First-principles study of electronic and magnetic properties of transition metal adsorbed h-BNC2 sheets

Adsorption of Fe, Co and Ni atoms on a hybrid hexagonal sheet of graphene and boron nitride is studied using density functional methods. Most favorable adsorption sites for these adatoms are identified for different widths of the graphene and boron nitride regions. Electronic structure and magnetic properties of the TM-adsorbed sheets are then studied in detail. The TM atoms change the electronic structure of the sheet significantly, and the resulting system can be a magnetic semiconductor, semi-metal, or a non-magnetic semiconductor depending on the TM chosen. This gives tunability of properties which can be useful in novel electronics applications. Finally, barriers for diffusion of the adatoms on the sheet are calculated, and their tendency to agglomerate on the sheet is estimated.     

A Graphene Composite Material with Single Cobalt Active Sites: A Highly Efficient Counter Electrode for Dye‐Sensitized Solar Cells

The design of catalysts that are both highly active and stable is always challenging. Herein, we report that the incorporation of single metal active sites attached to the nitrogen atoms in the basal plane of graphene leads to composite materials with superior activity and stability when used as counter electrodes in dye‐sensitized solar cells (DSSCs). A series of composite materials based on different metals (Mn, Fe, Co, Ni, and Cu) were synthesized and characterized. Electrochemical measurements revealed that CoN₄/GN is a highly active and stable counter electrode for the interconversion of the redox couple I^?/I₃^?. DFT calculations revealed that the superior properties of CoN₄/GN are due to the appropriate adsorption energy of iodine on the confined Co sites, leading to a good balance between adsorption and desorption processes. Its superior electrochemical performance was further confirmed by fabricating DSSCs with CoN₄ /GN electrodes, which displayed a better power conversion efficiency than the Pt counterpart.     

Influence of the colloidal environment on the magnetic behavior of cobalt nanoparticles

The magnetic properties of 10 nm diameter surfactant-coated cobalt (Co) nanoparticles in 1,2-dichlorobenzene (DCB) are investigated by a series of sequential magnetic moment (m) vs temperature (T) measurements. A rapid rise in magnetic moment around 250 K during warming and an abrupt drop at 234 K during cooling are observed when a nonsaturating external magnetic field is applied. Differential scanning calorimetry (DSC) measurements demonstrate that the rapid rise and abrupt drop in magnetization are associated with the melting and freezing of the solvent. Magnetic measurements of these Co nanoparticles in DCB are also used to probe their aging over a period of 70 days. The saturation magnetic moment of Co nanoparticles in DCB stored in air at room temperature decreases by nearly 40% over 70 days. Transmission electron microscopy (TEM) characterizations are reported to show the time evolution in the size, shape, and crystalline structures of DCB-immersed nanoparticles.     

“Metal‐Free” Catalytic Oxygen Reduction Reaction on Heteroatom‐Doped Graphene is Caused by Trace Metal Impurities

The oxygen reduction reaction (ORR) is of high industrial importance. There is a large body of literature showing that metal‐based catalytic nanoparticles (e.g. Co, Mn, Fe or hybrid Mn/Co‐based nanoparticles) supported on graphene act as efficient catalysts for the ORR. A significant research effort is also directed to the so‐called “metal‐free” oxygen reduction reaction on heteroatom‐doped graphene surfaces. While such studies of the ORR on nonmetallic heteroatom‐doped graphene are advertised as “metal‐free” there is typically no sufficient effort to characterize the doped materials to verify that they are indeed free of any trace metal. Here we argue that the claimed “metal‐free” electrocatalysis of the oxygen reduction reaction on heteroatom‐doped graphene is caused by metallic impurities present within the graphene materials.     

M(III)Dy(III)3 (M = Fe(III), Co(III)) complexes: three-blade propellers exhibiting slow relaxation of magnetization

[Dy(III)(HBpz(3))(2)](2+) moieties (HBpz(3)(-) = hydrotris(pyrazolyl)borate) and a 3d transition-metal ion (Fe(III) or Co(III)) have been rationally assembled using an dithiooxalato dianion ligand into 3d-4f [MDy(3)(HBpz(3))(6)(dto)(3)]·4CH(3)CN·2CH(2)Cl(2) (M = Fe (1), Co (2) complexes. Single-crystal X-ray studies reveal that three eight-coordinated Dy(III) centers in a square antiprismatic coordination environment are connecting to a central octahedral trivalent Fe or Co ion forming a propeller-type complex. The dynamics of the magnetization in the two isostructural compounds, modulated by the nature of the central M(III) metal ion, are remarkably different despite their analogous direct current (dc) magnetic properties. The slow relaxation of the magnetization observed for 2 mainly originates from isolated Dy ions, since a diamagnetic Co(III) metal ion links the magnetic Dy(III) ions. In the case of 1, the magnetic interaction between S = 1/2 Fe(III) ion and the three Dy(III) magnetic centers, although weak, generates a complex energy spectrum of magnetic states with low-lying excited states that induce a smaller energy gap than for 2 and thus a faster relaxation of the magnetization.     

缺陷石墨烯吸附Au、Ag、Cu的第一性原理计算

采用基于密度泛函理论的投影缀加波方法研究了Au、Ag、Cu吸附在缺陷石墨烯单侧和双侧的体系,对吸附体系的吸附能、磁性、电荷转移和电子结构进行了计算和分析.缺陷石墨烯吸附Au、Ag、Cu体系的吸附能比本征石墨烯增加2 eV以上,说明三种金属原子更容易吸附在缺陷位置;吸附体系的电荷密度差分和电子结构的结果表明,Au、Ag、Cu与缺陷石墨烯之间均为化学吸附.计算吸附体系的磁性发现,单侧吸附时三种吸附体系均有磁性,磁矩大约为1μB;双侧吸附时,三种吸附体系磁矩大约为2μB.     

Single‐Crystal‐like Nanoporous Spinel Oxides: A Strategy for Synthesis of Nanoporous Metal Oxides Utilizing Metal‐Cyanide Hybrid Coordination Polymers

Development of a new method to synthesize nanoporous metal oxides with highly crystallized frameworks is of great interest because of their wide use in practical applications. Here we demonstrate a thermal decomposition of metal‐cyanide hybrid coordination polymers (CPs) to prepare nanoporous metal oxides. During the thermal treatment, the organic units (carbon and nitrogen) are completely removed, and only metal contents are retained to prepare nanoporous metal oxides. The original nanocube shapes are well‐retained even after the thermal treatment. When both Fe and Co atoms are contained in the precursors, nanoporous Fe?Co oxide with a highly oriented crystalline framework is obtained. On the other hand, when nanoporous Co oxide and Fe oxide are obtained from Co‐ and Fe‐contacting precursors, their frameworks are amorphous and/or poorly crystallized. Single‐crystal‐like nanoporous Fe?Co oxide shows a stable magnetic property at room temperature compared to poly‐crystalline metal oxides. We further extend this concept to prepare nanoporous metal oxides with hollow interiors. Core‐shell heterostructures consisting of different metal‐cyanide hybrid CPs are prepared first. Then the cores are dissolved by chemical etching using a hydrochloric acid solution (i.e., the cores are used as sacrificial templates), leading to the formation of hollow interiors in the nanocubes. These hollow nanocubes are also successfully converted to nanoporous metal oxides with hollow interiors by thermal treatment. The present approach is entirely different from the surfactant‐templating approaches that traditionally have been utilized for the preparation of mesoporous metal oxides. We believe the present work proves a new way to synthesize nanoporous metal oxides with controlled crystalline frameworks and architectures.     

Metals on graphene: correlation between adatom adsorption behavior and growth morphology

We present a systematic study of metal adatom adsorption on graphene by ab initio calculations. The calculations cover alkali metals, sp-simple metals, 3d and group 10 transition metals, noble metals, as well as rare earth metals. The correlation between the adatom adsorption properties and the growth morphology of the metals on graphene is also investigated. We show that the growth morphology is related to the ratio of the metal adsorption energy to its bulk cohesive energy (E(a)/E(c)) and the diffusion barrier (ΔE) of the metal adatom on graphene. Charge transfer, electric dipole and magnetic moments, and graphene lattice distortion induced by metal adsorption would also affect the growth morphologies of the metal islands. We also show that most of the metal nanostructures on graphene would be thermally stable against coarsening.     

Facile Synthesis of High‐Quality Plasma‐Reduced Graphene Oxide with Ultrahigh 4,4′‐Dichlorobiphenyl Adsorption Capacity

High‐quality reduced graphene, termed PG, has been synthesized by a simple, low‐cost, and green plasma approach, and applied as adsorbent to remove 4,4′‐dichloribiphenyl (4,4′‐DCB) from aqueous solutions. As a comparison, the adsorption of 4,4′‐DCB on graphene oxide (GO) and multiwalled carbon nanotubes (MWCNTs) was also studied under the same experimental conditions. PG performs significantly better with regard to 4,4′‐DCB adsorption than GO and MWCNTs, or any reported nanomaterials, with a maximum adsorption capacity (q_max) of 1552 mg g^?1 at pH 7.0. The high affinity of 4,4′‐DCB to PG is mainly a result of strong π–π interactions, as also confirmed by DFT calculations. The results reveal that PG sheets hold promise for the removal of persistent organic pollutants. We expect possible applications of this fast and mild plasma technique in the fabrication of nanomaterials and envisage their use in a variety of advanced chemical processes.     

多巴胺用量对Fe3O4@PDA@PAMAM磁性纳米吸附材料的微观结构及吸附性能的影响

以自制的Fe3O4磁性纳米材料为核,多巴胺(DA)为表面修饰剂,成功地将2.0 G聚酰胺-胺(PAMAM)树状大分子接枝在Fe3O4磁核表面,制备出了一系列不同DA含量的Fe3O4@PDA@PAMAM磁性纳米吸附材料。采用X射线衍射仪(XRD)、红外光谱仪(IR)、振动样品磁强计(VSM)、透射电子显微镜(TEM)和电感耦合等离子体发射光谱仪(ICP-OES)等分析测试手段对材料组成、微观结构、磁性能和对重金属Cd(Ⅱ)离子的吸附性能进行了测试和表征。研究了修饰剂DA用量对Fe3O4@PDA@PAMAM磁性纳米吸附材料的相组成、微观结构、磁性能和吸附性能的影响。实验结果表明,Fe3O4@PDA@PAMAM磁性纳米吸附材料均呈典型的核-壳结构,材料晶型均呈现尖晶石结构,且壳层厚度随DA用量增加而增厚;材料的饱和磁化强度(Ms)均比Fe3O4的小,且随着DA用量的增加而降低,并且材料的矫顽力(Hc)和剩余磁化强度(Mr)均较低,其磁响应特性适合于做为可回收磁性纳米吸附材料。材料对Cd(Ⅱ)离子的平衡吸附容量随着DA用量的增加呈先增加后减小趋势。当Fe3O4和DA的质量比为8∶4时,吸附剂对Cd(Ⅱ)离子的吸附容量达到最大值165.13 mg·g^-1。     

PtFe掺杂石墨烯抗CO中毒性能的理论研究

基于密度泛函理论第一性原理研究了以单空位缺陷(SV)石墨烯为载体的Pt,Fe及PtFe二元金属催化剂的抗CO中毒能力.结果表明,对于单金属原子Pt和Fe,Fe更易吸附在SV石墨烯上;而对于PtFe二元金属催化剂,SV石墨烯对其固定能力明显好于Pt-SV,即Pt催化剂中掺杂Fe大大增加了SV石墨烯对金属催化剂的稳定性.Pt,Fe及PtFe二元金属催化剂抗CO中毒能力的研究结果表明,PtFe-6结构的抗CO中毒能力明显强于Pt-SV,接近于Fe-SV的抗CO中毒能力,在所有二元金属催化剂中PtFe-6的稳定性最好,明显优于Pt在SV石墨烯上的稳定性.通过在Pt中加入非贵金属Fe既可提高DMFC中阳极Pt催化剂的抗CO中毒能力,又可提高其催化活性.     

缺陷石墨烯吸附Au、Ag、Cu的第一性原理计算

采用基于密度泛函理论的投影缀加波方法研究了Au、Ag、Cu吸附在缺陷石墨烯单侧和双侧的体系,对吸附体系的吸附能、磁性、电荷转移和电子结构进行了计算和分析. 缺陷石墨烯吸附Au、Ag、Cu体系的吸附能比本征石墨烯增加2 eV以上,说明三种金属原子更容易吸附在缺陷位置;吸附体系的电荷密度差分和电子结构的结果表明,Au、Ag、Cu与缺陷石墨烯之间均为化学吸附. 计算吸附体系的磁性发现,单侧吸附时三种吸附体系均有磁性,磁矩大约为1μ_B;双侧吸附时,三种吸附体系磁矩大约为2μ_B.     

Fe元素及点缺陷对焦炭表面NH_3异相吸附的影响:密度泛函理论研究

采用密度泛函理论,并使用具有周期性边界条件的石墨烯模型近似模拟焦炭表面,研究了Fe原子修饰及点缺陷对NH_3在焦炭表面异相吸附的影响。计算结果表明,NH_3分子在点缺陷石墨烯表面的吸附属于物理吸附,结合能为-0.381 e V;NH_3分子吸附在Fe修饰的完整石墨烯表面属于化学吸附,吸附能为-1.442 eV; Fe原子修饰及点缺陷单独存在下NH_3的吸附能均大于NH_3在完整石墨烯表面的吸附(吸附能为-0.190 eV)。此外,Fe原子修饰与点缺陷共存对NH_3的吸附具有协同作用,结合能达到-3.538 eV,明显大于两者单独存在下NH_3的吸附能之和,综合分析Mulliken布居数与态密度,Fe原子与石墨烯表面、NH_3分子之间有更多地电荷转移,可以解释两者共存对NH_3吸附协同促进的原因。     

Spin-transport selectivity upon Co adsorption on antiferromagnetic graphene nanoribbons

We investigate from first principles the electronic and transport properties of zigzag graphene nanoribbons in the presence of Co adatoms. Comparing different adsorption sites across the width, we find that the Co-C coupling is rather sensitive to the local environment. While a net spin polarization appears in all cases, the spin filtering effect is significantly enhanced when the Co adatom is at the edge, where the adsorption energy is maximized and a partial suppression of edge-associated transport channels occurs. We also probe the magnetic interaction in the nonbonding regime, for Co-graphene nanoribbon (GNR) distances ranging from adsorption to π-π typical configurations. Our results indicate that Co-GNR coupling is still appreciable in an intermediate range, whereas it becomes vanishingly small in the limit of π-π distances.     

石墨烯衍生物负载的纳米催化剂用于氧还原反应

综述了用于燃料电池中氧还原反应(ORR)的石墨烯衍生物负载的各种纳米催化剂的最新进展。介绍了用于表征石墨烯基电催化剂的常规电化学技术以及石墨烯基电催化剂最新的研究进展。负载于还原氧化石墨烯(RGO)上的Pt催化剂的电化学活性和稳定性均得到显著提高。其它贵金属催化剂,如Pd, Au和Ag也表现出较高的催化活性。当以RGO或少层石墨烯为载体时, Pd催化剂的稳定性提高。讨论了氧化石墨烯负载Au或Ag催化剂的合成方法。另外,以N4螯合络合物形式存在的非贵过渡金属可降低氧的电化学性能。 Fe和Co是可替代的廉价ORR催化剂。在大多数情况下,这些催化剂稳定性和耐受性的问题均可得到解决,但其整体性能还很难超越Pt/C催化剂。     

三聚氰胺磁性印迹固相萃取材料的制备及其应用

采用磁性氧化石墨烯(GO)为载体,三聚氰胺(MEL)为模板分子,甲基丙烯酸(MAA)为功能单体,乙二醇二甲基丙烯酸酯(EGDMA)为交联剂,制备了新型三聚氰胺磁性印迹聚合物。 采用扫描电子显微镜(SEM)、透射电子显微（TEM）、差热分析(TG)和样品振动磁强计(VSM)对该磁性印迹聚合物进行表征和分析,结果表明,在氧化石墨烯表面成功制备磁性印迹聚合物。 结合高效液相色谱分析技术对该印迹聚合物的吸附性能进行检测,结果表明,该磁性印迹聚合物对三聚氰胺表现出特异性吸附性能,最大吸附容量为33.11 mg/g;相对于环丙氨嗪和三聚氰酸,三聚氰胺的选择因子(β)分别是2.43和2.84。 结合磁固相萃取与液相色谱检测技术,实现了牛奶样品溶液中三聚氰胺的分离、富集和检测。     

Facile synthesis of magnetic zinc metal‐organic framework for extraction of nitrogen‐containing heterocyclic fungicides from lettuce vegetable samples

We present a simple method for the fabrication of a magnetic amino‐functionalized zinc metal‐organic framework based on a magnetic graphene oxide composite. The resultant framework exhibited a porous 3D structure, high surface area and good adsorption properties for nitrogen‐containing heterocyclic fungicides. The adsorption process and capacity indicated that the primary adsorption mechanism might be hydrogen bonding and π‐π conjugation. In addition, an optimized protocol for magnetic solid phase extraction was developed (such as adsorbent content, pH, and desorption solvent), and utilized for the extraction of nitrogen‐containing heterocyclic fungicides from vegetable samples. Quantitation by high performance liquid chromatography coupled with tandem mass spectrometry offered a detection limit of 0.21–1.0 μg/L (S/N = 3) with correlation coefficients larger than 0.9975. These results demonstrate that magnetic amino‐functionalized zinc metal‐organic framewor is a promising adsorbent for the extraction and quantitation of nitrogen‐containing heterocyclic fungicides.     

氧化石墨烯表面新型磁性四溴双酚A印迹复合材料的制备及吸附性能

以二氧化硅包覆的磁性氧化石墨烯为载体, 利用热聚合方法制备了对四溴双酚A(TBBPA)有特异吸附效果的新型磁性印迹复合材料. 采用透射电子显微镜(TEM)、 扫描电子显微镜(SEM)、 傅里叶变换红外光谱(FTIR)、 热重分析(TGA)和样品振动磁强计(VSM)对该印迹复合材料进行了表征. 结果表明, 在氧化石墨烯表面制备了一层厚度为55~65 nm、 热稳定良好的磁性印迹层. 结合磁固相萃取技术(M-SPE)和高效液相色谱(HPLC)检测技术研究了该磁性印迹复合材料对四溴双酚A的吸附行为, 结果表明该印迹复合材料对四溴双酚A具有良好的选择吸附能力, 最大吸附量为16.33 mg/g. 结合HPLC检测技术, 该印迹复合材料可用于分离富集饮用水中的四溴双酚A.     

Chemical Bonding of Transition‐Metal Co13 Clusters with Graphene

We carried out density functional calculations to study the adsorption of Co₁₃ clusters on graphene. Several free isomers were deposited at different positions with respect to the hexagonal lattice nodes, allowing us to study even the hcp 2d isomer, which was recently obtained as the most stable one. Surprisingly, the Co₁₃ clusters attached to graphene prefer icosahedron‐like structures in which the low‐lying isomer is much distorted; in such structures, they are linked with more bonds than those reported in previous works. For any isomer, the most stable position binds to graphene by the Co atoms that can lose electrons. We find that the charge transfer between graphene and the clusters is small enough to conclude that the Co–graphene binding is not ionic‐like but chemical. Besides, the same order of stability among the different isomers on doped graphene is kept. These findings could also be of interest for magnetic clusters on graphenic nanostructures such as ribbons and nanotubes.     

铜族金属与完整及氮掺杂石墨烯的相互作用

基于广义梯度密度泛函理论和周期平板模型,研究了铜族金属单原子和双原子簇与完整及氮掺杂石墨烯的结合情况.结果表明,氮掺杂后石墨烯的电子结构特性由半金属性变为金属性;铜族金属在完整及石墨型氮掺杂石墨烯上的吸附较弱,结合能约为0.5eV,而在吡啶型氮掺杂和吡咯型氮掺杂石墨烯上有较强的化学吸附,结合能一般大于1eV;吡咯型氮掺杂后的构型不稳定,金属原子及簇与包含该结构的石墨烯衬底作用时会使其向吡啶型氮掺杂转变,并最终得到基于吡啶型氮掺杂的稳定吸附构型.Mulliken电荷布居分析显示,吸附在吡啶型氮掺杂石墨烯上的金属单原子与金属双原子簇带电性质相反.态密度及轨道分析表明,Cu与吡啶型氮掺杂石墨烯空位处留有悬挂键的三个原子成键,而Au与其中两个C原子成键.