5‐(2‐Mercaptoethyl)‐1H‐tetrazole: Facile Synthesis and Application for the Preparation of Water Soluble Nanocrystals and Their Gels

A facile method for the preparation of the novel capping ligand 5‐(2‐mercaptoethyl)‐1H‐tetrazole for the stabilization of water‐soluble nanocrystals was developed. This effective synthetic procedure is based on the cycloaddition of sodium azide to 3,3′‐dithiobis(propionitrile) followed by the reductive cleavage of a S?S bond with triphenylphosphine. The structure of the synthesized compound was confirmed by single‐crystal X‐ray analysis. A target tetrazole was successfully applied for the direct aqueous synthesis of CdTe and Au nanocrystals. CdTe nanocrystals capped with 5‐(2‐mercaptoethyl)‐1H‐tetrazole were found to reveal high photoluminescence efficiencies (up to 77 %). Nanocrystals capped with this tetrazole ligand are able to build 3D structures in a metal‐ion‐assisted gelation process in aqueous solution. Critical point drying of the as‐formed hydrogels allowed the preparation of the corresponding aerogels, while preserving the mesoporous structure.     

Sol-Gel Synthesis of Hybrid Organic-Inorganic Monoliths Doped with Colloidal CdSe/ZnS Core-Shell Nanocrystals

Colloidal CdSe/ZnS core-shell nanocrystals, with a narrow size distribution, were dispersed in a hybrid sol resulting from the hydrolysis of tetraethylorthosilicate and 3-glycidoxypropyltrimethoxysilane (GLYMO). In order to reduce the gelation time and the exposure of the nanoparticles to air, several catalysts of the GLYMO epoxy ring opening were employed for the sol preparation, such as imidazole, methyl-imidazole, pyridine, benzylamine, propylamine. The role of the various catalysts was monitored by optical absorption measurements in the near infrared region, by observing the evolution of the epoxy bands. Imidazole was found to provide the fastest gelation and the best results in terms of bubble disappearance from the gel structure. The variation in the optical properties of the semiconductor nanoparticles embedded in the matrix was monitored as a function of the gelation time and was compared to the optical absorption and photoluminescence spectra of the nanoparticles dissolved in a chloroform solution. A decrease in the gelation-time results in a closer resemblance between the optical properties of the CdSe/ZnS doped monoliths and those of the particles dissolved in the solvent, before incorporation in the matrix. The photoluminescence of the CdSe/ZnS nanocrystals is not bleached after they are trapped in the glassy matrix.     

Porous CdTe nanocrystal assemblies: ligation effects on the gelation process and the properties of resultant aerogels

Highly porous CdTe nanoarchitectures (aerogels) were prepared by sol-gel assembly of discrete nanocrystals followed by supercritical CO(2) drying. CdTe nanocrystal surface functionalization (either phosphine oxide or thiolate) is found to be immaterial to oxidation induced gel formation suggesting that the standard thiolate capping procedure is not a necessary step in the gelation process. On the basis of this observation, and reduction induced dispersion of the gel network, the exposure of reactive sites and the subsequent surface oxidation reaction to form polychalcogenide linkages are key steps in the gelation mechanism. Consequently, CdTe aerogels exhibit similar physicochemical properties, regardless of original ligating functionality. The aerogels are mesoporous, with surface area >100 m(2)/g, and exhibit an optical bandgap of 1.92 eV, consistent with quantum confinement within the 3-D linked network. Photoluminescence is suppressed in the aerogels, but can be partially recovered upon heating.     

碳纳米管向金刚石纳米晶粒的转变

在碳60（C60）[1]和碳纳米管(CNTs)[2]发现之前,人们知道碳通常显示石墨和金刚石两种晶体结构.自从C60和碳纳米管发现后,由于其独特的纳米结构而具有广泛的应用前景,国内外许多学者致力于研究它们的物理和化学特性,而C60、巴基葱（多层碳纳米球）、碳纳米管和金刚石之间的转变是所研究的焦点之一.目前,由碳的其他形式向金刚石转变的主要方法有：Meilunas等人[3]以C60和C70薄膜为基底气相生长多晶金刚石,C60和C70的稳定性和微平面结构在外界条件下,有利于金刚石成核和外延生长;Banhart[4]小组研究了在电子束辐射作用下巴基葱转变…     

Gelation of native beta-lactoglobulin induced by electrostatic attractive interaction with xanthan gum

The mechanism and kinetics of the electrostatic gelation of native beta-lactoglobulin-xanthan gum mixtures in aqueous solution is reported. The total biopolymer concentration at which gelation was obtained was extremely low (0.1 wt %) compared to the usually tested concentrations for protein-polysaccharide mixed gels (4-12 wt %). This is, to our knowledge, the first time that oppositely charged proteins and polysaccharides are reported to form a gel without applying any treatment to denature the protein (e.g. heating, enzymatic hydrolysis) and at such low concentrations. Static light-scattering and viscoelastic measurements allowed determination of the gelation kinetics. It was found that the gelation process initiated following a similar path as that of an associative phase separation process, i.e., with the formation of primary and interpolymeric electrostatic complexes. However, interpolymeric complexes were able to form clusters and junction zones that resulted in the freeze-in of the whole structure at the point of gelation. The formed gel is therefore a coupled-gel, that is, a gel that has junction zones involving two different molecules. The structuration of xanthan gum, even at these low concentrations, may have played a role in the structuration process. Due to the electrostatic nature of the gels, there was an optimum pH and macromolecular ratio at which the stability of the gels was maximal. This was related to the existence of a stoichiometric electrical charge equivalence pH, where molecules carry equal but opposite charges and protein-polysaccharide interactions are at their maximum.     

Curcumin-loaded PLGA-PEG-PLGA triblock copolymeric micelles: Preparation, pharmacokinetics and distribution in vivo

Rod-shaped cellulose nanocrystals (CNCs) were manufactured and used to reinforce polyacrylamide (PAM) hydrogels through in situ free-radical polymerization. The gelation process of the nanocomposite hydrogels was monitored on a rheometer using oscillatory shear. The chemical structure, morphology, swelling property, and compression strength of the formed gels were investigated. A possible mechanism for forming hydrogels was proposed. The results showed that CNCs accelerated the formation of hydrogels and increased the effective crosslink density of hydrogels. Thus CNCs were not only a reinforcing agent for hydrogel, but also acted as a multifunctional cross-linker for gelation. The shear storage modulus, compression strength and elastic modulus of the nanocomposite hydrogels were significantly improved because of good dispersion of CNCs in PAM as well as enhanced interfacial interaction between these two components. Among the CNC contents used, a loading of 6.7 w/w% led to the maximum mechanical properties for nanocomposite hydrogels.     

Role of urea in the preparation of highly porous nanocomposite aerogels

The preparation of highly porous CoFe2O4-SiO2 nanocomposite aerogels was successfully achieved by a novel sol-gel procedure involving urea-assisted co-gelation of the precursor phases. This method allows fast gelation, giving rise to an aerogel with 97% porosity. The formation of CoFe2O4 nanocrystals homogeneously distributed within the matrix occurs after calcination at 750 degrees C and is complete at 900 degrees C. Despite the high temperature required for the formation of the CoFe2O4 nanocrystals, the high porosity typical of aerogels is still retained.     

Gelation of cellulose nanocrystal suspensions in glycerol

Aqueous suspensions of cellulose nanocrystals (NCC) produced by sulfuric acid hydrolysis of natural cellulose fibres display a number of unique properties. In addition to forming equilibrium chiral nematic phases above some critical concentration, cellulose nanocrystal suspensions tend to gel or aggregate if the stability of the suspension decreases, for example because of a decrease in the surface charge density of sulfate ester groups, or a change in the properties of the suspending medium. Direct incorporation of unmodified nanocrystals into organic media usually leads to aggregation. We have found that it is possible to circumvent this difficulty and form clear thixotropic gels of unmodified NCC in glycerol, by careful evaporation of water from aqueous glycerol suspensions of NCC. The physical gels form at a fairly low (<3 wt%) concentrations of cellulose. The initial composition of the suspension, the temperature and rate of evaporation, and the time resting at room temperature all influence the formation of thixotropic gels. Desulfation of the acid-form nanocrystals, enhanced in the glycerol-rich suspensions, is shown to be a key step in this gelation process.     

凝胶化反应中标度行为及凝胶化点关系

在苯乙烯(St)-二乙烯苯(DVB)自由基聚合的凝胶化反应过程中,定时取样,得到凝胶化点前后及直至反应终点的一系列溶胶样品,利用光散射技术研究了溶胶相的重均分子量M_w、尺寸均方旋转半径R_g的变化过程,建立了M_w、R_g和反应时间t的标度关系,并在此基础上提出一神新的准确求取凝胶化时间t_gel的方法.     

Shape-Controlled Nanocrystals for Catalytic Applications

The activity, selectivity, and long-term stability of catalyst nanoparticles can be enhanced by shape modulation. Such shaped catalytic nanocrystals have well-defined surface crystalline structures on which the cleavage and recombination of chemical bonds can be rationally controlled. Metal and metal oxide nanocrystals have been synthesized in various shapes using wet chemistry techniques such as reducing metal precursors in the presence of the surface-capping agents. The surface-capping agents should be removed prior to the catalytic chemical reaction, which necessitates clean catalytically active surface. The removal process should be performed very carefully because this removal often causes shape deformation. A few examples in which the surface-capping agents contribute positively to the chemical reactions have been reported. The examples described in this review include shaped metal, metal composite, and metal oxide nanocrystals that show enhanced catalytic activity, selectivity, and long-term stability for various gas-phase, liquid-phase, or electrocatalytic reactions. Although most of the studies using these shaped nanocrystals for catalytic applications have focused on low-index surfaces, nanocrystals with high-index facets and their catalytic applications have recently been reported. By bridging surface studies with nanoparticle catalysts using shape modulation, catalysts with improved properties can be rationally designed.     

CdS:Mn nanocrystals passivated by ZnS: synthesis and luminescent properties

Synthesis and characterization of highly luminescent ZnS-passivated CdS:Mn (CdS:Mn/ZnS) core/shell structured nanocrystals are reported. Mn-doped CdS core nanocrystals are produced ranging from 1.5 to 2.3 nm in diameter with epitaxial ZnS shell of wider band gap via a reverse micelle process. UV irradiation-stimulated photo-oxidation of the ZnS shell results in formation of sulfate (ZnSO(4)) as determined by x-ray photoelectron spectroscopy, which increases the photoluminescence emission intensity and subsequent photostability. Luminescent relaxation lifetime data present two different decay components, consisting of slow decay emission from the Mn center and a fast decay emission from a defect-related center. The impact of the density of surface defect states upon the emission spectra is discussed.     

Facile route to Zn-based II-VI semiconductor spheres, hollow spheres, and core/shell nanocrystals and their optical properties

A convenient chemical conversion method that allows the direct preparation of nanocrystalline ZnE (E = O, S, Se) semiconductor spheres and hollow spheres as well as their core/shell structures is reported. By using monodisperse ZnO nanospheres as a starting reactant and in situ template, ZnS, ZnSe solid and hollow nanospheres, and ZnO/ZnS and ZnO/ZnSe core/shell nanostructures have been obtained through an ultrasound-assisted solution-phase conversion process. The formation mechanism of these nanocrystals is connected with the sonochemical effect of ultrasound irradiation. The photoluminescence and electrogenerated chemiluminescence properties of the as-prepared nanocrystals were investigated.     

Synthesis of Highly Monodisperse Cu2O Nanocrystals and Their Applications as Hole-Transporting Layers in Solution-Processed Light-Emitting Diodes

The synthesis of phase-pure, narrow-size-distributed and highly stable Cu₂O nanocrystals is reported, which can be processed as hole-transporting layers (HTLs) in solution-processed optoelectronic devices. The synthesis is based on a thermal decomposition process with a ligand protection strategy. The reactivity of precursor can be tuned by simply modulating the concentration of oleylamine in non-coordinated solvent, resulting in effectively controlling the size and size distribution of Cu₂O nanocrystals. Combined with ligand protection strategy of using lithium stearate and moderate reaction temperature of 170 °C, in situ aggregation of Cu₂O nanocrystals could be inhibited, exhibiting excellent stability in hexane for several months. The resulting phase-pure colloidal Cu₂O particles (after ozone-treatment) were applied as HTLs in polymer light-emitting diodes, the performance of which are comparable to that of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) based devices.     

用金胺O作荧光探针研究PVA-H_2O-DMSO体系的凝胶过程

<正> 它在可见光区发荧光,其荧光量子效率随环境的粘度不同有较明显的变化。这是由于其分子中的芳香基团与中心碳是单键连接,易于转动。当环境的粘度增加时,这种转动受到阻碍,因而分子吸收激发光能后,损失于这种转动的热能相对减少,荧光量子效率则相对     

Multifunctional particles: Magnetic nanocrystals and gold nanorods coated with fluorescent dye-doped silica shells

Multifunctional colloidal core-shell nanoparticles of magnetic nanocrystals (of iron oxide or FePt) or gold nanorods encapsulated in silica shells doped with the fluorescent dye, Tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy) were synthesized. The as-prepared magnetic nanocrystals are initially hydrophobic and were coated with silica using a microemulsion approach, while the as-prepared gold nanorods are hydrophilic and were coated with silica using a Stöber type of process. Each approach yielded monodisperse nanoparticles with uniform fluorescent dye-doped silica shells. These colloidal heterostructures have the potential to be used as dual-purpose tags—exhibiting a fluorescent signal that could be combined with either dark-field optical contrast (in the case of the gold nanorods), or enhanced contrast in magnetic resonance images (in the case of magnetic nanocrystal cores). The optical and magnetic properties of the fluorescent silica-coated gold nanorods and magnetic nanocrystals are reported.     

流变学法研究部分水解聚丙烯酰胺/Cr(III)交联反应I.浓度的影响

采用流变学法系统地考察了部分水解聚丙烯酰胺（HPAM）/Cr(III)交联体系的 反应动力学。HPAM溶液的粘性模量G”大于弹性模量G’,且其数值随时间不发生变 化,体系为粘性溶液。而HPAM/Cr(III)体系的G’和G”的数值都随时间变化,G” 在反应开始阶段大于G’,当反应进行一段时间后,G’超过G”占据主要地位,体 系成为弹性体系。交联过程可分为三个阶段：第一上升阶段,平缓上升阶段和第二 上升阶段。利用G’～ t曲线可以推测反应机理。实验发现成胶速率随反应物HPAM 和Cr(III)的浓度的增加而增加,而成胶时间缩短。在羧基浓度过量的情况下,交 联反应对Cr(III)浓度的反应级数是1。凝胶的有效弹性交联密度随聚合物浓度的增 加而增,且随凝胶反应的进行而增加。凝胶的交联点间的平均分子量随Cr(III)浓 度的增加和交联反应的进行而下降。     

Radial-position-controlled doping in CdS/ZnS core/shell nanocrystals

In this paper, we report a new doping approach using a three-step synthesis to make high-quality Mn-doped CdS/ZnS core/shell nanocrystals. This approach allows precise control of the Mn radial position and doping level in the core/shell nanocrystals. On the basis of this synthetic advance, we have demonstrated the first example in which optical properties of Mn-doped nanocrystals strongly depend on Mn radial positions inside the nanocrystals. In addition, we have synthesized nanocrystals with a room-temperature Mn-emission quantum yield of 56%, which is nearly twice as high as that of the best Mn-doped nanocrystals reported previously. Nanocrystals with such a high-emission quantum yield are very important to applications such as nanocrystal-based biomedical diagnosis.     

Surface Iron Species in Palladium–Iron Intermetallic Nanocrystals that Promote and Stabilize CO2 Methanation

It is of pivotal importance to develop efficient catalysts and investigate the intrinsic mechanism for CO₂ methanation. Now, it is reported that PdFe intermetallic nanocrystals afforded high activity and stability for CO₂ methanation. The mass activity of fct‐PdFe nanocrystals reached 5.3 mmol g^?1 h^?1, under 1 bar (CO₂:H₂=1:4) at 180 °C, being 6.6, 1.6, 3.3, and 5.3 times as high as that of fcc‐PdFe nanocrystals, Ru/C, Ni/C, and Pd/C, respectively. After 20 rounds of successive reaction, 98 % of the original activity was retained for PdFe intermetallic nanocrystals. Further mechanistic studies revealed that PdFe intermetallic nanocrystals enabled the maintenance of metallic Fe species via a reversible oxidation–reduction process in CO₂ methanation. The metallic Fe in PdFe intermetallic nanocrystals induced the direct conversion of CO₂ into CO* as the intermediate, contributing to the enhanced activity.     

Controlled synthesis of tuned bandgap nanodimensional alloys of PbS(x)Se(1-x)

Truly alloyed PbS(x)Se(1-x) (x = 0-1) nanocrystals (～5 nm in size) have been prepared, and their resulting optical properties are red-shifted systematically as the sulfur content of the materials increases. Their optical properties are discussed using a modified Vegard's approach and the bowing parameter for these nanoalloys is reported for the first time. The alloyed structure of the nanocrystals is supported by the energy-filtered transmission electron microscope images of the samples, which show a homogeneous distribution of sulfur and selenium within the nanocrystals. X-ray photoelectron spectroscopy studies on ligand-exchanged nanocrystals confirmed the expected stoichiometry and various oxidized species.     

Surface Iron Species in Palladium–Iron Intermetallic Nanocrystals that Promote and Stabilize CO2 Methanation

It is of pivotal importance to develop efficient catalysts and investigate the intrinsic mechanism for CO₂ methanation. Now, it is reported that PdFe intermetallic nanocrystals afforded high activity and stability for CO₂ methanation. The mass activity of fct-PdFe nanocrystals reached 5.3 mmol g⁻¹ h⁻¹, under 1 bar (CO₂:H₂=1:4) at 180 °C, being 6.6, 1.6, 3.3, and 5.3 times as high as that of fcc-PdFe nanocrystals, Ru/C, Ni/C, and Pd/C, respectively. After 20 rounds of successive reaction, 98 % of the original activity was retained for PdFe intermetallic nanocrystals. Further mechanistic studies revealed that PdFe intermetallic nanocrystals enabled the maintenance of metallic Fe species via a reversible oxidation–reduction process in CO₂ methanation. The metallic Fe in PdFe intermetallic nanocrystals induced the direct conversion of CO₂ into CO* as the intermediate, contributing to the enhanced activity.