Chunhong Li

Lanthanide−Organic Cation Frameworks with Zeolite Gismondine Topology and Large Cavities from Intersected Channels Templated by Polyoxometalate Counterions

A family of organic-inorganic hybrid frameworks, {[Ln(H(2)O)(4)(pdc)](4)} [XMo(12)O(40)].2H(2)O (Ln = La, Ce, and Nd; X = Si and Ge; H(2)pdc = pyridine-2,6-dicarboxylate), have been prepared under hydrothermal conditions and characterized by single crystal X-ray diffraction analyses, elemental analyses, IR, and thermal gravimetric analyses. Single crystal X-ray diffraction reveals that all six compounds are isostructural, and each consists of a zeolite-like four-connected three-dimensional cationic framework {[Ln(H(2)O)(4)(pdc)](4)}(4+) and ball-shaped Keggin type [XMo(12)O(40)](4-) as templates. Interesting channels exist in the cationic framework with the gismondine topology, and these channels intersect each other to form large cavities, which array in a zigzag fashion and are occupied by nanosized [XMo(12)O(40)](4-) counterions. Moreover, these compounds display strong photoluminescent properties in the solid state at room temperature.

Transesterification of dimethyl carbonate with phenol to diphenyl carbonate over hexagonal Mg(OH)2 nanoflakes

Hexagonal Mg(OH)2 nanoflakes were synthesized via a hydrothermal method in the presence of polyethylene glycol 20000 (PEG-20000). X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were applied to characterize the composition, morphologies and structure of the Mg(OH)2 nanoflakes. Brunauer–Emmett–Teller (BET) analysis was performed to investigate the porous structure and surface area of the as-obtained nanoflakes. The transesterification of dimethyl carbonate (DMC) with phenol to produce diphenyl carbonate (DPC) was carried out over the hexagonal Mg(OH)2 nanoflakes. The evaluation results showed that the hexagonal Mg(OH)2 nanoflakes had better activity and excellent selectivity to target products compared with many conventional ester exchange catalysts. Compared with other catalysts, such as AlCl3, ZnCl2, and irregular Mg(OH)2 synthesized via a hydrothermal method without PEG-20000, which all have been widely used as catalysts for this transesterification reaction, Mg(OH)2 nanoflakes were more stable and showed a relatively high activity with a low catalyst amount. The transesterification reaction process was also analyzed with the classic thermodynamic theory, and when the reaction was carried out at 453 K, with a molar ratio of phenol to DMC of 2 : 1, a reaction time of 13 h, and a catalyst amount of 0.2% (molar ratio to phenol), the selectivity of the transesterification reaction reached 92.3%. Moreover, the deactivated hexagonal Mg(OH)2 nanoflakes could be easily reactivated by calcination under vacuum, and the regenerated Mg(OH)2 nanoflakes showed the catalytic activity almost as high as that of the fresh sample.

Controllable synthesis of zirconia nano-powders using vapor-phase hydrolysis and theoretical analysis

The feasibility of controllable synthesis of nano-crystalline ZrO2 powders using vapor-phase hydrolysis was studied. XRD, SEM, TEM, BET and TG-DTA methods were used to investigate the phase composition, particle size, and agglomeration. The formation process of the nano-particles was also analyzed with the classic Smoluchowski theory, the coupled cluster theory [CCSD(T)]/aT and/or Moller–Plesset perturbation theory (MP2)/aT. The results show that the morphology and size of the ZrO2 nano-particles were very much dependent on the ratio of ZrCl4 : H2O, which played an important part in determining the characteristics of the ZrO2 nano-particles. By increasing the concentration of water to decrease their collision rate and prevent nano-particle agglomeration, the size distribution of the nano-particle product would be decreased and a more monodisperse nano-particle product would be collected. In particular, the best characteristics were obtained using a precursor ratio of 1 : 40 (ZrCl4 : H2O). The nano-powders had a small particle size (15 nm), a high degree of crystallinity and very weak agglomeration, in a continuous instead of batch operation. This route is free of powder drying and calcination processes that are essential for wet chemical preparation, contributing to less agglomeration.

Carbamide promoted polyol synthesis and transmittance properties of silver nanocubes

In this work, silver (Ag) nanocubes with different sizes were rapidly synthesized with a modified HCl-based polyol approach by employing carbamide (CO(NH2)2) as the additive or promoter, which could shorten the reaction time from about 25 h to less than 4 h and the method could be confirmed as facile and robust. In the reaction system, the NH3 molecules play the role of aggregating Ag+ and [Ag(NH3)2]+ could gradually release Ag+, which in turn results in formation of a more homogeneous product in a short time (50 min–4 h). Some factors affecting the synthesis including the concentration, reaction time and agitator speed have also been investigated, which could be adjusted to control the size, morphology, purity and uniformity of the Ag nanocubes. A mechanism for the rapid synthesis of the Ag nanocubes was proposed. To overcome the lower repeatability of reported methods, we have supplied a robust method to synthesize Ag nanocubes and this procedure may provide a useful guide for the future synthesis of Ag or other metal nanoparticles. The transmittance properties of the different Ag nanocubes have also been detected, which demonstrated that the transmittance of the Au film coupled with the Ag nanocubes is very sensitive to not only the size of the Ag nanocubes but also the thickness of the polyelectrolyte molecular spacer layers.

One step hydrothermal synthesis of CeO2–ZrO2 nanocomposites and investigation of the morphological evolution

Uniform cauliflower-like and rough nano-spheres of CeO2–ZrO2 composites were synthesized by a facile hydrothermal process using only urea as a mineralizer without any surfactant or template. The structural morphologies were found to vary with the reaction time, calcination temperature and dosage of urea and the urea was verified to play an important role in the determination of the CeO2–ZrO2 composite nanostructures. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and other techniques. On the basis of the characterizations, it was proven that there existed migrations or movements during the hydrothermal process especially with long hydrothermal time and a possible mechanism was proposed which would go through a series of procedures of nucleation, Ostwald ripening and Kirkendall effect to account for the structural dynamics and morphological evolutions. Subsequently, the hybrid Ce0.9Zr0.1O2–GO was reduced by a hydrothermal method, which showed good adsorption for RhB.

Surfaces enhanced with film-coupled silver nanopolyhedrons for optical transmittance

A metallic nanoparticle positioned over a metal film offers enormous advantages as a highly controllable system relevant for probing field-enhancement and designing controlled-emissivity surfaces for thermo-photovoltaic devices. The film-coupled silver (Ag) nanoparticle is of particular interest due to the formation of waveguide cavity-like modes between the NPs and film. The ability of individual nanopolyhedron (NP) patch antennas, consisting of Ag NP separated from gold (Au) film by a dielectric spacer layer spacer, to act as efficient and tunable absorption elements is demonstrated. The size and shape of the gap between the nanoparticle and film can be precisely controlled using relatively simple, bottom-up fabrication approaches. We show that the film-coupled NPs provide a transmission spectrum that can be tailored by varying the geometry (the size of the NPs and/or the thickness of the spacer). We perform both experimental spectroscopy and numerical simulations of individual NPs positioned over Au film, finding excellent agreement between experiment and simulation. The waveguide mode description serves as a starting point to explain the optical properties observed.

Efficient reduction of nitric oxide using zirconium phosphide powders synthesized by elemental combination method

Zirconium phosphide (ZrP) powders were synthesized by elemental combination method via the direct reaction of zirconium powders with red phosphorus, and characterized by XRD, SEM, XPS, XRF, SAED and TEM measurements. The obtained ZrP powders were found to exhibit apparent activity in the ready eliminateion of nitric oxide (NO) via facile redox reactions, and the elimination dynamics was evaluated within the context of various important experimental parameters, such as reaction temperature and gas concentration. At a fixed amount of ZrP powders, an increasing amount of NO would be eliminated with increasing reaction temperature, and complete conversion of NO to N2 could be reached in the range of 700 to 800 °C. The addition of NH3 also facilitated NO elimination at a fixed reaction temperature. Furthermore, of the products of the elimination process, zirconia (ZrO2) powder is a kind of biocompatible material, red phosphorus can be used to produce safety matches, organophosphorous pesticide and phosphor bronze, and the produced N2 might be collected and used as a protective gas or be converted into liquid nitrogen for other purposes.

Polyol synthesis of silver nanopolyhedrons and transmittance property

ABSTRACT In this article, we report a robust method for the facile synthesis of small silver nanopolyhedrons (Ag NPs) with edge lengths controlled in the range of 50–120 nm using a facile, one-pot, and totally green method. The keys to the success of this synthesis is that the rapid nucleation of Ag atoms was facilitated through the addition of a trace amount of zinc as the additive or promoter which will react with Ag+ through a galvanic replacement reaction. By modifying the amount of additive, we were able to optimize the reduction kinetics and effectively direct the Ag atom to grow. As a result of the understanding gained during the course of this study, we have proposed the mechanism for the rapid synthesis of the Ag NPs and this ideology may provide a useful guide for the future synthesis of Au or other metal nanoparticles. Based on the Ag NPs, we have built the film-coupled colloidal nanoantennas with controlled-transmittance surfaces through the above method. The transmittance property of the metamaterial absorber is very sensitive to the thickness of the polyelectrolyte molecular spacer layers, which making it ideal absorptivity of large surface areas in the infrared and visible range.

Rapid fabrication and characterization of spherical Mumetal nanoparticles by an electrical wire explosion process

abstract Spherical Mumetal nanoparticles fabricated by the electrical wire explosion process in 1% solution of poly(acrylamide-co-acrylic acid) partial sodium salt as the explosion medium and capping agent to prevent particle agglomeration and control the size of nanoparticles. The structure, morphological features were studied by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and Transmission Electron Microscope (TEM). The size distribution and the principle elements analysis of Mumetal nanoparticles were analyzed. The DC magnetic properties of Mumetal nanoparticles were carried out on a Quantum Design superconducting quantum interference device (SQUID) and the temperature-dependence of mass magnetic susceptibility χ (T) and its inverse 1/χ for the Mumetal nanoparticles were measured in field-cooling (FC) procedures in an applied magnetic field of 50000 Oe between 2 and 300 K.