Synthesis and characterization of rice grains like Nitrogen-doped TiO2 nanostructures by electrospinning–photocatalysis

Rice grain-shaped Nitrogen-doped titanium dioxide (N–TiO₂) nano/mesostructures were fabricated through a combination of sol–gel and electrospinning methods. As-spun nanofibers were continuous and upon thermal treatment at 500° C for 1 h in air, the continuous fibers break into rice grain-shaped TiO₂ nanostructures of average diameter 50–80 nm. The nanostructures were characterized by spectroscopy, microscopy and powder X-ray diffraction. The rice grains consist of spherical particles of average diameter of ~ 18 nm and with N doping, their average diameters decrease from ~ 18 to ~ 12 nm. The presence of N in the TiO₂ lattice was confirmed by X-ray photoelectron spectroscopy (XPS). The band-gap of TiO₂ reduced from 3.19 eV to 2.83 eV upon increasing doping level of N from 0% to 5% (w/w), respectively. The N–TiO₂ rice grains showed an enhanced UV light-assisted photocatalysis compared to pure TiO₂ in the photodegradation of Alizarin Red S dye, an industrially important anthraquinone dye.     

Preparation and properties of sliver and nitrogen co-doped TiO2 photocatalyst

TiO₂ photocatalysts co-doped with different content of Ag and N were prepared by sol–gel method combined with microwave chemical method. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), ultraviolet–visible diffuse reflectance spectrum (UV–vis) and photo-luminescence emission spectrum (PL). The photocatalytic activity was investigated by photocatalytic degradation of methylene blue (MB) under irradiation of fluorescent lamp. The results indicate that Ag and N co-doping can restrain the increase of grain size, broaden the absorption spectrum to visible light region, and inhibit the recombination of the photo-generated electron–hole pairs. Moreover, the photocatalytic activity of Ag–N–TiO₂ in MB degradation is remarkable improved. The degradation rate of the sample with Ag:TiO₂ = 0.05 at%, N:TiO₂ = 18.50 wt% in 5 h is 93.44%, which is much higher than that of Degussa P25 (39.40%).     

Electrical conductivity and stability of A-site deficient (La,Sc) co-doped SrTiO3 mixed ionic-electronic conductor

Mixed ionic–electronic conductors with high ionic conductivity play an important role in modern solid-state ionic devices. The ionic conductivity of SrTiO₃-based materials can be significantly improved by creating deficiency on the A-site and acceptor-doping on the B-site. We report in this paper a remarkable enhancement of ionic conductivity, sinterability and thermal stability of (La, Sc) co-doped SrTiO₃ by creating deficiency on the A-site. The ionic conductivity of (La_0.3Sr_0.7)_0.95Sc_0.10Ti_0.90O_3–δ varies from 0.005 S/cm at 500 °C to 0.01 S/cm at 700 °C and to 0.018 S/cm at 950 °C in 5%H₂/Ar. These values are nearly eight times higher than that of La_0.3Sr_0.7TiO_3–δ at T ≥ 700 °C. The A-site deficiency in (La, Sc) co-doped SrTiO₃ also improves the thermal and electrical stabilities in various atmospheres. A possible charge compensation mechanism among defects in the (La_0.3Sr_0.7)_0.95Sc_0.10Ti_0.90O_3–δ is also discussed.     

Phase transition and microstructure evolution during the carbothermal preparation of Ti(C,N) powders in an open system

Phase transition and microstructure evolution during carbothermal reduction–nitridation of TiO₂ in an open system were investigated using XRD, TGA, SEM and laser particle analysis device. The results show that, the phase evolution sequences are: TiO₂ (anatase) → TiO₂(rutile) → Ti_nO_2n-1(n ? 4) → Ti₃O₅ → Ti(N,O) → Ti(C,N,O) → Ti(C,N). In the reaction process, the predominant reaction mechanism is TiO₂/C solid–solid reaction in the beginning and subsequent the gas–solid reactions mainly between oxides and CO, C and CO₂. The synthesizing powders gradually become finer in form of uniform spherical particles with the formation of cubic phase.     

Titanium and iron oxides produced by sol–gel processing of [FeCl{Ti2(OPri)9}]: structural,spectroscopic and morphological features

The first structurally characterised titanium and iron isopropoxide, [FeCl{Ti₂(OPrⁱ)₉}] (1), has been used as a single-source precursor for TiO₂/Fe₂TiO₅ composites prepared by the sol–gel route. Two distinct hydrolysis and condensation conditions were employed, followed by drying and thermal treatment up to 1000 °C. Product composition and oxide phase transitions were characterised by powder X-ray diffractometry and Raman, electron paramagnetic resonance, Mössbauer and Fourier-transformed infrared spectroscopies. A mixture of nanometric-size TiO₂ (anatase, 3.6–5.8 nm) and amorphous iron(III) oxide was obtained up to 500 °C, while TiO₂ (rutile), α-Fe₂O₃ (hematite) and Fe₂TiO₅ (pseudobrookite) were found at 700 °C. At 1000 °C, only rutile and pseudobrookite were observed. These results suggest that 1 behaves as a type III single-source precursor. Powders calcined at 1000 °C were analysed for surface morphology, microstructure and elemental composition by scanning electron microscopy/energy dispersive X-ray spectroscopy. Results suggest no phase segregation on a sub-micrometer level. Different morphologies were observed for the materials produced by the N₂ route, and this could relate to early crystal growth in an oxygen-deficient environment.     

Synthesis of TiO2 thin films using single molecular precursors by MOCVD method for dye-sensitized solar cells application and study on film growth mechanism

For dye-sensitized solar cells application, in this study, we have synthesized TiO₂ thin films at deposition temperature in the range of 300–750 °C by metalorganic chemical vapor deposition (MOCVD) method. Titanium(IV) isopropoxide, {TIP, Ti(OⁱPr)₄} and Bis(dimethylamido)titanium diisopropoxide, {BTDIP, (Me₂N)₂Ti(OⁱPr)₂} were used as single source precursors that contain Ti and O atoms in the same molecule, respectively. Crack-free, highly oriented TiO₂ polycrystalline thin films with anatase phase were deposited on Si(1 0 0) with TIP at temperature as low as 450 °C. XRD and TED data showed that below 500 °C, the TiO₂ thin films were dominantly grown in the [2 1 1] direction on Si(1 0 0), whereas with increasing the deposition temperature to 700 °C, the main film growth direction was changed to [2 0 0]. Above 700 °C, however, rutile phase TiO₂ thin films have only been obtained. In the case of BTDIP, on the other hand, only amorphous film was grown on Si(1 0 0) below 450 °C while a highly oriented anatase TiO₂ film in the [2 0 0] direction was obtained at 500 °C. With further increasing deposition temperatures over 600 °C, the main film growth direction shows a sequential change from rutile [1 0 1] to rutile [4 0 0], indicating a possibility of getting single crystalline TiO₂ film with rutile phase. This means that the precursor together with deposition temperature can be one of important parameters to influence film growth direction, crystallinity as well as crystal structure. To investigate the CVD mechanism of both precursors in detail, temperature dependence of growth rate was also carried out, and we then obtained different activation energy of deposition to be 77.9 and 55.4 kJ/mol for TIP and BTDIP, respectively. Also, we are tested some TiO₂ film synthesized with BTDIP precursor to apply dye-sensitized solar cell.     

Dielectric behavior of TiO2 ceramic prepared by plasma activated sintering

Rutile-phase TiO₂ ceramic was rapidly fabricated by plasma activated sintering (PAS) at 650–850 °C for 3 min under 30 MPa. The temperature and frequency dependences of the dielectric properties (dielectric constant and dielectric loss) for the dense TiO₂ ceramic were investigated, and the dielectric behavior was briefly discussed. It was demonstrated that extraordinarily high dielectric constant (2–5 × 10⁴) was observed in the whole experimental ranges of ? 160 to 200 °C and 1 kHz–1 MHz. Moreover, the dielectric loss kept a relatively normal level, however, its temperature and frequency dependences were markedly different with those of the rutile-phase TiO₂ preforms. The unusual dielectric behavior was related with the particular dielectric polarizations of the TiO₂ ceramic and its dominant form of loss under different conditions.     

Synthesis and characterization of anatase photocatalyst powder from sodium titanate compounds

The synthesis of anatase photocatalyst powder from sodium titanate compounds prepared from rutile and sodium carbonate powder was studied. The sodium titanate compounds were derived from the solid-state reactions of three different (1:4, 1:1.58 and 1:0.73) (m/m) ratios of TiO₂:Na₂CO₃ at 850 °C. Then, the powder was dissolved in 5 M H₂SO₄ solution, filtered, washed, dried and calcined at 400, 500 or 600 °C for 2 h. The effects of processing parameters on the resultant phase structure, crystallite size, morphology and the surface area of the synthesized powders were investigated. It was found that the anatase powder with a crystallite size of about 102 nm and a specific surface area of 16.7 m²/g synthesized from sodium titanate compounds with a 1:1.58 (m/m) ratio of TiO₂:Na₂CO₃ and calcined at 600 °C showed the best photocatalytic activity to degrade of methylene blue in aqueous solution under UV irradiation.     

Wear characteristics of mechanically milled TiO2 nanoparticles incorporated in electroless Ni–P coatings

Nanosized TiO₂ particles have been prepared by top down approach using mechanical milling with high energy planetary ball mill at 250 rpm for different extents of time (5, 10, 20, 30 and 40 h). Electroless (EL) Ni–P–TiO₂ nanocomposite coatings were developed using alkaline bath containing milled TiO₂ nanoparticles (4 g/l). The results show that, the morphology of TiO₂ particles milled for 40 h exhibit irregular shape with a particle diameter in the range of 33–45 nm. Wear studies of the coatings with 30 μm thickness were investigated using 1, 1.5 and 2 N loads with 0.1 and 0.2 m/s rotation speeds. The Ni–P–TiO₂ nanocomposite coatings exhibit the enhanced hardness and wear resistance as compared to that of Ni–P alloy coatings. Also the composite after heat treatment at 400 °C for 1 h in argon atmosphere showed improved hardness (1010 VHN) and wear resistance (1.5e-06 mm³/N m).     

Fabrication of the CN co-doped rod-like TiO2 photocatalyst with visible-light responsive photocatalytic activity

The CN co-doped TiO₂ nanorods were synthesized by the vapor transport method of water molecules, and urea was used as the carbon and nitrogen source. The samples were characterized by X-ray diffraction and photoelectron spectroscopy analysis. The scanning electron microscope images showed that as-prepared TiO₂ powders were nanorods, which were formed by the stacking of nanoparticles with a uniform size around 40 nm. The degradation of methylene blue with the prepared nanorods demonstrated the photocatalytic activities of TiO₂ under visible light are improved by doping with C and N elements. The main reasons were discussed: doping with C and N elements could enhance the corresponding visible-light absorption of TiO₂. On the other hand, doping C and N could create more oxygen vacancies in the TiO₂ crystals, which could capture the photogenerated electrons more effectively. Thus, more photogenerated holes could be left to improve the photocatalytic activity of TiO₂.     

Photoluminescent properties of Eu3+ doped electrospun CeO2 nanofibers

In this study, CeO₂ nanofibers and that doped with Eu³⁺ were prepared via a facile electrospinning route and annealed at different temperatures ranging from 500 to 900 °C. Their structures were investigated using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Photoluminescence properties of the nanofibers were studied in detail. It was found that the nanofibers with Eu% concentration of 0.67 mol.% and annealed at 700 °C exhibited the highest intensities of the luminescence peaks between 550 and 650 nm.     

Fabrication of partially crystalline TiO2 nanotube arrays using 1, 2-propanediol electrolytes and application in dye-sensitized solar cells

We report the fabrication of self-organized partial crystalline TiO₂ nanotube arrays in 1, 2-propanediol containing fluoride ion. The influence of anodization parameters including NH₄F concentration, water content, anodization voltage and time on the morphology, diameter and length of TiO₂ nanotube were investigated in detail. The prepared TiO₂ nanotube has diameter in 30–120 nm and length in 0.6–3 μm. TiO₂ nanotube arrays are used as photoanode for the application in dye-sensitized solar cell and the photovoltaic performance of 1.91% is achieved with a TiO₂ nanotube sample of 2.2 μm in length combining with N719 dye, and the corresponding photovoltaic parameters of 3.6 mA cm^?2 in short circuit photocurrent density, 840 mV in open circuit potential, and 63.2% in fill factor.     

Synthesis and photocatalytic activity of N-doped TiO2/ZrO2 visible-light photocatalysts

Visible-light responsive N-doped ZrO₂/TiO₂ photocatalysts were synthesized via a sol–gel process. To obtain the optimum nitrogen doping content and operational conditions for photodegradation of NO, several key factors (including nitrogen doping, initial NO concentration, light intensity, reactor temperature, etc.) were investigated under both UV and visible light irradiation. Physical characterization of the photocatalysts was performed using X-ray diffraction (XRD), UV–visible absorption spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). The observed results suggest that nitrogen was doped in the lattice of TiO₂ and had an effect on the translation of phase, photodegradation activity, and visible-light response. Among synthesized photocatalysts, 0.1 M Zr and 0.15 M N supported on TiO₂ exhibited the best visible-light response and the highest NO photodegradation activity.     

Effects of post-annealing on the microstructure and mechanical properties of friction stir processed Al–Mg–TiO2 nanocomposites

Aluminum matrix nanocomposites were fabricated via friction stir processing of an Al–Mg alloy with pre-inserted TiO₂ nanoparticles at different volume fractions of 3%, 5% and 6%. The nanocomposites were annealed at 300–500 °C for 1–5 h in air to study the effect of annealing on the microstructural changes and mechanical properties. Microstructural studies by scanning and transmission electron microscopy showed that new phases were formed during friction stir processing due to chemical reactions at the interface of TiO₂ with the aluminum matrix alloy. Reactive annealing completed the solid-state reactions, which led to a significant improvement in the ductility of the nanocomposites (more than three times) without deteriorating their tensile strength and hardness. Evaluation of the grain structure revealed that the presence of TiO₂ nanoparticles refined the grains during friction stir processing while the in situ formed nanoparticles hindered the grain growth upon the post-annealing treatment. Abnormal grain growth was observed after a prolonged annealing at 500 °C. The highest strength and ductility were obtained for the nanocomposites annealed at 400 °C for 3 h.     

Enhanced stability of catalase covalently immobilized on functionalized titania submicrospheres

In this study, a novel approach combing the chelation and covalent binding was explored for facile and efficient enzyme immobilization. The unique capability of titania to chelate with catecholic derivatives at ambient conditions was utilized for titania surface functionalization. The functionalized titania was then used for enzyme immobilization. Titania submicrospheres (500–600 nm) were synthesized by a modified sol–gel method and functionalized with carboxylic acid groups through a facile chelation method by using 3-(3,4-dihydroxyphenyl) propionic acid as the chelating agent. Then, catalase (CAT) was covalently immobilized on these functionalized titania submicrospheres through 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) coupling reaction. The immobilized CAT retained 65% of its free form activity with a loading capacity of 100–150 mg/g titania. The pH stability, thermostability, recycling stability and storage stability of the immobilized CAT were evaluated. A remarkable enhancement in enzyme stability was achieved. The immobilized CAT retained 90% and 76% of its initial activity after 10 and 16 successive cycles of decomposition of hydrogen peroxide, respectively. Both the K_m and the V_max values of the immobilized CAT (27.4 mM, 13.36 mM/min) were close to those of the free CAT (25.7 mM, 13.46 mM/min).     

Ultraviolet–green photoluminescence of β-Ga2O3 films deposited on MgAl6O10 (1 0 0) substrate

β-Ga₂O₃ films were grown on double-side polished MgAl₆O₁₀ (1 0 0) substrate by metal organic chemical vapor deposition (MOCVD) at 600, 650 and 700 °C. The refractive index dispersive behaviors of Ga₂O₃ films have the typical shape of the normal dispersion curve. Photoluminescence (PL) spectra measured at room temperature revealed that all the films exhibited intense ultraviolet (UV)–green emission from 300 to 650 nm. A minor deep UV emission around 275 nm (∼4.51 eV) was observed for the sample prepared at 700 °C. The intensity of the emission increased markedly when measured at low temperature. The corresponding PL mechanisms were discussed in detail and a schematic diagram was proposed.     

Characterization of fracture behavior of a Ti alloyed supermartensitic 12%Cr stainless steel using Charpy instrumented impact tests

In this work, the toughness of a Ti-alloyed supermartensitic stainless steel with 12%Cr was evaluated by instrumented Charpy impact tests at − 46 °C. The material was heat treated by quenching and tempering at 500 °C or 650 °C. The temper embrittlement phenomena was detected in the specimen tempered at 500 °C, while the specimens as quenched and quenched and tempered at 650 °C presented a ductile fracture with high impact energy values. The predominance of cleavage fracture instead of intergranular cracks suggests that the temper embrittlement was caused by fine and disperse precipitation observed in the specimen tempered at 500 °C. The dynamic initiation fracture toughness (J_Id) was calculated from the force versus deflection curves using three different methods suggested in the literature to obtain the initiation energy.     

Upconversion emission in antimony–germanate double-clad optical fiber co-doped with Yb3+/Tm3+ ions

In the paper upconversion luminescence properties in Yb³⁺/Tm³⁺ co-doped antimony–germanate glass and double-clad optical fiber were studied. The concentration of lanthanides, which has shown the highest upconversion emission intensity at 478 nm (¹G₄ → ³H₆) and 650 nm (¹G₄ → ³F₄), is 1Yb₂O₃/0.1Tm₂O₃ (mol%) as a result of exciting with a laser diode (976 nm). The lifetime of ²F_5/2 (Yb³⁺) level decreases from 781 μs to 71 μs in the presence of Tm³⁺ 0.1–0.75 mol% respectively. Luminescence decay curve of glass co-doped with 1Yb₂O₃/0.75Tm₂O₃ suggests donor–donor fast migration followed by Tm³⁺ → Yb³⁺ energy transfer. Glass characterized by highest intensity of upconversion luminescence (1Yb₂O₃/0.1Tm₂O₃ mol%) was used as core of double-clad optical fiber made by modified rod-in-tube method. Mechanisms influencing differences in upconversion amplified spontaneous emission of the fabricated optical fiber and bulk glass were discussed. Reabsorption of the amplified spontaneous emission signal along the fibre resulting from Tm³⁺:³H₆ → ¹G₄, transition was observed.     

Effect of the Ti/Na molar ratio on the acidity and the structure of TiO2 nanostructures: Nanotubes,nanofibers and nanowires

TiO₂ nanotubes were prepared by the hydrothermal treatment of TiO₂ particles with different NaOH concentrations (5, 7, 10 and 12 N) at 140 °C; afterwards, HCl was added until reaching pH 1. Both the crystalline phase and coordination of the TiO₂ nanotubes, composed principally of H₂Ti₃O₇ and H₂Ti₄O₉·2H₂O, were significantly affected by the NaOH rinsing treatment. Likewise, the surface area, pore volume and pore size of the TiO₂ nanotubes changed with the NaOH rinsing treatment. Finally, the NaOH rinsing treatment exerted a notable effect on the generation of Brönsted sites, which is shown by the following sequence: NT7 > NT10 > NT12 > NT5; meanwhile Lewis sites were only present on the NT5 sample.     

Improving 1.54 μm emission by inducting Ti ion in Er3+/Yb3+ codoped phosphate glass ceramic

Er³⁺/Yb³⁺ doped phosphate glasses were prepared by high-temperature melting method. Under 975 nm excitation, the intensity of the visible light in the sample doped with TiO₂ is weaker compared to that of the sample un-doped with TiO₂ However, the intensity of the 1540 nm emission in the sample doped with TiO₂ is stronger than that in the sample un-doped with TiO₂ The sample can efficiently improve the 1540 nm emission by absorbing visible light.