Solution Synthesis of Porous Silicon Particles as an Anode Material for Lithium Ion Batteries

Nanostructured silicon-based materials with porous structures have recently been found to be impressive anode materials with high capacity and cycling performance for lithium-ion batteries. However, the current methods of preparing porous silicon have generally been confronted with the requirement for multiple steps and complex synthesis. In the present study, porous silicon with high surface area was prepared by using a high yielding and simple reaction in which commercial magnesium powder readily reacts with HSiCl₃ with the help of an amine catalyst under mild conditions. The obtained porous silicon was coated with a nitrogen-doped carbon layer and used as the anode for lithium-ion batteries. The porous Si-carbon nanocomposites exhibited excellent cycling performance with a retained discharge capacity of 1300 mA h g⁻¹ after 200 cycles at 1 A g⁻¹ and a discharge capacity of 750 mA h g⁻¹ at a current density of 2 A g⁻¹ after 250 cycles. Remarkably, the Coulombic efficiency was maintained at nearly 100 % throughout the measurements.     

有序介孔硅包碳复合结构的制备及其储锂行为

以P123嵌段模板法合成SiO2-有序介孔(SiO2-OMPs)短棒状结构,以此为前驱体通过镁热还原和酚醛树脂碳包覆处理,成功制备出有序介孔硅/碳复合结构(Si/C-OMPs),用于锂离子电池负极材料测试。从扫描电镜图(SEM)和透射电图(TEM)观察发现,SiO2-OMPs形态可以通过HCl溶液浓度有效调控,在高浓度下获得高堆积密度的粒状有序介孔结构,并在镁热还原和碳包覆处理后这种有序介孔结构均得到完美保持。X射线衍射(XRD)数据的分析表明,镁热还原反应包括两步串连反应:Mg和SiO2先反应形成Mg2Si中间相,而后该相再还原剩余SiO2并获得终产物Si。第二步反应属于缓慢的固/固扩散过程,抑制了整个还原反应的完成,导致Si产率低且存在杂质相。电化学测试表明,由于其坚固的结构和畅通的介孔系统,有序介孔Si/C复合结构具有优异的循环稳定性和倍率性能。     

Simplified Synthesis of Biomass-Derived Si/C Composites as Stable Anode Materials for Lithium-Ion Batteries

Synthesis of silicon/carbon (Si/C) composites from biomass resources could enable the effective utilization of agricultural products in the battery industry with economical as well as environmental benefits. Herein, a simplified process was developed to synthesize Si/C from biomass, by using a low-cost agricultural byproduct “rice husk (RH)” as a model. This process includes the calcination of RH for SiO₂/C and the reduction of SiO₂/C by Al in molten salts at a moderate temperature. This process does not need the removal of carbon before thermal reduction of SiO₂, which is thought to be necessary to avoid the formation of SiC at elevated temperatures. Thus, carbon derived from biomass can be directly used for Si/C composites for anode materials. The resultant Si/C shows a high reversible capacity of 1309 mAh g⁻¹ and long cycle life (300 cycles). This research advocates a new and simplified strategy for the synthesis of RH-based biomass-derived Si/C, which is beneficial for low-cost, environmentally friendly, and green energy storage applications.     

SiOx encapsulated FeSi2–Si eutectic nanoparticles as durable anode of lithium-ion batteries

Low-cost and high-efficiency production of silicon-based material is the key to improve the energy density of lithium-ion batteries. Herein, we propose a novel structure of FeSi₂–Si eutectic nanoparticles protected by the SiO_x shell. FeSi₂, as a buffer phase can improve the electrochemical stability of the electrode. A SiO_x shell is formed on the surface of the nanoparticles through the passivation process. SiO_x encapsulated FeSi₂–Si eutectic nanoparticles exhibit excellent capacity of 674.9 mAh/g after 500 charge/discharge cycles. The capacity retention rate is above 90% after the stabilization process. This work provides a new nanomaterial design for high performance silicon-based anode materials of lithium-ion batteries.     

Rational Design of Carbon-Based 2D Nanostructures for Enhanced Photocatalytic CO2 Reduction: A Dimensionality Perspective

Photocatalytic CO₂ reduction is a revolutionary approach to solve imminent energy and environmental issues by replicating the ingenuity of nature. The past decade has witnessed an impetus in the rise of two-dimensional (2D) structure materials as advanced nanomaterials to boost photocatalytic activities. In particular, the use of 2D carbon-based materials is deemed as highly favorable, not only as a green material choice, but also due to their exceptional physicochemical and electrical properties. This Review article presents a diverse range of alterations and compositions derived from 2D carbon-based nanomaterials, mainly graphene and graphitic carbon nitride (g-C₃N₄), which have remarkably ameliorated the photocatalytic CO₂ performance. Herein, the rational design of the photocatalyst systems with consideration of the aspect of dimensionality and the resultant heterostructures at the interface are systematically analyzed to elucidate an insightful perspective on this pacey subject. Finally, a conclusion and outlook on the limitations and prospects of the cutting-edge research field are highlighted.     

Supercritical CO2-induced New Chemical Bond of C−O−Si in Graphdiyne to Achieve Robust Room-Temperature Ferromagnetism

The realization of ferromagnetic ordering of two-dimensional (2D) carbon material graphdiyne (GDY) has attracted great attention due to its promising application in spin semiconductor devices. However, the absence of localized spins makes the pristine GDY intrinsically nonferromagnetic. Herein, we report the realization of robust room-temperature (RT) ferromagnetism (FM) with Curie temperature (T_C) up to 325 K for GDY Nanosheets (GDYNs) by supercritical CO₂ (SC CO₂). Experimental and theoretical calculations reveal that the new chemical bond of C−O−Si can be formed because of the unique effect of SC CO₂, which help to enhance the charge transfer and generates long-range ferromagnetic order. The RT saturation magnetization (M_S) reaches 1.125 emu/g, which is much higher than that of carbon-based materials reported up to now. Meanwhile, by changing the conditions of SC CO₂ such as pressure, ferromagnetic responses can be manipulated, which is great for potential spintronics applications of GDY.     

Comparison of catalytic activity of carbon-based AgBr nanocomposites for conversion of CO2 under visible light

The catalytic activities of carbon-based AgBr nanocomposites (AgBr/CNT, AgBr/GP, AgBr/EG, and AgBr/AC) for CO₂ reduction to hydrocarbons under visible light were investigated in this study. The carbon-based AgBr nanocomposites were prepared on carbon-based supporting materials (CNT, GP, EG, and AC) by the deposition–precipitation method in the presence of cetyltrimethylammonium bromide (CTAB). The photocatalytic activities of AgBr nanocomposites on different supporting materials (CNT, GP, EG, and AC) were investigated by CO₂ reduction yield in the presence of water under visible light (λ > 420 nm). The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that AgBr nanoparticles were well dispersed on the surface of supporting materials. AgBr/CNT and AgBr/GP had a relatively higher reduction yield under visible light due to the transfer of photoexcited electrons from the conduction band of well-dispersed AgBr to carbon supporting materials. In addition, the carbon-based AgBr nanocomposites were stable in the repeated uses under visible light. The total product yields of carbon-based AgBr nanocomposites after the 5 repeated uses almost remained about 83% of the first run. Therefore, carbon-based AgBr nanocomposite is an effective and stable visible-light-driven photocatalyst for CO₂ photoreduction.     

The adsorption of acidic gaseous pollutants on metal and nonmetallic surface studied by first-principles calculation: A review

The acidic gases such as SO₂, NO_x, H₂S and CO₂ are typical harmful pollutants and greenhouse gases in the atmosphere, which are also the main sources of PM_2.5. The most widely used method of treating these gas molecules is to capture them with different adsorption materials, i.e., metal and nonmetallic materials such as MnO₂, MoS₂ and carbon-based materials. And doping transition metal atoms in adsorption materials are beneficial to the gas adsorption process. The first-principles calculation is a powerful tool for studying the adsorption properties of contaminant molecules on different materials at the molecular and atomic levels to understand surface adsorption reactions, adsorption reactivity, and structure-activity relationships which can provide theoretical guidance for laboratory researches and industrial applications. This review introduces the adsorption models and surface properties of these gas molecules on metal and nonmetallic surfaces by first-principles calculation in recent years. The purpose of this review is to provide the theoretical guidance for experimental research and industrial application, and to inspire scientists to benefit from first-principles calculation for applying similar methods in future work.     

Synthesis of selenium-doped carbon from glucose: An efficient antibacterial material against Xcc

Se/C as a novel carbon-based biomaterial was prepared by using cheap and abundant glucose as the carbon source. It was highly active and could well restrain Xanthomonas campestris pv. campestris (EC₅₀ = 4.7403 μg/mL), a very harmful germ causing the devastating cabbage black rot disease and resulting in huge economic losses. As a type of carbon material insoluble in water, Se/C is bio-compatible and can adhere onto the leaves of the plants to allow a slow and sustained release of its efficacy, affording an efficient method for the cabbage black rot disease prevention and cure. This work as the first report on the bioactivity studies of Se/C significantly expands the application scopes of the selenium-containing materials and may draw continuous attentions from a broad field.     

Periodic mesoporous organosilicas with co-existence of diurea and sulfanilamide as an effective drug delivery carrier

In this article we report the synthesis of new periodic mesoporous organosilicas (PMOs) with the co-existence of diurea and sulfanilamide-bridged organosilica that are potentially useful for controlled drug release system. The materials possess hexagonal pores with a high degree of uniformity and show long-range order as confirmed by the measurements of small-angle X-ray scattering (SAXS), N₂ adsorption isotherms, and transmission electron microscopy(TEM). FT-IR and solid state ²⁹Si MAS and ¹³C CP MAS NMR spectroscopic analyses proved that the bridging groups in the framework are not cleaved and covalently attached in the walls of the PMOs. It was found that the organic functionality could be introduced in a maximum of 10 mol% with respect to the total silicon content and be thermally stable up to 230 °C. The synthesized materials were shown to be particularly suitable for adsorption and desorption of hydrophilic/hydrophobic drugs from a phosphate buffer solution at pH 7.4.     

Silicon Nitride Capacitive Chemical Sensor for Phosphate Ion Detection Based on Copper Phthalocyanine – Acrylate‐polymer

In this work, we report the development of a highly sensitive capacitance chemical sensor based on a copper C,C,C,C‐ tetra‐carboxylic phthalocyanine‐acrylate polymer adduct (Cu(II)TCPc‐PAA) for phosphate ions detection. A capacitance silicon nitride substrate based Al−Cu/Si‐p/SiO₂/Si₃N₄ structure was used as transducer. These materials have provided good stability of electrochemical measurements. The functionalized silicon‐based transducers with a Cu(II)Pc‐PAA membrane were characterized by using Mott‐Schottky technique measurements at different frequency ranges and for different phosphate concentrations. The morphological surface of the Cu(II)Pc‐PAA modified silicon‐nitride based transducer was characterized by contact angle measurements and atomic force microscopy. The pH effect was also investigated by the Mott‐Schottcky technique for different Tris‐HCl buffer solutions. The sensitivity of silicon nitride was studied at different pH of Tris‐HCl buffer solutions. This pH test has provided a sensitivity value of 51 mV/decade. The developed chemical sensor showed a good performance for phosphate ions detection within the range of 10⁻¹⁰ to 10⁻⁵ M with a Nernstian sensitivity of 27.7 mV/decade. The limit of detection of phosphate ions was determined at 1 nM. This chemical sensor was highly specific for phosphate ions when compared to other interfering ions as chloride, sulfate, carbonate and perchlorate. The present capacitive chemical sensor is thus very promising for sensitive and rapid detection of phosphate in environmental applications.     

Cobalt–silicon mixed oxide nanocomposites by modified sol–gel method

Cobalt–silicon mixed oxide materials (Co/Si=0.111, 0.250 and 0.428) were synthesised starting from Co(NO₃)₂·6H₂O and Si(OC₂H₅)₄ using a modified sol–gel method. Structural, textural and surface chemical properties were investigated by thermogravimetric/differential thermal analyses (TG/DTA), XRD, UV–vis, FT-IR spectroscopy and N₂ adsorption at −196 °C. The nature of cobalt species and their interactions with the siloxane matrix were strongly depending on both the cobalt loading and the heat treatment. All dried gels were amorphous and contained Co²⁺ ions forming both tetrahedral and octahedral complexes with the siloxane matrix. After treatment at 400 °C, the sample with lowest Co content appeared amorphous and contained only Co²⁺ tetrahedral complexes, while at higher cobalt loading Co₃O₄ was present as the only crystalline phase, besides Co²⁺ ions strongly interacting with siloxane matrix. At 850 °C, in all samples crystalline Co₂SiO₄ was formed and was the only crystallising phase for the nanocomposite with the lowest cobalt content. All materials retained high surface areas also after treatments at 600 °C and exhibited surface Lewis acidity, due to cationic sites. The presence of cobalt affected the textural properties of the siloxane matrix decreasing microporosity and increasing mesoporosity.     

Detailed Structural Examinations of Covalently Immobilized Gold Nanoparticles onto Hydrogen‐Terminated Silicon Surfaces

The modification of flat semiconductor surfaces with nanoscale materials has been the subject of considerable interest. This paper provides detailed structural examinations of gold nanoparticles covalently immobilized onto hydrogen‐terminated silicon surfaces by a convenient thermal hydrosilylation to form Si? C bonds. Gold nanoparticles stabilized by ω‐alkene‐1‐thiols with different alkyl chain lengths (C₃, C₆, and C₁₁), with average diameters of 2–3 nm and a narrow size distribution were used. The thermal hydrosilylation reactions of these nanoparticles with hydrogen‐terminated Si(111) surfaces were carried out in toluene at various conditions under N₂. The obtained modified surfaces were observed by high‐resolution scanning electron microscopy (HR‐SEM). The obtained images indicate considerable changes in morphology with reaction time, reaction temperature, as well as the length of the stabilizing ω‐alkene‐1‐thiol molecules. These surfaces are stable and can be stored under ambient conditions for several weeks without measurable decomposition. It was also found that the aggregation of immobilized particles on a silicon surface occurred at high temperature (> 100 °C). Precise XPS measurements of modified surfaces were carried out by using a Au–S ligand‐exchange technique. The spectrum clearly showed the existence of Si? C bonds. Cross‐sectional HR‐TEM images also directly indicate that the particles were covalently attached to the silicon surface through Si? C bonds.     

UV laser deposition of nanostructured Si/C/O/N/H from disilazane precursors and evolution to silicon oxycarbonitride

Megawatt ArF laser photolysis of gaseous methyldisilazanes [(CH₃)_nH_3?nSi]₂NH (n = 2, 3) in excess of Ar yields hydrocarbons (major volatile products), methylsilanes (minor volatile products) and allows chemical vapour deposition of solid amorphous Si/C/O/N/H powder containing Si? X (X? C, H, O, N) bonds. The incorporation of O is due to a high reactivity of the primarily formed products towards air moisture. The resulting solid materials possess nanometer‐sized texture and high specific area, contain Si‐centered radicals and anneal under argon to silicon oxycarbonitride, whose structure is described as a network of O‐ and N‐interconnected Si and C atoms. Copyright © 2006 John Wiley & Sons, Ltd.     

The Crucial Role of Charge Accumulation and Spin Polarization in Activating Carbon-Based Catalysts for Electrocatalytic Nitrogen Reduction

Cost-effective carbon-based catalysts are promising for catalyzing the electrochemical N₂ reduction reaction (NRR). However, the activity origin of carbon-based catalysts towards NRR remains unclear, and regularities and rules for the rational design of carbon-based NRR electrocatalysts are still lacking. Based on a combination of theoretical calculations and experimental observations, chalcogen/oxygen group element (O, S, Se, Te) doped carbon materials were systematically evaluated as potential NRR catalysts. Heteroatom-doping-induced charge accumulation facilitates N₂ adsorption on carbon atoms and spin polarization boosts the potential-determining step of the first protonation to form *NNH. Te-doped and Se-doped C catalysts exhibited high intrinsic NRR activity that is superior to most metal-based catalysts. Establishing the correlation between the electronic structure and NRR performance for carbon-based materials paves the pathway for their NRR application.     

Thermolysis of [tris(trimethylsilyl)methyl](diphenyl)fluorosilane. Isomerization of a sila-olefin intermediate

The compound (Me₃Si)₃CSiPh₂F loses Me₃SiF under reflux or on passage through a tube at 450°C to give three products, A, B, and C, in approximately 20/20/60 ratio. Products A and B, which are solids, were shown by X-ray crystallographic analysis to be the diastereoisomeric forms of 1-dimethylsila-2-trimethylsilyl-3-[(methyl)(phenyl)sila]indane. From its mass and ¹H NMR spectra, C (a liquid) was tentatively identified as 1,3-bis(dimethylsila)-2-[(dimethyl)(phenyl)silyl]indane. All three products are isomers of the sila-olefin (Me₃Si)₂CSiPh₂, and it is suggested that the latter is first formed by loss of Me₃SiF from (MeSi)₃CSiPh₂F, and the equilibrium (Me₃Si)₂CSiPh₂ ? (Me₃Si)(Ph₂MeSi)CSiMe₂ ? (Me₃Si)(PhMe₂Si)CSiMePh ? (Me₂PhSi)₂CSiMe₂ is then rapidly established; internal cyclizations involving addition of aryl CH bonds across SiC bonds then occur to give the observed products. Consistent with this is the observation that a mixture of silicon alkoxides, thought to be (Me₃Si)₂CHSiPh₂OMe and its isomers (which would be formed by addition of methanol across the SiC bonds of the four sila-olefins) is produced when methanol is passed through the hot tube with the (Me₃Si)₃CSiPh₂F.Full structural details are given for compounds A and B. Some features of interest are: (a) the conformation of the 5-membered ring is different in the two diastereoisomers; (b) the exocyclic SiCSiMe₃ bond angles, of ca. 120° are unusually large; and (c) there is a little distortion of the fused benzene ring, which is attributed to the effect of silicon substituents on the hybridization of carbon atoms to which they are attached.     

A direct solid sampling electrothermal atomic absorption spectrometry method for the determination of silicon in biological materials

A solid sampling electrothermal atomic absorption spectrometry method for direct determination of trace silicon in biological materials was developed and applied to analysis of pork liver, bovine liver SRM 1577b and pure cellulose. The organic matrix was destroyed and expelled from the furnace in the pyrolysis stage involving a step-wise increasing the temperature from 160 °C to 1200 °C. The mixed Pd/Mg(NO₃)₂ modifier has proved to be the optimum one with respect to the achievement of maximum sensitivity, elimination of the effect of the remaining inorganic substances and the possibility of using calibration curves measured with aqueous standard solutions for quantification. For the maximum applicable sample amount of 6 mg, the limit of detection was found to be 30 ng g^− 1. The results were compared with those obtained by different spectrometric methods involving sample digestion, by electrothermal atomic absorption spectrometry using slurry sampling, by wavelength dispersive X-ray fluorescence spectrometry and by radiochemical neutron activation analysis. The method seems to be a promising one for analysis of biological materials containing no significant fraction of silicon in form of not naturally occurring volatile organosilicon compounds. The still incessant serious limitations and uncertainties in the determination of trace silicon in solid biological materials are discussed.     

Preparation of nanostructured porous SiO2-Al2O3 oxycarbonitride materials obtained by a new chemical precursor method

Nanostructured hybrid materials containing Al₂O₃ were synthesized via a sol-gel method through hydrolysis and co-condensation reactions using trimethylsilyl isocyanate (TMSI) as a new silica source in the presence of tetramethoxysilane (TMOS) and three different quantities (10, 20 and 30 wt.%) of aluminum sec-butoxide (Al(OBu^sec)₃ as a modifying agent. The xerogel nanostructured materials are pyrolyzed in nitrogen atmosphere in the temperature range from 400°C to 1100°C. The transformation of the xerogel hybrid networks into Al-Si oxycarbonitride materials has been investigated by XRD, FTIR, SEM, AFM, and ²⁹Si MAS-NMR. To the best of our knowledge, the work reported here is the first synthesis of porous di-urethanesils modified with aluminum and one of the few examples of alumosilica oxycarbonitride materials      

Interfacial properties of thermally oxidized Ta2Si on Si

Many refractory metal silicides have received great attention due to their potential for innovative developments in the silicon‐based microelectronic industry. However, tantalum silicide, Ta₂Si, has remained practically unnoticed since its successful application in silicon carbide technology as a simple route for a high‐k dielectric formation. The thermal oxidation of Ta₂Si produces high‐k dielectric layers, (O? Ta₂Si)‐based on a combination of Ta₂O₅ and SiO₂. In this work, we investigate the interfacial properties of thermally oxidized (850–1050 °C) Ta₂Si on commercial silicon substrates. The implications of diffusion processes in the dielectric properties of an oxidized layer are analyzed. In particular, we observe migration of tantalum pentoxide nanocrystals into the substrate with increasing oxidation temperature. An estimation of the insulator charge and interfacial O? Ta₂Si/Si trap density is also presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Carbon-based H2-production photocatalytic materials

Photocatalytic hydrogen production from water splitting is of promising potential to resolve the energy shortage and environmental concerns. During the past decade, carbon materials have shown great ability to enhance the photocatalytic hydrogen-production performance of semiconductor photocatalysts. This review provides a comprehensive overview of carbon materials such as CNTs, graphene, C₆₀, carbon quantum dots, carbon fibers, activated carbon, carbon black, etc. in enhancing the performance of semiconductor photocatalysts for H₂ production from photocatalytic water splitting. The roles of carbon materials including supporting material, increasing adsorption and active sites, electron acceptor and transport channel, cocatalyst, photosensitization, photocatalyst, band gap narrowing effect are explicated in detail. Also, strategies for improving the photocatalytic hydrogen-production efficiency of carbon-based photocatalytic materials are discussed in terms of surface chemical functionalization of the carbon materials, doping effect of the carbon materials and interface engineering between semiconductors and carbon materials. Finally, the concluding remarks and the current challenges are highlighted with some perspectives for the future development of carbon-based photocatalytic materials.