NiCo2O4纳米线/SiC复合纤维制备及其电化学性能

以正硅酸乙酯(TEOS)为硅源,聚乙烯吡咯烷酮(PVP)为助纺剂,采用静电纺丝结合碳热还原制备出结晶度较高的β-SiC纤维,其比表面积为92.6 m2/g,表现出双电层电容储能特征,比电容为155.7 F/g。然后,利用水热法在SiC纤维表面生长出大量直径约为15 nm的NiCo₂O₄纳米线,得到NiCo₂O₄纳米线/SiC复合纤维。测试表明,NiCo₂O₄纳米线/SiC复合纤维中镍和钴元素分别以Ni2+/Ni3+和Co2+/Co3+价态形式存在,由于NiCo₂O₄纳米线与SiC纤维的协同作用,NiCo₂O₄纳米线/SiC复合纤维比电容显著提高,并表现出双电层和赝电容并存的特征,比电容可达300.3 F/g,当功率密度为58.1 W/kg时,NiCo₂O₄纳米线/SiC复合纤维能量密度为60.1 W·h/kg。      

核壳结构SiCNWs@SiO2/PVDF复合材料的制备与介电储能特性

为了加速新能源电子器件向微型化和集成化的方向发展，提高电子器件内部介电复合材料的性能至为重要，介电复合材料的介电性能和储能性能直接影响电子器件的质量，如何提高介电复合材料的介电性能和储能性能等引起了研究者们的广泛关注。以聚偏氟乙烯(PVDF)为基体，碳化硅纳米线(SiCNWs)和核壳结构碳化硅纳米线@二氧化硅(SiCNWs@SiO₂)为填料，通过溶液共混相转换法及热压工艺制备出一系列的SiCNWs/PVDF二元复合材料和SiCNWs@SiO₂/PVDF复合材料。探究介电纳米填料的表面修饰对PVDF基复合材料的微观结构、宏观介电性能和储能性能等的影响。实验结果表明，硅烷偶联剂KH550成功改性SiCNWs；通过一步法热氧化工艺成功制备出具有典型核壳结构的SiCNWs@SiO₂纳米线，SiO₂壳层的厚度随着SiCNWs热氧化时间的延长而增大，当SiCNWs热氧化时间为10 h,SiO₂壳层的厚度为6.5 nm；采用相转换法和热压处理成功制备一系列的SiCNWs/PVDF二元复合材料...     

高能微波辐照条件下SiC晶粒的生长过程分析

利用高能真空微波辐照, 仅以SiO₂和人造石墨粉为原料, 便捷快速地合成得到结晶良好的β-SiC晶粒。在利用各种表征手段综合分析SiC晶粒微观结构的基础上, 确认高能微波辐照条件下, β-SiC晶粒的生长过程符合“光滑界面的二维形核生长”机制。借助于电子背散射衍射技术(EBSD)进行的原位解析发现, 生长最快的{211}面在晶粒长大过程中逐渐被超覆, 通过形成{421}过渡晶面而最终演变为{220}晶面, 并成为晶粒的侧面; 而生长最慢的{111}面则成为最后保留下来的六角形规则晶面。EBSD的解析结果为SiC晶粒生长过程中晶面演变提供了直接的实验证据。     

SiO2@Ag@SiO2@TiO2核壳结构的制备及其光催化降解性能

光催化是一种绿色且高效的降解染料污染物的方式, 在水污染治理中应用广泛。本研究以SiO₂为核层, 依次采用氧化还原法、改进的Stöber法及水热法合成SiO₂@Ag@SiO₂@TiO₂多层核壳结构作为光催化剂用于染料污染物降解, 并探讨了硝酸银(AgNO₃)、正硅酸乙酯(TEOS)、钛酸四丁酯(TBOT)等用量对包覆效果的影响。采用不同表征手段对样品的微观形貌、物相结构、孔结构参数和光电性能进行分析表征。结果表明, 当AgNO₃、TEOS、TBOT与SiO₂的质量比为5 : 2.4 : 6 : 1, 多层核壳结构每层均达到最优包覆效果。与SiO₂@TiO₂和SiO₂@Ag@TiO₂催化剂相比较, SiO₂@Ag@SiO₂@TiO₂核壳结构的光催化剂具有更佳的光催化活性, 光照45 min可降解93%的MB溶液, 经4次循环后其光催化效率为90%。     

双亲性w/o-SiO2-void-TiO2中空核壳微球的合成及表征

采用双层包裹–夹层去除法合成了SiO₂-void-TiO₂中空核壳微球, 通过正十八烷基三甲氧基硅烷对SiO₂-void-TiO₂微球表面进行部分修饰, 制得了双亲性w/o-SiO₂-void-TiO₂中空核壳微球, 并采用XRD、TEM、BET、FT-IR和UV-Vis DRS等对样品的晶相结构、形貌、表面结构和吸光性能等进行了表征。以染料亚甲基蓝模拟环境污染物, 考察了SiO₂-void-TiO₂和w/o-SiO₂-void-TiO₂在紫外光下的光催化性能。结果表明: SiO₂-void-TiO₂样品呈微球状, 具有明显的核–多孔壳结构, 在核与多孔壳层之间存在纳米空间层, 样品中TiO₂核具有锐钛矿结构; w/o-SiO₂-void-TiO₂样品具有双亲性, 能分布于水/油两相界面处。在紫外光照射下, 反应180 min, SiO₂-void-TiO₂和w/o-SiO₂-void-TiO₂对亚甲基蓝的降解率分别达89.4% 和83.8%。在此基础上, 本研究探讨了SiO₂-void-TiO₂中空核壳微球的合成机理及表面部分改性机理。     

Fe催化生长β-SiC纳米分支结构北大核心CSCD

采用直流电弧等离子辅助法合成了β-SiC纳米分支结构。用扫描电镜和透射电镜,X射线电子能谱和拉曼光谱等对样品进行表征,发现分级生长的SiC纳米线为单晶结构,沿<111>方向生长。β-SiC纳米分支结构通过气-液-固(VSL)机制合成。β-SiC纳米分支结构在425 nm处有一个强的发光峰。     

双金属催化剂Ni-Co/SiO2空心球的可控制备及催化性能

以二氧化硅为模板, 采用牺牲模板/界面反应法制备具有介孔结构的碱式硅酸镍钴空心球。采用透射电子显微镜(TEM)、X 射线衍射(XRD)、氮气吸脱附曲线(BET)和程序升温还原(TPR)等方法, 对样品的结构和形貌进行了表征, 探索了碱式硅酸镍钴空心球还原规律, 并研究了双金属催化剂Ni-Co/SiO₂的催化性能。研究发现, 140℃下反应6 h, 产物为核壳结构, 反应12 h时变为空心球结构; 在氢气气氛中800℃下反应5 h, 碱式硅酸镍钴被完全还原为Ni-Co/SiO₂, 还原前后形貌基本不变, 但比表面积有所减小, 孔径增大。Ni-Co/SiO₂空心球用于催化硝基苯加氢反应1 h后, 硝基苯的转化率为67%, 比商用Raney Ni 提高约28%。     

氨化Ga2O3/Nb薄膜制备GaN纳米线

采用射频磁控溅射技术先在硅衬底上制备Ga2O3/ Nb薄膜,然后在900℃时于流动的氨气中进行氨化制备GaN纳米线.用X射线衍射(XRD)、傅立叶红外吸收光谱(FTIR)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)详细分析了GaN纳米线的结构和形貌.结果表明:采用此方法得到的GaN纳米线为六方纤锌矿结构,其纳米线的直径大约在50～100nm之间,纳米线的长约几个微米.室温下以325nm波长的光激发样品表面,只显示出一个位于364.4nm的很强的紫外发光峰.最后,简单讨论了GaN纳米线的生长机制.     

黄磷炉渣制SiO2:Tb3+荧光材料及其发光性能研究

以工业废弃物黄磷炉渣为原料，用硝酸浸出得到具有三维网状结构的二氧化硅(SiO₂)。采用化学沉淀法制备出荧光强度较高以及良好的光学稳定特性的SiO₂:Tb³⁺荧光材料。通过X射线衍射、热重-差热分析、红外吸收光谱、扫描电子显微镜和荧光光谱等现代分析手段对荧光材料表面形貌和内部结构特征以及发光性能进行表征测试。结果表明，SiO₂:Tb³⁺荧光材料为无定型结构。在激发光谱图中，377 nm(⁷F₆-⁵L₁₀)处有一较强的激发峰，其发射峰位于544 nm处，归属于Tb³⁺的⁵D₄-⁷F₅特征跃迁发射，在紫外光照射下呈现明亮的绿色荧光。经过30天的材料稳定性测试，荧光强度下降速度仅为38 a.u/天，基本保持稳定，证实了该材料具有良好的光学稳定特性。     

Fe催化生长β-SiC纳米分支结构

采用直流电弧等离子辅助法合成了β-SiC纳米分支结构。用扫描电镜和透射电镜,X射线电子能谱和拉曼光谱等对样品进行表征,发现分级生长的SiC纳米线为单晶结构,沿111方向生长。β-SiC纳米分支结构通过气-液-固(VSL)机制合成。β-SiC纳米分支结构在425 nm处有一个强的发光峰。     

壳层厚度对核-壳结构PS-SiO_2杂化颗粒压缩弹性模量的影响

基于正负电荷间的静电作用制备了具有核-壳结构的聚苯乙烯-氧化硅(PS-SiO2)杂化颗粒,通过调节正硅酸乙酯的用量对样品的SiO2壳层厚度进行控制。利用原子力显微镜(AFM)在微观尺度上测定杂化颗粒的力-位移曲线,根据Hertz接触模型和Sneddon接触模型,考查了SiO2壳层厚度对样品压缩弹性模量的影响。扫描电子显微镜(SEM)和透射电镜(TEM)结果显示,杂化颗粒中PS内核尺寸为(197±9)nm,壳层由SiO2纳米颗粒组成,在本试验范围内杂化颗粒样品的壳厚为11~16nm。在Hertz接触模型条件下,PS微球的弹性模量为(2.2±0.5)GPa,其数值略低于PS块体材料。当SiO2壳厚由11nm增至16nm时,杂化颗粒的弹性模量从(4.4±0.6)GPa增至(10.2±1.1)GPa,其数值明显低于纯SiO2,且更接近于PS内核。     

Characterization and microstructural evolution of SiC(OAl) fibers to SiC(Al) fibers derived from aluminum-containing polycarbosilane

The SiC(OAl) fibers and the SiC(Al) fibers were fabricated by the use of aluminum-containing polycarbosilane (Al–PCS) precursor. The two types of fibers have been characterized. Chemical element analysis, AES, SEM, XRD, RMS and NMR have been employed. The chemical formula of SiC(OAl) fibers is SiC_1.31O_0.25Al_0.018 with C and O rich on the surface. The microstructure of SiC(OAl) fibers is a mixture of β-SiC nanocrystals, free carbon, and an amorphous silicon oxycarbide (Si–C–O phase), which have been confirmed by an amount of SiC₂O₂, SiCO₃, SiO₄ and SiC₃O units in the ²⁹Si MAS NMR spectrum. A small quantity of aluminum is embedded uniformly in the Si–C–O amorphous continuous phase. For SiC(Al) fibers, nearly stoichiometric composition was confirmed as chemical composition of SiC_1.03O_0.013Al_0.024. The fiber is composed of a large number of β-SiC crystallites, a small amount of -SiC crystalline and SiC amorphous phase. The aluminum in the SiC(Al) fibers mainly exists in two manners: Al–C bonds connected with the surfaces of the β-SiC grains and Al–O bonds, or Al₂O₃, to the amorphous phase.     

YVO4:Eu3+@YPO4纳米核壳结构荧光粉的水热合成及表征

为了提高传统YVO₄:Eu³⁺荧光粉的发光效率及稳定性, 采用水热法制备合成了YVO₄:Eu³⁺@YPO₄纳米核壳结构荧光粉, 通过X射线衍射仪(XRD)、透射电镜(TEM)和荧光光谱仪(PL)等测试手段对所得样品进行表征. XRD和TEM测试结果表明: 由水热法合成的YVO₄:Eu³⁺@YPO₄荧光粉包含YVO₄:Eu³⁺核心和YPO₄壳层两种结构, 荧光粉粒径为10~30 nm, 壳厚为5~10 nm, 形态规则、粒径均匀、结晶度高; 荧光光谱测试结果表明: YVO₄:Eu³⁺@YPO₄荧光粉比单纯YVO₄:Eu³⁺荧光粉的发光效率高出66.75%, 且具有较高的色纯度. 结合第一性原理方法, 对YVO₄和YPO₄晶体的能带结构进行理论计算, 定性说明了电子跃迁和发光的关系.     

Direct growth of core-shell SiC-SiO(2) nanowires and field emission characteristics

A simple, direct synthesis method was used to grow core-shell SiC-SiO(2) nanowires by heating NiO-catalysed silicon substrates. A carbothermal reduction of WO(3) provided a reductive environment and carbon source to synthesize crystalline SiC nanowires covered with SiO(2) sheaths at the growth temperature of 1000-1100?°C. Transmission electron microscopy showed that the SiC core was 15-25?nm in diameter and the SiO(2) shell layer was an average of 20?nm in thickness. The thickness of the SiO(2) shell layer could be controlled using hydrofluoric acid (HF) etching. Field emission results of core-shell SiC-SiO(2) and bare SiC nanowires showed that the SiC nanowires coated with an optimum SiO(2) thickness (10?nm) have a higher field emission current than the bare SiC nanowires.     

Synthesis of SiC nanowires with in-situ deposition of carbon coating

SiC nanowires are effective reinforcement materials in ceramic matrix composites. A compliant coating such as carbon on nanowires is necessary in order to moderate the nanowire/matrix interfacial bounding for taking the most advantages of SiC nanowires. SiC nanowires with an in-situ deposition of carbon shell coating were fabricated by a novel chemical vapor growth process. Highresolution transmission electron microscopy examinations showed that the nanowires consisted of a single crystal beta-SiC core with an amorphous carbon shell 2-5 nm in thickness. The nanowires were straight with a length generally over 10 microm and a diameter 15-150 nm. The growth direction of the core SiC nanowires is (111). A simple three-step growth model for SiC nanowires was proposed based on a vapor-solid growth mechanism. Because the carbon-coated nanowires were grown directly on continuous Tyranno-SA SiC fibers, in-situ application of the present technique on the fabrication of SiC nanowire-reinforced SiC/SiC composites is expected.     

Preparation of silicon carbide nanowires via a rapid heating process

Silicon carbide (SiC) nanowires were fabricated in a large quantity by a rapid heating carbothermal reduction of a novel resorcinol-formaldehyde (RF)/SiO₂ hybrid aerogel in this study. SiC nanowires were grown at 1500 °C for 2 h in an argon atmosphere without any catalyst via vapor-solid (V-S) process. The β-SiC nanowires were characterized by field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM) equipped with energy dispersive X-ray (EDX) facility, Fourier transformed infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The analysis results show that the aspect ratio of the SiC nanowires via the rapid heating process is much larger than that of the sample produced via gradual heating process. The SiC nanowires are single crystalline β-SiC phase with diameters of about 20-80 nm and lengths of about several tens of micrometers, growing along the [1 1 1] direction with a fringe spacing of 0.25 nm. The role of the interpenetrating network of RF/SiO₂ hybrid aerogel in the carbothermal reduction was discussed and the possible growth mechanism of the nanowires is analyzed.     

Synthesis of chainlike In2Ge2O7/amorphous GeO2 core/shell nanocables and their luminescence

Novel chainlike In2Ge2O7/amorphous GeO2 core/shell nanocables were successfully synthesized by the simple thermal evaporation method without the presence of catalyst. The growth process of the nanocables is based on vapor-solid (VS) growth mechanism. Its morphology and microstructures were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. Studies indicate that typical chainlike nanocables consist of single crystalline In2Ge2O7 nanowires (core) with diameter of about 30 nm and amorphous GeO2 chainlike nanostructures (shell). Four emission peaks, namely 401 nm, 448.5 nm, 466.5 nm, and 491 nm, were observed in the room-temperature photoluminescence measurements.     

核壳材料Co3O4@SiO2催化环己基过氧化氢分解

环己基过氧化氢(CHHP)分解是环己烷无催化氧化工艺制备环己醇和环己酮的重要反应步骤.本研究以Co3O4纳米颗粒为内核,十六烷基三甲基溴化铵(CTAB)为模板剂,正硅酸四乙酯(TEOS)为硅源,采用模板法制备了核壳结构材料Co3O4@SiO2.考察了SiO2壳层制备条件:乙醇和水的比例、CTAB的浓度和TEOS的用量对...