[Si4]4– and [Si9]4– Clusters Crystallized from Liquid Ammonia Solution – Synthesis and Characterization of K8[Si4][Si9]·(NH3)14.6

The extraction of the silicide K₁₂Si₁₇ with liquid ammonia in the presence of a sequestering agent and AuPPh₃Cl or Zn(Cp*)₂ led to crystals of the solvate compound K₈[Si₄][Si₉] · (NH₃)_14.6, which was characterized by single‐crystal X‐ray diffraction. It is the first compound with an isolated and ligand‐free [Si₄]^4– cluster obtained from solution. It also contains one [Si₉]^4– cluster per formula unit, whereas the precursor K₁₂Si₁₇ is built from [Si₄]^4– and [Si₉]^4– clusters with a 2:1 ratio.     

Formation mechanisms of Si3N4 and Si2N2O in silicon powder nitridation

Commercial silicon powders are nitrided at constant temperatures (1453 K; 1513 K; 1633 K; 1693 K). The X-ray diffraction results show that small amounts of Si₃N₄ and Si₂N₂O are formed as the nitridation products in the samples. Fibroid and short columnar Si₃N₄ are detected in the samples. The formation mechanisms of Si₃N₄ and Si₂N₂O are analyzed. During the initial stage of silicon powder nitridation, Si on the outside of sample captures slight amount of O₂ in N₂ atmosphere, forming a thin film of SiO₂ on the surface which seals the residual silicon inside. And the oxygen partial pressure between the SiO₂ film and free silicon is decreasing gradually, so passive oxidation transforms to active oxidation and metastable SiO(g) is produced. When the SiO(g) partial pressure is high enough, the SiO₂ film will crack, and N₂ is infiltrated into the central section of the sample through cracks, generating Si₂N₂O and short columnar Si₃N₄ in situ. At the same time, metastable SiO(g) reacts with N₂ and form fibroid Si₃N₄. In the regions where the oxygen partial pressure is high, Si₃N₄ is oxidized into Si₂N₂O.     

The Behavior of Sulfur in Liquid Ammonia

Abstract

Spectrophotometric observations, electrochemical data, esr spectrum and cryoscopic measurements in solutions of sulfur in liquid ammonia are reported. They indicate that the sulfur species present at low temperatures is S₂NH₃. At room temperature the predominant species is SNH₃.     

原位制备具有增强光催化活性的S型Bi2Se3/g-C3N4光催化剂

光催化氧化是一种应用前景良好的环境治理技术.与絮凝、物理吸附和化学氧化等常见的方法相比,光催化氧化具有环境友好、氧化完全、方便和廉价等优势.特别是可见光光催化氧化,可利用太阳能中占比最高的可见光,在应用中更具优势.因而,探索可见光响应性能优异的光催化剂一直是光催化氧化领域的一个重要研究内容.硒化铋(Bi₂Se₃)是一种带隙(带隙宽度在0.3~1.3 e V)非常窄的半导体,能吸收全部波长范围的可见光和近红外光.此外,Bi₂Se₃还具有独特的金属表面态,其表面具有良好的导电性.这些特性使其在可见光光催化氧化领域具有很大的应用潜力.然而,由于Bi₂Se₃价带位置高,氧化能力很弱,其价带上的空穴在光催化反应中难以被消耗,导致空穴大量累积,并迅速与光生电子复合,大幅降低了Bi₂Se₃的光催化性能.因此,一直以来,Bi₂Se₃很少被用于光催化反应.如何充分利用Bi₂Se₃的光响应优势,制备出性能优异的光催化剂,仍是具有挑战性和吸引力的研究方向.本文采用预先制备的Bi2O3/g-C₃N₄复合物作为前驱体,通过原位转化的方法,将前驱体置于热的Se蒸汽中,使前驱体上的Bi2O3与Se蒸汽反应,完全转化为Bi₂Se₃纳米颗粒,从而制得Bi₂Se₃/g-C₃N₄复合光催化剂(Bi₂Se₃含量约为4 wt%).透射电镜结果表明,所形成的Bi₂Se₃纳米颗粒较均匀地分布在g-C₃N₄表面.表面功函数分析发现,Bi₂Se₃与g-C₃N₄结合后,它们的费米能级分别由原来的-0.55和-0.18 e V变为平衡时的-0.22 e V,可形成指向g-C₃N₄的内建电场,有利于形成梯型(S型)异质结.在此基础上,能级位移、荧光分析、结构计算和反应自由基测试等结果表明,Bi₂Se₃和g-C₃N₄之间形成了S型异质结.在可见光光催化降解苯酚的实验中,所制备的Bi₂Se₃/g-C₃N₄复合物的光催化活性明显优于单一的Bi₂Se₃和g-C₃N₄.结合比表面、孔结构、光吸收和荧光等对比分析,认为Bi₂Se₃/g-C₃N₄的这种S型异质结构在其光催化活性增强中起到了关键作用.在光照条件下,其g-C₃N₄导带中光生电子向Bi₂Se₃的价带迁移,并与光生空穴复合,从而使Bi₂Se₃导带上可保留更多的高活性光生电子参与光催化反应,由此Bi₂Se₃/g-C₃N₄的光催化活性增强.循环性能测试和光还原实验结果表明,所制备的Bi₂Se₃/g-C₃N₄复合光催化剂具有良好的稳定性.本文工作为高可见光吸收的光催化剂制备和性能增强提供了新途径和新视野.     

稀土硫化物—聚苯乙烯纳米复合材料的制备与表征

采用原位合成法制备了稀土硫化物—聚苯乙烯纳米复合材料 .通过荧光光谱、磁性、光电子能谱、透射电镜等手段对材料进行表征 .荧光光谱测试可见Eu3+ 的特征发射峰 ;磁性测试表明与H2 S反应后复合材料的饱和磁化强度降低 ;TEM测试表明反应后复合材料的微观结构发生了变化 .分析了产生上述变化的原因     

原位聚合制备聚乙烯/蒙脱土(MMT)纳米复合材料的研究

利用MgCl₂在醇中溶解和蒙脱土(MMT)在醇中层间膨胀的特性,制备了MgCl₂/TiC_l4负载于MMT层间的MMT/MgCl₂/TiC_l4催化剂,并通过原位聚合合成了聚乙烯/蒙脱土纳米复合材料.经广角X射线衍射(WAXD)和透射电子显微镜(TEM)分析表明,蒙脱土片层在乙烯聚合过程中发生了层间剥离,以单片层或几片层共存的形式无规地分散于聚乙烯基质中.与分子量相近的纯聚乙烯相比,极低的蒙脱土含量(质量分数<1%)能使复合材料的屈服强度、拉伸强度和拉伸模量有很大提高.复合材料中蒙脱土片层以纳米尺寸在聚乙烯基质中的良好分布和对聚乙烯分子链运动的限制作用是力学性能提高的主要因素.     

Fabrication of SiC and Si3N4 Whiskers under Pressurized Ar and N2 Atmosphere through High‐Energy Ball Milling

SiO_{2 (activated or mesoporous silica)}/Mg_{(magnesiothermic or metal sintering aid)}/C_{(activated or polymeric carbon)}/N_{2 (atmosphere)} systems were used in the one‐step synthesis of β‐SiC and β‐Si₃N₄ whiskers. In this study, a mixture of the active precursors was allowed to react via a self‐sustaining reaction (high‐energy ball milling process). Scanning electron micrographs and X‐ray diffraction (XRD ) analysis showed that the rod‐like SiC whiskers (~800 µm) were synthesized in situ by the direct carbothermal reduction of silicon nitride (or silicon) with activated carbon in N₂ (or Ar) atmosphere. The results show that β‐Si₃N₄ (without β‐SiC ) was fully formed after 5 h of milling with four different morphologies, namely whisker tip (droplet/no droplet) and nonuniform whiskers (short hexagonal/rhombohedral/rod‐like) with a length of 0.1–400 µm. By adding metal sintering aids, the liquid phase Mg–Si–O–N and the rate of carbothermal reduction increased (enhanced densification via particle rearrangement) and their hexagonal whiskers tended to assume a rod‐like shape. The effect of the concentration of CO (reduction of α‐Fe₂O₃ to Fe by CO ) on the whisker synthesis suggests that, in addition to the concentration of CO , the nature of the family of mesoporous silica/carbon template is an important factor in the synthesis of β‐SiC and β‐Si₃N₄ whiskers. The possible chemical reactions were investigated by studying the unwanted phases (MgO , Si, SiC , Fe₂O₃ , Fe₃O₄ , FeO , Fe, Fe₃C , MgCO₃ ) of comparable XRD graphs.     

Si44– in Solution – First Solvate Crystal Structure of the Ligand‐free Tetrasilicide Tetraanion in Rb1.2K2.8Si4·7NH3

We report the first solvate structure of the silicide anion Si₄^4–, which provides circumstantial evidence of the stability of the highly charged anion in liquid ammonia solutions. The solvate Rb_1.2K_2.8Si₄ · 7NH₃ crystallized from a mixture of the ternary compound K₆Rb₆Si₁₇ with the transition metal complex [(C₆H₅)₃P]₂Ni(CO)₂ [bis(triphenylphosphine)dicarbonylnickel] in the presence of the chelating agents 18‐crown‐6 (1,4,7,10,13,16‐hexaoxacyclooctadecane) and [2.2.2]cryptand (4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane) in liquid ammonia. Single X‐ray diffraction analysis confirms the presence of the Si₄^4– anion in the crystal structure of Rb_1.2K_2.8Si₄ · 7NH₃, which represents the first solvate compound of the naked tetrasilicide tetraanion. All five crystallographically independent cation positions show mixed occupancy by Rb⁺ and K⁺.     

Electrochemical Behavior of Azo Compounds in Liquid Ammonia

Abstract

At -40°C, the behavior of lO compounds, differing widely in their standard potentials, has been investigated in liquid ammonia, using cyclic voltammetry at a smooth platinum electrode. The purpose of this study was the realization of a redox scale with reversible systems. With azobenzene, pyridazine, cin-noline, benzocinnoline and 4,4′-azobis-(pyridine-N-oxide), the first electron transfer is reversible and leads to the formation of the corresponding radical anions which are stable; the second electron transferleads to the ciianions which can be protonated yielding the corresponding hydrazo. Other compounds, such as azoxybenzene, 3-amino-1,2,4-triazine, pyridine-N-oxide, 8-azaadenine and 1H-tetrazole, have an electrochemical behavior which i s more intricate.     

TiO2/聚丙烯酸丁酯纳米复合薄膜的制备及结构表征

利用微乳液原位聚合法在普通玻璃表面上制备了TiO2/聚丙烯酸丁酯纳米复合膜.采用傅立叶变换红外光谱、高分辨透射电子显微镜和X射线光电子能谱对膜的结构进行了表征.结果表明， TiO2以纳米线的形式弥散在聚丙烯酸丁酯的高分子网络中，并且所制备的TiO2纳米线具有板钛矿相结构.     

聚苯胺/钛酸钡纳米复合粒子的制备与表征

采用原位复合法制备出聚苯胺/钛酸钡复合粒子,借助TEM、XRD、FT-IR、 XPS、TG等分析手段研究了复合粒子的形貌、结构及其热性能.结果表明,复合粒子的粒径为1 μm左右,BaTiO3以40 nm左右的晶粒分散于聚苯胺基体之中,聚苯胺与钛酸钡之间存在化学键合作用,同时在一定程度上减少了纳米粒子的团聚.     

原位透射电子显微镜观察电荷驱动的氧化物纳米颗粒水中自组装

以四氧化三钴Co_3O_4纳米棒为研究对象,我们利用液体环境透射电子显微镜,原位观察了四氧化三钴纳米棒在水中的自组装过程。研究发现在电子束辐照的水环境下,四氧化三钴纳米棒的晶面存在互补式自组装现象。随着纳米棒之间的距离越来越近,纳米棒之间的相对运动速率逐渐增加,纳米棒之间的相互作用力逐渐增加。通过进一步分析纳米棒的形貌发现,纳米棒的暴露晶面大多数为{100}、{110}以及{111}晶面,而Co_3O_4属于极性氧化物,这些晶面往往会带有一定的电荷。在液体环境下,正是由于这些易暴露面都带有不同大小的电荷,在晶面电荷的驱动下,电荷属性相反的四氧化三钴纳米棒会互相吸引,形貌结构上进行互补,实现快速驱动的纳米棒之间自组装。     

氮化钛的制备及表征

以金红石为原料 ,金属铝作还原剂合成氮化钛 ,以X射线衍射、热分析等方法进行测定 ,结果表明该法合成得到的氮化钛纯度较高 ,经济可行。     

From cyclotetrasilazane [(CH3)2SiNH]4 via crystalline silicon nitride imide Si2N2NH to α-Si3N4

α-Si₃N₄ is synthesized by an ammonia thermal synthesis using a cyclic oligosilazane, [(CH₃)₂SiNH]₄, as the starting material. [(CH₃)₂SiNH]₄ reacts in the presence of ammonia at 900°C and 80 MPa pressure to give silicon nitride imide (Si₂N₂NH). Subsequently, Si₂N₂NH is converted into α-Si₃N₄ by thermal decomposition at 1500°C and 0.1 MPa nitrogen with the simultaneous loss of NH₃.     

Carbon determination in Si3N4 by slurry atomization ICP-AES

Carbon content in silicon nitride powders having mean particle size below 5 m was determined by slurry atomization inductively coupled plasmaatomic emission spectrometry (ICP-AES). A complete atomization of the solid particles was observed in a low power argon-ICP. The blank value of the carbon signal was reduced by using high purity argon, fresh bidistilled water and an extended torch. Silicon nitride slurries were analyzed by calibration and addition methods with acetic acid as reference. The results were in good agreement with data obtained by a LECO carbon analyzer. A blank restricted detection limit of 0.018% was calculated. The relative standard deviation of the analysis was below 7%.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

基于g-C3N4/P25复合光电敏感体系的中草药抗氧化容量测定

采用粒径为25 nm的锐钛矿和金红石型混合相二氧化钛(TiO₂)材料(P25)替代常规锐钛矿型TiO₂, 制备了基于石墨氮化碳(g-C₃N₄)/混合相TiO₂(g-C₃N₄/P25)的可见光激发光电敏感体系. 研究结果表明, 石墨氮化碳(g-C₃N₄)大的平面结构不仅能够成为TiO₂纳米材料合适的高分散载体, 其高效载流子传输能力还赋予了复合体系优异的光电性能. 当g-C₃N₄掺杂质量分数仅为0.5%时, 复合体系的光电流响应信号可提高至原来的4.5倍, 增敏效果最好. 该光敏体系的研制显著简化了制备工艺并降低了成本, 同时有效提高了体系的可见光利用效率. 基于该g-C₃N₄/P25光电敏感复合体系, 首次采用光电化学方法实现了中草药抗氧化容量的测定, 为量化中药体系抗氧化性能评估提供了新的思路.     

碳自掺杂g-C3N4光催化性能的原位光微量热-荧光光谱研究

通过在尿素前驱体中添加单宁酸, 原位缩聚形成碳自掺杂石墨相氮化碳(g-C₃N₄). 利用X射线光电子能谱(XPS)、 场发射扫描电子显微镜(FESEM)、 X射线衍射(XRD)仪和同步热分析(TG-DSC)等方法对碳自掺杂 g-C₃N₄的形貌、 物相结构和能带价态组分进行表征分析, 结合紫外-可见吸收光谱(UV-Vis)和原位光微量热-荧光光谱联用仪获得碳自掺杂g-C₃N₄降解罗丹明B的原位热/动力学信息和三维荧光光谱信息, 探讨了光催化降解罗丹明B的微观机制. 结果表明, 单宁酸浓度≤10 mg/mL时, 碳会取代七嗪单元结构的氮原子形成g-C₃N₄骨架碳自掺杂; 单宁酸浓度≥ 20 mg/mL时, 碳以无定形形式沉积负载在g-C₃N₄表面上形成无定形碳自掺杂. 骨架碳自掺杂g-C₃N₄形成的π电子有效缩短了禁带宽度, 减小了光生电子-空穴复合几率, 比无定形C掺杂g-C₃N₄显示出更优异的光催化性能, 催化主要活性物种为h⁺和·O{}_{\mathrm{2}}^{-}. 碳自掺杂g-C₃N₄光催化降解过程可分为光响应吸热、 降解污染物放热平衡过程和稳定放热3个过程. 其中骨架碳自掺杂g-C₃N₄(C/N摩尔比为0.844)在光照1000 s内, 三维荧光光谱检测的RhB降解率锐减, 光照1000 s后, 其RhB降解率为87.6%, 分别是原始g-C₃N₄和无定形碳自掺杂g-C₃N₄的3.13倍和1.95倍. 光照1000 s后, 光微量热计显示以矿化和降解非荧光发色中间产物为主, 并保持以热变速率为(0.9799±0.5356) μJ/s稳定放热, 为拟零级反应过程, 是光催化反应的决速步骤.     

Preparation and characterization of biodegradable aliphatic-aromatic copolyesters/nano-SiO_2 hybrids via in situ melt polycondensation

In situ melt polycondensation was proposed to prepare biodegradable aliphatic-aromatic copolyesters/nano-SiO_2 hybrids based on terephthalic acid(TPA),poly(L-lactic acid) oligomer(OLLA),1,4-butanediol(BDO) and nano-SiO_2.TEM and FT-IR characterizations confirmed that TPA,OLLA and BDO copolymerized to obtain biodegradable copolyesters,poly(burylene terephthalate-co-lactate)(PBTL),and the abundant hydroxyl groups on the surface of nano-SiO_2 provided potential sites for in situ grafting with the simultaneo...     

Theoretical Investigation of the Solid State Reaction of Silicon Nitride and Silicon Dioxide forming Silicon Oxynitride (Si2N2O) under Pressure

The high‐pressure behavior of Si₂N₂O is studied for pressures up to 100 GPa using density functional theory calculations. The investigation of a manifold of hypothetical polymorphs leads us to propose two dense phases of Si₂N₂O, succeeding the orthorhombic ambient‐pressure polymorph at higher pressures:a defect spinel structure at moderate pressures and a corundum‐type structure at very high pressures. Taking into account the formation of silicon oxynitride from silicon dioxide and silicon nitride and its pressure dependence, we propose five pressure regions of interest for Si₂N₂O within the pseudo‐binary phase diagram SiO₂‐Si₃N₄: (i) stability of the orthorhombic ternary phase of Si₂N₂O up to 6 GPa, (ii) a phase assemblage of coesite, stishovite, and β‐Si₃N₄ between 6 and 11 GPa, (iii) a possible defect spinel modification of Si₂N₂O between 11 and 16 GPa, (iv) a phase assemblage of stishovite and γ‐Si₃N₄ above 40 GPa, and (v) a possible ternary Si₂N₂O phase with corundum‐type structure beyond 80 GPa. The existence of both ternary high‐pressure phases of Si₂N₂O, however, depends on the delicate influence of configurational entropy to the free energy of the solid state reaction.