Effects of tungsten thickness and annealing temperature on the electrical properties of W-TiO2 thin films

TiO₂ thin films were prepared by RF magnetron sputtering onto glass substrates and tungsten was deposited onto these thin films (deposition time 15-60 s) to form W-TiO₂ bi-layer thin films. The crystal structure, morphology, and transmittance of these TiO₂ and W-TiO₂ bi-layer thin films were investigated. Amorphous, rutile, and anatase TiO₂ phases were observed in the TiO₂ and W-TiO₂ bi-layer thin films. Tungsten thickness and annealing temperature had large effects on the transmittance of the W-TiO₂ thin films. The W-TiO₂ bi-layer thin films with a tungsten deposition time of 60 s were annealed at 200 °C-400 °C. The band gap energies of the TiO₂ and the non-annealed and annealed W-TiO₂ bi-layer thin films were evaluated using (αhν)^1/2 versus energy plots, showing that tungsten thickness and annealing temperature had major effects on the transmittance and band gap energy of W-TiO₂ bi-layer thin films.     

Novel one-step preparation of tungsten loaded TiO2 nanotube arrays with enhanced photoelectrocatalytic activity for pollutant degradation and hydrogen production

Highly ordered tungsten doped TiO₂ nanotube arrays (W-TiO₂NTs) were prepared in glycerol/fluoride electrolyte solution containing sodium tungstate via the electrochemical oxidation of a Ti substrate. The resulting arrays were characterized by XRD, SEM, and XPS. The 15 mM W-TiO₂NTs exhibited better photoelectrochemical activity than the TiO₂NTs and W-TiO₂NTs fabricated using other W concentrations under Xe illumination. The W ion was successfully introduced into the TiO₂ crystal lattice in the W^6 + form according to the XPS analysis, which enhanced the photoelectrocatalytic activity of the W-TiO₂NTs, as indicated by the efficient removal of Rhodamine B and the production of hydrogen.     

Large enhancements in hydrogen production of TiO2 through a simple carbon decoration

A simple carbon decoration, involving only immersion in adipic acid followed by calcination in N₂ atmosphere, was developed to prepare thin carbon layer decorated TiO₂ nanoparticles. The thin carbon layer was in tight contact with the TiO₂ domain and served as an electron trapping center to improve charge separations necessary for enhancement in photocatalytic water splitting performance of the TiO₂ nanoparticles. With an optimal carbon loading of 0.3 wt%, a fourfold improvement was achieved for hydrogen production as compared with that achieved by pristine TiO₂ nanoparticles. This simple carbon decoration provides a promising low-cost alternative to traditional Pt-decoration approaches for enhancing hydrogen productions from photocatalytic water splitting.     

Nucleation effect of surface treated TiO2 on Poly(trimethylene terephthalate) (PTT) nanocomposites

A study of the nucleation effect of TiO₂ in poly(trimethylene terephthalate)/TiO₂ nanocomposite has been carried out using different theoretical models. The models were applied and developed with the aim to describe and better understand the influence of the TiO₂ dispersion on crystallization characteristics of PTT. The PTT/TiO₂ nanocomposites with untreated and surface‐treated TiO₂ were prepared by the melt mixing method. The nucleation efficiency of the TiO₂ nanoparticles has been analyzed with the use of the Avrami model and Mo's method. It was found that the PTT matrix incorporated with surface‐treated TiO₂ particles has a higher crystallization temperature and melting point than that incorporated with untreated TiO₂ particles. As per the models, unlike untreated TiO₂, surface‐treated TiO₂ particles had a lesser effect on the degree of crystallization of the PTT matrix. The TiO₂ nanoparticles act as a nucleating agent in the PTT matrix thereby reducing t_½ of the crystallization and leading to easier crystallization of the polymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of hydrothermally synthesized titanium nanotubes on the behaviour of polypropylene for antimicrobial applications

TiO₂ nanotubes (TiO₂‐Ntbs) synthesized by a hydrothermal method were used as filler to prepare polypropylene (PP) composites by melt blending. Their structural properties as well as their biocidal potential were studied. Nanotubes were used either as‐synthesized or organically modified with hexadecyltrimethoxysilane (Mod‐TiO₂). These nanoparticles form secondary structures with sizes around 100 nm that are well dispersed in the polymer matrix, but not homogeneously because agglomerates larger than 1 µm are also seen by transmission electron microscopy. Regarding the properties of the composites, the incorporation of the nanoparticles increased the polymer's crystallinity and thermal stability. The maximum decomposition temperature of the matrix increased by ca 13 °C compared to virgin PP. The nanotubes further increase the spherulite nucleation density, and therefore a reduction in the diameter of spherulites and an increase in their number were observed. Despite the above, the addition of TiO₂ nanoparticles did not modify the mechanical properties of PP. The PP/TiO₂‐Ntb nanocomposites exposed to UVA radiation showed a biocidal behaviour, reducing a colony of Escherichia coli by 81%. © 2015 Society of Chemical Industry     

Mechanical properties and nonisothermal crystallization kinetics of polyamide 6/functionalized TiO2 nanocomposites

Titanium dioxide (TiO₂) nanoparticles were pretreated with excessive toluene‐2,4‐diisocyanate (TDI) to synthesize TDI‐functionalized TiO₂ (TiO₂‐NCO), and then polymeric nanocomposites consisting of polyamide 6 (PA6) and functionalized‐TiO₂ nanoparticles were prepared via a melt compounding method. The interfacial interaction between TiO₂ nanoparticles and polymeric matrix has been greatly improved due to the isocyanate ( NCO) groups at the surface of the functionalized‐TiO₂ nanoparticles reacted with amino groups ( NH₂) or carboxyl ( COOH) groups of PA6 during the melt compounding and resulted in higher tensile and impact strength than that of pure PA6. The nonisothermal crystallization kinetics of PA6/functionalized TiO₂ nanocomposites was investigated by differential scanning calorimetry (DSC). The nonisothermal crystallization DSC data were analyzed by the modified‐Avrami (Jeziorny) methods. The results showed that the functionalized‐TiO₂ nanoparticles in the PA6 matrix acted as effective nucleation agents. The crystallization rate of the nanocomposites obtained was faster than that of the pure PA6. Thus, the presence of functionalized‐TiO₂ nanoparticles influenced the mechanism of nucleation and accelerated the growth of PA6 crystallites. POLYM. COMPOS., 35:294–300, 2014. © 2013 Society of Plastics Engineers     

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.     

Synergy between tungsten and palladium supported on titania for the catalytic total oxidation of propane

Titania-supported palladium catalysts modified by tungsten have been tested for the total oxidation of propane. The addition of tungsten significantly enhanced the catalytic activity. Highly active catalysts were prepared containing a low loading of 0.5 wt.% palladium, and activity increased as the tungsten loading was increased up to 6 wt.%. Catalysts were characterised using a variety of techniques, including powder X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and aberration-corrected scanning transmission electron microscopy. Highly dispersed palladium nanoparticles were present on the catalyst with and without the addition of WO_x. However, the addition of WO_x slightly increases the average palladium particle size, and there was some evidence for the Pd forming epitaxial islands on the support in the tungsten-doped samples. Surface analysis identified a combination of Pd⁰ and Pd²⁺ on a Pd/TiO₂ catalyst, whereas all of the Pd loading was found in the form of Pd²⁺ with the addition of tungsten into the catalysts. At low tungsten loadings, isolated monotungstate and some polytungstate species were highly dispersed over the titania support. The concentration of polytungstate species increased as the loading was increased, and it was also promoted by the presence of palladium. The coverage of the highly dispersed tungstate species over the titania also increased as the tungsten loading increased. Some tungstate species were also found to be associated with the palladium oxide particles, and there was an enrichment of oxidised tungsten species at the peripheral interface of the palladium oxide nanoparticles and the titania. Sub-ambient temperature–programmed reduction experiments identified an increased concentration of highly reactive species on catalysts with palladium and tungsten present together, and we propose that the new WO_x-decorated interface between PdO_x and TiO₂ particles may be responsible for the enhanced catalytic activity in the co-impregnated catalysts.     

Long Vertically Aligned TiO2 Nanotube Electrodes Prepared via Two-Step Anodization for Highly Efficient Photovoltaics

Vertically aligned long TiO₂ nanotube (NT) electrodes with optimized structures for photovoltaic application were prepared by a two-step anodization method. The structures of the conventional TiO₂ NT electrodes prepared by one-step anodization became severely bundled and disordered for tube lengths exceeding 20 μm. On the other hand, two-step anodization resulted in uniform and bundle-free TiO₂ NT electrodes, with tube lengths of up to 38 μm. When used in dye-sensitized solar cells (DSSCs) as photoanodes, the two-step TiO₂ NT electrodes exhibited enhanced short-circuit current density (J_sc) with increasing tube length, owing to an increased roughness factor, which resulted in high dye loading. However, the dark current and open-circuit voltage decay (OCVD) curves confirmed that the electron recombination rate increased, and the electron lifetime decreased, with increasing tube length. This reduced electron lifetime resulted in sharp reductions in the open-circuit voltage (V_oc) with increasing tube length. Owing to the trade-off between the enhanced current density and the reduced electron lifetime, an optimal conversion efficiency of 4.56 % was obtained for a tube length of 29 μm.     

Efficient synthesis of titania nanotubes and enhanced photoresponse of Pt decorated TiO2 for water splitting

We investigated the effect of HMT (hexamethylenetetraamine) on the anodic growth of TiO₂ nanotube arrays. The tube length increases to 4.3 μm with HMT concentration increasing to 0.04 mol·L⁻¹. Adsorption of HMT on the TiO₂ surface is shown to markedly decrease the chemical dissolution rate of tube mouth, resulting in longer nanotube length. Furthermore, Pt nanoparticles were successfully deposited on the surface of TiO₂ nanotubes by ac electrodeposition method. The TiO₂/Pt composites were characterized by field emission scanning electron microscope (FESEM), X-ray photoelectron spectra (XPS), and photoelectrochemistry. An enhancement in photocurrent density has been achieved upon modification of TiO₂ nanotubes with Pt nanoparticles.     

Retracted: Effect of surface‐treated TiO2 on non‐isothermal crystallization behavior of poly trimethylene terephthalate nanocomposites

The study of the non‐isothermal crystallization behavior of poly(trimethylene terephthalate) (PTT)/TiO₂ nanocomposites using untreated and surface‐treated TiO₂ has been carried out with different theoretical models. The PTT/untreated TiO₂ and surface‐treated TiO₂ nanocomposites were prepared employing batch mixing technique with an aim to investigate the influence of the TiO₂ dispersion on the crystallization behavior. The nucleation efficiency of the TiO₂ nanoparticles has been demonstrated with the use of Avrami and Jeziorny models. Test results indicated that the PTT matrix with surface‐treated TiO₂ particles has higher crystallization temperature and melting point than those with untreated PTT/TiO₂ nanocomposites. Unlike untreated TiO₂, surface‐treated TiO₂ particles also showed less effect on the degree of crystallization of the PTT matrix. The TiO₂ nanoparticles act as a nucleating agent in the PTT matrix by reducing the t_½ of the crystallization time, thus making it easy to form crystals. © 2012 Society of Plastics Engineers     

Effects of Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> nanometer particles on biological toxicity during zebrafish embryogenesis

This study investigated the toxicity of Cu (1, 10, 15, and 25 mol%) loaded TiO₂ and pure TiO₂ nanometersized photocatalysts during the development of zebrafish embryogenesis. The hatch rate decreased in the Cu _x TiO _y nanoparticles exposed groups (10, 20 ppt) compared to pure TiO₂ nano-particles (10, 20 ppt) exposed or control groups. These Cu _x TiO _y and TiO₂ nanoparticles led to developing mutated embryos with abnormal notochord formation, no tail, damaged eyes and abnormal heart development. Exposure to Cu _x TiO _y and pure TiO₂ nanoparticles led to glutathione increase, catalase activity increase, GST increase and GSR increase than control. Penetration of the Cu _x TiO _y and pure TiO₂ nanoparticles to the embryo was also tested. It was observed that Cu _x TiO _y and pure TiO₂ nanoparticles penetrated into cells. Moreover Cu _x TiO _y penetrated into the skin, nerve and yolk sac epithelium cells on the zebrafish larvae as aggregated particles, which may induce the direct interaction between nanoparticles and cell to cause adverse biological responses. As a result, the Cu-loaded TiO₂ nanoparticles had the toxicity of zebrafish embryo and larvae in the water environment.     

Synthesis,characterization, and performance evaluation of PES/EDA‐functionalized TiO2 mixed matrix membranes for CO2/CH4 separation

Poor adhesion between hydrophobic polymers and hydrophilic inorganic fillers is a challenge that encumbers a high separation performance of mixed matrix membrane (MMM). In this study, Titanium(IV) oxide (TiO₂) nanoparticles were functionalized using ethylenediamine (EDA) before embedment in poly(ether sulfone) (PES) polymer matrix. MMMs were synthesized through dry phase inversion technique. Membranes morphology and nanoparticles dispersion was drastically enhanced posterior amine modification indicating an improved adhesion between the polymer and filler particles. Membranes thermal stability was likewise improved as higher degradation temperatures were perceived for PES/EDA–TiO₂ MMMs. Gas separation evaluation for pure carbon dioxide (CO₂) and methane (CH₄) gases revealed a remarkably enhanced separation performance upon amine‐grafting of TiO₂ as EDA‐TiO₂ MMMs exhibited a higher separation performance as compared to MMMs with pristine TiO₂. The highest ideal separation factor achieved was 41.52 with CO₂ permeability of 10.11 Barrer at an optimum loading of 5% wt of EDA‐TiO₂ which is threefold higher as compared to neat PES membrane and approximately twofold higher than MMMs with pristine TiO₂, respectively, at the same filler loading. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45346.     

Laminar heat transfer of non-Newtonian nanofluids in a circular tube

Forced convection heat transfer behavior of three different types of nanofluids flowing through a uniformly heated horizontal tube under laminar regime has been investigated experimentally. Nanofluids were made by dispersion of γ-Al₂O₃, CuO, and TiO₂ nanoparticles in an aqueous solution of carboxymethyl cellulose (CMC). All nanofluids as well as the base fluid exhibit shear-thinning behavior. Results of heat transfer experiments indicate that both average and the local heat transfer coefficients of nanofluids are larger than that of the base fluid. The enhancement of heat transfer coefficient increases by increasing nanoparticle loading. At a given Peclet number and nanoparticle concentration the local heat transfer coefficient decreases by axial distance from the test section inlet. It seems that the thermal entry length of nanofluids is greater than the base fluid and becomes longer as nanoparticle concentration increases.     

Influence of TiO2 nanoparticles on nonisothermal crystallization of PP in a wide range of cooling rates analyzed by fast scanning DSC

The influence of titanium dioxide (TiO₂) nanoparticles on the crystallization behavior of polypropylene was investigated by conventional differential scanning calorimetry (DSC) and fast scanning DSC measurements. The data obtained from both methods were estimated for the first time using the Lauritzen‐Hoffmann equation to analyze the behavior over a wide cooling range under nonisothermal conditions. This provides more reliable values of nucleation parameters (K_g) and surface free energy (σ_e). The variation of the effective energy (ΔE) was determined with the Kissinger method. Regardless of the cooling rate, both K_g and σ_e indicate the role of titania as a nucleating agent enhances the crystallization rate. However, the ΔE denotes that TiO₂ acts as an obstacle to the mobility of chain segments at cooling rates below 150 °C/s, while, in contrast, the presence of titania enhances the chain mobility at cooling rates above 150 °C/s. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43944.     

Enhanced electron collection efficiency of nanostructured dye‐sensitized solar cells by incorporating TiO2 cubes

Herein, enhancement of dye‐sensitized solar cell (DSC) performance is reported by combining the merits of the dye loading of TiO₂ nanoparticles and light scattering, straight carrier transport path, and efficient electron collection efficiency of TiO₂ cubes. We fabricate DSC devices with various arrangement styles and compositions of the electrodes in the forms of monolayer and double layer films. For this purpose, the solvothermal synthesized TiO₂ cubic particles (100‐600 nm) are employed as the scattering layer, whereas TiO₂ nanoparticles (15‐30 nm) synthesized via a combination of solvothermal and sol‐gel routes are used as the active layer of devices. We improve the photovoltaic characteristics of DSCs by two mechanisms. First, the light harvesting of DSC devices made of nanoparticles is improved by controlling the thickness of monolayer films, reaching the highest efficiency of 7.0%. Second, the light scattering and electron collection efficiency are enhanced by controlling the composition of double layer films composed of mixtures of TiO₂ nanoparticles and cubes, obtaining the maximum efficiency of 8.21%. The enhancements are attributed to balance between charge transfer resistance and charge recombination of photo‐generated electrons as well as dye loading and light scattering.     

Investigation of the mechanical properties of a photocatalytic pseudo‐paint

Photocatalytic oxidative paints (e.g., a paint containing nano‐TiO₂) are used to break down volatile organic compounds to CO₂ by photooxidation reactions. In this research, a photocatalytic oxidative pseudo‐paint was made with acrylic–styrene copolymer latex, TiO₂ pigment, calcium carbonate extender, and TiO₂ nanoparticles as a photocatalyst. To investigate the effects of the pigment, extender, and nanoparticles on the mechanical properties of the samples and their relationship to their photocatalytic activity, different contents of the particles were dispersed in the paint formulation. The tensile strengths (TSs) of the samples were measured as the mechanical properties. The samples were characterized by scanning electron microscopy analysis. We found that up to 3% nano‐TiO₂ enhanced the mechanical properties of the pigmented resin, whereas beyond this, TS decreased. In samples containing 3% nanoparticles, the incorporation of 15% TiO₂ pigment caused optimized mechanical properties, and beyond that, TS decreased because of particle agglomeration. In the absence of nanoparticles, the samples showed improvements in the mechanical properties with up to a 40% loading of pigment. The results reveal that the samples containing nano‐TiO₂ and pigment showed the same trend for the mechanical and photocatalytic properties before the critical pigment volume concentration (CPVC). However, when the extender was incorporated or TiO₂ particles were loaded beyond CPVC, the mechanical and photocatalytic properties correlation was compromised, and they were not directly correlated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42885.     

A novel route for the synthesis of poly(2‐hydroxyethyl methacrylate) grafted TiO2 nanoparticles via surface thiol‐lactam initiated radical polymerization

Hybrid nanocomposites of poly(2‐hydroxyethyl methacrylate) (PHEMA) and TiO₂ nanoparticles were synthesized via surface thiol‐lactam initiated radical polymerization by following the grafting from strategy. Initially, TiO₂ nanoparticles were modified by 3‐mercaptopropyl trimethoxysilane to prepare thiol functionalized TiO₂ nanoparticles (TiO₂? SH). Subsequently, surface initiated polymerization of 2‐hydroxyethyl methacrylate was conducted by using TiO₂? SH and butyrolactam as an initiating system. The anchoring of PHEMA onto the surface of TiO₂ nanoparticles was investigated by FTIR, ¹H‐NMR, XPS, TGA, and XRD analyses. The experimental results indicated a strong interaction between PHEMA and TiO₂ nanoparticles owing to covalent bonding. The TEM and SEM images of PHEMA‐g‐TiO₂ showed that the agglomeration propensity of TiO₂ nanoparticles was significantly reduced upon the PHEMA functionalization. The molecular weight and polydispersity index of the cleaved PHEMA from the surface of TiO₂ nanocomposites were estimated by GPC analysis. An improved thermal property of the nanocomposites was observed from TGA analysis. PHEMA‐g‐TiO₂ nanocomposites were found to be highly dispersible in organic solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Rattle‐Structured Ag/TiO2 Nanocomposite Capsules with Bactericide and Photocatalysis Activities

A structural design featuring rattle‐type silver/titania (Ag/TiO₂) core/shell, that is, Ag@TiO₂, composite microcapsules is produced. The TiO₂ shell protects the encapsulated, movable Ag nanoparticles from breaking away under moderate loading, minimizing hence adverse environmental and biological exposure due to the metal loss, whereas the mesoporous shell serves as conduits for Ag ions released from the caged Ag nanoparticles to kill Escherichia coli in aqueous solutions under dark condition. The anatase TiO₂ shell imparts an additional, synergistic photocatalysis activity under ultraviolet irradiation. A pronouncedly enhanced photocatalysis activity results when the Ag@TiO₂ composite capsules were thermally annealed under vacuum. This “rattle‐in‐ball” hybrid architecture enables bifunctional bactericide and photocatalysis capability under both light and dark conditions, as well as mitigated environmental and biological impact in practical use.     

Ignition performance of TiO2 coated boron particles using a shock tube

This study coated the surface of irregularly shaped 5-μm boron particles with TiO₂ nanoparticles to improve the ignition performance of the boron. A simple and inexpensive chemical method was used to coat the surface of boron with TiO₂. Five different samples of boron coated with TiO₂ nanoparticles were obtained by varying the concentration of Ti precursor. Surface structures were analyzed using different characterization techniques, which showed the formation of nanocrystalline TiO₂ nanoparticles over the boron surface. The nanoparticles of TiO₂ were well dispersed over the boron surface, and exhibited strong interfacial contact with the boron. The oxidation of boron and boron coated with TiO₂ was analyzed by thermogravimetric technique in an air atmosphere from room temperature to 1000 °C. Results revealed that the oxidation of boron started at a temperature approximately 162 °C lower after coating with TiO₂. The ignition behavior of the boron and boron coated with TiO₂ particles was studied using a shock tube. The results of the shock tube experiments demonstrated the TiO₂ coated boron had a shorter ignition delay time than the bare boron. An approximate 35% reduction was observed in the ignition delay time of boron after coating with TiO₂ nanoparticles, showing its potential value in high energy density fuels.