Hydrothermal synthesis of hemisphere-like F-doped anatase TiO<Subscript>2</Subscript> with visible light photocatalytic activity

Hemisphere-like F-doped anatase TiO₂ has been synthesized by hydrothermal treatment of TiF₄ aqueous solution in the presence of starch at 130 °C for 10 h, and then calcined at 450 °C for 2.5 h in air. The as-synthesized product has been investigated by photocatalytic reaction test and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV–Vis diffuse reflectance spectra (DRS). The results showed that fluorine was successfully doped into the TiO₂ hemispheres. The F-doped TiO₂ hemispheres showed high visible light activity in degradation of acid orange II, which could be attributed to the creation of oxygen vacancies and good crystallinity.     

Synthesis and characterization of anatase and rutile TiO2 nanorods by template-assisted method

Well-aligned anatase and rutile TiO₂ nanorods and nanotubes with a diameter of about 80–130 nm have successfully been fabricated via sol-gel template method. The prepared samples were characterized by using thermogravimetric (TG) and differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The XRD results indicated that the TiO₂ nanorods were crystallized in the anatase and rutile phases, after annealing at 400–800 °C for different periods of time from 0.2 to 10 h.     

Functionalization of electrospun magnetically separable TiO<Subscript>2</Subscript>-coated SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers: strongly effective photocatalyst and magnetic separation

Magnetically separable TiO₂-coated SrFe₁₂O₁₉ electrospun nanofibers were obtained successfully by means of sol–gel, electrospinning, and coating technology, followed by heat treatment at 550–650 °C for 3 h. The average diameter of the electrospun fibers was 500–600 nm. The fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimized calcining temperature was determined by XRD and the analysis of decolorizing efficiency of methylene blue (MB) under UV–vis irradiation. The photocatalytic activity of the TiO₂-coated SrFe₁₂O₁₉ fibers was investigated using ultraviolet–visible absorbance by following the photooxidative decomposition of a model pollutant dye solution, MB in a photochemical reactor. In contrast to pure TiO₂ fibers, the TiO₂-coated SrFe₁₂O₁₉ fibers have higher absorption in 250–750 nm wavelength regions. The presence of SrFe₁₂O₁₉ not only broadened the response region of visible-light, but also enhanced the absorbance for UV light. The decolorizing efficiency of MB under UV–vis irradiation was up to 98.19%, which was a little higher than that of Degussa P25 (97.68%). Furthermore, these fibers could be recollected easily with a magnet in a photocatalytic process and had effectively avoided secondary pollution of treated water.     

SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> fibers from titanium-modified polycarbosilane

We developed a process for preparing SiO₂/TiO₂ fibers by means of precursor transformation method. After mixing PCS and titanium alkoxide, continuous SiO₂/TiO₂ fibers were fabricated by the thermal decomposition of titanium-modified PCS (PTC) precursor. The tensile strength and diameter of SiO₂/TiO₂ fibers are 2.0 GPa, 13 μm, respectively. Based on X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) measurements, the microstructure of the SiO₂/TiO₂ fibers is described as anatase–TiO₂ nanocrystallites with the mean size of ~10 nm embedded in an amorphous silica continuous phase.     

Facile tailoring of titanate nanostructures at low alkaline concentration by a solvothermal route

Nanostructured titanates with different morphologies such as nanoflakes, nanotubes, and nanofibers have been selectively synthesized by a simple solvothermal treatment of commercial anatase TiO₂ using the mixed water–ethanol cosolvent at low alkaline concentration. The effects of solvothermal temperature, volume ratio of H₂O to C₂H₅OH, amount of NaOH and solvents on the formation of titanate nanostructures have been systematically studied through X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). At low concentration of NaOH solution (the actual concentration of OH⁻ in the solution is only 0.58 M), different titanate nanostructures are achieved by simply changing the volume ratio of H₂O to C₂H₅OH at 180 °C and titanate nanotubes can be synthesized between 100 and 180 °C. A probable formation mechanism is proposed based on XRD, SEM and TEM analysis. The influence of cosolvent on the transformation from anatase TiO₂ to titanate is also investigated.     

An efficient visible light photocatalyst prepared from TiO<Subscript>2</Subscript> and polyvinyl chloride

An efficient visible light photocatalyst has been prepared from TiO₂ nanoparticles and a partly conjugated polymer derived from polyvinyl chloride (PVC). It was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–visible diffuse reflectance spectroscopy (UV–Vis DRS), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The visible light photocatalytic activity of the as-prepared photocatalyst was evaluated by the photocatalytic degradation of Rhodamine B (RhB) under visible light irradiation. The XPS, FT-IR, and Raman spectra show that the partly conjugated polymer derived from PVC exists on the surface of the TiO₂ nanoparticles. The UV–Vis DRS, XRD, and TEM results reveal that the modification of the partly conjugated polymer can obviously improve the absorbance of the TiO₂ nanoparticles in the range of visible light and hardly affect their size and crystallinity. The visible light photocatalytic activity of the as-prepared TiO₂ nanocomposites is higher than that of commercial TiO₂ (Degussa P25) and comparable with those of visible light photocatalysts reported in the literature. Their visible light photocatalytic stability is also good. The reasons for their excellent visible light photocatalytic activity and the major factors affecting their photocatalytic activity are discussed.     

Structural study of Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript> by electron microscopy

Detailed crystallographic data on high-quality Li₂MnO₃ material has been obtained using a combination of X-ray diffraction (XRD), selected-area electron diffraction (SAED), high-resolution electron microscopy (HREM), and 0.1 nm probe high-angle annular dark-field imaging (HAADF) in a scanning transmission electron microscope. A high-purity Li₂MnO₃ powder was annealed at 950 °C for 3 days to obtain predominantly defect-free grains which average size was 3.0 ± 1.5 μm. Rietveld refinement indicated that the C2/m spacegroup provided the best fit for the XRD data. Electron diffraction patterns obtained along various zone axes, on defect-free oxide particles, could be uniquely indexed to the monoclinic structure. HREM and HAADF images of defect-free grains were consistent with a Li–Mn–Mn– arrangement, i.e., lithium ordering in the transition metal planes. Low-magnification TEM images occasionally revealed stacking defects within oxide particles. HREM images of sample areas containing defects revealed a low density of stacking faults within the monoclinic sequence, resulting in a trigonal P3 ₁ 12 local arrangement.     

Synthesis of nano-MoS<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> composite and its catalytic degradation effect on methyl orange

A nano-MoS₂/TiO₂ composite was synthesized in H₂ atmosphere by calcining a MoS₃/TiO₂ precursor, which was obtained via a quick deposition of MoS₃ on anatase nano-TiO₂ under a strong acidic condition. The obtained nano-MoS₂/TiO₂ composite was characterized by X-ray diffraction spectroscopy, Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive spectrometry, ultraviolet–visible spectroscopy, and Fourier transform infrared spectroscopy. The results show that the composite had a high BET surface area because of its small size and irregularly layered structure. MoS₂ in the composite was composed of typical layered structures with thicknesses of 2–8 nm and lengths of 10–40 nm. The composite contained a wide and intensive absorption at 400–700 nm, which is in the visible light region, and presented a positive catalytic effect on removing methyl orange from the aqueous solution. The catalytic activity of the composite was influenced by the initial concentration of methyl orange, the amount of the catalyst, the pH value, and the degradation temperature. In addition, the composite catalyst could be regenerated and repeatedly used via filtration three times. The deactivating catalyst could be reactivated after catalytic reaction by heating at 450 °C for 30 min in H₂.     

Synthesis of silver and sulphur codoped TiO<Subscript>2</Subscript> nanoparticles for photocatalytic degradation of methylene blue

In the present work, silver and sulphur codoped TiO₂ (Ag–S/TiO₂) photocatalysts were effectively prepared by sol–gel technique. The prepared samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray analysis (EDX), Fourier transform infrared (FTIR) spectroscopy, diffuse reflectance UV–Vis spectroscopy (UV-DRS) and photoluminescence (PL). The XRD patterns consisted of anatase crystalline phases and the particle size and shape of the prepared samples were observed by SEM and HR-TEM. The presence of doping ions was confirmed by EDX analysis, the decreased band-gap energy of Ag–S codoped TiO₂ nanoparticles was investigated by UV-DRS. The decreased in the intensity of Ag–S codoped TiO₂ was absorbed due to the lower separation of electron–hole pairs were confirmed by PL spectrum. The Ag–S codoped TiO₂ showed higher photocatalytic activity than pure and single-doped TiO₂ in the photodegradation of methylene blue (MB) aqueous solution under visible light irradiation. The given work was a good model to associate the considering of the synergistic effect of metal and non-metal codoped TiO₂ in the photocatalysis and photo electrochemistry.     

Synthesis and variable temperature electrical conductivity studies of highly ordered TiO<Subscript>2</Subscript> nanotubes

Rafts of aligned, high aspect ratio TiO₂ nanotubes were fabricated by an electrochemical anodization method and their axial electrical conductivities were determined over the temperature range 225–400 °C. Length, outer diameter, and wall thickness of the nanotubes were approximately 60–80 μm, 160 nm, and 30 nm, respectively. Transmission electron microscopy studies confirmed that the TiO₂ nanotubes were initially amorphous, and became polycrystalline anatase after heat treatment at temperatures as low as 250 °C in air. The activation energy for conductivity over the temperature range 250–350 °C was found to be 0.87 eV. The conductivity values are comparable to those of nanocrystalline and nanoporous anatase thin films reported in literature.     

Nanocrystalline TiO<Subscript>2</Subscript> preparation by microwave route and nature of anatase–rutile phase transition in nano TiO<Subscript>2</Subscript>

Nanopowders of TiO₂ has been prepared using a microwave irradiation-assisted route, starting from a metalorganic precursor, bis(ethyl-3-oxo-butanoato)oxotitanium (IV), [TiO(etob)₂]₂. Polyvinylpyrrolidone (PVP) was used as a capping agent. The as-prepared amorphous powders crystallize into anatase phase, when calcined. At higher calcination temperature, the rutile phase is observed to form in increasing quantities as the calcination temperature is raised. The structural and physicochemical properties were measured using XRD, FT–IR, SEM, TEM and thermal analyses. The mechanisms of formation of nano-TiO₂ from the metal–organic precursor and the irreversible phase transformation of nano TiO₂ from anatase to rutile structure at higher temperatures have been discussed. It is suggested that a unique step of initiation of transformation takes place in Ti_1/2O layers in anatase which propagates. This mechanism rationalizes several key observations associated with the anatase–rutile transformation.     

Phase transformation and precipitation behavior of niobium component out of niobium-doped anatase-type TiO<Subscript>2</Subscript> nanoparticles synthesized via hydrothermal crystallization

The precipitation behavior of niobium component out of niobium-doped anatase-type TiO₂ and structural change in the course of heating were investigated. The samples were directly formed under hydrothermal conditions at 240 °C for 5 h in the presence of aqueous ammonia via crystallization from co-precipitates that were obtained from precursor solutions of TiOSO₄ and NbCl₅. The as-prepared niobium-doped anatase-type titania nanoparticles showed bluish color and absorption in the visible region, which was confirmed to be due to the presence of Ti(III) in the solid solutions using electron paramagnetic resonance measurement. The niobium-doped anatase-type titania existed stably without an appearance of any other phases after heating up to 500 °C for 1 h. In the course of heating at 500–800 °C, continual and clear decrease in the lattice parameters a ₀ and c ₀ of the anatase was observed, which was followed by the precipitation of Nb₂O₅ and TiNb₂O₇ out of the niobium-doped anatase, but the anatase phase was maintained without anatase-to-rutile phase transformation up to 850–1,000 °C. The anatase-to-rutile phase transformation was gradually retarded when the niobium content increased.     

Synthesis,structural characterization,and photocatalytic properties of iron-doped TiO<Subscript>2</Subscript> aerogels

Fe(III)-doped TiO₂ aerogels are prepared by acid catalyzed sol–gel method followed by supercritical drying, and then heat treatment. Raman spectra together with X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns of the iron-doped TiO₂ aerogel samples revealed the existence of both anatase and brookite crystalline phases. It was found that the brookite phase formation is favored by the increase of the iron content in the dried samples. XRD measurements show that the lattice constant c of anatase phase decreases with the dopant addition, while the value of a remains essentially unchanged. The microstructure of the investigated samples is relatively compact with small mesopores as revealed from transmission electron microscopy (TEM). The most enhanced photocatalytic activity was exhibited by the TiO₂ aerogel sample with 1.8 at.% Fe(III) whose apparent rate constant of the salicylic acid photodegradation was found to be of almost six times higher than that of Degussa P25.     

Influence of high velocity oxy-fuel parameters on properties of nanostructured TiO<Subscript>2</Subscript> coatings

A liquid fuel high velocity oxy-fuel (HVOF) thermal spray process has been used to deposit TiO₂ nanostructured coatings utilizing a commercially available nanopowder as the feedstock. The coatings were characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. Photocatalytic activity was evaluated as a rate constant of decomposition reaction of methylene blue (MB) determined from the changes of relative concentration of MB with UV irradiation time. The results indicate that the sprayed TiO₂ coatings were composed of both TiO₂ phases viz. anatase and rutile, with different phase contents and crystallite sizes. A high anatase content of 80% by volume was achieved at 0·00015, fuel-to-oxygen ratio with nanostructure coating by grain size smaller than feedstock powder. Photocatalytic activity evaluation results indicated that all the TiO₂ coatings are effective to degradation MB under UV radiation and their activities differ in different spray conditions. It is found that fuel flow rate strongly influenced on phase transformation of anatase to rutile and by optimizing the rate which can promote structural transformation and grain coarsening in coating and improving photocatalytic activity.     

Preparation of N-methylaniline capped mesoporous TiO2 spheres by simple wet chemical method

Pure anatase mesoporous TiO₂ nanospheres were synthesized by simple wet chemical treatment and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (XRD). The results revealed that the surface morphology of the TiO₂ spheres could be controlled by adjusting the concentration of N-methylaniline and that the average diameter of the TiO₂ spheres was 600 nm. FTIR results confirmed the formation of N-methylaniline capped TiO₂ nanospheres.     

Preparation,characterization and photocatalytic properties of nanoplate Bi<Subscript>2</Subscript>MoO<Subscript>6</Subscript> catalysts

Bismuth molybdate (Bi₂MoO₆) nanoplates have been successfully synthesized by a simple hydrothermal process. The nanoplates were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and IR spectroscopy. The effects of hydrothermal temperature and reaction time on the structures and morphologies of the nanoplates were investigated. On the basis of TEM observation of time series samples, a possible formation mechanism of the nanoplates was proposed. Optical absorption experiments revealed that Bi₂MoO₆ nanoplates had absorption in visible-light region, but a blue shift appeared compared with the corresponding bulk materials. Photocatalytic experiments showed that the nanoplates exhibited good photocatalytic activities for degradation of N,N,N′,N′-tetraethylated rhodamine (RhB) under visible-light irradiation (λ > 420 nm).     

Photocatalytic activity of polypyrrole/TiO<Subscript>2</Subscript> nanocomposites under visible and UV light

A series of polypyrrole (PPy)/titanium dioxide (TiO₂) nanocomposites were prepared in different polymerization conditions by ‘in situ’ chemical oxidative polymerization. The nanocomposites were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectra (XPS), and UV–Vis diffuse reflectance spectra. The photocatalytic degradation of methyl orange (MO) was chosen as a model reaction to evaluate the photocatalytic activities of TiO₂/PPy catalysts. The results show that a strong interaction exists at the interface between TiO₂ and PPy, the deposition of PPy on TiO₂ nanoparticles can alleviate their agglomeration, PPy/TiO₂ nanocomposites show stronger absorbance than neat TiO₂ under the whole range of visible light. The obtained PPy/TiO₂ nanocomposites exhibit significantly higher photocatalytic activity than the neat TiO₂ on the degradation of MO aqueous solution under visible and UV light illumination. The reasons for improving the photocatalytic activity were also discussed.     

Al-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles and Their Magnetic Properties

Al-doped Fe₃O₄ nanoparticles were synthesized for the first time via the Composite-Hydroxide-Mediated (CHM) method from Fe₃O₄ and Al₂O₃ without using any capping agent. The synthesis technique was one-step and cost effective. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS). Samples with a tunable size of 500–1500 nm, 200–800 nm, and 100–700 nm could be obtained by adjusting the reaction time and temperature. Magnetic property of the as-synthesized Al-doped Fe₃O₄ nanoparticles was investigated. Magnetic hysteresis loops measured in the field range of −10 kOe<H<10 kOe, indicated the ferromagnetic behavior with coercivity (H _c) of 470 and 110 Oe and remanence magnetization (M _r) of 13 and 6.4 emu/g at the temperature of 5 and 300 K, respectively. The saturation intensity (M _s) was 46.1 emu/g at 5 K, while it was about 43.6 emu/g at 300 K.     

The synthesis of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> nanobelts by vapor–liquid–solid method and their electrical transport properties

Bi₂Te₃ nanobelts were synthesized on quartz substrates by gold-mediated vapor–liquid–solid (VLS) growth through a thermal evaporation process. The structure and morphology were characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The temperature dependence of the conductivity of Bi₂Te₃ single crystal nanobelt shows a semiconductor behavior, and the activation energy was calculated as about 25 meV, indicating that the thermal activation of carriers from the impurity level dominates the transport property.     

On the synthesis,characterization and photocatalytic applications of nanostructured TiO<Subscript>2</Subscript>

Nanocrystalline semiconducting materials are attracting much attention due to their potential applications in solar energy conversion, nonlinear optics, and heterogeneous photocatalysis. In the present investigation, we have synthesized nanostructured TiO₂ photocatalysts, which have been used in the photocatalytic degradation of phenol (one of the most common water pollutants). These catalysts have been prepared through sol-gel technique using titanium tetra-isopropoxide as a raw material for synthesis. Characterization techniques such as XRD, SEM and TEM have been employed for structural/microstructural investigations. XRD results show that the as synthesized TiO₂ nanopowder exhibit anatase phase, TiO₂. The average sizes of the TiO₂ nanopowders are ∼ 5–10 nm. The optical properties of the samples were investigated through UV-visible and fluorescence techniques. It has been observed that absorption edge corresponds to ∼ 410 nm (bandgap, ∼ 3.02 eV). The emission peak in the fluorescence spectrum at ∼ 418 nm corresponds to the bandgap energy of ∼ 2.97 eV. Concentration of phenol (initial concentration, ∼ 100 ppm) with illumination time was monitored by measuring the absorbance of pure and illuminated phenol through UV-visible spectrophotometer. Salient feature of this study relates to the fact that the present sol-gel synthesized TiO₂ nanopowders have been found to be better photocatalysts for phenol degradation than the presently employed commercial TiO₂ (P-25, Degussa) photocatalyst. Thus, whereas phenol concentration, with the presently synthesized TiO₂ nanopowders, the concentration of phenol decreases up to ∼ 32% but for commercial TiO₂ nanopowder (P-25, Degussa), it decreased only up to ∼ 25%. The improved surface area is considered as an important factor for the aforesaid decrease in phenol concentration.