Synthesis of novel and stable g-C 3 N 4 -Bi 2 WO 6 hybrid nanocomposites and their enhanced photocatalytic activity under visible light irradiation

Graphitic carbon nitride (g-C 3 N 4 ) nanosheets with a thickness of only a few nanometres were obtained by a facile deammoniation treatment of bulk g-C 3 N 4 and were further hybridized with Bi 2 WO 6 nanoparticles on the surface via a solvothermal method. The composite photocatalysts were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis diffuse reflection spectroscopy and X-ray photoelectron spectroscopy (XPS). The HR-TEM results show that the nano-sized Bi 2 WO 6 particles were finely distributed on g-C 3 N 4 sheet surface, which forms heterojunction structure. The UV–vis diffuse reflectance spectra (DRS) show that the absorption edge of composite photocatalysts shifts towards lower energy region in comparison with those of pure g-C 3 N 4 and Bi 2 WO 6 . The degradation of methyl orange (MO) tests reveals that the optimum activity of 8 : 2 g-C 3 N 4 -Bi 2 WO 6 photocatalyst is almost 2.7 and 8.5 times higher than those of individual g-C 3 N 4 and Bi 2 WO 6 . Moreover, the recycle experiments depict high stability of the composite photocatalysts. Through the study of the influencing factors, a possible photocatalytic mechanism is proposed. The enhancement in both photocatalytic performance and stability was caused by the synergistic effect, including the effective separation of the photogenerated electron-hole pairs at the interface of g-C 3 N 4 and Bi 2 WO 6 , the smaller the particle size and the relatively larger specific surface area of the composite photocatalyst.

Effects of element doping on electronic structures and optical properties in cubic boron nitride from first-principles

Attractive potential applications of cubic boron nitride (c-BN) derive from the properties of semiconductors, widely used in optoelectronic and microelectronic devices. In this paper, the effects of element doping on the electronic structures and optical properties in cubic boron nitride are investigated. The Al- and Ga-doped systems have the lower bonding energies of −11.544 eV and −5.302 eV, respectively, indicating better stability. Difference charge density maps demonstrate that the electron loss increases after P doping and decreases after Al, Ga and As dopings, indicating that the covalent character of polar covalent bonds decreases by doping in the range of P, Al, Ga and As, which is in accordance with the calculated atom population values. The Al- and Ga-doped systems show lower dielectric loss, absorption and reflectivity in the lower energy region, displaying the “transparent-type” characteristic and their potential applications in electron devices.

IR analysis of the carboxylate forms in structurally determined [CuII(κ3-L)2] species isolated from different acidic solutions

Several copper(II) coordination compounds with the tridentate κ³-<em>N,N,O</em> bisligand (L = bis(3,5-dimethylpyrazol-1-yl)acetate or its molecular acid form HL = Hbdmpza) were synthesized from different starting metal salts in appropriate acidic water solutions as reported. The XRD single crystal structural analysis reveals neutral acidic ligand form in [Cu(HL)₂]·2(HSO₄) (<strong>1</strong>) and [Cu(HL)₂]·2Cl (<strong>2</strong>), while ionic in [Cu(L)₂]·(CH₃COOH)·(H₂O) (<strong>3</strong>), and [Cu(L)₂]·2(H₂O) (<strong>4</strong>). The molecular structures of <strong>2</strong> and <strong>3 </strong>are first reported herein, thus enabling a clearer insight for the IR - structural analysis. Two carboxylate C-O bond lengths ranges, namely differing 1.29/1.22 Ǻ for <strong>2</strong>, and the same 1.24/1.24 Ǻ for <strong>3</strong>, respectively, are in agreement with the single(longer)/double(shorter) character of both bonds for the neutral carboxylic HL in <strong>2</strong>, and the same character of both bonds for the carboxylate anionic L^- in <strong>3</strong>, as seen for the related <strong>1 </strong>(HL) and <strong>4 </strong>(L^-). The most distinguished IR spectra difference for the molecular (HL) / ionic (L^-) is at the 1700 cm^-1 carboxylate band. The C=O free ligand (HL) double bond position at 1740 cm^-1 is most similar with 1702 cm^-1 in <strong>1</strong>,<strong> </strong>while a split band at 1697, 1665 cm^-1 is seen for <strong>2</strong>. On the other hand, the anionic asymmetric carboxylate stretching IR band (<strong>`</strong>n_as(COO⁻)) for <strong>3</strong> (1642 cm^-1) and <strong>4 </strong>(1635 cm^-1) is found at lower energy region. Thus, the additional band within the same region, as seen only for <strong>3 </strong>at 1716 cm^-1, is assigned to the network neutral acetic acid C=O double bond.

Newly Determined Crystal Structure and Optical Property of the Intermetallic NiAl and Ni3Al Alloys: A First-Principles Computer Simulated Investigation

Using quantum mechanics plane-wave approach based on the density functional theory, the lattice constants of NixAl at different Ni concentrations (x=1, 3) are predicted. Optical properties such as dielectric function, energy loss function and reflectivity are also investigated. Results show that with the increase of Ni constituent, the location of the peak in loss function moves to the lower energy region, but the peak height increases. At 0eV, the reflectivity increases rapidly with the Ni concentration. The reflectivity of NiAl and Ni3Al are pronounced in the UV region (not in the visible light region). The dielectric properties, namely the real and imaginary parts of the dielectric function, changed significantly with Ni constituent.

Influence of Nd-Doping on Electronic Structure and Optical Properties of ZnO

A detailed first-principles study of electronic structure and optical properties of Nd-doping ZnO with various concentrations of Nd was performed using density functional theory. The results show that the band gap of Nd-doping ZnO slightly widens with the increasing Nd concentration, this is because the conduction band undergoes a greater shift toward the lower-energy region than the valence band, which is agreement with experimental results. Furthermore, in comparison to pure-ZnO, the Fermi level shifts into the conduction band after Nd-doping ZnO. And the calculated result of imaginary part of dielectric function of Nd-doping ZnO shows that there is a sharp peak in the lower-energy region, which is due to the electrons transition between d-d orbital of Nd atom.

Effects of Zinc Cations Doping and the Photo-Absorbed Mechanism for NaTaO3 Nanoparticles

Effects of zinc cations doping into wide band gap semiconductor photocatalysts of electronic structure, visible light response, and photo-absorbed mechanism were studied. A series of Zn-doped NaTaO3 catalysts were prepared by hydrothermal method. XRD results suggested that zinc were successfully doped into the NaTaO3 nanocrystal in the Zn2+ ions state. UV-vis diffuse reflectance spectra indicated no obvious red-shift was observed in the series of zinc doped NaTaO3 photo-catalysts. The simulation of energy band structure by density functional theory unfolded that d orbital of Zn2+ is lower than the Ta 5d and also O 2p orbital, thus it located at the lower energy region of the valence band. Therefore the substitution of Ta5+ ions by Zn2+ ions can not form an intermediate band (IB) between the top of the valence band (VB) and the bottom of conduct band. Meanwhile Zn species can become the recombination centers of photoinduced electrons and holes. Thus, the quickly recombination of e--h+ pairs is one of the most significant factors which deteriorate the photoactivity of Zn-doped NaTaO3

The Study on the Structural and Optical Properties of C-F Codoped Zinc Oxide from Ab Initio Calculations

The structural and optical properties of C-doped and C-F colonel Zoo compounds are investigated by using a first principle method with the plane wave pseudopotential calculations, based on the density functional theory(DFT), within generalized-gradient approximation (GGA). We discuss the structural properties by comparison with C-Al and C-Ga doped systems and the calculated results demonstrate that the c/a is smaller than C doped ZnO when incorporating F into the system and C-F codoping causes a smaller lattice mismatch compared with the C-Al codoped ZnO. Moreover, we focus on the complex dielectric function in order to investigate the optical properties. By analysing the results, we remark that the absorption edge shift the lower energy region(red shift) when incorporating C-F into ZnO compound.

Structures and Electronic Spectroscopy of Rhodium-Based Complexes: a Theoretical Study on Promising Optical Materials

A series of rhodium-based complexes were explored theoretically to understand their application in optical materials and potential photocatalytic activity. Better structural description of [RhAu(CNH)2(PH2CH2PH2)2]2+ (1) were achieved with the ab initio MP2, XαVWN, and SVWN methods. To fine-tune the electronic spectroscopy, two analogues of 1 were taken into account by varying its Au metal center and bridging bidentate ligand. The experimental spectra were well reproduced by our TD-DFT calculations. It was shown that the lowest-energy absorption of homobimetallic Rh-Rh complex occurs in lower-energy region than those of heterobimetallic Rh-Au complexes.