Effect of B2O3 on luminescence of erbium doped tellurite glasses

The B2O3 was introduced into the Er3+ doped TeO2-ZnO-Na2O glass to increase the phonon energy of the host. The effect of B2O3 on the non-radiative rate of the 4I11/2-->4I13/2 transition of Er3+, the lifetime of the 4I11/2 and 4I13/2 levels, the green and red upconversion emissions intensity, and the 4I13/2-->4I15/2 emission intensity was discussed. The results show that the phonon energy of boro-tellurite glass is close to that of germanate glass and is quite smaller than that of borate glass. The lifetime of 4I11/2 level and the upconversion emissions decrease with increasing B2O3 concentration. The higher OH group concentration presented in the boro-tellurite glass may shorten the lifetime of 4I13/2 level and also reduce the quantum efficiency of 4I13/2-->4I15/2 emission. The future dehydrating procedures are suggested to enhance the efficiency of amplification at 1.5 microm band.     

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.     

Searching for facet-dependent photoactivity of shape-controlled anatase TiO2

Improving the performance of mostly employed anatase TiO₂ photocatalysts by properly controlling their crystal shape represents a big challenge to improve their efficiency in photocatalytic applications. After the synthesis, reported in 2008, of anatase microcrystals enriched in high-energy {001} facets, many efforts have been made aimed at tuning the crystal morphology of anatase, by means of either fluorine-mediated or more environmentally friendly methods, producing a deviation from its regular crystal growth. In this relatively new field of investigation, controversial opinions emerged concerning the role of each type of facet and its relative amount in relation to photoefficiency optimization. This review addresses this topic by presenting a critical survey of selected literature reports. After a brief introduction on the main synthetic strategies adopted to obtain shape-controlled anatase photocatalysts, the attention is focused on the methods employed for their comprehensive characterization, including the identification and quantification of exposed facets and the assessment of their influence on bulk and surface properties relevant to photoactivity. Potential interferences, derived from synthetic routes and possibly affecting the conclusions of facet-dependent photoactivity investigations, are also discussed. Key examples of test reactions actually demonstrating how both the type and/or the amount of specific facets influence photocatalytic activity are finally reported, aiming at providing rational bases for the design of better performing shape-controlled anatase photocatalysts.     

Effect of amines on the peroxo-titanates and photoactivity of annealed TiO2

The aim of this study was to explore the influence of various n-propylamines (mono, di, and tri) and tert-butylamine on the properties of prepared peroxo-titanates and annealed TiO₂. Detailed structural characterization (SEM, TEM with EDX, XRD) confirmed the 2D-foil morphology of TiO₂ nanocrystals and the CHNS analysis together with XPS showed presence of carbon (under 1 wt%). The annealed TiO₂ showed excellent photocatalytic activity and up to four times higher decomposition rate constant upon UV irradiation than the P25. Favourable growth of TiO₂ crystals was observed especially when propylamine and tert-butylamine were used (as precursors for the peroxo-titanates). Increased photocatalytic efficiency of the highly crystalline nano-TiO₂ was confirmed due to high-reactive anatase facets and the morphology composed of microsheets formed by interconnected nanocrystals. The photoinduced electron transfer was confirmed via EPR spectroscopy. This synthesis’ procedure offers a novel preparation method of highly photoactive C-doped TiO₂ achieved relatively easily after annealing of lyophilized amino-peroxo-titanate.     

Surface properties and photoactivity of TiO2 treated with electron beam

The improvement of the TiO₂-photoactivitiy by electron beam treatment (1 MeV) as a function of the absorbed radiation dose (MGy) is reported. The radiation-induced effects in the TiO₂ crystal structure, e.g. change of the Ti³⁺/Ti⁴⁺ ratio, increase of the photoactivity, etc. were investigated. Three methods were implemented in this respect: for the change of the TiO₂ crystal structure X-ray photoelectron spectroscopy and photoluminescence spectroscopy were applied. The photocatalytic activity of the EB-treated TiO₂ was tested by taking the degree of methylene blue photodegradation as a measure of the achieved effect. The obtained experimental data of all testing methods showed that in TiO₂ at an absorbed dose of 0.5 MGy optimum changes in crystal structure of the catalyst occur, resulting in the highest photocatalytic efficiencies.     

Silane grafting of TiO2 nanoparticles: dispersibility and photoactivity in aqueous solutions

Titania nano‐sized particles were treated by various amounts of tetraethyl orthosilicate precursor. The extent of grafting was characterized using Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐Vis) spectroscopy techniques, thermal gravimetric analysis, X‐ray fluorescence and zeta potential measurements. Sedimentation behaviour of titanium dioxide (TiO₂) nanoparticles in aqueous solutions was evaluated visually and using a separation analyser. Photocatalytic activity of nanoparticles was studied by photo‐activated degradation reaction of Rhodamine B dyestuff in aqueous solutions. The results showed that grafted particles had acquired enhanced dispersion stability and lower photocatalytic activity in aqueous solutions. Untreated TiO₂ dispersions settled rapidly and sedimentation completed within 24 h through the coagulation mechanism, whereas that of the silica‐treated nanoparticles, depending on the silica content, showed different degrees of stability by flocculation mechanism. Photodebleaching of Rhodamine B in the presence of treated nanoparticles is evident by weaker intensity of UV absorption peak of 554 nm due to lowering concentration of Rhodamine B accompanied with the blue shift in UV absorption peaks. However, untreated TiO₂ nanoparticles showed only weaker intensity of UV absorption peak. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and photoactivity of nanostructured anatase, rutile and brookite TiO2 thin films

Photoactive films consisting of pure anatase, brookite or rutile TiO2 were prepared by dip coating from water dispersions obtained by using TiCl4 as the precursor under similar mild experimental conditions.     

Blue,green,red upconversion luminescence and optical characteristics of rare earth doped rare earth oxide and oxysulfide

The cold isostatic press pretreatment process was adopted to prepare fine rare earth oxysulfide up-conversion phosphors with spherical shape, narrow size distribution and high luminescence efficiency. The upconversion optical characteristics and brightness of the blue (Y2O2SYb,Tm), green (Y2O2S: Yb,Er), red (Y2O3Yb,Er) emitter were also investigated, and a novel method was successfully developed for the brightness measurement of upconversion luminescence (UPL). It is shown that a white color can be obtained by the appropriate mixture of these primary blue, green and red emissions components. The Er3 ions exhibit different upconversion mechanism in Y2O2S and Y2O3 host materials. The rare earth oxysulfide is an efficient upconversion matrix. The UPL brightness of Y2O2S: Yb,Er is 6.5 times higher than that of Y2O3: Yb,Er, and Y2O2S: Yb,Er shows UPL brightness of 1100 cd/m2 under 5.56 W/cm2 power density using a 980 nm laser diode.     

Photocatalysis and hydrophilicity of doped TiO2 thin films

TiO(2) thin films were prepared using the dip-coating method with a polymeric sol including additives such as Al, W, and Al+W to examine two major properties: photocatalysis and hydrophilicity. W-doped films showed the best photocatalytic efficiency, while Al-doped film was poorer than undoped samples. However, good hydrophilicity in terms of saturation contact angle and surface conversion rate was found in Al- and (Al+W)-mixed-doped films. It was found that deep electron-hole traps and high surface acidity of W-doped TiO(2) thin film were the major factors in high photocatalytic efficiency. In addition, low surface acidities of Al- and (Al+W)-doped films provided better hydrophilicity than W-doped ones. However, the amount of [Ti(3+)] point defects on the surface was another major factor, probably the most important, in getting the best hydrophilicity. Conclusively, it seemed that many parts of the photocatalysis mechanism depend more on bulk-related properties than do those of hydrophilicity, which can be defined as an interfacial (surface) or near-surface-restricted process.     

Spectroscopic study of polycrystalline TiO2 doped with vanadium

The structure of coordination sites (V⁴⁺ ions) and their spatial distribution in the polycrystalline titanium dioxide (rutile) lattice were studied by ESR. It was found that at low degrees of doping, at [V⁴⁺] < 0.5 at.%, the vanadium ions are isotropically distributed in the rutile lattice. At [V⁴⁺] > 0.5 at.% a new microphase with the mixed composition {TiO₂—VO²} is formed. The mixed microphase has a noticeably narrower band gap than the initial TiO₂. Comparison of the photocurrent spectra and the plots of the integral photocurrent vs. vanadium content with the structural data obtained using ESR spectroscopy showed that the formation of the {TiO₂—VO²} microphases deteriorates the photoelectrochemical properties of the modified photoelectrodes. Synthetic procedures interfering the formation of such microphases in the doped rutile are discussed.     

(I(2))(n) encapsulation inside TiO(2): a way to tune photoactivity in the visible region

We report on the synthesis of nanovoid-structured TiO(2) material via a sol-gel route using titanium isopropoxide as precursor. The nanovoids are formed during the thermal treatment in air at 773 K. The surfaces of internal cavities are populated by the partial oxidation products of the organic part of the Ti precursor (CO(2), hydrogen carbonates, and residual isopropoxide groups). The thermal treatment in air at 773 K allows the maintainence, in the internal voids, of the encapsulated species. Addition of iodine in the synthesis procedure results in a new nanovoid-structured titanium oxide able to absorb light in the whole visible part of the electromagnetic spectrum. The origin of this absorption is attributed to the presence of (I(2))(n) adducts encapsulated in the nanocavities. These species coexist with partial combustion products of isopropoxide groups. Due to the protection of the TiO(2) walls, the (I(2))(n) adducts are not destroyed by thermal treatments in air. We have investigated whether the electron promoted in the excited state of the dye molecule (upon absorption of visible light from the (I(2))(n) adducts) can be injected into either the TiO(2) conduction band or some titanium-localized acceptor, followed by migration of the injected electron to the surface where it reduces adsorbed organic molecules. Preliminarily experiments conducted with sunlight show that the surface-specific efficiency of this process, tested by following the degradation of methylene blue, is about 10 times higher than that of the P25 commercial TiO(2) photocatalyst.     

碳纳米管改性TiO2的光催化性能

本文研究碳纳米管改性TiO2光催化剂的制备和影响其光催化性能的因素。实验结果表明，CNT的加入方法，CNT的含量，催化剂的灼烧温度等均影响光催化剂的光催化性能。制备的CNT-TiO2光降解低浓度的甲胺脾农药(40．7lmg／L)具有很好的效果，光催化降解过程符合一级反应动力学方程。     

Continuous modification of upconversion luminescence of fluorescent dye in the crystalline colloidal arrays

The crystalline colloidal arrays with controllable photonic bandgaps were prepared by the change of volume fraction of the polystyrene microspheres. Upconversion emission property of fluorescent dye has investigated in crystalline colloidal array, and continuous modification of the upconversion emission of fluorescent dye was observed. A significant suppression of upconversion emission of dye in the range of the photonic bandgap as well as enhancement at the bandgap edge was obtained in the crystalline colloidal arrays. In addition, upconversion emission of dye was also enhanced when the excited light overlapped with the long or short bandgap edge of the crystalline colloidal arrays, which is due to slow photons effect near the edges of a photonic bandgap. The continuous modification and enhancement of upconversion emission may be important for the development of low-threshold upconversion lasers and displays.     

Al掺杂对锐钛矿型TiO2光催化性能影响的研究

采用平面波赝势(PWPP)方法进行密度泛函(DFT)计算,研究了Al掺杂对锐钛矿晶体能带、态密度的影响.分析发现掺杂后Al原子3s和3p轨道上的电子虽然对晶体的价带和导带贡献不大,却诱使导带发生较大程度下移,禁带宽度减小,理论预测可以发生红移.采用低温燃烧合成法制备了Al掺杂锐钛矿型纳米TiO2,紫外-可见吸收光谱检测和甲基橙降解实验证明,Al掺杂TiO2光吸收强度增强,吸收带边界发生红移;光催化性能较纯TiO2有所改善.理论计算结果与实验结果相符.     

Adsorption and solar light decomposition of acetone on anatase TiO2 and niobium doped TiO2 thin films

Adsorption and solar light decomposition of acetone was studied on nanostructured anatase TiO2 and Nb-doped TiO2 films made by sol-gel methods (10 and 20 mol % NbO2.5). A detailed characterization of the film materials show that films contain only nanoparticles with the anatase modification with pentavalent Nb oxide dissolved into the anatase structure, which is interpreted as formation of substituted Nb=O clusters in the anatase lattice. The Nb-doped films displayed a slight yellow color and an enhanced the visible light absorption with a red-shift of the optical absorption edge from 394 nm for the pure TiO2 film to 411 nm for 20 mol % NbO2.5. In-situ Fourier transform infrared (FTIR) transmission spectroscopy shows that acetone adsorbs associatively with eta1-coordination to the surface cations on all films. On Nb-doped TiO2 films, the carbonyl bonding to the surface is stabilized, which is evidenced by a lowering of the nu(C=O) frequency by about 20 cm(-1) to 1672 cm(-1). Upon solar light illumination acetone is readily decomposed on TiO2, and stable surface coordinated intermediates are formed. The decomposition rate is an order of magnitude smaller on the Nb-doped films despite an enhanced visible light absorption in these materials. The quantum yield is determined to be 0.053, 0.004 and 0.002 for the pure, 10% Nb:TiO2, and 20%Nb:TiO2, respectively. Using an interplay between FTIR and DFT calculations we show that the key surface intermediates are bidentate bridged formate and carbonate, and H-bonded bicarbonate, respectively, whose concentration on the surface can be correlated with their heats of formation and bond strength to coordinatively unsaturated surface Ti and Nb atoms at the surface. The oxidation rate of these intermediates is substantially slower than the initial acetone decomposition rate, and limits the total oxidation rate at t>7 min on TiO2, while no decrease of the rate is observed on the Nb-doped films. The rate of degradation of key surface intermediates is different on pure TiO2 and Nb-doped TiO2, but cannot explain the overall lower total oxidation rate for the Nb-doped films. Instead the inferior photocatalytic activity in Nb-doped TiO2 is attributed to an enhanced electron-hole pair recombination rate due to Nb=O cluster and cation vacancy formation.     

Preparation of mesophase pitch doped with TiO2 or TiC particles

The co-pyrolysis of a petroleum residue with two different sources of titanium (tetrabutyl-ortotitanate (TBO) or titanium carbide nano-powder) was carried out to obtain mesophase pitches containing TiO₂ or TiC nanoparticles. Co-pyrolysis is an appropriate technique to achieve a good dispersion and low particle size. In the case of TBO, TiO₂ nanoparticles (5–20 nm) are observed, which are forming aggregates, the largest of them being 1–2 μm. In the case of TiC nano-particles, they are more difficult to disperse and larger aggregates are formed, although the final material is rather homogenous. The chemistry of pyrolysis for the production of doped and undoped mesophase pitches has been followed by means of solvent insolubility, XRD, XPS, FTIR and elemental analysis. They show evidences of promotion of the formation of mesophase in the presence of the titanium-containing particles, especially in the presence of TiO₂. The final materials can be of great value as precursors to produce high density titanium doped graphites for nuclear and space applications.     

氯掺杂二氧化钛柱撑蒙脱土的合成及光催化性能

采用溶胶 凝胶法制备了氯掺杂二氧化钛柱撑蒙脱土催化剂。 利用XRD、SEM、UV-Vis-DRS、光致发光谱(PLS)、N2吸附-脱附和XPS等测试技术对其进行了表征。 结果表明,该催化剂具有明显的锐钛矿相结构,且氯掺杂与二氧化钛柱撑后,蒙脱土的层间结构没有完全被破坏;氯掺杂拓宽了其光吸收范围,在可见光区吸收增强;其带隙能由3.19 eV减小至3.14 eV;氯以阴离子形式存在于TiO2晶格中。 对硝基苯胺降解实验表明,氯掺杂可显著提高二氧化钛柱撑蒙脱土的光催化活性,氯掺杂量为6%(与钛的摩尔比)的催化剂具有较好光催化活性。     

Tribological properties of multilayer nanostructure TiO2 thin film doped by SiO2

Multilayer of TiO₂ and TiO₂:SiO₂ thin films were grown on a glass substrate by sol?Cgel processes, followed by high temperature treatment at 500?°C. The fine grained TiO₂ films controlled by SiO₂ dopant showed very good wear resistance and endurance life. Energy dispersive X-ray spectroscopy was used to indicate the elements in the films. X-ray diffraction analyses indicated that TiO₂ and TiO₂:SiO₂ film contain only anatase phase. The morphologies of the original and worn surfaces of the samples were analyzed by means of scanning tunneling microscope and scanning electron microscopy. The tribological properties of TiO₂ and TiO₂:SiO₂ thin films sliding against AISI52100 steel pin were evaluated on a pin on disk friction and wear tester. The results showed that 25-layer TiO₂:SiO₂ films are superior in reducing friction and resisting wear compared with the glass substrate.