【作者】 王翠青；

【导师】 陈代荣；

【作者基本信息】 山东大学 ， 纳米材料化学， 2009， 博士

【摘要】 本论文主要采用液相化学法控制合成In₂O₃级次结构纳米材料,并探讨其形成机制及内在规律。分别从纳米结构材料的制备、形成机理以及性质表征几个方面进行论述,内容涉及水溶液体系中小分子结构导向剂辅助下In₂O₃级次纳米结构的制备、形成机制以及光学性质,溶剂热体系中In₂O₃级次纳米结构的制备、形成机制和光学性质以及低分子量聚合物辅助下In₂O₃中空球的控制合成、形成机制、光学性质等。全文旨在探索液相体系中级次纳米结构材料形成的内在机制,寻找构建级次纳米结构材料的更加有效的手段和途径。1.藕状In₂O₃级次纳米结构的制备、表征及光学性质以InCl₃·4H₂O、水、无水乙醇以及甲酰胺为原料,通过简单的溶液反应得到了具有级次结构的藕状In（OH）₃纳米结构,通过进一步煅烧制备了In₂O₃藕状纳米结构。透射电镜观察表明这种藕状In₂O₃纳米结构的藕节是由长度为50-90nm、直径为15-40nm的纳米棒构筑而成。将In（OH）₃级次纳米结构进行切片处理后通过HRTEM观察发现构成藕状In（OH）₃的初级结构单元是大小约为10nm的纳米颗粒,在界面上可以观察到位错的存在,但是从整体上看,颗粒间的晶格条纹是连续的,这表明纳米粒子是按特定晶面定向聚集的,也就是说这种纳米结构形成的机理是纳米粒子的晶面选择性聚集机制,与文献中所报道的定向聚集生长机理相吻合。为研究藕状In（OH）₃纳米结构的形成机理,我们利用XRD和TEM技术对其形成过程进行了跟踪。在实验基础上,提出了In（OH）₃级次纳米结构的形成机理。首先,由于高温下甲酰胺的分解,In³⁺水解形成无定形胶态纳米颗粒;然后所形成的纳米颗粒由于表面能较高而进一步聚集形成小的椭球形颗粒,同时,也伴随着从无定形到立方相In（OH）₃的相转变。随着反应的进行,溶液中的反应物逐渐消耗,晶粒继续生长,反应进行到30min时形成直径约为500nm的纺锤形聚集体,这是由于In（OH）₃晶体结构的各向异性而导致了晶粒的生长也表现出了各向异性。此时反应物已完全消耗,晶粒的生长几乎停止。然后,由于（110）面具有较大的表面能,所以颗粒沿着[110]方向定向聚集,最终形成了In（OH）₃藕状级次纳米结构。藕状In₂O₃纳米结构的光致发光光谱显示了特殊的以445,468,551,632nm为中心的可见光发射,这些发射可能与制备过程中所形成的缺陷有关。2.花状In₂O₃级次纳米结构的合成、表征、形成机理及光学性质以InCl₃·4H₂O、丙三醇、甲酰胺为原料,通过简单的溶剂热反应得到了一种具有级次结构的新型花状In-丙三醇前驱体。该前驱体由纳米片组成。XRD、FT-IR以及TG表征结果与文献中报道的Mn,Co-丙三醇盐类似。经过煅烧之后,这种In-丙三醇前驱体可以转变为立方相In₂O₃,形貌保持不变,HRTEM观察表明组成该花状结构的纳米片为单晶结构,其上下表面为{210}晶面。基于XRD、TEM以及元素分析的结果,我们提出了花状前驱体的形成机理。首先,在热处理的过程中,甲酰胺分解产生OH^-诱导形成In（OH）₃纳米颗粒,由于纳米颗粒具有高的表面能,因此形成的纳米颗粒进一步聚集形成球形聚集体。然后,In（OH）₃与丙三醇反应形成纳米片。但是,由于体系中存在少量水,对醇盐的形成具有抑制作用,而且反应温度较低,该反应不能进行彻底。最后,得到了结晶的花状In-丙三醇盐前驱体,但其中仍有部分羟基保留下来,进一步通过煅烧得到In₂O₃,并保持其形貌不变。这种独特的In₂O₃纳米结构具有独特的发光性质,它在可见光区域有一个以442nm（蓝色）为中心的强发射峰,并在468nm（蓝色）和524nm（黄色）处存在两个肩峰,该发射峰及其肩峰应归因于光子激发的空穴和占据氧空位的电子的复合。3.低分子量聚乙二醇辅助下In₂O₃复合纳米空心球的合成、表征以及光学性质以In（NO₃）₃·4H₂O、PEG400、尿素为原料通过简单的溶剂热反应制备了具有介孔壳壁的In₂O₃/PEG400复合空心纳米结构,空心球由纳米晶聚集而成,壳壁厚度在10-20nm间。高分辨电镜观察表明空心球是由粒径约7nm的纳米颗粒构成,纳米颗粒之间存在纳米级孔洞。另外我们可以清晰地观察到单个空心球某些特定区域的晶格条纹,从整体上看,颗粒中的晶格条纹是连续的,但纳米粒子的轮廓仍可以清晰辨认,这表明纳米粒子是按特定晶面定向聚集的,也就是说这种空心结构形成的机理是纳米粒子的晶面选择性聚集机制。产物的N₂吸附-脱附等温线表现为带有滞后环的Ⅳ型吸附等温线,并出现比较明显的滞后环,说明产物具有介孔结构。样品的BJH孔径分布曲线表明产物孔径主要分布在3～10nm之间,集中于3.4nm处,与HR-TEM观察的结果基本吻合。样品的孔体积为0.19cm³/g,BET比表面积为94.1 m²/g。与文献报道的块体In₂O₃相比,这种具有介孔壳壁的In₂O₃/PEG400纳米空心球在330nm处的紫外吸收发生了大幅度的蓝移,这可能是由弱的量子限域效应导致的。另外该In₂O₃/PEG400纳米空心球还表现出特殊的光致发光特性,在461、538以及620nm处均有发射。我们推测这种特殊的光学性质可能与其空心结构或无机-有机复合结构有关。更多还原

【Abstract】 The controlled synthesis of indium oxide hierarchical nanostructures through liquid-phase chemical route is investigated in this thesis.The controlled synthesis,formation mechanism,and properties are investigated in detail.The thesis mainly focuses on the preparation,formation mechanism and photoluminescence properties of hierarchical nanostructured indium oxide obtained by simple solution method,which mainly includes the lotus-root-like In₂O₃ nanostructure from the aqueous solution route,the flower-like In₂O₃ nanostructure from a novel solvothermal indium precursor,and the In₂O₃/PEG400 hollow sphere from the solvothermal synthesis.This aims to study the intrinsic formation mechanism of hierarchical nanostructures in solution route and find the more effective strategy to fabricate novel nanostructures.1.Lotus-Root-Like In₂O₃ Nanostructures:Fabrication,Characterization,and Photoluminescence PropertiesNovel lotus-root-like In₂O₃ nanostructures with a diameter of ca.300 nm and a length of 1.5-4.0μm have been prepared by annealing In（OH）₃ nanostructures with the same morphology derived from a mild solution reaction.The hierarchical nanostructures are composed of several segments aggregated orderly from In₂O₃ nanorods with the length of 50-90 nm and diameter of 15-40 nm.The segments of the lotus-root-like In（OH）₃ nanostructures are composed of nanoparticles with the size of ca.10 nm and a small misorientation exists at the interface although the planar fringes are ordered in the particles,which implies an oriented aggregation growth mechanism.To track the fabrication process of lotus-root-like In（OH）₃ nanostructures, a detailed time course was studied.On the basis of the experimental results, the formation process of In（OH）₃ nanostructures was proposed.In the initial stages,when the solution was heated,the In³⁺ cations hydrolyzed to form the colloid particles due to the decomposition of formide at high temperature,and the as-formed amorphous nanoparticles subsequently aggregated to small elliptical particles to minimize their surface energy,which can be revealed by the HRTEM observation.At the same time,the transformation from the amorphous particles to cubic In（OH）₃ occurred.With the reaction proceeding, grain growth was carried out with the consumption of the reactants in the solution,the particles became larger and larger,and the spindles with the size of 500 nm were formed after the reaction was conducted for 30 min.At this stage,the grain growth exhibited anisotropy due to the anisotropy of the In（OH）₃ crystallographic structure.When the reactants were consumed completely,the grain growth almost stopped.Then the oriented aggregation along[110]direction started due to the large surface energy of（110） planes. As a result,the lotus root-like In（OH）₃ nanostructures were formed,which can be transformed to In₂O₃ nanostructures by calcination without changing the morphology of the nanostructures.The PL spectrum of In₂O₃ nanostructures at room temperature exhibits three peaks centered at 468,551,632 nm and a shoulder at 445 nm in the visible light region.These emissions may be related to the defect produced during the preparation process.2.Flower-like In₂O₃ Nanostructures Derived from Novel Precursor:Synthesis, Characterization and Formation MechanismThree-dimensional flower-like In precursor nanostructures were fabricated by glycerol-mediated solvothermal reaction using InCl₃·4H₂O and formide as reagents.The precursor composed of nanosheet and the corresponding XRD, FT-IR,TG is similar to the reported Co,Mn-based glycerol.And the as-formed indium precursor could be transformed to cubic In₂O₃ maintaining its original flower-like morphology after calcination.HR-TEM image of a nanoplate at the edge of the In₂O₃ flower-like nanostructure shows the continuous lattice fringes in the visible range,indicating its single crystalline nature with the dominated surface of {210}.To track the formation process of the precursor,TEM,FE-SEM,XRD and elemental analysis techniques were applied to investigate the samples collected at different reaction times.At first,the In（OH）₃ nanoparticles were formed due to the decomposition of formide during the heat-treatment,which aggregated to large spheres due to the high surface energy of the nanoparticles. The decomposition of formide was slow due to the small amount of water in the system,which further led to a slow formation rate of In（OH）₃ as well as the following aggregation.Then,the In（OH）₃ reacted with glycerol by replacing the hydroxyls in In（OH）₃ to form the nanoplates.However,this reaction could not carry out thoroughly because the presence of water in the system and a relatively low temperature.Finally,the crystalline flower-like In-glycerol complex precursor was formed,which can easily transforms to In₂O₃ without changing the morphology during calcination.The room temperature PL spectrum of flower-like In₂O₃ nanostructure exhibits a strong emission centered at 442 nm with two shoulders at 468 and 524 nm,as well as a weak peak at 627 nm in the range of visible light region. The emission at 442 nm and the shoulders can be attributed to the radioactive recombination of a photoexcited hole with an electron occupying the oxygen vacancies,while the emission at 627 nm may result from the Raman scattering.3.PEG-Assisted Synthesis of Nanosized In₂O₃ Hollow Structures and Their Optical PropertiesThe nanosized In₂O₃/PEG400 composite hollow spheres（70-100 nm in diameter） with mesoporous shells of 10-20 nm were synthesized by a poly（ethylene glycol）（PEG）-assisted solvothermal method using In（NO₃）₃·4H₂O and urea as reactants.The HR-TEM image shows that the hollow spheres aggregated orderly from In₂O₃ nanocrystals with the diameter of 7 nm.The continuous lattice fringes confirm the oriented-aggregation of the nanocrystals,although the interface between the particles can be clearly observed.The N₂ adsorption-desorption isotherms of the hollow spheres exhibit the typeⅣadsorption isotherm and a hysteresis loop in the relative pressure range of 0.4-1.0,indicating the presence of the inhomogeneous mesopores, which are formed through the aggregation of the nanocrystals.The corresponding pore size distribution curve calculated from the desorption branch by the BJH method displays a pore size distribution from 3 to 10 nm, centered at ca.3.4 nm,which is close to the result from the TEM images.The calculated pore volume is 0.19 cm³/g,and the specific surface area is 94.1 m²/g by the BET method.The UV-visible absorption spectrum of this novel In₂O₃/PEG400 nanosized hollow spheres shows absorptions at 310 nm.The absorption shows obvious blue shift compared to the absorption at 330 nm of bulk In₂O₃,which arises from the weak quantum confinement effect.The room temperature PL spectrum of In₂O₃/PEG400 nanosized hollow spheres exhibits emissions centered at 461,538 and 620 nm.It is speculated that the novel emissions are related to the defect produced during the preparation process and also relate to the hollow organic/inorganic composite nanostructure.更多还原