Visible-light Driven Photocatalysts: Al-, Ga-, and In-doped Monoclinic BiVO_4

The first-principles calculations were performed to investigate the stability, band structure, density of states and redox potential of Al-, Ga-, and In-doped monoclinic BiVO4（mBiVO4）. The calculated formation energies show that Al-doped mBiVO4 inducing an O vacancy is energetically favorable with a smaller defect formation value. With the incorporation of Al, Ga, and In, the band gap of the doped systems will be narrowed in the order of Al-doped 〈 Ga-doped 〈 In-doped mBiVO4, which is beneficial for the response to the visible light. And the substitution of an Al or Ga for a V atom will significantly enhance the reducibility of mBiVO4, improving the efficiency of H2 evolution from H2 O. Our results show that the photocatalytic activity of mBiVO4 can be modulated by substitutional doping of Al, Ga, and In.     

A density functional study on the electronic structures of TiN solid

The electronic structures of TiN bulk have been studied by using different theoretical formalisms, and the DFT method, especially the BLYP method can produce reasonable results. The band structure of TiN (001) surface is also investigated and two a type surface states are presented in our results. The state located at 2.9 eV below EF in angle resolved photoemis-sion in (ARPES) is well reproduced in this work, which consists essentially of 2pz orbital of surface N atom. Another surface state is associated with the bands originated from 3d orbital of surface Ti atom. Furthermore, the elastic constants of TiN are also calculated by using BLYP method.     

Effects of hydroxyl group on H2 dissociation on graphene:A density functional theory study

Graphene-based materials are promising for hydrogen production and storage.In this work,using density functional theory calculations, we explored how a hydroxyl group influences H₂ dissociation on graphene.Presence of the hydroxyl group makes the binding of H atom with graphene stronger,as the binding energy of H atom with the hydroxyl-modified graphene is higher than that with the pristine graphene. The para-site is the most favorable site for H₂ dissociation on both the pristine and hydroxyl-modified graphene.The energy barrier of H₂ dissociation at para-site on the pristine graphene is 3.10 eV whereas that on the hydroxyl-modified graphene is 2.46 eV,indicating a more facile H₂ dissociation on the hydroxyl-modified graphene.     

Theoretic and Experimental Studies on Titania Nanotube Doped with Ag Metal Ions

The electronic state density and energy bands of Ag-doped anatase TiO2 are studied by WIEN2k software package based on DFT. The calculation results show that the band-gap of anatase titania became bigger after doping with Ag metal ions. The band-gap transfers from 2.04 to 2.5 eV, but a new energy band appears among the forbidden band after the Ag atom substitution. The interband width of Ag-TiO2 is 0.17 eV, which is located at –0.07 eV; more excitation and jump routes are opened for the electrons. The lowest excitation energy can achieve 1.2 eV, which may allow the photons with lower energy (at longer wavelength, such as visible light) to be absorbed. Ag ions are implanted into the titania nanotube sample by MEVVA (Metal Vapor Vacuum Arc) implanter. The photo-electrochemical response and photo-degradation experiment of titania nanotube samples implanted with Ag ions are tested under UV and visible light; the results indicated that the performance of implanted titania naotubes is enhanced both under UV and visible light; it is worth mentioning that the photocurrent density can reach 0.145 mA/cm2 under visible light, which is 181 times higher than those of pure TiNT, and the k value of degradation methyl orange can obtain 0.30 h-1, which is 71 times higher than that of pure TiNT. All the experimental results are consistent well with the theoretic ones.     

Mesoporous cadmium bismuth niobate (CdBi_2Nb_2O_9) nanospheres for hydrogen generation under visible light

Herein, we report visible light active mesoporous cadmium bismuth niobate(CBN) nanospheres as a photocatalyst for hydrogen(H_2) generation from copious hydrogen sulfide(H_2S). CBN has been synthesized by solid state reaction(SSR) and also using combustion method(CM) at relatively lower temperatures.The as-synthesized materials were characterized using different techniques. X-ray diffraction analysis shows the formation of single phase orthorhombic CBN. Field emission scanning electron microscopy and high resolution-transmission electron microscopy showed the particle size in the range of ~0.5–1 μm for CBN obtained by SSR and 50–70 nm size nanospheres using CM, respectively. Interestingly, nanospheres of size 50–70 nm self assembled with 5–7 nm nanoparticles were observed in case of CBN prepared by CM.The optical properties were studied using UV–visible diffuse reflectance spectroscopy and showed band gap around ~3.0 eV for SSR and 3.1 eV for CM. The slight shift in band gap of CM is due to nanocrystalline nature of material. Considering the band gap in visible region, the photocatalytic activity of CBN for hydrogen production from H_2S has been performed under visible light. CBN prepared by CM has shown utmost hydrogen evolution i.e. 6912 μmol/h/0.5 g which is much higher than CBN prepared using SSR.The enhanced photocatalytic property can be attributed to the smaller particle size, crystalline nature,high surface area and mesoporous structure of CBN prepared by combustion method. The catalyst was found to be stable, active and can be utilized for water splitting.     

Tuning of NaTaO_3 Band Structure through Mn~（2＋） Ion Doping and the Enhanced Visible Light Response

Pure and Mn-doped NaTaO3 nanoparticles were synthesized by a simple hydro- thermal method. XRD and XPS results suggested that manganese ions were successfully doped into the NaTaO3 crystalline in Mn2＋ state. UV-vis diffuse reflectance spectra revealed the obvious red-shift in the series of manganese doped NaTaO3 nanoparticles, resulting in a decrease in the band gap of NaTaO3 with the increase of Mn2＋ doping concentration. The photo-degradation experiment indicated that manganese doped NaTaO3 showed good photocatalytic performance and methylene blue（MB） degradation is improved with lower doping concentration of manganese ions under visible light. The simulation of energy band structure by density functional theory unfolded that the substitution of Ta5＋ ions by Mn2＋ ions resulted in an intermediate band（IB） below the bottom of the conduction band（CB）, which was mainly attributed to the state of Mn 3d.     

Effects of Various Dopants on Solitons in Polyacetylene

The effects of various dopants on solitons in polyacetylene were studied by using CNDO/2 level semiempirical quantum chemical method. The width of solitons is reduced when dopant is present, and the charge density wave(CDW) is further gathered on the carbon atom in soliton center. The effects of p-type of dopants are greater than those of n-type of ones. The charge transfer in doped polyacetylene can be achieved by the propagation of CDW along the chain. The conductivity of doped polyacetylene is proportional to the quantity of charge transfer between dopant and polyacetylene chain.     

Effect of Zr and C Co-doping on the Optical Properties and Electronic Structure of TiO_2

The systematic trends and effect introduced by Zr and C co-doping to TiO2 of electronic structure and optical properties of anatase TiO2 have been calculated by the plane-wave ultra-soft pseudopotential density functional theory (DFT) method within the generalized gradient approximation (GGA) for the exchange-correlation potential. Through the current calculations, the density of states (DOS), energy band structure and optical absorption coefficients have been obtained for TiO2 and compared with the doped TiO2, and the influence of electronic structure and optical properties caused by Zr and C co-doping has been presented qualitatively together. The results revealed that the energy band gap has been decreased owing to the doped Zr and C, whereas the optical absorption coefficients have been increased in the region of 400～800 nm and a red shift of absorption band can be found. Accordingly, photo catalytic activity of TiO2 has been enhanced. The current calculations are in good agreement with the experimental data.     

Study on anti-fungal activity of nitrogen-doped TiO2 nanophotocatalyst under visible light irradiation

<正>Nitrogen-doped TiO_2 nanophotocatalysts were prepared,and characterized by XRD patterns and UV-vis spectroscopy.The results indicated that nitrogen was doped effectively and the shift of the absorption edge to a lower energy and a stronger absorption in the visible light region were observed.The calcinations temperature is a key factor to narrow the band gap of titania,and consequently affects the response to visible light of nitrogen-doped TiO_2 nanocrystals.This photocatalyst can effectively inhibit the growth of Helminthosporium maydis,whereas undoped TiO_2 nanocrystals cannot inhibit the growth of H.maydis under the same experimental conditions.     

Hydrothermal Synthesis and Structure Analysis of Indium Vanadate （InVO4）

1 INTRODUCTION Indium vanadate is a kind of vanadate compounds. There are two crystal phase structures, metastable monocline structure and stable orthogonal structure. Orel, B.[1] and his partners have discovered that V of tetrahedron VO4 has very sensitive energy gap band. Through XPS study of orthogonal InVO4, it is found that its band gap is shorter than those of InNbO4 and InTaO4, and its band-gap energy is 2.0 eV[4]. Ortho- gonal InVO4 can act during the range from short- wav…     

Direct Solvothermal Synthesis of B/N‐Doped Graphene

Heteroatom‐doping into graphitic networks has been utilized for opening the band gap of graphene. However, boron‐doping into the graphitic framework is extremely limited, whereas nitrogen‐doping is relatively feasible. Herein, boron/nitrogen co‐doped graphene (BCN‐graphene) is directly synthesized from the reaction of CCl₄, BBr₃, and N₂ in the presence of potassium. The resultant BCN‐graphene has boron and nitrogen contents of 2.38 and 2.66 atom %, respectively, and displays good dispersion stability in N‐methyl‐2‐pyrrolidone, allowing for solution casting fabrication of a field‐effect transistor. The device displays an on/off ratio of 10.7 with an optical band gap of 3.3 eV. Considering the scalability of the production method and the benefits of solution processability, BCN‐graphene has high potential for many practical applications.     

Rules of Boron–Nitrogen Doping in Defect Graphene Sheets: A First‐Principles Investigation of Band‐Gap Tuning and Oxygen Reduction Reaction Catalysis Capabilities

Introduction of defects and nitrogen doping are two of the most pursued methods to tailor the properties of graphene for better suitability to applications such as catalysis and energy conversion. Doping nitrogen atoms at defect sites of graphene and codoping them along with boron atoms can further increase the efficiency of such systems due to better stability of nitrogen at defect sites and stabilization provided by B?N bonding. Systematic exploration of the possible doping/codoping configurations reflecting defect regions of graphene presents a prevalent doping site for nitrogen‐rich BN clusters and they are also highly suitable for modulating (0.2–0.9 eV) the band gap of defect graphene. Such codoped systems perform significantly better than the platinum surface, undoped defect graphene, and the single nitrogen or boron atom doped defect graphene system for dioxygen adsorption. Significant stretching of the O?O bond indicates a lowering of the bond breakage barrier, which is advantageous for applications in the oxygen reduction reaction.     

Chemical Reactivity and Band‐Gap Opening of Graphene Doped with Gallium,Germanium, Arsenic,and Selenium Atoms

Herein, the effects of substitutional doping of graphene with Ga, Ge, As, and Se are shown. Ge exhibits the lowest formation energy, whereas Ga has the largest one. Ga‐ and As‐doped graphene display a reactivity that is larger than that corresponding to a double vacancy. They can decompose H₂ and O₂ easily. Variation of the type and concentration of dopant makes the adjustment of the interlayer interaction possible. In general, doping of monolayer graphene opens a band gap. At some concentrations, Ga doping induces a half metallic behavior. As is the element that offers the widest range of gap tuning. Heyd–Scuseria–Ernzerhof calculations indicate that it can be varied from 1.3 to 0.3 eV. For bilayer graphene, the doped sheet induces charge redistribution in the perfect underneath sheet, which opens a gap in the range of 0.05–0.4 eV. This value is useful for developing graphene‐based electronics, as the carrier mobility of the undoped sheet is not expected to alter.     

Opening of Band Gap of Graphene with High Electronic Mobility by Codoping BN Pairs

Two-dimensional(2D) materials with a high density and low power consumption have become the most popular candidates for next-generation semiconductor electronic devices. As a prototype 2D material, graphene has attracted much attention owing to its stability and ultrahigh mobility. However, zero band gap of graphene leads to very low on-off ratios and thus limits its applications in electronic devices, such as transistors. Although some new 2D materials and doped graphene have nonzero band gaps, the electronic mobility is sacrificed. In this study, to open the band gap of graphene with high electronic mobility, the structure and property of BN-doped graphene were evaluated using first-principles calculations. The formation energies indicate that the six-membered BN rings doped graphene has the most favorable configuration. The band structures show that the band gaps can be opened by such type of doping. Also, the Dirac-cone-like band dispersion of graphene is mostly inhibited, ensuring high electronic mobility. Therefore, codoping BN into graphene might provide 2D materials with nonzero band gaps and high electronic mobility.     

Electronic Properties of Transition‐Metal‐Decorated Silicene

The electronic properties of 3d transition metal (TM)‐decorated silicene were investigated by using density functional calculations in an attempt to replace graphene in electronic applications, owing to its better compatibility with Si‐based technology. Among the ten types of TM‐doped silicene (TM–silicene) studied, Ti‐, Ni‐, and Zn‐doped silicene became semiconductors, whereas Co and Cu doping changed the substrate to a half‐metallic material. Interestingly, in cases of Ti‐ and Cu‐doped silicene, the measured band gaps turned out to be significantly larger than the previously reported band gap in silicene. The observed band‐gap openings at the Fermi level were induced by breaking the sublattice symmetry caused by two structural changes, that is, the Jahn–Teller distortion and protrusion of the TM atom. The present calculation of the band gap in TM–silicene suggests useful guidance for future experiments to fabricate various silicene‐based applications such as a field‐effect transistor, single‐spin electron source, and nonvolatile magnetic random‐access memory.     

Electronic Structures,Bonding Configurations,and Band-Gap-Opening Properties of Graphene Binding with Low-Concentration Fluorine

To better understand the effects of low-level fluorine in graphene-based sensors, first-principles density functional theory (DFT) with van der Waals dispersion interactions has been employed to investigate the structure and impact of fluorine defects on the electrical properties of single-layer graphene films. The results show that both graphite-2 H and graphene have zero band gaps. When fluorine bonds to a carbon atom, the carbon atom is pulled slightly above the graphene plane, creating what is referred to as a C_F defect. The lowest-binding energy state is found to correspond to two C_F defects on nearest neighbor sites, with one fluorine above the carbon plane and the other below the plane. Overall this has the effect of buckling the graphene. The results further show that the addition of fluorine to graphene leads to the formation of an energy band (B_F) near the Fermi level, contributed mainly from the 2p orbitals of fluorine with a small contribution from the p orbitals of the carbon. Among the 11 binding configurations studied, our results show that only in two cases does the B_F serve as a conduction band and open a band gap of 0.37 eV and 0.24 eV respectively. The binding energy decreases with decreasing fluorine concentration due to the interaction between neighboring fluorine atoms. The obtained results are useful for sensor development and nanoelectronics.     

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.     

The Electronic and Optical Properties of Au Doped Single-Layer Phosphorene

The electronic properties and optical properties of single and double Au-doped phosphorene have been comparatively investigated using the first-principles plane-wave pseudopotential method based on density functional theory. The decrease from direct band gap 0.78 eV to indirect band gap 0.22 and 0.11 eV are observed in the single and double Au-doped phosphorene, respectively. The red shifts of absorbing edge occur in both doped systems, which consequently enhance the absorbing of infrared light in phosphorene. Band gap engineering can, therefore, be used to directly tune the optical absorption of phosphorene system by substitutional Au doping.     

Manipulating the electronic structures of silicon carbide nanotubes by selected hydrogenation

We show that the electronic and atomic structures of silicon carbide nanotubes (SiCNTs) undergo dramatic changes with hydrogenation from first-principles calculations based on density-functional theory. The exo-hydrogenation of a single C atom results in acceptor states close to the highest occupied valence band of pristine SiCNT, whereas donor states close to the lowest unoccupied conduction band appear as a Si atom being hydrogenated. Upon fully hydrogenating Si atoms, (8,0) and (6,6) SiCNTs become metallic with very high density of states at the Fermi level. The full hydrogenation of C atoms, on the other hand, increases the band gap to 2.6 eV for (8,0) SiCNT and decreases the band gap to 1.47 eV for (6,6) SiCNT, respectively. The band gap of SiCNTs can also be greatly increased through the hydrogenation of all the atoms.     

Isoelectronic doping of graphdiyne with boron and nitrogen: stable configurations and band gap modification

Graphdiyne, consisting of sp- and sp(2)-hybridized carbon atoms, is a new member of carbon allotropes which has a natural band gap ~1.0 eV. Here, we report our first-principles calculations on the stable configurations and electronic structures of graphdiyne doped with boron-nitrogen (BN) units. We show that BN unit prefers to replace the sp-hybridized carbon atoms in the chain at a low doping rate, forming linear BN atomic chains between carbon hexagons. At a high doping rate, BN units replace first the carbon atoms in the hexagons and then those in the chains. A comparison study indicates that these substitution reactions may be easier to occur than those on graphene which composes purely of sp(2)-hybridized carbon atoms. With the increase of BN component, the band gap increases first gradually and then abruptly, corresponding to the transition between the two substitution motifs. The direct-band gap feature is intact in these BN-doped graphdiyne regardless the doping rate. A simple tight-binding model is proposed to interpret the origin of the band gap opening behaviors. Such wide-range band gap modification in graphdiyne may find applications in nanoscaled electronic devices and solar cells.