Release of N(2) from the carbon nanotubes via high-temperature annealing

Nitrogen (N)-doped carbon nanotubes (CNTs) were heated to 1000 degrees C under an ultrahigh vacuum. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) reveal three different N structures; graphitelike, pyridine-like, and molecular N(2). The vibrationally resolved XANES peaks of N(2) were first observed, suggesting the existence of molecular N(2) as intercalated and trapped forms. The annealing process can decrease the average N content from 6.3 at. % to 3.3 at. %, mainly by releasing molecular N(2). Electron energy-loss spectroscopy (EELS) confirms that the annealing releases molecular N(2) from the CNTs.     

Weak epitaxy growth and phase behavior of planar phthalocyanines on p-sexiphenyl monolayer film

We systematically investigated the weak epitaxy growth (WEG) behavior of a series of planar phthalocyanine compounds (MPc), i.e., metal-free phthalocyanine (H2Pc), nickel phthalocyanine (NiPc), copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc), iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc), grown on a p-sexiphenyl ( p-6P) monolayer film by selected area electron diffraction (SAED) and atomic force microscopy (AFM). Two types of epitaxial relations, named as incommensurate epitaxy and commensurate epitaxy, were identified between phthalocyanine compounds and the substrate of the p-6P film. The tiny variation of the lattice constant of phthalocyanine compounds can result in different crystal orientations. The change rule of incommensurate and commensurate epitaxy was extracted. The tendency of commensurate epitaxy becomes weaker as the lattice constant b increases, while it gets stronger as the substrate temperature is elevated. Large size and continuous H2Pc films can be obtained by controlling the growth conditions. The WEG method is generally applicable in the whole family of planar phthalocyanine compounds and may be used to fabricate other high-quality organic films.     

Metal—ligand and π singlet—triplet transitions in phthalocyanine films studied by inelastic electron tunneling spectroscopy

Inelastic electron tunneling spectroscopy (IETS) on AlAl₂O₃/PcPb tunneling junctions at 4.2 K has been used to study electronic transitions involving π, π^≠ and metal-ligand orbitals of phthalocyanine (Pc) films (H₂Pc, FePc, CoPc, NiPc, CuPc, ZnPc). The results are compared with calculations for Pc molecules.     

Electrocatalytic activity of carbon-supported metallophthalocyanine catalysts toward oxygen reduction reaction in alkaline solution

Carbon-supported metallophthalocyanine catalysts, composed of a transition central metal M (M = Co, Mn, Ni, Fe) in the phthalocyanine ring, were synthesized in this work. As cathodic reaction in a fuel cell, the oxygen reduction reaction (ORR) was investigated in alkaline medium with linear scanning voltammetry at the surface of these electrocatalysts deposited onto a rotating disk electrode (RDE). It was found that the number of electrons transferred depended on the nature of the metallic cation in the catalyst. Evidences provided with Koutecky-Levich approach showed that iron phthalocyanine (FePc) exhibited the better electrocatalytic ability toward the ORR with four electrons exchanged and low activation overpotential. Among these different as-prepared materials, MnPc and FePc led to a four-electron pathway, while CoPc and NiPc proceeded by a two-electron route. The latter reaction process was also determined with a rotating ring-disk electrode (RRDE), which allowed the determination of hydrogen peroxide formed as O₂ reduction intermediate in a small amount, i.e., less than 1.2 %.     

Electronic structure and field emission of multiwalled carbon nanotubes depending on growth temperature

The electronic structure of multiwalled carbon nanotubes (CNTs) has been investigated, depending on the growth temperature, using synchrotron X-ray photoelectron spectroscopy (XPS) and field emission measurements. The vertically aligned CNTs are grown via pyrolysis of ferrocene and acetylene in a broad temperature range 600-1000 degrees C. The CNTs have a cylindrical structure with a uniform diameter of 20 nm. As growth temperature increases, due to an improved crystallinity of the graphitic sheets, the width of the XPS C 1s peak becomes narrower and the intensity of the valence band increases. Field emission from the as-grown CNTs exhibits a large enhancement of current density with growth temperature, strongly correlated with the electronic structure revealed by XPS.     

酞菁裂解法多壁碳纳米管的制备、表征和应用

In order to investigate the catalytic activity of high temperature treated CoPc toward oxygen reduction, and find the active site of the catalyst, using cobalt (Ⅱ) phthalocyanine (CoPc) as raw material, through thermal chemical vapor deposition method at 850℃ under a current of Ar/H2, two layer well-aligned multiwalled carbon nanotubes (CNTs) were made. The diameters of the well-aligned carbon nanotubes were distributed in the range of 60～120 nm and the length was about 40 μm. The Co particle with 10 nm in diameter was encapsulated in the CNTs compartment. The products were observed by field emission scanning electron microscope (SEM), and transmission electron microscope (TEM). The well-aligned carbon nanotubes were characteriszed by Raman scattering spectrum and X-ray diffraction (XRD). The cyclic voltammetric measurement demonstrates that the CNTs have some effect to prevent the metal nanoparticle encapsulated from eroding rapidly. It is assumed that the small amount of the N element in the CNTs is very necessary for the bamboo-like morphology and the protected action for metal particles against dissolution in the acid medium. The radian of the winding wall should be affected by the amount of the N and the interaction between the N in the carbon network and the metal cluster. In addition, the CNTs greater electrochemically active surface area is a great advantage for any electrocatalytic application.     

Nitrogen-doped multiwalled carbon nanotubes and their electrocatalysis towards oxidation of NO

Nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) were synthesized by thermal decomposition of pyridine and iron phthalocyanine over an iron catalyst in an atmosphere of ammonia. The N-MWCNTs thus obtained were analyzed by X-ray photoelectron spectroscopy. They were found to contain three types of nitrogen (N) atoms, namely pyridine-like, graphite-like, and molecular N. The effect of the pyridine-like N and the graphite-like N was investigated. The pyridine-like N is absorbing nitric oxide (NO) more easily than the graphite-like N. The N-MWCNTs with higher N content (especially the pyridine-like N) have higher catalytic activity (in terms of electrooxidation of NO) than those containing less N. The N-MWCNTs with high levels of pyridine N were incorporated into an electrode which suitable for sensing NO and for removal of NO due to its excellent electrocatalytic activity.     

FePc结构对Pd(OAc)2/HQ/FePc催化环己烯氧化活性的影响

在乙腈酸性水溶液中,不同来源酞菁铁(FePc)和Pd(OAc)2/HQ（氢醌）组成的催化体系在环己烯氧化反应中有明显不同的催化活性.通过IR、Mssbauer、XPS、XRD、SEM、BET等技术对酞菁铁的分析表明,由酞菁铁组成的多组份催化体系的催化活性与酞菁铁中的飒 氧酞菁铁含量、酞菁铁结晶度和表面形态有关.     

FePc结构对Pd(OAc)_2/HQ/FePc催化环己烯氧化活性的影响

在乙腈酸性水溶液中 ,不同来源酞菁铁 (FePc)和 Pd(OAc)2/HQ(氢醌)组成的催化体系在环己烯氧化反应中有明显不同的催化活性 .通过 IR、 M ssbauer、 XPS、 XRD、 SEM、 BET等技术对酞菁铁的分析表明 ,由酞菁铁组成的多组份催化体系的催化活性与酞菁铁中的μ 氧酞菁铁含量、酞菁铁结晶度和表面形态有关 .     

X-ray photoelectron spectroscopy and first principles calculation of BCN nanotubes

Multiwalled boron carbonitride (BCN) nanotubes with two different structures were synthesized via thermal chemical vapor deposition; one has 10% C atoms homogeneously doped into BN nanotubes (B0.45C0.1N0.45 NTs), and the other has BN layers sheathed with 5-nm-thick C outerlayers (BN-C NTs). The electronic structures of the B, C, and N atoms were thoroughly probed by synchrotron X-ray photoelectron spectroscopy and the X-ray absorption near-edge structure method. The B0.45C0.1N0.45 NTs contain a significant amount of B-C and C-N bonding with a pyridine-like structure (hole structure), which reduces the pi bonding states of the B and N atoms. From the XPS valence band spectrum, the band gap was estimated to be about 2.8 eV. In the BN-C NTs, the C and BN domains are separated without forming the pyridine-like structure. Using the first principles method, we investigated the relative stabilities and electronic structures of the various isomers of the double-walled (12,0)@(20,0) BCN NTs. The C-outerlayer BN nanotube structure is the most stable isomer, when there exist no defects in the tubes with B/N = 1.0 (i.e., graphite-like structure). In addition, a reasonable model, which is characterized by the motives consisted of three pyridine-like rings around a hollow site, is presented for the local structure of C atoms in the B0.45N0.45C0.1 NTs. A considerable decrease of the band gap due to the 10% C doping was predicted, which was consistent with the experimental results.     

Correlation between molecular orbitals and doping dependence of the electrical conductivity in electron-doped metal-phthalocyanine compounds

We have performed a comparative study of the electronic properties of six different electron-doped metal-phthalocyanine (MPc) compounds (ZnPc, CuPc, NiPc, CoPc, FePc, and MnPc), in which the electron density is controlled by means of potassium intercalation. Despite the complexity of these systems, we find that the nature of the underlying molecular orbitals produces observable effects in the doping dependence of the electrical conductivity of the materials. For all the MPc's in which the added electrons are expected to occupy orbitals centered on the ligands (ZnPc, CuPc, and NiPc), the doping dependence of the conductivity has an essentially identical shape. This shape is different from that observed in MPc materials in which electrons are also added to orbitals centered on the metal atom (CoPc, FePc, and MnPc). The observed relation between the macroscopic electronic properties of the MPc compounds and the properties of the molecular orbitals of the constituent molecules clearly indicates the richness of the alkali-doped metal-phthalocyanines as a model class of compounds for the investigation of the electronic properties of molecular systems.     

Magnetism of phthalocyanine-based organometallic single porous sheet

A two-dimensional (2D) periodic Fe phthalocyanine (FePc) single-layer sheet has very recently been synthesized experimentally (Abel, M.; et al. J. Am. Chem. Soc.2011, 133, 1203), providing a novel pathway for achieving 2D atomic sheets with regularly and separately distributed transition-metal atoms for unprecedented applications. Here we present first-principles calculations based on density functional theory to investigate systematically the electronic and magnetic properties of such novel organometallics (labeled as TMPc, TM = Cr-Zn) as free-standing sheets. Among them, we found that only the 2D MnPc framework is ferromagnetic, while 2D CrPc, FePc, CoPc, and CuPc are antiferromagnetic and 2D NiPc and ZnPc are nonmagnetic. The difference in magnetic couplings for the studied systems is related to the different orbital interactions. Only MnPc displays metallic d(xz) and d(yz) orbitals that can hybridize with p electrons of Pc, which mediates the long-range ferromagnetic coupling. Monte Carlo simulations based on the Ising model suggest that the Curie temperature (T(C)) of the 2D MnPc framework is ～150 K, which is comparable to the highest T(C) achieved experimentally, that of Mn-doped GaAs. The present study provides theoretical insight leading to a better understanding of novel phthalocyanine-based 2D structures beyond graphene and BN sheets.     

Oxidation, deformation, and destruction of carbon nanotubes in aqueous ceric sulfate

A simple wet chemical method involving only ultrasonic processing in dilute ceric sulfate (CS) was used to functionalize carbon nanotubes (CNTs). Unexpectedly, single-walled and multiwalled carbon nanotubes (SWCNTs and MWCNTs) were cut, oxidized, and disintegrated by sonication in 0.1 N CS for 2-5 h. Transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), Raman scattering, and photoacoustic Fourier transform infrared spectroscopy (FTIR) were used to probe wall damage during the chemical processing. Cyclic voltammetry and impedance spectroscopy were used to evaluate the conductivity of the CS-treated CNTs. This one-step process resulted in the destruction of SWCNTs to produce nonconducting amorphous carbon. MWCNTs were oxidized and converted to graphitic materials and amorphous carbon with retained conductivity.     

Assembly of metal nanoparticle-carbon nanotube composite materials at the liquid/liquid interface

Carbon nanotubes (CNTs)-mediated self-assembly of metal (Au and Ag) nanoparticles at the liquid/liquid interface in the form of a stable nanocomposite film is reported. The metallic luster results from the electronic coupling of nanoparticles, suggesting the formation of closely packed nanoparticle thin films. The interfacial film could be transferred to mica substrates and carbon-coated transmission electron microscopy (TEM) grids. The transferred films were very stable for a prolonged time. The samples were characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), TEM, and X-ray photoelectron spectroscopy (XPS). SEM and TEM results show that the films formed at the liquid/liquid interface are indeed composite materials consisting of CNTs and nanoparticles. XPS measurements further indicate the presence of the interaction between nanoparticles and CNTs.     

Preparation and Characterization of Electrodes Modified with Pyrrole Surfactant,Multiwalled Carbon Nanotubes and Metallophthalocyanines for the Electrochemical Detection of Thiols

Our aim was to prepare hybrid electrodes active towards the electrooxidation of thiols by the co‐immobilization of native carbon nanotubes (CNTs) and cobalt phthalocyanine (CoPc) from aqueous solutions. This strategy was adopted to avoid the oxidation of CNTs that can induce a modification of their exceptional properties. To do so, a hydrosoluble pyrrole surfactant was used to get homogeneous aqueous dispersions of CNTs and CoPc and to trap both materials on the electrode via the electropolymerization of the pyrrole surfactant. The hybrid electrodes exhibit a good electrocatalytic activity towards the oxidation of L ‐cysteine and glutathione. Their performances in terms of limit of detection (0.01 mM) are compatible with the detection of these thiols in biological samples.     

氮掺杂碳纳米管的制备及其电化学性能

采用弱反应性含氮有机物水合肼、二乙烯三胺对碳纳米管进行氮掺杂处理. 结合X射线光电子谱(XPS)分析和扫描电镜(SEM)观察, 发现两种含氮有机物处理均可使碳纳米管表面成功连接上含氮基团, 并保持了碳纳米管的本征形貌和结构. 水合肼处理的碳纳米管的氮含量(碳/氮原子比为95/2)明显高于二乙烯三胺处理的碳纳米管(碳/氮原子比为96/0.5). 氮掺杂后碳纳米管在水溶液中分散性明显改善, 且分散性随着氮含量增加进一步增强, 因此水合肼处理的碳纳米管分散性明显优于二乙烯三胺处理的碳纳米管. 作为电化学电容器电极材料, 碳纳米管含氮官能团贡献了赝电容, 但其循环性仍需进一步改进. 氮掺杂碳纳米管较好的亲水性, 改善了电解液的浸润, 循环后氮掺杂碳纳米管电极的比容量仍略高于纯碳纳米管电极的比容量.     

Facile preparation of tetrafluoro-substituted cobalt phthalocyanine nanorods attached on carbon nanotubes for efficient electrocatalytic CO2 reduction

Journal of Solid State Electrochemistry - A tetrafluoro substituted CoPc (CoF4Pc), which is well dispersed in N,N-dimethylformamide (DMF), was used to modify carbon nanotubes (CNTs) via a facile...     

Comparative study of metal-porphyrins, -porphyrazines,and -phthalocyanines

A theoretical comparative study of complexes of porphyrin (P), porphyrazine (Pz), and phthalocyanine (Pc) with metal (M) = Fe, Co, Ni, Cu, and Zn has been carried out using a DFT method. The calculations provide a clear elucidation of the ground states for the MP/Pz/Pc molecules and for a series of [MP/Pz/Pc](x-) and [MP/Pz/Pc](y+) ions (x = 1, 2, 3, 4; y = 1, 2). There are significant differences among MP, MPz, and MPc in the electronic structure and other calculated properties. For FeP/Pz and CoP/Pz, the first oxidation occurs at the central metal, while it is the macroring of FePc and CoPc that is the site of oxidation. The smaller coordination cavity results in a stronger ligand field in Pz than in P. However, the benzo annulation produces a surprisingly strong destabilizing effect on the metal-macrocycle bonding. The effects of Cl axial bonding upon the electronic structures of the iron(III) complexes of P, Pz, and Pc were examined, as was the bonding of pyridine (py) to NiP, NiPz, and NiPc. The porphinato core size plays a crucial role in controlling the spin state of Fe(III) in these complexes. FePc(Cl) is predicted to be a pure intermediate-spin system, whereas NiPz(py)(2) and NiPc(py)(2) are metastable in high-spin (S = 1) states. The NiPz/Pc-(py)(2) binding energy curve has only a shallow well that facilitates decomposition of the complex. The NiP-(py)(2) bond energy is small, but the relatively deep well in the binding energy curve ought to make this system stable to decomposition.     

金属酞菁类大环化合物对氧气还原反应催化行为的阻抗谱研究

通过电化学交流阻抗法研究了3种金属酞菁类大环化合物(FePc, CoPc, FeCoPc2)在碱性溶液中对氧气还原反应(ORR)的电化学催化行为, 各电极的交流阻抗 Nyquist 图谱在高频区和低频区均呈现出2个较明显的半圆和半圆之间(中频区)的压扁的弧形, 采用Zsimpwin阻抗谱分析软件对-02 V(vs. Hg/HgO)电位下的各交流阻抗谱进行等效电路拟合, 提出空气电极ORR反应的等效电路, 并对等效电路中各动力学参数进行了解释, 通过分析得出金属酞菁在碱性溶液中对ORR催化反应是一个伴随中间产物HO-2的2电子转移过程. 同时, 等效电路的拟合结果表明, FeCoPc2/C作为ORR催化剂对减小Rc+Rct效果比FePc/C和CoPc/C明显, 具有更高的催化活性.     

Electrode Modification through Click Chemistry Using Ni and Co Alkyne Phthalocyanines for Electrocatalytic Detection of Hydrazine

This work reports on the development of sensors for the detection of hydrazine using glassy carbon electrodes (GCE) modified with phthalocyanines through click chemistry. Tetrakis(5‐hexyn‐oxy) cobalt(II) phthalocyanine (complex 2 ) and tetrakis(5‐hexyn‐oxy) nickel(II) phthalocyanine (complex 3 ) were employed as electrode modifiers for hydrazine detection. The GCE was first grafted via the in situ diazotization of a diazonium salt, rendering the GCE surface layered with azide groups. From this point, the 1, 3‐dipolar cycloaddition reaction, catalysed by a copper catalyst was utilised to “click” the phthalocyanines to the surface of the grafted GCE. The modified electrodes were characterized by scanning electrochemical microscopy, X‐ray photoelectron spectroscopy and cyclic voltammetry. The electrografted CoP 2 ‐clicked‐GCE and NiP 3 ‐clicked‐GCE exhibited electrocatalytic activity towards the detection of hydrazine. The limit of detection (LoD) for the CoPc‐GCE was 6.09 μM, while the NiPc‐GCE had a LoD of 8.69 μM. The sensitivity was 51.32 μA mM⁻¹ for the CoPc‐GCE and 111.2 μA mM⁻¹ for the NiPc‐GCE.