Preparation of High Purity Crystalline Silicon by Electro-Catalytic Reduction of Sodium Hexafluorosilicate with Sodium below 180°C

<div><p>The growing field of silicon solar cells requires a substantial reduction in the cost of semiconductor grade silicon, which has been mainly produced by the rod-based Siemens method. Because silicon can react with almost all of the elements and form a number of alloys at high temperatures, it is highly desired to obtain high purity crystalline silicon at relatively low temperatures through low cost process. Here we report a fast, complete and inexpensive reduction method for converting sodium hexafluorosilicate into silicon at a relatively low reaction temperature (∼200°C). This temperature could be further decreased to less than 180°C in combination with an electrochemical approach. The residue sodium fluoride is dissolved away by pure water and hydrochloric acid solution in later purifying processes below 15°C. High purity silicon in particle form can be obtained. The relative simplicity of this method might lead to a low cost process in producing high purity silicon.</p></div

Results of Impurities analysis in silicon powder by ICP-MS.

<p>Not including H,C,N,B,O,F, Inert gas The detection limit of the analysis was 1 ppm wt., and accuracy and precision were estimated to be on the order of 10% relative.</p

XRD patterns of silicon particles washed with pure water and HCl at 10°C, 40°C and 60°C.

<p>XRD patterns of silicon particles washed with pure water and HCl at 10°C, 40°C and 60°C.</p

Silicon powder SEM micrographs recorded at different magnification after the sample was washed with pure water.

<p>Silicon powder SEM micrographs recorded at different magnification after the sample was washed with pure water.</p

HTEM image and SAED patterns of silicon particles washed with pure water and HCl at 10°C.

<p>HTEM image and SAED patterns of silicon particles washed with pure water and HCl at 10°C.</p

XRD pattern of the produced samples in glass flask.

<p>XRD pattern of the produced samples in glass flask.</p

Fourier transform infrared spectra of phage, sulfur nanoparticle and phage-sulfur composite.

<p>Fourier transform infrared spectra of phage, sulfur nanoparticle and phage-sulfur composite.</p

Origin spectra of N1s (A), S2p (C), O1s (E) and C1s (G) regions by X-ray Photoelectron Spectroscopy and deconvolution spectra of N1s (B), S2p (D), O1s (F) and C1s (H) for phage (blue), phage-sulfur composite (black) and sulfur nanoparticle (red).

<p>Origin spectra of N1s (A), S2p (C), O1s (E) and C1s (G) regions by X-ray Photoelectron Spectroscopy and deconvolution spectra of N1s (B), S2p (D), O1s (F) and C1s (H) for phage (blue), phage-sulfur composite (black) and sulfur nanoparticle (red).</p

Sequence-specific suppression of Wnt1 gene expression by miR-152.

<p>The two WT plasmids, pGL3-WNT1-1-wt-3′UTR and pGL3-WNT1-2-wt-3′UTR, including 90 nt spanning each seed match at the 3′UTR, as well as the two mutant controls, pGL3-WNT1-1-mut-3′UTR and pGL3-WNT1-2-mut-3′UTR, were generated based on the firefly luciferase expressing vector pGL3-promoter and confirmed by sequencing. HepG2 Cells were co-transfected with 250 ng of pGL3-WNT1-WT or pGL3-WNT1-Mut constructs with 23.5 nM of miR-152 mimics, miR-152 inhibitor, or their respective negative control. Each sample was co-transfected with 25 ng of pRL-TK plasmid expressing renilla luciferase to monitor the transfection efficiency. A luciferase activity assay was performed 48 hours after transfection with the dual luciferase reporter assay system (Promega). The relative luciferase activity was normalized with renilla luciferase activity. (<b>A</b>) WT and Mut 3′-UTRs of WNT1, indicating the interaction sites between miR-152 and 3′-UTR of WNT1. (<b>B</b>) Dual luciferase assay of HepG2 cells co-transfected with the firefly luciferase constructs containing the WNT1-1-WT or WNT1-1-Mut 3′-UTR and miR-152 mimics or its negative control (NC). (<b>C</b>) Dual luciferase assay of HepG2 cells co-transfected with the firefly luciferase constructs containing the WNT1-2-WT or WNT1-2-Mut 3′-UTR and miR-152 mimics or miR-152 mimics NC. (<b>D</b>) Dual luciferase assay of HepG2 cells co-transfected with the firefly luciferase constructs containing the WNT1-2-WT or WNT1-2-Mut 3′-UTR and miR-152 inhibitor or miR-152 inhibitor NC. Data are shown as means and standard deviations from at least three independent experiments. ** P<0.01.</p

MiR-152 regulates Wnt1 expression at both mRNA and protein level.

<p>HepG2 cells were transfected with double-stranded miR-152 mimics, single-stranded miR-152 inhibitor, or their relative negative control RNA at a final concentration of 5 nM with a HiPerFect Transfection Reagent kit as indicated for 48 h, and were collected for preparation of total RNA and protein. (<b>A</b>) Real time RT-PCR analysis for Wnt1 mRNA expression. (<b>B</b>) Western blot analysis for Wnt1 protein expression. Data are shown as means and standard deviations from triplicate experiments. * P<0.05. (inh NC: scrambled oligonucleotides as the negative control for miR-152 inhibitor; inh-152: miR-152 inhibitor; miR NC: scrambled oligonucleotides as the negative control for miR-152 mimics; miR-152: miR-152 mimics; Hcv+miR-152: Adenovirus expressing the HCV core protein+miR-152 mimics).</p