Synthesis, properties and applications of nanoscale nitrides, borides and carbides

Nanoscale nitrides, borides and carbides are a fascinating type of materials, which have aroused tremendous and continuous research interest for decades owing to their special mechanical, electrical, optical, photoelectronic, catalytic properties and widespread uses. In this feature article, recent developments and breakthroughs in the synthesis, properties and applications of nanometre scale nitrides (BN, Si(3)N(4), GaN, noble nitrides), borides (LnB(6), LnB(2), Fe(3)BO(5), LiMBO(3)) and carbides (carbon, SiC, TiC, NbC, WC) were briefly reviewed in sequence of their different dimensions (1D, 2D and 3D). In particular, our latest advances in the "autoclave route" fabrication of nanoscale nitrides, borides, and carbides were highlighted. The challenges, issues and perspectives of the synthetic methodologies and potential applications concerning the above-mentioned materials were also briefly discussed.     

醋酸纤维素的制备及其结构与性能

将微晶纤维素(MCC)在冰醋酸/醋酸酐/氯化铁体系下乙酰化,制备醋酸纤维素(CA),考察了催化剂类型及用量、反应温度、反应时间和醋酸酐用量等对CA的取代度和聚合度的影响。研究表明,以氯化铁为催化剂,在冰醋酸/醋酸酐体系下,MCC乙酰化最佳工艺为:0.5 g MCC,0.1 g氯化铁,反应温度50℃,反应时间40 min,5 mL醋酸酐。醋酸纤维素的各项性能均接近商品醋酸纤维素,具有一定的应用价值。     

新型两性壳聚糖的制备及结构表征

为了制备一种新型的两性壳聚糖,拓展壳聚糖的应用范围,以甲壳素为原料,通过化学修饰,制备一种亲疏水结构的两性壳聚糖。首先甲壳素的C6-OH与2-氯乙胺盐酸盐(ACH)反应,接着C2-氨基脱乙酰化,最后与柠檬醛进行希夫碱反应。采用紫外、红外和X-射线衍射(XRD)对目标产物进行结构表征。结果表明,两性壳聚糖在253 nm处具有最大紫外吸收峰,其酰胺Ⅰ、Ⅱ、Ⅲ谱带的特征吸收峰分别位于1 650,1 575,1 380 cm^(-1);与甲壳素在9°和19°处明显的特征衍射峰相比,两性壳聚糖9°处的特征峰消失,19°处的特征衍射峰变得弱而宽。一种新型两性壳聚糖已成功制备,工艺简便。     

Polymer-derived Ta4HfC5 nanoscale ultrahigh-temperature ceramics: Synthesis,microstructure and properties

Nanoscale Ta₄HfC₅ ceramics were synthesized from curing and pyrolysis of novel polymer precursors which were synthesized by cohydrolysis and polycondensation of acetyl acetone coordinated tantalum alkoxide and hafnium alkoxide followed by blending with phenolic resin as carbon source. Pyrolysis of the polymer precursor at 1600 °C in vacuum produced Ta₄HfC₅ nanocrystallites with an average grain size of 21 nm and well-distributed elements, encapsulated by an amorphous carbon shell. Near full dense Ta₄HfC₅ monoliths can be prepared by spark plasma sintering (SPS) at 1600 °C with 10 vol% MoSi₂ as an additive, of which the Vicker micro-hardness and flexural strength achieved 17.58 GPa and 466 MPa, respectively. The polymer precursor method shed light on the fabrication of ceramic matrix composites. Besides, the high electrical conductivity of 1.5 × 10⁴ S/m entitled the ceramics to a prospective of utilization in microwave absorbing/shielding fields under harsh conditions.     

Synthesis,structure, and properties of vanadium pentoxide nanotubes

Vanadium oxide nanotubes are synthesized by the hydrothermal method with the use of polycrystalline vanadium oxide V₂O₅ and 1-hexadecylamine as a structural template. The structure of the vanadium oxide nanotubes is investigated using small-angle X-ray diffraction and transmission electron microscopy. It is demonstrated that the structure of the vanadium oxide nanotubes is characterized by a combination of fragments with different interlayer distances associated with the twisting of oxide layers in the form of “nanorolls.” The thermal stability, morphology, and surface properties of the nanotubes, as well as the role of the organic template in the formation of their structure, are discussed.     

Synthesis, structure and properties of hydrophobically associating polymers

Hydrophobically modified water-soluble polymers have recently become the subject of extensive research because of their use as aqueous viscosity modifiers in oil recovery and latex paint systems. In this study, poly(acrylamide) samples modified with small amounts of a hydrophobic monomer (ethylphenylacrylamide) have been prepared by free radical copolymerization using an aqueous micellar process in which the use of a surfactant ensures the solubilization of the hydrophobe. The copolymers exhibit improved thickening properties with respect to homopoly(acrylamide) analogs due to intennolecular hydrophobic associations. The aqueous solution-copolymer properties strongly depend on the amount of surfactant used in the synthesis. The differences observed between the samples are directly related to the copolymer microstructure, that is to a more or less block distribution of the hydrophobic units. The interactions in aqueous solution of a surfactant (sodium dodecylsulfate (SDS)) with these copolymers have been examined. A strong increase in viscosity is observed upon the addition of SDS below its critical micelle concentration, owing to the formation of mixed micelles of SDS and hydrophobic monomers. The complex rheological behavior observed is explained in terms of the balance between inter and intrachain liaisons. The effects of hydrolysis on the hydrophobic interactions are also discussed.     

Synthesis,structure and properties of liquid crystalline polymers

The following is an extended abstract of a paper presented at the conference on Liquid Crystalline Polymers in Leeds, 1980, summarising the principles of the synthesis of thermotropic liquid crystalline polymers, their structure dependant phase behaviour and their orientation in electric and magnetic fields.     

Mixed alkali-zinc diphosphates: Synthesis, structure, and properties

A series of mixed alkali-zinc diphosphates in the form of poly- and single crystals have been synthesized. Their physical-chemical, structural, and thermal characteristics have been determined. The compounds Na₂ZnP₂O₇ and K₂ZnP₂O₇ have a layered structural type, whereas LiNaZnP₂O₇, LiKZnP₂O₇, NaKZnP₂O₇, Li₁₂Zn₄(P₂O₇)₅, and K₂Zn₃(P₂O₇)₂ have a framework structural type.     

Polymeric stannous dicarboxylates: Synthesis,properties, and structure

A series of polymeric stannous dicarboxylates (i.e., suberate, sebacate, do-decanedioate, terephthalate, propoxyterephthalate, and isophthalate) has been synthesized from aqueous solution using various conditions of temperature (20, 50, and 98°C) and pH (6.4, 8.0, and 11.6). These were obtained as highly viscous adhesive-like emulsion phases when synthesized at 50 and 98°C. Polymeric stannous suberate when synthesized at pH 11.6 and temperature of 50°C crystallized to spherulites. When molten they behaved like hot-melt adhesives. They could be spun into fibers. On the other hand, melt-synthesized stannous dicarboxylates exhibit simple non-polymeric salt structures.     

Synthesis,structure, and properties of high performance alternating copolyimides

Summary A new diamine monomer, N,N-bis(4-aminophenyl)-2,5-(diisopropoxycarbony)benzene-1,4-dicarboxamide was synthesized. Using the diamine, several alternating copolyimide precursors were successfully synthesized by its condensation polymerization with dianhydrides. The structure and properties (mechanical properties and thermal expansivity) of alternating copolyimides imidized thermally were characterized, and compared with those of the corresponding random copolyimides prepared from the copoly(amic acid)s. The alternating copolyimides exhibited relatively higher chain order and in-plane orientation in films than the random copolyimides. The higher chain order and in-plane orientation led to the higher tensile modulus and lower thermal expansivity in the alternating copolyimides. Such effect of comonomer sequence was found to be highly pronounced in copolyimides consisting of comonomers which have a large difference in the chain rigidity. It was demonstrated in this study that the formation of alternating copolyimides is a suitable route to improve the performance of properties.     

Synthesis, structure and properties of polyhydroxyalkanoates: biological polyesters

High molecular weight polyhydroxyalkanoates (PHA) are synthesized and stored in the cell cytoplasm as water-insoluble inclusions by various microorganisms. This intriguing biological polyester initially attracted the attention of microbiologists and managed to keep many polymer scientists occupied over the second half of the last century. Concerted multidisciplinary scientific approaches have been directed to the elucidation of various aspects of PHA. Of significant interest are the findings that PHA can consist of various hydroxyalkanoate monomers, and the cloning of its biosynthesis genes. This has resulted in the production of PHA with various physical properties by genetically engineered microorganisms. In fact, it is now possible that large-scale production of PHA by transgenic plants can be achieved in the near future. The physical properties of PHA homopolymers as well as co- and heteropolymers have been the subject of study in various laboratories all over the world. By controlling the monomer composition of PHA, polymer scientists have shown that the polymer's physical properties can be regulated to a great extent. Furthermore, it is also clear that the rate of degradation of PHA in various environments can be controlled by judiciously altering its monomer compositions. This review attempts to bring together the biochemical and physicochemical aspects of PHA along with new perspectives on its potential therapeutic applications.     

吡啶盐染料DEHSPI的合成、结构与光物理性质

合成了一种新型吡啶盐染料4-［4-（N,N-二乙胺基）-2-羟基-苯乙烯基］-N-甲基吡啶碘盐（DEHSPI〖HTSS〗）。用X射线衍射方法测定了其晶体结构,DEHSPI单晶属于单斜晶系,C2/c空间群。晶胞参数：a=3.5970（4）nm,b=1.16270（15）nm,c=2.2081（3）nm,β=114.341（7）°,V=8.4139（18）nm3,Z=8,F（000）=3632,μ=1.536 mm-1,Dc=1.417 g·cm-3,R=0.0501。DEHSPI〖HTSS〗与没有羟基取代化合物的晶体结构分析比较发现,分子中2-羟基基团的存在提高了分子阳离子骨架的平面性。研究了它在不同溶剂和聚合物浸泡的溶胶-凝胶复合玻璃基质中的光物理性质,发现在复合玻璃基质中的荧光强度相对于溶液中大大增强,即使掺杂浓度较高时也没有因生成分子的聚集体而发生明显的荧光猝灭,材料的稳定性提高。     

Synthesis, structure and catalytic properties of Fe-substituted barium hexaaluminates

A sol–gel method using Ba and Al isopropylates and iron nitrate has been used to synthesise barium hexaaluminate partially substituted with iron. After calcination under oxygen at 1200°C the -alumina structure was obtained. Formation of the mixed BaFe_xAl_12-xO₁₉ phase occurred for x=1–4. XRD measurements showed a good crystallinity of the structure and expansion of unit cell parameters due to the presence of larger Fe³⁺ ions substituting Al³⁺ ones in octahedral sites only. Mössbauer spectroscopy revealed that Fe³⁺ ions are present in four different octahedral sites slightly distorted. Catalytic activity in methane combustion showed that an optimum was obtained for solid containing 2 Fe ions per unit cell: the increase of the amount of introduced iron was counterbalanced by the decrease of specific surface area. Intrinsic activities have been calculated for the four solids in both the fresh and aged states. It is observed that increasing iron content increases relative activities in the same ratio as the populations of iron located in two sites as deduced from Mössbauer spectroscopy. It is then tentatively assumed that activity is attributed to octahedrally coordinated Fe³⁺ ions in some specific sites.     

杂原子磷铝分子筛BSiAPO-5的合成结构及催化性能的研究

用水热合成法合成了一种硼-硅磷铝分子筛,通过化学分析、测定晶胞参数及用XRD,MAS—NMR方法进行表征,证实了硼、硅原子进入了分子筛骨架,并且具有和AIPO4-5相似的结构;用IR,NH3-TPD表征方法测出了它的酸性,测定结果表明,它具有L酸和B酸中心,以中等强度酸为主。在苯与烯烃烷基化反应中表现出良好的催化活性和长寿命,并且对2-LAB和3-LAB具有高选择性,有可能替代HF成为一种环境友好的新型催化剂。     

聚合植物油脂表面活性剂的制备及其结构与性能

采用环氧大豆油(ESO)为原料,乙酸乙酯为溶剂,四氯化锡为催化剂,通过环氧大豆油的开环自聚,制备聚合环氧大豆油(PESO);再将PESO在碱性条件下水解,洗涤纯化后得到水解聚合环氧大豆油(HPESO)。通过傅里叶红外光谱(FTIR)、核磁共振氢谱(¹H NMR)和凝胶渗透色谱(GPC)对HPESO的结构及分子量分布进行了表征,并对得到的水解聚合环氧大豆油脂肪酸钾盐表面活性剂(HPESO-K)的临界胶束浓度cmc及其表面张力(γ_cmc)、Krafft点(KP)、液体石蜡/水体系的乳化能力(EP)与抑泡及消泡能力(FP)进行了研究。结果表明:HPESO的数均分子量范围为1056～1156g/mol,重均分子量范围为1255～1374g/mol。在水溶液pH值为9～12条件下,HPESO-K的cmc值为0.13～0.41g/L,γ_cmc值为25.6～31.2mN/m。在水溶液pH=9条件下测得HPESO-K的Krafft点为37℃,液体石蜡/水体系中分出10mL水的时间为130s,亲水亲油平衡(HLB)值范围为10～11。     

Solution Combustion Synthesis of nanoscale Cu-Cr-O spinels: Mechanism,properties and catalytic activity in CO oxidation

Nano-structured Cu-Cr-O-based catalysts were successfully prepared by Solution Combustion Synthesis (SCS), and it has been found that their physical properties and atomic structure depend (in a complex way) on the initial composition of SCS processing, that the temperature of combustion and composition of initial mixture influences metal concentration in the nanocomposite, and that metal formation is going through metal oxide reduction by NO, H₂, CO. Presence of CO, NH₃ and H₂ in the gas phase, during SCS, was determined chromatographically. Connection between structural changes during reaction and properties of final nanocomposite material was determined. The catalysts were characterized by XRD, SEM/EDX, and their catalytic activity has been determined in CO oxidation. The pore structure of the samples was calculated with the Barrett-Joyner-Halenda (BJH) academic model, and the specific surface area was calculated with the Brunauer-Emmett-Teller (BET) adsorption equation. The specific surface area of the catalysts is varied between 10 m²/g and 37 m²/g. Understanding the interrelationships between activity of catalyst and the ensuing atomic structure has allowed a degree of optimization of the catalytic properties of the new catalysts.     

室温自交联水性聚丙烯酸酯乳液的合成、结构与性能

以甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)、丙烯酸(AA)和双丙酮丙烯酰胺(DAAm)为共聚单体,采用半连续种子乳液聚合工艺,合成了具有核–壳结构的室温自交联水性聚丙烯酸酯乳液。以十二烷基硫酸钠(SDS)与辛基酚聚氧乙烯醚(OP-10)为复合乳化剂,研究了其用量对聚合反应稳定性的影响,讨论了不同DAAm用量下乳胶粒的粒径分布、漆膜耐水性和力学性能,确定了较佳的用量:复合乳化剂用量为单体质量的3.0%,w(DAAm)为4%。透射电镜(TEM)分析表明,乳胶粒具有明显的核–壳结构。热分析表明,以己二酰肼(ADH)为交联剂,交联后漆膜的玻璃化转变温度明显提高,红外光谱分析证明了酮肼交联反应的发生。     

Synthesis,crystal structure and properties of two antimony germanate compounds

Two antimony germanates formulated as [(enH₂)_2.5][SbGe₈O₁₈(OH)₄] (1) (en = ethylenediamine) and Sb₄Ge₃O₁₂ (2) have been solvothermally synthesized and structurally characterized. Compound 1 represents the first organic containing microporous antimony germanate with three-dimensional (3D) channels. Compound 2 is isostructural to the scintillation crystal BGO (Bi₄Ge₃O₁₂) with 3D inorganic compact structure. The thermal stability of compound 1 and the optical properties of compound 2 have been studied.     

Synthesis, structure and magnetic properties of β-MnO 2 nanorods

We present synthesis, structure and magnetic properties of structurally well-ordered single-crystalline β-MnO₂ nanorods of 50–100 nm diameter and several μm length. Thorough structural characterization shows that the basic β-MnO₂ material is covered by a thin surface layer (∼2.5 nm) of α-Mn₂O₃ phase with a reduced Mn valence that adds its own magnetic signal to the total magnetization of the β-MnO₂ nanorods. The relatively complicated temperature-dependent magnetism of the nanorods can be explained in terms of a superposition of bulk magnetic properties of spatially segregated β-MnO₂ and α-Mn₂O₃ constituent phases and the soft ferromagnetism of the thin interface layer between these two phases.     

Synthesis,structure and properties of doped Bi2O3

Oxide ion conductors have been increasingly studied for many years because of their application in devices with high economical interest such as solid oxide fuel cells (SOFC), oxygen sensors, dense ceramic membranes for oxygen separation, and membrane reactors for oxidative catalysis. Bismuth oxides present polymorph forms, such as δ-, β- or γ-Bi₂O₃, with great potential for such applications, alone or in combination with other oxides. The present study investigates the influence of selected ions (Fe³⁺, Sb³⁺/Sb⁵⁺, and Ta⁵⁺), introduced as dopant in α-Bi₂O₃ and their effect on the structure and properties of the oxide polymorph forms obtained at high temperature. The molar ratio was Bi₂O₃:M_xO_y 0.95:0.05 where M = Fe₂O₃, Sb₂O₃ or Ta₂O₅, respectively.The structural changes of α-Bi₂O₃ were analysed by powder X-ray diffraction, SEM/EDX analysis and infrared spectroscopy. The structural changes are correlated with bulk ceramic characteristics (density, porosity) and their electrical behaviour versus temperature. The presence of some dopants (antimony and tantalum) on bismuth sites enlarges and enhances the stability of the polymorph forms, which is relevant to potential application.