| With the development of industry and increase of automobiles, various toxic gases are increasingly released into the air, resulting in serious environmental pollution. It is important and urgent to develop semiconductor gas sensors with excellent sensing performance for the monitoring and controlling of air quality. On the other hand, the use of semiconductor photocatalysts and solar cells has attracted considerable attention for water purification and solar energy usage. One-dimensional (ID) molybdenum trioxide (MoO3)has show wide applications in many fields including energy storage, gas sensors, and photochromic and electrochromic devices. However, the synthetic strategies of high-quality MoO3 nanostructures are relatively rare. It is highly desirable to develop economic methods for large-scale preparation of MoO3 with different morphologies. Therefore, this thesis focuses on the synthesis of 1D MoO3 and the effect of synthetic methods on the morphology and properties of MoO3. The main results obtained in this work are listed in the following:1. Orthorhombic α-MoO3 nanorods with aspect ratio of nearly 40 was synthesized by a facile and fast chemical method under 85℃. The effect of stirring time, thermostatic aged time and HNO3 amount on product morphology was studied in detail. The obtained α-MoO3 nanorods exhibited the highest response of 321 to 40 ppm CO at operating temperature of 292℃. The MoO3 nanorods exhibits high sensitivity to CO and is not interfered by CH4, which makes the kind of material a competitive candidate for CO detection.2. 1D α-MoO3 with aspect ratio over 20 was successfully synthesized using a facile hydrothermal process with the assist of CTAB which acts the structure-directing agent to control the directed growth of the crystals. The synthesized process and mechanism is described in detail. The structure and morphology of the products are strongly dependent on the acidity of solution, and the temperature and time of hydrothermal reaction. The obtained MoO3 nanorods exhibited response of 37,21 and 15 to 10 ppm NO2, CO and CH4, respectively. The sensing performance is attributed to the intrinsic non-stoichiometry of the a-MoO3 due to the presence of Mo5+ in MoO3 lattice, which was confirmed by XPS and room temperature PL spectra.3. Hexagonal h-MoO3 nanorods with aspect ratio of 25 and 10 were successfully synthesized by CTAB-assited nomal ultrasonic approach and SDS-assited probe ultrasonic approach, respectively. The morphology, crystal structure and phase transformation of obtained nanorods were characterized by FESEM, XRD and DTA. Results showed that the phase transformation leading to the formation of orthorhombic structure (α-MoO3) at 436℃. The influence of synthetic methods on sample morphology was investigated in detail, and a possible growth mechanism of the MoO3 nanorods was also proposed. The sensing tests indicate that the NO2 response of MoO3 nanorods synthesized by probe ultrasonic approach (103) is much higher than that of nanorods synthesized by probe ultrasonic approach (79).4. Based on energy band engineering, Fe2(MoO4)3@a-MoO3 and MoO3/TiO2 composite photocatalysts with different compositions were prepared. Results show that the Fe2(MoO4)3@a-MoO3 improved the photocatalytic degradation of AO II by 50%under visible light irradiation, and the rate constant of MoO3/TiO2 for visible-light-driven photocatalytic degradation of Rhodamine B (RhB) was approximately 2 times of TiO2-It has been demonstrated that the photocatalytic activity of composites depends on the composition and annealing temperature of composites, and the degradation conditions of dye. The improvement of photocatalytic activity can be attributed to the lower electron-hole recombination rate due to the formation of heterostructures.5. The h-MoO3 nanobclts were prepared by hydrothermal process using molybdenum powder as raw material. The product was applied to dye-sensitized solar cells (DSSCs) for the first time to examine the photoelectric conversion efficiency. The experimental results indicate that the conversion efficiency was enhanced by doping of Fe, Co and Ni element. Among them,5wt% Fe-doped MoO3 nanobelts exhibit significant enhancement of conversion efficiency from 0.18% to 0.95%. The primary results show that the MoO3 doped with different elements may be developed as a promising photoelectrode material for high-efficiency DSSCs and other photoenergy conversion devices.Overall, 1D MoO3 nanostructures with different aspect ratio were synthesized by various methods, and the gas-sensing, photocatalytic and photochemical performance of 1D MoO3 was explored. The encouraging results suggest that the MoO3 as the promising functionary materials with widely applications in gas sensors, photocatalysts and DSSCs. |
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