Synthesis Of Porous Zinc Oxide Nanocomposites And Its Application In Gas Sensing

Zinc oxide (ZnO) is an important n-type semiconductor sensing material. Currently, much attention has been attracted to finding an effective method to prepare ZnO nanomaterials with high sensing sensitivity and excellent selectivity. Composition and structure of nanomaterials are important factors that affect the sensing properties. Trivalent Indium (In) doping in the ZnO will contribute free electron. Gold (Au) nanoparticles loaded in the ZnO act as catalyst for electron transfer. A three dimensionally ordered macroporous (3DOM) nanostructure provides many active sites due to its well-developed pore structure and large surface area. Up till now, in gas sensing field, there are many researches discussing about metal-doped or noble metal-loaded ZnO nanomaterials. However, the study focus on In-doped ZnO with Au-loaded nanocomposites is rarely reported, and the 3DOM ZnO nanocomposites have not been noticed. In this work, In-doped 3DOM ZnO and In-doped 3DOM ZnO with Au loaded nanocomposites have been synthesized successfully. In addition, the relevance between composition and structure of nanomaterials and sensing property has been explored deeply. The specific contents are summarized as follows:1. In-doped 3DOM ZnO samples were prepared, and the influence of different In-doping concentrations on the gas sensing properties of the 3DOM ZnO was explored. Our experimental results indicated that appropriate In doping concentration remarkably improved sensing sensitivity and selectivity. The 3DOM ZnO with 5 at.% of In-doping exhibited the highest sensitivity (?88) to 100 ppm ethanol at 250?, which was approximately 3 times higher than that of pure 3DOM ZnO. The results of SEM, HRTEM and nitrogen adsorption-desorption characterizations showed that the 3DOM structure has a large amount of active sites due to its well-developed pore structure and large surface, which leads to an enhancement of the gas sensitivity. Characterizations of XRD, Raman, Hall, and XPS were used to analyse the sensing mechanisms of the products. When the In concentration is below 5 at.%, the electron carrier concentration increases gradually, leading to increase of the amount of adsorbed oxygen, which results in an enhancement of the gas sensitivity. When the In concentration is over 5 at.%, the electron carrier concentration decreases gradually, which probably due to the poor crystallinity.2. In-doped 3DOM ZnO with Au loaded nanocomposites have been prepared using a simple one-step colloidal crystal-templating method. This method has the advantages of simple operation, low cost, high production efficiency, green non-pollution, so it is suitable for industrial production. The results of sensing tests showed that when the In doping concentration was 5 at.% and the Au loading concentration was 0.05 at.%, the sensitivity of the nanocomposite reached a maximum of 240 to 100 ppm ethanol at an operating temperature of 250?, that was greatly increased. The material modification has been achieved successfully. The gas sensing mechanism of the nanocomposites has been explored and the analysis results demonstrated that the moderate doping of In effectively increased electron carrier concentration, and the moderate loading of Au effectively enhanced the electron carrier mobility, and their synergism increased the adsorbed oxygen, which is helpful to improving the gas sensitivity.