Zhonghua Wu

A SMALL-ANGLE X-RAY SCATTERING STATION AT BEIJING SYNCHROTRON RADIATION FACILITY

This article presents the development and current state of a small-angle X-ray scattering station at beamline 1W2A of the Beijing Synchrotron Radiation Facility, China. The source of the beamline is introduced from a 14-pole wiggler. A triangular bending Si(111) crystal is used to horizontally focus the beam and provide a monochromatic X-ray beam (8.052 keV). A bending cylindrical mirror coated with rhodium downstream from the monochromator is used to vertically focus the beam. The X-ray beam is focused on the detector which is fixed at 30 m from the source. The focused beam size (full width at half maximum) is 1.4 × 0.2 mm2 (horizontal × vertical) with a flux of 5.5 × 1011 phs/s at 2.5 GeV and 250 mA. Besides the routine mode of small-angle X-ray scattering, the combination of small- and wide-angle X-ray scattering, grazing incidence small-angle X-ray scattering, and time-resolved small-angle X-ray scattering in sub-second level are also available for the users. Dependent on the measurement requirements, several detectors can be chosen for the collection of scattering signals. Furthermore, multiple sample environments, including temperature, stress-strain, and liquid sampling are available for in situ measurements. In a typical camera length of 1.5 m, the small-angle X-ray scattering resolution is about 115 nm. The steady operation of the small-angle X-ray scattering station at Beijing Synchrotron Radiation Facility not only provides the small-angle X-ray scattering beam time for users, but also promotes the development and application of these techniques in China.

One-step synthesis of highly efficient nanocatalysts on the supports with hierarchical pores using porous ionic liquid-water gel.

Stable porous ionic liquid-water gel induced by inorganic salts was created for the first time. The porous gel was used to develop a one-step method to synthesize supported metal nanocatalysts. Au/SiO2, Ru/SiO2, Pd/Cu(2-pymo)2 metal-organic framework (Cu-MOF), and Au/polyacrylamide (PAM) were synthesized, in which the supports had hierarchical meso- and macropores, the size of the metal nanocatalysts could be very small (<1 nm), and the size distribution was very narrow even when the metal loading amount was as high as 8 wt %. The catalysts were extremely active, selective, and stable for oxidative esterification of benzyl alcohol to methyl benzoate, benzene hydrogenation to cyclohexane, and oxidation of benzyl alcohol to benzaldehyde because they combined the advantages of the nanocatalysts of small size and hierarchical porosity of the supports. In addition, this method is very simple.

Shape and Size Controlled Synthesis of MOF Nanocrystals with the Assistance of Ionic Liquid Mircoemulsions

In this work, the La-metal-organic frameworks (La-MOFs) were synthesized using lanthanum(III) nitrate and 1,3,5-benzenetricarboxylic acid (BTC) in H2O-in-1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), bmimPF6-in-water, and the bicontinuous microemulsions stabilized by surfactant TX-100. The MOFs prepared were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and FT-IR methods, and the microstructures of the microemulsions in the H2O/bmimPF6/TX-100 system were studied by small-angle X-ray scattering (SXAS) technique. It was shown that the dispersed droplets in the water-in-bmimPF6, bicontinuous and bmimPF6-in-water microemulsions were spherical, lamellar, and cylindrical, respectively. The shapes of the La-MOFs synthesized were similar to that of the droplets in the corresponding microemulsions. This indicated that the morphology of MOFs could be controlled by the microstructures of the microemulsions. On the basis of the systematic experimental results, the mechanism for controlling the morphology of the MOFs was proposed.

Phase transitions in the Cu2S nanowires

Phase transitions in the Cu-2-S nanowires have been studied as a function of temperature and pressure. Differential scanning calorimetry (DSC) shows an endothermic process at 101.8degreesC upon heating, corresponding to the phase transition from gamma-Cu2S (monoclinic) to beta-Cu2S (hexagonal) in the bulk (103.5degreesC). However, the reverse phase transition was found to be much lower (74.8 degreesC). X-ray diffraction (XRD) demonstrates that the c-axis of gamma-Cu2S is transformed to the c-axis of beta-Cu2S owing to the positional disorder of the Cu atoms. Two high-pressure phases of Cu,S have been identified using a diamond anvil cell and the energy-dispersive XRD technique

XANES study on the valence transitions in cerium oxide nanoparticles

The aim of this work is the determination of Ce environment and valence state in Cerium oxide nanoparticles prepared by the microemulsion method. X-ray absorption near-edge structure measurements at Ce L3 edge were performed on the nanoparticles as a function of annealing temperature, ranging from 298K to 873K under air condition. The experimental results support the conclusion that Ce ion, in the investigated systems, is in trivalence state when the annealing temperature is below 473K. As the temperature increases up to 623K, the XANES spectrum shows the coexistence of Ce3+ and Ce4+ states. When the temperature is higher than 623K, the spectra become identical to that of CeO2 with a distinct double-peak structure, corresponding to the Ce4+ state.

Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO4

Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional spin freezing even at 0 K. Experimentally searching for the structurally perfect candidates is a big challenge in condensed matter physics. Here we report the successful synthesis of a new spin-1/2 triangular antiferromagnet YbMgGaO4 with symmetry. The compound with an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing magnetic defects and no antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No spin freezing down to 60 mK (despite θw ~ −4 K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (≤|θw|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, approaches zero (<0.6%). This indicates that the possible QSL ground state (GS) of the frustrated spin system has been experimentally achieved at the lowest measurement temperatures.

Local Mn structure and room temperature ferromagnetism in Mn-doped In2O3 films

Local Mn structure, magnetic, and transport properties in Mn-doped In2O3 films were investigated systematically. The detailed structural analysis and multiple-scattering calculations reveal that Mn2+ ions substitute for In3+ sites of the In2O3 lattice and form MnIn2+ + VO complex with the O vacancy in the nearest coordination shell. All films show clear room temperature ferromagnetism and Mott variable range hopping transport behavior. The saturation magnetization of films increases first, and then decreases with Mn doping, while carrier concentration nc decreases monotonically, implying that the ferromagnetism is not mediated by the charge carriers. These results provide strong evidence that oxygen vacancies play an important role in activating the ferromagnetic interactions in Mn-doped In2O3 films.

In-situ synchrotron SAXS and WAXS investigations on deformation and α–β transformation of uniaxial stretched poly(vinylidene fluoride)

The crystalline structure evolution of poly(vinylidene fluoride) (PVDF) during tensile deformation at 60 °C, 140 °C and 160 °C, i.e. between the glass transition temperature (Tg) and the melting temperature (Tm), was investigated by in-situ synchrotron SAXS and WAXS techniques. The analysis of the obtained scattering results indicated either yielding or α–β transformation in PVDF occurred and initiated at almost the same strain level with different stretching temperatures. A deformation mechanism was proposed for PVDF to illustrate the structure evolution during uniaxial stretching at high temperature indicating that the initial crystallite and crystalline lamellae structures of stretched PVDF are destroyed and orientated not simultaneously, which is intimately related to the yield point and the initial of α–β transformation on a certain degree of orientation. The long period along tensile direction increases to a maximum and then drops into a lower but stable value during this stage of deformation.

Cationic amphiphilic drugs self-assemble to the core-shell interface of PEGylated phospholipid micelles and stabilize micellar structure

Since polymeric micelles are promising and have potential in drug delivery systems, people have become more interested in studying the compatibility of polymeric carriers and drugs, which might help them to simplify the preparation method and increase the micellar stability. In this article, we report that cationic amphiphilic drugs can be easily encapsulated into PEGylated phospholipid (PEG–PE) micelles by self-assembly method and that they show high encapsulation efficiency, controllable drug release and better micellar stability than empty micelles. The representative drugs are doxorubicin and vinorelbine. However, gemcitabine and topotecan are not suitable for PEG–PE micelles due to lack of positive charge or hydrophobicity. Using a series of experiments and molecular modelling, we figured out the assembly mechanism, structure and stability of drug-loaded micelles, and the location of drugs in micelles. Integrating the above information, we explain the effect of the predominant force between drugs and polymers on the assembly mechanism and drug release behaviour. Furthermore, we discuss the importance of pKa and to evaluate the compatibility of drugs with PEG–PE in self-assembly preparation method. In summary, this work provides a scientific understanding for the reasonable designing of PEG–PE micelle-based drug encapsulation and might enlighten the future study on drug–polymer compatibility for other polymeric micelles.

Crystallization mechanism analysis of noncrystalline Ni-P nanoparticles through XRD, HRTEM and XAFS

The crystallization behavior of noncrystalline Ni–P nanoparticles prepared by a liquid-phase pulsed-discharge method was studied through XRD, HRTEM, and X-ray absorption fine structure (XAFS) spectra from both Ni K-edge and P K-edge. A competitive growth between Ni3P and Ni crystalline phases was found. The main phases within the particles are crystalline Ni3P and Ni, while the metastable phase Ni5(P, Ni)2 is presented as a coated shell outside the particles. The appearance of feature D in the P K-edge XANES spectrum could be used as a characteristic for the formation of long-range ordered Ni3P. The standard deviation (ΔR/R) of the fitting P–Ni bond length from the theoretical value of a Ni3P crystal could be used to define the crystallization process. Although the nanoparticles were observed as XRD amorphous at 250 °C, their magnetic properties can be attributed to the formation of FCC-Ni clusters. A crystallization mechanism has been proposed to describe the crystallization process of the as-prepared noncrystalline Ni–P nanoparticles.