Hollow cathode synthesis of crystalline CN films

We describe a novel carbon hollow-cathode RF plasma reactor which has been used to prepare deposits of carbon nitride. Results of the characterization of the deposits by Fourier transform infrared (FTIR) microscopy, Raman microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray analysis and X-ray diffraction are presented. The variation of the properties of the deposits as a function of the deposition conditions is discussed. The inclusion of small quantities of methane in the gas mixture was found to enhance the formation of the CN deposit, but for conditions of maximum enhancement C–H and N–H groups were observed in the deposit. Elemental analysis of the deposit showed that the nitrogen content was 57 at.%. A crystalline deposit was obtainable at low substrate temperatures, and the crystals were seen to grow preferentially on defects on the substrate surface.     

Effects of residual radicals on compositional and structural stability of silicon nitride fibers

In this study, amorphous silicon nitride fibers were prepared through the nitridation of cured polycarbosilane fibers. It was observed that their composition and properties can be controlled by adjusting the flow of NH₃ during the nitridation process. Based on their compositional and structural stability, the samples could be divided into two classes: stable fibers and unstable fibers. As indicated by the electron spin resonance spectra, the amount of the residual free radicals in the unstable fibers was significantly higher than that in the stable fibers. Because of the reactions of the radicals with the moisture in the air, the oxygen content of the unstable fibers increased day by day until the residual radicals were exhausted. Thus, to develop silicon nitride fibers with both low oxygen content and low carbon content, the amount of NH₃ used should be optimized to eliminate the free radicals. These results suggest that it is possible to tailor the nitridation conditions for preparing high-purity silicon nitride materials so that they exhibit desirable properties, such as compositional and structural stability, good mechanical properties, and high electrical resistivity.     

Synthesis and characterization of microporous carbon nitride

This research reports the preparation and characterization of amorphous microporous carbon nitride using HZSM-5 zeolite as template, and ethidene diamine and carbon tetrachloride as chemical precursors. Microporous amorphous carbon nitride is generated by removal of HZSM-5 zeolite in the obtained zeolite/carbon nitride composite using hydrofluoric acid after carbonization the precursor inside the channels of zeolite. The microporous carbon nitride was characterized by nitrogen sorption techniques, scanning electron microscopy, elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, IR spectroscopy, Ultraviolet–visible spectroscopy, Raman spectroscopy, and thermo-gravimetric analysis. Amorphous microporous carbon nitride with high surface area and narrow pore size distribution is thermal stable under atmosphere conditions up to 700 K.     

FeMn-MOF/CN异质结光芬顿催化剂制备及性能研究

通过一种简便的原位负载策略制备了铁锰双金属有机骨架/氮化碳异质结光芬顿催化剂FeMn-MOF/CN,并利用X射线衍射（XRD）、红外光谱（FT-IR）、扫描电镜（SEM）、光致发光（PL）光谱等测试手段对催化剂的组成、结构及光电化学性质进行了表征。以降解高浓度左氧氟沙星（LEV,100 mg/L）为模型反应评价了催化剂的光芬顿反应性能,并提出了可能的光芬顿反应机理。由于光催化和芬顿反应之间的协同作用,5%FeMn-MOF/CN（FeMn-MOF与CN的质量比为5%）异质结表现出优异的光芬顿反应性能,在40 min内对LEV的移除率达到98.8%。基于原位合成的策略,FeMn-MOF和CN之间形成了紧密的异质结界面,不但极大地提高了光生载流子的分离和传递效率,而且显著地促进了Fe（Ⅲ）/Fe（Ⅱ）和Mn（Ⅲ）/Mn（Ⅱ）的循环。该工作为高效光芬顿催化材料的设计和制备提供了新思路。     

Effect of nitrogen on the optoelectronic properties of a highly sp-rich amorphous carbon nitride films

In this study, we investigate the relationship between the nitrogen content and the optoelectronic properties in sputtered amorphous carbon nitride films (a-CN_x). The incorporation of nitrogen and the resulting microstructure changes reveal that the evolution of the optical gap is attributed to the connectivity of the Csp² clusters and their global organisation. The increase in the N content induces the formation of C≡N terminating bonds affecting this connectivity, and therefore, the Csp² cluster size and their relative disorder.     

Stabilization of free radicals in filled oligoesteracrylates

A study of the formation and decay of free radicals in the process of photocuring oligocarbonatmethacrylate (OCM-2), filled by two types of silica differing in particle size and hydroxylapatite, was carried out by electron spin resonance (ESR) spectroscopy. The results were correlated with the data for molecular mobility obtained by the means of a spin probe. It was shown that the interface layers are able to stabilize free radicals that appear in the process of photocuring. The lifetime of stabilized radicals is about 20–30 min at 50°C. The existence of a wide distribution of molecular mobility in filled oligomers was established. Sorption of oligomer molecules with filler surface was accompanied by their vitrification. When the content of filler achieved 25–35 mass%, vitrification of the half-volume of polymer matrix occurred. The strongest stabilizing effect was provided by hydroxylapatite.     

Evolution of metal nitriding and hydriding reactions during ammonia plasma-assisted ball milling

Nanocrystalline metal nitride and hydride powders were prepared using plasma-assisted ball milling in ammonia gas (NH₃-P-milling) via an in situ synthesis reaction. The gas–solid reactions were triggered by a short duration of plasma milling of Mg and Ti under a constant pressure of ammonia gas, and the products in the two systems were nanocrystalline Mg₃N₂ and TiN, TiH₂ after 10?h, respectively. During the NH₃-P-milling of Ti powder, TiH₂ and TiN were formed during the initial stages of milling, and then, the TiH₂ decomposed during further milling upon reaction with N radicals, transforming into the TiN phase. In contrast, no chemical reaction occurred between NH₃ and Mg/Ti after 10?h of C-milling. The discharge plasma activated and decomposed the ammonia gas and activated the surface of the powders, which, together with the mechanical effect of high-energy ball milling, accelerated the gas–solid reactions.     

Chemical Reactions During the Thermal Processing of Borazene Polymers

A class of borazene polymers was developed which consists of a two-dimensional array of six-membered borazene rings with the borons of adjacent borazene rings separated by -NH- groups. Pyrolysis of these polymers above ∼1000°C leads to crystalline graphite-like boron nitride ( h -BN). The thermal chemistry of thin films of one polymer deposited on KOH-eched aluminum was examined by thermal decomposition mass spectroscopy (TDMS) and thermal gravimetric analysis (TGA), and the gas evolution chemistry was found to be essentially complete at temperatures less than 400°C. All products desorb with the same temperature profile and the major desorbing species are NH₃ and N₂, consistent with a loss of excess nitrogen and hydrogen in the polymer, and HCl from decomposition of byproducts of the synthesis step. Since the formation of ordered crystalline h -BN films requires heating to temperatures of the order of 1000°C, whereas the gas evolution chemistry is complete by roughly 400°C, it is concluded that gas evolution chemical processes are not rate limiting in BN ceramic production.     

Interfacial Characterization of Silicon Nitride Powders

The composition of the surface and the behavior in aqueous suspensions of three silicon nitride powders were investigated using electron spectroscopy for chemical analysis (ESCA), potentiometric titrations, leaching experiments, and electrophoretic mobility. ESCA shows that the as-received powders have a surface-layer composition similar to that identified as an intermediate state between silica and silicon oxynitride. The original differences in pH_iep between the three powders disappears by aging the powders. The common pH_iep of 6.8 ± 0.3 for the three powders is interpreted as the equilibrium pH_iep for silicon nitride in aqueous suspensions.     

氮化碳负载钯催化剂催化苯酚加氢制环己酮

为了开发苯酚加氢制环己酮高效催化剂,将脲在550 ℃高温聚合,制备了片层状氮化碳催化剂载体g-CN;负载钯纳米粒子后,得到Pd/g-CN催化剂。采用红外光谱、X射线粉末衍射、透射电镜和X射线光电子能谱对催化剂进行表征。将Pd/g-CN催化剂用于催化苯酚水相加氢,考察了不同载体和反应温度对催化性能的影响,并对催化剂重复使用性能进行研究。结果表明,载体g-CN含有大量的含N基团,能有效稳定金属纳米粒子,从而获得粒径较小、分散较好的Pd纳米粒子;同时,g-CN具有较强碱性,有利于苯酚的吸附,可提高苯酚的反应速率和环己酮选择性。采用负载Pd质量分数2%的Pd/g-CN催化剂,在反应温度80 ℃、反应压力0.1 MPa、n(Pd)∶n(苯酚)=0.02、苯酚1 mmol、水3 mL和反应时间3 h条件下,苯酚可完全转化,环己酮选择性高达99%。Pd/g-CN催化剂制备工艺简单,原料价廉,催化性能优异。     

Study of elementary reactions of free radicals formed on oxide and platinum containing catalysts

The formation of alkylperoxy radicals on catalysts CuCr₂O₄/ -Al₂O₃, Pt /--Al₂O₃ and on alumina upon the interaction of amines and alcohols with oxygen has been observed applying the matrix isolation ESR technique. Surface-generated gas phase radicals are shown to initiate a radical chain reaction. The efficiency of the yield of radicals depends on the catalyst mass and its arrangement in a reactor: the desorption of radicals into the gas phase occurs primarily from the outer geometrical surface of catalyst granules.     

石墨相氮化碳电催化过氧化氢性能研究

石墨相氮化碳(g-C_3N_4)具有稳定的光学性质、化学性质等优点,但也存在一些缺点。因此,为了更好的利用石墨相氮化碳,改变石墨相氮化碳应用领域的探究是非常重要的。利用循环伏安法在过氧化氢溶液中对不同的石墨相氮化碳薄膜电极进行了氧化还原反应测试,进而研究了电极上发生的电化学反应的可逆性及其动力学特征,从而判断电极电催化活性的高低。研究表明,该修饰电极对过氧化氢具有电催化还原作用,铂基石墨相氮化碳的催化效果比纯的电催化优越。     

The Effects of Accelerated Aging and Contact with Food Simulants on the Adhesion of Amorphous Hydrogenated Carbon Films Deposited on Clarified Polypropylene

This work focuses mainly on the influence of time, temperature, and contact with food simulants on the adhesion of amorphous hydrogenated carbon (a-C:H) films obtained by plasma-enhanced chemical vapor deposition (PECVD) in clarified polypropylene (cPP). Two types of films prepared by PECVD were studied: diamond-like carbon (DLC) and polymer-like carbon (PLC) films that can both act as a functional barrier. The adhesion between the film and polymer substrates is critical in relation to the barrier effectiveness during the packaging shelf life. Therefore, the adhesion was analyzed by a tape test and scanning electron microscopy (SEM). The films were exposed to Food and Drug Administration (FDA) listed food simulants and were submitted to an accelerated aging test to evaluate the long-term adhesion performance of a-C:H films. The chemical alterations on the surface related to the accelerated aging test and the liquid simulants were analyzed by a contact angle test. It showed that the polarity of a-C:H films increased after immersion in liquid simulants, indicating a change on the surface. Before the accelerated aging test, the SEM micrographs and the tape test indicated that the PLC film has a structure with lower surface tension and, therefore, regions with fewer detachment points in relation to the DLC film. The results obtained in this study showed that the adhesion behavior and preservation of the a-C:H structure (DLC or PLC) are related to intrinsic factors such as the type of film structure (flexible or rigid) and the polymeric substrate.     

超临界CO2中CO2参与的化学反应

超临界CO2中的化学反应是目前的研究热点之一。超临界CO2既为反应介质又为反应物的化学反应的主要优势是将萃取与反应相耦合形成均相体系,排除了传质阻力,提高了反应的速率和选择性;产物与催化剂易于分离;同时CO2作为反应原料无毒、不燃、易得,不但可以代替有机溶剂和有毒原材料,而且可有效利用CO2。介绍了超临界CO2作为反应原料所参与化学反应的类型及特点,简单综述了这些化学反应的研究进展,并对未来的发展提出展望。     

Structure of the dense amorphous carbon phase synthesized in a mixture with diamond as a result of shock compression of carbon black

Soft X-ray emission and absorption spectroscopy methods were used in the present work to study experimentally the electronic structure of the dense amorphous carbon phase synthesized in a mixture with diamond as a result of shock compression of carbon black. The X-ray emission C Kα bands, representing the energy distribution of the C 2p-like states, have been recorded for the amorphous carbon phase and, for comparison, for diamond, lonsdaleite, graphite, and carbon black. For the amorphous carbon phase, diamond and lonsdaleite the spectra of quantum yields of the X-ray photoeffect in the area of the C K absorption edge have been recorded as well. Total and partial densities of states of the carbon H-6 and bct-4 phases, diamond and lonsdaleite have been calculated using the first-principles self-consistent full potential linearized augmented plane wave (FP-LAPW) method. Comparison on a common energy scale of the X-ray emission C Kα bands and C K quantum yields of the dense amorphous carbon phase as well as the theoretical curves of partial C 2p-like states of the carbon H-6 and bct-4 phases reveals that, the electronic structure of the amorphous carbon phase under consideration is well described by that of the carbon bct-4 phase. The experimental X-ray emission and absorption spectroscopy data indicate that the amorphous carbon phase studied is metallic, being in agreement with the results of the theoretical FP-LAPW calculations.     

反应条件对氮(碳/氧)化硅薄膜性能的影响

就氮(碳／氧)化硅薄膜的反应条件——组成和结构——性能之间关系的国内外研究进行了综述。     

荷移反应-荧光光谱法测定吡哌酸

采用荧光光谱研究了电子受体氯冉酸与电子给体吡哌酸之间的荷移反应。实验结果表明,在丙酮-甲醇介质中即可生成稳定的n-π络合物,其荧光发射显著增强。据此提出了一种基于荷移反应简便可靠地测定吡哌酸的荧光光谱新方法,用曲线交叉法和平衡移动法测定络合物的组成比为1：1。线性范围为0．10～7．0μg／mL,最低检出限为0．10μg／mL,回收率为97．4％～99．3％,相对标准偏差为1．3％。2．6％。最后探讨了荷移反应的机理,该方法用于PIP药片的测定,结果令人满意。     

Characteristics of carbon-related materials deposited in electron-energy controlled CH4/H2 RF discharge plasmas

The influence of electron temperature T_e on the production of carbon-related materials was investigated in a hollow-type magnetron radio-frequency (RF) CH₄/H₂ plasma. Here, the electron temperature decreased along the plasma column. Since the dissociation of CH₄ is determined by the electron energy in plasmas, the density ratio of radicals CH₂/CH₃ can be varied by the electron temperature. Therefore, the change of the electron temperature is quite important for controlling the characteristics of carbon-related materials. In the experiment, the production of diamond microparticles in low T_e plasma was detected. On the other hand, thin carbon films consisting of graphitic carbons were observed in the high T_e plasma. Therefore, it is shown that control of the electron temperature in the plasma has a key effect on the film quality.     

Methanol Tolerance of CN x Oxygen Reduction Catalysts

Nitrogen-containing carbon nanofiber (CN _x ) catalysts grown by acetonitrile pyrolysis over 2 wt% Fe, Co, and Ni impregnated supports of alumina, silica and magnesia were tested for methanol tolerance during the oxygen reduction reaction (ORR) by rotating ring disk electrode (RRDE) method. Catalysts tested in acidic electrolytes containing 1–3 M methanol showed no methanol poisoning during ORR and were inactive for methanol oxidation.     

Conversion of natural gas to hydrogen and carbon black by plasma and application of plasma carbon black

In a microwave plasma-catalytic system, methane decomposition was carried out with 2.45 GHz microwave plasma and then the high conversion and yield of hydrogen and carbon black were obtained efficiently. It was found that hydrogen and carbon black were produced at the mole ratio of 2:1, and carbon black of around 30 nm was produced, which is comparable to classical furnace black. In a study of catalyst effect, Pt-loaded catalysts showed higher activities than a Pd catalyst for the conversion of methane by plasma-catalytic process. The productivity of carbon black increased with platinum loading up to 3 wt.%.