【作者】 许静；

【导师】 胡陈果；

【作者基本信息】 重庆大学 ， 凝聚态物理， 2011， 博士

【摘要】 我国钒的储量非常丰富,为了充分开发利用钒资源,对钒系化合物的合成、性质、反应机理及应用研究引起人们广泛的兴趣和重视。但是目前合成钒化合物的方法主要为固相反应法、气相沉积法和水热法等,尽管它们都具有自身的各种优点,但是大部分方法都存在一些明显缺点,如能耗高（高温高压）、设备昂贵、工艺复杂、产物纯度低、易粘结等。因此,探索新方法制备钒氧化物和钒复杂氧化物纳米结构并研究其光学性质,对充分开发利用钒资源、寻找新型钒基发光材料和高活性催化剂具有重要的意义。本文采用水热法、复合盐媒介法和复合氢氧化物媒介法制备出了不同形貌的V₃O₇·H₂O、V₃O₇、AgVO₃、Pb₅（VO₄）₃OH、Ba₃V₂O₈、NdVO₄的纳米晶和微晶,并对热性能、光电响应性能、磁性、发光性能和光催化性能等进行了研究。本文的主要研究内容包括:①采用复合盐媒介法合成了钒酸钕（NdVO₄）纳米线。该钒酸钕纳米线为四方相结构,直径约100nm、长约3μm,且多根纳米线以根部为中心连接在一起。NdVO₄纳米线对紫外光和可见光都有很强的吸收,从紫外到近红外区有四个很强的吸收峰。以罗丹明B为光催化降解对象,测定了NdVO₄纳米线的光催化活性,结果表明该纳米线具有很好的光催化活性。为了研究其光吸收性能和光催化机理,我们计算钒酸钕晶体的态密度。②采用复合氢氧化物媒介法（CHM）合成了钒酸铅（Pb₅（VO₄）₃OH）的微、纳米晶体。该晶体的形貌可通过反应时间和原料比调控,从相互分离的短棒转变为分支为短棒的束状晶体。紫外可见反射谱表明Pb₅（VO₄）₃OH晶体的带隙为2.92eV。本文测定了Pb₅（VO₄）₃OH晶体在10～300K温度范围内的发光性能,325nm光激发下该晶体在室温下能发出蓝光（430nm）,在低温下能发出较强的红光（623nm和672nm）。本文还讨论了Pb₅（VO₄）₃OH晶体的发光机理。③以V₂O₅和BaCl₂为前驱物采用复合氢氧化物媒介法在200℃下制备了钒酸钡纳米花。X射线衍射谱表明该纳米晶体由六方相的Ba₃V₂O₈和极少量四方相Ba₃VO_4.8共同组成。纳米花是由厚度小于20nm的纳米片组成。该纳米晶体的光学带隙有两个（3.85eV和3.12eV）。该纳米晶体在室温下能激发出可见光（492nm和525nm）,其发光性能主要与晶体中VO₄对称四面体有关。本文还测定了钒酸钡纳米花的磁性,晶体的饱和磁化强度为83.50×10^-3emu/g,,矫顽力为18.89Oe,剩磁为4.63×10^-3 emu/g。该晶体的磁性主要源于非钒酸盐氧化态V⁴⁺（S=1/2）。同时还合成了Eu³⁺掺杂钒酸钡纳米花,并研究了掺杂后纳米花的发光性能和磁性。④采用水热法合成了V₃O₇·H₂O纳米带,该纳米带为正交相单晶体,宽度约100～500nm,长达100μm。由V₃O₇·H₂O纳米带的热重分析可知,该晶体在400℃下退火能完全热分解为V₃O₇和H₂O。因而在氮气保护下400℃退火1h得到单斜相的V₃O₇纳米带。最后分别测定了V₃O₇·H₂O纳米和V₃O₇纳米带在不同光强和偏压下的光电响应性能,在光开关过程中能观察到快速的光电流响应,纳米带对光的响应是完全可逆的,而且V₃O₇纳米带的光电流强度明显高于V₃O₇·H₂O纳米带。⑤以钒片和硝酸银为前驱物经水热过程合成了Ag修饰的β-AgVO₃纳米线。该纳米线为单斜相,长度大于300μm、直径约200⁷00nm,表面吸附了少量的Ag纳米颗粒,β-AgVO₃纳米线的带隙为2.25eV。可见光激发下的光催化性能测定结果表明,Ag修饰的β-AgVO₃纳米线在150min内能够将罗丹明B有效降解64%以上。该纳米线具有较高的光催化活性,主要归功于纳米线中金属Ag和β-AgVO₃半导体的异质结构、高度结晶和对可见光有效的吸收。更多还原

【Abstract】 Since vanadium and vanadium oxide resource are rich in our contry, it is very important to effectively utilize vanadium resource, and explore vanadium oxide–dependent solid luminescent materials and highly active photocatalysts. Intensive investigation has been done including the exploration of preparation methods, properties, reaction mechanism and application of the vanadium oxides and vanadates crystal. Nowadays, the synthetic methods mainly include solid reaction process, vapor deposition process, hydrothermal method, etc. Although all these methods have their own advantages, most of them involve high vacuum, a high temperature, high pressure, high cost, complex process, or low purity, and so on. Therefore, developing new methods to synthesize vanadium oxide and vanadates nanocrystals is siginifiacant for fully utilization of vanadium resource.In the thesis, different morphology of V₃O₇·H₂O、V₃O₇、AgVO₃、Pb₅（VO₄）₃OH、Ba₃V₂O₈、NdVO₄ micro- and nano-crystals were synthesized by hydrothermal method, composite-hydroxide-mediated method and composite-salt-mediated method. And, their thermal, photoelectric, magnetic, luminescent and photocatalytic properties have been studied. The main contents can be summarized as follows:①The NdVO₄ nanowires were synthesized by a facile composite molten salt method. The XRD, SEM and HRTEM results show that NdVO₄ nanowires with tetragonal phase are connected together in bases, rooted in one center, and have typical diameter of 100 nm and length up to 3μm. The UV-vis spectrum shows that NdVO₄ nanwires have four strong absorption peaks from UV to near infrared region. The photocatalytical degradation of Rhodamine B dye and methyl orange under visible light irradiation using the NdVO₄ nanowiresis were investigated, which shows an excellent catalytic degradation activity to RhB and suggests its possible application in the organic pollutant treatment under visible light irradiation. The electron density states of the NdVO₄ were calculated with the Vienna ab initio simulation package, by which we can explain the light absorption and photodegradation properties.②Lead vanadium oxide hydroxide nano- and micro-crystals have been synthesized by a simple composite-hydroxide-mediated （CHM） method. The morphology of the product could be tuned from separate rods to rod bunches by simply controlling the reaction parameters. The UV-visible spectrum shows that the band gap of the Pb₅（VO₄）₃OH is 2.92 eV. The photoluminescence have been investigated in the temperature range 10-300 K. The results indicate a blue luminescence （430 nm） at room temperature and a strong red luminescence （623 nm and 672 nm） at low temperatures under excitation of 325 nm laser. The luminescent mechanism of the Pb5（VO4）3OH was discussed.③The flower-shaped barium vanadate has been obtained by the composite hydroxide mediated （CHM） method from V₂O₅ and BaCl₂ at 200℃for 13 h. XRD and XPS spectrum of the as-synthesized sample indicate it is hexagonal Ba₃V₂O₈ with small amount of Ba₃VO_4.8 coexistence. Scan electron microscope and transmission electron microscope display that the flower-shaped crystals are composed of nanosheets with thickness of ²0 nm. The UV-visible spectrum shows that the barium vanadate sample has two optical gaps （3.85 eV and 3.12 eV）. Photoluminescence spectrum of the barium vanadate flowers exhibits a visible light emission centered at 492 and 525 nm which might be attributed to VO4 tetrahedron with Td symmetry in Ba₃V₂O₈. The ferromagnetic behavior of the barium vanadate nanoflowers has been found with saturation magnetization of about 83.50×10^-3 emu/g, coercivity of 18.89 Oe and remnant magnetization of 4.63×10^-3 emu/g, which is mainly due to the presence of a non-orthovanadate phase with spin S=1/2. Meanwhile, Eu³⁺ doped barium vanadate nanoflowers were also synthesized by the same method, and luminescent and magnetic properties of doped barium vanadate were investigation at room temperature.④V₃O₇·H₂O nanobelts have been synthesized via a hydrothermal route. The synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The V₃O₇·H₂O nanobelts are of orthorhombic phase and single crystalline nanobelts with width of 100-500 nm and length up to 100μm. Thermogravimetry was used to determine thermal decomposition temperature of V₃O₇·H₂O nanobelts. Monoclinic V₃O₇ nanobelts could be obtained by thermal decomposition of V₃O₇·H₂O nanobelts at 400℃. Light sensitivity in exposure to a simulated sunlight in different intensity and biases have been investigated on the electrode made from the V₃O₇·H₂O and V₃O₇ nanobelts. The photocurrent responses of the V₃O₇·H₂O and V₃O₇ nanobelts are fully reversible and periodic. The results show that the photocurrent intensity of the V₃O₇ nanobelts is much larger than that of the V₃O₇·H₂O nanobelts.⑤Ag decoratedβ-AgVO3 nanowires were synthesized by the hydrothermal method. The synthesis yields nanowires with a monoclinic phase structure. Typical nanowires have diameter of about 200-700 nm and length up to 300μm with some Ag nanoparticles attached on their surface. Theβ-AgVO₃ nanowires have a band gap of 2.25 eV. Photocatalytic degradation of Rhodamine B dye is investigated. Under the visible light irradiation, about 64% of RhB can be effectively photodegraded by the catalysis of the Ag decoratedβ-AgVO₃ nanowires within 150 min. It is found that the Ag decoratedβ-AgVO₃ nanowires possess excellent catalytic degradation activity owing to its effective visible light absorption, heterojunction structure and well crystallization.更多还原