钴纳米粒子催化水相费托合成

水相费托合成可以在远低于传统温度下实现,其低温高效的特点使其具有重要的应用潜力. 本文制备了水相稳定且可循环利用的Co纳米粒子并应用于水相费托反应,150℃下活性为7.4×10^-7mol_CO g_Co^-1 s^-1,C₅₊选择性接近40%,是目前纯钴水相费托合成的最好结果,而其它方法合成的催化剂在150℃时活性低下. 对催化剂进行了粒径、结构、成分测定和原位红外光谱检测,研究了催化剂在反应中的重构过程和B掺杂效应.     

Synthesis of silicon nanowires and nanoparticles by arc-discharge in water

Si nanowires of diameters 5-20 nm and nanoparticles of approximately 4 nm were synthesized by a simple arc-discharge method in water. The TEM analysis reveals that the growth direction of the observed Si nanowires is parallel to the {111} crystal planes.     

Formation of silver nanoparticles and nanocraters on silicon wafers

Silver nanocraters and monodisperse nanoparticles were formed on silicon wafers by spin-coating of an aqueous AgNO3/PVA solution and calcination of the resulting Ag+/PVA composite film. The monodisperse Ag nanoparicles were formed from small Ag+/PVA aggregates and were uniformly and stably distributed on the substrate surface. They were located as close as 2.8 nm apart (edge to edge) without coalescence. This nanoparticle stability was apparently derived from their interaction with the oxidized wafer surface. On the other hand, Ag metallic nanocraters with and without nanodots at their centers were produced from large Ag+/PVA aggregates. The explosive decomposition of AgNO3 and PVA by calcination could explain their formation. When Ag+ ions were reduced to Ag nanoparticles prior to calcination, larger Ag nanoparticles were produced probably due to aggregation of closely situated nanoparticles. Those nanoparticles that were located far enough stayed intact. Perspectives are discussed in terms of potential applications.     

Copper nanoparticles modified silicon nanowires with enhanced cross-coupling catalytic ability

Copper nanoparticles modified silicon nanowires show enhanced catalytic activity for the coupling reaction of benzene halides (iodobenzene, bromobenzene, and chlorobenzene) and aniline.     

Structural and photocatalytic properties of silicon carbide powder and nanowires modified by gold nanoparticles

Research on Chemical Intermediates - Commercial bulk powder of SiC and SHS-synthesized SiC nanowires were studied. Gold nanoparticles were deposited onto a surface of both samples. Basic...     

超细钴纳米粒子催化1-己烯低压氢甲酰化反应的原位红外光谱研究

利用原位透射红外光谱研究了2.8 nm超细钴纳米粒子在2~3 MPa合成气(CO:H₂ = 1:1)和100 ^oC条件下催化的1-己烯氢甲酰化反应. 结果表明, 在反应中出现与Co₂(CO)₈类似的红外吸收峰(2071, 2041和2022 cm^-1), 被证明是不同Co位点端式吸附CO. 首次观测到了位于2054 cm^-1处吸收峰处的物种, 可能归属为RCH₂CH₂COCo. 通过此中间物种,产物醛可以在钴催化剂表面经由结合一个氢原子脱除反应而获得.     

Organic cyclizations in microemulsions catalyzed by a cobalt corrin-polyion-scaffold on electrodes

Metallopolyion films of cobalt corrin vitamin B₁₂ hexacarboxylate and poly(l-lysine) [B₁₂(COOH)₆–PLL] covalently attached to carbon electrodes were used to cyclize n-bromoalkyl-2-cyclohexenones in microemulsions with good catalytic efficiency. Trans-1-decalone was obtained in up to 60% yields at reasonable current efficiency. Turnover rates were 30–85 fold greater for films compared to dissolved catalyst. There was no dependence of turnover rate on microemulsion composition, suggesting that cleavage of the alkyl-cobalt bond in the alkyl-Co^III intermediate is rate determining. 5-Endo-trig cyclization giving 4-hyndrindanone is disfavored by Baldwin's rules, but B₁₂(COOH)₆–PLL films in microemulsions still gave 24% yields at relatively high turnover numbers. It is possible that proton donors at film reaction sites protonate a carbanion intermediate to give competitive product 2-propyl-2-cyclohexen-1-one to decrease the yield of 4-hyndrindanone.     

Direct synthesis of aligned silicon carbide nanowires from the silicon substrates

Aligned silicon carbide nanowires were synthesized directly from the silicon substrates via a novel catalytic reaction with a methane-hydrogen mixture at 1,100 degrees C, with a mean diameter of 40 nm and length of 500 microm; they consist of a single-crystalline zinc blende structure crystal in the [111] growth direction; X-ray diffraction, Raman, and infrared spectroscopy confirm the synthesis of high-purity silicon carbide nanowires.     

氮掺杂碳包埋钴纳米粒子电催化合成过氧化氢

电催化还原氧是一种新兴的可持续生产过氧化氢(H2O2)的合成技术,寻找低成本、高活性和高选择性的电催化剂是该技术实际应用的关键.钴氮掺杂的碳材料因含有钴氮(Co-Nx)催化活性位,成为一类新兴的可促进H2O2电化学合成的材料.本文采用低能耗干式球磨外加控制热解的方法来制备包含许多Co-Nx结构的钴氮掺杂碳材料.该方法使用材料廉价,即将醋酸钴、2-甲基咪唑和Ketjenblack EC-600JD高纯度且导电的碳黑分别作为金属、氮和碳的前体.在酸性介质中的电化学测试结果表明,该材料的氧还原反应电流密度明显增加,同时起始电位向正方向移动.该催化剂在较大电位范围内对H2O2的选择性约为90％.H2O2整体电解实验表明,H2O2产率达到100mmol gcat?1 h?1,H2O2法拉第效率达到85％(0.3Vvs.RHE条件下2h).耐久性测试(在0.3Vvs.RHE条件下6h)表明,催化剂表现出相对稳定的性能,且在整个测试循环中,法拉第效率达到约85％,表明催化剂在实际应用中具有良好的耐久性.催化剂表现出较高的电催化合成H2O2活性和选择性可能是由于形成了Co-Nx活性位,以及酸性环境和应用电位等其它因素的影响.     

氮掺杂碳包埋钴纳米粒子电催化合成过氧化氢

电催化还原氧是一种新兴的可持续生产过氧化氢(H2O2)的合成技术,寻找低成本、高活性和高选择性的电催化剂是该技术实际应用的关键.钴氮掺杂的碳材料因含有钴氮(Co-Nx)催化活性位,成为一类新兴的可促进H2O2电化学合成的材料.本文采用低能耗干式球磨外加控制热解的方法来制备包含许多Co-Nx结构的钴氮掺杂碳材料.该方法使用材料廉价,即将醋酸钴、2-甲基咪唑和Ketjenblack EC-600JD高纯度且导电的碳黑分别作为金属、氮和碳的前体.在酸性介质中的电化学测试结果表明,该材料的氧还原反应电流密度明显增加,同时起始电位向正方向移动.该催化剂在较大电位范围内对H2O2的选择性约为90％.H2O2整体电解实验表明,H2O2产率达到100mmol gcat?1 h?1,H2O2法拉第效率达到85％(0.3Vvs.RHE条件下2h).耐久性测试(在0.3Vvs.RHE条件下6h)表明,催化剂表现出相对稳定的性能,且在整个测试循环中,法拉第效率达到约85％,表明催化剂在实际应用中具有良好的耐久性.催化剂表现出较高的电催化合成H2O2活性和选择性可能是由于形成了Co-Nx活性位,以及酸性环境和应用电位等其它因素的影响.     

Chemiluminescence from the decomposition of peroxymonocarbonate catalyzed by gold nanoparticles

In this work, an online preparation of peroxymonocarbonate was formed innovatively, which offered the reliable intermediate for further investigation. Gold colloids with nanoparticles of different sizes were found to enhance the chemiluminescence (CL) of the peroxymonocarbonate-eosin Y system, and the most intensive CL signals were obtained with 50 +/- 1 nm diameter gold nanoparticles. UV-visible adsorption spectra, fluorescence spectra, transmission electron microscopy images, electron paramagnetic resonance spin-trapping spectra, and mass spectra were obtained in order to study the CL enhancement mechanism. Peroxymonocarbonate, a reactive oxygen species, can be decomposed to singlet oxygen which transfers its energy to eosin Y. The CL can be induced by excited eosin Y. Gold nanoparticles facilitated the radical generation and singlet oxygen molecular formation on the surface of the gold nanoparticles. Thus, the CL emission enhanced greatly by adding gold nanoparticles into the system.     

Fine-tuning of catalytic tin nanoparticles by the reverse micelle method for direct deposition of silicon nanowires by a plasma-enhanced chemical vapour technique

The reverse micelle method was used for the reduction of a tin (Sn) salt solution to produce metallic Sn nanoparticles ranging from 85 nm to 140 nm in diameter. The reverse micellar system used in this process was hexane-butanol-cetyl trimethylammonium bromide (CTAB). The diameters of the Sn nanoparticles were proportional to the concentration of the aqueous Sn salt solution. Thus, the size of the Sn nanoparticles can easily be controlled, enabling a simple, reproducible mechanism for the growth of silicon nanowires (SiNWs) using plasma-enhanced chemical vapour deposition (PECVD). Both the Sn nanoparticles and silicon nanowires were characterised using field-emission scanning electron microscopy (FE-SEM). Further characterisations of the SiNW's were made using transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman spectroscopy. In addition, dynamic light scattering (DLS) was used to investigate particle size distributions. This procedure demonstrates an economical route for manufacturing reproducible silicon nanowires using fine-tuned Sn nanoparticles for possible solar cell applications.     

Proton-coupled electron-transfer reduction of dioxygen catalyzed by a saddle-distorted cobalt phthalocyanine

Proton-coupled electron-transfer reduction of dioxygen (O(2)) to afford hydrogen peroxide (H(2)O(2)) was investigated by using ferrocene derivatives as reductants and saddle-distorted (α-octaphenylphthalocyaninato)cobalt(II) (Co(II)(Ph(8)Pc)) as a catalyst under acidic conditions. The selective two-electron reduction of O(2) by dimethylferrocene (Me(2)Fc) and decamethylferrocene (Me(10)Fc) occurs to yield H(2)O(2) and the corresponding ferrocenium ions (Me(2)Fc(+) and Me(10)Fc(+), respectively). Mechanisms of the catalytic reduction of O(2) are discussed on the basis of detailed kinetics studies on the overall catalytic reactions as well as on each redox reaction in the catalytic cycle. The active species to react with O(2) in the catalytic reaction is switched from Co(II)(Ph(8)Pc) to protonated Co(I)(Ph(8)PcH), depending on the reducing ability of ferrocene derivatives employed. The protonation of Co(II)(Ph(8)Pc) inhibits the direct reduction of O(2); however, the proton-coupled electron transfer from Me(10)Fc to Co(II)(Ph(8)Pc) and the protonated [Co(II)(Ph(8)PcH)](+) occurs to produce Co(I)(Ph(8)PcH) and [Co(I)(Ph(8)PcH(2))](+), respectively, which react immediately with O(2). The rate-determining step is a proton-coupled electron-transfer reduction of O(2) by Co(II)(Ph(8)Pc) in the Co(II)(Ph(8)Pc)-catalyzed cycle with Me(2)Fc, whereas it is changed to the electron-transfer reduction of [Co(II)(Ph(8)PcH)](+) by Me(10)Fc in the Co(I)(Ph(8)PcH)-catalyzed cycle with Me(10)Fc. A single crystal of monoprotonated [Co(III)(Ph(8)Pc)](+), [Co(III)Cl(2)(Ph(8)PcH)], produced by the proton-coupled electron-transfer reduction of O(2) by Co(II)(Ph(8)Pc) with HCl, was obtained, and the crystal structure was determined in comparison with that of Co(II)(Ph(8)Pc).     

Dose determination of nickel implantations in silicon wafers

Summary The dose of nickel ions implanted with an energy of 300 keV or 6 MeV, respectively, into silicon wafers was measured by X-ray fluorescence analysis (XRFA) after the implantation process. Dose values for Ni were determined within the range from 5×10¹⁵ to 1×10¹⁸ ions/cm². The detection limit of this simple and non-destructive procedure amounts to about 10¹⁴ atoms/cm². The accuracy was confirmed by flame atomic absorption spectrometry (FAAS), total-reflection X-ray fluorescence analysis (TXRFA), and by Rutherford-backscattering spectroscopy (RBS). The study confirms XRFA to be a suitable method for dose determinations after the implantation process.     

DNA damage by sulfite autoxidation catalyzed by cobalt complexes

DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(II) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(II) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1-80 microM) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1-2.0 mM) after incubation for 4 h. In the presence of GGH, Co(II) and dissolved O2, DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(IV), due to the oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by the complex. SO3 -, HO and H radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(II) binds O2 in the presence of GGH, and leads to the formation of a DMPO-HO adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex.     

Wet-chemical templateless assembly of metal nanowires from nanoparticles

We describe a new, simple, room-temperature wet-chemical approach for assembling Au and Ag nanoparticles into nanowire networks, without the use of lithographic templates. Five to 35 nm-diameter nanowires passivated with a thin organic layer were synthesized by mechanically agitating a biphasic liquid mixture of an aqueous hydrosol containing the nanoparticles, and toluene. Nanowire structure and surface chemistry are discussed based on electron microscopy, UV-visible spectroscopy and thermogravimetric analyses.     

Pt3Te4 nanoparticles from tellurium nanowires

We report the synthesis of platinum telluride nanoparticles (Pt(3)Te(4) NPs) in the solution phase at room temperature using a template-assisted method. The dendrimeric aggregates formed are composed of several small units of Pt(3)Te(4) NPs of ～4 nm diameter. Tellurium nanowires (Te NWs) are used as the template and the reducing agent in the growth of NPs which occurs due to the galvanic replacement reaction between Te NWs and PtCl(6)(2-). Surface-enhanced Raman scattering (SERS) of the dispersed Pt(3)Te(4) NPs was studied using crystal violet (CV) as the analyte. SERS sensitivity up to 10(-8) M of CV was observed. The Raman enhancement factor (EF) of adsorbed CV on NP aggregates was calculated to be 1.74 × 10(5). The catalytic ability of the as-synthesized Pt(3)Te(4) NPs for the reduction of 4-nitrophenol (4-NP) was studied.     

Carbonylation of chlorobiphenyls catalyzed by modified cobalt carbonyl

Dichlorobiphenyls having both chlorine atoms in the same benzene ring undergo mild carbonylation in the presence of 1,2-epoxypropane-modified carbonyl cobalt complex to give biphenylcarboxylic acid esters. Monochlorobiphenyls fail to react under analogous conditions. The rate and selectivity of the reaction depend on the position of chlorine atoms. Carbonylation of dichlorobiphenyls having a chlorine atom in the meta position occurs preferentially at that position. 2,4-Dichlorobiphenyl gives rise mainly to the carbonylation product at the 2-position.