【作者】 王乐；

【导师】 钱逸泰； 占金华；

【作者基本信息】 山东大学 ， 无机化学， 2009， 博士

【摘要】 本论文主要致力于选择合适的生长条件与生长方式,以及研究不同固体材料的结构与功能特性来实现对半导体纳米结构的功能化组装,获得了一系列高质量的多功能化纳米结构单元,系统研究了功能组合的化学基础以及功能化纳米结构单元的物理化学性质,如磁学性质、光学性质以及可见光催化性能等,结果表明功能组装可以有效改善或改变纳米结构的物理、化学、机械性能或产生新的功能。具体归纳如下:1.一维CdS-Ni半导体-磁性功能复合纳米材料选择功能性强、应用广泛的半导体纳米结构作为研究对象。在合成高质量的CdS纳米线的基础上,利用水合肼诱导的溶液化学还原法得到的镍金属纳米颗粒对其进行磁性修饰,成功制备了一维CdS-Ni半导体-磁性复合纳米材料,研究了复合结构的生长过程和可能的形成机理。经过研究,我们发现在该实验条件下,Ni²⁺在CdS纳米线表面可以快速地进行离子交换反应生成厚度为5 nm左右的NiS壳层,该过程是动力学驱动的离子转换反应。我们在不添加N₂H₄·H₂O和NaOH溶液的条件下进行了对比试验,得到了一维CdS@NiS核/壳复合结构从而证明了该过程的发生。在我们的实验体系里,乙二醇（EG）起着至关重要的作用,它可以与CdS纳米线外层的Cd²⁺离子和溶液中的Ni²⁺离子螯合形成中间配合物从而促进离子转换过程的进行。值得指出的是,在加热的条件下离子转换反应进行地非常快,反应进行10分钟后（添加或不添加N₂H₄·H₂O和NaOH）我们只得到一维CdS@NiS核/壳复合结构。反应时间延长,NiS壳层逐渐变厚至一定的程度后达到一个平衡,即使反应时间延长至24小时也没有明显变化,这是由于壳层的形成可以阻止溶液中Ni²⁺离子与CdS进一步接触。阳离子转换反应的进行破坏了阴离子晶体格子排布的规整性,由此产生的晶体缺陷为溶液中的Ni²⁺发生氧化还原反应提供了结晶成核的位置,因而,NiS壳层的形成有利于Ni纳米颗粒在纳米线表面的沉积和非外延生长。延长反应时间,Ni纳米颗粒可能经历一个聚集驱动的形貌转化过程,趋向于生长成较大的颗粒,由于六方相CdS本身具有六方截面的结构特性,Ni颗粒甚至可以围绕CdS的六方截面生长成一个环。所得复合纳米材料的磁性在室温下进行了测定,结果显示Ni组份的铁磁性质在复合结构中得以保留。与Ni纳米颗粒或体相材料相比,复合纳米结构材料表现出明显减小的Ms和增强的Hc。通过对一维半导体CdS纳米结构进行磁性修饰,我们可以利用磁场方便地对其方向和位置进行操纵,可以解决纳米材料难以回收等难题,在实际应用方面具有特别重要的意义。2.外延、非外延生长制备一维CdS/α-Fe₂O₃、CdS/Fe₃O₄异质、功能组合纳米材料我们以Fe（NO₃）₃·9H₂O为原料,通过溶剂热反应,将准立方形α-Fe₂O₃纳米粒子修饰到CdS纳米线表面,制备了一维CdS/α-Fe₂O₃半导体异质复合纳米材料。通过分析,我们发现两种半导体单晶组分之间具有清晰而且连续的界面,表明新化学键的形成。通过两种化合物的模拟ED衍射花样和晶体结构模型进一步研究了它们的晶体结构相关性和晶格匹配程度,对α-Fe₂O₃纳米颗粒围绕CdS纳米线的取向外延生长方式给予了合理的解释和说明,为对称性不同或晶格不匹配的纳米组份构建异质结构材料具有指导意义。有趣的是,经过深入观察我们甚至发现在CdS的同一晶面上生长的α-Fe₂O₃纳米颗粒具有相同的形貌和生长取向。探究了半导体复合纳米材料可见光催化降解污染物的性能,由于两种半导体导带能级的差异,CdS经光照后的光生载流子能够运输到其表面的Fe₂O₃上面。半导体Fe₂O₃对CdS纳米线的表面修饰能够起到促进CdS光生电子和空穴分离的作用,从而表现出优异的可见光催化性能。以FeCl₃·6H₂O为原料,通过溶剂热反应,将磁性Fe₃O₄微球修饰到CdS纳米线表面得到一维CdS/Fe₃O₄半导体-磁性功能复合纳米材料。分析发现表面粗糙的磁性微球是由许多小Fe₃O₄纳米粒子组装而成,整体表现为多晶态,其具有与Ni纳米颗粒相似的沉积成核和非外延生长行为。实验结果表明S^2-与Fe³⁺(或Fe²⁺)之间存在着强作用力,S^2-在外延、非外延生长合成异质结构的过程中起着非常关键的作用。我们探究了一维CdS/Fe₃O₄半导体-磁性功能复合纳米材料的光学、磁学性质及其可见光催化性能,CdS的荧光行为和Fe₃O₄的铁磁性质在复合结构中均得以保留,而且CdS的可见光催化性能亦未受到明显的影响。总之,我们的研究结果表明,将铁磁性或半导体组份与一维半导体结构进行组合,可以提高、改良半导体纳米结构性能或者产生新的功能,在纳米科技领域具有潜在的应用价值。3.基于一维CdS纳米结构的核壳型复合半导体的制备及其光催化性能研究以醋酸锌和硫脲为原料,无需任何预处理或者表面修饰,通过溶剂热反应直接将一层ZnS均匀沉积到CdS纳米线表面得到一维CdS@ZnS核-壳结构复合半导体。经过观察我们发现表面不平滑的ZnS壳层是由粒径为4 nm左右的ZnS纳米颗粒沿CdS纳米线表面生长形成的,其厚度在5～10 nm之间,CdS纳米线核的直径未发生明显变化。研究了反应条件对最终产物形貌的影响,发现溶剂对于核-壳复合结构的形成起着非常重要的作用;提高体系的反应温度,CdS表面的ZnS纳米颗粒具有较大的粒径尺寸,因而ZnS壳层变厚。宽带隙半导体ZnS对窄带隙CdS的修饰可以有效地钝化其表面电子态、抑制电子空穴复合,从而改善了材料的光学性质,发光强度有很大提高。复合材料可见光催化降解亚甲基蓝（MS）和对氯苯酚（4-CP）废水溶液性能的提高,亦证明了ZnS壳层对CdS纳米线核表面电子态的有效钝化作用。近年来,人们已经成功地将CdS纳米结构与多种半导体材料进行多种方式的组合,以提高其光效率。可是,既具有高的光催化效率,又能提高CdS热、机械或化学稳定性的半导体组合方式却鲜有报道。我们利用TBT的缓慢均匀水解反应对CdS纳米线进行包覆,500℃退火后成功合成了一维CdS@TiO₂纳米电缆。研究发现TiO₂壳层的存在既可以提高CdS纳米线的热稳定性,又有助于CdS光生电子-空穴的快速分离,从而能提高其光催化性能,在实际应用方面具有特别重要的意义。4.新型Bi-Ca-O体系可见光催化剂的制备及性能研究目前,提高半导体纳米结构光催化材料的可见光利用率及光催化效率,寻找新型、高效光催化剂已经成为一个新的研究热点。结合前几章的研究思路:功能复合能够有效地提高或者改良半导体纳米结构的性能。我们用聚合物配位与共沉淀相结合的方法,通过控制退火温度得到了一系列新型的纯相和复合相Bi-Ca-O系可见光光催化材料,并对其光学性质和可见光（λ＞420 nm）范围内的光催化性能进行了探究。更多还原

【Abstract】 In this dissertation,various chemical methods are explored to realize the functional-assembly of semiconductor-based nanostructures and modulate novel properties,accompanied by understanding the structural and functional correlations of separate constituents.A series of multi-functional nanosructure unit are successfully synthesized,and their physical or chemical properties are systematically studied,such as magnetic,optical properties and photocatalytic activities.Further study shows that the chemical,physical or mechanical properties of theses chemically distinct heterostructures have been largely enhanced or modified,or even resulting in novel functions.1.1-D CdS-Ni semiconductor-magnetic functionally-assembled nanocompositesWidely-used semiconductors were chosen as object,1D CdS-Ni semiconductor-magnetic nanocomposites was achieved by means of electroless plating of nickel nanoparticles on preformed CdS nanowires.The growth of Ni nanoparticles onto CdS nanowires may be attributed to a nonepitaxial process.Conversion phenomena have been detected and verified in our experiments,during which the substitution rate of Cd²⁺ by Ni²⁺ on the surface of CdS nanowire is very fast,generating a layer of NiS shell with a thickness of about 5 nm.A kinetically driven conversion growth is proposed to elucidate the formation of NiS on the nanometre scale.In a parallel experiment,in the absence of hydrazine and NaOH,we obtained only CdS@NiS core/shell 1D nanostructures.In our experiment, EG as typical polyol played a crucial role.It can also bind to both Cd²⁺ ions in the shells and Ni²⁺ ions in solution,forming intermediate complexes to favour the forward reaction.It is worth pointing out that the substitution rate of Cd²⁺ by Ni²⁺ is very fast after heating.We found that only conversion of CdS to NiS on the surface of nanowires was observed for the sample（with,or without hydrazine and NaOH） processed for 10 min.With longer reaction times,the NiS layer became a little thicker and gradually reached a constant level.After that,the thickness of the NiS shell did not increase significantly even after 24 h.This suggests that once a surface layer of CdS has been substituted by NiS,it caused a passivation against further Ni²⁺ attack. The anion sublattice can be partially disrupted owning to the replacement of Cd²⁺ ions by Ni²⁺ ions.Thus,structural defects appeared in the crystal structures acting as nucleation sites for the redox reaction.The NiS shell can act as nucleation sites for the redox reaction and the nonepitaxial process of Ni nanoparticles.With the reaction proceeding,an aggregation-driven shapetransformation process may be involved to increase the size of the nanocrystal on the nanorod.Some nanoparticles could also develop into loops around the nanowires owing to the structural nature of the hexagonal-faced CdS.The six surfaces around the CdS nanowires have equal chemical activity.The M-H curves of 1-D CdS-Ni nanocomposites showed the ferromagnetic property of Ni are conserved.Compared with the neat Ni samples and bulk materials, nanocomposites showed decreased Ms and enhanced Hc value.The incorporation of magnetic Ni into the semiconductor makes it possible that the CdS nanowires can be aligned exactly at the intended positions or in a certain direction and recycled conveniently using a magnetic field,exhibiting special significance in practical applications.2.Epitaxial,nonepitaxial process to synthesis 1-D CdS/α-Fe₂O₃,CdS/Fe₃O₄ hetero-,functional-assembly nanomaterials1-D CdS/α-Fe₂O₃ semiconductor heterostructures were prepared by decorating quasicubicα-Fe₂O₃ nanoparticles onto CdS nanowires through a simple solvothermal method using Fe（NO₃）₃·9H₂O as the source materials.Both components are single-crystalline with distinguished and coherent interfaces,indicating the formation of chemical bonds between them.The structural homogeneity and the possibility of preferential crystal growth on multiple nucleation sites around the c axis of CdS nanowire have been illuminated by the simulated ED patterns and structural model of both constituents,providing insights into heterostructure formation in large lattice mismatched systems and how different geometries may be synthesized,More interestingly,We detect that even someα-Fe₂O₃ nanoparticles grown on the same facets of CdS nearly have identical shape and orientation.The optical properties and photocatalytic activities of the semiconductor nanocomposites towards organic pollutants under visible light（λ>420 nm） were investigated.Upon light absorption, difference in the positions of conduction bands drives photoelectrons generated in CdS nanowires to surroundingα-Fe₂O₃ nanoparticles,resulting in the enhanced photocatalytic activities.1-D CdS/Fe₃O₄ semiconductor-magnetic functionally-assembled nanocomposites were prepared by decorating Fe₃O₄ microspheres onto CdS nanowires through a simple solvothermal method using FeCl₃·6H₂O as the source materials.The whole Fe₃O₄ microspheres exhibited a remarkable polycrystalline feature,resulted from assembly of small nanoparticles.The growth of Fe₃O₄ microspheres onto CdS nanowires may be also attributed to a nonepitaxial process.The presence of S^2- is critical to nanocomposites formation:it can bond Fe³⁺(or Fe²⁺ after heating up) strongly and appear to aid in the attaching ofα-Fe₂O₃ and Fe₃O₄ nanoparticles on multiple nucleation sites.The optical,magnetic properties and photocatalytic activities were separately investigated.The PL behavior of CdS and ferromagnetic property of Fe₃O₄ are conserved,and the photocatalytic activities were not weakened distinctly.In summary,these types of nanocomposites are likely to find potential applications in nanoscience owing to the combination of the ferromagnetic or catalytic domain with 1D semiconductor nanostructure into hybrid nanocomposites.3.Synthesis and Photocatalytic activity of 1-D CdS nanostructure-based core/shell semiconductor composites1D CdS@ZnS core-shell nanocomposites were successfully synthesized by coating a layer of ZnS shell via a solvothermal method,using zinc acetate and thiourea as the source materials.Our results indicate that the ZnS shell with rough surface is made up of ZnS nanoparticles of～4 nm diameter growing along the surface of the CdS nanowires,while the thickness of the shell layer was calculated to be 5～10 nm.The surface modification of a wide band gap ZnS shell around a narrow band gap CdS core can passivate nonradiative recombination sites leading to high optical properties and enhanced photocatalytic activity to MB and 4CP solutions. Over the past few years,both shape and compositional control have been applied to CdS-included nanostructures,attempting to improve its stability or functional properties.However,few of the above results have been proven successful regarding both the stability and the efficiency of CdS.1-D CdS@TiO₂ nanocables were synthesized by slow,uniform hydrolysis of TBT under the presence of CdS nanowires. The experimental results showed that appropriate TiO₂ shell can protect the CdS core from contamination and promote its stability,while the presence of the interface can promote charge separation to favor high efficiency in the photocatalytic reaction, exhibiting important significance in practical applications.4.Synthesis and performance of novel Bi-Ca-O system photocatalystsA series of Bi-based photocatalysts were prepared by conventional polymer-coordination and co-precipatation methods.The details of the reaction processes were investigated and the different intermediate products were identified by X-ray diffraction after the pure phases were obtained.Moreover,the optical behavior and photocatalytic activities under visible light were investigated.更多还原