首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
Wen M  Zhang F  Cheng M  Wu Q  Sun B  Sun Y 《Chemphyschem》2011,12(18):3573-3577
Newly designed magnetic FeNi-Pt match-like heterostructured nanorods were synthesized by means of induced growth of FeNi nanorods on Pt nanotips. The proposed synthesis mechanism is corroborated by SEM, TEM, XRD and XPS. The magnetic behavior shows that the magnetic saturation and coercivity are strongly dependent on both the shape and the alloy composition. The saturation magnetizations (Ms) and the coercivity (Hc) of nanorods synthesized are larger than those of nanoparticles because of the relatively large anisotropy of nanorods. Maximum saturation magnetization is obtained for Fe(82) Ni(15) -Pt(3) at 226.6 emu g(-1), whereas maximum coercivity is obtained for Fe(20)Ni(77)-Pt(3) at 136.8 Oe. Shape-dependent reactivity toward the reduction of chlorinated solvents was observed for the FeNi-Pt heterostructured nanomaterials. In particular, the Fe(82)Ni(15)-Pt(3) nanorods are highly reactive in the dechlorination process of 1,1,2,2-tetrachloroethane.  相似文献   

2.
Metal–carbon nanocomposites that represent FeCo alloy nanoparticles uniformly distributed over the carbon matrix, were prepared by the IR pyrolysis of precursors comprising polyacrylonitrile (PAN), iron acetylacetonate, and cobalt acetate (the metal ratio in the precursors was Fe: Co = 1: 1, 3: 1). The composition of FeCo alloy nanoparticles satisfies the tailored ratio Fe: Co. The FeCo phase is formed at synthesis temperatures in the range 500–600°С; at T ≤ 500°С only FCC-Co-base solid solutions are observed. The nanocomposites prepared at T ≥ 600°С simultaneously contain FeCo intermetallic nanoparticles and an insignificant amount of a FCC-Co phase or a cobalt-base solid solution phase. The saturation magnetization of FeCo/C metal–carbon nanocomposites is determined by the mean nanoparticle size and the alloy composition, and ranges from 36 to 64 (A m2)/kg (when Fe: Co = 1: 1) and from 35 to 52 (A m2)/kg (when Fe: Co = 3: 1) at synthesis temperatures in the range 600–800°С.  相似文献   

3.
电结晶制Co/Pt多层膜的结构及磁性研究   总被引:2,自引:0,他引:2  
印仁和  曾绍海  曹为民  董晓明 《化学学报》2005,63(20):1871-1874
以单晶Si(111)为基底, 在以P盐[主要成分Pt(NO2)2(NH3)2]和CoSO4为主盐的硼酸体系中电结晶Co/Pt多层膜. SEM观察多层膜的断面形貌, 证实多层膜具有周期结构. 经XRD测试, 首次证实了Co-Pt界面上有CoPt3化合物的存在. 用PPMS测试了多层膜的磁滞回线, 平行于外磁场时膜的矫顽力约为165 Oe, 垂直于外磁场时的矫顽力随Co含量的增加而增加, 最大达到396 Oe. 首次用电结晶方法制得了易磁化轴垂直于膜面的Co/Pt多层膜.  相似文献   

4.
Platinum (Pt) is recognized as an excellent cocatalyst which not only suppresses the charge carrier recombination of the photocatalyst but also reduces the overpotential for photocatalytic H2 generation. Albeit of its good performance, the high cost and low abundance restricted the utilization of Pt in large-scale photocatalytic H2 generation. Pt based transition metal alloys are demonstrated to reveal enhanced activities towards various catalytic reactions, suggesting the possibility to substitute Pt as the cocatalyst. In the present work, Pt was partially substituted with Co, Ni, and Fe and Pt-M (M = Co, Ni, and Fe)/g-C3N4 composites were constructed through co-reduction of H2PtCl6 and transition metal salts by the reductant of ethylene glycol. The crystal structure and valence states were measured by X-ray diffractometer (XRD) and X-ray photoelectron spectrometer (XPS), respectively. The higher degree of XRD peaks and larger binding energies for Pt 4f5/2 and Pt 4f7/2 after incorporating Co2+ ions indicated that Co was successfully introduced into the lattice of Pt and Pt-Co bimetallic alloys was attained through the solvothermal treatment. The morphology was subsequently observed by transmission electron microscope (TEM), which showed a good dispersion of Pt-Co nanoparticles on the surface of g-C3N4. Meanwhile, the shrinkage of lattice fringe after introducing cobalt salt further confirmed the presence of Pt-Co bimetallic alloys. The UV-Vis absorption spectra of g-C3N4 and Pt, Pt-Co deposited g-C3N4 were subsequently performed. It was found that the absorption edges were all consistent for all three samples as anticipated, implying that the band gap energy was maintained after hybridizing with Pt or Pt-Co alloys. Furthermore, the photocatalytic H2 generation was carried out over the as-prepared composites with triethanolamine (TEOA) as sacrificial reagent. Under visible-light illumination, the1% (w) Pt2.5M/g-C3N4 (M = Co, Fe, Ni) composites all exhibited higher or comparable activity towards photocatalytic H2 generation when compared to 1% (w) Pt loaded counterpart. In addition, the atomic ratios of Pt/Co and the loading amount of Pt-Co cocatalyst were modified to optimize the photocatalytic performance, among which, 1% (w) Pt2.5Co/g-C3N4 composite revealed the highest activity with a 1.6-time enhancement. Electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra indicated that the enhancement might be attributed to improved charge transfer from g-C3N4 to Pt2.5Co cocatalyst and inhibited charge carrier recombination in the presence of Pt2.5Co cocatalyst. Therefore, the present study demonstrates the great potential to partially replace Pt with low-cost and abundant transition metals and to fabricate Pt based bimetallic alloys as promising cocatalysts for highly efficient photocatalytic H2 generation.  相似文献   

5.
The soft magnetic nanocomposites with equiatomic FeCo particles dispersed in Al2O3 matrix were synthesized via a sol-gel technique combined with H2 reduction method. The samples were characterized by X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The FeCo nanoparticles in all the samples have the typical bcc structure. With the decreasing of Al2O3 content, the mean grain size of FeCo in the nanocomposites and the saturation magnetization of the samples increase, while the coercivity of samples increases firstly and then decreases due to different magnetic mechanisms.  相似文献   

6.
许多化学工作者对单齿膦配体(PPh3,PBun3,PEt2Ph,P(OEt)3,P(OC6H5)3)与母体簇合物FeCo2(CO)9(μ3-S)的取代反应进行过详细研究[1-3],但对双齿膦配体与母体簇合物的取代反应研究报导较少.Aime[4]合成了含双齿膦配体的簇合物FeCo2(CO)7(μ3-S)(Ph2PCH2PPh2),并用13CNMR和IR光谱方法对其结构进行了表征.到目前为止,含双齿膦配体的该类簇合物的晶体与分子结构还未见报导.RosannaRossetti[2]通过研究母体簇合物与…  相似文献   

7.
Despite the recent progress in increasing the power generation of Anion-exchange membrane fuel cells (AEMFCs), their durability is still far lower than that of Proton exchange membrane fuel cells (PEMFCs). Using the complementary techniques of X-ray micro-computed tomography (CT), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectroscopy, we have identified Pt ion migration as an important factor to explain the decay in performance of AEMFCs. In alkaline media Pt+2 ions are easily formed which then either undergo dissolution into the carbon support or migrate to the membrane. In contrast to PEMFCs, where hydrogen cross over reduces the ions forming a vertical “Pt line” within the membrane, the ions in the AEM are trapped by charged groups within the membrane, leading to disintegration of the membrane and failure. Diffusion of the metal components is still observed when the Pt/C of the cathode is substituted with a FeCo−N−C catalyst, but in this case the Fe and Co ions are not trapped within the membrane, but rather migrate into the anode, thereby increasing the stability of the membrane.  相似文献   

8.
胡龙兴  杨帆  邹联沛  袁航  胡星 《催化学报》2015,(10):1785-1797
由于硫酸根自由基(SO4?-)的强氧化性,基于SO4?-的高级氧化技术受到人们的高度关注.采用过渡金属活化过一硫酸盐(PMS)产生SO4?-用以分解有机物,反应体系简单,反应条件温和,且不需要额外的能量供给,因此,成为人们优先选用的方法,其中,采用高效、环境友好的非均相过渡金属催化剂活化PMS处理难降解有机物成为研究热点.本文研究了非均相CoFe/SBA-15-PMS体系对水中难降解染料罗丹明B(RhB)的降解.以SBA-15为载体, Co(NO3)2·6H2O和Fe(NO3)3·9H2O为前驱物,采用一步等体积浸渍法制备了CoFe/SBA-15,通过X射线衍射(XRD)、N2吸附-脱附、扫描电镜(SEM)、能谱(EDS)、透射电镜(TEM)和振动样品磁强计(VSM)等对其进行了表征.考察了焙烧温度、Co与Fe的负载量对CoFe/SBA-15催化性能的影响和该催化剂的重复使用性能,还考察了RhB降解动力学及催化剂CoFe/SBA-15投加量、氧化剂PMS投加量和反应物(RhB和PMS)初始浓度对其性能的影响,探讨了RhB的降解机理.结果表明:对于催化剂CoFe/SBA-15,合成焙烧后在SBA-15上负载的Fe、Co化合物主要是CoFe2O4复合物,它作为催化剂的活性中心负载在SBA-15的孔道内外.制备的焙烧温度对CoFe/SBA-15催化性能几乎无影响,但对Co浸出影响显著.与SBA-15相比,催化剂10Co9.5Fe/SBA-15-700(Co和Fe负载量分别为10 wt%和9.5 wt%,焙烧温度700 oC)的比表面积、孔体积和孔径均减小,分别为506.1 m2/g,0.669 cm3/g和7.4 nm,但仍然保持SBA-15的有序六方介孔结构.该催化剂以棒状体的聚集态存在,聚集体直径大于0.25μm,其磁化强度为8.3 emu/g,因此,可通过外磁铁容易地从水中分离.相比之下,10Co9.5Fe/SBA-15-700具有最佳的催化性能和稳定性,可使RhB的降解率达到96%以上, Co的浸出量小于32.4μg/L.在CoFe/SBA-15和PMS共存下, RhB的降解符合一级动力学方程, RhB降解速率随CoFe/SBA-15和PMS投加量的增加和初始反应物浓度的减小而提高.淬灭实验结果表明,在CoFe/SBA-15, PMS和RhB水溶液体系中,存在的主要活性自由基为SO4?-,它是由CoFe/SBA-15活化PMS产生的,对RhB的降解起决定性的作用. RhB降解过程的UV-vis结果表明, RhB的降解途径主要是蒽环打开, SO4?-优先攻击RhB的有色芳香烃环,然后RhB进一步分解为小分子有机物. CoFe/SBA-15循环使用10次仍能保持高催化活性和稳定性,在每次反应中RhB的降解率均大于84%, Co和Fe的浸出量均分别小于72.1和35μg/L. CoFe/SBA-15作为高效、环境友好的非均相催化剂可有效地活化PMS产生SO4?-降解水中RhB,具有实际应用的潜力.  相似文献   

9.
Pt催化剂是电催化领域用途最为广泛的贵金属催化剂.Pt资源稀缺,价格昂贵,同时它的物理化学特性又决定了其在多种催化反应中难以被替代.在质子交换膜燃料电池的小分子醇类电氧化过程中,难免存在Pt的毒化现象,其催化性能有待进一步提升.因此,围绕着Pt催化剂纳米结构的设计、抗毒性及反应机理的探索一直是电催化研究面临的重要课题.目前,已被广泛认可的提高Pt催化性能的方法之一是引入第二种金属,通过金属间协同效应(双功能机理)、张力效应或电子效应等对Pt的催化行为进行改性.对于由双/多金属组成的纳米结构催化剂,无论是协同效应还是电子效应,催化活性的提高都需要金属间有丰富的接触界面和恰当的邻近状态.通过调变两组元的种类、原子比和接触状态等可以实现对金属-金属界面的调控,进而调变催化剂性能.除金属助剂外,金属氧化物对Pt催化剂的助催化作用也引起广泛关注.由于金属氧化物与Pt之间的密切接触作用,氧化物的形貌特点对Pt的催化性能可产生重要影响.到目前为止,有关催化剂形貌效应的研究主要集中于贵金属纳米颗粒上(Pt,Au,Pd等),但关于金属氧化物载体/助剂的形貌对贵金属催化性能影响的研究尚不多.具有明确形貌的金属氧化物载体/助剂,暴露的晶面不同,表面原子的配位状态也不同,从而造成与之密切接触的Pt的性质发生改变.因此,金属氧化物的表面性质以及Pt-金属氧化物的界面性质将对电催化性能产生重要影响,深入阐释贵金属-金属氧化物的表/界面性质以及建立有效的构效关系,对设计和制备高效电催化剂具有一定的指导意义.为了提高Pt基催化剂活性、抗CO中毒能力以及稳定性,本文采用共沉淀法和水热法分别制备了纳米棒和六边形纳米片状的Fe2O3作为Pt催化剂的助剂,考察了助剂形貌对Pt催化剂在碱性介质中催化氧化甲醇的促进作用.通过X射线衍射、扫描电子显微镜、透射电子显微镜、X射线光电子能谱以及电化学技术对催化剂进行了表征.结果显示,Fe2O3的存在能显著提高Pt催化剂在碱性介质中对甲醇氧化的电催化性能,而且以Fe2O3纳米棒为助剂制备的Pt-Fe2O3/C-R催化剂催化活性以及稳定性比Fe2O3纳米片为助剂制备的Pt-Fe2O3/C-P催化剂更高.这种促进效应可能与助剂Fe2O3的形态有关.Pt-Fe2O3/C-R催化剂中Pt的质量比活性为5.32 A/mgPt,本征活性为162.7 A/m2Pt,分别是Pt-Fe2O3/C-P催化剂的1.67和2.04倍,是商业PtRu/C样品的4.19和6.16倍.协同效应和电子效应是Pt催化性能提升的主要原因.此外,Pt-Fe2O3/C-R样品中高价态Pt的含量较高,可能也是加速甲醇氧化反应动力学的原因之一.高价态的Pt可能会增强甲醇分子在Pt表面的吸附强度,促进Pt上甲醇氧化反应初始步.这些发现不仅可对甲醇电催化氧化机理有了更深的理解,而且对设计和制备高性能甲醇氧化电催化剂也具有一定的指导意义.  相似文献   

10.
A series of alumina supported cobalt oxide based catalysts doped with noble metals such as ruthenium and platinum were prepared by wet impregnation method.The variables studied were difference ratio and calcination temperatures.Pt/Co(10∶90)/Al2O3 catalyst calcined at 700 ℃ was found to be the best catalyst which able to convert 70.10% of CO2 into methane with 47% of CH4 formation at maximum temperature studied of 400 ℃.X-ray diffraction analysis showed that this catalyst possessed the active site Co3O4 in face-centered cubic and PtO2 in the orthorhombic phase with Al2O3 existed in the cubic phase.According to the FESEM micrographs,both fresh and spent Pt/Co(10∶90)/Al2O3 catalysts displayed small particle size with undefined shape.Nitrogen Adsorption analysis showed that 5.50% reduction of the total surface area for the spent Pt/Co(10∶90)/Al2O3 catalyst.Meanwhile,Energy Dispersive X-ray analysis(EDX) indicated that Co and Pt were reduced by 0.74% and 0.14% respectively on the spent Pt/Co(10∶90)/Al2O3catalyst.Characterization using FT-IR and TGA-DTA analysis revealed the existence of residual nitrate and hydroxyl compounds on the Pt/Co(10∶90)/Al2O3 catalyst.  相似文献   

11.
One-dimensional (1D) CoPt nanorods were synthesized by a galvanic displacement reaction. The morphology of the nanomaterials was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). Energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the coexistence of Co and Pt in the 1D nanorods. Studies of cyclic voltammetry (CV) demonstrated that the 1D CoPt nanorods exhibit a better electrocatalytic property for CO oxidation than that of bulk Pt electrode does. In situ electrochemical FTIRS illustrated, for the first time, that the 1D CoPt nanorods display abnormal infrared effects (AIREs), which was previously revealed mainly on 2D film nanomaterials.  相似文献   

12.
A series of FeCo-SiO(2) nanocomposite aerogels having different FeCo loadings of 3, 5, and 8 wt % were prepared using a novel urea-assisted sol-gel route. The size of the nanoparticles, which was estimated using Scherrer analysis of the main peak of the x-ray diffraction pattern, varies from 3 to 8 nm. X-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) techniques at both Fe and Co K edges were used to investigate the structure of the FeCo nanoparticles. EXAFS and XANES show that FeCo nanoparticles have the typical bcc structure. Evidence of oxidation was observed in low FeCo content aerogels. Spatially resolved electron energy loss spectroscopy analysis suggests the formation of a passivation layer of predominantly iron oxide.  相似文献   

13.
Research on Chemical Intermediates - Oxide Ni(80)Fe(20)/SiO2, Co(93)Fe(7)/SiO2, and Ni(19)Co(77)Fe(4)/SiO2 nanocomposites (NCs) were prepared using highly dispersed silica. It was modified by...  相似文献   

14.
The cation radical of lead(II)tetraphenylporphyrin was produced by γ-radiolysis and by photolysis of the 1,1,2,2-tetrachloroethane solutions at 77 K. The hfcc (0.0391 cm?1) due to 207Pb observed in the ESR spectrum indicates that the unpaired electron is predominantly located in the porphyrin ring.  相似文献   

15.
We study the local reactivity of molecular oxygen with bimetallic substrates of a platinum trimer island supported on nanotips of CoPt, Pt, Co, Ni, and Fe. Because of the reduced interatomic distances and varying interaction strengths with the substrates, the supported island interaction with oxygen can be tuned from stronger to weaker relative to the interaction of a freestanding island with oxygen despite that there is no well-behaved trend with the binding energy of the island to the substrates.  相似文献   

16.
A novel hyperbranched conjugated chemosensor with bipyridyl groups as periphery groups(BPY-HPV) was synthesized.BPY-HPV was highly sensitive to metal ions(Cu2+,Ni2+) for the strong coordination interaction(Ksv at the order of 107 mol-1 L) monitored by fluorescence spectroscopy.Moreover,by hydrogen bonds and charge transfer interaction,BPY-HPV shows strong interaction with 1,1,2,2-tetrachloroethane whatever in CH2Cl2(Ksv~106 mol-1 L) or film.  相似文献   

17.
A versatile route has been explored for the synthesis of nanorods of transition metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates using reverse micelles. Transmission electron microscopy shows that the as-prepared nanorods of nickel and copper oxalates have diameter of 250 nm and 130 nm while the length is of the order of 2.5 μm and 480 nm, respectively. The aspect ratio of the nanorods of copper oxalate could be modified by changing the solvent. The average dimensions of manganese, zinc and cobalt oxalate nanorods were 100 μm, 120 μm and 300 nm, respectively, in diameter and 2.5 μm, 600 nm and 6.5 μm, respectively, in length. The aspect ratio of the cobalt oxalate nanorods could be modified by controlling the temperature.The nanorods of metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates were found to be suitable precursors to obtain a variety of transition metal oxide nanoparticles. Our studies show that the grain size of CuO nanoparticles is highly dependent on the nature of non-polar solvent used to initially synthesize the oxalate rods. All the commonly known manganese oxides could be obtained as pure phases from the single manganese oxalate precursor by decomposing in different atmospheres (air, vacuum or nitrogen). The ZnO nanoparticles obtained from zinc oxalate rods are ~55 nm in diameter. Oxides with different morphology, Fe3O4 nanoparticles faceted (cuboidal) and Fe2O3 nanoparticles (spherical) could be obtained.  相似文献   

18.
Co(30)Fe(70) nanoparticles with mean particle size of about 8 nm were successfully synthesized by the chemical reduction of cobalt chloride and iron chloride with borohydride as a reducing agent in aqueous solution. The composition and size of the Co(30)Fe(70) nanoparticles were optimized by controlling the molar ratio of starting materials, reaction time, and dropping rate of aqueous reducing agent. As alloy powders prepared by chemical reduction tend to be amorphous in the as-synthesized state, the as-precipitated Co(30)Fe(70) nanoparticles were heat-treated to achieve crystallinity at the different temperatures for 1 h. The Co(30)Fe(70) nanocrystallite by chemical reduction shows excellent soft magnetic behavior, such as high permeability, negligible coercivity, and high saturation magnetization like that of Co(30)Fe(70) bulk.  相似文献   

19.
We have developed a highly stable and magnetically recyclable nanocatalyst system for alkene hydrogenation. The materials are composed of mesoporous silica spheres (MSS) embedded with FeCo/graphitic shell (FeCo/GC) magnetic nanoparticles and Pt nanocatalysts (Pt‐FeCo/GC@MSS). The Pt‐FeCo/GC@MSS have superparamagnetism at room temperature and show type IV isotherm typical for mesoporous silica, thereby ensuring a large enough inner space (surface area of 235.3 m2 g?1, pore volume of 0.165 cm3 g?1, and pore diameter of 2.8 nm) to undergo catalytic reactions. We have shown that the Pt‐FeCo/GC@MSS system readily converts cyclohexene into cyclohexane, which is the only product isolated and Pt‐FeCo/GC@MSS can be seperated very quickly by an external magnetic field after the catalytic reaction is finished. We have demonstrated that the recycled Pt‐FeCo/GC@MSS can be reused further for the same hydrogenation reaction at least four times without loss in the initial catalytic activity.  相似文献   

20.
Superior catalytic performance for selective 1,3-butadiene (1,3-BD) hydrogenation can usually be achieved with supported bimetallic catalysts. In this work, Pt−Co nanoparticles and Pt nanoparticles supported on metal–organic framework MIL-100(Fe) catalysts (MIL=Materials of Institut Lavoisier, PtCo/MIL-100(Fe) and Pt/MIL-100(Fe)) were synthesized via a simple impregnation reduction method, and their catalytic performance was investigated for the hydrogenation of 1,3-BD. Pt1Co1/MIL-100(Fe) presented better catalytic performance than Pt/MIL-100(Fe), with significantly enhanced total butene selectivity. Moreover, the secondary hydrogenation of butenes was effectively inhibited after doping with Co. The Pt1Co1/MIL-100(Fe) catalyst displayed good stability in the 1,3-BD hydrogenation reaction. No significant catalyst deactivation was observed during 9 h of hydrogenation, but its catalytic activity gradually reduces for the next 17 h. Carbon deposition on Pt1Co1/MIL-100(Fe) is the reason for its deactivation in 1,3-BD hydrogenation reaction. The spent Pt1Co1/MIL-100(Fe) catalyst could be regenerated at 200 °C, and regenerated catalysts displayed the similar 1,3-BD conversion and butene selectivity with fresh catalysts. Moreover, the rate-determining step of this reaction was hydrogen dissociation. The outstanding activity and total butene selectivity of the Pt1Co1/MIL-100(Fe) catalyst illustrate that Pt−Co bimetallic catalysts are an ideal alternative for replacing mono-noble-metal-based catalysts in selective 1,3-BD hydrogenation reactions.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号