Enhanced photocatalytic performance of TiO2 particles via effect of anatase–rutile ratio

In the present work anatase–rutile transformation temperature and its effect on physical/chemical properties as well as photocatalytic activity of TiO₂ particles were investigated. The characterisation of the synthesised and annealed TiO₂ particles were determined by X-Ray Powder Diffraction (XRD), scanning electron microscope (SEM), dynamic light scattering (DLS) and Brunauer–Emmett–Teller surface area analysis (BET). The refraction in the ultraviolet–visible (UV–vis) range was assessed using a dual-beam spectrophotometer. The photocatalytic performance of the particles was tested on methylene blue solution. The XRD data indicated that the percentage of rutile increased with the annealing temperature and almost 100% of anatase transformed to rutile at 1000 °C. In addition, the phase transformation was a linear function of annealing temperature so phase composition of TiO₂ can be controlled by changing the annealing temperature. The SEM and BET results presented the increase of agglomerate size and the decrease of specific surface area with the increasing annealing temperature. This proved that anatase has smaller particle size and higher surface area than rutile. The photocatalytic activity of the annealed TiO₂ powders reduced with the increase of annealing temperature. The samples annealed at 900 °C and 925 °C with anatase: rutile ratio of 92:8 and 77:23, respectively, showed the best activity. These results suggested that the photocatalytic activity of TiO₂ particles is a function of phase composition. Thus it can be enhanced by changing its phase composition which can be controlled by annealing temperature.     

Effect of manganese ions concentration on the anatase–rutile phase transformation of TiO2 films

The phase structures of Ti_1?xMn_xO₂ (0?x<0.08) films synthesized by sol–gel spin coating have been investigated. The effect of Mn dopants on the stability of titanium dioxide (TiO₂) was studied by X-ray diffraction and Raman spectra for isochronally annealed samples. The increased Mn dopant concentration decreased the onset temperature of anatase–rutile (A–R) phase transformation. The calculated activation energy for the phase transformation decreased from 173.6 to 89.4 kJ/mol with Mn dopants concentration increasing from 0% to 7.51%. The Mn ions incorporated into the TiO₂ lattice reduce the rutile nucleation barrier and promote the nucleation rate.     

Structure,optical, and magnetic properties of rutile Sn1−xMnxO2 thin films

Sn_1?xMn_xO₂ (x ≤ 0.11) thin films were fabricated by sol–gel and spin-coated method on Si (1 1 1) substrate. X-ray diffraction revealed that single-phase rutile polycrystalline structure was obtained for x up to about 0.078. Evolution of the lattice parameters and X-ray photoelectron spectroscopy studies confirmed the incorporation of Mn³⁺ cations into rutile SnO₂ lattice. Optical transmission studies show that the band gap energy (E_g) broadens with the increasing of Mn content. Magnetic measurements revealed that all samples exhibit room temperature ferromagnetism (RTFM), which is identified as an intrinsic characteristic. Interestingly, the magnetic moment per Mn atom decreases with the increasing Mn content. The origin of RTFM can be interpreted in terms of the bound magnetic polaron model.     

First-principles study of the electronic and optical properties of the （Y,N）-codoped anatase TiO2 photocatalyst

First-principles plane-wave pseudopotential calculations are performed to study the geometrical structures,formation energies,and electronic and optical properties of Y-doped,N-doped,and(Y,N)-codoped TiO 2.The calculated results show that Y and N codoping leads to lattice distortion,easier separation of photogenerated electron-hole pairs and band gap narrowing.The optical absorption spectra indicate that an obvious red-shift occurs upon Y and N codoping,which enhances visible-light photocatalytic activity.     

Electrical conductivity of slightly reduced rutile between 2° and 370°K

Abstract

The electrical resistivity and the Hall coefficient of slightly reduced rutile crystals were measured in the temperature range between about 2 °K and 370 °K. The time of reduction treatments between 900 °C and 1300 °C was usually as long as 300 hrs, which assures the homogeneous reduction of crystals, The conduction mechanisms in three temperature ranges, i. e. 1. 9～3°K, 3～100°K and 100～250°K, were discussed in terms of lattice defects evidenced by ESR studies.     

Ab initio calculations of electronic structure of anatase TiO2

This paper presents the results of the self-consistent calculations on the electronic structure of anatase phase of TiO2. The calculations were performed using the full potential-linearized augmented plane wave method (FP-LAPW)in the framework of the density functional theory (DFT) with the generalized gradient approximation (GGA). The fullyoptimized structure, obtained by minimizing the total energy and atomic forces, is in good agreement with experiment.We also calculated the band structure and the density of states. In particular, the calculated band structure prefers an indirect transition between valence and conduction bands of anatase TiO2, which may be helpful for clarifying theambiguity in other theoretical works.     

Spectrum redshift effect of anatase TiO2 codoped with nitrogen and first transition elements

The electronic and optical properties, including band structure, density of states(DOS), absorption rate, refractive index, and dielectric function, of anatase TiO2 codoped with N and first transition elements are investigated using the plane wave pseudopotential method based on the density functional theory. The calculation results show that TiO2 codoping with N and first transition elements(Sc, V, Cr, Mn, and Fe) lead to significant reduction of conduction band relative to the Fermi level, reduction of band gap width, formation of new donor, and acceptor impurity levels below the conduction band and above the valence band, and cause some redshifts of optical absorption band edge with the amount of redshift decrease in the following order: N–Fe N–Cr N–Mn. Further, the synergistic effect of shallow donor and acceptor levels enhances light excitation for effective separation of electron–hole pairs and enhancement of light absorption ability, thereby increasing the TiO2 photocatalytic properties. This study reveals that the visible-light absorption ability of the codoped anatase TiO2 decreases in the order of N–Fe N–Cr N–Mn N–Sc N–V N, and does not monotonically follow the dopant atomic number. Especially, in N–Cr codoped TiO2, the 4s atomic orbit of Cr is not completely filled, which hybridized with the p electronic orbit most probably acts as photo-generated electron trap centers resulting in higher photocatalytic activity than that of N–Mn codoped TiO2.     

A structure study of copper oxide for monolayer dispersion of anatase supported

The monolayer dispersion of copper oxide on the surface of anatase and its effect on the properties have been studied by X-ray photoelectron spectroscopy(XPS) and X-ray extended absorption fine structure(EXAFS).XPS results give an utmost dispersion capacity of 7.2mg/gTiO2.Strong interactions between copper oxide and anatase can be seen from EXAFS results.The structure of the supported CuO species is strongly dependent on the amount of CuO loading.When the content of CuO loading is below the utmost dispersion capacity,the surface of CuO/TiO2 is dominated by the highly dispersed CuO species having no-Cu-O-Cu-chains,The copper ion is located in an octahedral coordination environment,and the Cu－O-coordination distance is much longer than that in pure crystalline CuO,when CuO loading is exceeds the utmost dispersion capacity,crystalline CuO is formed on the surface of CuO/TiO2,From the result of the sturcture study,it is Cu-O octahedral Coordination and coordination distance change in comparation with pure crystalline Cuo on the surface CuO/TiO2 that have catalytic activity.     

Surface reconstruction on stishovite Si02, HfO2 and rutile TiO2 （001）

This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO2, HfO2 and rutile TiO2 （001） by using classical molecular dynamics. It is found that these three surfaces relax instead of reconstruction at 0 K, and have little possibility to reconstruct below 40 K. Above 40 K, surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain. Several reconstruction patterns with approximate surface energies are found, and electrostatic potentials on them are also provided in comparison with possible microscopic results.     

HREM analysis of structure and defects in a Σ5 (210) grain boundary in rutile

The structure of a 5 (210) boundary in rutile was investigated by high resolution electron microscopy (HREM). The boundary was stepped with an average inclination of about 5° from the symmetrical (210) plane. The steps were associated with 1/5[210] DSC lattice dislocations accommodating a deviation of about 2° from the exact 5 misorientation of 53.1°, and resulting in a misorientation of 51°. The boundary topography, the location of structural units and the local symmetry were determined using pattern recognition techniques. Flat terraces between steps had a periodic 5 (210) structure which exhibited mirror glide symmetry. Image simulations showed best agreement with experimental images for a model structure with a rigid body shift of 0.21 nm parallel, and a 0.10 nm volume contraction normal to the interface. This structure requires a high density of defects or an excess of Ti ions, presumably of lower oxidation state.     

Effects of pressure on structural,electronic, and mechanical properties of α,β,and γ uranium

The first-principles methods have been employed to calculate the structural, electronic, and mechanical properties of the α, β, and γ phases of uranium under pressure up to 100 GPa. The electronic structure has been viewed in forms of density of states and band structure. The mechanical stability of metal U in the α, β, and γ phases have been examined.The independent elastic constants, polycrystalline elastic moduli, as well as Poisson's ratio have been obtained. Upon compression, the elastic constants, elastic moduli, elastic wave velocities, and Debye temperature of α phase are enhanced pronouncedly. The value of B/G illustrates that α and γ phases are brittle in ground state.     

The interfacial effect on ionic conduction of AgI–anatase TiO2 composites

AgI–anatase TiO₂ nanoparticle composites, (x)AgI–(1 ? x)anatase, with different porosities were fabricated over a wide range of 0–1 of AgI content. The electrical conductivity was measured at room temperature as function of AgI content (x) and porosity (p). The conductivity varies considerably with both x and p. In the vicinity of x = 0.4 and p = 0.31, the conductivity attains a maximum (2.5 × 10^? 3 S/cm). The conductivity is enhanced by three orders of magnitude in comparison with that of pristine AgI. The mechanism of the observed conductivity enhancement is discussed in the light of the scanning electron microscope images and X-ray diffraction patterns of the different (x)AgI–(1 ? x)anatase composites.     

Electronic structure and hot carrier relaxation in ⟨001⟩ anatase TiO2 nanowire

We present an electronic structure and non-adiabatic excited state dynamics study of ?001? anatase TiO₂ nanowire (NW) by combining density matrix formalism and ab initio electronic structure calculations. Our results show that quantum confinement increases the energy gap as the dimension of TiO₂ is reduced from the bulk to a NW with a diameter of several nanometres and that the probability of electronic transitions induced by lattice vibrations for the NW follows band gap law. The electron non-radiative relaxation to the bottom of the conduction band is involving Ti 3d orbitals, while the hole non-radiative relaxation of holes to the top of the valence band occurs by subsequent occupation of O 2p orbitals.     

Dependence of sonochemical parameters on the platinization of rutile titania – An observation of a pronounced increase in photocatalytic efficiencies

Using a standing wave sonochemical reactor (SWSR), the influences of parameters of ultrasonic power input, sonication time, sonication temperature and the amount of propanol (which generates the reducing radicals) were systemically investigated to ascertain and optimize the best conditions for the sonochemical reduction of Pt from its precursor hexachloroplatinic acid and then its deposition on rutile TiO₂ (platinization of rutile titania) catalysts. Catalytic activity of the prepared platinized catalysts was tested in the reaction of methyl orange degradation. The results of photocatalytic activity study in the degradation of methyl orange further demonstrate that sonochemically as-prepared Pt/TiO₂ catalysts show a pronounced increase (～2 times) in photodegradation, even with a deposition of small amounts of platinum (1.4 wt.%), as compared to the unsupported or naked rutile titania. Although there are various parameters that influence the sonochemical platinization of rutile titania, the present optimization results clearly indicate that the best photocatalytic degradation of methyl orange can be obtained when the experimental conditions of the preparation were with an input power of 50 W, an initial hexachloroplatinic acid volume of 70 ml (which results into 1.4 wt.% Pt on TiO₂), sonication time of 90 min, 0.18 g of propanol and a temperature of 10 °C were adopted. The method of ultrasound application to prepare metal supported semiconductors has many advantages such as convenience, safety and high efficiency. Furthermore, it is hopeful that this optimization study can also be extended to the generation of similar metal supported semiconductors.     

Pressure–temperature dependence of thermodynamic properties of rutile (TiO2): A first-principles study

Ab-initio calculations of thermal properties of rutile (TiO₂) have been performed by using the projector augmented-wave (PAW) method within the generalized gradient approximation (GGA). Both pressure- and temperature-dependent thermodynamic properties such as the bulk modulus, thermal expansion, thermal expansion coefficient, heat capacity at constant volume and constant pressure were calculated using two different models based on the quasiharmonic approximation (QHA): the Debye–Slater and Debye–Grüneisen model with Dugdale–MacDonald (DM) approximation. Also, the empirical energy corrections were applied to the results to correct the systematic errors introduced by the functional. It is found that the Debye–Grüneisen model provides more accurate estimates than the Debye-Slater models, especially after empirical energy correction.     

Densities and mixing volumes of mixtures of fluorobenzene, α,α,α-trifluorotoluene, tert-butylmethyl ether, and ethanol at temperature 298.15 K and pressure 0.1 MPa

The volumetric properties were evaluated from density data for the binary mixtures of (fluorobenzene + tert-butylmethyl ether), (α,α,α-trifluorotoluene + tert-butylmethyl ether), (tert-butylmethyl ether + ethanol), and the ternary mixtures of (fluorobenzene + tert-butylmethyl ether + ethanol) and (α,α,α-trifluorotoluene + tert-butylmethyl ether + ethanol). The observed densities were obtained by means of a vibrating-tube densimeter at the temperature 298.15 K and the pressure 101 kPa.The excess molar volumes of the ternary mixtures were estimated from binary solution data using several empirical equations with mean standard deviation less than 0.03 cm³·mol^-1. Stable chemical cross-associations among the molecules forming the mixtures were revealed.     

Temperature dependence of pressure broadening and shifts of acetylene at 1550 nm by He, Ne, and Ar

Pressure broadening and shift coefficients for the ν₁+ν₃ band of ¹²C₂H₂ have been measured for He, Ne, and Ar at a temperature of 195 K using high resolution diode laser spectroscopy. The pressure broadening and shifts follow patterns with rotational assignment that are similar to those at room temperature but are generally larger in magnitude. The change in magnitude is qualitatively described by assuming, for each transition, a constant cross section for pressure broadening or shifting. Better agreement may be obtained for pressure broadening coefficients by using empirically determined temperature exponents; better agreement still is obtained from close coupling calculations of the pressure broadening cross sections. PACS 33.70.Jg     

Role of Ti 3d carriers in mediating the ferromagnetism of Co∶TiO2 anatase thin films

We study the surface and bulk electronic structure of the room-temperature ferromagnet Co∶TiO(2) anatase films using soft- and hard-x-ray photoemission spectroscopy with probe sensitivities of ～1 and ～10 nm, respectively. We obtain direct evidence of metallic Ti(3+) states in the bulk, which get suppressed to give a surface semiconductor, thus indicating the difference in electronic structure between surface and bulk. X-ray absorption and resonant photoemission spectroscopy reveal Ti(3+) electrons at the Fermi level (E(F)) and high-spin Co(2+) electrons occurring away from E(F). The results show the importance of the charge neutrality condition: Co(2+)+V(O)(2-)+2Ti(4+)?Co(2+)+2Ti(3+) (V(O) is oxygen vacancy), which gives rise to the elusive Ti 3d carriers mediating ferromagnetism via the Co 3d-O 2p-Ti 3d exchange interaction pathway of the occupied orbitals.     

Effect of ultrasound on the activity and conformation of α-amylase,papain and pepsin

The effect of ultrasound on the activity of α-amylase, papain and pepsin was investigated and the mechanism of the effect was explored by determining their conformational changes. With the irradiation of power ultrasound, the activity of α-amylase and papain was inhibited, while the activity of pepsin was activated. According to the analysis of circular dichroism, Fourier transform infrared and fluorescence spectroscopy, the π_o → π¹ amide transitions and secondary structural components, especially β-sheet, of these three enzymes were significantly influenced by ultrasound. The tryptophan fluorescence intensity of the three enzymes was also observed to be affected by sonication. Furthermore, it was found that the pepsin molecule might gradually be resistant to prolonged ultrasonic treatment and recover from the ultrasound-induced damage to its original structure. The results suggested that the activity of α-amylase, papain and pepsin could be modified by ultrasonic treatment mainly due to the variation of their secondary and tertiary structures.     

Stability,metastability and spectroscopic constants of electronic states of NH− and CH−

Highly correlated ab initio methods were used in order to calculate potential energy curves (PECs) of the bound electronic states of CH^? and NH^? anions and the long-range parts of their excited states. The spin–orbit interaction between electronic states has been calculated for the cases in which the couplings were assumed to be responsible for perturbations. The spectroscopic constants of bound states were calculated from the PECs and compared with previous theoretical and/or available experimental values. Also, from the ground states of CH/CH^? and NH/NH^?, the adiabatic electron affinities were given and discussed.