A comparative first-principles study of orbital hybridization in two-dimensional C, Si, and Ge

Information on orbital hybridization is very important to understand the structural, physical, and chemical properties of a material. Results of a comparative first-principles study on the behaviours of orbital hybridization in the two-dimensional single-element phases by carbon, silicon, and germanium are presented. From the well-known three-dimensional hexagonal lonsdaleite structure, in which the atoms are in ideal sp(3)-bonding, the layer spacing along c-axis is gradually stretched to simulate the evolutions of structural and electronic properties from three-dimensional to two-dimensional lattice configurations in the three materials. A turning point of the total system energy due to the sp(3) to sp(2) transition is observed during this process in carbon. In contrast, no such phenomenon is found in silicon and germanium. The differences in electronic structure and bonding behaviour are further examined through comparative investigation of atomic angular-momentum projected density of states and electronic energy band spectrums of these materials. We demonstrate that the valence electronic orbital in the two-dimensional hexagonal crystals of Si and Ge shows sp(3)-like behaviour for the partial hybridization of s and p(z), which leads to their different lattice configurations to graphene. The role of π-bonds in stabilizing the flat configuration of graphene is also discussed.     

Modeling of nontraditional structures of carbon

The present contribution deals with one of the possible structure types of nongraphitic carbon adsorbents. The proposed structure consists of infinite strips of condensed aromatic rings arranged into a hexagonal honeycomb-like structure with the edge formed only by sp2 carbon atoms. Quantum chemical calculations were performed at the UHF/STO-3G level using the CRYSTAL95 program package for periodical approach. The extremely high adsorption ability of some low-density paramagnetic carbon forms can be elucidated by the presence of the sp2 honeycomb carbon structure and the specific properties of its electronic structure.     

A Triazine-Based Analogue of Graphyne: Scalable Synthesis and Applications in Photocatalytic Dye Degradation and Bacterial Inactivation

Graphyne, a theorized carbon allotrope possessing only sp- and sp²-hybridized carbon atoms, holds great potentials in many fields, especially in catalysis and energy-transfer/storage devices. Using a bottom-up strategy, we synthesized a new N-doped graphyne analogue, triazine- and 1,4-diethynylbenzene-based graphyne TA-BGY , in solution in gram-scale. The unique sp/sp² carbon-conjugated TA-BGY possesses an extended porous network structure with a BET surface area of approximately 300 m² g⁻¹. Owing to its low optical band gap (1.44 eV), TA-BGY was expected to have many applications, which were exemplified by the photodegradation of methyl orange and photocatalytic bacterial inactivation.     

Supramolecular graphyne: a C(sp)-H...N hydrogen-bonded unique network structure of 2,4,6-triethynyl-1,3,5-triazine

The crystallization of 2,4,6-triethynyl-1,3,5-triazine (2) leads to a pi-stacked layered structure of a C(sp)-H...N hydrogen-bonded unique hexagonal network structure, which may be regarded as a supramolecular analogue of a hitherto unknown graphyne network: in-plane intermolecular interactions are short and linear H...N contacts (2.31 and 2.34 A) and the interlayer separation is 3.23 A.     

A first principle study of pristine and BN-doped graphyne family

Based on first principle calculation using generalized gradient approximation, we report electronic properties of graphyne and its related structures (graphdiyne, graphyne-3, graphyne-4). Boron and nitrogen atoms are systematically substituted into the position of carbon atom and the corresponding changes of the properties are reported. All the structures are found to be direct band gap semiconductors with band gap depending on the concentration and position of the doping material. Our band structure calculation clearly shows that the band gap can be tuned by B–N doping and the spin-polarized calculation depicts the nonmagnetic nature of these structures. The possibility of modulating the band gap provides flexibility for its use in nanoelectronic devices. Projected density of state (PDOS) analysis shed insights on the bonding nature of these novel materials, whereas from the view point of Crystal Orbital Hamilton Population (–COHP) analysis, the nature of chemical bonding between neighbouring atoms and the orbital participating in bonding and antibonding have been explored in details.     

Preparation and structure of a solid-state hypervalent-iodine polymer containing iodine and oxygen atoms in fused 12-atom hexagonal rings

The treatment of dilute aqueous solutions of [hydroxy(tosyloxy)iodo]benzene with aqueous Mg(ClO4)2 produced thin elongated-hexagonal plates exhibiting a supramolecular structure in which tetra-mu-oxopentaiodanyl dication repeat units are joined to each other by significantly ionic bonds and each unit is associated with two perchlorate ions. The linearly extended cationic structure is formed from the 12-atom hexagonal rings of alternating iodine and oxygen atoms, a novel structure. Each 12-membered ring forms a nearly planar hexagonal shape with sides defined by almost linear O-I-O segments (175.7+/-1.6) degrees. The apexes are occupied by bridging oxide ligands where the I-O-I angles deviate only slightly from an ideal 120 degrees hexagonal angle (116.8+/-1.2) degrees, consistent with sp2 hybridization of the bridging oxygen atoms that participate in three-center four-electron bonds with iodine. These 12-atom hexagons are slightly "chair" distorted at the oxygen atoms. The planes of the rings are separated by layers containing the phenyl rings. The perchlorate ions reside in void spaces created by the three-up, three-down arrangement of the phenyl rings around each 12-membered I-O ring and are positioned directly above and below the I-O rings.     

Influence of the composition of BCN films deposited by reactive magnetron sputtering on their properties

Compounds of the B--C--N system are very promising to produce superhard coatings with good tribological, chemical, and thermal properties. To investigate the influence of the composition of BCN films on their properties, films with five different compositions at nearly constant nitrogen content were deposited on silicon wafers by magnetron sputtering from hexagonal boron nitride and graphite targets operated in RF and DC mode, respectively. The compositions and binding states of the films were determined by XPS. The nitrogen content was found to be almost constant for all films at about a 40 at-%, whereas boron and carbon compositions ranged between 15-35 and 25-50 at-%, respectively. The electronic and bonding structure of the coatings were analyzed by REELS using three different electron beam energies to obtain information at different depths. An increase of the carbon content of the films resulted in a significant shift of the pi-pi* interband transition with respect to the energy loss corresponding to h-BN. The absence of the pi-pi* transition in the energy loss spectra acquired at a beam energy of 1900 eV indicates the existence of a very thin overlayer mostly sp(2) bonded and probably with a distorted hexagonal structure. The position of the bulk plasmon losses corresponded to the hexagonal phase for the overlayer and presented a shift of more than 1.5 eV to the higher energy loss direction for the spectra obtained at 1900 eV beam energy. This shift and the absence of the sp(2)-bond fingerprint induced the possibility of an underlying disordered structure with a majority of sp(3) bonds.     

Adsorption of polycyclic aromatic hydrocarbons onto graphyne: Comparisons with graphene

Density functional theory calculations were implemented to expand the knowledge about graphyne and its interaction with polycyclic aromatic hydrocarbons (PAHs). Due to the porous character of graphyne, the adsorption strength of PAHs onto graphyne surfaces is expected to be lower with respect to graphene (a perfect π‐extended system). However, there are not quantitative evidences for this assumption. This work shows that the adsorption strength of adsorbed PAHs onto γ‐graphyne nanosheets (GY) is weakened in 12 ? 23% with respect to the adsorption onto graphene, with a decrease of 10 ? 20% in the dispersive interactions. The adsorption energies (in eV) of the GY–PAH systems can be straightforward obtained as E _ads/eV≈0.033N _H + 0.031N _C, where N _H and N _C is the number of H and C atoms in the aromatic molecule, respectively. This equation predicts the binding energy of graphene–graphyne bilayers with a value of ～31 meV/atom. Analysis of the electronic properties shows that PAHs behaves as n‐dopants for GY, introducing electrons in GY and also reducing its bandgap in up to ～0.5 eV. Strong acceptor or donor substituted PAHs decrease the bandgap of γ‐graphyne in up to ～0.8 eV, with changes in its valence or conduction band, depending on the chemical nature of the adsorbate. Finally, these data will serve for future studies related to the bandgap engineering of graphyne surfaces by nonaggressive molecular doping, and for the development of graphyne‐based materials with potential applications in the removal of persistent aromatic pollutants.     

氢取代石墨单炔的机械化学合成及其电催化特性

氢取代石墨单炔是一种仅由苯环上的sp²杂化碳和氢与乙炔基上的sp杂化碳组成具有与石墨炔相似平面网状结构的二维富碳材料。本文以碳化钙和三溴苯为原料,通过机械化学方法合成了氢取代石墨单炔,并通过X射线电子能谱、拉曼光谱、固体核磁共振成像¹H谱和透射电子显微镜加以证实。紫外可见漫反射吸收光谱和电化学测试表明样品为p型半导体,带隙为2.30 eV,在硫酸钠溶液(pH = 7)中的析氧起始过电位为0.04 V,在催化产氧和光催化方面具有应用潜力。     

Periodic ab initio approach for the cooperative effect of CH/pi interaction in crystals: relative energy of CH/pi and hydrogen-bonding interactions

The bonding property of the CH/pi interaction in organic crystals has been investigated by the means of a periodic ab initio method. The energy of the CH(sp(2))/pi interaction in crystals, estimated with periodic RHF/6-21G*, showed a reasonable attractive CH(sp(2))/pi interaction owing to a cooperative effect, whereas the results calculated with RHF/cc-pVDZ indicate a negligibly small or repulsive interaction. The relative contribution of the CH(sp(2))/pi interaction to the column packing energy was found to be roughly half of the energy of a conventional hydrogen bond. The calculation of the charge distributions on the aromatic rings participating in the CH(sp(2))/pi interaction in crystals revealed that the atoms were more ionic than those in the gas phase. These theoretical calculations suggest a hydrogen-bonding characteristic for the CH(sp(2))/pi interaction in crystals, which does not occur in solution nor gas phase. We present computational evidence of the existence of the cooperative effect of CH(sp(2))/pi interaction in crystals.     

二维碳石墨炔的结构及其在能源领域的应用

从二维碳材料石墨炔(GDY)的分子和电子结构出发,重点论述石墨炔在能源存储和转换两个领域的应用,包括最新的理论和实验进展。石墨炔独特的三维孔隙结构,使得石墨炔在锂存储和氢气存储应用中具备天然的优势,既可以用作锂离子相关的储能器件,包括锂离子电池、锂离子电容器等;也可作为储氢材料,用于燃料电池等。通过掺杂的方法,还能进一步提高石墨炔储锂和储氢的性能。由于sp炔键和sp²苯环的存在,使石墨炔具有多重共轭的电子结构,在具备狄拉克锥的同时,其带隙也可通过多种途径调控,使得石墨炔不仅可以作为非金属高活性催化剂替代贵金属在光催化等方面应用,还可以在太阳能电池的空穴传输层和电子传输层方面获得应用,展现了石墨炔在能源方面独特的应用价值。我们将从理论预测和实验研究两方面介绍该领域目前的研究现状和发展趋势。     

Research on the Preparation of Graphdiyne and Its Derivatives

As a new 2D carbon material allotrope composed of sp and sp² carbon atoms, graphdiyne (GDY) possesses a highly conjugated porous structure, easily tunable intrinsic bandgap, and various excellent properties. Such properties allowed researchers to develop methods to prepare GDY, so that it can be applied for energy storage and conversion, environmental protection, various electronic devices and so on. In this review, the authors systematically discuss the methods and strategies developed for preparing GDY and its derivatives, including the synthesis of GDY by using liquid-, solid-, and gas-phase methods, the synthesis of heteroatom-doped GDY, the preparation of GDY-based composites, and the synthesis of GDY analogues. All these preparation methods can provide the way to obtain GDY for specific studies and applications.     

Spectroscopic characterization of carbon chains in nanostructured tetrahedral carbon films synthesized by femtosecond pulsed laser deposition

A comparative study of carbon bonding states and Raman spectra is reported for amorphous diamondlike carbon films deposited using 120 fs and 30 ns pulsed laser ablation of graphite. The presence of sp(1) chains in femtosecond carbon films is confirmed by the appearance of a broad excitation band at 2000-2200 cm(-1) in UV-Raman spectra. Analysis of Raman spectra indicates that the concentrations of sp(1)-, sp(2)-, and sp(3)-bonded carbon are approximately 6%, approximately 43%, and approximately 51%, respectively, in carbon films prepared by femtosecond laser ablation. Using surface enhanced Raman spectroscopy, specific vibrational frequencies associated with polycumulene, polyyne, and trans-polyacetylene chains have been identified. The present study provides further insight into the composition and structure of tetrahedral carbon films containing both sp(2) clusters and sp(1) chains.     

Density-functional calculations of HCN adsorption on the pristine and Si-doped graphynes

Graphyne, a lattice of benzene rings connected by acetylene bonds, is one-atom-thick planar sheet of sp- and sp²-bonded carbons differing from the hybridization of graphene (considered as pure sp²). Here, HCN adsorption on the pristine and Si-doped graphynes was studied using density-functional calculations in terms of geometric, energetic, and electronic properties. It was found that HCN molecule is weakly adsorbed on the pristine graphyne and slightly affects its electronic properties. While, Si-doped graphyne shows high reactivity toward HCN, and, in the most favorable state, the calculated adsorption energy is about ?10.1 kcal/mol. The graphyne, in which sp-carbon was substituted by Si atom, is more favorable for HCN adsorption in comparison with sp²-carbon. It was shown that the electronic properties of Si-doped graphyne are strongly sensitive to the presence of HCN molecule and therefore it may be used in sensor devices.     

Lanthanum gallium bismuthide,LaGaBi2

The ternary rare-earth gallium bismuthide LaGaBi(2) has been prepared through reaction of the elements. Its structure (Pearson symbol hP24, hexagonal, space group P6/mmm, Z = 6, a = 13.5483(4) A, c = 4.3937(1) A) contains columns of La(6) trigonal prisms centered by Bi atoms. These columns are surrounded by a framework consisting of three-atom-wide Bi ribbons and Ga(6) rings. Additional Bi atoms are sandwiched between pairs of Ga(6) rings. LaGaBi(2) is structurally closely related to La(13)Ga(8)Sb(21). A retrotheoretical analysis of the structure through extended Hückel band structure calculations suggests an interesting electronic situation in which strong multiple bonding in the Ga-Ga network coexists with weak hypervalent bonding in the Bi-Bi network and confirms the metallic behavior seen in electrical resistivity measurements.     

Chemical Bonding as a New Avenue for Controlling Excited-State Properties and Excitation Energy-Transfer Processes in Zinc Phthalocyanine–Fullerene Dyads

Whether chemical bonding can regulate the excited-state and optoelectronic properties of donor–acceptor dyads has been largely elusive. In this work, we used electronic structure and nonadiabatic dynamics methods to explore the excited-state properties of covalently bonded zinc phthalocyanine (ZnPc)-fullerene (C₆₀) dyads with a 6–6 (or 5–6) bonding configuration in which ZnPc is bonded to two carbon atoms shared by the two hexagonal rings (or a pentagonal and a hexagonal ring) in C₆₀. In both cases, the locally excited (LE) states on ZnPc are spectroscopically bright. However, their different chemical bonding differentiates the electronic interactions between ZnPc and C₆₀. In the 5–6 bonding configuration, the LE states on ZnPc are much higher in energy than the LE states on C₆₀. Thus, the excitation energy transfer from ZnPc to C₆₀ is thermodynamically favorable. On the other hand, in the 6–6 bonding configuration, such a process is inhibited because the LE states on ZnPc are the lowest ones. More detailed mechanisms are elucidated from nonadiabatic dynamics simulations. In the 6–6 bonding configuration, no excitation energy transfer was observed. In contrast, in the 5–6 bonding configuration, several LE and charge-transfer (CT) excitons were shown to participate in the energy-transfer process. Further analysis reveals that the photoinduced energy transfer is mediated by a CT exciton, such that electron- and hole-transfer processes take place in a concerted but asynchronous manner in the excitation energy transfer. It is also found that high-level electronic structure methods including exciton effects are indispensable to accurately describe photoinduced energy- and electron-transfer processes. Furthermore, this work opens up new avenues for regulating the excited-state properties of molecular donor–acceptor dyads by means of chemical bonding.     

轰击离子能量对CNx薄膜中sp3型C-N键含量的影响

对磁控溅射生长在单晶Si(001)衬底上的CNx薄膜样品的化学键合及结构进行了研究,利用不同的衬底负偏压(Vh)来控制轰击衬底表面的入射离子能量,从而影响膜中的化学键合的状态.样品的FTIR,Ra-man和XPS分析结果表明,CNx薄膜中N原子分别与sp,sp2和sp3杂化状态的C原子结合,其中sp3型C-N键含量先随着衬底偏压(Vb)的升高而增加,并在偏压Vb=-50V时达到最大值,但随着Vb继续升高,sp3型C-N键含量减少,这表明CNx薄膜中,sp3型C-N键的含量与轰击离子的能量变化密切相关.     

Graphdiyne:A Versatile Material in Electrochemical Energy Conversion and Storage

Graphdiyne(GDY),which is composed of sp2-/sp-hybridized carbon atoms,has attracted increasing attention.In the structure of GDY,the existence of large triangular-like pores,well dispersed electron-rich cavities as well as a large π-conjugated structure endows GDY with a natural bandgap,fast electron/ion transport,and tunable electronic properties.These unique features make GDY competitive in areas of gas separation and capture,electronics,detectors,catalysts,biomedicine and therapy,and energy-related fields.Benefiting from the facile synthesis method,various GDY structures and GDY-based composites have been successfully prepared and show great potential in the practical application of energy storage and catalysis areas.Here,this review aims at providing a timely and comprehensive update on the preparation and application of GDY materials.The current development of GDY materials in various electrochemical fields especially in energy conversion,energy storage,and catalysis is mainly summarized.Moreover,the potential development prospects are also discussed.     

石墨炔的化学修饰及功能化

石墨炔特殊的电子结构和孔洞结构使其在信息技术、电子、能源、催化以及光电等领域具有潜在、重要的应用前景。近几年石墨炔的基础和应用研究已取得了重要成果,并迅速成为了碳材料研究中的新领域。石墨炔中炔键单元的高活性为其化学修饰与掺杂提供了良好的平台。在这篇综述中,我们将重点介绍石墨炔的非金属杂原子掺杂、金属原子修饰以及表面改性,并深入探讨掺杂与衍生化对石墨炔材料的电子性质的影响及其对光电化学催化性能的协同增强。     

Dimensional dependence of electronic structure of fullerene polymers

Fullerene polymers made of C(60) are systematically investigated by means of a first-principles pseudopotential approach within the local density approximation of the density functional theory. We assume 10 different structures of fullerene polymers. The first three are C(60) polymer networks cross-linked by [2+2] cycloadditional four-membered rings, and the other seven are composed of peanut-shaped fused C(60) polymer chains cross-linked by either seven-membered rings or eight-membered rings. Owing to the overlap of wave functions as well as the hybrid networks of sp(2)-like (3-fold coordinated) and sp(3)-like (4-fold coordinated) carbon atoms, the electronic structure is considerably different from each other. We find that the resulting electronic structure is either semiconductor or semimetal depending on the spatial dimensionality of materials.