Surface electronic structure of detonation nanodiamonds after oxidative treatment

X-ray absorption spectroscopy has been used for comparative study of electronic structure of detonation nanodiamonds (ND) purified using different oxidative treatments. The treatment of detonation soot with a mixture of nitric and sulphuric acids followed by ion exchange and ultrafiltration of hydrosol obtained was found to result in developing of ND surface coverage consisting of oxidized carbon species, which electronic state is close to that of strongly oxidized graphite. The deeper purification of ND was demonstrated to allow cleaning of ND particles from most of the oxidized carbon contaminations.     

Where and when are nanodiamonds formed under explosion?

The formation of nano-sized diamonds during the detonation of a TNT/RDX explosive with 50/50 composition was investigated experimentally in situ by means of small-angle X-ray scattering using synchrotron radiation with nanosecond time resolution. No nanodiamonds were observed immediately after the detonation front, as only the nucleation of nanodiamonds takes place at this moment. The increase in small-angle X-ray scattering which was observed during 2 μs was the cause of the dynamic growth of nanodiamonds. The inclusion of a very thin shell around the explosive causes a significant increase in this time, because the kinetic of nanodiamonds growth was changed.

In another set of experiments, the nanodiamonds were artificially introduced into different explosives before explosion. The nanodiamonds were not destroyed in RDX immediately after the detonation front, but burned in an oxidants with some delay. In TNT, the nanodiamonds were not destroyed at all.     

Stability of poly(N‐propargylamide)s under ultraviolet irradiation

This article investigates the photostability of poly(N‐propargylamide)s under different conditions, on the basis of which application research for this class of highly functional polymers can be performed. With helical polymer 1 [monomer: C?CCH₂NHCOCH(C₂H₅)₂] taken as a representative, some affecting factors, including the ultraviolet (UV)‐light intensity, presence of oxygen, far‐UV and near‐UV light, and temperature, were investigated. It was found that increasing the UV‐light intensity accelerated the degradation of polymer 1 . When oxygen was present, it also facilitated the degradation. Far‐UV light rather than near‐UV light played a predominant role in initiating the degradation of polymer main chains. Elevating the temperature of the polymer solution during UV irradiation made the degradation accelerate. Storing the polymer under weak UV light, in the absence of oxygen, and at a low temperature was favorable for keeping the polymer stable. These findings are important not only from a scientific point of view but especially for developing practical applications of this type of polymer on the basis of its photodegradability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Properties of individual fractions of detonation nanodiamond

Detonation nanodiamonds synthesized and purified on an industrial scale were additionally purified and separated into narrow size fractions by centrifugation. The average particle size for the smallest fraction was lower than 30 nm and the yield was about 20 wt.%. Using FTIR spectra analysis, it was demonstrated that ND aggregates of different sizes, separated from the same pristine ND, have different surface compositions of active surface groups, particularly oxygen-containing groups, which finally influence their zeta potential values and hydrosol stability. Using DTA analysis, the higher reactivity of the smallest fractions during heat treatment in air was also demonstrated.     

Modification of detonation nanodiamonds by heat treatment in air

In order to readily utilize nanodiamond (ND) particulates produced by detonation synthesis in many nanotechnology applications, it is necessary to modify the surface chemistry and to separate the particles into a more narrow range of particle sizes. Surface functionalization and fractionalization are highly dependent upon the method of ND synthesis and purification. For example, when material purified through the use of strong liquid oxidizers is used to produce hydrosols, they are unstable and difficult to fractionalize. In this study we developed a method of preparation that overcomes these two barriers. ND powder previously purified with a mixture of sulfuric acid and chromic anhydride was treated as follows: annealed in air followed by dispersion in water using a high power sonicator and multi-step ultracentrifugation. This treatment resulted in stable hydrosols formed from the smallest particle-size fractions.     

Degradation of polyimide film under vacuum ultraviolet irradiation

The degradation of PI film irradiated with VUV in a wavelength of 5 to 200 nm is investigated. The results show that transparency of PI film decreases obviously after irradiation and more obviously for the film irradiated with VUV of higher intensity. In addition, the absorption line red‐shifts for the PI film. The XPS and FTIR analyses results indicate that decarbonylation and the condensation of the benzene group take place under the irradiation and that carbonification takes place under 100 VUV suns. The change of optical property could be attributed to the stabilizing of the conjugation group and as well as to the carbonification to some extent. The character of VUV on polymer degradation is discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1370–1374, 2004     

Analysis of trapping–detrapping defects in high quality single crystal diamond films grown by Chemical Vapor Deposition

The photoresponse of high quality single crystal diamond films homoepitaxially grown by Chemical Vapor Deposition (CVD) onto low cost diamond substrates has been studied. The time evolution electrical response to the excitation by 5 ns laser pulses at 215 nm closely reproduces the laser pulse shape. The single crystal diamond response is therefore much faster than the laser pulse duration. The output signal is also very stable and reproducible, without significant priming or memory effects. Single crystal diamond films can therefore be grown by CVD having enough high quality to be used as photodetectors.However, a minor slow component shows up in the charge-integrated sample response. A systematic speed up of this slow component when increasing the detector temperature from − 25 °C to + 50 °C demonstrates its thermally activated origin. The slow component is therefore attributed to detrapping effects from shallow trapping centres.A model of the charge transport mechanism in the presence of trapping–detrapping centres can be developed and the results can be compared to the experimental ones. The activation energy of the shallow defects is accordingly determined as E_a = 0.4 eV.     

紫外线照射下由苯乙烯合成β-溴乙苯的研究

在紫外线的照射下,苯乙烯与溴化氢气体发生反马氏规则自由基加成反应,可合成β-溴乙苯(-βBEB)。考察了反应条件对实验结果的影响,发现当紫外线强度为0.5mW/cm2,反应时间60min,反应温度60℃,溶剂CCl4用量为苯乙烯5倍的体积时,苯乙烯的转化率>99%,-βBEB的产率≥96%。使用铁粉精制后-βBEB的最终收率≥93%(以苯乙烯计),-βBEB的纯度≥99%。     

共缩聚聚酰胺酸和聚酰亚胺的微波辐射合成研究

在N,N′-二甲基甲酰胺(DMF)溶剂中,选用3,3,′4,4′-二苯酮四羧酸二酐(BTDA)、均苯四甲酸酐(PMDA)和4,4′-二氨基二苯醚(ODA)为单体,微波辐射低温溶液缩聚合成一种共缩聚聚酰亚胺的前驱体聚酰胺酸(PAA),然后亚胺化脱水环化生成共缩聚聚酰亚胺(PI)。通过特性黏数([η])、红外光谱(FT-IR)和热重分析(TGA)对聚合物进行了结构表征和性能测试。结果表明,微波辐射溶液聚合能够提高PAA的特性黏数及产率,微波的引入大大缩短了反应时间;IR表明,在1778 cm-1和1723 cm-1处观察到聚酰亚胺特征峰;TG表明,PI在氮气中535℃左右开始降解,10%热失重温度(Td10%)为587℃。     

Kinetic investigation on steam gasification of charcoal under direct high-flux irradiation

The reaction kinetics of steam gasification of coal are investigated for a quartz tubular reactor containing a fluidized bed and directly exposed to an external source of concentrated radiation. Rate laws are formulated based on elementary reaction mechanisms describing reversible adsorption/desorption processes and irreversible surface chemistry. Assuming plug flow conditions, the rate constants are computed by matching theoretical and experimental results and their temperature dependence is determined by imposing an Arrhenius-type rate law. High-quality syngas containing an equimolar mixture of H₂ and CO, and less than 5% CO₂, was produced at above . The advantages of using a concentrated radiation source for supplying high-temperature process heat are three-fold: (1) the calorific value of the fuel is upgraded; (2) the gaseous products are not contaminated by combustion by-products; and (3) if the radiation source is derived from renewable energy, e.g. solar energy, the emission of greenhouse gases is avoided.     

Feasibility of CVD diamond radiation energy conversion devices

We analyzed the feasibility of CVD diamond to operate as the main component in active devices for conversion of high-energy radiation into electrical power. A self-sustained radiation dosimeter based on the electron emission effect was designed and tested under low-energy X-ray beam (Mg X-ray tube). The device operative conditions (absence of applied bias voltage) represented also the first experimental test towards the development of diamond energy conversion systems. On this basis, we designed a CVD diamond vacuum radiation energy converter and analyzed it using electron beams. An analysis of the performance was obtained letting both electron flux I₀ and kinetic energy E₀ to vary. For E₀ = 1 keV the power exploited by a load was estimated as tenths of nW and the total conversion efficiency was between 0.2 and 0.4%. This performance makes the device nominally competitive if compared to other similar solid-state converters. A discussion about the device design and possible improvements was performed in order to rationalize the conditions able to maximize the energy conversion efficiency.     

Effect of grafted polymeric foaming agent on the structure and properties of nano-silica/polypropylene composites

To promote dispersion of nano-silica in polypropylene (PP), a polymerizable foaming agent p-vinylphenylsulfonylhydrazide was synthesized and grafted onto the nanoparticles via free-radical polymerization. It was found that the grafted poly(p-vinylphenylsulfonylhydrazide) played dual role when being melt mixed with PP. The side sulfonylhydrazide groups were gasified to form polymer bubbles, leading to rapid inflation of the surrounding matrix that pulled apart the agglomerated nanoparticles, while the remaining backbone of the grafted polymer helped to improve the filler/matrix interaction through chain entanglement and interdiffusion at the interface. Mechanical tests indicated that the grafted nano-SiO₂/PP composites prepared according to the above strategy were simultaneously toughened, strengthened and stiffened. Compared with conventional graft polymerization treatment where no blowing function is associated, the technique proposed in this work could significantly enhance notch impact strength of PP.     

单分散超顺磁性Fe_3O_4纳米粒子的合成及表征

利用高温裂解法制备了油酸修饰的Fe3O4磁性纳米粒子,采用TEM、VSM、XRD以及FT-IR对粒子的结构和性能进行了表征和分析。结果表明:Fe3O4纳米粒子粒径为2nm,呈单分散性,结晶性能良好,室温下为超顺磁性,饱和磁化强度为11.73emu/g,可应用于磁流体、磁性分离等领域。     

Characteristics of jet fuels produced from hydrogenated shale oils

Shale oils from the United States (Geokinetics, Occidental, Paraho and Tosco II) were hydrotreated, fractionated into jet fuel cuts (boiling range 121–300°C), then characterized to evaluate their suitability as jet fuels. Nitrogen content was considerably higher, though the amount of hydrogen was relatively lower, than in typical petroleum jet fuels. Sulfur content was significantly below the acceptable limit. Trace metal contents in shale oil jet fuels were below the maximum levels for those in petroleum jet fuels. Vanadium, copper, lead and alkali metals were not present. Physical properties, except freezing points, were comparable to those of standard jet fuels.     

The mechanism of the reaction of graphite oxide to reduced graphene oxide under ultraviolet irradiation

Under ultraviolet (UV) irradiation, the formation and reduction mechanism of reduced graphene oxide (rGO) layers prepared from graphite oxide (GO) sheets have been investigated. The effects of hydroxyl free radicals (HO), hydroxide ions (OH⁻) or hydrazine molecules (N₂H₄) are considered. It has been demonstrated that the HO radicals, UV-induced from H₂O₂ molecules in aqueous solution, cannot reduce GO into rGO, but to some extent oxidize and damage the GO structure, simultaneously accompanied by a slight increase of acidity, possibly because of a release of H⁺ from H₂O₂ and GO during the reaction. The existence of OH⁻ ions or N₂H₄ instead of H₂O₂ molecules enables GO sheets to be quickly reduced into rGO due to the effect of photo-induced electrons on the GO sheets. The electrons are photogenerated mainly from OH⁻ or N₂H₄ in a GO aqueous dispersion. Because GO in diluted N₂H₄ aqueous solution can be photo-reduced almost completely within half an hour at room temperature, it is inferred that many more electrons are generated from N₂H₄ than from OH⁻.     

紫外光下水合电子降解卤代有机物的研究进展

卤代有机物污染问题在世界范围内普遍存在,氧化是一种常见的降解技术,但部分全氯代烃及氟代化合物很难被氧化.水合电子因其极强的还原能力,近年来广泛用于卤代有机物的降解研究,并取得良好的降解和脱卤效果,同时也受到光强、反应介质条件等多种因素的影响,对水合电子的性质、产生方式、卤代有机物降解的影响因素及降解机理进行了介绍,以期...     

Thermodynamics of surface self‐developing structure formation on polyamide films under ultraviolet irradiation

Polyamide terpolymer films can be obtained by the evaporation of a solvent–terpolymer–photoinitiator mixture on a glass plate. Through ultraviolet (UV) irradiation, self‐developing properties are observed. The nuclear magnetic resonance (NMR) study of the photochemical reaction involved in such a process permits us to propose a mechanism with a diffusion of solvent in the irradiated areas. The thermodynamics of irreversible process have been applied to the analysis of such a system behavior, and an analysis of the stability of the system resulting from its residual solvent content has been made. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 645–653, 2002     

Electrocatalytic Oxidation of Glucose on Gold Nanocomposite Electrodes

The electrocatalytic oxidation of glucose on gold nanocomposite electrodes was investigated with cyclic voltammetry. The gold nanocomposite electrodes were prepared by precipitating gold nanoparticles of different sizes from the corresponding colloidal solutions onto planar substrates, and the electrodes exhibited higher catalytic activity for the oxidation of glucose in alkaline solution with a negative shift in oxidation potential and a larger current as compared with bare gold electrodes. The high catalytic activity of the gold nanocomposite electrodes also resulted in easy oxidation of gluconolactone produced in the reaction. The modification of the gold nanocomposite electrodes with silver underpotential deposition led to a further negative shift in potential but a drop in current for the glucose oxidation.