Synthesis of TiO2/WO3 nanoparticles via sonochemical approach for the photocatalytic degradation of methylene blue under visible light illumination

Through an ultrasound assisted method, TiO₂/WO₃ nanoparticles were synthesized at room temperature. The XRD pattern of as-prepared TiO₂/WO₃ nanoparticles matches well with that of pure monoclinic WO₃ and rutile TiO₂ nanoparticles. TEM images show that the prepared TiO₂/WO₃ nanoparticles consist of mixed square and hexagonal shape particles about 8–12 nm in diameter. The photocatalytic activity of TiO₂/WO₃ nanoparticles was tested for the degradation of a wastewater containing methylene blue (MB) under visible light illumination. The TiO₂/WO₃ nanoparticles exhibits a higher degradation rate constant (6.72 × 10⁻⁴ s⁻¹) than bare TiO₂ nanoparticles (1.72 × 10⁻⁴ s⁻¹) under similar experimental conditions.     

Observation of record flux pinning in melt-textured NEG-123 superconductor doped by Nb, Mo, and Ti nanoparticles

Flux pinning in melt-processed (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y “NEG-123” + 35 mol% Gd₂BaCuO₅ “NEG-211” (70 nm in size) composite doped by TiO₃, MoO₃ and Nb₂O₅ achieved record values. The optimum values of all three dopands were found to be around 0.1 mol%. Transmission electron microscope (TEM) analysis found clouds of <10 nm sized particles in the NEG-123 matrix, shifting the pinning particle size distribution to significantly lower values. TEM by energy dispersive X-ray spectroscopy (EDX) analysis clarified that these nanoparticles contained a significant amount of Nb, Mo, and Ti. Appearance of nanometer-sized defects correlated with a significantly improved flux pining at low and medium magnetic fields, which was particularly significant at high temperatures. In the Nb-doped sample, a record J_c value of 925 kA/cm² at the secondary peak field (4.5 T) was achieved at 65 K, 640 kA/cm² at zero field at 77 K, and 100 kA/cm² at 90.2 K, the last value having been up to now considered as a good standard for REBa₂Cu₃O_y “RE-123” materials at 77 K. The greatly improved J_c–B performance in Nb/Mo/Ti doped samples can be easily translated to large-scale LRE-123 (LRE = light rare earths, Nd, Eu, Gd, Sm) blocks intended for real superconducting super-magnets applications.     

Effects of electrode film modifications on the open-circuit photovoltage in enhanced dye-sensitized solar cells

In this study, the open-circuit photovoltage (V _oc) decay technique was used to investigate the relationship between the electrode film morphology and the open-circuit photovoltage. Results indicate that dye-sensitized solar cells (DSCs) based on ordered arrays of TiO₂ nanostructures (100 nm external diameters and 20–50 nm internal diameters) generally show higher open-circuit photovoltage (V _oc) values than those based on sintered TiO₂ nanoparticles (20–40 nm diameters). In particular, cells based on thick nanotubules (wall thickness ≥ 45 nm in our research) and on nanorods (100 nm diameters) show particularly high V _oc values, indicating slow recombination kinetics under open-circuit conditions. It can be argued that the nanorods and the thick nanotubules act like singles crystals and therefore the injected electrons in the inner TiO₂ molecules are shielded from holes in the electrolyte under open-circuit conditions. The open-circuit recombination time constant of electrons accumulated in the TiO₂ conduction band is therefore prolonged and resulting in high V _oc values.     

Metal-on-oxide nanoparticles produced using laser ablation of microparticle aerosols

A continuous aerosol process has been studied for producing nanoparticles of oxides that were decorated with smaller metallic nanoparticles and are free of organic stabilizers. To produce the oxide carrier nanoparticles, an aerosol of 3–6 μm oxide particles was ablated using a pulsed excimer laser. The resulting oxide nanoparticle aerosol was then mixed with 1.5–2.0 μm metallic particles and this mixed aerosol was exposed to the laser for a second time. The metallic micron-sized particles were ablated during this second exposure, and the resulting nanoparticles deposited on the surface of the oxide nanoparticles producing an aerosol of 10–60 nm oxide nanoparticles that were decorated with smaller 1–5 nm metallic nanoparticles. The metal and oxide nanoparticle sizes were varied by changing the laser fluence and gas type in the aerosol. The flexibility of this approach was demonstrated by producing metal-decorated oxide nanoparticles using two oxides, SiO₂ and TiO₂, and two metals, Au and Ag.     

Ultrasound assisted synthesis of TiO2–WO3 heterostructures for the catalytic degradation of Tergitol (NP-9) in water

TiO₂–WO₃ heterostructures were synthesized at room temperature, ambient pressure, and short reaction time via a sonochemical approach. TEM and EDX images show that the prepared TiO₂–WO₃ heterostructures consist of globular agglomerates (∼250 nm in diameter) composed of very small (<5 nm) dense particles (WO₃) dispersed inside the globules. The observed less intense monoclinic WO₃ diffraction peak (around 2θ = 22° belonging to (0 0 1) plane) and the high intense hexagonal WO₃ diffraction peak (around 2θ = 28° belonging to (2 0 0) plane) in XRD indicate that there may be phase transition occurring due to the formation of intimate bond between TiO₂ and WO₃. In addition, the formation of such new phase was also observed from Raman spectra with a new peak at 955 cm⁻¹, which is due to the symmetric stretching of W = O terminal. The catalytic activity of TiO₂–WO₃ heterostructures was tested for the degradation of wastewater pollutant containing Tergitol (NP-9) by a process combined with ozonation and it showed two-fold degradation rate compared with ozone process alone.     

One-step flame method for the synthesis of coated composite nanoparticles

A simple in situ flame coating method has been developed by designing a new type of coflow diffusion flame burner having a sliding unit. The sliding unit was shown to be very effective in finding a right position where the precursor for coating layer should meet with core particles. SiO₂-coated TiO₂ nanoparticles were first prepared and whether most surfaces of particles were coated was examined by both direct observation of particles through a transmission electron microscope and Zeta potential measurements. Mean core sizes varied from 28 to 109 nm and mean coating thickness was about 2.4 nm for silica-coated titania particles. By simply changing chemical precursors, we demonstrated that SiO₂-coated SnO₂, SnO₂-coated TiO₂, SiO₂–SnO₂-coated TiO₂ nanoparticles could be also synthesized.     

Preparation, structures and photoluminescent enhancement effect of PbWO4–TiO2 composite nanofilms

A novel route for preparing PbWO₄–TiO₂ nanofilms on a glass substrate is firstly proposed. The collodion is used as a dispersant and film-forming agent. The nanofilms are characterized through SEM, XRD, TG/DTA, PL and IR, respectively. The results of XRD indicate PbWO₄ particles with tetragonal scheelite structure and TiO₂ particles with Anatase phase, and SEM shows they are well dispersed in the substrate. Compared with nanoparticles, when TiO₂ nanoparticles are added in 5% ratio, the PL intensities at 395 nm of PbWO₄ nanofilms are enhanced obviously. IR spectrum reveals a large absorption band between 750 and 870 cm⁻¹, which is the W–O stretching vibration in WO₄ tetrahedron.     

From TiCl3 to TiO2 nanoparticles (anatase,brookite and rutile): Thermohydrolysis and oxidation in aqueous medium

Titania nanoparticles were synthesized by hydrolysis and oxidation of titanium trichloride (TiCl₃) in aqueous medium. The TiO₂ synthesis via the hydrolysis of Ti(III) proceeds in two steps: a condensation step and an oxidation step, which can be separated or simultaneous and they could take place in both orders. The importance of the medium acidity (0.5<pH<6.5) at 60 °C on the precipitation was underlined in this study. According to the pH, brookite (diamond-shape platelets) or rutile (rods) were obtained under particularly soft conditions, as well in acidity as in temperature whereas these particles are classically obtained under drastic conditions. Moreover, the control of the TiCl₃ hydrolysis allowed the synthesis of non-usual morphologies of TiO₂ nanoparticles, especially rods of anatase, small square platelets (3 nm) of rutile.     

Experimental evaluation of individual protection devices against different types of nanoaerosols: graphite,TiO<Subscript>2,</Subscript> and Pt

In this study different conventional individual protection devices, well-qualified for submicron particles were tested for different types of polydispersed nanoaerosols of TiO₂, Pt, and graphite. The electrical mobility diameters of the generated particles are ranging from 9 to 19 nm for Pt, 9 to 90 nm for TiO₂, and 15 to 90 nm for graphite. Toward this purpose, two specific test benches were used: one for the filter-based devices which are tested under a controlled air flow, and the other one for protective clothing and gloves under diffusion and without air flow. Different types of nanoaerosols, such as TiO₂, Pt, and graphite, were generated. Electrostatic and HEPA (High Efficiency Particle Air) filters have shown the highest efficiency for graphite nanoparticles. The main hypothesis for explaining this effect is that electrostatic forces could enhance the graphite nanoparticles capture. Air-tight fabrics made of non-woven textile seem much more efficient in protecting workers against Pt, and TiO₂ nanoparticles than cotton and polypropylene. With regard to protective clothing, no obvious effect linked to the aerosol type was observed. Gloves are found very efficient for TiO₂ and Pt nanoaerosols. Therefore, no effect of aerosol on the protection efficiency of gloves was evidenced.     

Size-controllable synthesis of functional heterostructured TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> core–shell nanoparticles

Mono and bicomponent TiO₂ and WO₃ nanoparticles were synthesized inside Vycor^® glass pores, by cycles of impregnation of the glass with the respective oxide precursor followed by its thermal decomposition. The impregnation-decomposition cycle (IDC) methodology promoted a linear mass increase of the glass matrix, and allowed tuning the nanoparticle size. X-ray diffraction and Raman spectroscopy data allowed identifying the formation of TiO₂ as anatase phase, while WO₃ is a mixture of the γ-WO₃ (monoclinic) and δ-WO₃ (triclinic) phases. High resolution transmission electron microscopy images revealed that for 3, 5, and 7 IDC, the TiO₂ nanoparticles obtained presented average diameters of 3.4, 4.3, and 5.1 nm, and the WO₃ nanoparticles have 2.9, 4.6, and 5.7 nm sizes. These TiO₂ and WO₃ monocomponent nanoparticles were submitted to IDC with the other oxide precursor, resulting in bicomponent nanoparticles. The broadening and shift of the Raman bands related to titanium and tungsten oxides suggest the formation of hetero-structure core–shell nanoparticles with tunable core sizes and shell thicknesses.     

Influence of pH on the preparation of dispersed Ag–TiO<Subscript>2</Subscript> nanocomposite

In this paper, data concerning the effect of pH on the morphology of Ag–TiO₂ nanocomposite during photodeposition of Ag on TiO₂ nanoparticles is reported. TiO₂ nanoparticles prepared by sol–gel method were coated with Ag by photodeposition from an aqueous solution of AgNO₃ at various pH levels ranging from 1 to 10 in a titania sol, under UV light. The as-prepared nanocomposite particles were characterized by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and N₂ adsorption/desorption method at liquid nitrogen temperature (−196 °C) from Brunauer–Emmett–Teller (BET) measurements. It is shown that at a Ag loading of 1.25 wt.% on TiO₂, a high-surface area nanocomposite morphology corresponding to an average of one Ag nanoparticle per titania nanoparticle was achieved. The diameter of the titania crystallites/particles were in the range of 10–20 nm while the size of Ag particles attached to the larger titania particles were 3 ± 1 nm as deduced from crystallite size by XRD and particle size by TEM. Ag recovery by photo harvesting from the solution was nearly 100%. TEM micrographs revealed that Ag-coated TiO₂ nanoparticles showed a sharp increase in the degree of agglomeration for nanocomposites prepared at basic pH values, with a corresponding sharp decrease in BET surface area especially at pH > 9. The BET surface area of the Ag–TiO₂ nanoparticles was nearly constant at around a value of 140 m² g⁻¹ at all pH from 1–8 with an anomalous maximum of 164 m² g⁻¹ when prepared from a sol at pH of 4, and a sharp decrease to 78 m² g⁻¹ at pH of 10.     

Fabrication of polyaniline/ heterojunction structure using plasma enhanced polymerization technique

The work reports on the fabrication of a p–n heterojunction structure comprised of polyaniline (PANI) and TiO₂ nanoparticles. PANI was deposited by plasma enhanced polymerization on TiO₂ thin film substrates. The structural and the crystalline properties demonstrated the coherence and the substantive interaction of the plasma polymerized PANI molecules with the TiO₂ nanoparticle thin film. The UV–Vis studies of PANI/TiO₂ thin film supported the internalization of PANI with TiO₂ nanoparticles due to π–π^* transition of the phenyl rings with the lone pair electrons () of the nitrogen atom present in the PANI molecules. The I–V characteristics of the PANI/TiO₂ heterojunction structure were obtained in the forward and the reverse biased at applied voltage ranging from −1 V to +1 V with a scan rate of 2 mV/s. The proficient current in the PANI/TiO₂ heterojunction structure was attributed to the well penetration of PANI molecules into the pores of the TiO₂ nanoparticle thin film. The I–V characteristics ensured an efficient charge movement at the junction of PANI/TiO₂ interface and thus, behaved as a typical ohmic system.     

Effect of Particle Size and Phase Composition of Titanium Dioxide Nanoparticles on the Photocatalytic Properties

Titanium dioxide (TiO₂) nanoparticles were prepared by the oxidation of titanium tetrachloride (TiCl₄) in a diffusion flame reactor. The average diameter of particles was 15–30 nm and mass fraction of anatase ranged from 40% to 80%. Effects of particle size and phase composition of those TiO₂ nanoparticles on photocatalytic properties such as decomposition of methylene blue, bacteria and ammonia gas were investigated. The degree of decomposition of methylene blue by the TiO₂ nanoparticles under the illumination of the black light was directly proportional to the anatase mass fraction, but inversely to the particle size. The decomposition of bacteria and ammonia gas by the TiO₂ nanoparticles under the illumination of the fluorescent light showed the same trend as in the case of the methylene blue.     

Comparison of the performances of dye-sensitized solar cells based on different TiO2 electrode nanostructures

This article reports on the performances of dye-sensitized solar cells based on three different working electrode structures, i.e., (i) sintered TiO₂ nanoparticles (20–40 nm diameters), (ii) ordered arrays of TiO₂ nanotubules (150 nm external diameters and 80 nm internal diameters), and (iii) ordered arrays of TiO₂ nanorods (150 nm diameters). Even though the highest short-circuit current density was achieved with systems based on TiO₂ nanotubules, the most efficient cells were those based on ordered arrays of TiO₂ nanorods. This is probably due to higher open-circuit photovoltage values attained with TiO₂ nanorods than with TiO₂ nanotubules. The nanorods are thicker than the nanotubules and therefore the injected electrons, stored in the trap states of the inner TiO₂ molecules, are shielded from recombination with holes in the redox electrolyte at open circuit. The high short-circuit photocurrent densities seen in the ordered TiO₂ systems can be explained by the fact that, as opposed to the sintered nanoparticles, the parallel and vertical orientation of the ordered nanostructures provide well-defined electrons percolation paths thus significantly reduce the diffusion distance and time constant.     

SnO2/TiO2 mixed oxide particles synthesized in doped premixed H2/O2/Ar flames

SnO₂/TiO₂ mixed oxides with primary particle size ranging between 5 nm d_p 12 nm were synthesized by doping a H₂/O₂/Ar flame with Sn(CH₃)₄ and Ti(OC₃H₇)₄ co-currently. The effects of “flow coordinate,” concentration and flame configurations were investigated with respect to particle size and morphology of the generated mixed oxides. In situ characterization of the mixed oxides was performed using the particle mass spectrometer (PMS), while XRD, TEM, BET and UV–Vis were performed ex situ. Results obtained showed that primary particle size of mixed oxides can be controlled by varying experimental parameters. The mixed oxides have interesting properties compared to those of the pure oxides of TiO₂ and SnO₂, which were also synthesized in flames earlier. Band gap tuning opportunities are possible using mixed oxides.     

Electrochemical properties of TiO2 nanotube-Li4Ti5O12 composite anodes for lithium-ion batteries

For application as an anode material in lithium batteries, composite anodes consisting of TiO₂ nanotubes (TNT) and Li₄Ti₅O₁₂ (LTO) nanocrystalline particles are prepared by hydrothermal reaction of rutile TiO₂ particles, physical blending with LTO, and subsequent heat treatment at 300 °C. The TNT-LTO composites with varying the composition are characterized by electron microscopy, X-ray diffraction, potentiostatic cyclic voltammetry, and galvanostatic charge-discharge tests at various current rates. With higher LTO content, short TNTs with the average tube diameter of 10 nm are distributed among the potato-shaped LTO particles with the average diameter of 200 nm. At higher content of TNT, however, the LTO particles are sparsely distributed in the fibrillar aggregates of TNT with more lengthened image. As a result, the samples of TNT:LTO = 2:8 and 4:6 show superior cycle performance and high-rate capability, mainly due to their higher electrode densities to yield nanotubular TNT distributed on and supported by potato-shaped LTO nanoparticles.     

Nanoparticle Tracking Analysis: Enhanced Detection of Transparent Materials

This study proposes a novel and simple in-house design of a nanoparticle tracking analysis (NTA) device for the online characterization of nanoparticles in an aqueous solution. The particle size distribution of two sets of model nanoparticles, for example, transparent (SiO₂) and opaque (TiO₂) materials with respect to water as a dispersion medium could be successfully analyzed. Experiments are conducted using two different laser wavelengths of 632.8 (red) and 510 nm (green) and a range of concentrations. The accuracy of the green laser is larger compared to the red laser for all particle concentrations used. The measured average diameter using the presented in-house NTA setup is in the acceptable range compared to the electron microscopy data. The average diameter of the transparent (SiO₂) and opaque (TiO₂) samples is calculated as 36.29 and 27.26 nm using NTA, 36.44 and 27.8 nm analyzing field emission scanning electron microscopy images, and 23.97 and 19.7 nm analyzing transmission electron microscopy images. In the new viewing sample holder, nanoparticles undergo mere Brownian motion with no bulk drift velocity. The effect of solid concentration and wavelength of the laser light on the performance of the NTA sensor is investigated, and the optimal concentration range for model particles is reported.     

Tuning of crystal phase structure in hydrated WO3 nanoparticles under wet chemical conditions and studies on their photochromic properties

Hydrated tungsten oxide nanoparticles have been synthesized using a simple wet chemical method while varying the concentration of HCl. XRD studies show that the variation in HCl concentration from 1 M to 6 M in the reaction results into gradual change in crystal structure of hydrated WO₃ from hexagonal (WO₃·0.33H₂O) to pure orthorhombic (WO₃·H₂O), through a series of samples with mixed phase of the two indifferent ratios. The similar variations in the degree of hydration and phase variations have also been observed from Raman, FTIR and TGA studies. The average crystallite size of the hydrated WO₃ particles was estimated to be ～26 nm from XRD line broadening and AFM studies showed the formation of spherical shaped particles for all the samples. The photochromic studies were carried out on the composite films of these materials in the polymeric matrix of polyvinyl alcohol (PVA) while exposing to UV light. The composite films show interesting variations in the photochromic behavior depending on the crystal structure of hydrated WO₃ filler. The photochromic behavior has been explained on the basis of EPR spectra of hydrated WO₃.     

Preparation of WO3 nanoparticles and application to NO2 sensor

WO₃ nanoparticles were prepared by evaporating tungsten filament under a low pressure of oxygen gas, namely, by a gas evaporation method. The crystal structure, morphology, and NO₂ gas sensing properties of WO₃ nanoparticles deposited under various oxygen pressures and annealed at different temperatures were investigated. The particles obtained were identified as monoclinic WO₃. The particle size increased with increasing oxygen pressure and with increasing annealing temperature. The sensitivity increased with decreasing particle size, irrespective of the oxygen pressure during deposition and annealing temperature. The highest sensitivity of 4700 to NO₂ at 1 ppm observed in this study was measured at a relatively low operating temperature of 50 °C; this sensitivity was observed for a sensor made of particles as small as 36 nm.     

Improving the electrical catalytic activity of Pt/TiO<Subscript>2</Subscript> nanocomposites by a combination of electrospinning and microwave irradiation

One of the greatest challenges in preparing TiO₂-based oxygen electrodes for PEM fuel cells is increasing the electrical catalytic activity of Pt nanoparticle/TiO₂ composites by improving the dispersion of Pt. This article describes a new way for improving the dispersion of Pt nanoparticles by depositing them on TiO₂ fibers and using microwave irradiation. The Pt nanoparticles used in this experiment is about 5 nm in diameter and the diameter of TiO₂ fibers could be controlled ranging from 30 to 60 nm and Pt nanoparticles still keep their size when the deposition amount is increased on the surface of TiO₂ fibers. The Pt nanoparticles were highly dispersed without agglomeration even at a weight percentage of composites as high as 40%. The position of Pt nanoparticles located in the fiber and the composition of Pt/TiO₂, which had great influence on the electric conductivity and electrical catalytic activity of the composite, could be easily controlled.