| This paper includes two parts:the fabrication and characterization of In2O3nanostructures and CeO2nanostructures.This paper focused on controlled synthesis of In2O3nanostructures and CeO2nanostructures including the nanorods, nanospheres, nanocages and hollow spindle-like nanostructures (HSNs) via the liquid-phase chemistry routes. The investigations are based on three aspects:controlled synthesis, formation mechanism, and properties. The contents mainly include the phase-controlled synthesis of stable cubic In2O3and metastable corundum-type In2O3via the an organic acid-assisted hydrothermal process, solvothermal synthesis of In(OH)3nanorods and their conversion to In2O3, novel Zn-doped In2O3nanostructures via a facile template-free hydrothermal method and their gas-sensing properties, synthesis of Ce1-xCuxO2nanospheres and their enhanced catalytic performance to CO, intending to study the intrinsic controlling mechanism of the nanostructure formation and find the suitable synthesis method.The detailed information of the paper is listed as follows:1. The synthesis of the novel In2O3nanorods through the facile solvothermal method.After the dissolving the In(NO3)3.4.5H2O in the mixture of H2O and CH3CH2OH, the acrylamide was added into the mixture, then all the chemicals were transferred to the25ml autoclave which was then heated at180℃for8h. The product were the monodispersed and uniform In(OH)3nanorods and the In2O3nanorods were obtained from In(OH)3via calcination in a boat crucible at500℃for3h under air. The nanorods (length of200nm and width of70nm) were made of nanowires with length of200nm and width of10nm. The in situ growth mechanisms-oriented aggregation for the formation of regular nanorods are proposed based on detailed evidences of morphological evolutions with reaction time. Besides, the ratio between H2O and CH3CH2OH is very important for the morphology of the final products. 2. Phase-controlled synthesis of monodispersed porous In2O3nanospheres and their PL properties.Phase-pure porous nanospheres, both In(OH)3and InOOH, have been prepared through a facile hydrothermal method using different organic acids as the assistant agents. The organic acids play an important role in the phase change, and the phase composition of the precursors could be deliberately controlled by adjusting the organic acid (citric acid or tartaric acid). Cubic and hexagonal In2O3monodispersed nanospheres with porosity can be obtained from In(OH)3and InOOH, respectively, while size and morphology can be maintained to a certain extent. The as-synthesized porous In2O3nanospheres are composed of numerous small nanocrystallites and possess good size uniformity. Influencing factors such as the reaction time and the type and amount of organic acids were systematically investigated. The XRD patterns and FT-IR spectrum indicates that tartaric acid is extremely critical for the formation of InOOH. The tartaric acid is the coordinating agent in the system. The system without or with a shortage of tartaric acid leads to In(OH)3or a mixture of In(OH)3and InOOH, otherwise, InOOH is the only product. However, ethylenediamine always acts as a coordinating agent in the system with the addition of citric acid and also provides an alkaline media for the In3+cations, which facilitates the hydrolysis of In3+to form In(OH)3. A possible ethylenediamine or tartaric acid coordinated mechanism of the phase-control synthesis of In2O3was proposed based on the experimental results.Furthermore, the potentialities of the porous InO3nanospheres were also studied by room-temperature photoluminescence (PL) spectroscopy. PL peaks in the visible region, located at465nm (blue),550nm (green), and680nm (red) with the excitation wave of260nm were observed in the photoluminescence spectra which results from the existence of oxygen vacancies. These oxygen vacancies normally act as deep defect donors in semiconductors and would induce the formation of new energy levels in the band gap. The emission thus results from the radioactive recombination of a photoexcited holes and electrons occupying the oxygen vacancies. 3. Zn-doped In2O3nanostructures:preparation, structure and gas-sensing properties. Novel Zn-doped In2O3nanocages and hollow spindle-like nanostructures (HSNs) have been prepared by calcining precursors obtained via a facile template-free hydrothermal method. The change in morphology, size, and phase compositions in a controlled synthesis of the Zn-doped In2O3nanostructures are achieved by simple adjustments of the amount of water. The result of this formation mechanism investigation reveals that the amount of water and the reaction time make significant contributions to the growth of Zn-doped In2O3nanostructures. The driving forces for the formation of the nanostructures are the precipitation-dissolution-renucleation-growth and Ostwald ripening processes based on time-dependent experimental results. The gas-sensing properties of Zn-doped In2O3nanocages and HSNs have shown high sensitivity toward formaldehyde (HCHO) vapor at a relatively low operating temperature. Note that the gas sensor fabricated with Zn-doped In2O3HSNs exhibit a higher and faster response than those fabricated with Zn-doped In2O3nanocages due to the larger surface area and the decreasing size of the particle.4. Facile synthesis of Ce1-xCuxO2nanospheres:structural studies and enhanced catalytic performance.The Cu-doped CeO2-CuO nanospheres were obtained by two steps:the Cu-doped CeO2nanospheres were synthesized by hydrothermal method and then were calcined with Cu(NO3)3solution to obtained Cu-doped CeO2-CuO. The XRD of the final products showed the typical peaks of CeO2and CuO. The morphology of the product before and after the calcination did not change a lot. The crystalline lattice of CuO can be found in the HRTEM of the Cu-doped CeO2-CuO nanospheres and no other products except nanospheres can be seen, which means that the CuO has coated on the CeO2nanospheres. The result of the XPS shows the existence of Ce3+/Ce4+which facilitates the conversion of CO into CO2. The CeO2contacting with Cu2+facilitates the formation of Cu+due to its redox process of Ce4+/Ce3+which could transfer electrons to Cu2+resulting in formation of Cu+,thus enhancing the adsorption of CO to form Cu-carbonyl species. Such synergistic redox properties are produced by the formation of CuO-CeO2interfacial sites. Besides, CeO2serves as an oxygen supplier through either the formation of superoxide species (O2) by gas phase oxygen reacting with oxygen vacancies on its surface or the direct involvement of lattice oxygen. Furthermore, the oxygen vacancies are easily formed in the CeO2support due to its high oxygen mobility, and the oxygen vacancies, even in small amounts, seem to favor activity. Therefore, oxygen vacancies play an important role in the reaction since they provide sites for oxygen activation to form superoxide (O2-), which was considered as the intermediate species in the oxidative reactions occurring on the catalyst surface. The best Ce1-xCuxO2nanospheres were got by changing the CuO amount and calcination condition. And compared with the commercial CeO2, the obtained Ce1-xCuxO2nanospheres showed an enhanced catalytic performance and the CO can be totally transformed into CO2at140"C... |
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