Solvothermal synthesis of cerium oxides

A review of the various hydrothermal and solvothermal methods that have been used for the preparation of cerium oxides is presented. Much work has focussed on the preparation of cerium dioxide (ceria) and its doped analogues because of their extensive applications in catalysis, solid-oxide fuel cells and other technologies. It is shown how the solvothermal method offers a number of distinct advantages in the one-step formation of ceria materials, including control of crystal form and morphology in the nanometre regime from spherical and cubic particles to anisotropic polyhedra and rods. The use of solution additives allows surface capping either preventing aggregation of particles or permitting their assembly into complex hierarchical structures. In terms of doping, the solvothermal synthesis method allows access to phases not possible using high temperatures synthesis, including ceria doped by transition-metal ions. These synthetic advantages all allow fine-tuning of the properties of ceria for practical applications. Finally, some recent work that has focussed on the synthesis of complex mixed-oxide phases containing cerium, both in the +3 and the +4 oxidation state, is presented: this illustrates the potential of solvothermal synthesis in the discovery of new materials.     

Laser damage of glycidoxypropyltrimethoxysilane based hybrid materials

The preparation of solid samples, having specific optical properties, is one of the main goals for the realization of devices in the photonic field. To this end, it is important to attain the best control of the optical properties in the final materials. The sol-gel technique is a powerful synthesis method allowing the preparation of matrices with high stability, mechanical resistance and high optical quality. The use of hybrid organic-inorganic precursors permits samples with different thicknesses, ranging from films of hundreds of nanometers to bulk samples of millimeters, to be obtained. The control of the synthesis protocol and the choice of precursors and catalyst allows the control of the final matrix microstructure, which is related to optical properties, like the laser damage threshold. In this work four different matrices, based on glycidoxypropyltrimethoxysilane and Zr alcoxide, have been prepared through sol-gel synthesis. An interpenetrating organic and inorganic network, controlled by the synthesis protocol, characterizes these matrices. The obtained materials show high resistance to the optical damage and long term stability.     

The role of silica and alkaline earth metals with biomolecules in the biomineralization processes: the eggshell's formation and the crystallization in vivo for x-ray crystallography

This contribution is a scientific journey divided into three parts. In the first part, we review the role that silica biomorphs of alkaline earth metals have played in the formation of complex structures as a reminiscence of the chemistry of the primitive life on Earth. These biomorphs, and their variety of forms synthesized by simple chemical reactions, can nowadays be experimentally used to explain some mechanisms of biomineralization in living organisms. In the second part, we review the role of calcium carbonates in the formation of eggshells in avian. The mechanism of the mineral eggshell´s formation of the biogenic calcite deposited on an organic matrix is revised. The competitive crystal growth mechanism of the mineralized part orientates these crystals preserving the semispherical shape of the egg. We are using these eggshell formations as a second model to understand the biomineralization processes in Nature. The third and final part is about the importance that biomineralization concepts have to produce hybrid materials for the future. This has allowed us to obtain tailored size control of complex morphologies by synthetic chemical procedures that give rise to these new materials’ specific forms and ad hoc properties. We conclude this part with the advantage of knowing the biological mechanisms, based on molecular biology concepts, to obtain protein crystals in vivo and in cellulo techniques. Both methods use the cellular machinery of growing biocrystals in specialized cells that have evolved through millions of years. This new way of producing protein crystals has been trending topic for modern crystallography when using the facilities of the X-ray free-electron lasers (four generation of synchrotrons) for megahertz serial crystallography.     

Preparation and properties of europium-doped phosphosilicate glasses obtained by the sol–gel method

In this work, we report the synthesis of europium-doped phosphosilicate glasses from tetraethylorthosilicate (TEOS), phenyltrietoxysilane (PTES) and ammonium phosphate (NH₄H₂PO₄) prepared by the sol–gel process. The matrix was synthesized by modified Stöber methodology. The alkoxide precursors PTES and TEOS were mixed with NH₄H₂PO₄, in the presence of europium III chloride, using ethanol as solvent in basic catalysis. These materials were studied by photoluminescence spectroscopy (PL), thermal analysis (TGA/DTA), transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). The results obtained for the materials show the formation of conchoidal-fractures, which are characteristics of glass materials. The thermal analysis showed the thermal stability of materials up to 300 °C. Eu III has been used as structural probe due to its photophysical properties. The PL spectra displays the lines characteristics of the Eu (III) ion ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3 and 4). Wide bands were observed, indicating non-homogeneous sites that are characteristic of amorphous systems.     

Quantum dot nanostructures and molecular beam epitaxy

In order to fulfil the requirements of the information society there is a growing demand for nanoelectronic devices with new or largely improved performances; these devices are based on low-dimensional carrier systems, and in particular on zero-dimensional ones, that have peculiar properties as compared to the three- and two-dimensional counterparts.

In this paper we review and discuss the basic features of the Molecular Beam Epitaxy growth of quantum dots that are very interesting archetypes of zero-dimensional nanostructures; quantum dots can be obtained by the three-dimensional growth of self-assembled nanoislands that takes place during the preparation of structures based on highly lattice-mismatched materials. Aspects of the morphological, electronic and optical properties of quantum dots will be reviewed and it will be shown how the energy of confined levels for carriers is determined by design and growth parameters of nanostructures and how quantum dot emission wavelengths can be tuned in the windows of optoelectronic and photonic interest, such as that at 0.98, 1.31 and 1.55 μm. An overview of quantum dot devices will be given, with particular attention paid to the quantum dot laser, unarguably the most important application of quantum dots so far.     

化学气相沉积法制备二维过渡金属硫族化合物研究进展

二维过渡金属硫族化合物(TMDs)是继石墨烯之后的新型二维材料，由于其自身的独特物理化学性质在半导体、光电材料、能源储存和催化制氢等方面备受瞩目。化学气相沉积(CVD)是目前适合实现大规模制备二维材料的工艺之一，制备过程中参数的高度可控性使其具有很大优势。本文综述了近期通过CVD制备TMDs的研究进展，探讨了在CVD制备工艺中各种参数对产物生长和最终形貌的影响，包括前驱体、温度、衬底、辅助剂、压力和载气流量等。列举了一些改进的CVD制备工艺，并对其特点进行了总结。最后讨论了目前CVD制备TMDs所面临的挑战并对其发展前景进行展望。     

Review: Recent research progress on preparation of silver nanowires by soft solution method and their applications

Owing to the unique and tunable optical, plasmonic and electrical properties of silver nanowires, they are widely used as the templates for the preparation of Au or Pt nanotubes, as substrates for surface‐enhanced Raman scattering (SERS) and detectors for some chemicals. Soft solution method is a facile and effective method for the preparation of silver nanowires with well‐controlled morphology and uniform size. By this approach, silver nanowires can be readily prepared with mild reaction condition, general materials available and facile procedure. This review concentrates on the preparation of silver nanowires via various soft solution methods and their applications in the formation of metallic nanotubes, SERS and detection for some chemicals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Progress in the growth of CaCu3Ti4O12 and related functional dielectric perovskites

Calcium copper titanate, CaCu₃Ti₄O₁₂, (CCTO), a potential electro-ceramic is a member of a very important perovskite family and has been found to a show dielectric constant of the order of 10⁴–10⁵. It has a remarkable ability to undergo a series of cationic exchange reactions resulting in corresponding isomorphs. In the past decade there has been immense activity in the search of an isomorph of CCTO with high dielectric constant and low loss which enables its use as capacitor material for the storage of energy and miniaturization of electronic based equipment. Despite intensive research in the area there is no source of any literature that gives all the possible relevant information regarding various synthetic methods, characterizations, effect of sintering parameters (temperature, duration, and atmosphere). This review article is an effort to review the synthesis, grain growth, morphological evolution, effect of impurities, substitution and interface anisotropy on the dielectric constant, resistivity and other materials parameters.     

Preparation of Nd2O3-doped calcium aluminosilicate glasses and thermo-optical and mechanical characterization

The calcium aluminosilicate glass (CAS) is an important class of optical materials due to the many applications envisaged, including its use as active media for glass lasers. In order to study how Nd₂O₃ doping affects the mechanical and the thermo-optical properties of CAS glass, two series of CAS glass, doped with Nd₂O₃ up to 5 wt%, were prepared in a vacuum atmosphere. The rare earth changes the physical properties, and this influence of doping ion content is discussed for both the series of samples in terms of mechanical, thermal, and thermo-optical properties. The study analyzed hardness and elastic moduli, glass transition temperature, crystallization temperature, thermal diffusivity, specific heat, density, thermal conductivity, refractive index, and thermo-optical properties, like temperature coefficient of the optical path length (dS/dT). The results presented provide information about the sample’s structure, and show that for Nd₂O₃ concentration up to 5 wt% there were no significant changes in the glass host material.     

Developments and future directions of phase diagram,physicochemical and optical studies of binary organic complexes

The aim of this review is to emphasize solvent free or green synthesis, a most efficient utilization of starting materials to give maximum yield, and an alternative route to producing novel promising materials. In this regard the phase diagram study has shown applications in the determination of the precise composition of binary compounds of a specific nature and in the identification of the parameters that affect the crystal growth. To provide an overview worthy of phase diagram, physicochemical, thermal and structure investigations; studies of eleven systems, namely, urea–m-nitrobenzoic acid, urea–p-nitrophenol, urea–resorcinol, benzoin–o-phenylenediamine, pyrene–m-dinitrobenzene, vanillin–p-anisidine, resorcinol–p-dimethylaminobenzaldehyde, benzophenone–diphenylamine, anthracene–picric acid, 8-hydroxyquinoline–salicylic acid and 8-hydroxyqunoline–1,2,3-trihydroxybenzene forming organic complexes, have been reported. In addition, the original data of a newly synthesized complex of m-hydroxybenzaldehyde (HB) and p-chloroaniline (CA) is being reported for the first time. The phase diagram of HB–CA system also shows the formation of a complex in 1:1 M ratio, and two eutectics on either side of the complex. The complex's formation was studied using FTIR, NMR, DSC and powder X-ray diffraction techniques. The thermodynamic parameters such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated using the heat of fusion values. The single crystal growth and the atomic packing studies of some of the complexes have confirmed the formation of complexes. The optical transmittance efficiency and transparency of novel HB–CA complex crystal were found to be 70% and 399 nm, respectively.     

双折射YVO4晶体原料的合成及最佳制备工艺的探讨

本文介绍了液相法合成用于双折射单晶生长的钒酸钇原料的工艺。着重讨论了制备条件对原料纯度的影响,确定了最佳合成方案。为了适应工业化生产的需要,探讨了原料合成的规范化(以保证保纯性,均匀性,重复性),合成出的原料已成功生长出φ42×42mm的大尺寸优质钒酸钇单晶,且剩料可重复使用10次左右。     

Recent progress on triphenylamine materials: synthesis,properties, and applications

Triphenylamine is a propeller-like structural chromophore with a nitrogen atom center. The compound has a large steric hindrance and hyper conjugation electronic effect, which can enhance the stability of the nitrogen atomic radical. Triphenylamine materials also have a high hole mobility due to their unique free radicals nature. In this review, we started with the methods of the synthesis including traditional Ullmann, Suzuki Coupling, Heck, Wittig, Stille, and Sonogashira Reaction synthesis, and also the basic experimental and theoretical methods for the characterization of triphenylamine materials. Then, we discussed the properties of triphenylamine, including the optoelectronics, electroluminescence, and electrochromism. Finally, we reviewed the recent progress in the main applications of triphenylamine materials in the field of organic optoelectronic solar cells, electroluminescence materials, and electrochromic materials. In conclusion, this review of triphenylamine materials is a valuable resource for both theorists and experimentalists who are focus on these exciting compound materials.     

Spectroscopic characterization of intrinsic losses in an organic-inorganic hybrid waveguide synthesized by the sol-gel process

A promising way of fabricating integrated optics components is based on the sol-gel synthesis and photocuring of hybrid materials. However, the presence of OH groups in these materials is a major factor in optical amplification inhibition. In particular, high losses at 1550 nm are mainly due to non-condensed OH groups originating from the sol-gel process at low temperature. Thus, improvement of the final properties of these materials is correlated with the inhibition of OH group concentration. In this study, we used ²⁹Si NMR and near infrared spectroscopy to demonstrate the catalytic effect of zirconium (IV) n-propoxide on the condensation reactions of silanol groups. ²⁹Si NMR showed the absence of silanol species at the end of the synthesis. This result is attributed to the zirconate hydrophilic effect which consumes OH groups by catalysing the polycondensation of Si-OH bonds. In parallel, near-infrared experiments showed the presence of a high proportion of OH species at the end of the synthesis showing that the remaining OH groups are only present in the zirconium species.     

In-situ liquid phase TEM observations of nucleation and growth processes

Nucleation and growth of crystals is a pervasive phenomenon in the synthesis of man-made materials, as well as mineral formation within geochemical and biological environments. Over the past two decades, numerous ex situ studies of crystallization have concluded that nucleation and growth pathways are more complex than envisioned within classical models. The recent development of in situ liquid phase TEM (LP-TEM) has led to new insights into such pathways by enabling direct, real-time observations of nucleation and growth events. Here we report results from LP-TEM studies of Au nanoparticle, CaCO₃ and iron oxide formation. We show how these in situ data can be used to obtain direct evidence for the mechanisms underlying crystallization, as well as dynamic information that provides constraints on important kinetic and thermodynamic parameters not available through ex situ methods.     

弛豫铁电单晶的生长及性能优化研究进展

钙钛矿型(ABO₃)弛豫铁电单晶具有优异的机电耦合性能,被认为是研制下一代医疗超声换能器、高精度压电驱动器、水声换能器等机电耦合器件的核心关键材料。针对弛豫铁电单晶材料制备与物理性能方面尚存在的基础科学与工艺问题,本文综述了近些年弛豫铁电单晶生长与性能优化方面的研究进展,包括若干新的单晶生长方法用以改善弛豫铁电单晶的成分和性能均匀性,提升弛豫铁电单晶压电性能的系列新方法,通过铁电畴结构调控以获得高透光率的弛豫铁电单晶,以及高性能弛豫铁电单晶在电光技术领域的应用等。     

Polysaccharide-based aerogels as drug carriers

The application of aerogels as drug delivery system was successfully demonstrated for silica aerogels previously. However, being biocompatible silica matrices are not biodegradable, which is a certain disadvantage for a number of pharmaceutically oriented applications. For these purposes biodegradable materials are beneficial. Supercritical drying of polysaccharide gels results in highly porous biodegradable aerogel matrices with large surface areas. Structural properties of the polysaccharide aerogels depend on the preparation method and chemical nature of the gel phase. In this work different polysaccharide precursors (starch, alginate) were used to produce aerogels, which later on were loaded with the drugs ibuprofen and paracetamol. Furthermore release kinetics was studied in vitro. Thereby it has been shown that the release rate depends primary on the properties of the matrix. The presented results demonstrate for the first time the high potential of polysaccharide aerogels for pharmaceutical applications.     

过渡金属二硫族化合物在FET中的应用研究进展

过渡金属二硫族化合物(Transition-metal dichalcogenides,TMDs)作为一组二维材料具有丰富的物理特性,近几年因其半导特性在半导体器件上具有重要的应用前景而引其了学界的普遍关注.总结了TMDs材料的制备方法及其在场效应管(FET)上的应用研究进展,并对存在的问题以及潜在的研究方向做了展望.     

Preparation of mesoporous silicas using food grade emulsifiers and its application for enzyme supports

A novel mesoporous silica (TMPS) was synthesized via self-assembly using a myristic acid ester of pentaglycerol. The ester is obtained from catalytic esterification and it is commercially available as a food grade emulsifier. TMPS material was employed for preparation of a biocatalyst in order to examine the ability as an enzyme support in comparison with the other mesoporous silica materials having a channel or a cage-like pore system. The used TMPS materials possessed the interconnected channel-like pore system with the pore sizes of 9.2, 12, and 16 nm. The materials successfully entrapped lipase into their mesopores with the high loadings. The resultant lipase/TMPS conjugates functioned as the biocatalyst for hydrolysis of p-nitrophenyl propionate (p-NPP), having the higher activity than those of the used mesoporous silica conjugates. The high activities were ascribed to the textural properties such as the small particle length, large pore size and the three-dimensional pore connectivity that permit the accessibility of p-NPP to the immobilized lipases during the reactions. Consequently, we concluded that TMPS materials are of the suitable mesoporous support for the enzymes.     

Synthesis, properties, and applications of magnetic iron oxide nanoparticles

Magnetic nanoparticles exhibit many interesting properties that can be exploited in a variety of applications such as catalysis and in biomedicine. This review discusses the properties, applications, and syntheses of three magnetic iron oxides – hematite, magnetite, and maghemite – and outlines methods of preparation that allow control over the size, morphology, surface treatment and magnetic properties of their nanoparticles. Some challenges to further development of these materials and methods are also presented.     

Crystallization field study for the formation of single phase sodium clinoptilolite: Batch composition,seed and temperature effects

Although clinoptilolite is the most abundant zeolite mineral in nature, its synthesis under laboratory conditions has been difficult. A partial crystallization field study was done for the synthesis of clinoptilolite based on a nominal batch composition of 2.1Na₂O:Al₂O₃:10Si₂O:110H₂O to delineate the limits of composition and temperature within which sodium clinoptilolite can be produced as a single phase in high yields. Effects of temperature, SiO₂/Al₂O₃ molar ratio in the batch composition, and the use of different raw materials in batch preparation were studied. The need for the use of seed crystals for reproducible synthesis of clinoptilolite was established. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)