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.     

空位缺陷金红石型TiO2电子结构和光学性质的理论研究

基于密度泛函理论(DFT)的第一性原理模守恒赝势 方法,对纯金红石型TiO₂和Ti、O两种空位缺 陷相的几何结构、能带结构、态密度(DOS)以及光学性质进行了 系统地对比研究。结果发现,含有空 位缺陷的TiO₂键长增大,原子布局值减小并出现微弱的磁性;空位缺陷导致导带变窄,导 带和价带 都向低能级方向移动,由空位原子贡献的载流子增强了体系的电导率,费米能级上移进入导 带;与 纯金红石型TiO₂的直接带隙宽度(3.0eV)相比较,Ti空位缺陷相转 变为P型半导体且直接带隙为1.816 eV,而O空位缺陷相转变为n型半导体且间接带隙为1.961eV。同时, 两种空位缺陷结构的介电峰显 著红移,折射率有明显变化,对可见光区的吸收系数均比纯TiO₂高。与O空位结构相比,Ti 空位结构的 介电常数、折射率、消光因子和对可见光的吸收强度更大,更能增强电子在低能端的光学跃 迁,具有更佳的可见光催化性能。     

Density functional theory study of tin and titanium dioxides: Structural and mechanical properties in the tetragonal rutile phase

Structural and mechanical properties in rutile (tetragonal) phases of SnO₂ and TiO₂ are investigated by performing first-principle density functional theory (DFT) calculations. Generalized Gradient Approximation (GGA) potentials of electronic exchange and correlation part parameterized by Perdew–Burke–Ernzerhof (PBE) are used. Second order elastic stiffness constants, bulk modulus, first-derivative of bulk modulus, and pressure behavior of these mechanical properties are studied up to pressure of 10 GPa. Structural properties and elastic constants of SnO₂ and TiO₂ calculated in this study are compatible with experimental and other available theoretical studies. Electronic band gap energies of these semiconductors are also calculated. As expected, the calculated values by standard DFT calculations are underestimated in comparison to experimental values.     

Local electronic structure,optical bandgap and photoluminescence (PL) properties of Ba(Zr0.75Ti0.25)O3 powders

Ba(Zr_0.75Ti_0.25)O₃ (BZT-75/25) powders were synthesized by the polymeric precursor method. Samples were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques. Their electronic structures were evaluated by first-principle quantum mechanical calculations based on density functional theory at the B3LYP level. Their optical properties were investigated by ultraviolet-visible (UV-Vis) spectroscopy and photoluminescence (PL) measurements at room temperature. XRD patterns and Rietveld refinement data indicate that the samples have a cubic structure. XANES spectra confirm the presence of pyramidal [TiO₅] clusters and octahedral [TiO₆] clusters in the disordered BZT-75/25 powders. EXAFS spectra indicate distortion of Ti–O and Ti–O–Ti bonds the first and second coordination shells, respectively. UV-Vis absorption spectra confirm the presence of different optical bandgap values and the band structure indicates an indirect bandgap for this material. The density of states demonstrates that intermediate energy levels occur between the valence band (VB) and the conduction band (CB). These electronic levels are due to the predominance of 4d orbitals of Zr atoms in relation to 3d orbitals of Ti atoms in the CB, while the VB is dominated by 2p orbitals related to O atoms. There was good correlation between the experimental and theoretical optical bandgap values. When excited at 482 nm at room temperature, BZT-75/25 powder treated at 500 °C for 2 h exhibited broad and intense PL emission with a maximum at 578 nm in the yellow region.     

Effect of sputtering power on optical properties of prepared TiO2 thin films by thermal oxidation of sputtered Ti layers

In this research, TiO₂ thin films prepared via thermal oxidation of Ti layers were deposited by RF-magnetron sputtering method at three different sputtering powers. The effects of sputtering power on structure, surface and optical properties of TiO₂ thin films grown on glass substrate were studied by X-ray diffraction (XRD), atomic force microscopic (AFM) and UV–visible spectrophotometer. The results reveal that, the structure of layers is changed from amorphous to crystalline at anatase phase by thermal oxidation of deposited Ti layers and rutile phase is formed when sputtering power is increased. The optical parameters: absorption coefficient, dielectric constants, extinction coefficient, refractive index, optical conductivity and dissipation factor are decreased with increase in sputtering power, but increase in optical band gap is observed. The roughness of thin films surface is affected by changes in sputtering power which is obtained by AFM images.     

Hf掺杂锐钛矿TiO2电子结构的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法对Hf掺杂锐钛矿型TiO2的电子结构进行了第一性原理研究。对通过对能带和电子态密度的分析,发现在Hf掺杂后,导带底和价带顶同时降低,但是由于价带顶下降的比导带底多,从而使得锐钛矿型TiO2的禁带宽度变窄。     

Preparation and characterization of TiO2 thin film by thermal oxidation of sputtered Ti film

Titanium dioxide (TiO₂) thin films were successfully prepared on quartz substrate by thermal oxidation of sputtered titanium film in air. The structure, composition, morphology and optical properties of oxidized TiO₂ films were characterized by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and UV-visible spectroscopy. Meanwhile, the photocatalytic activity of the films was evaluated on the basis of the degradation of methyl orange solution under UV irradiation. Ti films after oxidation present mainly in TiO₂ form with a larger amount of adsorbed O₂, and oxidation temperature has a strong impact on the crystal structure and properties of the films. A phase transformation of anatase to rutile for oxidized TiO₂ films occurred in the temperature range of 700–800 °C. The energy band gap of oxidized TiO₂ films decreased first and then increased with annealing temperature. Furthermore, TiO₂ film oxidized at 600 °C exhibited the best photocatalytic activity due to suitable crystal phase and size. These results might contribute to the synthesis of metal oxide thin films with expectant structural morphology and properties by thermal oxidation methods.     

Syntheses,Li Insertion,and Photoactivity of Mesoporous Crystalline TiO2

Ordered mesoporous rutile and anatase TiO₂ samples are prepared using mesoporous silica SBA‐15 as template and freshly synthesized titanium nitrate and titanium chloride solutions as precursors. The rutile material formed from the nitrate solution is monocrystalline and contains minimal amounts of Si with a Si:Ti ratio of 0.031(4), whereas the anatase material formed from the chloride solution comprises nanocrystals and contains a higher content of Si with a Si:Ti ratio of 0.18(3). It is found that control of temperature and selection of Ti‐containing precursor play important roles in determining the crystal phase and crystallinity. A possible formation mechanism of porous crystalline TiO₂ is suggested. Characterization of these porous materials is performed by XRD, HRTEM, and nitrogen adsorption/desorption. SBA‐15‐templated mesoporous rutile TiO₂ exhibits a higher Li ion insertion capability than KIT‐6‐templated TiO₂ due to its larger surface area. Likewise mesoporous anatase TiO₂:SiO₂ composite has a better photoactivity than bulk TiO₂ or TiO₂‐loaded SBA‐15 for bleaching methylene blue.     

Tuning the Phase and Microstructural Properties of TiO<Subscript>2</Subscript> Films Through Pulsed Laser Deposition and Exploring Their Role as Buffer Layers for Conductive Films

Titanium oxide (TiO₂) is a semiconducting oxide of increasing interest due to its chemical and thermal stability and broad applicability. In this study, thin films of TiO₂ were deposited by pulsed laser deposition on sapphire and silicon substrates under various growth conditions, and characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), optical absorption spectroscopy and Hall-effect measurements. XRD patterns revealed that a sapphire substrate is more suitable for the formation of the rutile phase in TiO₂, while a silicon substrate yields a pure anatase phase, even at high-temperature growth. AFM images showed that the rutile TiO₂ films grown at 805°C on a sapphire substrate have a smoother surface than anatase films grown at 620°C. Optical absorption spectra confirmed the band gap energy of 3.08 eV for the rutile phase and 3.29 eV for the anatase phase. All the deposited films exhibited the usual high resistivity of TiO₂; however, when employed as a buffer layer, anatase TiO₂ deposited on sapphire significantly improves the conductivity of indium gallium zinc oxide thin films. The study illustrates how to control the formation of TiO₂ phases and reveals another interesting application for TiO₂ as a buffer layer for transparent conducting oxides.     

锐钛矿TiO2(101)面电子性质和光学性质的第一性原理研究

The TiO₂（101） surface was studied using the plane-wave ultrasoft pseudopotential method based on the density functional theory,with emphasis on the structure,surface energy,band structure,density of states, and charge population.The anatase TiO₂（101） crystal surface structure,whose outermost and second layers were terminated by twofold coordinated oxygen atoms and fivefold coordinated titanium atoms,was found to be much more stable.The surface energy of the 18-layer atoms model was 0.580 J/m2.The surface electronic structure was similar to that of the bulk and no surface state.Compared with the bulk structure,the band gap increased 0.36 eV, the Ti5c-02c bond lengths reduced 0.171（?） after relaxation,and the charges of the surface were transferred to the body.Analysis of the optical properties of the TiO₂（101） surface showed that it did not absorb in the low-energy region.An absorption edge in the ultraviolet region corresponding to the energy of 3.06 eV was found.     

Photoemission Electron Microscopy of TiO2 Anatase Films Embedded with Rutile Nanocrystals

Photoemission electron microscopy (PEEM) excited by X‐ray and UV sources is used to investigate epitaxial anatase thin films with embedded rutile nanocrystals, a model system for the study of heterocatalysis on mixed‐phase TiO₂. Both excitation sources show distinct contrast between the two TiO₂ phases; however, the contrast is reversed. Rutile nanocrystals appear darker than the anatase film in X‐ray PEEM images but brighter in UV‐PEEM images. We observe that topography‐induced contrast is dominant in X‐ray PEEM imaging, whereas work function and density‐of‐state‐based contrast, dominates in UV‐PEEM. This assertion is confirmed by UPS and conducting AFM data that shows the rutile work function to be 0.2 eV lower and a greater occupied valence band density‐of‐states in rutile (100) than in anatase (001). Since the boundaries between rutile nanocrystals and the anatase film are clearly resolved, these results indicate that PEEM studies of excited state dynamics and heterocatalysis are possible at chemically intriguing mixed‐phase TiO₂ interfaces and grain boundaries.     

Molybdenum-Loaded Anatase TiO<Subscript>2</Subscript> Nanoparticles With Enhanced Optoelectronics Properties

The structural, optical and electrical properties of molybdenum nanoparticles (Mo-NPs)-loaded anatase TiO₂ were investigated using x-ray diffraction, UV–Vis diffuse reflectance, and Fourier transform infrared and complex impedance spectroscopy. x-ray diffraction showed that Mo-NPs incorporation induced a decrease in particle size from 30 nm to 21 nm of TiO₂ and TiO₂-Mo, respectively, producing a slight structure expansion. Mo-NPs dispersion resulted in a slight decrease in the optical band gap energy from 3.85 eV to 3.51 eV. Slight shifts towards higher wavelengths were attributed to the change in the acceptor capacity level induced by Mo-NPs. In addition, the ac impedance studies show the effect of Mo-NPs incorporation that appeared to be responsible for conductance of enhancement. The conduction mechanism is based on space charge-limited current via deep levels with different energy positions in the band gap. The temperature dependence of electrical properties showed that both capacitance and conductance of TiO₂-Mo samples increased with increasing temperature. At low frequency, the relaxation phenomenon is related to the surface effect. The results will be beneficial to further developing titanium dioxide photo-catalysts.     

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。     

Capturing transiently charged states at the C60/TiO2(110) interface by time-resolved soft X-ray photoelectron spectroscopy

Time-resolved soft X-ray photoelectron spectroscopy is utilized to determine an energy level alignment and the photoexcited carrier dynamics at a C₆₀/TiO₂(110) interface. The interface electronic structure is characterized by a type II junction, which favors an injection of photoexcited electrons from C₆₀ to TiO₂. Ultraviolet (UV) laser pulse irradiation induces transient shifts of both C 1s and Ti 2p core levels towards the higher binding energies. These energy shifts are caused by a laser-induced charge transfer between the C₆₀ layer and the TiO₂(110) surface. Upon UV absorption, valence electrons of C₆₀ are promoted to unoccupied levels, followed by a resonant transfer to TiO₂, leaving C₆₀ in a cationized state. On the TiO₂(110) side, the electrons are injected into the conduction band to raise the carrier density so that downward bending of the TiO₂ band is induced. The UV-excited states of C₆₀ and TiO₂ have sufficiently longer lifetime than the lifetime of the electron–hole pairs in solid C₆₀. The C₆₀/TiO₂(110) interface is, thus, proved to be efficient for separating the electron–hole pairs generated within the C₆₀ layer.     

First principle study of Nb defects in anatase (101) TiO2 surface

In this work, effects of Niobium (Nb) defects on TiO₂ surface using density functional theory (DFT) are investigated. Based on formation energy of the defects, their occurrences in two different extreme conditions, O-rich and O-poor conditions, are evaluated. Effects of Nb defects on surface and its electronic structure are studied and it is demonstrated that Nb doping widens valence band in deep energy level leaving the band gap without any change and it also lowers oxygen vacancy defect concentration due to the stronger bonding of Nb_sub defect with oxygen atoms specially bridging oxygen (most probable defect site for Oxygen vacancy). Higher density of Nb substitutional defects (Nb_sub) are examined and it is shown that higher density doping of TiO₂ surface leads to uniform distribution of defects over the anatase structure as a result of interaction of Nb defects when they are close and this fact prevents segregation of Nb atoms in Nb-doped TiO₂.     

Hydrothermal synthesis of TiO2 nanosheets photoelectrocatalyst on Ti mesh for degradation of norfloxacin: Influence of pickling agents

TiO₂ nanosheets (TiO₂-NSs) photoanodes were synthesized on the surface of Ti meshes via the hydrothermal method, and then washed by HCl, HNO₃ and H₃PO₄, respectively. The TiO₂-NSs washed by different pickling agents were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electrons microscopy (SEM), and UV–vis diffuse reflectance spectra (DRS). The results showed that P and N were transferred into the lattice of TiO₂. The TiO₂-NSs samples washed by HCl and HNO₃ both had a mixture of anatase and rutile structures, while the TiO₂-NSs washed by H₃PO₄ only contained anatase phase. It could be concluded that H₃PO₄ pickling inhibited the formation of rutile phase. Moreover, TiO₂-NSs washed by HNO₃ (TiO₂-NSs-HNO₃) exhibited the strongest light absorption ability in visible region. Photoelectrochemical properties of the TiO₂-NSs photoelectrodes washed by different agents were investigated via transient photocurrent response (TPR), open-circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). The photocatalytic (PC) and photoelectrocatalytic (PEC) performances were evaluated by the degradation of norfloxacin and the yield of •OH radicals in the reactors. The results showed that the TiO₂-NSs-HNO₃ photoelectrode revealed the highest photoinduced current of 1.08 mA/cm², open-circuit photovoltage of −0.22 V, PEC efficiency of 93% for the removal of norfloxacin. In addition, the enhanced PEC mechanism for TiO₂-NSs-HNO₃ was proposed. The high PEC activity of TiO₂-NSs-HNO₃ could be attributed to the introduction of N during acid-washing procedure, which could not only reduce the band gap energy but also accelerate the separation and transportation of photogenerated charge carriers.     

二氧化钛掺杂系统的电子结构和光学性质的研究

采用总能量平面波赝势方法研究了Sc掺杂、含氧空位、氧空位与Sc掺杂共存时的锐钛矿TiO2系统的电子结构和光学性质。结果表明,Sc掺杂对系统的主要贡献在价带区,在可见光区有明显的光吸收;氧空位可以使系统发生莫特相变,系统在可见光区也有较强的吸收;氧空位与Sc掺杂共存时系统在可见光区的吸收相干加强。     

First-Principles Study of Electronic Structure,Mechanical, and Thermoelectric Properties of Ternary Palladates CdPd<Subscript>3</Subscript>O<Subscript>4</Subscript> and TlPd<Subscript>3</Subscript>O<Subscript>4</Subscript>

Ternary palladates CdPd₃O₄ and TlPd₃O₄ have been studied theoretically using the generalized gradient approximation (GGA), modified Becke–Johnson, and spin–orbit coupling (GGA–SOC) exchange–correlation functionals in the density functional theory (DFT) framework. From the calculated ground-state properties, it is found that SOC effects are dominant in these palladates. Mechanical properties reveal that both compounds are ductile in nature. The electronic band structures show that CdPd₃O₄ is metallic, whereas TlPd₃O₄ is an indirect-bandgap semiconductor with energy gap of 1.1 eV. The optical properties show that TlPd₃O₄ is a good dielectric material. The dense electronic states, narrow-gap semiconductor nature, and Seebeck coefficient of TlPd₃O₄ suggest that it could be used as a good thermoelectric material. The magnetic susceptibility calculated by post-DFT treatment confirmed the paramagnetic behavior of these compounds.     

Tuning the Electronic Properties of Graphene Oxide Nanoribbons Through Different Oxygen Doping Configurations

The electronic properties of armchair graphene oxide nanoribbons (AGONRs) with different doped oxygen configurations are studied based on density functional theory using first principle calculations. The electronic properties of the AGONRs are tuned by different oxygen configurations for top edges, center, bottom edges and fifth width. The AGONRs for top-edge O doping configuration are indirect band gap semiconductors with an energy gap of 1.268 eV involving hybridization among C-2p and O-2s, 2p electrons and electrical conductivity of oxygen atoms. The center and bottom edges are direct band gap semiconductors with 1.317 eV and 1.151 eV, respectively. The valence band is contributed from C-2p, O-2p and H-1s for top-edge O doping. The electronic properties of AGONRs are changed due to localization in ?2.94 eV of O-2p states. The center O-doped AGONRs are n-type semiconductors with Fermi levels near the conduction band bottom. This is due to hybridization among C-2s, 2p and O-2p electrons. However, bottom-edge O-doped AGONRs are p-type semiconductors, due to the electrical conductivity of oxygen atoms. The fifth-width O-doped AGONRs are indirect band gap semiconductors with an energy gap of 0.375 eV. The projected density of states shows that the localization and hybridization between C-2 s, 2p, O-2p and H-1s electronic states are rising in the conduction band and valence band from the projected density of states. The localization is induced by O-2p electronic states at a Fermi level.     

Recent Progress in the Synthesis of Spherical Titania Nanostructures and Their Applications

Recent progress in the fabrication and application of diverse spherical titania nanostructures, including mesoporous spheres, spherical flaky assemblies, and dendritic particles of variable diameter and monodispersity in size, is summarized in this article. Utilizing different synthesis strategies, spherical titania nanostructures with tailored polymorphs (including amorphous, anatase, rutile, brookite and TiO₂‐B), particle sizes (from tens of nanometers to millimeters), monodispersity, porosity, and variable surface properties have been produced. Such spherical titania nanostructures show realized and potential applications in the areas of chromatographic separation, lithium‐ion batteries, dye‐sensitized solar cells, photocatalytic oxidation and water splitting, photoluminescence, electrorheological fluids, catalysis, gas sensing, and anticancer intracellular drug delivery. Gaining further understanding of both synthesis design and application of these materials will promote the commercialization of such spherical titania nanostructures in the future.