V-doped TiO2 Research Articles

Co-precipitation synthesis of V-doped titania: influence of vanadium concentration on the structural and optical properties

V-doped TiO2 nanoparticles with different proportions were prepared by co-precipitation method. XRD patterns indicate that the TiO2 nanoparticles obtained after calcination at 500 °C in air has the anatase phase with a tetragonal structure and the crystallite sizes were in the range 11.4–9.5 nm, which are consistent with the results obtained from TEM images. The functional groups present in the samples were identified by FTIR study. From the optical studies, there is a blue shift in the absorption edge for our samples that can be attributed to the presence of V in the TiO2. For V doped TiO2 nanoparticles the optical band gap varies between 3.19 and 2.83 eV with the increase of V concentration. It was found that the doping V5+ ions have a significant influence on the optical properties. The room temperature photoluminescence (PL) spectra showed characteristic UV emission peaks of anatase at 529 nm and appropriate amount of V doping could slow the radiative recombination process of photogenerated electrons and holes in TiO2.

Doped TiO2 aerogels as alternative catalyst supports for proton exchange membrane fuel cells: A comparative study of Nb, V and Ta dopants

Nb, Ta and V-doped TiO2 aerogels and xerogels have been synthesized as possible new alternatives to carbon blacks for Proton Exchange Membrane Fuel Cells catalyst supports. A comparative study of different dopants was realized in a single study. Nb, Ta and V showed different behaviors with respect to the final material structure and morphology, composition and electronic conductivity. They are all prone to surface segregation, to different extents. V-doped TiO2 apart, the rutile structure could only be obtained after calcination in a reducing atmosphere at 800 °C for Nb or Ta-doped TiO2. The electronic conductivity exhibited a maximum at 10 at.% for Nb and Ta, 5 at.% for V. Nb revealed to be the most appropriate dopant to increase the electronic conductivity of TiO2, followed by Ta and V. 4–5 orders of magnitude were gained after Nb doping for xerogels conductivity to reach almost 0.1 S cm−1. The role of point defects was discussed to account for phase transition and evolution of conductivity.

Niobium/Vanadium doped TiO2 multilayered sol-gel films: Structure, surface chemistry and optical properties

In this work multilayered TiO2 films deposited on glass and Si substrates by the sol-gel – dipping method were studied, focusing on the influence of Niobium/Vanadium doping on the structure, surface chemistry and their optical properties. The TiO2 films doped with 1.2at% Nb(V) crystallized in anatase phase as evidenced by XRD analysis. It was found that thicker films are obtained in the case of V-doped TiO2 films, while the values of the optical band-gap show similar values. Bands related to the vibration of oxygen in the Ti–O, Nb–O and V–O bonds were identified based on Infrared Spectroscopic Ellipsometry, proving the incorporation of the dopants in the matrix of the TiO2 films. Both types of doped films exhibit around 80% transparency on a wide spectral range (300–1700nm). Niobium and Vanadium have been identified in the surface / subsurface region in the 5+ oxidation state (although a high sensitivity of the Vanadium oxidation states during profiling experiments was found due to the preferential sputtering effect). From a morphological point of view, all titania films show a very uniform and compact microstructure, with a homogeneous superficial structure of small grains with diameters in the range of 10–20nm.

Visible light responsive noble metal-free nanocomposite of V-doped TiO2 nanorod with highly reduced graphene oxide for enhanced solar H2 production

The visible light responsive nanocomposite of vanadium-doped TiO2 nanorod anchoring on highly reduced graphene oxide (RGO) has been successfully synthesized using a simple one step low temperature hydrothermal method. The nanoparticles, loaded on RGO, were intentionally fabricated as nanorods to enhance their contact with the RGO sheets. Compared to undoped TiO2 and non-composited V-TiO2 nanoparticles, the nanocomposite exhibited enhanced H2 evolution under visible light illumination. Density Functional Theory (DFT) computation also confirms the bandgap narrowing of TiO2 by doping vanadium. Furthermore, the photogenerated electrons could be effectively trapped by the conducting RGO sheets, thereby suppressing electron–hole recombination. This noble metal-free nanocomposite material composed of highly conducting sheets also offers promise for other energy applications such as lithium ion batteries.

Structure and properties of the V-doped TiO2 thin films obtained by sol–gel and microwave-assisted sol–gel method

In the present work, TiO2 and V-doped TiO2 films with TiO2/V2O5 molar ratios 98:2 and 99.95:0.05 were prepared by sol–gel and microwave (MW) assisted sol–gel syntheses. The reagents used were tetraethyl orthotitanate, vanadyl acetylacetonate and ethanol as solvent. The solutions were prepared either by stirring for 2 h at room temperature or by exposing them for 5 min to microwaves at 300 W in an oven operated at frequency of 2.45 GHz. The deposition of the films was realized by dip-coating on microscope glass substrate. The multilayer films were obtained by successive deposition. The first benefit of using MW-assisted sol–gel preparation was the essentially increased stability of the resulted solution against gelling, behavior that is of great interest for multilayer depositions. A comprehensive structural, morphological and optical characterization of the obtained films was realized. Differences between the films obtained by the two types of preparation routes are reflected in a more compact and continuous structure with very low roughness, increased thickness and higher refractive index as well as increased transmission when MW-assisted sol–gel method was used.

Synthesis and room-temperature ferromagnetism of porous V-doped rutile TiO2 microspheres

Porous V-doped TiO2 microspheres were synthesized by simply co-precipitating V and Ti precursors. Vanadium could be homogenously inserted into TiO2 lattice, and promotes the phase transition of TiO2 from anatase to rutile. V-doped TiO2 demonstrates ferromagnetism at room temperature of around 15 memu/g, which is highly associated with structure defects. Both surface defects and bulk oxygen vacancy contribute to the introduction of ferromagnetism in V-doped TiO2. It provides some experimental facts and is helpful for further understanding on the room-temperature ferromagnetism in DMSs.

Novel synergistic photocatalytic degradation of antibiotics and bacteria using V–N doped TiO2 under visible light: the state of nitrogen in V-doped TiO2

Interstitial and substitutional nitrogen co-doped in vanadium–TiO2 for simultaneous photocatalytic antibiotic degradation and bacterial inactivation.

Synthesis and photocatalytic activity of V-doped mesoporous TiO2 photosensitized with porphyrin supported by SBA-15

A highly efficient photocatalyst was produced by immobilizing V-doped mesoporous TiO2/tetrakis(4-carboxyphenyl)porphyrin (V-TiO2/TCPP) onto SBA-15 walls, and was then investigated for photodecomposition of 2,4-dichlorophenol (2,4-DCP) in aqueous solutions. In the present paper, first, in order to activate titanium dioxide by visible light, the TiO2 mesoporous was doped by vanadium (V-TiO2) and then it was sensitized by tetrakis(4-carboxyphenyl)porphyrin (TCPP). To improve the photocatalytic activity of the prepared catalyst, SBA-15 was functionalized with the prepared V-TiO2/TCPP by pre-anchorage of 3-(aminopropyl)-triethoxysilane via post-synthesis method (V-TiO2/TCPP/SBA). The obtained materials were characterized by UV–Vis absorption, FT-IR spectroscopy, diffuse reflectance (DRS), scanning electron microscopy, X-Ray diffraction, and N2 adsorption–desorption. Furthermore, a comparative study on the photodegradation of 2,4-DCP between V-TiO2/TCPP/SBA and V-TiO2/TCPP composites was performed and the role of SBA-15 was investigated. The results showed that the decomposition efficiency of the 2,4-DCP by using the V-TiO2/TCPP/SBA was much more than that of applying TCPP/V-TiO2 in high initial concentration of pollutant (up to 99 % in 300 mg/L). In addition, the photocatalytic degradations of 2,4-DCP using above photocatalysts all followed a first-order kinetic model. The V-TiO2/TCPP/SBA was recycled four times without significant loss of photocatalytic activity.

Novel adsorption and photocatalytic oxidation for removal of gaseous toluene by V-doped TiO2/PU under visible light

In this study, V was used as a dopant to defect into the TiO2 lattice, leading to formation of Ti3+ and V4+ in the lattice. The presence of Ti3+ and V4+ introduced into the TiO2 lattice increased the electron–hole pair generation capacity and electron–hole pair separation efficiency of the TiO2, leading to enhancement of the photocatalytic activity of the photocatalyst. Porous polyurethane (PU) was used to immobilize the V-doped TiO2 by creating chemical bonds. The use of porous substrate contributed to the increased adsorption ability of the enhanced photocatalyst, as well as expanded its application for the removal of toluene from aerosols. Under dark conditions, the V-TiO2/PU only exhibited adsorption ability for toluene treatment in aerosol. Under visible light conditions, the V-TiO2/PU exhibited high photocatalytic oxidation ability for the removal of toluene in aerosol. The photocatalytic oxidation ability was found to depend on the V to TiO2 ratio. The optimal V content in V/TiO2 for enhancing the photocatalytic activity of TiO2 was determined to be 6wt%. Even under visible light irradiation, the 6% V-TiO2/PU sample could photocatalytically remove 80% of the toluene in 200-ppmV inlet gas, while 89.3% of the removed amount was mineralized into CO2 and H2O.

A comparative study about the influence of metal ions (Ce, La and V) doping on the solar-light-induced photodegradation toward rhodamine B

Water contamination by the textile dye effluents has become a serious environmental issue, which are threatening to the human health and biological diversity. The TiO2 photocatalysis has been proven to be used to remove textile dyes in water. In order to improve its solar-light activity, three metal ions, including cerium (Ce), lanthanum (La) and vanadium (V), were selected as dopants to prepare metal ions doped TiO2 particles by sol–gel method. The synthesized particles were characterized by X-ray diffraction, field scanning electron microscopy, UV–vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. Through the physicochemical properties of the resulting metal ions doped TiO2 particles, we found that characteristics of dopants could strongly affect the crystalline phase and crystallite size, the optical absorption spectrum and the bandgap energy of the modified TiO2 catalysts, and consequently influence the photocatalytic ability. We investigated the link between dopant’s characteristics and photoactivity of the doped catalysts, and deduced that the existence of dopant in the modified catalysts is crucial. In the case of Ce or La doping, the dopants homogeneously dispersed on the surface of TiO2 particles as oxides and interacted with TiO2 particles via REOTi bond. Nevertheless, the V species successfully entered the TiO2 lattice and substituted for Ti4+ due to its similar ionic radius with Ti. The photocatalytic activities of Ce-, La-, or V-doped TiO2 photocatalysts were evaluated by the degradation of rhodamine B under simulated solar-light illumination. In our case, only the doping of Ce or V could drive efficient solar-light activity. The bandgap energy of 1.0%-Ce–TiO2 was narrowed to 2.70eV and the removal ratio for dye could raise up to 83% with a relatively high calcination temperature.

Electronic properties of TiO2 doped with Sc, Y, La, Zr, Hf, V, Nb and Ta

The segregation of dopant inevitably affects the thermodynamic stability and electronic properties of transition metal (TM) doped TiO2 which were studied using first principles calculations. Here we show that the thermodynamic stability of doped systems is related with the doped position which is different for the considered TM dopants. The second phase could appear in V-doped TiO2 due to the VOV bonding. The thermodynamic stability and electronic properties of the doped systems will be slightly infected by dopant concentration. Moreover, the band gaps are approximately proportional to the Mulliken population values of TMO bond.

Enhanced photocatalytic oxidation of propylene over V-doped TiO2 photocatalyst: Reaction mechanism between V5+ and single-electron-trapped oxygen vacancy

The novel V-doped TiO2 (V-TiO2[NTA]) samples with different (0–10%) concentration have been successfully prepared by a facile solid state sintering method using the nanotubular titanic acid (NTA) as titanium precursor for the first time, which shows remarkable photocatalytic activity for degradation of propylene under visible-light irradiation. Based on the density function theory (DFT) calculations in conjunction with a series of experimental characterization techniques including Raman spectra, TEM, XPS, ESR, and UV–vis DRS, a new V4+ ions formation mechanism by means of the electron trapped at single-electron-trapped oxygen vacancy (SETOV, Vo) not Ti3+ has been proposed, and the origin of the observed remarkable improved photocatalytic activity of the V-TiO2[NTA] samples has also been investigated. At low concentration, the enhancement of photocatalytic activity for the V-TiO2[NTA] samples firstly come from the synergistic effect of V and Vo co-doping: a part of V5+ is reduced to V4+ by Vo into TiO2 lattice, others exist on the surface in the form of V2O5. The incorporation of V4+ in TiO2 lattice induces some new states (around the top of the valence band, due to O 2p and V 3d orbitals; around the bottom of the conduction band, due to Ti 3d, O 2p, and V 3d orbitals) near the edge of the valence and conduction bands, respectively, causing an effective narrowing of the band gap. The narrowing of gap is responsible for the red-shifted and increased light-absorption. The presence of V5+/V4+ redox couple facilitates the efficient separation and migration of photo-induced e−/h+ pairs to generate active species. Secondly, the enhancement of photocatalytic activity with low doping concentration may also be ascribed to the increased surface area. At high doping concentration, the reasons for the decreased photocatalytic activity is that the same trapping sites may act as the recombination centers and excess V dopant may occupy the active sites of surface.

Preparation of vanadium-doped titanium dioxide neutral sol and its photocatalytic applications under UV light irradiation

A sol–gel method was used to prepare V-doped TiO2 sol. TiCl4 was converted to Ti(OH)4 and H2O2 was then added to convert it to TiO2 at high temperature. The sols with various contents of V were used to prepared thin films on glass substrate by dip-coating method. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, high resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy, and UV–vis spectroscopy. The photocatalytic activities of the V-TiO2 thin films were investigated by the degradation of methylene blue under UV light irradiation. The as-prepared V-TiO2 sol was neutral and showed high stability of nanoparticles suspended in the sol without any surfactant. The shape of particle was rhombus and possessed high aspect ratio. The V-TiO2 particles were in anatase and nanosize, so they do not need annealing process to form crystals after coating on the substrate. V doping can produce more photogenerated electrons and holes, which improved the photocatalytic activity. However, overdoes V in TiO2 would lead to form the recombination centers and suppressed the activity. The optimum NH4VO3/TiO2 weight ratio in starting materials was 3%.

Above Room Temperature Ferromagnetism in Co- and V-Doped TiO2 — Revealing the Different Contributions of Defects and Impurities

We report recent experimental results on the mag- netic, magnetotransport, and magneto-optical properties of Co- and V-doped TiO2−δ magnetic oxides at the doping level around 1 at. %. The samples were prepared using rf magnetron sputtering in identical conditions that allows to compare the mechanisms of above-room-temperature ferro- magnetism observed in both cases of doping. In spite of the comparable values of magnetic moment around 1 ÷ 2.5 µB per 3d impurity derived from macroscopic magnetic mea- surements for both systems, the magneto-optical response

Preparation of V-doped TiO2 photocatalysts by the solution combustion method and their visible light photocatalysis activities

A series of nanocrystalline V-doped (0.0–3.0 at.%) TiO2 catalysts have been successfully prepared by the one-step solution combustion method using urea as a fuel. The obtained powders were characterized by XRD, SEM, Raman, XPS and UV-Vis DRS. The effects of V doping concentration on the phase structure and photocatalytic properties were investigated. XRD, Raman, and XPS show that V doping diffuses into TiO2 crystal lattice mainly in the form of V5+ and causes a phase transition from anatase to rutile. V doping can widen the light absorption range of TiO2, with the absorption threshold wavelength shifting from 425 to 625 nm. The photocatalytic activity of V-doped TiO2 powders were evaluated by the photocatalytic degradation of methyl orange (MO) under visible light irradiation. It is found that V doping enhances the photocatalytic activity under visible light irradiation and the optimal degradation rate of MO is about 95.8% with 1.0 at% V-doped TiO2.

A study on the band gap and the doping level of V-doped TiO2 with respect to the visible-light photocatalytic activity.

The visible-light response is a necessary but not a sufficient condition for semiconductor photocatalyst to function as a visible-light active photocatalyst. To shed more light on the issue of visible-light response of semiconductor photocatalysts, the band-gaps and the doping levels of multivalency vanadium-doped TiO2 were investigated from sonochemically prepared samples. Sonochemical doping, which relies on acoustic cavitation phenomena, is a one step process excluding chemical synthesis, and three types of vanadium doped TiO2 nanopowder were prepared using such vanadium oxides as V2O3, V2O4, and V2O5. The band-gaps of as-prepared samples were obtained from the diffuse reflectance measurement, and the doping levels of vanadium in these samples were measured using electron probe micro analyzer. In addition, X-ray photoelectron spectrometer was introduced to complement electron probe micro analyzer. Furthermore, quantum-chemical calculations on simple cluster models for TiO2 and V-doped TiO2 were performed, and the resulting computational results in conjunction with experimental findings provided valuable information on oxygen vacancy and doping mechanism.

Effect of Transition Metal Oxide Doping (Cr, Co, V) in the Photocatalytic Activity of TiO2 for Congo Red Degradation under Visible Light

Comparative study of Cr, Co or V-doped TiO2 was carried out. The photocatalysts were synthesized via sol-gel method. The results indicated that the dopants of Cr, Co, and V induced anatase to rutile phase transition of TiO2 at different dopant amounts of 1, 4, 2 mol%, respectively. Besides that, the existence of dopant extended the absorption wavelength of TiO2 to visible light region, thus making it a visible-driven photocatalyst. The doped transition metal exhibited different oxidation states on the TiO2 surface. The prepared photocatalysts were tested over photodegradation of Congo Red. Amongst all, Cr-doped TiO2 (3 mol%) was the best photocatalyst attributed to the presence of 45% rutile phase, reduced band gap energy of 2.30 eV and formation of Cr6+, which acted as an electron scavenger to delay the hole-electron recombination.

Study on the Influencing Factors of V-Doped TiO<sub>2</sub> Photocatalysis

V-doped TiO2 was prepared by the sol-gel method. The different reaction and preparation conditions of TiO2 and V-doped TiO2were evaluated through the formaldehyde degradation under the visible light. Results showed that the formaldehyde degradation efficiency reached 70.8% when the doping amount of V was 1%(mol), the calcining temperature was 700 oC and pH was 3.5; It improved to 88.5% with 20g activated carbon as support and the 89W energy-saving lamp as light source; The formaldehyde degradation products were H2O and CO2; The specific surface area and pore distribution of TiO2 were analyzed by BET and its crystalline structure was analyzed by XRD,which indicated that mixture of anatase and rutile have large surface area and strong photocatalytic activity due to the V-doping. These suggested that the photocatalytic reactions of formaldehyde included adsorption and photocatalytic oxidation which was obvious for the V-doped TiO2.

Doping mechanism of Vanadia/Titania nanoparticles in flame synthesis by a novel optical spectroscopy technique

Flame synthesis of V-doping TiO2 is studied by in situ diagnostic of phase selective laser-induced breakdown spectroscopy (LIBS). We apply this novel optical spectroscopy to tracing the gas-to-particle phase transition of V and Ti elements, as low-intensity laser only excites V and Ti atoms present in the particle phase but not in the gas phase. Both V and Ti atomic signals appear early at the burner exit and plateau downstream after a distance about 14mm. Compared with signals in pure TiO2 synthesis, the signal of Ti in the doping synthesis is significantly strengthened due to the lower band gap of V-doped TiO2. The doping mechanism is then inferred from the observations. It is deduced that the substantial collision and mixing of the nucleated V and Ti oxides occur even at the burner rim and persist through the entire process. The signal intensities of both V and Ti atoms increase with laser power and tend to plateau at about 20mJ/pulse. In the flatten region, the ratio of V and Ti signal intensities is almost proportional to the doping ratio of V and Ti elements in the particle phase, showing feasibility of utilizing the optical method in the doping ratio measurement.

Ti3+-defected and V-doped TiO2quantum dots loaded on MCM-41

V-doped TiO2 quantum dots (QDs) possessing many Ti(3+) defects were fabricated by simple hydrolysis using MCM-41 as a support. The QDs show high charge-separation efficiency and high photocatalytic activity due to the quantum size effect and the newly formed defect- and dopant-mediated band levels.