纳米碳化钼复合物的制备及其CO加氢反应性能

利用溶胶-凝胶法成功地制备了纳米碳化钼复合物,采用热重、TEM和XRD等对合成的纳米碳化钼复合物的形貌和结构进行了表征,以CO加氢反应为探针对其催化性能进行了评价。结果表明:纳米碳化钼粒度分布均匀,包覆在无定型碳中,随着柠檬酸含量的增加粒径逐渐变小,表面Mo物种越不易被还原。用于CO加氢反应具有较高的活性,主要生成低碳烷烃,当CA/Mo=2.0时具有最高的反应活性。     

新型纳米碳/碳化钼的制备及应用研究

碳化钼具有类铂的催化性能,因而纳米碳/碳化钼作为催化剂在许多催化反应、能源和环境领域具有潜在的应用价值。对近年来制备新型纳米碳与碳化钼的方法、在催化等领域的应用研究进行了综述和总结,并展望了在传感领域的应用前景。     

纳米碳颗粒在催化中的应用及前景

概述了多壁富勒烯和新型纳米碳结构(纳米碳球)的表面修饰方法以及在催化中的应用研究现状,结果表明,化学氧化法对纳米碳颗粒进行表面修饰是有效的方法,可以改善其惰性表面,使其功能化.由于结构的独特性,纳米碳颗粒作为载体材料在电催化和某些脱氢反应中已经显示了较好的催化性能.预测了纳米碳在合成低碳烯烃中的潜在应用前景并为其在能源、化工领域中的应用提供了新的思路.     

新型喷雾干燥法制备LiFePO_4/C复合材料及其性能研究

通过新型喷雾干燥技术及热处理制备出具有球形二次形貌结构的纳米LiFePO4/C复合材料。首先合成了纳米FePO4颗粒(约20nm),并与Li2CO3和一定量的蔗糖均匀混合,对材料前驱体进行碳包覆,通过喷雾干燥获得了前驱体二次颗粒;经过热处理获得了由一次颗粒组成的二次颗粒。详细研究了碳含量对一次颗粒粒径及复合材料性能及形貌的影响,发现当LiFePO4/C复合材料中碳含量为5.3%(质量分数),样品拥有良好的形貌结构和最佳的性能,0.1,1和5C下的比容量分别为162,145和116mAh/g。     

直接还原碳化法制备纳米复合WC-Co粉末

用直接还原碳化法制备了纳米复合WC-Co粉末.根据X射线衍射图研究了直接还原碳化温度及时间对反应产物的影响,用扫描电镜观察了粉末颗粒形貌和粒度分布.结果表明用直接还原碳化法在950℃碳化4h可以得到100～300nm、无η相的WC-Co复合粉末,该法具有碳化温度低、碳含量容易控制、适合工业化生产的优点.     

α-MoC在无介体微生物燃料电池阳极的应用研究

采用溶体法结合碳热还原法制备了碳化钼,用XRD表征了碳化钼的结构,用SEM观察了所制备碳化钼的形貌。使用循环伏安法和交流阻抗法测试了碳化钼的电催化性能。把制备的碳化钼用于无介体微生物燃料电池阳极,电池最大功率密度达到商业铂碳的92%,表现出优越的电催化性能和良好的生物相容性。因此α-MoC可望成为一种具有广泛应用前景的无介体微生物燃料电池阳极材料。     

TiO2/Co3O4复合纳米颗粒的制备及其光催化制氢性能

通过碳辅助法和溶胶-凝胶法制备了具有可见光下光催化制氢性能的TiO₂/Co₃O₄复合纳米颗粒。采用X射线衍射仪(XRD)、透射电子显微镜(TEM)和高分辨率透射电子显微镜(HRTEM), 以及紫外可见分光光度计表征了复合纳米颗粒的晶体结构、微观形貌和紫外-可见光谱吸收能力。结果表明, 制备的复合纳米颗粒具有良好的晶型、结构以及紫外可见光吸收能力。实验测试了TiO₂/Co₃O₄复合纳米颗粒在模拟太阳光下的光催化制氢性能, 并研究了其光催化制氢的可重复利用性。结果表明, 在模拟太阳光照射下, 该复合纳米颗粒催化纯水产生氢气的速率约为8.25 μmol/(g·h), 且该复合纳米颗粒具有良好的可重复利用性。     

纳米纤维素修饰的碳纳米纤维制备及其疏水性研究

为拓展碳纳米纤维在环境清洁领域的应用，提高碳纳米纤维的水接触角，改善膜表面的疏水性能，获得疏水性较好的碳纳米纤维薄膜，利用静电纺丝法将纳米纤维素(CNFs)与碳纳米纤维前驱体复合，获得具有低表面能和良好疏水性能的纳米碳纤维/纳米纤维素复合纤维膜。通过对纳米纤维素含量进行调控，经预氧化和碳化处理后得到一系列具有规则三维空间网络结构的复合纤维膜，并探究不同纳米纤维素含量对复合纤维膜疏水性能的影响。结果表明：纳米纤维素修饰复合纤维膜随着碳化程度的提高其表面能呈现逐渐降低的趋势，其对水的接触角也逐渐增大，疏水效果得到较大幅度提升。随着纳米纤维素含量继续增加，复合纤维膜的水接触角呈上升趋势，未添加前接触角为36.13°,当纳米纤维素添加质量为20%时，水接触角最大为132.14°,提高了366%。     

负载纳米氧化锌多孔碳吸附剂的制备及其结构研究

半导体纳米粒子光催化降解VOC是一种有效、经济的有机废气处理方法,本论文研究了纳米氧化锌改性的多孔碳材料的制备、结构及其对挥发性有机物的光催化分解性能.结果表明,可利用微乳液法合成并经高温煅烧得到负载于多孔碳材料上的纳米氧化锌.制备条件如反应物浓度、配比、沉淀剂种类等条件对产品的形貌、氧化锌纳米颗粒大小和负载量有明显的影响.负载纳米氧化锌微粒多孔炭吸附剂既保持了多孔炭材料的多孔性,又具有一定催化分解低浓度挥发性有机污染物的能力.     

石墨烯负载硫化锌/硫化铜异质结的制备及光催化性能EI北大核心CSCD

采用微波辅助加热方法制备石墨烯负载硫化锌纳米颗粒,在其基础上,通过离子交换反应形成石墨烯负载硫化锌/硫化铜异质结的复合物(rGO-ZnS/CuS)。通过SEM,TEM,XRD等手段对样品进行形貌观察和物相分析,并分别讨论氧化石墨烯含量、不同硫源和微波加热时间对复合物形貌和光催化性能的影响。结果表明:硫代乙酰胺为硫源,微波反应时间为30min,氧化石墨烯质量分数为10%时,能够在石墨烯表面获得均匀分布的硫化锌/硫化铜异质纳米结的复合物,在可见光照射下,150min内降解水中81.2%的甲基橙,显示出优异的光催化效果,异质结内形成的界面电子转移现象以及石墨烯作为电子受体进一步促进内部光生电子空穴的分离是提高光催化效果的原因。     

Molybdenum Carbide‐Decorated Metallic Cobalt@Nitrogen‐Doped Carbon Polyhedrons for Enhanced Electrocatalytic Hydrogen Evolution

Electrocatalytic hydrogen evolution reaction (HER) based on water splitting holds great promise for clean energy technologies, in which the key issue is exploring cost‐effective materials to replace noble metal catalysts. Here, a sequential chemical etching and pyrolysis strategy are developed to prepare molybdenum carbide‐decorated metallic cobalt@nitrogen‐doped porous carbon polyhedrons (denoted as Mo/Co@N–C) hybrids for enhanced electrocatalytic hydrogen evolution. The obtained metallic Co nanoparticles are coated by N‐doped carbon thin layers while the formed molybdenum carbide nanoparticles are well‐dispersed in the whole Co@N–C frames. Benefiting from the additionally implanted molybdenum carbide active sites, the HER performance of Mo/Co@N–C hybrids is significantly promoted compared with the single Co@N–C that is derived from the pristine ZIF‐67 both in alkaline and acidic media. As a result, the as‐synthesized Mo/Co@N–C hybrids exhibit superior HER electrocatalytic activity, and only very low overpotentials of 157 and 187 mV are needed at 10 mA cm^?2 in 1 m KOH and 0.5 m H₂SO₄, respectively, opening a door for rational design and fabrication of novel low‐cost electrocatalysts with hierarchical structures toward electrochemical energy storage and conversion.     

火焰法沉积金刚石薄膜过程中碳在基底中的行为

采用火焰法在Ｍｏ基底上沉积金刚石薄膜，研究了在沉积过程中Ｃ在Ｍｏ基底中的行为，结果表明，在Ｍｏ基层上沉积金刚石时，碳原子与Ｍｏ反应形成Ｍｏ２Ｃ，随时间延长，Ｍｏ２Ｃ层加厚，Ｃ原子扩散进入基底的速率下降，之后Ｃ原子在Ｍｏ２Ｃ层表面达到过饱和开始金刚石形核。     

Horizontally oriented carbon nanotubes coated with nanocrystalline carbon

Single-walled carbon nanotubes (CNTs) and multi-walled CNTs of length 2-5 mm were grown from Fe/Mo nanoparticles and Fe thin film catalyst, respectively, by thermal chemical vapor deposition. Following CNT growth, the CNTs were in-situ coated with nanocrystalline carbon shells of thickness 100-1500 nm. Horizontally oriented CNTs with carbon shells in the direction of the feeding gas were visible under a regular optical microscope. They were easily manipulated by optical manipulators, and CNT probes can thus be fabricated.     

C/C复合材料高温长寿命抗氧化复合涂层研究

采用包埋技术在C/C复合材料表面制备SiC-WSi₂/MoSi₂抗氧化复合涂层; 通过恒温氧化实验以及X射线衍射分析、扫描电镜观察及能谱分析, 研究了W、Mo含量对复合涂层微观结构和高温抗氧化性能的影响. 结果表明: 随着包埋粉料中W、Mo含量的增加, 所制备复合涂层的厚度先增加后减小; 含有10.0at％ W和Mo制备的复合涂层具有相对较大的厚度和较为致密的结构, 且WSi₂和MoSi₂含量相对较高; 氧化过程中在涂层表面形成致密和稳定的SiO₂玻璃保护膜; 在1500℃氧化315h后, 带有该涂层的C/C试样仍然没有失重, 且经过18次1500℃←→室温急冷急热后涂层没有开裂和脱落, 说明该涂层具有优异的抗氧化和抗热震性能.     

硒化温度对CIGS/Mo界面微观结构和化学成分的影响

采用磁控溅射和硒化热处理的方法在钠钙玻璃上沉积了一系列铜铟镓硒(CIGS)薄膜。利用X射线衍射(XRD)、高分辨透射电子显微术(HR-TEM)、高角环形暗场相(HAADF)和X射线能量散射光谱(EDS)元素面扫描分析等表征手段,研究了铜铟镓硒/钼(CIGS/Mo)界面特性随硒化温度的变化规律。结果表明,400℃硒化的薄膜中CIGS与Mo层之间界面清晰;当硒化温度为500℃时,CIGS/Mo界面上出现MoSe_2薄层和富Na的二次相纳米颗粒;当硒化温度升至600℃时,MoSe_2层增厚,同时富Na二次相纳米颗粒连接形成不平整的条带,CIGS/Mo界面演变为CIGS/富Na的二次相/MoSe_2/Mo多层结构。此外,MoSe_2的取向对富Na二次相的形成有一定的影响。     

Synergizing Mo Single Atoms and Mo2C Nanoparticles on CNTs Synchronizes Selectivity and Activity of Electrocatalytic N2 Reduction to Ammonia

Previous research of molybdenum-based electrocatalysts for nitrogen reduction reaction (NRR) has been largely considered on either isolated Mo single atoms (MoSAs) or Mo carbide particles (e.g., Mo₂C) separately, while an integrated synergy (MoSAs-Mo₂C) of the two has never been considered. The theoretical calculations show that the Mo single atoms and Mo₂C nanoparticles exhibit, respectively, different catalytic hydrogen evolution reaction and NRR selectivity. Therefore, a new role-playing synergistic mechanism can be well enabled for the multistep NRR, when the two are combined on the same N-doped carbon nanotubes (NCNTs). This hypothesis is confirmed experimentally, where the MoSAs-Mo₂C assembled on NCNTs (MoSAs-Mo₂C/NCNTs) yields an ammonia formation rate of 16.1 µg h⁻¹ cm_cat⁻² at −0.25 V versus reversible hydrogen electrode, which is about four times that by the Mo₂C alone (Mo₂C/NCNTs) and 4.5 times that by the MoSAs alone (MoSAs/NCNTs). Moreover, the Faradic efficiency of the MoSAs-Mo₂C/NCNTs is raised up to twofold and sevenfold of the Mo₂C/NCNTs and MoSAs/NCNTs, respectively. The MoSAs-Mo₂C/NCNTs also demonstrate outstanding stability by the almost unchanged catalytic performance over 10 h of the chronoamperometric test. The present study provides a promising new prototype of synchronizing the selectivity and activity for the multistep catalytic reactions.     

Tribological behavior of PTFE nanocomposite films reinforced with carbon nanoparticles

Carbon-based nanoparticles synthesized by heat treatment of nanodiamond in the temperature range of 1000–1900 °C were added to PTFE film to investigate the structural effect of the carbon particles on the tribological properties of PTFE composite film. Carbon-based nanoparticles were prepared by milling with micron sized beads in chemically treated water before their addition to PTFE film. The wear and frictional properties of PTFE nanocomposite film were measured by the ball on plate type wear test. The wear resistance of PTFE film was found to be enhanced by the addition of 2 wt% of carbon nanoparticles. The wear coefficient of PTFE film was decreased from 16.2 to 3.5 × 10⁻⁶ mm³/N m by the addition of carbon-based nanoparticles heat-treated at 1000 °C. Increasing the heating temperature of the nanodiamonds caused the extent of aggregation and particle size to increase. The wear resistance of PTFE nanocomposite film was enhanced by the addition of nanodiamonds heat-treated at 1000 °C, but decreased when the heat treatment temperature of carbon nanoparticles was further increased. Tribological behavior of PTFE nanocomposite films depending on the types of carbon nanoparticles were explained based on the structural, physical and chemical modification of carbon nanoparticles.     

Synthesis of core/shell spinel ferrite/carbon nanoparticles with enhanced cycling stability for lithium ion battery anodes

Monodispersed core/shell spinel ferrite/carbon nanoparticles are formed by thermolysis of metal (Fe3+, Co2+) oleates followed by carbon coating. The phase and morphology of nanoparticles are characterized by x-ray diffraction and transmission electron microscopy. Pure Fe3O4 and CoFe2O4 nanoparticles are initially prepared through thermal decomposition of metal–oleate precursors at 310 degrees C and they are found to exhibit poor electrochemical performance because of the easy aggregation of nanoparticles and the resulting increase in the interparticle contact resistance. In contrast, uniform carbon coating of Fe3O4 and CoFe2O4 nanoparticles by low-temperature (180 degrees C) decomposition of malic acid allowed each nanoparticle to be electrically wired to a current collector through a conducting percolative path. Core/shell Fe3O4/C and CoFe2O4/C nanocomposite electrodes show a high specific capacity that can exceed 700 mAh g(-1) after 200 cycles, along with enhanced cycling stability.     

Improvement in the weldability of molybdenum alloy by pre-welding solid carburising

Molybdenum (Mo),with its high chemical stability and resistance to neutron irradiation,has wide appli-cation prospects in the nuclear industry;however,the embrittlement of welded Mo joints limits its further application.In this study,the brittleness of the welded joints of Mo alloy was reduced and their strength was enhanced by adding carbon to the fusion zone (FZ) during laser welding.In the FZ of the Mo joints,carbon mainly existed as Mo2C,and some free C atoms,and MoC and MoOxCy phases were also present.The distribution of Mo2C directly influenced the bonding strength of the grain boundaries.As Mo2C was dispersedly distributed as particles or discontinuous lines at the grain boundaries of Mo,it improved the resistance of the grain boundaries to the propagation of cracks and thereby increasing their strength.However,the Mo2C phases distributed in a reticular pattern at the grain boundaries of Mo provided channels that enabled cracks to rapidly propagate,thereby reducing the resistance of the grain boundaries to crack propagation and weakening their strength.The emergence of the MoOxCy phase reduced the weakening effect of free oxygen atoms on the strength of grain boundaries of Mo.     

碳化钼的制备与表征

以MoO₃为前体, CH₄/H₂为还原碳化气, 经程序升温还原碳化反应制备了Mo₂C样品, 并用TG-DTA、XRD、BET、SEM、XPS进行了表征. 结果表明, MoO₃在CH₄/H₂气氛中的还原碳化历程为MoO₃→MoO₂→MoO_xC_y→Mo₂C, 适宜的还原碳化温度为675℃. 实验条件下制得的碳化钼晶相为β-Mo₂C, 表面呈现出形状规整、大小相对均一的片状颗粒, 平均粒径约3.9μm. 碳化钼表面有两种不同价态的钼原子, 分别归属于Mo--C 物种的Mo²⁺和Mo--O物种的Mo^δ+ , 以前者为主; 碳物种由四种不同价态的碳原子组成, 分别归属于C--Mo、C--C、C--H和C--O物种, 以前者为主. 随还原碳化反应温度的升高, 制备的碳化钼颗粒增大, 比表面积下降, C--C物种和C--H物种增加, 表面积炭增多. 由于积炭的覆盖和保护作用, 碳化钼表面的Mo原子主要以Mo²⁺ 的Mo--C物种存在, 只有少部分被氧钝化.