Metal Oxide Assisted Preparation of Core–Shell Beads with Dense Metal–Organic Framework Coatings for the Enhanced Extraction of Organic Pollutants

Dense and homogeneous metal–organic framework (MOF) coatings on functional bead surfaces are easily prepared by using intermediate sacrificial metal oxide coatings containing the metal precursor of the MOF. Polystyrene (PS) beads are coated with a ZnO layer to give ZnO@PS core–shell beads. The ZnO@PS beads are reactive in the presence of 2‐methylimidazole to transform part of the ZnO coating into a porous zeolitic imidazolate framework‐8 (ZIF‐8) external shell positioned above the internal ZnO precursor shell. The obtained ZIF‐8@ZnO@PS beads can be easily packed in column format for flow‐through applications, such as the solid‐phase extraction of trace priority‐listed environmental pollutants. The prepared material shows an excellent permeance to flow when packed as a column to give high enrichment factors, facile regeneration, and excellent reusability for the extraction of the pollutant bisphenol A. It also shows an outstanding performance for the simultaneous enrichment of mixtures of endocrine disrupting chemicals (bisphenol A, 4‐tert‐octylphenol and 4‐n‐nonylphenol), facilitating their analysis when present at very low levels (<1 μg L^?1) in drinking waters. For the extraction of the pollutant bisphenol A, the prepared ZIF‐8@ZnO@PS beads also show a superior extraction and preconcentration capacity to that of the PS beads used as precursors and the composite materials obtained by the direct growth of ZIF‐8 on the surface of the PS beads in the absence of metal oxide intermediate coatings.     

Colorimetric Chemosensor for Chloramphenicol Based on Colloidal Magnetically Assembled Molecularly Imprinted Photonic Crystals

A novel colorimetric chemosensor with good sensitivity, specificity, and self‐reporting capability for chloramphenicol (CAP ) has been successfully constructed based on colloidal, magnetically assembled photonic crystals coupled with molecular imprinting. The colloidal, magnetically assembled, molecularly imprinted photonic crystals (CMA ‐MIPCs ) were prepared by assembling CAP in magnetic, molecularly imprinted nanohydrogels (MMIHs ) in a magnetic field. The magnetic assembly of photonic crystals and the sensing processes could be completed simultaneously when MMIHs were dispersed in CAP solutions and in a magnetic field, and the response time was less than 1 min. The CAP concentration could be visually determined from the color change of the CMA ‐MIPCs sensor. The diffraction color blue‐shifted from luminous yellow of the blank to purple in a 1.0 mg/mL CAP solution, with a determination limit of 1.0 × 10⁻³ mg/mL. It could provide a new strategy for qualitative or semiquantitative detection of CAP .     

On the minimal sum of Betti numbers of an almost complex manifold

We show that the only rational homology spheres which can admit almost complex structures occur in dimensions two and six. Moreover, we provide infinitely many examples of six-dimensional rational homology spheres which admit almost complex structures, and infinitely many which do not. We then show that if a closed almost complex manifold has sum of Betti numbers three, then its dimension must be a power of two.     

Like‐Charge Attraction: A Combined Electrostatic–Hydrodynamic Approach

Abstract

This article discusses the like‐charge attraction of colloidal spheres close to a charged plate and compares results produced by an electrostatic and a hydrodynamic model with experimental data. Hydrodynamic coupling is shown to be the dominating effect, while the electrostatic influence may often be neglected. Some observations, however, can be explained only by means of a combined electrostatic–hydrodynamic model, which is derived in this work. The combined model is able to predict not only the attractive force between particles of similar charge close to a charged plate but also the change to a purely repulsive force once the sphere‐plate distance is further reduced. This prediction matches qualitatively results of experiments reported in the literature.     

Étude des Interactions du Zinc et de l'Or dans l'Étain Liquide

Abstract

Les auteurs ont étudié par voie électroehimique l'influence de faibles additions d'or sur les propriétés thermodynamiques du zinc en solution diluée dans l'étain fondu. Le paramètre d'interaction de Wagner ?_Zn ^Au et sa variation avec la température ont été déterminés dans l'intervalle de température 420–650°C: ?_Zn ^Au = 2.71 – 5.92. 10³/T.     

First and second coordination spheres in 8-azaxanthinato salts of divalent metal aquacomplexes – Ab initio and DFT study

The hydrogen bonding pattern in complexes of the type [M²⁺(H₂O)₆](dmax)₂ (M = Mn, Ni, Co, Zn, Cd, Hdmax = 1,3-dimethyl-8-azaxanthine), [M²⁺(H₂O)₄(py)₂](dmax)₂ (M = Mn, Co, Zn, Cd, py = pyridine) and [M²⁺(dmax)₂(H₂O)₂(py)₂]·2H₂O (M = Ni, Cu) were studied by ab initio (MP2/LANL2DZ//B3LYP/LANL2DZ) and density functional theory methods (B3LYP/LANL2DZ, B3LYP/6-31G^∗∗ and B3PW91/6-31G^∗∗). The investigation includes a variety of theoretical analyses, which include interaction energy, many body analyses, electron density analysis, topological analysis, Mulliken atomic charges, natural atomic charges and harmonic vibrational analysis. The geometrical parameters and vibrational frequencies of dmax (the mono anion of 1,3-dimethyl-8-azaxanthine), [M²⁺(H₂O)₆] (M = Mn, Ni, Co, Zn, Cd), [M²⁺(H₂O)₄·(py)₂] (M = Mn, Co, Zn, Cd) and the complexes, calculated by the theoretical methods, were compared with the recent X-ray crystallographic results and it was observed that the results are found to agree well with the crystallographic results. The present calculations provide an important physicochemical insight into metal cations with 1,3-dimethyl-8-azaxanthine. The results also reveal the active role of coordinated water molecules in modulating the binding of the cation through a specific network of hydrogen bonds. The topology of the motifs generated by these hydrogen bonds has been characterized, adapting to the second coordination sphere concepts usually applied to the first (monodentate, chelate, and bridge) coordination sphere. The optimized structures of the Cd²⁺, Zn²⁺ and Cu²⁺ complexes further interact among themselves in a less tight fashion to generate three dimensional structures (a tape-like hydrogen bond network). Finally these tape-like hydrogen bond network were optimized using the B3LYP/LANL2DZ basis set.     

Star-PDMAEMA-β-CD-Stabilized Colloidal Gold Nanoparticles: Synthesis,Characterization and pH-Controlled Assembly

Colloidal gold nanoparticles were prepared through in situ reduction in the presence of water-soluble star homopolymer with β-cyclodextrin core and poly[2-(dimethylamino) ethyl methacrylate] arms (star PDMAEMA-β-CD) at ambient temperature. In this process, star PDMAEMA-β-CD acted as both reducing agent and stabilizing agent for gold nanoparticles. More importantly, the optical properties and the morphology of star-PDMAEMA-β-CD-stabilized colloidal gold nanoparticles were sensitive to the solution pH due to structural changes of the polymer. Different assemblies can be formed by tuning the pH of the medium. Fourier transform infrared (FT-IR), UV-Vis absorption spectroscopy, transmission electron microscopy (TEM), dynamic laser light scattering (DLS) and X-ray diffraction (XRD) were used to characterize the synthetic gold nanoparticles and the pH-controlled assembly of gold nanoparticles.     

纳米镍钴铁氧体空心微球的制备与性能

以乙二醇为溶剂,氯化铁、氯化钴、氯化镍和醋酸铵为反应试剂,采用溶剂热法制备纳米Ni_xCo_1-xFe₂O₄(x=0、0.3、0.5、0.7、1)铁氧体空心微球,研究镍含量对铁氧体空心球的磁性与吸波性能的影响。借助X-射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、振动样品磁强计(VSM)和网络分析仪对试样的物相组成、微观形貌和电磁特性进行表征。结果表明制备的镍钴铁氧体为尖晶石结构,且形貌为空心球,粒径在200 nm左右。当x=0时,镍钴铁氧体空心球饱和磁化强度最大为81.7 emu·g^-1,反射损耗在1 658.8 MHz有最小值为-16.9 dB。     

骨架结构多孔TiO2薄膜增强染料敏化太阳能电池性能

以空心球状TiO₂为基体、以片状TiO₂为骨架,采用刮刀法制备了染料敏化太阳能电池的多孔TiO₂光阳极薄膜。光电转化效率测试结果表明,当作为骨架支撑材料的片状TiO₂含量为20wt%时,光阳极薄膜组装成太阳能电池的光电转化效率达到最高值4.53%,比商业P25制备的无孔无骨架TiO₂薄膜电池(4.06%)及无骨架结构的多孔TiO₂薄膜电池(4.17%)的性能均有显著提高。当片状TiO₂的最佳含量为20wt%电池薄膜厚度为33 μm时,太阳能电池光电转化效率进一步提升为7.06%。光电性能增强的原因是骨架结构有利于快速传输电子并增大染料吸附量。本研究通过设计制备具有骨架结构的多孔TiO₂薄膜为提高染料敏化太阳能电池性能提供了新的思路。