Oxygen vacancy and dopant concentration dependent magnetic properties of Mn doped TiO2 nanoparticle

Mn doped TiO₂ nanoparticles are synthesized by sol–gel method. Incorporation of Mn shifts the diffraction peak of TiO₂ to lower angle. The position and width of the Raman peak and photoluminescence intensity of the doped nanoparticles varies with oxygen vacancy and Mn doping level. The electron spin resonance spectra of the Mn doped TiO₂ show peaks at g = 1.99 and 4.39, characteristic of Mn²⁺ state. Reduction in the emission intensity, on Mn doping, is owing to the increase of nonradiative oxygen vacancy centers. Mn doped TiO₂, with 2% Mn, shows ferromagnetic ordering at low applied field. Paramagnetic contribution increases as Mn loading increases to 4% and 6%. Temperature dependent magnetic measurement shows a small kink in the ZFC curve at about 40 K, characteristic of Mn₃O₄. The ferromagnetic ordering is possibly due to the interaction of the neighboring Mn²⁺ ions via oxygen vacancy (F⁺ center). Increase in Mn concentration increases the fraction of Mn₃O₄ phase and thereby increases the paramagnetic ordering.     

Short electrospun composite nanofibers: Effects of nanoparticle concentration and surface charge on fiber length

Short composite nanofibers were fabricated by electrospinning polymer/TiO₂ nanoparticle solutions of 13 wt. % cellulose acetate as a polymer under a voltage of 5.5 kV and at a flow rate of 0.1 μL/min, and the nanoparticles could be added in concentrations as high as 50 wt. %. The length of the short composite nanofibers was significantly decreased from 112 to 70 μm by the addition of at least a 5 wt. % concentration of nanoparticles, and it gradually continued to decrease as the nanoparticle concentration was increased. The length of the short composite nanofibers with a low concentration of nanoparticles was affected by the surface charge of the nanoparticles, and negatively charged nanoparticles readily dispersed to the negatively charged polymers in solution, which resulted in an elongation of the fabricated short composite nanofibers.     

S掺杂对锐钛矿相TiO2电子结构与光催化性能的影响

采用基于第一性原理的平面波超软赝势方法研究了掺杂不同价态S的锐钛矿相TiO2的晶体结构、杂质形成能、电子结构及光学性质.计算结果表明硫在掺杂体系中的存在形态与实验中的制备条件有关;掺杂后晶格发生畸变、原子间的键长及原子的电荷量也发生了变化,导致晶体中的八面体偶极矩增大;S 3p态与O 2p态、Ti 3d态杂化而使导带位置下移、价带位置上移及价带宽化,从而导致TiO2的禁带宽度变窄、光吸收曲线红移到可见光区.这些结果很好地解释了S掺杂锐钛矿相TiO2在可见光下具有优良的光催化性能的内在原因.根据计算结果分析比较了硫以不同离子价态掺杂对锐钛矿相TiO2电子结构和光催化性能影响的差别.     

Phase transformations and crystallization kinetics in electrospun TiO2 nanofibers in air and argon atmospheres

The effects of atmospheric air and argon environments on thermal-induced phase transformations in electrospun TiO₂ nanofibers have been investigated in situ using synchrotron radiation diffraction. Diffraction results showed that the as-synthesized TiO₂ nanofibers were initially amorphous, but crystallized to form anatase and rutile after thermal annealing in air or argon at elevated temperatures. The crystallization temperature of anatase was delayed by 100 °C in argon relative to in air, and the transformation of anatase into rutile occurs faster in argon atmosphere than in air due to the formation of oxygen vacancies. Non-linear strains formed in both polymorphs and the substantial elevation of rutile thermal expansion pointed to strain anisotropy in the rutile phase and the concomitant fibre breakage.     

C自掺杂TiO2纳米棒的制备与光催化性能研究

本文以TiC为前驱体和掺杂源,采用一步水热法合成了具有可见光吸收的C自掺杂金红石相TiO_2纳米棒.样品的结构、形貌、化学态和光学性质等可通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)、傅里叶变换红外光谱仪(FT-IR)、X射线光电子能谱仪(XPS)以及紫外可见分光光度计(UV-vis)来表征.所合成的样品具有较强的光催化活性,可通过在可见光照射下降解有机染料罗丹明B(RhB)来验证.C自掺杂TiO_2所呈现的较强光催化活性是由于其具有小的能带间隙(2.74 eV)、大的比表面积和高的电子-空穴对分离率.     

C自掺杂TiO2纳米棒的制备与光催化性能研究

本文以TiC为前驱体和掺杂源,采用一步水热法合成了具有可见光吸收的C自掺杂金红石相TiO2纳米棒．样品的结构、形貌、化学态和光学性质等可通过X射线衍射仪（XRD）、扫描电子显微镜（SEM）、傅里叶变换红外光谱仪（FT-IR）、X射线光电子能谱仪（XPS）以及紫外可见分光光度计（UV-vis）来表征．所合成的样品具有较强的光催化活性,可通过在可见光照射下降解有机染料罗丹明B（RhB）来验证．C自掺杂TiO2所呈现的较强光催化活性是由于其具有小的能带间隙（2.74 eV）、大的比表面积和高的电子-空穴对分离率．     

C自掺杂TiO2纳米棒的制备与光催化性能研究

本文以TiC为前驱体和掺杂源,采用一步水热法合成了具有可见光吸收的C自掺杂金红石相TiO2纳米棒．样品的结构、形貌、化学态和光学性质等可通过X射线衍射仪（XRD）、扫描电子显微镜（SEM）、傅里叶变换红外光谱仪（FT-IR）、X射线光电子能谱仪（XPS）以及紫外可见分光光度计（UV-vis）来表征．所合成的样品具有较强的光催化活性,可通过在可见光照射下降解有机染料罗丹明B（RhB）来验证．C自掺杂TiO2所呈现的较强光催化活性是由于其具有小的能带间隙（2.74 eV）、大的比表面积和高的电子-空穴对分离率．     

Effect of hydrothermal temperature on photocatalytic properties of TiO2 nanotubes

This work presents a study on the effect of hydrothermal temperature and structure on the photocatalytic activity of TiO₂ nanotubes (TNT) prepared using commercially available TiO₂ nanoparticles (P25). From the results, it was found that a higher hydrothermal temperature led to an increase in the specific surface area, total pore volume, and the size of mesopores in TNT. Moreover, the TNTs synthesized by the hydrothermal method had a new structure, which was very different from the anatase and rutile structures found in P25. The TNTs synthesized at 150 °C had the highest specific surface area of 371 m²/g. However, the TNTs synthesized at 180 °C exhibited the best photocatalytic efficiency and dye adsorption capacity, as compared to other TNTs, resulting from their well-developed mesopores.     

Preparation and photocatalytic activity of bicrystal phase TiO2 nanotubes containing TiO2-B and anatase

Bicrystal phase TiO₂ nanotubes (NTS) containing monoclinic TiO₂-B and anatase were prepared by the hydrothermal reaction of anatase nanoparticles with NaOH aqueous solution and a heat treatment. Their structure was characterized by XRD, TEM and Raman spectra. The results showed that the bicrystal phase TiO₂ NTS were formed after calcining H₂Ti₄O₉·H₂O NTS at 573 K. The bicrystal phase TiO₂ NTS exhibit significantly higher photocatalytic activity than the single phase anatase NTS and Dessuga P-25 nanoparticles in the degradation of Methyl Orange aqueous solution under ultraviolet light irradiation, which is attributed to the large surface and interface areas of the bicrystal phase TiO₂ NTS.     

Enhanced photocatalytic activity of In2O3-decorated TiO2

Titania (TiO₂)-based photocatalysts decorated with different amounts of indium oxide (In₂O₃) were prepared by a pore impregnating method and characterized by the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The separation efficiency of photogenerated charges was investigated using benzoquinone (BQ) as scavenger. The activities of the photocatalysts were evaluated by decolorization of methyl orange (MO) aqueous solution under ultraviolet-light irradiation. Compared to TiO₂, In₂O₃/TiO₂ composites show improved photocatalytic performance due to the coupling effect of TiO₂ and In₂O₃, which greatly improves the separation of photogenerated electrons and holes.     

Influence of the dopant concentration in In-doped SrTiO3 on the structural and transport properties

thin films are grown epitaxially on NdGaO₃ (001) and characterized for x=0, 0.005, 0.02, 0.1, 0.2, 0.5. While films with x=0, 0.2 and 0.5 are insulating, the ones with x=0.005, 0.02 and 0.1 are semiconducting and show a p-type behaviour. Highly rectifying diodes composed of SrIn_0.005Ti_0.995O₃ grown on SrNb_0.02Ti_0.98O₃ thin films confirm this behavior. Therefore the use of In as a dopant in SrTiO₃ is promising in the field of semiconductors.     

Triblock copolymer-templated synthesis of porous TiO2 and its photocatalytic activity

Mixed amorphous and anatase-type titania particles were synthesized using non-ionic triblock copolymer as surfactant template and TiOSO₄ as inorganic precursor through sol–gel process. The as-prepared materials were characterized by X-ray diffraction spectroscopy, scanning and transmission electron microscopy, specific surface area, Fourier-transformed infrared spectroscopy, and diffuse reflectance ultraviolet–visible spectroscopy. The template material could be easily removed by extracting with dichloromethane and was confirmed by infrared spectroscopy. X-ray diffraction pattern reveals the crystalline part of as-prepared product as a framework of anatase phase. From the N₂ adsorption–desorption analysis, the as-prepared sample has a surface area of 301 m²/g with pore size distribution narrowly centered around 6 nm. The photodegradation of indigo carmine including kinetics, effect of pH, and recyclability of the product were investigated. The photocatalytic results showed that the as-synthesized titania could efficiently degrade indigo carmine under ultraviolet irradiation and showed higher photocatalytic activity than the commercial Degussa P25–TiO₂.     

Effects of temperature and humidity on electrospun conductive nanofibers based on polyaniline blends

This study focuses and discusses the effects of temperature and humidity on electrospun conductive nanofibers, made with different polymer blends, deposited directly on interdigitated electrodes. The selected conductive polymers were based on blends of polyaniline emeraldine salt form and three different carrier hosting polymers: polyvinilpyrrolidone, polystyrene, and polyethylene oxide respectively. The obtained fibrous layers were investigated by the electrical measurements and morphological analysis (scanning electron microscopy). The study was made on the correlation between the electrical changes and morphological discrepancies due to temperature treatment. Moreover, this article reports the effects of relative humidity variations on electrical parameters. Since polyaniline is a well-known sensing material for different gases and volatile organic compounds, this study could be considered a supportive study for employing of the mentioned polymer blends as chemical interactive materials in gas sensor applications.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Preparation and photoluminescence properties of electrospun nanofibers of C60/PVK

Ultrafine fullerene (C60)/poly(N-vinylcarbazole) (PVK) composite fibers with 1 μm diameter were prepared by electrospinning C60/PVK blend solutions in solvent mixtures of N,N-dimethylformamide (DMF)/toluene. The UV absorption spectra of nanofibers have a similar behavior as observed in the thin films for the same doping condition. It is interesting to observe that the PVK nanofibers have a very strong blue-violet luminescence, while ‘bright spots’ due to C60 can be observed on the C60/PVK fibers under UV irradiation in a fluorescence optical microscope. Compared to the emission spectra of PVK thin films, the photoluminescence of the PVK nanofibers shows a new emission peak at 437 nm. Efficient energy transfer was observed in C60/PVK thin films, as well as in blend nanofibers.     

Structural and magnetic properties of electrospun FeCoNi magnetic nanofibers with nanogranular phases

Structural and magnetic properties of silicon/aluminum-added and -free FeCoNi magnetic alloy nanofibers with nanogranular phases prepared by electrospinning and subsequent annealing of the PVP-blended ternary metal precursors in hydrogen atmosphere were investigated. The FeCoNi magnetic alloy nanofibers with evenly distributed nanocrystalline phases were formed, which are identified as γ-Fe_1−x Ni _x binary phase with face-centered cubic structure and α-CoFe phase with body-centered cubic structure. At elevated temperature, the α → γ structural martensitic transformation in the FeCoNi ternary alloys occurred due to the inhomogeneities in composition of the matrix during annealing of the alloy with metastable α-phase. In the Si/Al-added FeCoNi nanofibers, more than two phases with complicated-boundaries of the grains in and/or outside the nanofibers were formed as crystalline phases and amorphous phase. The amorphous phase consisted of Si and/or Al acted as an inhibitor diminishing α → γ transformation as well as an interparticle insulation layer. At low annealing temperature of 450 °C, the Si/Al-added nanofiber mainly consisted of metastable α-phase with a low-crystallinity surface structure and very small diameter of 13 nm was formed and showed an unexpectedly high coercivity, which attributed to the surface effects and/or high surface/volume ratio.     

Synthesis of Zr-doped TiO2 templated from cloth and its photocatalytic activity

Biomorphic Zr-doped TiO₂ (Zr _x Ti_{1 ? x} O₂) with hierarchical micro- and nanostructures was successfully fabricated using cloth as the host template. We found that the resulting Zr _x Ti_{1 ? x} O₂ faithfully duplicated the morphologic microstructures of the initial cloth with grain size of about 10–50 nm. The photocatalytic activity of the as-prepared Zr _x Ti_{1 ? x} O₂ was examined by the degradation of rhodamine B in aqueous solution under simulated solar light, which showed that templates pretreated with NaOH solution followed by mixed acid and an appropriate amount of doped Zr (3 mol%) could significantly enhance the photocatalytic activities of Zr _x Ti_{1 ? x} O₂. This simple template method provides a cost-effective and ecofriendly route to synthesize other metal-doped semiconductor materials of predicted morphology.