第一性原理研究N/V 和 C/Cr双掺杂锐钛矿型TiO2光催化剂的协同效应

非金属（C或N）和过渡金属（V或Cr）掺杂是一种能够有效地调整锐钛矿型TiO2的光电化学性能的补偿型掺杂方法。本文采用平面波超软赝势方法计算了不同物种掺杂的补偿型双掺杂TiO2的形成能和电子结构来研究其稳定性和在可见光区域的光敏性,计算结果表明采用过渡金属双掺杂有利于提高p型掺杂（N和C）的浓度。尤其是补偿型掺杂不仅可以通过减小能隙来提高光吸收性能,消除局域捕获来提高载流子的移动和转化效率,并且能够保持导带边缘的氧化还原势。这些结果有助于理解双掺杂提高TiO2光催化活性的协同作用机制。     

N 和 Fe 共掺杂对TiO2电子结构和光学性质影响的第一性原理研究

本文采用基于密度泛函理论的第一性原理研究了N 和 Fe共掺杂锐钛矿相TiO2的电子结构和光学特性。计算结果表明,不同位置N 和 Fe共掺杂影响共掺TiO2的稳定性。通过态密度讨论了掺杂TiO2带隙变窄的机理。 不同位置N 和 Fe共掺杂影响了可见光吸收。N 和 Fe共掺杂的协同效应导致了可见光吸收的增强。因此,N 和 Fe共掺杂也许增强TiO2在可见光区的光催化能力。     

Reactive pulsed laser deposited N–C codoped TiO2 thin films

TiO₂ is a large bandgap chemically stable oxide useful for several applications that involve photo-activated processes, including photocatalysis, photovoltaics, photoelectrolysis, etc. However, the large band gap renders this material not a very efficient absorber of the solar spectrum. Various schemes of cation and anion doping have been utilized that reduce this deficiency to a certain extent. In this paper we present the results of N–C codoping of TiO₂ thin films deposited by a reactive pulsed laser deposition technique. These films were compared for their optical and structural properties with undoped, N doped and C doped TiO₂ films prepared by the same technique. While all samples contained polycrystalline anatase phase, varying N₂ and CH₄ partial pressures resulted in change in TiO₂ lattice parameters due to codoping. X-ray diffraction high-resolution scans show the evidence of C incorporation into TiO₂ lattice by 2θ shift in (101) reflections due to large ionic radius of C. N doping was confirmed by XPS analyses. Direct relationship between oxygen vacancies and doping concentration was established by the deconvolution of XPS peaks. Considerable bandgap reduction occurred that was measured by using UV–vis diffuse reflectance spectroscopy. Results show that reactive pulsed laser deposition is indeed a useful method for the synthesis of codoped TiO₂ thin films as bandgap reduction of ~1.00 eV via N–C codoping was successfully achieved.     

碱金属掺杂SnO2材料的电子结构和光学性质

文章基于第一性原理研究了碱金属掺杂的SnO2的能带结构以及态密度.研究结果表明:掺杂能够使能级增多,很好地调节带隙值.Li,Na,K,Rb掺杂的SnO2材料,价带顶有能级穿过费米线,材料呈现出半导体特性.其中Rb掺杂使材料在费米面附近产生杂质能级.而Cs,Fr掺杂的SnO2材料,价带顶向低能级方向移动,费米能级不再穿过价带,费米线附近出现轨道杂化,两者相比Fr掺杂使费米面附近能级分布更加离散.掺杂后SnO2的反射率变化主要体现在可见光以及紫外区域,吸收边发生了红移,对实现SnO2光催化起很大作用.     

Oxygen Rich Titania: A Dopant Free,High Temperature Stable,and Visible‐Light Active Anatase Photocatalyst

The simultaneous existence of visible light photocatalytic activity and high temperature anatase phase stability up to 900 °C in undoped TiO₂ is reported for the first time. These properties are achieved by the in‐situ generation of oxygen through the thermal decomposition of peroxo‐titania complex (formed by the precursor modification with H₂O₂). Titania containing the highest amount of oxygen (16 H₂O₂‐TiO₂) retains 100% anatase phase even at 900 °C, where as the control sample exists as 100% rutile at this temperature. The same composition exhibits a six‐fold and two‐fold increase in visible light photocatalytic activities in comparison to the control sample and the standard photocatalyst Degussa P‐25 respectively. Among the various para­meters affecting the photocatalytic action, such as band gap narrowing, textural properties, crystallite size, and anatase phase stability, band gap narrowing was identified as the major factor responsible for the visible light photocatalytic activity. Increased Ti–O–Ti bond strength and upward shifting of the valence band (VB) maximum, which is responsible for the high temperature stability and visible light activity respectively, are identified from FT–IR, XPS, and photoluminescence (PL) spectroscopic studies. It is therefore proposed that the oxygen excess defects present in these titania samples are responsible for the high temperature stability and enhanced visible light photocatalytic activities.     

A Theoretical Search for Efficient Dopants in Mg<Subscript>2</Subscript>X (X = Si,Ge, Sn) Thermoelectric Materials

Intentional alloying and doping are well-established ways of improving the thermoelectric properties of Mg₂X (X = Si, Ge, Sn). In this study the results of electronic structure calculations for alloying and impurity dilution are presented. We have adapted the fully self-consistent Korringa–Kohn–Rostoker method with the coherent potential approximation (KKR-CPA) to treat various types of chemical disorders and to calculate an electronic band structure with complex energy. In Mg₂Si_1−x Sn _x , as the Sn content increases, the conduction and valence bands near the Fermi energy tend to overlap but do not cross each other. In contrast, in Mg₂Si_1−x Ge _x , an energy gap was detected for 0 ≤ x ≤ 1. Moreover, the site preference of selected impurities (Al, P, Zn, Ga, Ag, Cd, In, Sb) in Mg₂Si is discussed in view of total energy calculations. It was found that In, Cd, Ag, and Zn preferentially occupy the Mg site, whereas in other cases site selectivity markedly depends on impurity amount as well as chemical potentials. The sign of the thermopower in the doped systems is analyzed from the position of the Fermi level with respect to valence/conduction band edges. The Seebeck coefficient was estimated from the simplified Mott formula at standard dopant concentrations, diluted at both crystallographic sites in Mg₂Si.     

Low temperature synthesis of pure anatase carbon doped titanium dioxide: An efficient visible light active photocatalyst

Low temperature pure anatase Carbon Doped Titanium Dioxide (C-TiO₂) is successfully synthesized by using starch as an effective, economical, and nonhazardous carbon source. The synthesized C-TiO₂ has been further characterized by X-Ray Diffraction, SEM, TEM, BET, XPS and UV- DRS techniques, which reveal that the particles are crystalline with spherical morphology, high surface area and an optical band gap of 2.79 eV for C-TiO₂ calcined at 400 °C. Furthermore photocatalytic degradation of Rhodamine B dye was carried out using as-prepared C-TiO₂ under visible light irradiation. Prepared C-TiO₂ calcined at 200 °C and 400 °C show higher degradation efficiency (85% and 100% in 120 min respectively) as compared to that of undoped TiO₂ and commercial Degussa P-25. Result shows that the C-TiO₂ containing lower carbon percentage has higher photocatalytic activity. Thus enhanced photocatalytic activity of C-TiO_2, may be due to synergic effect of carbon doping and [101] facet enhanced synthesis of anatase C-TiO₂.     

基于密度泛函理论计算的3d过渡金属掺杂CuGaS2电子结构分析

3d transition metals doped CuGaS2 are considered as possible absorbing material candidates for intermediated band thin film solar cells. The electronic structure and optical properties of 3d transition metals doped CuGaS2 are investigated by using density functional theory calculations with the GGA ＋ U method in the present work. The doping with 3d transition metals does not obviously change the crystal structure, band gap, and optical absorption edge of the CuGaS2 host. However, in the case of CuGa1-χTMχS2 （TM = Ti, V, Cr, Fe, and Ni）, there is at least one distinct isolated impurity energy level in the band gap, and the optical absorption is enhanced in the ultraviolet-light region. Therefore, these materials are band thin film solar ceils. The calculated results are very well better explain them. ideal absorber material candidates for intermediated consistent with experimental observations, and could better explain them.     

Nitrogen doped anatase TiO2 sheets with dominant {001} facets for enhancing visible-light photocatalytic activity

The photocatalytic activity of TiO₂ can be mainly improved from three approaches: (1) enhancing surface energy; (2) increasing availability of visible light and (3) improving the separation efficiency of photo-induced electrons and holes. Here, we report a one-step route to obtain nitrogen (N) doped TiO₂ sheets with dominant {001} facets by a hydrothermal process. The XRD patterns confirm the better crystallinity. XPS spectrums show nitrogen acting as interstitial N or an O–Ti–N structure in TiO₂ sheets. Compared with that of TiO₂ sheets, the N doped TiO₂ sheets not only absorb visible light, but also have a large percentage of high reactive {001} facets, so the photocatalytic activities are greatly enhanced, as confirmed by the decomposition of methylene orange.     

掺杂对二维SiC材料光电性质的影响

利用第一性原理赝势平面波方法计算了Si-C邻 近元素(B、N、Al、P)掺杂二维SiC的几何结构、 电子结构和光学性质。结果表明:掺杂后的二维SiC晶格常数(a、b)、键长及角度均发生了明显变化;同时, 在禁带中引入了杂质能级,导带和价带均向低能方向发生了明显的移动,带隙发生变化,费 米能级附近引入了 杂质的2p及3p态电子。光学性质的计算表明:在低能端B、N、Al掺杂使二维SiC吸收电磁波 的能力明显增 强;静态介电常数增大而能量损失峰降低。以上结果说明可以根据需要利用B、N、Al、P掺 杂来调制二维SiC材料的光电性质。     

Se和Cd掺杂GaN电子结构与光学性质的第一性原理研究

基于密度泛函理论的第一性原理,使用GGA+U方法分别计算Se和Cd单掺与共掺杂GaN体系的晶格常数、电子结构及光学性质.结果表明:与本征GaN相比,掺杂后体系的晶格常数发生了改变,禁带宽度减小,吸收光谱均发生红移,表明掺杂使体系的光谱响应范围得到更大拓展.其中,Cd单掺GaN体系的禁带宽度最小,并在费米能级附近有杂质能...     

Structure,luminescence and photocatalytic activity of Mg-doped ZnO nanoparticles prepared by auto combustion method

A series of Zn_1−xMg_xO nanoparticles with x=0 to 0.15 were prepared by auto combustion method using citric acid as the fuel and chelating agent. Structure, luminescence and photocatalytic properties were systematically investigated by means of X-ray diffraction, scanning electron microscopy, photoluminescence spectra, ultraviolet–visible absorbance measurement and photochemical reactions etc. The samples retained hexagonal wurtzite structure of ZnO and single phase below x=0.13, and the sizes of the nanoparticles were 60–70 nm. The photoluminescence spectroscopy demonstrated blue shift of ultraviolet emission with increasing Mg doping concentration. Both optical measurements of the as grown and Mg doped ZnO nanoparticles showed that the optical band gap could be modified from ~3.28 eV to 3.56 eV as the Mg content x increased from 0 to 0.13. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange, and the results showed that the doping of Mg into ZnO nanoparticles could enhance photocatalytic activity compared to the undoped ZnO nanoparticles, which was attributed to increased band gap and superior textural properties. In addition, according to the PL and photocatalytic studies, the critical doping content of effective Mg in ZnO is up to 0.09.     

Cobalt-doped cerium oxide nanoparticles: Enhanced photocatalytic activity under UV and visible light irradiation

CeO₂ nanoparticles (NPs) were synthesized by coprecipitation using cerium(III) nitrate hexahydrate as the precursor and ethanol as the solvent. Different concentration of cobalt-doped cerium oxide NPs (3mol % and 6 mol %) were prepared by adding various concentrations of cobalt chloride to cerium nitrate. The as-synthesized NPs were characterized through X-ray diffraction (XRD) measurements, ultraviolet (UV)–visible spectroscopy, Photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). XRD results reveal that the as-prepared CeO₂ NPs had a face-centered cubic structure with crystallite size in the range of 5–8 nm. TEM analyses showed that the CeO₂ NPs and Co-doped CeO₂ NPs had a homogenous size distribution (sizes were within 5–12 nm). Band-edge absorption of CeO₂ NPs redshifted upon increasing the Co concentration as compared to undoped CeO₂ NPs. PL spectra reveal a peak shift of CeO₂ emission upon cobalt doping, which were due to an increase in oxygen defects localized between the Ce4f and O2p energy levels (i.e., via formation of Ce³⁺ states). Photocatalytic degradation of methylene blue in aqueous solution under UV and visible (sunlight) irradiation in the presence of pure CeO₂ NPs and of Co-doped CeO₂ NPs was investigated. The efficiency of photocatalytic degradation of CeO₂ NPs increased with the Co concentration both under UV irradiation and under visible light. Co-doped CeO₂ NPs (6 mol%) showed degradation efficiencies of 98% and 89% at 420 min of exposure to UV irradiation and to visible light, respectively.     

Localized states in Hg3In2Te6: Cr compounds

The effect of chromium doping on the energy spectrum of the density of states N(E) in the band gap of the Hg₃In₂Te₆ semiconductor compound was studied. Although the chromium impurity has no significant effect on the electrical properties and the Fermi level position, it increases the band tail extent and the density of localized states within the band gap E _g . Comparison of the data on the field effect and on light absorption for photon energies hν lower than E _g made it possible to ascertain that the density of states is distributed continuously and rapidly increases near the edges of the valence and conduction bands. The obtained spectra are discussed on the assumption that the chromium content growth increases the structure disorder and the random potential, which increases N(E). It is shown that localized states control the screening length and pin the Fermi level near the midgap and are also responsible for the compensation of impurity ion charges.     

Zero-valent nanophase iron and nitrogen co-modified titania nanotube arrays: Synthesis,characterization, and enhanced visible-light photocatalytic performance

We prepared nano-zero-valent iron (nZVI) and N co-modified TiO₂ (nZVI/N–TiO₂) nanotube arrays as an enhanced visible-light photocatalyst. The TiO₂ nanotube arrays were synthesized by electrochemical anodization of Ti foil in a two-electrode system. Amorphous TiO₂ nanotube arrays were immersed in ammonia and then annealed to produce crystalline N-doped TiO₂ (N–TiO₂) nanotube arrays. nZVI spheres were directly deposited on the N–TiO₂ nanotube arrays by borohydride reduction. The photocatalysts were characterized by field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and electrochemical impedance spectroscopy (EIS). The environmental applicability and photocatalytic activity of the proposed nZVI/N–TiO₂ nanotube arrays were tested by phenol degradation in an aqueous system under UV and visible light irradiation. The phenol degradation rate constants of each sample under visible light irradiation were in the following order: nZVI/N–TiO₂ (k_obs=0.006 min⁻¹⁾>N–TiO₂ (k_obs=0.002 min⁻¹) ⪢ nZVI/TiO₂ (k_obs=0.0003 min⁻¹)>TiO₂ (k_obs=0.0001 min⁻¹). This result can be attributed to the synergistic effect of the N–TiO₂ nanotubes with lower energy band gap and the electron transfer from the conduction band (CB) of N–TiO₂ to nZVI spheres highly-dispersed on the N–TiO₂ for enhanced separation of photogenerated electrons and holes.     

Enhanced Electron Mobility Due to Dopant‐Defect Pairing in Conductive ZnMgO

The increase of the band gap in Zn_1‐xMg_xO alloys with added Mg facilitates tunable control of the conduction band alignment and the Fermi‐level position in oxide‐heterostructures. However, the maximal conductivity achievable by doping decreases considerably at higher Mg compositions, which limits practical application as a wide‐gap transparent conductive oxide. In this work, first‐principles calculations and material synthesis and characterization are combined to show that the leading cause of the conductivity decrease is the increased formation of acceptor‐like compensating intrinsic defects, such as zinc vacancies (V_Zn), which reduce the free electron concentration and decrease the mobility through ionized impurity scattering. Following the expectation that non‐equilibrium deposition techniques should create a more random distribution of oppositely charged dopants and defects compared to the thermodynamic limit, the paring between dopant Ga_Zn and intrinsic defects V_Zn is studied as a means to reduce the ionized impurity scattering. Indeed, the post‐deposition annealing of Ga‐doped Zn_0.7Mg_0.3O films grown by pulsed laser deposition increases the mobility by 50% resulting in a conductivity as high as σ = 475 S cm^‐1.     

Valency configuration of transition metal impurities in ZnO

We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM=Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn_1−xTM_xO, the localized TM²⁺ configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy ε_F close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with ε_F close to the valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.     

Enhanced visible light-photocatalysis by hydrothermally synthesized thallium-doped bismuth vanadate nanoparticles

Thallium-doped (1.5, 2.3 and 19.3 at%) bismuth vanadate (BiVO₄) and pristine BiVO₄ nanoparticles were hydrothermally synthesized. They were characterized by powder X-ray and selected area electron diffractometries, high resolution scanning electron and transmission electron microscopies, and energy dispersive X-ray, Raman, UV–visible diffuse reflectance and photoluminescence spectroscopies. Tl-doping reduces the band gap energy and recombination of charge carriers. The visible light photocatalytic activity of 19.3% Tl-doped BiVO₄ nanoparticles is larger than those of the other Tl-doped BiVO₄ and pristine BiVO₄ nanoparticles. The synthesized Tl-doped BiVO₄ nanoparticles displaying enhanced photodegradation of dye could find potential applications as visible light photocatalyst for the abatement of various organic pollutants.     

A new approach to regulate the photoelectric properties of two-dimensional SiC materials:first-principles calculation on B-N co-doping

This paper describes a new approach to regulate the photoelectric properties of two-dimensional SiC materials. The first-principles pseudo-potential plane wave method is used to calculate the geometric structure, electronic structure and optical properties of two-dimensional (2D) SiC co-doped by the adjacent elements of C-Si (such as B and N). The results show that:after B-N co-doping, the supercell lattices of 2D SiC are observed obviously deformation near the doped atoms. Meanwhile, the band structures of 2D SiC co-doped by B-N become rich. As the impurity level enters the forbidden band, the band gap decreases, and the distribution of density of states near the Fermi level changes accordingly. The calculation of optical properties shows that the ability to absorb electromagnetic waves of 2D SiC has been enhanced obviously in the low energy range after B-N co-doping. The reason is originated from the transition of the 2p state of B and N. At the same time, the static dielectric constant increases and the peak of reflectivity decreases. The above results indicate that the optoelectronic properties of 2D SiC can be modulated by co-doping B-N.     

N掺杂和氧空位对PbTiO3电子结构和导电性的影响研究

用第一性原理计算了P型N掺杂PbTiO3的电子密度差分、能带结构和态密度,讨论了氧空位对N掺杂PbTiO3性能的影响。在PbTiO3中掺杂N杂质后,PbTiO3的价带向高能级发生移动,费米能级进入价带顶部,带隙变窄,N掺杂PbTiO3表现出典型的P型半导体性能。当N掺杂PbTiO3中含有氧空位时,导带发生下移,受主被完全补偿。计算结果与实验数据相吻合。