Sixiu Sun

Solvothermal synthesis of Mg(OH)2 nanotubes using Mg10(OH)18Cl2·5H2O nanowires as precursors

Nanotubes of Mg(OH)2 have been synthesized by a simple solvothermal method using Mg10(OH)18Cl2·5H2O nanowires as precursors without any surfactant or catalyst. XRD, TEM, ED and HRTEM have been used to characterize the structure, morphology and composition of the nanotubes. The significant variation of intensity between the (001) and other lattice planes indicates preferential growth of the nanotubes. TEM results show the nanotubes are well-crystallized, and the nanotubes are 80–150 nm in outer diameter, 30–50 nm in wall thickness, and 5–10 µm in length. The ED pattern reveals that the Mg(OH)2 nanotubes are single crystals, and the nanotubes grow along the [110] direction. This conclusion was supported by HRTEM studies. The advantages of our method for the nanotubes synthesis lie in the high yield and the low temperature and mild reaction conditions, which permit large scale production at low cost.

Formation of CeO2 nanotubes from Ce(OH)CO3 nanorods through Kirkendall diffusion.

In this paper, CeO(2) nanotubes based on the Kirkendall effect (for simplicity, this type of nanotubes is denoted as K-type CeO(2) nanotubes) are fabricated through a solid-liquid interface reaction between Ce(OH)CO(3) nanorods and NaOH solutions. Our studies indicate the formation mechanism of K-type CeO(2) nanotubes is quite different from those of CeO(2) nanotubes subjected to template (T-type CeO(2) nanotubes) and lamellar rolling (L-type CeO(2) nanotubes) reported previously by our group. The K-type CeO(2) nanotubes are prepared by congregating Kirkendall voids and subsequent calcinations. The time evolution processes are imaged by TEM, and the results show that as the reaction processes, interior spaces are formed and enlarged in Ce(OH)CO(3) nanorods to form K-type CeO(2) nanotubes. In contrast, the interior space in T-type CeO(2) nanotubes decreases with reaction time. XRD is applied to study the phase transformation in the formation process of K-type CeO(2) nanotubes. Our study also indicates NaOH and reaction temperature are two key factors responsible for formation of K-type CeO(2) nanotubes. Combined with the T- and L-type nanotubes, three types of CeO(2) nanotubes with different formation mechanisms are successfully synthesized in one reaction system, which might afford some guidance for the synthesis of other inorganic nanotubes.

In situ growth of Au@CeO2 core–shell nanoparticles and CeO2 nanotubes from Ce(OH)CO3 nanorods

Core–shell (CS) nanoparticles (NPs) have many applications in areas such as catalysis and sensing. The utilization of hollow nanostructured materials as the supports, such as nanotubes (NT), is a growing interest to anchor NPs. Generally, several steps are necessary to prepare CS NP–NT nanocomposites, including: (i) the synthesis of CS NPs; (ii) the preparation of NTs; and (iii) the combination of CS NPs and NTs. Moreover, surface modifications with organic ligands are often involved during the synthesis of CS NPs and/or the step combining CS NPs and supports. Here we report a facile method for in situ growth of Au@CeO2 CS NPs and CeO2 NTs by mixing HAuCl4 and Ce(OH)CO3 nanorods under mild conditions. The formation of Au–CeO2 nanocomposite is due to the interfacial oxidation–reduction reaction between HAuCl4 and Ce(OH)CO3, where Au(III) in HAuCl4 is reduced to Au(0) by Ce(III) in Ce(OH)CO3, while Ce(III) is oxidized into Ce(IV), followed by hydrolysis to generate CeO2. The slow hydrolysis rate of Ce(IV) leads to the coverage of CeO2 on the Au NPs, and on the residual Ce(OH)CO3 surface, developing into Au@CeO2 and Ce(OH)CO3@CeO2 CS structures. Further depletion/dissolution of Ce(OH)CO3 results in Au@CeO2 CS NP–CeO2 NT nanocomposite eventually. The advantages of our synthetic strategy are independent of foreign reducing agents and additional surface modification. And, such CS NP–NT nanocomposite can be obtained in one step, simplifying the synthesis procedures greatly. This method based on interfacial oxidation–reduction may be employed as a unique entry to other nanocomposites.

Synthesis, growth, and characterization of Nd-doped SrGdGa3O7 crystal

A disordered Nd:SrGdGa3O7 (Nd:SGGM) laser crystal was grown by the Czochralski method. The space group and effective segregation coefficient of Nd3+ were determined to be P4¯21m and 1.36, respectively. Thermal properties, including the average linear thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity were measured. It was found that the thermal conductivity increases with increasing temperature, indicating glasslike behavior. Sellmeier’s equations were fitted by measuring the refractive indices in the range of 253–2325 nm. The polarization absorption and emission spectra were measured at room temperature, and Judd–Ofelt analysis was carried out to calculate the fluorescence branching ratios from the upper F43/2 state and the fluorescence lifetime. The stimulated emission cross section for the F43/2→I411/2 transition was calculated to be 2.00×10−20 cm2. Finally, a diode-pumped laser experiment at 1.06 μm is described. Thermal, optical, and laser properties have show...

Preparation of different morphologies of calcium sulfate in organic media

In this paper, we reported an effective method for controlling CaSO4 crystal growth in organic media. Ca2+ and SO42− ions were extracted into the organic phase using different extractants. Different morphologies and sizes of CaSO4 nanocrystals including nanoparticles and nanosheets and long fibers were prepared by changing the molar ratio of [SO42−]∶[Ca2+] in the organic solvent at room temperature. The effect of the molar ratio of [SO42−]∶[Ca2+] on the CaSO4 growth process was studied principally by TEM. In addition, it was found that the diluent polarity could also affect the growth process of CaSO4 crystals.

Thermal properties of monoclinic crystal Er3+:Yb3+:Ca4YO(BO3)3

A large Er3+–Yb3+ co-doped yttrium calcium oxoborate [Er3+:Yb3+:Ca4YO(BO3)3, abbreviated as Er:Yb:YCOB] single crystal, with dimensions of 2.5 cm in diameter and 9.0 cm in length, has been grown along the crystallographic b axis by the Czochralski method. X-ray powder diffraction results show that the as-grown Er:Yb:YCOB crystal belongs to the monoclinic system with space group Cm; the unit-cell constants are a = 8.085, b = 16.048, c = 3.528 A and β = 101.11°. The high crystalline quality of the as-grown single crystal was confirmed by high-resolution X-ray diffraction, which showed the full width at half-maximum of the rocking curves to be less than 20 arcseconds on the (060) and (\overline 201) diffraction planes. The measurement and calculation of the symmetrical second-rank tensor for the monoclinic crystal are described in detail in this paper. The principal coefficients of thermal expansion of the as-grown Er:Yb:YCOB crystal are αI = 11.95 × 10−6 K−1, αII = 9.20 × 10−6 K−1 and αIII = 18.93 × 10−6 K−1 over the temperature range 303.15–873.15 K. The specific heat of the crystal is 725.6 J kg−1 K−1 at 328.15 K. The principal thermal conductivity parameters are KI = 2.882 W m−1 K−1, KII = 2.687 W m−1 K−1 and KIII = 2.692 W m−1 K−1 at 328.15 K.

Thermal characterization of lowly Nd 3+ doped disordered Nd:CNGG crystal

Thermal properties of a lowly Nd(3+)-doped disordered Nd:CNGG crystal have been symmetrically investigated. At room temperature, the specific heat, thermal diffusion coefficient and density were determined to be 0.595 J/g.K, 1.223 mm(2)/s and 4.718 g/cm(3), corresponding the thermal conductivity of 3.43 W/m.K. By measuring the thermal lens at different pump power, the thermal-optical coefficient was calculated to be 9.2x10(-6) K(-1) for the first time to our knowledge. All the thermal properties recovered that this material can be used in the moderate and even high pump power.

The study on formation of the reversed micelle in extraction system of primary amine N1923 sulfate

The formation of reversed micelles in extraction systems of primary amine N1923 sulfate and its effect on the extraction mechanism have been investigated by the determination of the interfacial tension and the electrical conductivity in the organic phase. It has been proved by infrared spectroscopy and TEM imaging that the ammonium salt can form a reversed micelle or microemulsion. In addition, theoretical calculations are carried out in order to study further the microstructure of the reversed micelles. We are able to rationalize the unusual features of this extraction system that are found in our experiments.

Diode-pumped Q-switched intracavity frequency-doubled Nd:LuVO4/KTP green laser

A simple and compact diode-pumped acousto-optically Q-switched intracavity frequency-doubled Nd:LuVO4/KTP green laser were demonstrated successfully for the first time. At an incident pump power of 6.5 W, an average output power of 663 mW, a pulse width of 26 ns were obtained with a PRF of 10 kHz. The pulse energy and peak power of the green light were determined to be 66.3 μJ and 2.55 kW, respectively.

Synthesis and characterization of a new metal-organic NLO material: Dibromo bis(triphenylphosphine oxide) mercury(II)

A new metal-organic nonlinear optical dibromo bis(triphenylphosphine oxide) mercury(II) (HgBr(2)(TPPO)(2), TPPO=triphenylphosphine oxide) crystal has been synthesized. Single-crystal X-ray diffraction reveals that HgBr(2)(TPPO)(2) crystallizes in the orthorhombic system, space group Pna2(1), a=21.174A, b=9.1979A, c=17.468A, and Z=4. The crystal was also characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), thermal gravity analysis (TGA), and UV-vis-IR spectroscopy. Thermal analyses confirmed that the crystal is stable up to 151 degrees C. The transmission spectrum of the crystal shows that the lower cut off wavelength lies at 340nm. The nonlinear optical (NLO) property of HgBr(2)(TPPO)(2) has been estimated by Kurtz-powder second harmonic generation (SHG) test.