Impact of Tungsten, Iron and Molybdenum on the TiO 2 Geometrical network and Optoelectronic properties

The geometry, electronic structure and optical properties of pure and 3d transition metals-doped anatase-phase TiO2 were studied by using the plane-wave ultrasoft pseudopotential method based on the density functional theory. The calculations show that the formation of impurity energy level is mainly contributed by 3d orbital of the transition metal doped in TiO2, and the position of impurity energy levels in the band gap is the dominating factor that decides whether the absorption threshold wavelength has a red-shift or not. The doping of Cr, Mn, Fe, Ni, Co and Cu causes the absorption wavelength to red-shift, and the absorption coefficient in the visible light region is increased; whereas the doping of Sc, Zn causes the absorption wavelength to blue-shift, but leads to higher absorption coefficients in the visible region. The doping of V not only causes the absorption wavelength to red-shift and strengthens the absorption in the ultraviolet light region, but also gives rise to extremely big absorption coefficient in the visible region.

Ab initio studies of Nb–N–S tri-doped TiO2 with enhanced visible light photocatalytic activity

We systematically investigated the effects of Al-impurity type on the formation energy, crystal structure, charge density, electronic structure, and optical properties of ZnO by using density functional theory and the Hubbard-U method. Al-related defects, such as those caused by the substitution of Zn and O atoms by Al atoms (Als(Zn) and Als(O), respectively) and the presence of an interstitial Al atom at the center of a tetrahedron (Ali(tet)) or an octahedron (Ali(oct)), and various Al concentrations were evaluated. The calculated formation energy follows the order Ef(Als(Zn)) < Ef(Ali(tet)) < Ef(Ali(oct)) < Ef(Als(O)). Electronic structure analysis showed that the Als(Zn), Als(O), Ali(tet), and Ali(oct) models follow n-type conduction, and the optical band gaps are higher than that of pure ZnO. The calculated carrier concentrations of the Als(O) and Ali(tet)/Ali(oct) models are higher than that of the Als(Zn) model. However, according to the curvature of the band structure, the occurrence of interstitial Al atoms or the substitution of O atoms by Al atoms results in a high effective mass, possibly reducing the carrier mobility. The average transmittance levels in the visible light and ultraviolet (UV) regions of the Als(Zn) model are higher than those of pure ZnO. However, the presence of an interstitial Al atom within the ZnO crystal reduces transmittance in the visible light region; Als(O) substantially reduces the transmittance in the visible light and UV regions. In addition, the properties of ZnO doped with various Als(Zn) concentrations were analyzed.

Ab initio study of electronic and optical properties of [formula omitted] doped anatase [formula omitted] (1 0 1) surface

Electronic and optical properties of pure and Mo doped anatase TiO2 using GGA and GGA+U calculations

Janus Ga2STe monolayer under strain and electric field: Theoretical prediction of electronic and optical properties

Simultaneous visible and ultraviolet photoresponse improvement of MoS2/ZnO heterostructure photodetector via direct resonant coupling of Au nanoparticles localized surface plasmon resonance

Since the discovery and synthesis of graphene, two-dimensional graphether and silicether materials have been predicted as novel semiconductors. A novel two-dimensional silicether/graphether heterostructure is designed by combining silicether and graphether, which has unique optical and electronic properties due to the properties of a single material synthesized by heterostructures. The electronic and optical properties of silicether/graphether heterostructure are studied by the first-principles calculations based on density functional theory. The binding energy and layer spacing for each of all considered 16 stacking patterns of the heterostructures are calculated. The results show that different stacking patterns have a small effect on the binding energy of the heterostructure. When the layer spacing is 2.21 Å, the stacking pattern in which the concave oxygen atoms of graphether are on the top of the concave oxygen atoms of silicether is the most stable. In addition, it has an indirect band gap of 0.63 eV, which is smaller than that of the silicether and graphether, respectively. By changing the external electric field and the biaxial strain strength, the band gap of the silicether/graphether heterostructure shows tunability. The compressive strain can increase the band gap of silicether/graphether heterostructure, while the band gap decreases with the tensile strain increasing. Especially, when the compressive strain is greater than –6%, the heterostructure undergoes an indirect-to-direct band gap transition, which is beneficial to its applications in optical devices. When the external electric field is applied, the band gap of the heterostructure changes linearly with the strength of the electric field, and the indirect band gap characteristic is maintained. The absorption coefficient of silicether/graphether heterostructure shows a strong peak in the ultraviolet light region. The maximum absorption coefficient can reach up to 1.7 × 10&lt;sup&gt;5&lt;/sup&gt; cm&lt;sup&gt;–1&lt;/sup&gt; around 110 nm. Compared with that of monolayer graphether and silicether, the optical absorption of the heterostructure is significantly enhanced within the range from more than 80 nm to less than 170 nm. The results show that silicether/graphether heterostructure has an outstanding optical absorption in the ultraviolet region. Moreover, the silicether/graphether heterostructure also shows considerable absorption coefficient (1 × 10&lt;sup&gt;4&lt;/sup&gt;—4 × 10&lt;sup&gt;4&lt;/sup&gt; cm&lt;sup&gt;–1&lt;/sup&gt;) in the visible region, which makes it a potential material in photovoltaic applications. This work may provide a novel material with a promising prospect of potential applications in nanodevices.

Air pollution has become a focused issue worldwide with the rapid development of industry. As one of the major air pollutants, nitric oxide (NO) could cause to serious atmospheric problems, such as acid rain, haze and photochemical smog. Photocatalysis as a green technology has received increasing attention, because it has represented greatly potential application over the late decades. As a novel photocatalyst, LaCO3OH possesses relatively negative conduction band and positive valence band edges, which can be enable to sufficient potential for photocatalytic air decomposition. But the band gap of LaCO3OH (4.1 eV) allows only a small portion of solar spectrum in the ultraviolet (UV) light region to be absorbed. To extend the light absorption spectra into the visible light region, the combination of narrow band gap Ag/AgCl with the wide band gap LaCO3OH to build heterojunction could utilize abundant solar light. Noble metal nanoparticles (NPs) showed strong visible light absorption due to surface Plasmon resonance effect (SPR). In particular, silver NPs show SPR in the visible region, which has been utilized to develop efficient plasmonic photocatalysts. In this study, a three-component Ag/AgCl-LaCO3OH nanorod photocatalyst has been fabricated successfully through a chemical precipitation treatment and applied to photocatalytic NO removal. The as-prepared samples were characterized by XRD, SEM, TEM, XPS, UV-vis DRS, PL and ESR. The photocatalytic NO oxidation process was monitored by in situ DRIFTS. The results indicated that the visible-light harvesting and the photogenerated carrier separation can be enhanced simultaneously, which could result from introduction of Ag/AgCl into LaCO3OH (LCO) nanorod photocatalyst. Under visible-light irradiation, the photogenerated electron-hole pairs separation is promoted by the plasma resonance (SPR) effect of the metallic Ag0. The hot electrons would be transferred to the defect level endowed by the oxygen vacancies of the LCO. Subsequently, the electron can be transferred to the surface of LCO, captured by O2 to form ·O2− radicals, which plays a dominant role in the photocatalytic NO oxidation. In addition, the holes would be transferred to the surface of AgCl, and interact with Cl− to transform Cl0, which can directly participate in the oxidation of NO. Furthermore, Cl0 can be reduced to Cl− and react with Ag+ to forming AgCl, avoiding the photocorrosion of AgCl effectively. Meanwhile, the effect of the mol ratio of Ag/AgCl on the photocatalytic performance was also evaluated. The optimized Ag/AgCl-LCO (mol ratio at 75%) nanorods demonstrated a high NO removal ratio of 54.0%, which far exceeding that of the individual LCO (3.1%) or Ag/AgCl (18.0%) photocatalyst. Moreover, the in situ FT-IR spectra was used to dynamically monitor the intermediate toxic by-products, in combination with the active species, and further reveal the mechanism of photocatalytic NO oxidation from the molecular level. The reaction mechanism can be described as Ag + visible light → e−+h+, e−+O2→ ·O2−, h++AgCl→Cl0+Ag+, ·O2−+NO→NO3−, Cl0+ NO→NO3−+Cl−, NO+2·OH→NO2+H2O, NO2+·OH→NO3−+H+ and Cl−+Ag+→AgCl. The present work could provide navel perspectives for advancing the photocatalysis efficiency, offer a new insight of the photocatalytic reaction mechanism and promote large-scale environmental decontamination applications of plasma-based semiconductor composites.

Hybrid functional study on optical properties of Sr2M2O7−xNx(M = Nb, Ta) photocatalysts with perovskite-slab structures

Using the density functional theory (DFT), we study the electronic structure and linear optical properties of pyrite and monolayer structure of FeSe2. Calculated results show that pyrite FeSe2 is a non-magnetic semiconductor material, while hexagonal monolayer FeSe2 show completely metallic features. There have strong hybridizations between Fe-d orbitals and Se-p orbitals. All optical properties such as real and imaginary parts of dielectric function, absorption coefficient, reflectivity and loss function are obtained and analyzed. The results present obvious anisotropy in optical features of monolayer FeSe2 and excellent absorption properties in ultraviolet and visible light regions. Results show that the anti-ferromagnetic character in pyrite FeSe2 turn into ferromagnetic character for hexagonal monolayer and the main transitions near the Fermi level mainly contributed by down-spin carriers. From the density of states, we found thet the Fe-d orbitals play an important role in the interband and intraband transitions. These results made monolayer FeSe2 an ideal candidate for photovoltaic, opto-electric and spintronic applications.

Arylene Diimide Derivatives as Anolyte Materials with Two-Electron Storage for Ultrastable Neutral Aqueous Organic Redox Flow Batteries

The type-II PtSe2/WS2 van der Waals heterostructure: A high efficiency water-splitting photocatalyst

Silicon (Si) nanostructures that exhibit a significantly low reflectance in ultraviolet (UV) and visible light wavelength regions are fabricated using a hydrogen etching process. The fabricated Si nanostructures have aperiodic subwavelength structures with pyramid-like morphologies. The detailed morphologies of the nanostructures can be controlled by changing the etching condition. The nanostructured Si exhibited much more reduced reflectance than a flat Si surface: an average reflectance of the nanostructured Si was approximately 6.8% in visible light region and a slight high reflectance of approximately 17% in UV region. The reflectance was further reduced in both UV and visible light region through the deposition of a poly(dimethylsiloxane) layer with a rough surface on the Si nanostructure: the reflectance can be decreased down to 2.5%. The enhancement of the antireflection properties was analyzed with a finite difference time domain simulation method.

Role of Titanium replacement with Pd atom on band gap reduction in the anatase Titanium Dioxide: First-Principles calculation approach