Synthesis, Modification And Gas Sensing Investigation Of Semiconductor Metal Oxide Nanomaterials

The rapid developments of nanotechnology and nanomaterials have profoundly improved human lives. Besides fabricating various nanomaterials with routine ways, it is of great importance in the development of nanoscience to explore and develop facile, efficient, economic, environmental-benign and novel paths to synthesize new nanostructured materials and exploit their new applications, which is also the crucial center in modern research of nanomaterials. This dissertation mainly focuses on preparing semiconductor metal oxide (SMO) micro/nanomaterials via different modulation methods, and obtains various gas sensing materials with high performance. We have systematically fabricated micro/nanomaterials with unique morphologies and structures, such as one-dimensional (1D),2D,3D, hierarchical, hollow and porous nanostructures. The composition adjustment has also been realized to get the hybrid micro/nanomaterials, such as multiple SMO-combined hybrids and noble metal (NM) nanoparticles (NPs) supported SMOs. The main research contents in this dissertation are summarized as follows:1. Porous a-Fe2O3hollow microspheres were synthesized through a simple and efficient carbon sphere template method. A series of characterizations have proved the porous and thin shells and large inner voids of the microspheres. Gas sensing test showed that the unique porous structures of a-Fe2O3hollow microspheres could remarkably enhance the sensor properties. Such work provides a new idea or pathway to develop high performance hollow and porous sensing materials for the detection of noxious gases.2. A simple low-temperature hydrothennal method without subsequent calcination was developed to successfully fabricate the unifonn1D ZnO nanorods with a high yield ratio of85%. Due to the unique electron transportation properties, lower tendency to agglomerate and large surface-to-volume ratio, which are favorable for gases to diffuse and transport on the surfaces,1D ZnO nanorods exhibited excellent ethanol sensing performnance, indicating their potential application as ethanol sensor. 3. A facile one-pot low-temperature hydrothermal strategy was introduced to synthesize the3D hierarchical SnO2nanoflowers(NFs) constructed by2D nanosheets. The morphologies of the3D hierarchical SnO2nanostructures can be tailored by rational modulating the molar ratio of OH-to Sn2+, reaction time and reaction temperature in the process of hydrothermal synthesis. The unique3D hierarchical structures of SnO2NFs supply large accessible surface area and commodious inter space to facilitate the gases pervasion and diffusion, thus speed up the gas sensing response. Such method also gives directions to prepare other advanced nanomaterials, which can also be expected to use in catalyst, dye-sensitive solar cell, Li ion battery and other fields.4. A two-stage solution process was proposed to adjust material compositions, and CuO NP decorated porous ZnO nanorods p-n hybrid nanomaterials have been synthesized. The synergetic effect between different components can modulate the electrons at the interface of p-n heterojunctions and increase the energy barrier height, so the hybrid materials combined with unique1D porous structure from ZnO nanorods exhibited excellent H2S sensing performance at low temperatures. This work also provides new foundation to fabricate different hybrid oxide sensing materials with high selectivity, response, stability and low working temperature.5. ZnO micro/nanomaterial supports with different morphologies were fabricated via a simple hydrothermal method, and then NMs were loaded onto the supports to form hybrid metal oxides through different composition adjustments, then their gas sensing properties were investigated:(1) A conventional ammonia hydrolysis-precipitation method was adopted to prepare Au/ZnO nanowires and their gas sensing performances were examined. The clear distribution of Au NPs on ZnO nanowires was firstly reported, and Au/ZnO nanowire sensor was firstly used to detect noxious gases like benzene and toluene, and exhibited enhanced responses and extremely high response-recovery speeds. The unique electron interaction and chemical effect of NMs, as well as the special morphologies of metal oxide supports can promote the sensor performances.(2) A one-pot hydrothermal method combined with subsequent calcination was used to fabricate2D ZnO porous microsheet supports, then the NM NPs were uniformly and in situ anchored on the surface of the supports via a simple lysine assisted one-pot strategy to obtain porous Au/ZnO microsheet hybrids, and the enhanced sensing properties were also got. This method is non-toxic, facile and environmental-friendly, which can control the NM size more efficiently compared with the conventional ammonia precipitation method. It’s universal to various supports and no pre-functionalization of the materials is needed. The preparation and loading of NM NPs were finished simultaneously, which greatly simplifies the synthesizing steps.