A polyacrylamide gel route to different-sized CaTiO3 nanoparticles and their photocatalytic activity for dye degradation

Calcium titanate (CaTiO₃) nanoparticles with different average sizes were prepared by a polyacrylamide gel route, where the particle size was tailored by using different chelating agents. Scanning electron microscope observation shows that the samples prepared by using the chelating agents EDTA, acetic acid, tartaric acid, and citric acid have an average particle size of 25, 33, 36, and 55 nm, respectively. All the particles are regularly shaped like spheres. The bandgap energy of the four samples is measured to be 3.66–3.59 eV by ultraviolet (UV)–visible diffuse reflectance spectroscopy. The photocatalytic activity of the prepared CaTiO₃ samples was evaluated by the degradation of methyl orange under 254 nm UV irradiation, revealing that they exhibit a good photocatalytic activity. Hydroxyl radicals are revealed, by the photoluminescence technique using terephthalic acid as a probe molecule, to be produced on the irradiated CaTiO₃ nanoparticles and suggested to be the primary active species toward the dye degradation.     

Fluorine‐Doped Porous Single‐Crystal Rutile TiO2 Nanorods for Enhancing Photoelectrochemical Water Splitting

Fluorine‐doped hierarchical porous single‐crystal rutile TiO₂ nanorods have been synthesized through a silica template method, in which F^? ions acts as both n‐type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F‐doped porous single crystals displays a remarkably enhanced solar‐to‐hydrogen conversion efficiency (≈0.35 % at ?0.33 V vs. Ag/AgCl) under 100 mW cm^?2 of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO₂ single crystals.     

Palladium Nanoparticles Bonded to Two‐Dimensional Iron Oxide Graphene Nanosheets: A Synergistic and Highly Reusable Catalyst for the Tsuji–Trost Reaction in Water and Air

Low cost, high activity and selectivity, convenient separation, and increased reusability are the main requirements for noble‐metal‐nanocatalyst‐catalyzed reactions. Despite tremendous efforts, developing noble‐metal nanocatalysts to meet the above requirements remains a significant challenge. Here we present a general strategy for the preparation of strongly coupled Fe₃O₄ and palladium nanoparticles (PdNPs) to graphene sheets by employing polyethyleneimine as the coupling linker. Transmission electron microscopic images show that Pd and Fe₃O₄ nanoparticles are highly dispersed on the graphene surface, and the mean particle size of Pd is around 3 nm. This nanocatalyst exhibits synergistic catalysis by Pd nanoparticles supported on reduced graphene oxide (rGO) and a tertiary amine of polyethyleneimine (Pd/Fe₃O₄/PEI/rGO) for the Tsuji–Trost reaction in water and air. For example, the reaction of ethyl acetoacetate with allyl ethyl carbonate afforded the allylated product in more than 99 % isolated yield, and the turnover frequency reached 2200 h^?1. The yield of allylated products was 66 % for Pd/rGO without polyethyleneimine. The catalyst could be readily recycled by a magnet and reused more than 30 times without appreciable loss of activity. In addition, only about 7.5 % of Pd species leached off after 20 cycles, thus rendering this catalyst safer for the environment.     

Impact of substituents on the luminescent properties and thermostability of Zn(II) 8-hydroxyquinolinates: insight from experimental and theoretical approach

Four unique 2-arylethenyl-8-hydroxyquinoline ligands (B1–B4) and their corresponding Zn(II) complexes (C1–C4) were synthesized and characterized by ¹H NMR, ESI-MS, FTIR, and elemental analysis. The aggregation behavior of Zinc salt and ligands in solution was investigated by several techniques, including ¹H NMR, UV–vis, and photoluminescence (PL). The electronic nature of arylethenyl substituents affects the absorption wavelength, the emission color, fluorescence lifetime, fluorescence quantum yield, and thermostability of Zn(II) complexes. Luminescent properties of the Zn(II) complexes correspond to the electron-withdrawing/-donating character of the arylethenyl substituents. Photophysical analyses combined with density functional theory (DFT) calculations established that the introduction of strong electron-withdrawing group (CN) decreased the HOMO–LUMO energy gap, and the introduction of electron-donating group (tert-butyl) enlarged the HOMO–LUMO energy gap.     

Tailoring the Structure of Hierarchically Porous Zeolite Beta through Modified Orientated Attachment Growth in a Dry Gel System

The crystallization of zeolite beta in a dry gel system is found to follow the orientated attachment growth route, escorted with a temporal morphology change from bulky gel, through aggregation of the particulate to large zeolitic crystals. Modification of the precrystallized gel with organosilanes can be used to tune the morphology of the ultimate beta. When hexadecyltrimethoxysilane (HTS) is employed to modify precrystallized gel, a resumed secondary growth produces a hybrid mesocrystal of agglomerated nanozeolites. Combustive removal of organics leads to the formation of hierarchically porous zeolite beta of 100 to 160 nm, composed of nanocrystal building units ranging from 20 to 40 nm, with a noticeable micropore volume of 0.19 mL g^?1 and a meso/macropore size between 5 and 80 nm. Conversely, when 1,8‐bis(triethoxysilyl)octane (BTO) is utilized to modify the same precrystallized gel, assemblages of discrete beta nanozeolite of around 35 nm are generated. These assemblages construct a hierarchical zeolite beta with a micropore volume of 0.20 mL g^?1 and auxiliary pores ranging from 5 to 100 nm. Both organosilanes bring about well‐connected hierarchical pore networks. HTS has little effect on the Brønsted/Lewis acidity, whereas BTO causes a substantial reduction of strong Brønsted acid sites. The hierarchical beta zeolite‐supported Pt catalyst exhibits improved catalytic performance for the hydroisomerization of n‐heptane.     

Effect of Electrical Contact on the Performance of Bi2S3 Single Nanowire Photodetectors

Bi₂S₃ single‐crystalline nanowires are synthesized through a hydrothermal method and then fabricated into single nanowire photodetectors. Due to the different contact barrier between the gold electrode and Bi₂S₃ nanowires, two kinds of devices with different electrical contacts are obtained and their photoresponsive properties are investigated. The non‐ohmic contact devices show larger photocurrent gains and shorter response times than those of ohmic contact devices. Furthermore, the influence of a focused laser on the barrier height between gold and Bi₂S₃ is explored in both kinds of devices and shows that laser illumination on the Au?Bi₂S₃ interface can greatly affect the barrier height in non‐ohmic contact devices, while keeping it intact in ohmic contact devices. A model based on the surface photovoltage effect is used to explain this phenomenon.     

One-pot synthesis,crystal structure,and fluorescence property of a cadmium(II) complex based on mono salicylaldehyde Schiff base ligand

A new cadmium(II) complex [Cd(NO₂-Salen)₂] containing Schiff base ligand (NO₂-Salen = N-mono-5-nitro-salicylideneamino ethanato) has been prepared through facile condensation reaction of sub-stituted salicylaldehyde with ethylene-diamine and has been structurally characterized by elemental analysis, IR spectra and X-ray diffraction. It is formulated as C₁₈H₂₀CdN₆O₆ crystallizes in the orthorhombic system, space group of Pccn. The ligand of 5-nitrosalicylaldehyde-ethylene-diamine exhibits unusual mono asymmetry tridentate mode. The Cd²⁺ ion has a coordination number of six and assumes a distorted octahedral geometry. It exhibits an offset π-π stacking interaction between the substituted benzene ligands of adjacent mononuclear complexes. The neutral monomeric units of [Cd(NO₂-Salen)₂] are linked into a one-dimensional (1D) array via the intermolecular hydrogen bonds and π-π stacking interactions. The complex exhibits strong emission in visible region with the maximum wavelength of 428 nm, which is tentatively assigned to the π → π* intraligand fluorescence.     

Norbornene/n‐Butyl methacrylate copolymerization over α‐Diimine nickel and palladium catalysts supported on multiwalled carbon nanotubes

The covalently immobilized multiwalled carbon nanotubes (MWNTs) supported three‐dimensional geometry α‐diimine nickel, palladium catalysts are prepared by corresponding α‐diimine nickel, palladium complexes and activated MWNTs. The molecular structures of the catalysts have been confirmed by X‐ray single‐crystal analyses, NMR and XPS, as well as elemental analysis. Compared with nickel, palladium catalysts without modification and physical mixing of nickel, palladium catalysts with MWNTs, the MWNTs supported nickel, palladium catalysts show improved activity and productivity in norbornene homopolymerization and copolymerization with polar monomer. The morphology of the resulting polymers obtained from MWNTs‐supported nickel(II) complex reveals that the MWNTs are dispersed uniformly in polymer and wrapped by polymers to squeeze out of spherical particles, leading to the enhanced processability and mechanical properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3213–3220     

High repetition rate optical switch using an electroabsorption modulator in TOAD configuration

A novel optical switch featured with high repetition rate, short switching window width, and high contrast ratio is proposed and demonstrated for the first time by placing an electroabsorption modulator (EAM) in a terahertz optical asymmetric demultiplexer (TOAD) configuration. The feasibility and main characteristics of the switch are investigated by numerical simulations and experiments. With this EAM-based TOAD, an error-free return-to-zero signal wavelength conversion with 0.62 dB power penalty at 20 Gbit/s is demonstrated.     

国家同步辐射实验室反射率计误差分析

中国科技大学国家同步辐射实验室"光谱辐射标准与计量实验站"上的反射率计主要用于测量各种光学元器件在X射线、真空紫外波段的反射率.为保证测试结果的精确性和可靠性,在大量实验数据的基础上,结合必要的理论推导,对反射率计测试误差来源及影响程度进行了分析,确定影响反射率计测试精度的主要因素包括光源、探测器、样品安装等.总结了光源波动、探测器损坏的几种典型形式,定性、定量地分析了这些因素和样品安装、光斑尺寸对测试精度的影响,针对性地提出了应对办法,把测试误差控制在2%以内,从而有效地保证了测试精度.