Experimental evidence for the formation mechanism of metallic catalyst-free carbon nanotubes

Our work reported that the so-called pure carbon nanotubes(CNTs)can be synthesized without metallic catalyst by chemical vapor deposition(CVD).The as-prepared CNTs have average diameter of 50 nm and length over several microns.Analysis of intermediate objects in the products indicates that their formation mechanism follows the wire-to-tube model.Besides,according to thermodynamic analysis of the driving force combing with experimental results,we find that the thermal gradient can effectively favor the formation of CNTs in our metallic catalyst-free CVD.

Characterization of free carbon in the as-thermolyzed Si-B-C-N ceramic from a polyorganoborosilazane precursor

Polyorganoborosilazane((B[C_(2)H_(4)-Si(CH_(3))NH]_(3))n)was synthesized via monomer route from a single-source precursor and thermolyzed at 1300℃in argon atmosphere.The as-thermolyzed Si-B-C-N ceramic was characterized using X-ray diffraction(XRD)and Raman spectroscopy.The crystallization behavior of silicon carbide in the as-thermolyzed amorphous Si-B-C-N matrix was understood by XRD studies,and the crystallite size calculated using Scherrer equation was found to increase from 2 nm to 8 nm with increase in dwelling time.Concomitantly,Raman spectroscopy was used to characterize the free carbon present in the as-thermolyzed ceramic.The peak positions,intensities and full width at half maximum(FWHM)of D and G bands in the Raman spectra were used to study and understand the structural disorder of the free carbon.The G peak shift towards 1600 cm-1 indicated the decrease in cluster size of the free carbon.The cluster diameter of the free carbon calculated using TK(Tuinstra and Koenl)equation was found to decrease from 6.2 nm to 5.4 nm with increase in dwelling time,indicating increase in structural disorder.

Rational design of carbon-based metal-free catalysts for electrochemical carbon dioxide reduction: A review

Electrochemical CO2 reduction to chemicals or fuels presents one of the most promising strategies for managing the global carbon balance, which yet poses a significant challenge due to lack of efficient and durable electrocatalyst as well as the understanding of the CO2 reduction reaction(CO2RR) mechanism.Benefiting from the large surface area, high electrical conductivity, and tunable structure, carbon-based metal-free materials(CMs) have been extensively studied as cost-effective electrocatalysts for CO2RR.The development of CMs with low cost, high activity and durability for CO2RR has been considered as one of the most active and competitive directions in electrochemistry and material science.In this review article,some up-to-date strategies in improving the CO2RR performance on CMs are summarized.Specifically, the approaches to optimize the adsorption of CO2RR intermediates, such as tuning the physical and electronic structure are introduced, which can enhance the electrocatalytic activity of CMs effectively.Finally, some design strategies are proposed to prepare CMs with high activity and selectivity for CO2RR.

Grain size characteristics of the carbonate-free fraction of surface sediments from the Southwest Indian Ridge area and its geological significance

The carbonate-free fraction of 20 surface sediments collected from the ultraslow-spreading Southwest Indian Ridge(SWIR) was studied by grain size analysis and mineralogical analysis with X-ray powder diffraction(XRD),stereo microscopy and scanning electron microscopy(SEM). The characteristics of the carbonate-free fraction of the sediments were obtained, and related influential factors were discussed. The results show that the mean grain size of this fraction is in 1.96Φ–8.19Φ, with poorly sorting and unimodal, bimodal or irregular bimodal distribution patterns. Four grain size end members of the fraction are derived with the End Member Model method. The finest end member EM1 shows a significant contribution of terrigenous materials of the aeolian input and sediment carried by the bottom current. End member EM2 with medium size mainly reflects sediment of a siliceous bioclast origin. EM3 and EM4 are interpreted as representing the coarser volcanic materials related to bedrock weathering or volcanic activities. Multi-provenance is the dominant factor controlling the grain size pattern of the carbonate-free fraction of the sediments in that area. In addition, sediment transport processes such as the bottom current and wind are the minor factors that influence the grain size distribution of the carbonate-free fraction sediments.

Probing the intrinsic catalytic activity of carbon nanotubes for the metal-free oxidation of aromatic thiophene compounds in ionic liquids

A metal-free catalytic system combining oxidized carbon nanotubes (oCNTs) and ionic liquids (ILs) is presented for the oxidation of aromatic thiophene compounds with H2O2 as an oxidant. The oCNTs exhibit impressively high activity and stability in the system, which show an even better performance than those of some reported metal catalysts. The ILs are proved to have indispensable influence on the enhanced catalytic performance of the oCNTs. Detailed characterization by TG-MS and XPS demonstrates that the carbonyl groups are the active sites for the oxidation process, which is further supported by the deactivation and the model catalysts experiments. The quantitative analysis of different oxygen groups in oCNTs could be achieved by an isothermal temperature programmed TG-MS method. The concentration of carbonyl groups is 1.46 mmol per 1 g oCNTs and the tuiriover frequency of oCNTs could also be obtained (10.7 h^-1 in the presence of OmimPF6). H2O2 decomposition experiments combined with the EPR results reveal that the presence of OmimPF6 can avoid the intermediate HO· to form O2 and then improve the catalytic performance of oCNTs for the oxidation of dibenzothiophene.

Free Radicals in Organic Matter for Thermal History Reconstruction of Carbonate Succession

Geothermometer is one of the most useful methods to reconstruct the thermal history of sedimentary basins. This paper introduces the application of free radicals concentration of organic matter as a thermal indicator in the thermal history reconstruction of carbonate succession, based on anhydrous thermal simulation results of type I and H1 kerogen. A series of free radicals data are obtained under thermal simulation of different heating temperatures and times, and quantitative modds between free radical concentration （Ng） of organic matter and time-temperature index （TTI） for types I and type H1 kerogen are also obtained. This Ng.TTI relation was used to model the Ordovician thermal gradients of Well TZ12 in the Tarim Basin. The modeling result is corresponding to the results obtained by apatite fission track data and published data. This new method of thermal history reconstruction will be benefit to the hydrocarbon generation and accumulation study and resource assessment of carbonate succession.

Millimeter-Wave Absorption Properties of Thin Wave Absorber in Free Space with New Porous Carbon Material

In this paper, we focus on PHYTOPOROUS, a porous carbon material made entirely from plant-based ingredients, as a new broadband-wave absorber material that acts in the millimeter wave band. We created prototypes of thin rubber-sheet wave absorbers that contain porous carbon (PHYTOPOROUS) made from rice chaff and soybean hulls, which are both agricultural residue products that are generated in large quantities. We investigated the permittivity and reflectance characteristics of this material using the free-space time-domain method. The thin rubber-sheet wave absorber that contained PHYTOPOROUS made from soybean hulls exhibited a frequency band that was approximately 18 GHz wide and centered at 90 GHz. The return loss for this material was greater than −20 dB. This demonstrates that the material provides nearly constant reflection absorption over a wide frequency band.

Ultrahigh rate binder-free Na_3V_2(PO_4)_3/carbon cathode for sodium-ion battery

Sodium ion batteries （SIBs） are very promising for large-scale energy storage in virtue of its high energy density, abundant sodium resources and low environmental impact, etc. However, it is still a big chal- lenge to develop high-performance and durable cathode materials for SIBs. Among different candidate materials, Na_3V_2（PO_4）_3 has attracted great attentions due to its high theoretical capacity （117 mAh/g）, stable framework structure and excellent ionic conductivity. However, Na_3V_2（PO_4）_3 delivers inferior rate capability and cycling stability due to its poor electronic conductivity. In this work, free-standing Na_3V_2（PO_4）_3/carbon nanofiber membranes are synthesized by an electrospinning-sintering mute. The sample could deliver excellent cycling capability with specific capacity of 112 mAh/g at 1 C after 250 cycles and ultrahigh rate capability with 76.9 mAh/g even at 100 C, which is superior to many state-of- the-art SIB cathode materials. This can be attributed to the hierarchically distributed Na_3V_2（PO_4）_3 crystals in carbon nanofiber network, which possesses outstanding electronicfionic conductivity and thus leads to an ultrahigh rate capabilitY.

Liver Nuclear Activation of Carbon Tetrachloride or Bromotrichloromethane to Trichloromethyl and Trichloromethylperoxyl Free Radicals.Their Reactions With Lipids and Proteins

The formation of·CCl3 radicals in liver nuclei was suggested by spin trapping of them with N-t-butyl-α-phenylnitrone followed by GC/MS detection of the resulting adduct. Comparison of its formation in microsomal biotransformation of CCl4 was made. In aerobic nuclear activation mixtures containing NADPH and CCl4, significant decrease in the arachidonic acid content of nuclear lipids was observed (27. 8%, compared to control), the intensity of this decrease was lower than that occurring in the corresponding microsomal incubation mixtures (29.1%). Significant decreases in arachidonic acid content of nuclear and endoplasmic reticulum lipids were also observed in animals at 6 hours of poisoning with the haloalkane. During aerobic nuclear metabolism of CCl4 or CBrCl3, cholesterol oxidation products were detected: a ketocholesterol, an epoxide like structure and 7-ketocholesterol. Nuclear protein carbonyl formation was not promoted during nuclear CCl4 biotransformation. NADPH by itself may lead to protein carbonyl formation during prolonged periods of incubation. CBrCl3 in contrast, led to decreased protein carbonyl formation. No increase in nuclear protein carbonyl formation was observed in CCl4 intoxicated animals during periods of time between 1 to 6 hours after treatment. The results indicate that during nuclear biotransformation of CCl4 or CBrCl3 reactive free radicals, PUFA degradation, reactive aldehydes and cholesterol oxidation products are formed, nearby DNA and regulatory proteins.

Research on Properties of Metasilicate Bonded Carbon-free Basic Dry Vibration Mix

Carbon-free basic dry vibration mix was prepared using middle grade magnesia and fused magnesia as main starting materials,metasilicate replacing phenolic resin as binder,adding a certain amount of medium and low temperature intensifiers. Effects of binder,grain composition,and additives on basic dry vibration mix for tundish were studied,and the bonding mechanism was also analyzed. The results show that：（1） when using metasilicate as binder,the higher strength can be acquired; （2） the suitable grain composition is q=0.48,the critical granularity is 5 or 3 mm,the fines addition is 10%-20% （mass percent）; （3） the strength and corrosion resistance of the basic dry vibration mix can be improved by the melting compound of metasilicate and additives; （4） with temperature rising,the bonding type in dry vibration mix changes from cohere bonding to reaction bonding,and then to ceramic bonding at last.

Development and application of fluorine-free mold powder for low carbon steel

Fluorine in mold powder is known as harmful to human health and the environment. Being the advocate of green production, Baosteel developed an environmentally friendly mold powder without fluorine. The main problem of fluorine-free flux film is small heat resistance and thus the heat transfer intensity of the mold is too large, which to some extent hinders the increase of the casting speed. With the heat flow simulation equipment, controlling precipitation of crystal in flux and solidification temperature properly, fluorine-free mold powder for low carbon steel,which substitutes F with B203 ,was successfully developed and applied in industrial production. The production results show that, by using boronic fluorine-free mold powder,the boron increment in molten steel is less than 1.3ppm for conventional aluminium killed low carbon steel.

High-performance doping-free carbon-nanotube-based CMOS devices and integrated circuits

Ballistic n-type carbon nanotube(CNT)-based field-effect transistors(FETs) have been fabricated by contacting semiconducting single-walled CNTs(SWCNTs) using Sc or Y.The n-type CNT FETs were pushed to their performance limits through further optimizing their gate structure and insulator.The CNT FETs outperformed n-type Si metal-oxide-semiconductor(MOS) FETs with the same gate length and displayed better downscaling behavior than the Si MOS FETs.Together with the demonstration of ballistic p-type CNT FETs using Pd contacts,this technological advance is a step toward the doping-free fabrication of CNT-based ballistic complementary metal-oxide-semiconductor(CMOS) devices and integrated circuits.Taking full advantage of the perfectly symmetric band structure of the semiconductor SWCNT,a perfect SWCNT-based CMOS inverter was demonstrated,which had a voltage gain of over 160.Two adjacent n-and p-type FETs fabricated on the same SWCNT with a self-aligned top-gate realized high field mobility simultaneously for electrons(3000 cm2 V-1 s-1) and holes(3300 cm2 V-1 s-1).The CNT FETs also had excellent potential for high-frequency applications,such as a high-performance frequency doubler.

N, F?Codoped Microporous Carbon Nanofibers as Efficient Metal?Free Electrocatalysts for ORR

Currently, the oxygen reduction reaction(ORR) mainly depends on precious metal platinum(Pt) catalysts. However, Pt-based catalysts have several shortcomings, such as high cost, scarcity, and poor long-term stability. Therefore, development of e cient metal-free electrocatalysts to replace Pt-based electrocatalysts is important. In this study, we successfully prepared nitrogen-and fluorinecodoped microporous carbon nanofibers(N, F-MCFs) via electrospinning polyacrylonitrile/polyvinylidene fluoride/polyvinylpyrrolidone(PAN/PVDF/PVP) tricomponent polymers followed by a hydrothermal process and thermal treatment, which was achieved for the first time in the literature. The results indicated that N, F-MCFs exhibit a high catalytic activity(E_(onset): 0.94 V vs. RHE, E_(1/2): 0.81 V vs. RHE, and electron transfer number: 4.0) and considerably better stability and methanol tolerance for ORR in alkaline solutions as compared to commercial Pt/carbon(Pt/C, 20 wt%) catalysts. Furthermore, in acidic media, N, F-MCFs showed a four-electron transfer pathway for ORR. This study provides a new strategy for in situ synthesis of N, F-MCFs as highly e cient metal-free electrocatalysts for ORR in fuel cells.

Doping-free carbon nanotube optoelectronic devices

Semiconducting carbon nanotubes(CNTs) possess outstanding electrical and optical properties because of their special one-dimen-sional(1D) structure.CNTs are direct bandgap materials,which makes them ideal for use in optoelectronic devices,e.g.light emitters and light detectors.Excitons determine their light absorption and light emission processes due to the strong Coulomb interactions between electrons and holes in CNTs.In this paper,we review recent progress in CNT photodetectors,photovoltaic devices and light emitters.In particular,we focus on the doping-free CNT optoelectronic devices developed by our group in recent years.

Wet carbon-based solid acid/NaNO_3 as a mild and efficient reagent for nitration of aromatic compound under solvent free conditions

Nitro aromatic compound can be obtained in high yields via nitration of aromatic compound with wet carbon-based solid acid and NaNO_3 under solvent free oxidation at room temperature.

Glycerol-Based Carbon-SO₃H Catalyzed Benign Synthetic Protocol for the Acetylation of Alcohols, Phenols and Amines under Solvent-Free Conditions

A simple and efficient solvent-free method was developed for the acetylation of alcohols, phenols and amines in excellent yields employing glycerol-based sulfonic acid (-SO3H) functionalized carbon catalyst under environmentally benign reaction conditions. The salient features of this protocol are the short reaction time, ease of product isolation and reusability of the carbon catalyst.

开环轨迹无碳小车设计与误差分析

为实现无碳小车开环轨迹运动,设计并制作了一种基于凸轮机构的无碳小车,可以通过更换凸轮实现不同开环轨迹的运动。首先,结合小车功能要求,设计出小车的整体结构和基本参数,其次,根据已知坐标点利用贝塞尔曲线对理论轨迹进行拟合,获得前轮转角曲线及推程曲线并将其极坐标化得到理论凸轮轮廓,经凸轮原理分析,对凸轮轮廓包络处理,获得实际凸轮轮廓曲线。最后,根据小车实际运行轨迹在MATLAB中进行参数反推仿真,模拟误差产生方式,得出最优调整方案。结果表明,凸轮基圆直径和转向偏距对开环运动轨迹均有影响,其中,凸轮基圆直径对整体运动轨迹影响较大,可作为整体轨迹修正参数;转向偏距对中后程运动轨迹产生旋转偏移,可作为局部轨迹修正参数。文中所述模型及对轨迹误差的研究具有普适性,对开环轨迹小车调试具有较高的指导意义。

混合填料不同配比对免垫片硅酮密封胶性能的影响

免垫片硅酮密封胶是一种可以用于要求高密封性的场合,如汽车、高铁、航天航空等领域的单组分室温硫化型密封胶。通过在密封胶中加入填料,可以提升密封胶的理化性能。以纳米碳酸钙和硅微粉作为填料,在填料总质量固定的情况下研究不同填料比例对免垫片硅酮橡胶性能的影响。试验发现,当纳米碳酸钙与硅微粉的质量比减小时,免垫片硅酮胶的表干速度、固化深度和耐高温性有所增加,而力学性能和对金属基材的粘接性能逐渐减弱。结合综合性能,纳米碳酸钙与硅微粉的质量比为5∶2时制备的免垫片硅酮密封胶具有更全面的理化性能。

Nitrogen doped carbon catalyzing acetylene conversion to vinyl chloride

Commercial production of vinyl chloride from acetylene relies on the use of HgCla as the catalyst, which has caused severe environmental problem and threats to human health because of its toxicity. Therefore, it is vital to explore alternative catalysts without mercury. We report here that N-doped carbon can catalyze directly transformation of acetylene to vinyl chloride. Particularly, N-doped high surface area mesoporous carbon exhibits a rather high activity with the acetylene conversion reaching 77% and vinyl chloride selectivity above 98% at a space velocity of 1.0 mL.min-l.g-1 and 200 ~C. It delivers a stable performa℃nce within a test period of 100h and no obvious deactivation is observed, demonstrating potentials to substitute the notoriously toxic mercuric chloride catalyst.

Facile fabrication of hierarchical porous Co_3O_4 nanoarrays as a free-standing cathode for lithium–oxygen batteries

Two shapes of Co_3O_4 nanoarrays(i.e., nanosheets, nanowires) with different densities of exposed catalytic active sites were synthesized through a facile hydrothermal method on Ni foam substrates and tested as the binder/carbon free and free-standing cathodes for Li–O_2 batteries. Particularly, the single crystalline feature of Co_3O_4 nanosheets with a predominant high reactivity {112} exposed crystal plane and hierarchical porous nanostructure displayed better catalytic performance for both oxygen reduction reaction(during discharge process) and oxygen evolution reaction(during charge process). Li–O_2 battery with Co_3O_4 nanosheets cathode exhibited a higher discharge specific capacity(965 m Ah g^(-1)), lower discharge/charge over-potential and better cycling performance over 63 cycles at 100 mA g^(-1) with the specific capacity limited at 300 mAh g^(-1). The superior catalytic performance of Co_3O_4 nanosheets cathode is ascribed to the enlarging specific area and increasing the exposed Co^(3+) catalytic active sites within predominant {112} crystal plane which plays the key role in determining the adsorption energy for the reactants, enabling high round-trip efficiency and cyclic life.