Chlorination of trichlorosilane/chlorodimethylsilane using metal chlorides: experimental and mechanistic investigations.

Removal of carbonaceous impurities from trichlorosilane (SiHCl3) reduces the carbon content of solar grade polysilicon produced with the improved Siemens method. The separation of chlorodimethylsilane (CH3)2SiHCl from SiHCl3 by distillation remains challenging due to the small difference in their boiling points. Herein, the chlorination of (CH3)2SiHCl/SiHCl3 with metal chlorides (WCl6, MoCl5) were studied. The aim was to convert (CH3)2SiHCl into (CH3)2SiCl2, increase the relative volatility of (CH3)2SiHCl and SiHCl3 and facilitate the distillation. The optimum reaction conditions were 60 °C, 60 min and n(WCl6 or MoCl5): n(SiHCl3 or (CH3)2SiHCl) = 0.7 at 0.8 MPa. Under these conditions, and when WCl6 and MoCl5 were used as the chlorine sources, the extents of (CH3)2SiHCl conversion were 22.7 and 18.5 times higher than those of SiHCl3, respectively. In addition, a mechanistic study showed that the difference between the reactions of SiHCl3 and (CH3)2SiHCl resulted from the different energy barriers for the reactions of the and (CH3)2SiCl· radicals with WCl x or MoCl x , and the barrier for the reaction was higher than that for the (CH3)2SiCl· reaction.

Experimental and DFT study of Cu(II) removed by Na-montmorillonite.

The experimental and theoretical studies on the adsorption of Cu(II) on the surface of Na-montmorillonite (Na-Mt) were reported. Effects of batch adsorption experimental parameters were studied. Density functional theory and molecular dynamics simulations were used to study the adsorption of Cu(II) on montmorillonite (001) surface. The adsorption reached equilibrium within 80 min and the adsorption capacity was 35.23 mg·g-1 at 25 °C. The adsorption data of Cu(II) were consistent with pseudo-second-order kinetics and Langmuir isotherm models. The adsorption process was dominated by physical adsorption (Ea was 37.08 kJ·mol-1) with spontaneous endothermic behavior. The influence of coexisting cations on the adsorption capacity of Cu(II) was Mg(II) > Co(II) > Ca(II) > Na(I). The simulation results demonstrated that there were no significant differences in the adsorption energy of Cu(II) at the four adsorption sites on the montmorillonite (001) surface. Cu(II) had more electron transfer than Na(I). The diffusion coefficient of Cu(II) in the aqueous solution system containing montmorillonite was 0.85×10-10 m2·s-1. Considerable amounts of Cu(II) ions were adsorbed at a distance of 0.26 and 2.25 Å from the montmorillonite (001) surface. The simulation results provided strong supporting evidence for experimental conclusions.

Synthesis of nano-octahedral MgO via a solvothermal-solid-decomposition method for the removal of methyl orange from aqueous solutions.

Nano magnesium oxide has wide applications, and MgO with (111) facets has wider potential applications than MgO with (100) facets (e.g., in catalysis and adsorption). However, nano MgO with (111) polar faces has not been studied throughly, so the preparation of nano-octahedral MgO (N-O-MgO) with eight exposed (111) facets remains a great challenge. Herein, we successfully synthesised N-O-MgO via an effective solvothermal-solid-decomposition method and studied its adsorption performance. The obtained N-O-MgO showed excellent performance (229.36 mg g-1) for methyl orange (MO). The adsorption follows the pseudo-second-order kinetic equation and the Langmuir isotherm model. The dimensionless parameter R L (0.042) and Gibbs free energy ΔG (-6.538 kJ mol-1) revealed that the adsorption of MO on N-O-MgO was a spontaneous and feasible process. The adsorption of MO and methyl blue (MB) on N-O-MgO were studied to determine the adsorption sites. Based on these experiments and analysis, it was determined that the adsorption sites were magnesium ions and the adsorption mechanism was proposed to describe the adsorption process.

Enhanced upconversion emission in crystallization-controllable glass-ceramic fiber containing Yb(3+)-Er(3+) codoped CaF2 nanocrystals.

Functional nanocrystal-containing materials have been a hot topic in recent years. However, few researches have focused on functional nanocrystals contained in optical glass fibers. In this research, transparent CaF2 glass-ceramic was prepared by a melt-quenching method. Greatly enhanced upconversion luminescence was observed after heat treatment. By applying a novel method called melt-in-tube, precursor fiber free of crystals was fabricated at the drawing temperature where the clad was softened while the core was melted. Glass-ceramic fiber with fiber core containing Yb(3+)-Er(3+) codoped CaF2 nanocrystals was obtained after heat treatment at a relatively low temperature. Electron probe micro-analyzer measurement shows no obvious element diffusion between the core and clad. Greatly enhanced upconversion emission was detected in the glass-ceramic fiber excited by a 980 nm laser, suggesting the developed glass-ceramic fiber is a promising material for upconversion laser.

Ni(2+) doped glass ceramic fiber fabricated by melt-in-tube method and successive heat treatment.

Glass ceramic fibers containing Ni(2+) doped LiGa(5)O(8) nanocrystals were fabricated by a melt-in-tube method and successive heat treatment. Fiber precursors were prepared by drawing at high temperature where fiber core glass was melted while fiber clad glass was softened. After heat treatment, LiGa(5)O(8) nanocrystals were precipitated in the fiber core. Excited by 980 nm laser, efficient broadband near-infrared emission was observed in the glass ceramic fiber compared to that of precursor fiber. The melt-in-tube method can realize controllable crystallization and is suitable for fabrication of novel glass ceramic fibers. The Ni(2+)-doped glass ceramic fiber is promising for broadband optical amplification.