Template Synthesis Of Porous ZnO Nanostructures And Their Gas Sensing Properties

Recently èhierarchically self-assembled3D ZnO constructed using1D and2DZnO nanoscale building blocks have attracted intensive attention because the structureis often associated with large speci c surface area and and facile mass transport inmaterials, leading to enhanced properties for applications like gas sensors, lithium-ionbattery, photocatalysts, solar cells and water treatment in comparison withconventional nanocrystallites. In this thesis èthree-dimensional flower-like ZnOhierarchical nanostructures were fabricated by using block copolymer F127andsodium dodecyl sulfate (SDS) as structure-directing agents, respectively, and weproposed a surfactant-self-assembly and transformation mechanism of porous ZnOhierarchical nanostructures. Their optical properties and gas sensing properties werealso studied. The main contents are as follows:In the first part èthree-dimensional flower-like ZnO hierarchical nanostructureswere fabricated from the thermal-decomposition of3D zinc hydroxide carbonateprecursor, which were synthesized by an urea hydrothermal method with blockcopolymer F127(EO106-PO70-EO106) as the morphology director. XRD, IR, UV-vis,SEM, TEM, TG and N2adsorption-desorption isotherms have been employed tocharacterize the products. The in àuences of the synthesis parameters such as thereaction time, the type of the zinc sources, and species concentration on themorphologies of the products were systematically studied. On the basis ofexperimental results, a possible formation mechanism of the3D flower-like ZnOhierarchical nanostructures was discussed. More importantly, the gas sensing testsindicated that the sensor made from porous ZnO hierarchical nanostructures exhibitedbetter gas sensitivity and selectivity to n-butanol compared with the sensor based onthe commercial ZnO nanoparticles. The enhancement in gas sensing properties wasattributed to their unique3D hierarchical nanostructures and high surface areas.In the second part, three-dimensional porous ZnO nanostructures were fabricatedby calcining a layered precursor of zinc hydroxide carbonate (ZHC), which weresynthesized by an urea hydrothermal method with sodium dodecyl sulfate (SDS) as the structure-directing agent. X-ray diffraction (XRD) and scanning electronmicroscopy (SEM) were used to characterize the ZHC precursors and porous ZnOnanostructures. It was observed that the experimental parameters such as theconcentration of the urea and surfactants determined the nal morphology. On thebasis of experimental results, a possible mechanism for the formation of the3D ZnOnanostructure was speculated. Gas sensing tests showed that the sensor using theporous ZnO nanostructures exhibited good gas sensing properties to higher alcoholssuch as n-butanol and isopropanol.From the above researches, the author have known more about porous ZnOnanomaterials including synthesis mechanisms, preparation methods and theirinfluencing factors, as well as the correlative theorie.