Synthesis and self-assembly of monodisperse silver-nanocrystal-doped silica particles

A simple method based on the St?ber reaction was developed to prepare silver-nanocrystal-doped silica composite particles. The silane coupling agent N-[3-(trimethoxysilyl)dropyl]ethylene diamine (TSD) incorporated Ag+ into a siloxane framework and a further chemical reducer reduced Ag+ to silver nanoparticles. TEM images showed that, in the presence of TSD, silver nanocrystals (fcc) of 2-8 nm were homogeneously doped in the silica particles, which showed a typical surface plasmon resonance (SPR) peak. The as-prepared Ag/SiO2 composite particles can be self-assembled into long-range ordered lattices (or photonic crystals) over large areas.     

Nanoparticle assemblies as probes for self-assembled monolayer characterization: correlation between surface functionalization and agglomeration behavior

The ordering of dodecyl chains has been investigated in mixed monolayers of phosphonic acid capping agents on the surface of hydrothermally prepared zirconia nanocrystals. Methyl-, phenyl-, pyryl-, and tert-butylphosphonic acids have been used to investigate series with different mixing ratios with dodecylphosphonic acid as the cocapping agent for the mixed monolayer formation. Fourier transform infrared (FTIR) studies revealed that an increasing amount (different for each type) of coadsorbed capping agent reduces the ordering of the dodecyl chains significantly. Small-angle X-ray scattering (SAXS) verified that with increasing amount of cocapping agent the agglomeration of the particles decreases. The strong correlation of the agglomeration behavior with the ordering of the surface-bound alkyl chains leads to the conclusion that interparticle bilayers, formed via long alkyl chain packing, are responsible and can be controlled on a molecular level by coadsorbing various molecules. On the basis of this correlation, nanoparticles can be used as probes for self-assembled monolayer investigation by an indirect structural method (SAXS) and correlated with the routine spectroscopical method for the chemical analysis of surface groups (FTIR).     

Dispersion and functionalization of nonaqueous synthesized zirconia nanocrystals via attachment of silane coupling agents

Zirconia (ZrO 2) nanocrystals, synthesized from zirconium(IV) isopropoxide isopropanol complex and benzyl alcohol, were dispersed and functionalized in organic solvents using three kinds of bifunctional silane coupling agents (SCAs), 3-glycidoxypropyltrimethoxysilane (GPTMS), 3-aminopropyltriethoxysilane (APTES), and 3-isocyanatopropyltriethoxysilane (IPTES). Completely transparent ZrO 2 dispersions were achieved in tetrahydrofuran (THF) with all three SCAs, in pyridine and toluene with APTES and IPTES, and in N, N-dimethylformamide with IPTES. Dynamic laser scattering (DLS) measurements and high-resolution transmission electron microscopical (HRTEM) observation indicated that the ZrO 2 nanocrystals are dispersed on a primary particle size level. Fourier transform infrared spectroscopy, solid-state (13)C- and (29)Si NMR spectroscopy, and thermogravimetric analysis demonstrated that all three SCAs are chemically attached to the surface of the ZrO 2 nanoparticles, however, in different bonding modes. Except for GPTMS/ZrO 2/THF dispersion and IPTES/ZrO 2/pyridine dispersion, all other transparent dispersions have poor long-term stability. The increasing polarity, due to high amount of APTES attached and high hydrolysis and condensation degree of the bonded APTES, and the aggregation, due to interparticle coupling via the bonded triethoxysilyl group, are the causes of the poor long-term stability for the ZrO 2 dispersions with APTES and IPTES, respectively. Nevertheless, the APTES-functionalized ZrO 2 precipitates can be deagglomerated in water to get a stable and transparent aqueous ZrO 2 dispersion via addition of a little hydrochloric acid.     

Ozonolysis and photolysis of alkene-terminated self-assembled monolayers on quartz nanoparticles: implications for photochemical aging of organic aerosol particles

Photolysis of alkene-terminated self assembled monolayers (SAM) deposited on Degussa SiO(2) nanoparticles is studied following oxidation of SAM with a gaseous ozone/oxygen mixture. Infrared cavity ring-down spectroscopy is used to observe gas-phase products generated during ozonolysis and subsequent photolysis of SAM in real time. Reactions taking place during ozonolysis transform alkene-terminated SAM into a photochemically active state capable of photolysis in the tropospheric actinic window (lambda > 295 nm). Formaldehyde and formic acid are the observed photolysis products. Photodissociation action spectra of oxidized SAM and the observed pattern of gas-phase products are consistent with the well-established Criegee mechanism of ozonolysis of terminal alkenes. There is strong evidence for the presence of secondary ozonides (1,3,4-trioxalones) and other peroxides on the oxidized SAM surface. The data imply that photolysis plays a role in atmospheric aging of primary and secondary organic aerosol particles.     

PdCu合金纳米晶体的制备和电催化活性研究

改变表面活性剂1-十八烯（ODE）和油胺（OLA）或油酸（OA）的配比,以1,2-二羟基十六烷二醇作还原剂同时还原乙酰丙酮铜Cu(acac)2和乙酰丙酮钯Pd(acac)2一步法制备了单分散的球形和米花形的PdCu纳米粒子.透射电子显微镜和XRD等结构表征表明,两种形状的PdCu纳米粒子均为（111）面占优的合金纳米晶体,其平均粒径分别为12.7 ± 0.18 和 20.4 ± 0.31 nm.电化学循环伏安法（CV）测定了两种PdCu合金纳米粒子对甲酸氧化的电催化活性.结果表明,在球形PdCu纳米粒子上得到的甲酸氧化峰电流密度约为米花状纳米粒子（PdCu-B）上的5.6倍.同时,前者显示出了更好的抗CO毒化能力.计时电流测量也表明,球状PdCu纳米粒子比米花状纳米粒子有更好的电催化稳定性能.     

Interaction of Au with thin ZrO2 films: influence of ZrO2 morphology on the adsorption and thermal stability of Au nanoparticles

The model catalysts of ZrO(2)-supported Au nanoparticles have been prepared by deposition of Au atoms onto the surfaces of thin ZrO(2) films with different morphologies. The adsorption and thermal stability of Au nanoparticles on thin ZrO(2) films have been investigated using synchrotron radiation photoemission spectroscopy (SRPES) and X-ray photoelectron spectroscopy (XPS). The thin ZrO(2) films were prepared by two different methods, giving rise to different morphologies. The first method utilized wet chemical impregnation to synthesize the thin ZrO(2) film through the procedure of first spin-coating a zirconium ethoxide (Zr(OC(2)H(5))(4)) precursor onto a SiO(2)/Si(100) substrate at room temperature followed by calcination at 773 K for 12 h. Scanning electron microscopy (SEM) investigations indicate that highly porous "sponge-like nanostructures" were obtained in this case. The second method was epitaxial growth of a ZrO(2)(111) film through vacuum evaporation of Zr metal onto Pt(111) in 1 × 10(-6) Torr of oxygen at 550 K followed by annealing at 1000 K. The structural analysis with low energy electron diffraction (LEED) of this film exhibits good long-range ordering. It has been found that Au forms smaller particles on the porous ZrO(2) film as compared to those on the ordered ZrO(2)(111) film at a given coverage. Thermal annealing experiments demonstrate that Au particles are more thermally stable on the porous ZrO(2) surface than on the ZrO(2)(111) surface, although on both surfaces, Au particles experience significant sintering at elevated temperatures. In addition, by annealing the surfaces to 1100 K, Au particles desorb completely from ZrO(2)(111) but not from porous ZrO(2). The enhanced thermal stability for Au on porous ZrO(2) can be attributed to the stronger interaction of the adsorbed Au with the defects and the hindered migration or coalescence resulting from the porous structures.     

Adsorption of 2-chloropyridine on oxides--an infrared spectroscopic study

The adsorption of 2-chloropyridine on SiO(2), TiO(2), ZrO(2), SiO(2)-Al(2)O(3) and H-mordenite has been studied by IR spectroscopy. The different modes of interaction with oxide surfaces, i.e. hydrogen-bonding and adsorption at Br?nsted or Lewis acid sites, was modelled by ab initio calculations at the B3LYP/DZ+(d) level. Adsorption on SiO(2) results in hydrogen bonding to surface hydroxyl groups, whereas the spectra obtained following adsorption on TiO(2) and ZrO(2) display evidence for electron transfer at Lewis acidic surface sites. Protonation of 2-chloropyridine at Br?nsted acidic sites was detected only for adsorption on SiO(2)-Al(2)O(3) and H-mordenite, indicating the presence of Br?nsted acidic sites on these oxide surfaces with pK(a) values 相似文献   

Dispersion of SiO2-based nanocomposites with high performance liquid chromatography

Core-shell structured Ag/SiO2 nanocomposite has been synthesized by a cyclohexane/Igepal/water reverse micelle system. The spherical nanocomposite particles were washed and concentrated with high performance liquid chromatography (HPLC) to remove the surfactant added during synthesis. Spherical SiO2 micrometer-scale particles were packed in the HPLC column as a stationary phase for the washing and dispersing of Ag/SiO2 nanocomposite particles. Surface modification of Ag/SiO2 nanocomposite particles and SiO2 microspheres with silane coupling agent enhanced the surface charge of the particles and improved the efficiency of washing with HPLC. Well-dispersed Ag/SiO2 stable suspensions were successfully attained in ethanol/water mixed solvents after HPLC washing. The state of dispersion for the Ag/SiO2 nanocomposite suspension was systematically assessed using dynamic light scattering (DLS) and transmission electron microscope (TEM) and spin coat/atomic force microscope (AFM) analyses. The mechanism of the enabling HPLC washing protocol for SiO2-based nanoparticles is discussed.     

Directing alkyl chain ordering of functional phosphorus coupling agents on ZrO2

ZrO(2) powder (6.6 m(2)/g) was modified using polymerizable phosphorus-based coupling agents (P-CAs) (i.e., phosphonic acid, phosphoric acid, and bis-phosphonic acid), resulting in densely grafted layers as determined by thermogravimetry and elemental analysis (up to 4.2 molecules/nm(2)). The applied P-CAs contained a methacrylate group, which led to the covalent incorporation of a polymerizable moiety into the grafted layer. To direct the ordering of the alkyl chains in the layer, three different approaches were evaluated with respect to their structure-directing ability by means of FT-IR and nitrogen sorption at 77 K: (i) variation of the chain length, (ii) variation of the anchoring group and (iii) comodification with a defined amount of a nonfunctional phosphonic acid (variation of the functional/nonfunctional acid ratio). It was shown that the chain length and anchoring group size have significant effects on the alkyl chain ordering and morphology of the layer.     

High-yield sol-gel synthesis of well-dispersed, colorless ZrO(2) nanocrystals

A 93% high-yield synthesis of well-dispersed, colorless zirconium dioxide (ZrO(2)) nanocrystals is reported. In this synthesis, hydrolysis and condensation reactions of zirconium(IV) tert-butoxide in the presence of oleic acid (100 degrees C) formed ZrO(2) precursors. The ZrO(2) precursors were made of -Zr-O-Zr- networks surrounded by oleic acid molecules. Annealing (280 degrees C) the precursors dispersed in dioctyl ether caused crystallization of the -Zr-O-Zr- networks, thereby generating 4 nm ZrO(2) nanocrystals stabilized with oleic acid. The particles were highly crystalline and tetragonal phase. A dense ZrO(2) nanocrystal dispersion in toluene (280 mg/mL) showed a transmittance of about 90% (3 mm optical path length) in the whole visible region.     

Preparation and self-assembly of carboxylic acid-functionalized silica

A simple method for the fabrication of silica nanoparticle film based on the covalent-bonding interaction between carboxylic acid-functionalized silica nanoparticles (SiO(2)-COOH) and amino-terminated silicon wafer was developed. Prior to assembly, silica nanoparticles with an average diameter 80 nm were prepared using the St?ber method, amino-functionalized silica nanoparticles (SiO(2)-NH(2)) were prepared by a silanization with 3-aminopropyltriethoxysilane (APTES), while carboxylic acid-functionalized silica nanoparticles (SiO(2)-COOH) were prepared by a ring opening linker elongation reaction of the amine functions with succinic anhydride, at the same time, amino-terminated silicon wafer (Si-NH(2)) was obtained by self-assembling 3-aminopropyltriethoxysilane, then one layer relative close-packed carboxylic acid-functionalized silica nanoparticles (SiO(2)-COOH) was arranged on silicon wafer through amidation reaction under DCC coupling agent.     

Thermal wetting of platinum nanocrystals on silica surface

Thermal stability of facetted Pt nanocrystals on amorphous silica support films was investigated using in situ transmission electron microscopy in a temperature range between 25 and 800 degrees C. The particles started to change their shapes at approximately 350 degrees C. Above 500 degrees C, the particles spread on the support film with increasing temperature, rather than becoming more spherical. Such temperature-induced wetting of Pt nanoparticles on silica surface can be attributed to the interfacial mixing of Pt and SiO(2) and the resulting negative interface energy.     

Selective adsorption and alignment behaviors of double- and multiwalled carbon nanotubes on bare Au and SiO2 surfaces

We present the study of selective adsorption and alignment behaviors of double- and multiwalled carbon nanotubes (dwCNTs and mwCNTs) on self-assembled monolayer (SAM) patterns, bare Au, and SiO2 surfaces. dwCNTs and mwCNTs exhibited stronger affinity to polar SAMs, bare Au, and SiO2 surfaces than to nonpolar SAM surfaces. Furthermore, we found the adsorption probability of smaller carbon nanotubes (CNTs) was higher than that of larger CNTs. As proof of concept, we successfully assembled and aligned dwCNTs and mwCNTs on Au and SiO2 substrates without relying on external forces and demonstrated wafer-scale fabrication of back-gate transistors based on dwCNTs with a high yield.     

Oleic acid assisted glycothermal synthesis of cuboidal Ba(0.6)Sr(0.4)TiO3 nanocrystals and their ordered architectures via self-assembly

The size-controllable and highly monodispersed cuboidal barium strontium titanate (BST) nanocrystals have been successfully synthesized through a glycothermal process with no mineralizers but oleic acid as growth-directing agent. The synthesized BST nanocrystals under different glycothermal conditions were structurally characterized by XRD, IR, FESEM, TEM and HRTEM and investigated with respect to the effects of key influencing factors including the amount of oleic acid, duration of glycothermal process and 1,4-butanediol/water volume ratio in the reaction media on the formation of BST nanocrystals and their size and morphological evolution. It has been found that the oleic acid incorporated into the glycothermal system plays a decisive role in promoting the formation of cuboidal nanocrystals. It allows the BST nanocrystals to form via a nucleation-growth mechanism instead of in situ reactions and the selective chemical adsorption of oleic acid molecules on the facets with lower plane indices of newly-built BST nuclei directs them to grow into uniform cuboidal BST nanocrystals. The duration of glycothermal reactions and the polarity of reaction media can remarkably affect the dynamic process of the formation of BST nanocrystals. These regularly-shaped and highly monodispersed nanocrystals show a spontaneity of self-assembling into 2D ordered architectures when they were dispersed in organic solvents like cyclohexane and droped onto a hydrophobic surface of substrates, which creates a chance for the ferroelectric oxide nanocrystals to self-assemble into nanoscale electronic devices.     

球状、立方状及空心立方状PbS纳米晶的控制合成及其形成机理

以醋酸铅为铅源,硫代乙酰胺为硫源,在表面活性剂十二烷基硫酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)共同作用下,通过简单地调节水热反应的反应温度控制合成出球状、立方状和空心立方状PbS纳米晶。利用XRD、TEM对合成产物的结构和形貌进行了表征,发现合成的球状、立方状和空心立方状PbS纳米晶尺寸均一,直径为100 nm左右。对球状、立方状和空心立方状PbS纳米晶的形成机理进行了初探,结果表明反应温度较低时,水热反应初始阶段形成的PbS小颗粒呈球形,在表面活性剂SDS的烷基链模板和CTAB微胶束软模板共同作用下生成球状PbS纳米晶;反应温度较高时,水热反应初始阶段形成的PbS小颗粒由于自身的立方相岩盐晶体结构的影响有呈立方状趋势,在SDS和CTAB共同作用下产物堆积成空心立方体状或立方状。     

Matter of age: growing anisotropic gold nanocrystals in organic media

We investigated the influence of the reduction state of gold ions on the growth of gold nanocrystals in N,N-dimethyl formamide (DMF). While freshly prepared solutions of AuCl3 produce spherical nanocrystals, aged precursor solutions containing mainly Au+ ions and Au(0) atoms lead to various branched nanoparticles. Furthermore, we show that also the amount of the reducing and stabilisation agent tetra-n-octylammonium formate (TOAF) plays a decisive role on the shape of the nanocrystals, allowing us to grow triangular and cubic nanoparticles.     

Biotinylated thermoresponsive core cross-linked nanoparticles via RAFT polymerization and "click" chemistry

A straightforward approach to the synthesis of "clickable" thermoresponsive core cross-linked (CCL) nanoparticles was developed. This approach was based on reversible addition-fragmentation chain transfer (RAFT) radical cross-linking polymerization of styrene and divinylbenzene with azide-functionalized poly(N-isopropylacrylamide) (PNIPAM-N(3)) as macro chain transfer agent in a selective solvent. Spherical nanoparticles with a diameter of 12nm were obtained after 24h polymerization. When the lyophilized CCL nanoparticles were dispersed in THF, spherical nanoparticles were observed, confirming the stability of CCL nanoparticles. The transmission electron microscopy (TEM) studies demonstrated that spherical nanoparticles and wormlike structure coexisted in the aqueous solution. The CCL nanoparticles have a lower critical solution temperature (LCST) at about 29.6°C, a little lower than that of PNIPAM homopolymer. Biotin molecules were conjugated to the surface of CCL nanoparticles via "click" chemistry in aqueous media. After bioconjugation, the LCST shifted to 28.3°C. The bioavailability of biotin to protein avidin was evaluated by a 4'-hydroxyazobenzene-2-carboxylic acid/avidin (HABA/avidin) binding assay and TEM.     

Calorimetric study of the reactions of n-alkylphosphonic acids with metal oxide surfaces

The reaction enthalpies for the solution-phase self-assembly of n-alkylphosphonic acids on the surfaces of TiO2 and ZrO2 have been determined using isothermal titration calorimetry at 298 K. The reaction enthalpies were negative (exothermic) for methyl- and n-octylphosphonic acids and positive (endothermic) for n-octadecylphosphonic acid with both metal oxides. The enthalpy/energy analysis showed that the net enthalpy of the formation of self-assembled monolayers (SAMs) at solid-liquid interface can be presented as follows: DeltaHr=-D-(DeltaHsol+DeltaHdil)-(ES-ESAM), where D is the binding energy of the SAM molecules with the solid; DeltaHsol and DeltaHdil are the enthalpies of dissolution and dilution; ES and ESAM are the surface energies of bare solid and SAM, respectively. This equation predicted an increase (and the sign change) of the reaction enthalpy as the alkyl group in n-alkylphosphonic acid increased, which explained the experimental data. Using this equation, the binding energy (D) in the SAMs of n-octyl- and n-octadecylphosphonic acids were estimated: 55+/-5 kJ/mol (for ZrO2) and 58+/-7 kJ/mol (for TiO2).     

Modification of the surface properties of porous nanometric zirconia particles by covalent grafting

We here report on the covalent grafting of various phosphated species (phosphoric acid, phenylphosphonic acid, and octyl phosphate) onto the surface of monoclinic zirconia nanoparticles obtained by hydrothermal treatment of zirconium acetate. The initial particles are 60 nm aggregates of nanometric primary grains and present an inner porosity. Small-angle X-ray scattering shows that the high specific area of the colloidal particles (450 m2 x g(-1)) decreases to 150 m2 x g(-1) upon drying. Therefore, phosphated reactants can access the whole internal surface of the aggregates only before drying. The surface of the particles can be covered with functional groups bound through a variable number of Zr-O-P bonds. Several factors probably enhance the reaction between the particles and the phosphates or phosphonates: the large specific area of the particles, a fully accessible porous network, and a large concentration of surface terminal groups. At the same time, the morphology of the particles is well preserved upon grafting. This is due to the good crystallinity of the primary grains that constitute the particles. In addition, the grafting drastically modifies the surface properties of the colloids. For example, the polarizability of the particles decreases in the sequence -POH > as-prepared ZrO2 > -PC6H5 > -POC8H17. Furthermore, the grafting of octyl phosphate allows exclusion of water from pores of 2 nm radius, up to hydrostatic pressures of 20 MPa.     

A novel method for the preparation of C18 ester-bonded RP-HPLC packings

Summary A novel procedure had been developed for the preparation of RP packings. A C₁₈ alkyl-chain was bound onto spherical silica (particle size d_p=5 μm, s=300 m²g⁻¹) with glycidoxypropyltrimethoxysilane as coupling agent. Elemental analysis, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) and chromatographic evaluation confirmed the bonding of the packings and their RP behavior.