高热稳定性二氧化硅包覆的Au25纳米簇的制备和催化应用

具有独特的电子和几何结构,原子精确控制的金纳米簇(<2 nm)成为一种新的具有广泛研究和应用前景的纳米催化剂.负载在氧化物表面的金纳米簇通常会在高于300°C时聚集或长大.人们已经通过多种方法成功制备了对于非原子精确控制的热稳定性的金纳米颗粒.主要包括利用金属与载体强相互作用,用可还原的金属氧化物来稳定金纳米颗粒;利用物理阻隔作用使用高比表面积的载体或制备核壳、纳米粒子镶嵌在载体中来稳定金纳米颗粒.对于原子精确控制的金纳米簇,由于其外边包覆着一层配体,将其负载到载体上时要保证配体不被破坏才能保证金纳米簇的结构完整性,负载后通常要除去配体才能使催化活性位曝露出来.目前,高热稳定性(>300°C)的金纳米簇的制备方法还较少.由于金与 SiO2相互作用较弱,将超小(<2 nm)的金纳米粒子包覆于其中非常困难.因此,本文首先制备了1.3 nm的含有硅酯键的巯基配体(3-巯丙基三甲氧基硅烷)保护的 Au25[SC3H6Si(OCH3)3]18,然后将其在刚成核的 SiO2表面与正硅酸四乙酯共水解,得到了既保留了 Au25的完整结构,又避免了 Au25之间相互水解的 Au25(SC3H6SiO3)18@SiO2纳米材料.漫反射固体紫外-可见光谱证明了 Au25在包覆完成后结构的完整性.透射电镜结果表明, Au25纳米簇焙烧至400°C未发生明显聚集长大.对硝基苯酚还原实验结果表明,不同温度处理后的 Au25@SiO2配体在200°C开始脱除,温度高于传统的负载型 Au25催化剂,表明 Au25是在 SiO2内部而不是在表面,从而使配体不易离去.400°C处理后的 Au25@SiO2对4-硝基苯酚还原表现出最高的反应活性,表明该纳米簇在400°C处理后没有发生明显聚集长大.     

An ambient self‐curable latex based on colloidal dispersions in water of two functionalized polymers and the thermally reversible crosslinked films generated

An ambient self‐curable latex (ASCL) was prepared by mixing colloidal dispersions in water of a chloromethylstyrene (CMS)‐functionalized polymer and a tertiary‐amine‐functionalized polymer. The two dispersions were obtained via the conventional emulsion copolymerization of CMS and 2‐(dimethylamino)ethylacrylate (DMAEA), respectively, with styrene (St), butyl acrylate (BA), or both. No visible coagulation was observed either in the blends after 6 months of storage or after the latexes were introduced into aqueous media with pHs in the range of 3–11. Continuous, transparent, crosslinked elastic films with smooth surfaces were obtained via casting and drying the ASCL at room temperature, when one or both of the two functional polymer particles contained BA monomeric units. Thermocompression cycles; swelling experiments; solubility tests; and ¹H NMR, IR, DSC, and transmission electron microscopy tests were carried out to investigate the crosslinking and morphology of the films. The following observations were made: (1) the crosslinks in the films were generated via the Menschutkin reaction (quaternization) between the  CH₂‐Cl groups of the CMS containing particles and the amine groups of the DMAEA containing particles; (2) the crosslinked films were thermally remoldable due to reversible decrosslinking (dequaternization) on heating and recrosslinking (requaternization) on cooling; and (3) phase separation in the films was observed when one of the functional polymers (for instance, the nonpolar CMS‐St copolymer) was incompatible with the other one (for instance, the polar BA‐DMAEA copolymer). The present ASCL might be useful in producing water‐borne coatings and adhesives, elastic films, and functional membranes. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 389–397, 2001     

Preparation of Antibacterial Waterborne Polyurethane/silver Nanocomposite

Stable aqueous dispersions of silver (Ag) nanoparticles were prepared by reducing silver nitrate solutions with sodium borohydride (NaBH₄) in the presence of waterborne polyurethane as a stabilizing agent. WPU/Ag nanocomposites were obtained after evaporating water. Transmission electron microscope (TEM) shows nanoscale Ag particles are well dispersed in WPU matrix at a lower concentration, while particles exhibit a little aggregation at a higher concentration. UV‐visible spectra, X‐ray powder diffraction, and energy dispersive X‐ray spectrometer (EDS) confirm the existence of Ag particle in WPU matrix. The WPU/Ag composite films show good antibiotic ability.     

Revisit of wall‐induced lateral migration in particle electrophoresis through a straight rectangular microchannel: Effects of particle zeta potential

Previous studies have reported a lateral migration in particle electrophoresis through a straight rectangular microchannel. This phenomenon arises from the inherent wall‐induced electrical lift that can be exploited to focus and separate particles for microfluidic applications. Such a dielectrophoretic‐like force has been recently found to vary with the buffer concentration. We demonstrate in this work that the particle zeta potential also has a significant effect on the wall‐induced electrical lift. We perform an experimental study of the lateral migration of equal‐sized polystyrene particles with varying surface charges under identical electrokinetic flow conditions. Surprisingly, an enhanced focusing is observed for particles with a faster electrokinetic motion, which indicates a substantially larger electrical lift for particles with a smaller zeta potential. We speculate this phenomenon may be correlated with the particle surface conduction that is a strong function of particle and fluid properties.     

In situ UV–visible and IR absorption study of the aggregation of silver colloidal particles via chemisorption of octadecanethiol

Aggregation of silver colloidal particles in the hydrosol via chemisorption of octadecanethiol (ODT) molecules was investigated based on in situ UV–visible transmission and infrared attenuated total reflection (ATR) measurements. As‐prepared silver hydrosol exhibits a single absorption peak at 395 nm because of the plasma resonance of the metal particles. Upon addition of ODT‐dissolved ethanol to the hydrosol, the resonance band red‐shifts and broadens, the detailed features of which depend on the ODT concentration and elapsed time. Both the red‐shift and the broadening are attributed to particle aggregation in the solution via ODT chemisorption. Aggregation on a germanium prism surface by the addition of ODT‐dissolved ethanol to the hydrosol was investigated using infrared ATR spectroscopy. At moderate ODT concentrations, intense aggregation via ODT chemisorption occurs strongly on the prism surface, allowing observation of ODT absorption bands. Angle‐dependent infrared ATR measurements for the ethanol and ODT molecules at the prism/solution interface clearly show that aggregation on the prism surface proceeds via the exclusion of ethanol. Copyright © 2004 John Wiley & Sons, Ltd.     

Extended light absorption and enhanced photoelectrochemical activity of palladium‐decorated hematite nanotubes prepared by photodeposition method

Palladium particles were deposited on hematite nanotube surfaces via a facile photodeposition method. Anodization method was then used for direct vertical growth of hematite nanotube arrays (HNTs) on a pretreated iron substrate. Field emission scanning electron microscopy, X‐ray diffraction, diffraction reflection spectroscopy and X‐ray photoelectron spectroscopy analyses were then used to carry out morphological and structural investigations. Compared with the bare HNTs, Pd‐decorated hematite films (Pd/HNTs) exhibit intense visible light absorption and show a red shift of the band edge. Pd/HNTs are more photoelectrochemically active than the non‐decorated films, according to chronoamperometry measurements. Thus, a promising methodology has been developed for the design of a simple and effective photoelectrode for application in photoelectrochemical water splitting systems.     

The effect of different stabilizers on the formation of self‐assembled porous film via the breath‐figure technique

The Breath‐Figure technique was employed to imprint honeycomb structures in the polymer films via the condensation of water vapor on the surface of an evaporating polymer solution. Generally, the condensed water droplets can be stabilized by an end‐functional polymer or by particles added to the polymer solution. In this study, we carried out a systematic experiment on the effect of different stabilizers on the porous honeycomb structure under identical physical conditions. The end‐functional polymer produced a large area of regular spherical bubbles, whereas adding particles to the polymer solution leads to smaller arrays of the flattened bottom bubbles. The separation length between pores was larger for polymer/particle sample than that of the end‐functional polymer films. In the regular area of polymer/particle film many bubbles were not decorated by particles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1430–1436, 2011     

Facile fabrication and self‐assembly of polystyrene–silica asymmetric colloid spheres

This study presents a very simple method to fabricate organic–inorganic asymmetric colloid spheres. In this approach, when silica particles are used as the Pickering emulsifier to stabilize the monomer droplets (styrene) in water via acid–base interaction between silica particles and auxiliary monomer (1‐vinylimidazole), the exposed surfaces of silica particles are very easy to be locally modified with 3‐(trimethoxysilyl)propyl methacrylate. When water‐based initiator is added, polystyrene–silica asymmetric colloid spheres are highly yielded. The sizes of silica and polymer particles can be tunable. These organic–inorganic anisotropic colloid spheres can self‐assemble into an interesting thickness‐dependent film. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of raspberry‐like silica/polystyrene/silica multilayer hybrid particles via miniemulsion polymerization

Organic–inorganic hybrid particles have many potential applications, but almost all research has been focused on hybrid particles with one kind of inorganic nanoparticle. This article presents a novel and facile preparation approach for raspberry‐like silica/polystyrene/silica multilayer hybrid particles via miniemulsion polymerization. In this method, larger, surface‐modified silica particles are first dispersed into monomer droplets to form a miniemulsion, and then raspberry‐like silica/polystyrene/silica multilayer hybrid particles are directly obtained when miniemulsion polymerization is performed in the presence of smaller, unmodified silica particles with 4‐vinylpyridine as an auxiliary monomer. Influential parameters such as the amount of 4‐vinylpyridine, the surfactant concentration, and the pH value of the system have been investigated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1028–1037, 2007     

pH调控合成溴氧铋纳米片的底物依赖光催化特性

近年来,半导体光催化技术已广泛用于去除水中有机污染物.在各类光催化剂中,具有合适禁带宽度的溴氧铋(BiOBr,2.7 eV)材料吸引了众多研究者兴趣.通常情况下,半导体光催化降解有机污染物性能主要与光催化材料的结构性质,如物相组成、颗粒粒径、材料表面结构等相关.研究已经证实了TiO2光催化降解有机污染物具有底物依赖的特性,但是BiOBr的有机物降解特性与底物性质的关系研究尚未见文献报道.为发展高效的BiOBr太阳光催化污染净化技术,研究有机底物与BiOBr光催化降解性能的关系具有重要意义.本文分别在pH =1和pH =3条件下采用水热法合成了BiOBr纳米片(BOB-1和BOB-3),并通过X射线粉末衍射(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM),紫外-可见漫反射(DRS)等技术表征了所制备半导体光催化材料.结果表明,在不同pH条件下均能合成具有高结晶度的四方相BiOBr, BOB-1和BOB-3均由不规则的纳米片组成, BOB-3纳米片宽度大约为0.6–1.5μm,厚度大约27–44 nm,而BOB-1纳米片宽度大约为0.7–2.0μm,厚度大约50 nm.选区电子衍射观察到了BOB-1和BOB-3清晰的晶格条纹,晶格间距为0.20和0.28 nm,分别对应着四方晶系的(020)面和(110)面.选取罗丹明B(RhB)和水杨酸(SA)为典型有机底物分子,研究了BOB-1和BOB-3纳米片的底物依赖光催化特性.结果表明, BOB-1吸附SA和RhB 1 h后,吸附率分别仅为0.2%和0.8%,而BOB-3对SA和RhB的效率分别可达9.1%和12.7%;光催化降解两种底物分子的结果表明, BOB-1和BOB-3降解RhB的速率分别为4.00以及16.10 g·min–1·m2,而降解SA的速率分别为和2.35 g·min–1·m2.可见, BOB-1显示了高效降解SA的能力,而, BOB-3则表现出更强的降解RhB活性.电化学Mott-Schottky和电动电位测试结果表明, BOB-1比BOB-3有更正的价带电位和更低的表面电荷.捕获实验(KI捕获空穴, K2Cr2O7捕获电子,氩气捕获超氧负离子,异丙醇捕获羟基自由基)表明光生空穴与超氧负离子是BOB-3降解RhB的主要活性物种,而BOB-1降解SA主要是光生空穴作用,电子顺磁共振(ESR)测试进一步证实了以上结果.光电流密度测试结果表明,可见光作用下RhB可被激发到RhB*,导致BOB-3的电子空穴对分离效率高;而当电解质中存在SA时,催化剂的表面羟基与SA形成氢键,致使光生电子与空穴分离效果变差,因而光电流减少.本文提出了pH调控合成溴氧铋纳米片的底物依赖光催化降解RhB和SA机理,与BiOBr导带电位、底物分子吸附量、底物分子物理化学性质相关. BOB-1和BOB-3纳米片催化剂在可见光激发下能产生光生导带电子和价带空穴,这些光生载流子可迁移到催化剂表面.染料分子RhB在可见光作用下能发生光敏化作用生成激发态RhB*, RhB*可以将电子注入BOB-3催化剂的导带,导带上的光生电子与RhB*注入电子与吸附在其表面的氧气共同作用生成更多的超氧负离子,从而高效降解RhB.由于BOB-1比BOB-3有更正导带电势,导带电子无法直接还原氧气生成超氧负离子,仅能依靠光生空穴直接氧化RhB,导致BOB-1表现出降解RhB性能弱;对于无色的底物SA,吸附较多SA的BOB-3催化剂上的表面羟基与SA之间形成氢键作用,抑制了光生电子与空穴对的分离,导致BOB-3在可见光光催化降解SA活性弱,而BOB-1表面吸附SA较少,同时BOB-1有更负的价带电位,利用光生空穴与吸附在催化剂表面的SA反应,从而表现出高效降解SA的性能.     

Metallo‐supramolecular micelles: Studies by analytical ultracentrifugation and electron microscopy

In aqueous solutions, amphiphilic block copolymers in which a polystyrene (PS) segment is connected to a poly(ethylene oxide) (PEO) block via a bis(2,2′:6′,2″‐ terpyridine ruthenium) complex can form micelles. Such micelles of the protomer type PS₂₀‐[Ru]‐PEO₇₀, according to the preparation procedure representing frozen micelles, were studied by sedimentation velocity and sedimentation equilibrium analysis in an analytical ultracentrifuge and by transmission electron microscopy, with different techniques applied for the sample preparation. The particles obtained were surprisingly multifarious in size. In ultracentrifugation experiments performed at relatively low salt concentrations, the distributions of the sedimentation coefficient s_20,w showed a pronounced peak at 9.6 S and a broad, only partly separated second peak around 14 S. The molar mass of the particles at the peak was around 430,000 g/mol, corresponding to an aggregation number of approximately 85. The average hydrodynamic diameter of the particles in the peak fraction was approximately 13 nm. In electron micrographs of negatively stained samples, spheres of diameters between 10 and 25 nm were the most abundant particles, but larger ones with a wide size range were also visible. The latter particles apparently were composed of smaller ones. The data from both sedimentation analysis and electron microscopy showed that (1) the studied compound formed primary micelles of diameters around 20 nm and (2) the primary micelles had a tendency toward aggregation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3159–3168, 2003     

Recent advances in direct current electrokinetic manipulation of particles for microfluidic applications

Microfluidic devices have been extensively used to achieve precise transport and placement of a variety of particles for numerous applications. A range of force fields have thus far been demonstrated to control the motion of particles in microchannels. Among them, electric field‐driven particle manipulation may be the most popular and versatile technique because of its general applicability and adaptability as well as the ease of operation and integration into lab‐on‐a‐chip systems. This article is aimed to review the recent advances in direct current (DC) (and as well DC‐biased alternating current) electrokinetic manipulation of particles for microfluidic applications. The electric voltages are applied through electrodes that are positioned into the distant channel‐end reservoirs for a concurrent transport of the suspending fluid and manipulation of the suspended particles. The focus of this review is upon the cross‐stream nonlinear electrokinetic motions of particles in the linear electroosmotic flow of fluids, which enable the diverse control of particle transport in microchannels via the wall‐induced electrical lift and/or the insulating structure‐induced dielectrophoretic force.     

Synthesis and Characterization of β‐CD‐Coated Polystyrene Microspheres by γ‐Ray Radiation Emulsion Polymerization

Polystyrene (PS) microspheres coated with β‐cyclodextrin (β‐CD) were fabricated via γ‐ray‐induced emulsion polymerization in a ternary system of styrene/β‐CD/water (St/β‐CD/water). The solid inclusion complex of St and β‐CD particles formed at the St droplets–water interface can stabilize the emulsion as the surfactant. TEM and XPS results showed that β‐CD remains on the surface of PS particles. The average size of the PS particles increases from 186 to 294 nm as the weight ratio of β‐CD to St rises from 5% to 12.5%. The water contact angle (CA) of PS latex film is lower than 90°, and reduces with the β‐CD content even to 36°. Thus, this work provides a new and one‐pot strategy to surface hydrophilic modification on hydrophobic polymer particles with cyclodextrins through radiation emulsion polymerization.     

Modification of Wide‐Band‐Gap Oxide Semiconductors with Cobalt Hydroxide Nanoclusters for Visible‐Light Water Oxidation

Cobalt‐based compounds, such as cobalt(II) hydroxide, are known to be good catalysts for water oxidation. Herein, we report that such cobalt species can also activate wide‐band‐gap semiconductors towards visible‐light water oxidation. Rutile TiO₂ powder, a well‐known wide‐band‐gap semiconductor, was capable of harvesting visible light with wavelengths of up to 850 nm, and thus catalyzed water oxidation to produce molecular oxygen, when decorated with cobalt(II) hydroxide nanoclusters. To the best of our knowledge, this system constitutes the first example that a particulate photocatalytic material that is capable of water oxidation upon excitation by visible light can also operate at such long wavelengths, even when it is based on earth‐abundant elements only.     

Hydrogel Microellipsoids that Form Robust String‐Like Assemblies at the Air/Water Interface

Soft colloidal particles such as hydrogel microspheres assemble at air/water or oil/water interfaces, where the soft colloids are highly deformed and their surface polymer chains are highly entangled with each other. Herein, we report the formation of robust one‐dimensional, string‐like colloidal assemblies through self‐organization of hydrogel microspheres with shape anisotropy at the air/water interface of sessile droplets. Shape‐anisotropic hydrogel microspheres were synthesized via two‐step polymerization, whereby a hydrogel shell was formed onto preformed rigid microellipsoids. The shape anisotropy of the hydrogel microspheres was confirmed by transmission electron microscopy and high‐speed atomic force microscopy as well as by light‐scattering measurements. The present findings are crucial for the understanding of natural self‐organization phenomena, where “softness” influences microscopic assembled structures such as those of Nostoc bacteria.     

高效稳定的Ag_xS的制备及其光催化性能(英文)

分别采用水热法(AgxS-H)和原位离子交换法(AgxS-IE)制备了AgxS.采用扫描电镜(SEM)、X射线衍射光谱、紫外可见近红外吸收光谱、N2吸附-脱附、X射线光电子能谱和表面光电压测试对催化剂进行了表征.以光(λ≥420 nm)降解亚甲基蓝为模型反应,考察了AgxS的光催化性能.与AgxS-IE相比,AgxS-H具有较小的粒径、较大的禁带宽度、较低光生电荷复合率,因此具有较高的光催化活性.此外,AgxS-H还表现了较好的稳定性,循环使用五次仍能够保持较高的光催化活性.结果表明,AgxS光催化降解亚甲基蓝主要以羟基自由基氧化为主,光生空穴氧化为辅的光催化氧化过程.AgxS-H作为一种有效的光催化剂,在降解有机染料污水方面具有潜在的应用价值.     

Design and Preparation of Highly Filled Water‐Borne Polymer–Gibbsite Nanocomposites

Highly filled, high solids content, water‐borne polymer–Gibbsite nanocomposites are prepared with Gibbsite contents as high as 35 wt%. The polymer–Gibbsite nanocomposites are synthesised via conventional starved feed emulsion polymerization using negatively charged butyl acrylate‐co‐acrylic acid oligomers, which functioned as electrosteric stabilizers for the initial platelets and the subsequently formed latex particles. A simple mathematical model describing the amount of cooligomer required for the colloidal stability of the initial Gibbsite platelets and the subsequently formed particles was derived. This model was used to determine the reaction conditions required for obtaining colloidally stable nanocomposites with a targeted filler content. Cryogenic transmission electron microscopy characterization of the resulting nanocomposites with filler contents up to 20 wt% revealed fully encapsulated Gibbsite platelets and a mixed morphology of “muffin‐like” and encapsulated particles was obtained at higher filler contents.     

Water molecule adsorption properties on the BiVO4 (100) surface

The water absorption properties at the surface of BiVO4 are attracting a great deal of attention because the system is a promising candidate as a photocatalyst operating in the visible light range. This has motivated the present investigation via first principles molecular dynamics, which has revealed that a H2O molecule is adsorbed molecularly, instead of dissociatively, at the fivefold Bi site with an adsorption energy of approximately 0.58 eV/molecule. The band gap of the system shrinks slightly (by approximately 0.2 eV) upon water adsorption and it is likely that oxygen atoms belonging to the adsorbed water molecules to the Bi sites are oxidized, as inferred by the small Bi-Owater equilibrium distance (approximately 2.6-2.8 A) very close to the Bi-O bond in the bulk crystal. In the case of water adsorption at a Bi site, the distance between Hwater and V, which is a reduction site, is larger than in the case of adsorption at a V site, indicating that the proton reduction processes may be suppressed.     

Characterization and kinetic performance of 2.1 × 100 mm production columns packed with new 1.6 μm superficially porous particles

The overall kinetic performance of three production columns (2.1 mm × 100 mm format) packed with 1.6 μm superficially porous CORTECS‐C₁₈+ particles was assessed on a low‐dispersive I‐class ACQUITY instrument. The values of their minimum intrinsic reduced plate heights (h_min = 1.42, 1.57, and 1.75) were measured at room temperature (295 K) for a small molecule (naphthalene) with an acetonitrile/water eluent mixture (75:25, v/v). These narrow‐bore columns provide an average intrinsic efficiency of 395 000 plates per meter. The gradient separation of 14 small molecules shows that these columns have a peak capacity about 25% larger than similar ones packed with fully porous BEH‐C₁₈ particles (1.7 μm) or shorter (50 mm) columns packed with smaller core–shell particles (1.3 μm) operated under very high pressure (>1000 bar) for steep gradient elution (analysis time 80 s). In contrast, because their permeabilities are lower than those of columns packed with larger core–shell particles, their peak capacities are 25% smaller than those of narrow‐bore columns packed with standard 2.7 μm core–shell particles.     

Visible-Light Initiated Dispersion Photopolymerization of Styrene

Polystyrene (PS) particles were synthesized in ethanol/water mixture by dispersion polymerization using visible light irradiation, with either a N-heterocyclic carbene borane-based photoinitiating system (PIS) or a disulfide. With the full PIS and poly(ethylene glycol) methyl ether methacrylate (PEGMA) as stabilizer, the size distributions were broad and the amount of PEGMA had a strong impact on the experiment reproducibility. The addition of a base solved the problem, leading to faster polymerizations, narrower size distributions and larger particles. With the disulfide as sole PIS, bigger and narrowly distributed PS particles were again formed. Quantitative conversion was achieved in each system, with particle size ranging between 100 and 350 nm. The use of poly(N-vinylpyrrolidone) as stabilizer led to significantly larger particles, up to 1.2 μm, with narrow size distributions. The production of such large latex particles by photoinitiated polymerizations is unprecedented.