Melt-spinning and thermal stability behavior of TiO<Subscript>2</Subscript> nanoparticle/polypropylene nanocomposite fibers

The elongational flow properties of TiO₂ nanoparticle/polypropylene (PP) nanocomposite fibers were studied via melt spinning. The diameter, tension, and flow rate of fibers were directly measured and used to calculate the apparent elongational viscosity and apparent elongational strain rate using Cogswell’s theory. Thermal gravimetric analysis (TGA) was used to demonstrate that the TiO₂ nanoparticles improved the thermal stability of the PP fibers. With a 1–3 wt % loading of the TiO₂ nanoparticles, the PP fiber decomposition temperatures ranged from 338 °C for the pristine polymer to 342, 349, and 367 °C; the decomposition was accompamied by an initial 95 wt % weight loss. In addition, the well-distributed morphology of the TiO₂ nanoparticles on the side surface of the PP matrix was observed using atomic force microscopy (AFM). At 1 wt % loading of the TiO₂ nanoparticles, the surfaces of the PP nanofibers contained mono-disperse nanoparticles with sizes of 20–50 nm. Furthermore, the TiO₂ nanoparticle/PP nanocomposite fibers were shown to be thermally stable and are suitable for application as an antibacterial polymer.     

Al-doped TiO<Subscript>2</Subscript> mesoporous materials: synthesis and photodegradation properties

Aluminium-doped TiO₂ mesoporous material was successfully fabricated by solid-state reaction with cetyltrimethylammonium bromide as a template agent and tetrabutyl orthotitanate as a precursor. The characteristic results from low-angle and wide-angle X-ray diffraction, high resolution transmission electron microscopy and energy dispersive spectroscopy, N₂ absorption–desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, ultraviolet visible light spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly showed that the mesoporous architecture of aluminium-doped TiO₂ was composed of crystal wall and micro-/mesopore formed gradually by the mesopore degradation of anatase TiO₂, and aluminium had been doped into the framework of anatase TiO₂. The mesoporous Al-doped TiO₂ material, not only possessed high thermal stability hexahedral mesostructure, large BET surface area and narrow distribution of pore size, but also showed excellent photodegradation behavior for Congo Red. Furthermore the medium UV–Vis absorption peak of mesoporous aluminium-doped TiO₂ in the range 210–370 nm was the absorption peak of aluminium oxide nanoparticles locating the extraframework of TiO₂. A small quantity of aluminium doped into anatase TiO₂ could obviously improve photodegradation activity, and the photodegradation activity of aluminium-doped TiO₂ was higher than that of pure TiO₂.     

Preparation and Characterization of Mesoporous MoO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> Composite with High Surface Area by Self-Supporting and Ammonia Method

Abstract  

A mesoporous MoO₃/TiO₂ composite was prepared from titanate derivative by consecutive self-supporting and ammonia method. All samples were characterized by X-ray Diffraction, N₂ adsorption–desorption, Raman Spectra and Field-Emission Scanning Electron Microscopy. The results showed that mesoporous MoO₃/TiO₂ composite had a higher surface area (173 m²/g) and a better MoO₃ dispersion than that prepared by traditional impregnation (90 m²/g). As for hydrodesulfurization tests, mesoporous MoO₃/TiO₂ composite in this case presented a better catalytic performance, attributed to its high surface area and good dispersion of MoO₃. It can be found that self-supporting played a key role in preparing mesoporous MoO₃/TiO₂ composite with high surface area. Additionally, aqueous ammonia could effectively dissolve excess MoO₃, which helped to obtain mesoporous MoO₃/TiO₂ composite with better dispersion of MoO₃.     

Effect of surfactant in a modified sol on the physicochemical properties and photocatalytic activity of crystalline TiO<Subscript>2</Subscript> nanoparticles

This study describes the effect of amphiphilic organic molecules (surfactants) in a sol on the physicochemical properties and photocatalytic activity of crystalline TiO₂ nanoparticles prepared via a simple sol–gel route at high temperatures from 400 to 800 °C. Addition of polyoxyethylenesorbitan surfactant and polyethylene oxide and polypropylene oxide triblock copolymer as particle size inhibitors and pore directing agents into a stable titania sol affected the physicochemical properties of TiO₂ nanoparticles such as their crystallographic structure, morphology, and defect structure. With the addition of the surfactants, the ratio of anatase and rutile crystal phases of TiO₂ was controlled and an active anatase crystal phase was maintained during heat treatment up to 800 °C. Decrease in the sintering rate and inhibition in crystal growth were also observed, which resulted in higher surface area and inhibition of crystallite aggregation. Bulk defects in TiO₂ were reduced while surface defects were increased as a result of the addition of surfactants. These physicochemical properties of TiO₂ nanoparticles were correlated with photocatalytic degradation of 4-chlorophenol in water. The results revealed that high crystallinity, anatase crystal phase, high specific surface area, surface defects, and segregated morphology of TiO₂ nanoparticles, which were induced by the addition of surfactants, were more advantageous for enhancing photocatalytic destruction of the model organic compound tested in the study.     

Synthesis and study of photoacoustic properties of (Pd/TiO<Subscript>2</Subscript>)/polystyrene nanocomposites

In this work, nanocomposites (Ncs) from Pd nanoparticles and TiO₂ (Pd-Nps-TiO₂) were supported on a polystyrene matrix (PS). Chemical liquid deposition, solvated metal atom dispersion and in situ polymerization were used in order to synthesize these Ncs. Colloid and nanocomposite characterization were performed by TEM, SEM, EDX, SAED and TGA. TEM analysis revealed a particle size of 7 nm for Coll-Styrene and 11 nm for Pd-Nps supported on TiO₂ after radical polymerization. SAED showed phases corresponding to both metallic Pd and TiO₂ anatase in the polymeric matrix. Molecular weight (MW) was determined by viscosimetric method. MW varies according to the initiator concentration and nanoparticle amount used for polymerization. The amount of nanoparticles increased the decomposition temperature of the Ncs by 10 °C, improving the thermal stability of these hybrid materials. Photoacoustic properties were evaluated in order to determine the effect of nanoparticles on thermal diffusivity (α) inside the matrix. Significant values of (α) were found for Ncs with Pd-Nps in contrast to PS and Pd/TiO₂ Ncs. Structural aspects and colloidal aggregation of Ncs were also studied.     

Preparation and characterization of mesoporous TiO<Subscript>2</Subscript> thin film

Ordered hexagonal mesoporous TiO₂ thin film was prepared by the evaporation-induced self-assembly (EISA) method using triblock copolymer (Pluronic P123) and tetrabutyl orthotitanate (Ti(OBu ⁿ )₄, TBOT) in 1-methoxy-2-propanol (C₄H₁₀O₂, PGME) solvent. The arrangement of mesopores was identified by small-angle X-ray diffraction and transmission electron microscopy (TEM). The well-ordered hexagonal mesoporous TiO₂ had a high specific surface area of 239 m²/g and an average pore size of 6.3 nm. The structure of mesoporous TiO₂ thin film was anatase with a 5.1 nm crystallite. The absorption band shift of the mesoporous TiO₂ toward longer wavelengths as calcined at 350 °C due to the residual carbon.     

Synthesis of TiO<Subscript>2</Subscript> Nanoparticles by Microemulsion/Heat Treated Method and Photodegradation of Methylene Blue

In this work, TiO₂ nanoparticles were prepared by microemulsion (ME)/heat treated method and its photodecomposition property of methylene blue. Microemulsion (ME) consisted of water, cyclohexane and an anionic surfactant such as bis (2-ethylhexyl) sodium sulfosuccinate (AOT). Titanium tetraisopropoxide (TTIP) was dropped into the ME solution and then then TiO₂ nanoparticles were formed by the hydrolysis reaction between TTIP in the organic solvent and the water in the core of ME. The smallest diameter of the particles was 20 nm in the system of cyclohexane with surfactant when the molar ratio of water to surfactant was 2. The effect of the process parameters (water/surfactant ratio, different temperatures) on the final characteristics has been investigated, in terms of structural phase and particle size. The TiO₂ nanoparticles were characterized by means of X-ray diffraction, Transmission and scanning electron microscopy, Fourier-Transformed infrared and differential thermal analysis. TiO₂ nanoparticles prepared in this condition were collected as amorphous powder, and converted to anatase phase at less than 350 °C, which is lower than the ordinal phase transition temperature. The crystallite size and crystallinity increase with an increase of heat treated s temperature. The particles are shown to have a spherical shape and have a uniform size distribution. The size of nanoparticles raises with an increase of water/surfactant ratio. In the photocatalytic decomposition of methylene blue, the photocatalytic activity is mainly determined by the crystallinity of TiO₂. In addition, the TiO₂ heat treated at 350 °C shows the highest activity on the photocatalytic decomposition of methylene blue (k = 1.7 × 10⁻² min⁻¹).     

Low temperature hydrothermal synthesis of monodispersed flower-like titanate nanosheets

Monodispersed flower-like titanate superstructure was successfully prepared by simple hydrothermal process without any surfactant or template. N₂-sorption analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD) observation of as-synthesized product revealed the formation of flower-like titanate with diameter of about 250–450 nm and BET surface area (S_BET) of 350.7 m² g^?1. Upon thermal treatment at 500 °C, the titanate nanosheets were converted into anatase TiO₂ with moderate deformation of their structures. The as-prepared flower-like titanate showed high photocatalytic activity for H₂ evolution from water splitting reaction. Moreover, the sample heat treated at 500 °C exhibited higher photocatalytic activity than that of commercial TiO₂ anatase powder (ST-01).     

Solar photocatalytic detoxification of cyanide by different forms of TiO<Subscript>2</Subscript>

The photocatalytic efficiencies of TiO₂ nanocrystals of different modifications (anatase, rutile, P25 Degussa, Hombikat), to oxidize cyanide ion and subsequently the cyanate also, under natural sunlight at 950±25W m⁻² in alkaline solution have been compared. The oxides have been characterized by powder XRD, UV-visible diffuse reflectance and impedance spectroscopies. Under identical solar irradiance, the reaction follows Langmuir-Hinshelwood kinetics on cyanide, and depends on the apparent area of the catalyst bed and dissolved oxygen. However, the adsorption of cyanide on TiO₂ in dark is too small to be measured analytically. The photocatalytic activity of TiO₂ is not solely governed by the band gap or charge-transfer resistance or capacitance or phase composition but is in accordance with the specific surface area or the average crystallite size; rutile is an exception.     

Synthesis and characterization of mesoporous anatase TiO2 nanostructures via organic acid precursor process for dye-sensitized solar cells applications

Titania (TiO₂) nanoparticles have been synthesized using organic precursor technique. The titania nanoparticles were characterized. The results indicated that the prepared titanium oxalate and citrate precursors were transformed to anatase TiO₂ phase at temperature 400 °C for 2 h. Dye-sensitized solar cells were assembled using the prepared nanocrystalline TiO₂ with large surface area. The specific surface area S_BET was 80.9 and 78.6 m²/g using oxalic and citric acids, respectively. The power efficiency was 3.5 and 2.4%. A brief discussion on the possible reasons behind the low power conversion efficiency observed for these type of solar cells was reported.     

One-step preparation of size-defined aggregates of TiO2 nanocrystals with tuning of their phase and composition

One-step route based on the thermal decomposition of the double salt (NH₄)₂TiO(SO₄)₂ (ammonium titanyl sulfate, ATS) is presented to prepare size-defined aggregates of Ti-based nanoparticles with structural hierarchy. The component of Ti-based networks is tunable from anatase/rutile TiO₂, nitrogen-doped TiO₂, TiN_xO_1−x, to TiN depending on the atmospheres and reaction temperatures. The as-prepared Ti-based powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS), and BET surface area techniques. It is found that TiO₂ in the predominant rutile phase could be achieved by the thermal decomposition of ATS in flowing Ar gas. Furthermore, the nitrogen-doped TiO₂, TiN_xO_1−x solid solution and TiN were prepared by the thermal decomposition of ATS in flowing NH₃ gas by varying the temperatures. The network of anatase TiO₂ with a specific surface area up to 64 m² g⁻¹ contains large mesopores with a mean diameter of ca. 15 nm, and the large pore size allows more accessible surface and interface available for the photocatalytic degradation of large-molecule dyes. The photocatalytic activity of the prepared TiO₂ and nitrogen-doped TiO₂ under UV–vis light irradiation is compared to Degussa P-25 using the photocatalytic degradation of methylene blue (MB) as a model reaction. The anatase TiO₂ nanoparticles derived from one-step route show the highly efficient photocatalytic activity for the degradation of MB in comparison with Degussa P-25. The presence of large-sized rutile in the TiO₂ powder decreases the specific surface area and thus the powder exhibits a lower photocatalytic activity.     

Fabrication of Porous TiO<Subscript>2</Subscript> Hollow Spheres and Their Application in Gas Sensing

In this work, porous TiO₂ hollow spheres with an average diameter of 100 nm and shell thickness of 20 nm were synthesized by a facile hydrothermal method with NH₄HCO₃ as the structure-directing agent, and the formation mechanism for this porous hollow structure was proved to be the Ostwald ripening process by tracking the morphology of the products at different reaction stages. The product was characterized by SEM, TEM, XRD and BET analyses, and the results show that the as-synthesized products are anatase phase with a high surface area up to 132.5 m²/g. Gas-sensing investigation reveals that the product possesses sensitive response to methanal gas at 200°C due to its high surface area.     

Mesoporous polyaniline or polypyrrole/anatase TiO2 nanocomposite as anode materials for lithium-ion batteries

A functional composite as anode materials for lithium-ion batteries, which contains highly dispersed TiO₂ nanocrystals in polyaniline matrix and well-defined mesopores, is fabricated by employing a novel one-step approach. The as-prepared mesoporous polyaniline/anatase TiO₂ nanocomposite has a high specific surface area of 224 m² g⁻¹ and a predominant pore size of 3.6 nm. The electrochemical performance of the as-prepared composite as anode material is investigated by cyclic voltammograms and galvanostatic method. The results demonstrate that the polyaniline/anatase nanocomposite provides larger initial discharge capacity of 233 mAh g⁻¹ and good cycle stability at the high current density of 2000 mA g⁻¹. After 70th cycles, the discharge capacity is maintained at 140 mAh g⁻¹. The excellent electrochemical performance of the polyaniline/TiO₂ nanocomposite is mainly attributed to its special structure. Furthermore, it is accessible to extend the novel strategy to other polymer/TiO₂ composites, and the mesoporous polypyrrole/anatase TiO₂ is also successfully fabricated.     

Micro-mesoporous TiO2/SiO2 nanocomposites: Sol-gel synthesis,characterization, and enhanced photodegradation of quinoline

Micro-mesoporous TiO₂/SiO₂ nanocomposite powders have been successfully synthesized by the sol-gel process with different TiO₂/SiO₂ molar ratios and were applied in the UV-photodegradation of quinoline (λ = 254 nm). The structural, morphological, and textural characterization of the powders showed a homogeneous distribution of TiO2 nanoparticles within a porous amorphous SiO2 matrix. Due to the micro-mesoporous character of the materials, their textural characteristics were evaluated by the N2 adsorption method, by comparing BET, DR, Langmuir, and DFT theories. Si₆₀Ti₄₀ powders (60%SiO₂/40%TiO₂) presented the highest specific surface area (SSA) obtained from BET (SSA = 363 m²g^-1), DR (SSA = 482 m²g^-1), and Langmuir (SSA = 492 m²g^-1) due to the adequate particle size of TiO₂ and its high dispersion in the porous matrix. A higher degradation of quinoline in the presence of H₂O₂ (66%) was achieved using Si₈₀Ti₂₀ powders (80%SiO₂/20%TiO₂), as compared to pure sol-gel TiO₂ powders, (51%) under the same reaction conditions (1 UVC lamp - 250W, t = 180 min). The better performance of the Si₈₀Ti₂₀ nanocomposite could be attributed to the small TiO₂ anatase crystallite size (<5.7 nm), high dispersion of these crystallites in the SiO₂ matrix, great specific surface area (DR SSA = 342 m² g^?1), and the formation of Ti–O–Si bond, which is associated with new catalytic sites in TiO₂/SiO₂ composite.     

The influence of the acidic scouring treatment on the wastewater treatment of TiO<Subscript>2</Subscript> loaded activated carbon electrode

Activated carbon (AC) electrodes were loaded with TiO₂ by using sol–gel method after a pretreatment process, the effect of the acidic pretreatment of the TiO₂ loaded electrode on its deionization efficiency of the wastewater containing NaCl solutions was studied; the physical, chemical and electrochemical properties of the electrode were characterized. The physical and chemical properties of the activated carbon before and after loaded with TiO₂ nanoparticles are characterized by using scanning electron microscopy, energy dispersion spectrum analyzer, Brunauer–Emmett–Teller gas adsorption method, thermal gravimetric analysis, Fourier transform infrared spectroscopy respectively. Electrochemical properties were characterized by employing electrochemical workstation and electrical adsorption deionization test. It was found that both the specific capacitance and the ions removal efficiency of the activated carbon loaded with TiO₂ had an increase of 16.4 and 49.8 % respectively in comparison with original activated carbon electrode. It was believed that this is due to the presence of crystal anatase TiO₂ nanoparticles (the mass content of titanium element in the TiO₂/AC complex is about 24.91 %) on the surface and pores in the activated carbon; while Ti–O–C bonds was found on the surface of the activated carbon, its surface wetting properties was significantly improved. However, it was also noticed that and the specific surface area of the activated carbon was decreased from 680.5 to 523.35 m² g^?1. This might lead to the decrease of the physical adsorption properties of the activated carbon electrodes, but its Electrical double-layer capacitance increases, electrical adsorption efficiency was improved.     

Preparation and characterization of high-surface-area titanium dioxide by sol-gel process

One of the important ways to improve photocatalytic efficiency is to prepare catalyst with enhanced surface area. In this work, titanium dioxide (TiO₂) nanoparticles having enhanced surface area were synthesized under the interference of SiO₂. The mixed oxide, SiO₂-TiO₂ (10% mol% Si), was prepared by a sol-gel procedure using titanium tetra-n-butoxide as Ti-precursor. The commercial SiO₂ nanoparticles were added into the TiO₂ sols after hydrolysis. After condensation and calcination heat treatment, the SiO₂-TiO₂ nanoparticles were obtained. To achieve the purpose of obtaining the high-surface-area TiO₂, the SiO₂ was removed subsequently by aqueous NaOH solution. The TiO₂ products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), and by N₂ adsorption-desorption isotherm. A fine mesoporous structure was formed for as-prepared TiO₂ after calcination at 400^∘C and the average pore diameter was about 7 nm. The porous TiO₂ products possess mixing phases of anatase and rutile. Phase transformation from anatase to rutile occurred when the samples were calcined. The phase transition temperature is sensitive to the silicon content. The particle size of ∼43 nm remained constant upon calcinations from 500 to 700^∘C. The specific surface area was increased up to 66% compared to regular TiO₂ samples that were prepared by the similar sol-gel procedure. The porous TiO₂ nanostructures exhibited enhanced photocatalytic performance to decompose methylene blue under UV irradiation.     

The role of TiO<Subscript>2</Subscript> layers deposited on YSZ on the electrochemical promotion of C<Subscript>2</Subscript>H<Subscript>4</Subscript> oxidation on Pt

The electrochemical promotion of Pt/YSZ and Pt/TiO₂/YSZ catalyst-electrodes has been investigated for the model reaction of C₂H₄ oxidation in an atmospheric pressure single chamber reactor, under oxygen excess between 280 and 375 °C. It has been found that the presence of a dispersed TiO₂ thin layer between the catalyst electrode and the solid electrolyte (YSZ), results in a significant increase of the magnitude of the electrochemical promotion of catalysis (EPOC) effect. The rate enhancement ratio upon current application and the faradaic efficiency values, were found to be a factor of 2.5 and 4 respectively, higher than those in absence of TiO₂. This significantly enhanced EPOC effect via the addition of TiO₂ suggests that the presence of the porous TiO₂ layer enhances the transport of promoting O²⁻ species onto the Pt catalyst surface. This enhancement may be partly due to morphological factors, such as increased Pt dispersion and three-phase-boundary length in presence of the TiO₂ porous layer, but appears to be mainly caused by the mixed ionic-electronic conductivity of the TiO₂ layer which results to enhanced O²⁻ transport to the Pt surface via a self-driven electrochemical promotion O²⁻ transport mechanism.     

Enhanced photoelectric efficiency by surface modification of TiO<Subscript>2</Subscript> thin film using various acidic species

This study examined the photoelectric conversion efficiency of the dye-sensitized solar cell (DSSC) when the surface of a nanometer-sized TiO₂ film, which was prepared using the solvothermal method, was modified by five acid compounds. The TiO₂ film exhibited an anatase structure with an average particle size in the range of 10–15 nm, and the maximum absorption band was shown in the UV-visible spectrum around 360 nm. The surface colors of the carboxylic acid-modified TiO₂ films were changed to light or dark with differing energy conversion efficiencies. Particularly, the conversion efficiency was considerably enhanced from approximately 6.25% for the non-modified TiO₂ film to approximately 7.50% for the film treated by acetic acid of 1.0 mole, with the N719 dye under 100 mW/cm² of simulated sunlight. FT-IR analysis of the films after N719 dye adsorption confirmed that the IR spectrum of the modified TiO₂ showed a sharp and strong band at 500 cm⁻¹, which was assigned to a metal-O bond, due to the formation of a new Ti-O bond between the O of COO⁻ and the Ti atom, which was relatively weaker in the non-modified TiO₂. Furthermore, these results were in agreement with an electrostatic force microscopy (EFM) study showing that the electrons were transferred rapidly to the surface of the acetic acid-modified TiO₂ film, compared with that on the nonmodified TiO₂ film.     

Nanocasting Synthesis of Ultrafine WO<Subscript>3</Subscript> Nanoparticles for Gas Sensing Applications

Ultrafine WO₃ nanoparticles were synthesized by nanocasting route, using mesoporous SiO₂ as a template. BET measurements showed a specific surface area of 700 m²/gr for synthesized SiO_2, while after impregnation and template removal, this area was reduced to 43 m²/gr for WO3 nanoparticles. HRTEM results showed single crystalline nanoparticles with average particle size of about 5 nm possessing a monoclinic structure, which is the favorite crystal structure for gas sensing applications. Gas sensor was fabricated by deposition of WO₃ nanoparticles between electrodes via low frequency AC electrophoretic deposition. Gas sensing measurements showed that this material has a high sensitivity to very low concentrations of NO₂ at 250°C and 300°C.     

Photocatalytic activity of metal-decorated SiO<Subscript>2</Subscript>@TiO<Subscript>2</Subscript> hybrid photocatalysts under water splitting

We report the fabrication of a metal-decorated hybrid nanocomposite with TiO₂ encapsulation (Metal/SiO₂@TiO₂, Metal=Pt or Ru) using a simple surface-modification chemical process. Metal nanoparticles capped with polyvinylpyrrolidone were successfully assembled on functionalized SiO₂ via electrostatic interactions, after which a thin layer of TiO₂ was coated on the surface by the sol-gel process to avoid agglomeration of the coated silica spheres. Transmission electron microscopy studies confirmed that the metal nanoparticles were uniformly distributed throughout the surface of the SiO₂ with a thin layer of TiO₂. In addition, X-ray diffraction was employed to ensure the crystal structure of the uniformly coated thin TiO₂ layer. Even after calcination at 500 °C, the structure remained intact, confirming high thermal stability. The photocatalytic activity of the metal-decorated SiO₂/TiO₂ nanocomposites was evaluated using the H₂ evolution reaction. The Metal/SiO₂@TiO₂ catalysts show the photocatalytic water splitting efficiency for H₂ generation (i.e., 0.14% for Pt/SiO₂@TiO₂ and 0.12% for Ru/SiO₂@TiO₂), while there is no generation of H₂ on the Metal/SiO₂ without a coating layer. These results indicate that the anatase crystalline coating layer has good thermal and chemical stability and plays a significant role in photocatalytic H₂ production.