Jintang Li

Sonocrystallization of ZIF-8 on Electrostatic Spinning TiO2 Nanofibers Surface with Enhanced Photocatalysis Property through Synergistic Effect

Semiconductor-metal-organic framework (MOF) hybrid photocatalysts have attracted increasing attention because of their enhanced photocatalytic activity. However, the effect of the interface reaction between semiconductor and MOFs is rarely studied. In this work, we studied the synthesis and photocatalytic activity of zeolitic imidazolate framework-8 (ZIF-8) decorated electrostatic spinning TiO2 nanofibers (TiO2 ESNFs). TiO2/ZIF-8 hybrid photocatalysts were prepared via a facile sonochemical route. It was crucial that the ZIF-8 was assembled homogeneously on the surface of TiO2 ESNFs and formed a N-Ti-O bond under sonochemical treatment, which may result in reducing recombination of the electron-hole pairs. The chemically bonded TiO2/ZIF-8 nanocomposites displayed excellent performance of thermal stability, controllable crystallinity, and great enhancement of photocatalytic activity in Rhodamine B (Rh B) photodegradation. Furthermore, the UV-vis light adsorption spectra of TiO2/ZIF-8 nanocomposites showed that the ZIF-8 photosensitizer extended the spectral response of TiO2 to the visible region. The new strategy reported here can enrich the method for designing new semiconductor-MOF hybrid photocatalysts.

LiF-assisted crystallization of zinc 4-carboxyphenylphosphonates with pillared layered structures

Two novel zinc phosphonates, namely Zn2Li2(OOCC6H4PO3)2 (1) and Zn2(OOCC6H4PO3)F (2) were hydrothermally synthesized by reacting zinc sulfate with 4-carboxyphenylphosphonic acid in the presence of additional LiF. Both display pillared layered structures, but with different layer topologies. In compound 1, {ZnO4} and {LiO4} tetrahedra are connected by {CPO3} tetrahedra via corner-sharing, forming an inorganic net-like layer containing 3-membered rings. In compound 2, the fluoride anion serves as a µ3-bridging ligand coordinating to three Zn atoms. The inorganic layer consists of chain (I) made up of edge-sharing {ZnO3F2} and chain (II) made up of edge-shared dimers of {ZnO4F} and O–P–O units, which are fused together in an alternative way. The organic groups of 4-carboxyphenylphosphonate ligands fill in the interlayer spaces in both cases.

Fabrication of SiO2@silicalite-1 and its use as a catalyst support

SiO2@silicalite-1, using silica sol (pH = 9.47, SiO2 ≈ 30 wt%) as the silica source, was directly synthesized in a eutectic mixture where silicalite-1 grains were formed in the three-dimensional net structure of silica gel, grown in situ by transforming amorphous SiO2 into an MFI-type structure and coated with amorphous SiO2. The alkalinity, template agent, and crystallization time strongly affect the physicochemical properties of SiO2@silicalite-1. The physicochemical properties of these samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra and nitrogen adsorption. The results show that the SiO2@silicalite-1 is synthesized in a eutectic mixture and its physicochemical properties can be tuned by controlling the content of sodium hydroxide and tetrapropyl ammonium bromide (TPABr). A time-dependent study reveals that the formation process obeys an in situ epitaxial growth and phase transformation mechanism. Finally, SiO2@silicalite-1 was used as the support to prepare TiO2-loaded SiO2@silicalite-1 (TiO2@SiO2@silicalite-1). After five loading procedures, it could load 0.44% TiO2 nanoparticles, which is higher than the TiO2 nanoparticle loading in traditional silicalite-1 (0.13%). When the catalysts were used as a catalyst for the degradation of rhodamine B (RhB) aqueous solution under UV light, the photocatalytic efficiency of TiO2@SiO2@silicalite-1 (89.2%) is higher than TiO2@silicalite-1 (only 34.6%). The rate of degradation using TiO2@SiO2@silicalite-1 is 4.3 times faster than that using TiO2@silicalite-1. Furthermore, SiO2@TiO2@silicalite-1 exhibits high stability of photocatalytic performance. After five repeated cycles, the photocatalytic efficiency of TiO2@SiO2@silicalite-1 is 88.09%, which reduces only by 1.1%.

Effects of Slag Refining on Boron Removal from Metallurgical-Grade Silicon Using Recycled Slag with Active Component

A new slag refining method to remove boron from metallurgical silicon (MG-Si) by mixed reused slag and active component was proposed. The silicon was refined with CaCl2-CaO-SiO2 slag system in this work. The boron removal efficiency under different temperature and holding time was investigated, particularly for the recycle of the used slag mixed with different amount of CaCl2 in the 2nd and the 3rd run. The multiple slag refining was adopted to test the effect of reused slag; the boron removal ratio was 96% and 94% at 1923 K and 1873 K, respectively. These methods could significantly reduce the slag amount in refining. The total transfer coefficient of boron was also derived by the boron content. The overall boron removal mechanism and effect of slag recycle on boron removal was also discussed.

Separation of Metal Impurities from Metallurgical Grade Silicon via CaO-SiO2-CaF2 Slag Treatment Followed by Leaching with Hydrochloric Acid

The separation of metal impurities from metallurgical grade silicon by a combination of slag treatment and acid leaching was investigated. Based on a detailed analysis of microstructure evolution in metallurgical grade silicon, the primary precipitated phase in silicon was tended to form Si-Ca system intermetallics after CaO-SiO2-CaF2 slag treatment. Moreover, the extraction efficiency of metal impurities from silicon with slag treatment was higher than that without slag treatment in the leaching process. Some parameters such as acid concentration, temperature, particle size, stirring speed and leaching time were also discussed. The extraction of impurities Fe, Al and Ca increased with increasing acid concentration, leaching time and decreasing particle size. Besides, the leaching kinetics of these metal impurities was confirmed to be controlled by chemical reaction with the application of cracking shrinking model.

Preparation and Characterization of Silicate-1@Kaolin Clay Ceramic with Different Na+ Concentration

In order to explore the synthesis of silicate-1 membrane on kaolin clay ceramic and the effect of Na+ ion substitution on the dielectric properties of ceramic, silicate-1@kaolin clay ceramics containing different content of Na+ were successfully synthesized by combining sintering, sol-gel, and ion exchange method. Samples were analyzed by chemical composition (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), digital hardness tester, and microwave dielectric measurement system. SEM images exhibited that a layer of silicate-1 was successfully grown on the surface of the kaolin clay ceramic. The energy dispersive spectrometer (EDS) revealed that the content of Na+ in silicate-1 decreased with increase of ion exchange time. The content of Na+ in silicate-1@kaolin clay ceramic decreased from 1.46 to 0.29% when the silicate-1@kaolin clay ceramic was treated by the unsaturated solution of NH3 from zero to two times. In this process, the dielectric constant of the silicate-1@kaolin clay ceramic almost kept the same. But the dielectric loss of silicate-1@kaolin clay ceramic decreased from 0.474 to 0.131. Silicate-1@kaolin clay ceramic is expected to be used as sensor to detect some metal ions.

Effect of solidification rate on representative impurities distribution in Si-Cu alloy

Abstract The main purpose of this article is to demonstrate that solvent refining in combination with directional solidification can be used for preparation of high purity metallurgical grade silicon for solar cells. Silicon was alloyed with copper and grew under different solidification rates from Si–Cu alloy melt. A detailed analysis of the microstructures and morphologies of Si–Cu alloy has been carried out, focusing on the distribution characteristic of representative impurities affected by solidification rate. The experimental results indicated that copper addition promotes segregation of metal impurities Fe, Al and Ca from metallurgical grade silicon, and the purification effect is more pronounced with the solidification rate decreases. It was also determined that the representative non-metallic impurity phosphorus has a remarkable separation performance after alloying with copper, which can be helpful for the phosphorus removal.

Synthesis and Characterization of Zeolitic Imidazolate Framework-8@Sodalite Composite Particles

We demonstrate the preparation of hierarchical porous structure composite particles containing sodalite cores,and outer zeolitic imidazolate framework-8 (ZIF-8) shells. The synthesis involved first synthesis of sodalite zeolites by hydrothermal reaction from alkali-activated kaolin with polyacrylamide acting as structure-directing agent, and followed by the directly in stu growth ZIF-8 nanoparticles shells over the sodalite microparticles. The resulting core shell structure ZIF-8@Sodalite composites were characterized by powder X-ray diffraction (PXRD) and scanning electron microscope (SEM) Nitrogen adsorption, Fourier Transform infrared spectroscopy (FTIR), hermogravimetry analysis (TGA) and differential thermal analysis (DTA). SEM picture showed ZIF-8 particles adhesive on the surface of Sodalite. The composites have a nitrogen sorption capability as high as around 120 cm3/g and a BET surface area of over 328.86 m2/g, which are much higher than that of pure sodalites. The weight percentage of ZIF-8 loading on sodalite external surface can be calculated to be approximately 12% by mass loss on the TG curves. It is believed that the designed ZIF-8@Sodalite particles could broaden the application areas of zeolites in heterogeneous catalysis.

Defects and Electrical Properties of Crystalline Silicon at Different Metallurgical Route

To investigate the effects of the metallurgical route on the defects in mc-Si, various metallurgical routes were conducted. Dislocation formation and the resistivity of the mc-Si were also studied. The results showed that high inhomogeneity in dislocation distribution within individual grains and paralleled tacking faults could be observed when the ingot was grown by using the feedstock prepared by adopting the sequence of slag treatment, acid leaching and vacuum refining. Different grains have various dislocation density, which was showed in ingot grown by utilizing the feedstock prepared by adopting the sequence of vacuum refining, slag treatment and acid leaching, tacking faults could also be seen, as well as some dislocation clusters. The resistivity of this two ingots was detected at various height by using the a 4-point probe silicon tester, it was expected that the resistivity of these two ingots has the same tendency of the change, and the value of the resistivity of the ingot obtained using the previous technology was relatively higher than that of the ingot obtained using the latter technology.

Effect of Na2O-SiO2 slag treatment on hydrometallurgical purification of metallurgical grade silicon

The effects of Na2O-SiO2 slag treatment on purification of metallurgical grade silicon by leaching with hydrogen fluoride have been investigated. A comparative analysis of microstructure evolution was carried out to examine the leaching behavior of impurities from metallurgical grade silicon. It was found that the distribution of metal impurities Al, Ca, Ti and Na, which co-deposited with Si and formed different intermetallic phases at grain boundaries, had manifest distinction between precipitated phase and silicon. Moreover, acid corrosion experiment results revealed that slag treatment improved the dissolution rate of metal impurities from metallurgical grade silicon as contrasted to that without slag treatment.