Layered Polysilane Research Articles

Efficient reducibility of layered polysilane (SiH)n for selective recovery of platinum ions from aqueous media

Pt ions dissolved in artificial seawater were recovered using layered polysilane (LpSi). Hydrosilyl groups (Si–H) in LpSi selectively reduced Pt ions, and the resulting Pt0 loaded LpSi catalysed the hydrogen evolution reaction as an electrocatalyst.

Photo-energy Transfer in σ-π Conjugated Polysilanes Prepared by Platinum-catalyzed Reactions of Arylacetylenes with Layered Polysilane

Platinum-catalyzed reactions of layered polysilane (Si6H6)n with arylacetylenes provided arylethenyl-substituted polysilanes. The polymers exhibited σ-π conjugation between the arylethenyl units an...

Optical Properties of Silicon Nanosheets Modified with Triphenylamine and Quinoline Units: Charge and Energy Transfer from Conjugated Substituents to the Catenated Silicon Backbone

The optical properties of triphenylamine- and quinoline-containing silicon nanosheets prepared by treatment of layered polysilane (Si6H6)n with p-(aminomethyl)triphenylamine and 4-(aminomethyl)quin...

Versatile Reducing Reaction Field within Layered Polysilane for Efficient One‐Pot Synthesis of Metal Nanoparticles

AbstractMetal nanoparticles (MNPs) have received a great deal of attention in both scientific and industrial fields because of their special characteristics originating in the nanostructure. Herein, we developed a new synthesis strategy for MNPs based on the utilization of layered polysilane (Si6H6). The special arrangements of layers in this material allows the formation of an interlayer space with both suitable dimensions and surface chemistry characteristics for reducing metal ions to MNPs in a simple and efficient manner. The interlayer space assimilates a metal ion by a capillary condensation effect. These metal ions are subsequently reduced by the hydrosilyl groups on layered polysilane, thereby forming MNPs within the interlayer space. The synthesis strategies for MNPs presented in this paper can be utilized as a method for recovering and absorbing noble or toxic metal elements.

Preparation and Photocurrent Generation of Silicon Nanosheets with Aromatic Substituents on the Surface

Soluble silicon nanosheets whose surfaces were modified with benzene-, naphthalene-, and carbazole-containing amino substituents (NS-Ph, NS-Np, and NS-Cz) were prepared by dehydrogenative coupling of layered polysilane Si6H6 with the corresponding amines. X-ray diffraction (XRD) analysis of the dried samples revealed a clear diffraction peak at 13.2 A for NS-Np, which was likely due to the stacked layers, whereas no clear signals were observed for NS-Ph and NS-Cz. The nanosheets produced UV–vis absorption and photoluminescence (PL) bands that were due to both the aromatic units and the silicon sheets consisting of two-dimensional silicon catenation. The strong tendency of NS-Np to form stacked layers was confirmed also from the PL spectrum that revealed a broad band likely ascribed to π-stacking. Photocurrent generation by use of the NS-Np and NS-Cz films was also investigated.

Surface Modification of Layered Polysilane with n-Alkylamines, α,ω-Diaminoalkanes, and ω-Aminocarboxylic Acids

Surface modification of a layered polysilane consisting of two-dimensional crystalline silicon layers was investigated using n-alkylamines, α,ω-diaminoalkanes, and ω-aminocarboxylic acids. All products of the reactions with n-butyl- to n-hexadecylamines were dispersed as nanosheets in chloroform and exhibited the same blue light emission and photoluminescence spectra when exposed to UV light. After removal of the solvent, these products formed regularly stacked structures with an interlayer distance that increased in proportion to the alkyl length. The structure consists of bilayered alkyl chains with a tilt angle of ca. 47°. When the layered polysilane was reacted with α,ω-diaminoalkanes, the products were not dispersed in chloroform, because the silicon layers were covalently bonded by the diamines. The interlayer distances for these products also increased in proportion to the alkyl length. The layered polysilane was also successfully reacted with 12-aminododecanoic acid in pyridine or other polar solv...

Characteristics of layered polysilane and its application to lithium ion battery anodes

Although layered polysilane (LPS) has a graphitelike structure and a higher electric capacity than Si powder, LPS shows poor cycling performance. Therefore, to improve its cyclability, the synthesis of composite materials of LPS and carbon was attempted. Carbon-coated LPS (C-LPS) was prepared by pulsed laser deposition (PLD), and a silicon–carbon (Si–C) composite consisting of silicon plates coated onto carbon particles was obtained by reacting LPS with sucrose. The cycling performance characteristics of the C-LPS and Si–C composite electrodes were better than that of the LPS electrode. On galvanostatic discharge–charge curves, although the Si–C composite showed no plateau at 0.3 V on the first discharge, the LPS and C-LPS electrodes showed a 0.3 V plateau that was due to the dissociation of the Si–H bonds of LPS, which led to a high initial irreversible capacity.

Synthesis and modification of two-dimensional crystalline silicon nanosheets

Soft chemical synthesis of silicon nanosheets (SiNSs) and functionalized modified SiNSs are reviewed. Free standing SiNSs with sub-nanometer thicknesses have been prepared by exfoliating layered silicon compounds, and they are found to be composed of crystalline single-atom-thick silicon layers. SiNSs are new silicon nanomaterials, as are silicon nanoparticles and nanowires. Organic modified SiNS can be prepared by modifying a layered polysilane, which has an analogous structure to that of graphite, and this allows the properties of the SiNS to be controlled in order to make it suitable for particular applications. The potential applications of these SiNSs and organic modified SiNSs are also reviewed.

Mechanochemical lithiation of layered polysilane.

Lithiated polysilane was synthesized by the mechanochemical reaction of layered polysilane with metallic lithium. The resulting dark green powder formed a Si-Li bond on the surface and demonstrated electroconductivity.

Preparation of Alkyl-Modified Silicon Nanosheets by Hydrosilylation of Layered Polysilane (Si6H6)

Alkyl-modified crystalline silicon nanosheets 2 were synthesized and maintained the crystal structure of a Si(111) plane, in which the dangling silicon bond is stabilized by capping with the alkyl group. 2 was characterized using UV-vis, Fourier transform-infrared, and X-ray photoelectron spectroscopies; X-ray diffraction; and X-ray absorption near edge structure analysis. A model structure is proposed that has a periodicity through the nanosheet surface.

Properties and Mechanism of Layered Polysilane (Si6H6) Anode

Layered polysilane (Si6H6) is graphite-like structure which has higher capacity than crystalline silicon. The rate of increase of the thickness of a layered polysilane electrode after 10 charge-discharge cycles was smaller than that for a Si powder electrode, although layered polysilane electrode has higher capacity. The structural changes of electrochemically lithiated and delithiated layered polysilane at room temperature were studied using X-ray diffraction and Raman spectroscopy. Layered polysilane became amorphous by insertion of lithium to 0 V, whereas insertion of lithium into crystalline silicon produces Li15Si4. Layered polysilane maintained the amorphous state during lithium insertion and deinsertion, whereas silicon changed between Li15Si4 and amorphous LixSi, which explains the smaller volume change of a layered polysilane electrode compared with a Si powder electrode.

Si–C composite anode of layered polysilane (Si6H6) and sucrose for lithium ion rechargeable batteries

Silicon–carbon (Si–C) composites were formed by mixing layered polysilane with sucrose, and then sintering. The Si–C composites had a unique form, which consisted of Si plates coated onto carbon particles. These composites were completely different from other Si–C composites made from silicon powder, which consist of carbon-coated silicon particles. Electrodes consisting of Si–C composites made from layered polysilane had a high capacity and a high capacity retention compared to layered polysilane electrodes, because the layered polysilane attached to carbon particles had a higher conductivity than a simple mixture of layered polysilane and carbon powder.

Characteristics and structural change of layered polysilane (Si 6H 6) anode for lithium ion batteries

Layered polysilane (Si 6H 6) has a graphite-like structure with higher capacity than crystalline silicon. The rate of increase of the thickness of a layered polysilane electrode after 10 charge–discharge cycles was smaller than that for a Si powder electrode, although the layered polysilane electrode has higher capacity. The structural changes of electrochemically lithiated and delithiated layered polysilane at room temperature were studied using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Layered polysilane became amorphous by insertion of lithium to 0 V, whereas insertion of lithium into crystalline silicon produces Li 15Si 4. Layered polysilane maintained an amorphous state during lithium insertion and deinsertion, whereas silicon changed between Li 15Si 4 and amorphous Li x Si, which explains the smaller volume change of a layered polysilane electrode compared with a Si powder electrode.

Silicon Nanosheets and Their Self-Assembled Regular Stacking Structure

Silicon nanomaterials are encouraging candidates for application to photonic, electronic, or biosensing devices, due to their size-quantization effects. Two-dimensional silicon nanosheets could help to realize a widespread quantum field, because of their nanoscale thickness and microscale area. However, there has been no example of a successful synthesis of two-dimensional silicon nanomaterials with large lateral size and oxygen-free surfaces. Here we report that oxygen-free silicon nanosheets covered with organic groups can be obtained by exfoliation of layered polysilane as a result of reaction with n-decylamine and dissolution in an organic solvent. The amine residues are covalently bound to the Si(111) planes. It is estimated that there is ca. 0.7 mol of residue per mole of Si atoms in the reaction product. The amine-modified layered polysilane can dissolve in chloroform and exfoliate into nanosheets that are 1-2 microm wide in the lateral direction and with thicknesses on the order of nanometers. The nanosheets have very flat and smooth surfaces due to dense coverage of n-decylamine, and they are easily self-assembled in a concentrated state to form a regularly stacked structure. The nanosheets could be useful as building blocks to create various composite materials.

Icosahedral Polysilane Nanostructures

The existence of a family of stable Ih-symmetric polysilane nanostructures is predicted. The smallest member of the family is the dodecahedral Si20H20 cage, followed by Si80H80, Si180H180, and larger structures. The structures and stabilities of the polysilane nanostructures were determined on the basis of B3LYP and MP2 calculations. The larger cages become increasingly stable, consisting of polysilane monolayers sewed up to icosahedral shape. The structures and electronic properties of the polysilane nanostructures resemble those of the experimentally known layered polysilane, suggesting possible applications in optoelectronics.

Synthesis and Their Photo Luminescence of SiO2 Nanosheets Derived from Layered Polysilane

Synthesis and Their Photo Luminescence of SiO2 Nanosheets Derived from Layered Polysilane

Layered polysilane: thermolysis and photoluminescence

Layered polysilane (Si6H6) and its thermolysis have been studied using FTIR spectroscopy, thermogravimetry/differential thermal analysis, mass spectrometry, electron paramagnetic resonance, Si K-edge absorption and photoluminescence spectroscopy. It is found that cross-linking between (–Si6H6–)nlayers occurs through dehydrocoupling reactions when the layered polysilane is heated under vacuum or an inert atmosphere at temperatures of 100–200 °C. Structural changes in the silicon network are evident during thermolysis: the layered structure of polysilane starts to collapse at 200 °C and is transformed to amorphous hydrogenated silicon and subsequently to crystalline silicon (c-Si) at temperatures higher than 450 °C. This process is accompanied by the evolution of H2 and SiH4 gases. The resulting layered polysilane exhibits strong room temperature photoluminescence at 560 nm (ca. 2.2 eV) and a blue-shift of Si K-edge absorption (0.6 eV) relative to c-Si. Annealing the layered polysilane results in red-shifts of luminescence peak energy with the increase of annealing temperature, consistent with the trend observed in the Si K-edge absorption measurement. These results are interpreted in terms of the growth of silicon network dimension during the thermolysis. The reduction in visible luminescence intensity for the annealed product at 300 °C (or higher) is further attributed to the creation of defects, e.g., silicon dangling bonds ( g=2.0047) which provide pathways for non-radiative recombination. The relationship between layered polysilane (as well as its annealed products) and porous Si is discussed.

New deintercalation reaction of calcium from calcium disilicide. Synthesis of layered polysilane

Deintercalation of calcium from the interlayer of CaSi 2 was performed by using concentrated HCl solutions at low temperatures, 0 and −30 °C. In the reaction at 0 °C, the deintercalation took place in two steps with evolution of 1 2 mole of hydrogen per mole of CaSi 2 in each step. In the reaction at −30 °C, little evolution of hydrogen was observed. The quantitative chemical analysis, infrared and X-ray photoelectron spectroscopies, and X-ray powder diffraction measurements revealed that the solid obtained by the reaction at −30 °C was a non-oxidized layered polysilane (Si 6H 6) n with incorporation of chlorine in a molar ratio of Cl Si = 1 6 . The optical band gap of the layered polysilane was measured to be 2.4 eV. The deintercalation was topotactic, and the layered polysilane reverted to Si platelet crystals on heating at 900 °C in vacuum.

X-ray diffraction and x-ray absorption studies of porous silicon, siloxene, heat-treated siloxene, and layered polysilane

Several porous silicon, siloxene (Si6H6O3), heat-treated siloxene, and layered polysilane (Si6H6) samples have been studied with K- and L-edge x-ray photoabsorption, photoemission, and powder x-ray diffraction. The x-ray absorption of layered polysilane and porous-Si are found to be remarkably similar. In particular, the K absorption edges of these samples shift by about 0.4–0.6 eV to higher energy relative to crystalline silicon. Siloxene samples heated to 400 °C in inert gas are best described as a mixture of SiO2 and amorphous-Si. When heat-treated siloxene is studied by photoelectron spectroscopy (surface sensitive) it resembles SiO2, when it is studied by x-ray absorption (bulk and surface) features from both SiO2 and amorphous-Si are observed and when it is studied by x-ray diffraction (bulk measurement) it resembles amorphous-Si. The SiO2 is therefore predominantly at the surface and heat-treated siloxene is very small amorphous-Si particles coated with SiO2. The Si L edge of heat-treated siloxene is not shifted significantly with respect to crystalline Si, unlike that of porous-Si, as-prepared siloxene, or layered polysilane. Taken together, these results suggest that heat-treated siloxene does not resemble electrochemically prepared porous-Si but that it might resemble rapid thermal annealed porous-Si. On the other hand, we believe that layered polysilane and unheated porous-Si may be related.

Structure of siloxene and layered polysilane (Si6H6).

Powder-x-ray-diffraction measurements on siloxene and calculations of the diffraction patterns for the three commonly proposed structures of siloxene (${\mathrm{Si}}_{6}$${\mathrm{H}}_{6}$${\mathrm{O}}_{3}$) clearly show that only a structure with silicon layers is ever observed. The formation of siloxene from ${\mathrm{CaSi}}_{2}$ is topotactic, with the Si layers remaining intact and with no oxygen insertion into these layers. Siloxene prepared at 0 \ifmmode^\circ\else\textdegree\fi{}C has very little oxygen incorporated into the interlayer gaps, and can be described as hydrogen terminated silicon layers (${\mathrm{Si}}_{6}$${\mathrm{H}}_{6}$), which we call layered polysilane. Layered polysilane can be purified by reaction with aqueous HF and is pyrophoric on contact with air. In some sense, layered polysilane can be considered the silicon equivalent of graphite.