Coaction of sub-band and doped nitrogen on visible light photoactivity of N-doped TiO2

We found in our previous work that the high photoactivity of N-doped TiO₂ for the oxidation of propylene under visible light was attributed to the photoactive center V_o^•-NO-Ti and the formation of sub-band originated from a large amount of single-electron-trapped oxygen vacancies (denoted as V_o^•; C. X. Feng, Y. Wang, Z. S. Jin, J. W. Zhang, S. L. Zhang, Z. S. Wu, Z. J. Zhang [2008], New J. Chem. 32 , 1038). In the present study, the structure of the sub-band within E_g of a representative sample N-NTA-400 was investigated by means of photoluminescence (PL) spectrometry and ultraviolet-visible light-near infrared diffuse reflectance spectra. The coaction of the sub-band and doped nitrogen on visible light photocatalytic activity of N-doped TiO₂ was also investigated. The electron spin resonance spectra measured under laser irradiation (λ = 532 nm) indicate that the doped nitrogen may contribute to stabilize the trapping electron center, i.e. surface oxygen vacancy (V_o^••), and hence suppress the PL, enhancing the photocatalytic activity.     

Tungsten and nitrogen co‐doped TiO2 nanobelts with significant visible light photoactivity

Tungsten and nitrogen co‐doped TiO₂ nanobelts (W/N‐TNBs) have been successfully synthesized via 1‐step hydrothermal method. The structure, morphology, and composition of prepared samples were characterized by X‐ray diffraction, scanning electron microscopy, and X‐ray photoelectron spectroscopy, respectively. The prominent phase of all as‐prepared samples is anatase crystal. For samples with N doping, new energy states can be introduced on top of O 2p states which reduced the band gap by 1.1 eV. The reduced band gap leads to efficient visible light activity. The 3%‐W/N‐TNBs were found to exhibit the highest activity. The photocatalytic performance of 3%‐W/N‐TNBs under visible light is about 4.8 times than that of pure TiO₂ nanobelts, which emphasizes the synergistic effect of W and N co‐doping for effectively inhibiting the recombination of photogenerated electrons and holes. In addition, our results testify the different redox potentials of the photoelectrons at different final states.     

Origin of photoactivity of nitrogen-doped titanium dioxide under visible light

Nitrogen-doped titanium dioxide (N-TiO2), a photocatalytic material active in visible light, has been investigated by a combined experimental and theoretical approach. The material contains single-atom nitrogen impurities that form either diamagnetic (Nb-) or paramagnetic (Nb*) bulk centers. Both types of Nb centers give rise to localized states in the band gap of the oxide. The relative abundance of these species depends on the oxidation state of the solid, as, upon reduction, electron transfer from Ti3+ ions to Nb* results in the formation of Ti4+ and Nb-. EPR spectra measured under irradiation show that Nb centers are responsible for visible light absorption with promotion of electrons from the band gap localized states to the conduction band or to surface-adsorbed electron scavengers. These results provide a characterization of the electronic states associated with N impurities in TiO2 and, for the first time, a picture of the processes occurring in the solid under irradiation with visible light.     

Water-mediated promotion of dye sensitization of TiO2 under visible light

Preadsorbed water along with surrounding bulk water significantly modulates the surface electronic structure of TiO(2), switches the adsorption mode of dyes, and promotes dye sensitization of TiO(2) under visible-light irradiation. This opens a door toward facile improvement in the efficiency of photodegradation of dyes and dye-sensitized solar cells under visible-light irradiation without any complicated and expensive surface modulation.     

Oxygen vacancies enable the visible light photoactivity of chromium-implanted TiO_2 nanowires

Although computational studies have demonstrated that metal ion doping can effectively narrow the bandgap of TiO₂,the visible-light photoactivity of metal-doped TiO₂ photoanodes is still far from satisfactory.Herein,we report an effective strategy to activate the visible-light photoactivity of chromiumimplanted TiO₂ via the incorporation of oxygen vacancies.The chromium-doped TiO₂ activated by oxygen vacancies(Cr-TiO₂-vac)exhibited an incident photon-to-electron conversion efficiency(IPCE)of~6.8%at450 nm,which is one of the best values reported for metal-doped TiO₂.Moreover,Cr-TiO₂-vac showed no obvious photocurrent decay after 100 h under visible-light illumination.     

Photocatalytic activity of Fe and Cu co-doped TiO2 nanoparticles under visible light

Journal of Sol-Gel Science and Technology - The photocatalytic activity of single transition metal-doped TiO2 nanoparticles is well established. This article reports the synthesis of Fe and Cu...     

Photocatalysis of Au25-modified TiO2 under visible and near infrared light

Visible light-driven photocatalysis of Au₂₅-modified TiO₂ was investigated. It induces oxidation of phenol derivates and ferrocyanide and reduction of Ag⁺, Cu²⁺ and dissolved oxygen. Thermodynamically uphill reactions such as oxidation of phenol accompanied by reduction of Cu²⁺ are also driven. The photocatalysis, which is based on the excitation of Au₂₅, is observed even under 860 nm light.     

Study on anti-fungal activity of nitrogen-doped TiO2 nanophotocatalyst under visible light irradiation

<正>Nitrogen-doped TiO_2 nanophotocatalysts were prepared,and characterized by XRD patterns and UV-vis spectroscopy.The results indicated that nitrogen was doped effectively and the shift of the absorption edge to a lower energy and a stronger absorption in the visible light region were observed.The calcinations temperature is a key factor to narrow the band gap of titania,and consequently affects the response to visible light of nitrogen-doped TiO_2 nanocrystals.This photocatalyst can effectively inhibit the growth of Helminthosporium maydis,whereas undoped TiO_2 nanocrystals cannot inhibit the growth of H.maydis under the same experimental conditions.     

Significantly enhanced photocatalytic activity of TiO2/TiC coatings under visible light

Journal of Solid State Electrochemistry - Rutile TiO2 forms on TiC coatings (TiO2/TiC coatings) during carbon-embedding heat treatment (cHT) for TiC coatings. The photocatalytic activity of...     

Photocatalytic degradation of pathogenic bacteria with AgI/TiO2 under visible light irradiation

The photocatalytic disinfection of pathogenic bacteria in water was investigated systematically with AgI/TiO2 under visible light (lambda > 420 nm) irradiation. The catalyst was found to be highly effective in killing Escherichia coli and Staphylococcus aureus. The adsorbed *OH and hVB+ on the surface of the catalyst were proposed to be the main active oxygen species by study of electron spin resonance and the effect of radical scavengers. The process of destruction of the cell wall and the cell membrane was verified by TEM, potassium ion leakage, lipid peroxidation, and FT-IR measurements. Some products from photocatalytic degradation of bacteria such as aldehydes, ketones, and carboxylic acids were identified by FT-IR spectroscopy. These results suggested that the photocatalytic degradation of the cell structure caused the cell death. The electrostatic force interaction of the bacteria-catalyst significantly affected the efficiency of disinfection on the basis of the E. coli inactivation under different conditions.     

Synthesis of BiVO4 nanosheets-graphene composites toward improved visible light photoactivity

Two-dimensional (2-D) BiVO₄ nanosheets-graphene (GR) composites with different weight addition ratios of GR have been prepared via a facile wet chemistry process. X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectra (XPS), UV-vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption, transient photocurrent response and photoluminescence (PL) spectra were employed to determine the properties of the samples. It is found that BiVO₄ nanosheets could pave well on the surface of graphene sheets. BiVO₄ nanosheets-GR composites with a proper addition amount of GR exhibited higher photocatalytic activity than bare BiVO₄ nanosheets toward liquid-phase degradation of rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. The enhancement of photocatalytic activities of BiVO₄ nanosheets-GR composites can be attributed to the effective separation of photoexcited electron-hole pairs. This work not only provides a simple strategy for fabricating specific 2-D semiconductor-2-D GR composites, but also opens a new window of such 2-D semiconductor-2-D GR composites as visible light photocatalysts toward an improved visible light photoactivity in purifying polluted water resources.     

Phosphorous,nitrogen, and molybdenum ternary co-doped TiO2: preparation and photocatalytic activities under visible light

P, N, and Mo ternary co-doped nano TiO₂ photocatalysts ((P, N, Mo)-TiO₂) were prepared by a single step sol–gel method, which show much enhanced photocatalytic activities over Mo-TiO₂, (P, N)-TiO₂, un-doped TiO₂ and Degussa P25 under visible light irradiation. The degradation rate of 0.72Mo–P-TiO₂ is as high as 65.3%, which is about 6.7 times of that of Degussa P25. Possible reasons for the improvement of photocatalytic activities were analyzed.     

Synthesis of BiVO_4 nanosheets-graphene composites toward improved visible light photoactivity

Two-dimensional （2-D） BiVO4 nanosheets-graphene （GR） composites with different weight addition ratios of GR have been prepared via a facile wet chemistry process. X-ray diffraction （XRD）, Raman spectra, X-ray photoelectron spectra （XPS）, UV-vis diffuse reflectance spectra （DRS）, field-emission scanning electron microscopy （FE-SEM）, transmission electron microscopy （TEM）, nitrogen adsorption-desorption, transient photocurrent response and photoluminescence （PL） spectra were employed to determine the properties of the samples. It is found that BiVO4 nanosheets could pave well on the surface of graphene sheets. BiVO4 nanosheets-GR composites with a proper addition amount of GR exhibited higher photocatalytic activity than bare BiVO4 nanosheets toward liquid-phase degradation of rhodamine B （RhB） and methyl orange （MO） under visible light irradiation. The enhancement of photocatalytic activities of BiVO4 nanosheets-GR composites can be attributed to the effective separation of photoexcited electron-hole pairs. This work not only provides a simple strategy for fabricating specific 2-D semiconductor-2-D GR composites, but also opens a new window of such 2-D semiconductor-2-D GR composites as visible light photocatalysts toward an improved visible light photoactivity in purifying polluted water resources.     

Nitrogen-doped TiO2 from TiN and its visible light photoelectrochemical properties

Homogeneous titanium nitride (TiN) thin film was produced by simple electrophoreic deposition process on Ti substrate in an aqueous suspension of nanosized TiN powder. Nitrogen-doped titanium dioxide (TiO_2−xN_x) was synthesized by oxidative annealing the resulted TiN thin film in air. Photoelectrochemical measurements demonstrated visible light photoresponse for the electrode of annealed electrophoreic deposited TiN samples. It is found that the synthesized TiO_2−xN_x electrode showed higher photo potential under white and visible light illumination than the pure TiO₂ electrode. The photocurrent under visible light illumination was also observed, which increased with the increase of deposition time of TiN thin films.     

One-step synthesis of nanocrystalline N-doped TiO2 powders and their photocatalytic activity under visible light irradiation

Nanocrystalline N-doped TiO₂ powders were successfully prepared by hydrothermal reaction for 2 h at low temperature (120 °C) and at an applied pressure of 3 MPa. The grain size of the powders (calculated by use of Scherrer’s method) ranged from 8.2 to 10.2 nm. The BET specific surface area ranged from 151.0 to 220.0 m²/g. A significant shift of the light absorption edge toward the visible light zone was observed in the UV–visible spectra. XPS results showed that nitrogen atoms were incorporated into the TiO₂ lattice. The photocatalytic activity of the synthesized N-doped TiO₂ powders was evaluated by measurement of photodegradation of methylene blue (MB) in aqueous solution under visible light irradiation. The amount of MB degraded increased with increasing illumination intensity.     

Surface-modified anodic TiO2 films for visible light photocurrent response

N-doped titania thin films were prepared by anodic oxidation of titanium sheets and subsequent heat treatment in the presence of urea pyrolysis products at 400 °C. The resulting films are modified predominantly at the surface. They exhibited a significant photocurrent response upon visible light irradiation inducing an incident photon-to-current efficiency of 1.5% at 400 nm. The flatband potential was anodically shifted by 0.2 V as compared to the unmodified film. Photocurrent transients revealed that nitrogen-centered intra-bandgap states, responsible for visible light response, induce also enhanced recombination as indicated by a cathodic “overshoot” after turning off the light. This recombination can be inhibited by the presence of iodide.     

介孔AgBr/TiO_2-SiO_2光催化剂的制备及其可见光催化活性

通过沉积法将光活性AgBr半导体负载到介孔TiO_2-SiO_2载体上合成了新型的AgBr/TiO_2-SiO_2复合光催化剂.采用X射线衍射仪、高分辨透射电镜、紫外-可见吸收光谱仪等分析了AgBr/TiO_2-SiO_2复合光催化剂的结构和光谱性质;并采用BET法测定了样品的比表面积和孔分布.结果表明,介孔TiO_2-SiO_2载体的比表面积为135.5m2/g,平均孔径约为3.8nm,AgBr的负载可以有效地将AgBr/TiO_2-SiO_2复合光催化剂的吸收光谱从紫外光区扩展到可见光区,且AgBr和TiO_2形成了异质结结构,强化了AgBr与介孔TiO_2-SiO_2载体的协同作用.以罗丹明B作为探针分子,评价了AgBr负载量对复合光催化剂可见光催化活性的影响.结果发现,当AgBr∶TiO_2=0.1,0.2,0.3和0.4(物质的量之比,下同)时,复合光催化剂的光催化反应速率常数分别为0.008 5、0.028 6、0.024 6和0.019 3min-1,活性先增加后减小,当AgBr∶TiO_2=0.2时,复合光催化剂表现出最高的光催化活性,并且在5次循环测试中均表现出较高的光催化活性.     

Preparation of magnetically supported chromium and sulfur co-doped TiO2 and use for photocatalysis under visible light

Novel magnetic chromium and sulfur co-doped TiO₂ photocatalysts (M-Cr/S/TiO₂) have been prepared by a sol?Cgel process, using magnetic hollow fly ash microspheres as support material. The crystal phase of M-Cr/S/TiO₂ was characterized by X-ray diffraction, UV?Cvisible absorption spectroscopy, and transmission electron microscopy. The photocatalytic activity of the photocatalysts was examined by photodegradation of methyl orange in aqueous solution under visible light irradiation. The results showed that chromium and sulfur co-doped catalysts (Cr/S/TiO₂) containing 0.60?% (atomic ratio) chromium and 1.2?% (atomic ratio) sulfur calcined at 450?°C for 2?h had high catalytic efficiency under visible irradiation. It is worth mentioning that the floating M-Cr/S/TiO₂ catalyst had greater photocatalytic activity than Cr/S/TiO₂ powder. Therefore, M-Cr/S/TiO₂ is a promising, high-performing, visible-light-driven photocatalyst.     

Nb and N co-doped TiO2 for a high-performance deNO x photocatalyst under visible LED light irradiation

By a facile and rapid microwave-assisted hydrothermal reaction at 190 °C for 30 min, niobium and nitrogen co-doping TiO₂ nanoparticles were prepared. The obtained samples were characterized by XRD, UV–Vis spectroscopy, EDX analysis, and BET measurements. To evaluate the photocatalytic activity, destruction of NO _x gas under the irradiation of several LED lamps with various wavelengths were carried out. Although co-doping of Nb with N into TiO₂ resulted in the decrement of the specific surface area, it was useful to improve the photocatalytic activity for the oxidative destruction of NO, probably due to the effective reduction of the anion vacancy in the lattice which acts as the recombination center of the photo-induced electrons and holes.