and analyzed, and ammonia-sensing characteristics were systematically measured. Furthermore, the gas sensing mechanism model was established. This paper mainly includes the following two aspects of work:1. Zinc Oxide/reduced graphene oxide(ZnO/rGO) bilayer film was prepared by combining the spray process with thermal reduction process. The ammonia-sensing properties of sensors were investigated at room temperature, and the spray amount of graphene oxide(GO) was optimized. UV-Vis absorption spectra and X-ray photoelectron spectroscope(XPS) analyses showed that GO was partially reduced to r GO. The sensing characteristics results showed that ZnO/rGO bilayer film exhibited higher sensitivity and faster response-recovery; ZnO/rGO bilayer film sensor possesses optimal sensing performance when the spray amount of GO was 1.5 ml. Meanwhile, the sensor showed good reversibility, repeatability and selectivity to NH3 while humidity had a great influence on gas sensing properties. The P-N heterojunction mechanism model of ZnO/rGO bilayer film sensor was established, the remarkably enhanced NH3-sensing characteristics were speculated to be attributed to both supporting role of ZnO nanoparticles and P-N heterojunction at the interface between ZnO and rGO.2. TiO2/rGO composites were prepared by hydrothermal method using titanium tetraisopropoxide and GO as raw materials. Then the composite sensitive films were prepared on IDEs by spraying process and preliminary characterize and gas sensing analysis of composite film were carried out. UV-Vis absorption spectra and infrared spectra showed obvious interface interaction between TiO2 nanoparticles and rGO sheets. The morphology analysis showed that the prepared TiO2 exhibited nano-particles. The gas-sensing properties results indicated that, compared to the pure rGO-based sensor, the TiO2-rGO film sensor exhibited higher sensitivity and better recovery and repeatability. Besides, The sensor has good linearity for 10-50 ppm ammonia and selectivity. The ammonia-sensitive response mechanism model of TiO2-rGO composite film was initially established. The model revealed that TiO2 nanoparticles played a role as catalytically active centers which can effectively reduce the energy barrier between ammonia molecules and rGO, and thus improve the gas-sensing characteristics of single graphene.