中空结构纳米TiO2微球的可控制备

纳米TiO_2作为一种氧化还原能力强、化学性质稳定、来源广泛和环境友好的多功能材料,被认为是非常有前景的半导体光催化材料之一。在各种形貌的纳米TiO_2中,中空结构TiO_2微球因具有密度低、比表面积大、渗透性好和稳定性高的特点而受到越来越多研究者的青睐。寻求工艺简单、重复性好和产物形貌可控的中空纳米TiO_2微球的制备方法显得尤为重要。中空纳米TiO_2微球的制备方法根据制备原理可分为溶胶-凝胶法、水热法、溶剂热法、喷雾干燥法和层层自组装法等;根据制备过程中是否加入模板剂又可分为硬模板法、软模板法和无模板法。本文针对硬模板法、软模板法和无模板法进行了综述。其中,硬模板是最早应用于中空TiO_2微球制备的方法,最终所得中空TiO_2的形貌、空腔大小和表面所带电荷与所用模板剂种类密切相关。目前常用的模板剂有三大类,包括聚合物、碳球和无机氧化物。而在制备模板剂过程中需要消耗大量的时间和有机溶剂,造成成本升高和环境污染。软模板法是目前最高效的一种制备方法,其制备机理与硬模板法较为相似,主要区别在于模板剂的选择上,前者的模板剂大多为刚性较强的无机粒子,而软模板剂通常为乳液液滴、超分子胶束、聚合物聚集体/囊泡等强度较低的气体或者液体。相比于硬模板法其最明显的优势在于后期对于模板剂的去除较为容易,不需要高温处理,多次洗涤即可除去,因此具有效率高、工艺简单等优势。无模板法是一种最具应用潜力的中空TiO_2微球制备方法。此法大多为一步反应,因此其可控性较差,尚未实现大范围应用与生产。但是,该法具有制备步骤少、成本低和产率高等优势,在后期的批量生产和规模化制备中空TiO_2微球方面具有潜在的优势。目前,对于中空纳米TiO_2微球的研究除了有效且成熟的制备工艺外,其高效的光催化性能也是研究者追求的目标。笔者认为通过以下三方面可以进一步提高中空纳米TiO_2的光催化性能:其一,多种半导体材料的复合可拓宽其在可见光下的响应区域;其二,非金属阴离子(氮、碳)或金属(铁、铜)离子参杂等可提高光诱导二氧化钛电子空穴对的分离效率;其三,金属氧化物的表面修饰或双原位聚合改性等多种手段共同作用可降低电子-空穴对的重组。延长光生载流子的寿命、提高光催化活性将成为今后中空TiO_2微球研究的重点。     

TiO_2空心球的制备、修饰及应用

TiO_2空心球由于其具有比表面积大、吸附能力强、渗透能力强和电子迁移率高等特点,在锂离子电池、染料敏化太阳能电池、光催化和电流变流体等领域中展现出巨大的应用潜力。综述了TiO_2空心球常用的几种制备方法,如水热法、溶胶-凝胶法、液相沉积法和阳极氧化法,同时还介绍了TiO_2空心球的修饰研究以及其在相关应用领域中的最新研究进展。     

空心球壳材料的制备研究进展

空心球壳材料的制备通常采用硬模板法或软模板法,评述了它们在制备空心球壳材料时的机理和优缺点,并综述了国内外应用模板法制备各种空心球壳材料(无机材料、金属、高分子材料以及无机-有机复合材料)的研究进展.     

软模法制备无机空心球

结构与组成可控、性能可调的微米-亚微米尺度的无机空心球具有极大的应用潜力.系统评述了以气腔、液滴为模板的无机空心球软模制备方法及其应用,以及软模法制备无机空心球的最新进展.     

有序纳米结构体系的模板合成法

利用具有特定结构的物质作为模板,来引导纳米有序结构的制备与组装,从而实现对纳米材料的组成、结构、形貌、尺寸、取向和排布等的控制,为研究纳米有序体系的性质提供了有利途径.模板可以分为软模板和硬模板两种,本文介绍了氧化铝、胶体晶体、胶束、生物大分子等几种常见模板的特点.利用模板法,可以制备金属、合金、氧化物、半导体和聚合物及其复合组份等多种纳米结构有序体系.本文结合我实验室最近的研究工作综述了利用模板法制备纳米有序结构体系的研究进展.     

氧化锌空心球的制备及光致发光特征

采用水热和硬模板辅助技术,成功制备得到ZnO空心球结构.以葡萄糖和锌盐为原料,首先通过催化葡萄糖聚合-原位离子吸附一步进行(一步法)或葡萄糖聚合成球-离子吸附分步进行(二步法)制备锌/炭复合微球,然后经空气低温氧化制得ZnO空心球.用XRD、SEM、TEM研究产物的组成和结构及形貌,用光致发光光谱(PL)测试产物的室温光致发光性能.研究发现,两种方法得到的空心球壳均属多孔结构,由ZnO纳米粒子构成;与聚合-吸附分步法相比,聚合-原位离子吸附一步法更加简单快捷;制得的ZnO空心球结构材料具有良好的近紫外发光性能.对ZnO空心球结构的形成过程和可能的机制进行了分析和讨论.     

煅烧条件对介孔TiO_2空心球成形的影响及其结构与性能研究

以三聚氰胺甲醛(MF)微球为硬模板和十六烷基三甲基溴化铵(CTAB)为介孔导向剂,经溶胶-凝胶法和高温煅烧模板辅助法合成了具有介孔结构的TiO_2空心球。探讨了煅烧温度和煅烧时间的改变对介孔TiO_2空心球完整性形成的影响,采用扫描电镜(SEM)、透射电镜(TEM)、红外光谱(FT-IR)、氮气吸附-脱附(BET)、X射线衍射(XRD)、紫外-可见分光光度法等测试手段对成形完整的TiO_2空心球的表面形貌、结构、组分和光谱性质进行了表征。结果表明,在500℃的条件下煅烧3h能形成结构完整的锐钛矿型TiO_2空心球,具有完整的球形空腔、较高的比表面积,其粒径在700nm左右,形成介孔的壳层厚度在75nm左右。另外,介孔TiO_2空心球对亚甲基蓝在紫外光照射下有较高的光催化活性。     

Bi_2MoO_6空心球的水热沉淀法制备及其光催化性能

以葡萄糖为前躯体,采用水热法制备胶体碳球,以其为模板通过水热沉淀法制备C/Bi2MoO6核壳结构,然后在350℃空气中煅烧,获得了具有良好光催化性能的Bi2MoO6空心球.通过SEM、XRD、FT-IR和BET等测试方法对该催化剂进行了表征;并对其形成机理及反应过程进行了初步探讨,以亚甲基蓝作为被降解物质,研究了其光催化活性。结果表明,Bi2MoO6空心球是由纳米晶粒组成的,壁厚约为30～50nm,平均直径约为0.6～0.8μm,采用胶体碳球作模板时制得的Bi2MoO6空心球比表面积为11.315m2/g,而直接合成的粉体比表面积为3.378m2/g。在黑管灯照射下,2.5h亚甲基蓝的降解率达到了91.95%。     

模板法制备结构可控纳米材料的研究进展

综述了模板法制备结构可控纳米材料的研究进展,讨论了模板法可控制备纳米材料的原理及高度有序自组装的纳米多孔Al2O3模板的形成机理.重点介绍了纳米材料的可控制备方法,主要包括纳米多孔Al2O3模板法、聚合物模板法和生物模板法.其中纳米多孔Al2O3模板法又分为电化学纳米多孔Al2O3模板合成法和电化学诱导的溶胶-凝胶方法等.根据材料的物化性能,选用适合的模板,采用合理的工艺路线,可以制备出结构可控的纳米材料.     

CeO_2纳米空心球的制备与光催化性能研究

采用乳液聚合法制备了聚苯乙烯-丙烯酸微球(P(St-AA))为模板,通过无机物前驱体颗粒的自组装制备出CeO2/P(St-AA)复合微球,煅烧去除聚合物模板后,得到CeO2纳米空心球。通过扫描电子显微镜、透射电子显微镜、傅里叶红外光谱、X射线光电子能谱、X射线衍射和热重分析仪等测试手段对复合微球和CeO2纳米空心球的表面形貌和结构进行了表征。实验结果表明,CeO2空心球由面心立方相颗粒构成,内空心直径约为250nm,壳厚度约为20nm。CeO2纳米空心球对甲基蓝模拟染料废水具有良好的脱色能力,经4h处理后脱色率达到95%以上。     

中空氧化锌微球的制备及应用研究进展

中空ZnO微球具有密度低、比表面积大、渗透性好、光电性能优异等特点,受到科研工作者的广泛关注。综述了中空ZnO微球的制备方法及其应用领域,首先,主要阐述了硬模板法、软模板法、自模板法和无模板法4大类制备方法的研究进展,其次,介绍了中空ZnO微球在光催化、太阳能电池、气体传感器及生物医药等领域的应用进展,最后,对中空ZnO结构材料的发展前景进行了展望。     

Synthesis and photo-degradation application of WO3/TiO2 hollow spheres

A WO(3)/TiO(2) composite, hollow-sphere photocatalyst with average diameter of 320 nm and shell thickness of 50 nm was successfully prepared using a template method. UV-vis diffuse reflectance spectra illustrated that the main absorption edges of the WO(3)/TiO(2) hollow spheres were red-shifted compared to the TiO(2) hollow spheres, indicating an extension of light absorption into the visible region of the composite photocatalyst. The WO(3) and TiO(2) phases were confirmed by X-ray diffraction analysis. BET isotherms revealed that the specific surface area and average pore diameter of the hollow spheres were 40.95 m(2)/g and 19 nm, respectively. Photocatalytic experiments indicate that 78% MB was degraded by WO(3)/TiO(2) hollow spheres under visible light within 80 min. Under the same conditions, only 24% MB can be photodegraded by TiO(2). The photocatalytic mineralization of MB, catalyzed by TiO(2) and WO(3)/TiO(2), proceeded at a significantly higher rate under UV irradiation than that under visible light, and more significant was the increase in the apparent rate constant with the WO(3)/TiO(2) composite semiconductor material which was 3.2- and 3.5-fold higher than with the TiO(2) material under both UV and visible light irradiation. The increased photocatalytic activity of the coupled nanocomposites was attributed to photoelectron/hole separation efficiency and the extension of the wavelength range of photoexcitation.     

四方排列有序Ag/TiO2空心微球的制备及光催化性能

采用低温垂直沉积法制备了聚苯乙烯(PS)胶体模板,由于低温下粒子热运动受到抑制,排列时发生位错,因此模板中存在大面积四方排列结构。然后采用化学镀法、溶胶-凝胶法在PS微球表面依次沉积银纳米粒子、纳米TiO2,最后高温煅烧除去模板制备了四方排列有序Ag/TiO2空心微球。通过扫描电镜(SEM)、X射线衍射(XRD)对样品进行表征。结果表明这种材料很好地保持了模板的四方排列,具有高度有序的纳米结构。选择降解甲基橙溶液来检验样品的光催化性能,并与纳米TiO2薄膜、四方排列TiO2空心微球的光催化性能进行比较,结果表明四方排列Ag/TiO2空心微球具有最佳的光催化性能。这是有序空心纳米结构和银纳米粒子的沉积共同作用的结果。     

Hollow Micro/Nanostructured Ceria‐Based Materials: Synthetic Strategies and Versatile Applications

Hollow micro/nanostructured CeO₂‐based materials (HMNCMs) have triggered intensive attention as a result of their unique structural traits, which arise from their hollowness and the fascinating physicochemical properties of CeO₂. This attention has led to widespread applications with improved performance. Herein, a comprehensive overview of methodologies applied for the synthesis of various hollow structures, such as hollow spheres, nanotubes, nanoboxes, and multishelled hollow spheres, is provided. The synthetic strategies toward CeO₂ hollow structures are classified into three major categories: 1) well‐established template‐assisted (hard‐, soft‐, and in situ template) methods; 2) newly emerging self‐template approaches, including selective etching, Ostwald ripening, the Kirkendall effect, galvanic replacement, etc.; 3) bottom‐up self‐organized formation synthesis (namely, oriented attachment and self‐deformation). Their underlying mechanisms are concisely described and discussed in detail, the differences and similarities of which are compared transversely and longitudinally. Niche applications of HMNCMs in a wide range of fields including catalysis, energy conversion and storage, sensors, absorbents, photoluminescence, and biomedicines are reviewed. Finally, an outlook of future opportunities and challenges in the synthesis and application of CeO₂‐based hollow structures is also presented.     

Gas sensors with porous three-dimensional framework using TiO2/polymer double-shell hollow microsphere

The correlations between the structures and gas-sensing properties of porous thin-film gas sensors made of packed hollow spheres are investigated. For this purpose, hollow polymeric spheres were used as templates. Double-shell hollow spheres were prepared by encapsulating the polymeric hollow spheres with TiO₂ shells. Solid polymeric spheres were used as templates for comparison. Porous thin-film gas sensor with interconnected three-dimensional pores was prepared by using the TiO₂ encapsulated hollow spheres. The double-shell hollow spheres and porous titania films were characterized by XRD, BET, TEM and SEM. The gas-sensing properties of the sensors toward NO₂ depend on the type of template and the three-dimensional porous structure of the films. Using the hollow sphere template and adding precursors during the film formation procedure help to prevent the collapse of hollow sphere and form the mesopores in films after removing the template. These films show enhanced gas sensitivity when compared to TiO₂ polycrystalline films. Such improvement in sensitivity results from the porous architecture of the hollow microsphere films which not only increase the active surface area but also promotes the gas diffusion.     

Intelligent hydrated-sulfate template assisted preparation of nanoporous TiO(2) spheres and their visible-light application

Hydrated metal sulfates (MSO(4)·xH(2)O, M = Zn, Fe, Co, Mg, etc.) were proposed to be intelligent templates to solvothermally synthesize nanoporous TiO(2) spheres with tunable chamber structures from hollow to solid and hybrid compositions. During the reaction, hydrated sulfate serves simultaneously as spherical template, water supplier, and composition controller, and it can be easily removed by washing. The as-prepared anatase TiO(2) spheres were evidenced to contain highly crystallized TiO(2) nanocrystals hybridized with a small amount of metal oxide from the hydrated sulfate. The formation mechanism of the hollow spheres involves the self-conglobation of hydrated sulfate, the hydrolysis of tetrabutyl titanate on the spherical templates, and the subsequent process of solvothermal crystallization. The proposed hydrated-sulfate assisted solvothermal (HAS) strategy was demonstrated to be widely applicable to various systems. When applied to visible-light photocatalysis, the hybrid TiO(2) spheres exhibit excellent photocatalytic performance, benefiting from the reduced charge recombination rate contributed by the heterojunctions of TiO(2) and the hybridized metal oxides.     

Growth of semiconducting GaN hollow spheres and nanotubes with very thin shells via a controllable liquid gallium-gas interface chemical reaction

An in situ liquid gallium-gas interface chemical reaction route has been developed to synthesize semiconducting hollow GaN nanospheres with very small shell size by carefully controlling the synthesis temperature and the ammonia reaction gas partial pressure. In this process the gallium droplet does not act as a catalyst but rather as a reactant and a template for the formation of hollow GaN structures. The diameter of the synthesized hollow GaN spheres is typically 20-25 nm and the shell thickness is 3.5-4.5 nm. The GaN nanotubes obtained at higher synthesis temperatures have a length of several hundreds of nanometers and a wall thickness of 3.5-5.0 nm. Both the hollow GaN spheres and nanotubes are polycrystalline and are composed of very fine GaN nanocrystalline particles with a diameter of 3.0-3.5 nm. The room-temperature photoluminescence (PL) spectra for the synthesized hollow GaN spheres and nanotubes, which have a narrow size distribution, display a sharp, blue-shifted band-edge emission peak at 3.52 eV (352 nm) due to quantum size effects.     

模板法制备介孔TiO2光催化剂的研究进展

介绍了各样模板及相关介孔制备体系,包含表面活性剂模板制备,非表面活性剂模板制备,其它模板制备及非模板制备。结果显示介孔结构可以很好的提高纳米TiO2的光催化活性,虽然在少数例子中介孔结构对光催化活性产生的影响很小或是没有影响。重点论述了上述研究方法的原理、优缺点和在改变TiO2性能中的应用,以及这些方法相结合所取得的一些研究进展;并指出这些方法在TiO2光催化剂的研究中发挥的重要作用。     

The Design and Synthesis of Hollow Micro‐/Nanostructures: Present and Future Trends

Hollow micro‐/nanostructures have attracted tremendous interest owing to their intriguing structure‐induced physicochemical properties and great potential for widespread applications. With the development of modern synthetic methodology and analytical instruments, a rapid structural/compositional evolution of hollow structures from simple to complex has occurred in recent decades. Here, an updated overview of research progress made in the synthesis of hollow structures is provided. After an introduction of definition and classification, achievements in synthetic approaches for these delicate hollow architectures are presented in detail. According to formation mechanisms, these strategies can be categorized into four different types, including hard‐templating, soft‐templating, self‐templated, and template‐free methods. In particular, the rationales and emerging innovations in conventional templating syntheses are in focus. The development of burgeoning self‐templating strategies based on controlled etching, outward diffusion, and heterogeneous contraction is also summarized. In addition, a brief overview of template‐free methods and recent advances on combined mechanisms is provided. Notably, the strengths and weaknesses of each category are discussed in detail. In conclusion, a perspective on future trends in the research of hollow micro‐/nanostructures is given.