Photocatalytic Activity Of Anatase TiO2 Research Articles

Influence of oxidation process on photocatalytic activity of photocatalyst coatings by mechanical coating technique

Titanium (Ti) coatings on alumina (Al2O3) balls fabricated by mechanical coating technique (MCT) were oxidized in air at a series of relatively low temperatures with the oxidation time of 3h and 50h. Crystal structure and microstructure of the coatings were investigated. Photocatalytic activity of the coatings was evaluated and discussed. The results showed that titanium dioxide (TiO2) films on Ti or Ti/TiO2 coatings were fabricated by the MCT and subsequent heat oxidation. The oxidized coatings started to show the mixed-phase of anatase and rutile, at the temperature of 873K for 3h and 773K for 50h. With extending the oxidation time from 3h to 50h, the oxidative effect of relatively lower temperatures of 773K to 973K almost reached to that of higher temperatures, which is similar to the time–temperature equivalence principle. Photocatalytic activity of anatase TiO2 at 673K is higher than that of mixed-phase or rutile TiO2 under UV irradiation.

Photocatalytic activity and formation of oxygen vacancies in cation doped anatase TiO2 nanoparticles

We report the influence of iron doping on structure, stoichiometry, and photocatalytic efficiency of single phase anatase TiO2 nanoparticles which were synthesized via the sol gel technique. The XPS and FTIR results reveal the formation of oxygen vacancies and Ti3+ defects following doping with iron which was further confirmed by PL studies. XRD and TEM investigations indicate that the phase structure of TiO2 nanoparticles is preserved after incorporation of iron to the crystallographic lattice. XRD peak shift and broadening, observed in the doped nanoparticles, were attributed to the formation of point defects and the resulted strains. Photocatalytic activity of the samples was examined through measuring the decomposition rate of rhodamine B under ultraviolet illumination. It was found that Fe-doping significantly improves the photocatalytic activity of anatase TiO2. We envisage that a more effective use of the UV photon energy, higher charge carrier mobility, and suppressed charge recombination due to the point defects are the primary reasons behind the enhanced photocatalytic activity.

Larger Effect of Sintering Temperature Than Particle Size on the Photocatalytic Activity of Anatase TiO2

Photocatalytic activity of anatase TiO2 that increases with the increase of its synthesis temperature has been widely reported, but the reason for that remains incompletely understood. In this work, the positive effect of synthesis temperature, presumably due to the growth of particle size, has been examined. Three series of anatase samples with various particle sizes were prepared from the hydrolysis of TiOSO4 in water at 150 °C, followed by calcinations in air. The particle size of TiO2, estimated by X-ray diffraction and N2 adsorption, increased with the increase of the hydrothermal time, calcination time, and calcination temperature. For phenol photodegradation in aerated aqueous suspension, three series of the catalysts showed different correlation between the activity and particle size of TiO2. However, with the same amount of Ag+ adsorbed on the oxide surface for phenol photodegradation in a N2-purged aqueous suspension, those catalysts showed activities all increasing with the particle size of TiO...

First-Principles Calculations on Pure and Y-Doped Anatase TiO<sub>2</sub>

Using the First principles calculations, the crystal structure, band gap, total and partial density of states (DOS) of anatase TiO2and anatase TiO2doped with Yttrium were calculated by a plane-wave pseudopotential (PWPP) method based on density functional theory (DFT). The generalized gradient approximation (GGA) based on exchange-correlation energy optimization was employed to calculate them. From the calculation results, the band gap of anatase TiO2and Y3+doped TiO2are about 2.15eV and 0.86eV. The calculated results demonstrated that the mixing of Yttrium (Y) dopants induces states with original titanium 3d and oxygen 2p valence band attributes to the band gap narrowing. This can enhance the photocatalytic activity of anatase TiO2.

First-Principle Calculation of the Co Doped Anatase TiO<sub>2</sub>

Using first-principle calculations based on density function theory (DFT), the geometry , band structure and electronic density of states of Co-doped anatase titanium dioxide (Co/TiO2) have been studied at plane wave ultra-soft pseudo-potential (PWPP). The states of the valence bands and conduction bands of pure and Co doped TiO2 with anatase structure were calculated. The density of states of pure anataseTiO2 and Co-doped TiO2 is analyzed in detail based on the calculations using the first-principles. From the calculated results, the band gaps of anataseTiO2 and Co doped TiO2 are about 2.15 and 0.78eV, respectively. It shows that Co doped anatase titanium dioxide may lead to the narrowing of the band gap in Co/TiO2. The Co doped anataseTiO2 could be a potential candidate for photocatalyst because it can enhance the photocatalytic activity of anatase TiO2.

Antibacterial and photocatalytic activity of TiO2 and ZnO nanomaterials in phosphate buffer and saline solution

We studied antibacterial and photocatalytic activity of anatase TiO2 and ZnO in phosphate buffer and saline solution. We found that the different anions in the suspension medium (chloride and phosphate) significantly affected the following suspension properties: the stability of nanoparticle suspension, the release of metal ions from the nanoparticles, and the production of the reactive oxygen species by the nanoparticles. As a result, antibacterial activity and photocatalytic dye degradation were also affected. However, the effect of the suspension medium was different for ZnO and TiO2. Obtained results are discussed.

Effect of Sn surface states on the photocatalytic activity of anatase TiO2

The influence of surface Sn-doping on the photocatalytic properties of anatase TiO2 has been investigated in samples prepared by a grafting route using Sn(IV) tert-butoxide as Sn precursor. The grafting procedure leads to the formation of isolated Sn(IV) sites on the surface of anatase TiO2 powders as gauged by structural characterisation based on XRD, Raman spectroscopy and XAS. Studies of the surface reduction based on TPR experiments and XPS provide the conditions for a selective reduction of surface Sn(IV) to the divalent oxidation state. Electronic structure characterisation based on valence band XPS and DRS shows that there is a slight widening of the band gap upon Sn(IV)-grafting, but Sn(II) related states emerge at the top of the main valence band upon reduction at temperatures up to 350°C, and this induces visible light absorption. Grafting of TiO2 with Sn(IV) increases the formation rate of OH radicals on the surface of the material. Reduction of the Sn(IV)-grafted TiO2 to form surface Sn(II) brings about substantial increase of the photocatalytic efficiency for the methylene blue degradation under irradiation with λ≥320nm compared with Sn(IV)-grafted and pure anatase TiO2. This observation is explained based on a surface hole trapping by the Sn(II)-related surface states which lie above the top of the main valence band and can therefore act as trapping sites for holes produced under photoexcitation.

Simultaneous Photocatalytic Removal of Cr(IV) Ions and Methylene Blue Using InVO<sub>4</sub>/TiO<sub>2</sub> Nanocomposites under the Sunlight Irradiation

InVO4/TiO2 nanocomposites were synthesized via a sol-gel process, and their microstructure and morphology were characterized by XRD and FESEM. XRD analysis indicated that incorporation of InVO4 with low content (In:Ti mole ratio of 1:200) could not change the crystallinity of anatase TiO2. The photocatalytic activity of anatase TiO2 increased for more than 2 folds by incorporating small amount of InVO4 into TiO2. The MB degradation rate kapp increased from 1.147×10-2 to 1.75×10-2 min-1 while the added Cr(IV) concentration was 5mg/L. The results indicated that simultaneous removal of aqueous Cr(IV) ions and organic compounds was feasible in the photocataltyic reactions under sunlight irradiation.

The replacement of {1 0 1} by {0 1 0} facets inhibits the photocatalytic activity of anatase TiO2

Anatase TiO2 crystals with {101}–{001} and {010}–{001} two facets coexistence were synthesized by (NH4)2TiF6 acting as titanium and fluorine sources and the photocatalytic activity of the samples were investigated. The replacement of {101} by {010} facets inhibits the photocatalytic activity of anatase TiO2. The mechanism was examined by photoluminescence spectrum, time-resolved photoluminescence spectra, field emission scanning electron microscope (FESEM) images of selected deposition of Ag, surface atoms structures and electronic band structures of anatase TiO2 facets. The results demonstrated that photoinduced charge transfer properties between {101} facets and {001} facets resulted in the efficient charge separation. Replacing {101} by {010}, the charge transfer mechanism was altered and the photoinduced electron–hole pairs cannot be separated well. The photocatalytic activity of it has thus been inhibited.

Effects of N and F doping on structure and photocatalytic properties of anatase TiO2 nanoparticles

A facile solvothermal method has been developed for preparing anatase TiO2 nanoparticles doped with nitrogen (N) or co-doped with N and fluorine (F). The effects of N and F doping or co-doping on the structural and photocatalytic properties of anatase TiO2 nanoparticles were investigated. X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, X-ray photoelectron spectroscopy, and Raman spectroscopy were used to characterize the synthesized nanoparticles, confirming the successful synthesis of anatase TiO2. The crystal cell parameters and crystal size decreased with the doping of N or codoping of N and F. Photocatalytic degradation of methyl orange under both UV and visible light irradiation revealed that the photocatalytic activity of anatase TiO2 was greatly improved by N doping or N and F co-doping. The effect of TiO2 bandgap narrowing and the synergistic effect between co-dopants N and F on photocatalytic performance of TiO2 were also discussed. The N–F-co-doped TiO2 is thus a promising material for photocatalytic applications.

Photochemical Removal of Gaseous Elemental Mercury in a Dielectric Barrier Discharge Plasma Reactor

The plasma process has the potential to serve as a low cost mercury oxidation technology that will facilitate elemental mercury removal in a downstream of Flue Gas Desulfurization system. The performance of the main gas constituents, such as H2O, O2 and HCl on elemental mercury oxidation under plasma atmosphere was investigated in simulated flue gas. Experiments were carried out in a dielectric barrier discharge reactor operated at 140 °C. Photochemical effects of nanocrystalline titania on oxidation of elemental mercury were also tested. The results indicated that both H2O and O2 promote the oxidation of elemental mercury significantly. Active radicals generated by ionization, such as O, O2 and OH, play the crucial roles in oxidation process. The presence of HCl in N2/O2 stream in plasma system is a very effective way of oxidizing elemental mercury, the nearly complete oxidation of elemental mercury was observed by 4 kV of applied voltage only. The best photocatalytic activity of anatase TiO2 which was calcined at 600 °C was found in our tests. Compared with the plasma process alone, the oxidation efficiency increased 18.7–26.3 % with the addition of photocatalyst.

Enhanced visible-light photocatalytic activity of anatase TiO2 through N and S codoping

The density of states and optical properties of N, S, and (N, S)-doped anatase TiO2 are calculated based on the density functional theory. The results indicate that the doping S atoms occupy the Ti-atom sites in anatase TiO2 lattice. The mixing of O 2p, N 2p, S 3p, and Ti 3d states in the forbidden gap of (N, S)-codoped TiO2 can result in the higher visible-light photocatalytic activities than those monodoped TiO2. For comparison, (N, S)-codoped TiO2 was also synthesized by one-step hydrothermal method, and the optical absorption spectra obtained by experiments verified the reliability of our calculation.

Hydrothermal synthesis of nanosized anatase TiO<SUB align="right">2: photocatalytic activity

Phase–pure anatase TiO2 nanocrystallites (620 nm) were synthesised from amorphous titania by hydrothermal process under relatively low temperatures (413453 K) in the presence of water. The precursor used for the hydrothermal synthesis was obtained by the precipitation stripping of the TiCl4 loaded organic solvent (tributylphosphate = TBP). TiCl4 was selectively extracted from the synthetic waste chloride liquors of titania industry by solvent extraction using TBP in kerosene as an extractant. The synthesised anatase TiO2 powders were characterised by XRD, SEM, IR and BET surface area. The influence of hydrothermal treatment conditions on the formation features, phase composition, particle size, morphology and properties of the products were investigated and discussed. The fact that the nucleation of anatase was accelerated by the presence of water suggested that water bonding with the surfaces of the primary particles of the amorphous titania forces the TiO6 octahedra units to rearrange to the anatase structure and acts as a catalyst for the structural rearrangement. The crystal growth of TiO2 to phase–pure anatase was proposed to proceed by face–sharing process through dissolution–precipitation of the dissolved TiO6 octahedra from the amorphous phase. It is evident from the XRD patterns that neither rutile nor brookite phases are present in the hydrothermally synthesised anatase TiO2 powders. Application of these nonocrystallites as photocatalyst was evaluated by photocatalytic degradation of methyl orange in water. The photocatalytic activity of anatase TiO2 was also compared with that of commercial photocatalysts, Hombikat UV 100 and Degussa P25.

First-Principles Calculations on Pure and Ga-Doped Anatase TiO2

First-principles calculations using the plane-wave pseudo-potential (PWPP) method based on the density functional theory (DFT) is employed to study the crystal structure, band gap, density of states of anatase TiO2 doped with gadolinium (Gd). The generalized gradient approximation (GGA) based on exchange-correlation energy optimization is employed to calculate them. The calculated results demonstrate that the mixing of gadolinium dopants induces states with original titanium 3d and oxygen 2p valence band attributes to the band gap narrowing. This can enhance the photocatalytic activity of anatase TiO2.

Improvement in Photocatalytic Activity of TiO2under Visible Irradiation through Addition of N-TiO2

This work is focused on improvement in photocatalytic activity of anatase-TiO2 (a-TiO2) photocatalyst under visible-light irradiation by adding nitrogen-doped TiO2 (N-TiO2) for depression of recombination rate between photoexcited electron and hole. The composites (a-TiO2/N-TiO2) were prepared by grinding in ethanol solvent at 200 rpm for 15 min with change in weight ratio of N-TiO2. In addition to the characterizations by X-ray diffraction and X-ray photoelectron spectroscopy, measurements of existing singlet oxygen by chemiluminescens method and photocatalytic activity by using NO(x) decomposition were conducted. The increases in singlet oxygen and photocatalytic activity have been observed and the phenomena are discussed based on the efficient prevention of recombination between photoexcited electron and hole within the prepared composite.

Mechanism of higher photocatalytic activity of anatase TiO2 doped with nitrogen under visible-light irradiation from density functional theory calculation

We have systematically investigated the modification mechanism of anatase TiO2 doped with nitrogen using the plane-wave ultrasoft pseudopotentials method based on density functional theory. The crystal structure, impurity formation energy, electronic structure and optical properties of TiO2 supercells containing subsitutional nitrogen, interstitial nitrogen or oxygen vacancies were calculated. TiO2 doped with substitutional nitrogen has shallow acceptor states above the valence band. In contrast, TiO2 doped with interstitial nitrogen has isolated impurity states in the middle of the band gap. These impurity energy levels are mainly hybridized by N 2p states with O 2p states and Ti 3d states. TiO2 containing oxygen vacancy has shallow donor states below the conduction band, which consists of Ti 3d states. Except for containing oxygen vacancies, the band gaps of N-doped TiO2 are narrowed in the range 0.03–0.23 eV, and thus their fundamental absorption edges extend to the visible-light region. By nitrogen doping, the octahedral dipole moments in TiO2 increase due to the changes in lattice parameters, bond length and charges on atoms, which is very effective for the separation of photoexcited electron–hole pairs. The calculated results are consistent with the existing experimental data. Based on these results, the effects on the electronic structure and photocatalytic activity of anatase TiO2 doped with nitrogen were analysed and compared in detail, and the mechanism by which anatase TiO2 doped with nitrogen has higher photocatalytic activity than that of pure TiO2 was explained. The conclusions have important significance for understanding and further developing TiO2 photocatalysts that are active under visible-light irradiation.

Photocatalytic dehydrogenation of aliphatic alcohols by aqueous suspensions of platinized titanium dioxide

Photoirradiation (λex > 300 nm) of Ar-purged aqueous propan-2-ol solution gave hydrogen and acetone in the presence of platinum- and/or ruthenium dioxide-loaded TiO2. The photocatalytic activity of anatase TiO2 depended significantly on the amount of metal or metal oxide present; the effect on the activity increased in the order platinum black ≫ platinum powder > ruthenium dioxide. The photocatalytic activity of rutile TiO2 was negligible even when loaded with platinum black. The effective wavelengths for the photocatalytic dehydrogenation of propan-2-ol were below ca. 390 nm, in agreement with the u.v. absorption spectrum of anatase TiO2. In a similar way primary, secondary and tertiary aliphatic alcohols underwent photocatalytic oxidation, accompanied by hydrogen liberation, by the platinized TiO2. The primary and secondary alcohols gave the corresponding carbonyl derivatives, while 2-methylpropan-2-ol and acetone gave dimeric products accompanied by stoichiometric hydrogen evolution. The initial rate of dehydrogenation in these photocatalytic systems was in proportion to the rate constants of hydrogen abstraction by hydroxyl radical in the homogeneous systems.