Preparation and characterization of low density polystyrene/TiO2 core–shell particles for electronic paper application

In order to reduce the density mismatch between TiO₂ and the low dielectric medium and improve the dispersion stability of the electrophoretic particles in the low dielectric medium for electrophoretic display application, polystyrene/titanium dioxide (PS/TiO₂) core–shell particles were prepared via in-situ sol–gel method by depositing TiO₂ on the PS particle which was positively charged with 2-(methacryloyloxy)ehyl trimethylammonium chloride (DMC). The morphology and average particle size of PS/TiO₂ core–shell particles were observed by transmission electron microscopy (TEM), scanning electron microscope (SEM) and particle size analyzer. It was found that density of PS/TiO₂ core–shell particles were reduced obviously and the particles can suspend in the low dielectric medium of low density. The PS/TiO₂ core–shell particles can endure ultrasonic treatment because of the interaction between TiO₂ and PS. Zeta potential and electrophoretic mobility of the fabricated core–shell particles in a low dielectric medium with charge control agent was measured to be −44.3 mV and −6.07 × 10⁻⁶ cm²/Vs, respectively, which presents potential in electronic paper application.     

Preparation of PS/TiO2 as a white pigment for electrophoretic displays

PS (polystyrene)/TiO₂, TiO₂ coated onto PS by a hydrolysis reaction, was prepared as a white pigment for electronic paper (e-paper). Two key parameters, density and zetapotential, were precisely controlled for use as a white pigment. The density was manipulated by changing the mixture ratio of EtOH to H₂O, and the concentration of titanium tetrabutoxide (TBO) in the hydrolysis reaction. The modification of PS/TiO₂ with (3-aminopropyl)triethoxy silane (APTES) and acetic acid showed positive zetapotential originated from the mutual effects between an amino functional group in APTES, and a proton from acetic acid. The mutual effect was studied, and PS/TiO₂ with density of 1.6 g/cm² and zetapotential of 75 mV was prepared using the results.     

Synthesis and nanostructural investigation of TiO<Subscript>2</Subscript> nanorods doped by SiO<Subscript>2</Subscript>

TiO₂ Nano rods can be used as dye-sensitized solar cells, various sensors and photocatalysts. These nanorods are synthesized by a hydrothermal corrosion process in NaOH solution at 200°C using TiO₂ powder as the source material. In the present work, the synthesis of TiO₂ nanorods in anatase, rutile and Ti₇O₁₃ phases and synthesis of TiO₂ nanorods by incorporating SiO₂ dopant, using the sol–gel method and alkaline corrosion are reported. The morphologies and crystal structures of the TiO₂ nanorods are characterized using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) study. The obtained results show not only an aggregation structure at high calcination temperatures with spherical particles but also Ti–O–Si bonds having four-fold coordination with oxygen in SiO^4 −.     

Effect of ZnS layers on optical properties of prepared CdS/TiO<Subscript>2</Subscript> nanotube arrays for photocatalyst

The TiO₂ nanotube arrays (TiO₂ NTAs) prepared by re-oxidation were chosen as basement. The NTAs prepared through re-oxidation show smoother surface and more uniform tube mouth on large scale compared with the first as-grown one. We use successive ionic layer adsorption and reaction method to deposit quantum dots (ZnS and CdS) onto the sample successively. The findings reveal that two kinds of quantum dots (～10 nm) distribute regularly and the nanotube mouth is open. From the UV–Vis absorption spectrum of samples, the red shift occurs after the sedimentation of the two quantum dots, which proves that the double modification can expand the absorption to 650 nm. Among all specimens, the sample produced by co-deposition has the highest speed of catalytic efficiency of 90.7% compared with bare TiO₂ NTAs (52.9%) and just CdS QDs sensitized sample (65.8%). In the test of photocatalysis durability, the decay percentages of CdS/TiO₂ NTAs and ZnS/CdS/TiO₂ NTAs were 35.8 and 48.4%, respectively, which means that the ZnS passivation layer plays a crucial role in enhancing photocatalytic activities.     

Computational study on the structural and surface properties of amorphous hydroxylated TiO<Subscript>2</Subscript> spherical nanoparticles

Monte Carlo simulations were carried out on amorphous titanium dioxide (TiO₂) for both bulk and hydroxylated nanoparticles with particle sizes ranging from 1 to 10 nm. The potential developed by the Matsui and Akaogi (MA) was used to model the interatomic interactions of TiO₂ in both cases (bulk and nanoparticles). Besides, Angular and Morse potentials proposed by the Tether, Cormack, Du et. al. (TCD) were introduced to model the interactions of hydroxyl groups on the TiO₂ surfaces, i.e., the Ti-O-H groups with an experimental and theoretical angles of 125 ^o . The bulk system was developed using periodic boundary conditions. The TiO₂ nanoparticles were extracted by applying a spherical cut section in the bulk TiO₂ melt structure to obtain the required size. Free valences on the nanoparticle surfaces were saturated via additional hydroxyl groups and then quenched to 300 K under free boundary conditions. The bulk and surface properties of the nanoparticles were calculated at 300 K and zero pressure and characterized via radial distribution functions, bond angle distributions, bond distances, coordination numbers, OH group concentrations and radial density profiles. In addition, to understand the difference in properties of amorphous hydroxylated TiO₂ nanoparticles and bulk amorphous TiO₂, a comparative study was done at the same thermodynamic conditions. The study shows that the bulk properties of amorphous hydroxylated TiO₂ nanoparticles are strongly size-dependent and different from those of the bulk TiO₂. As expected, increasing the particle size leads to an approach of the particle’s bulk properties to the bulk properties of the (quasi) infinite system. The size effects show that decreasing the particle size results in increasing the surface effects and surface OH group concentrations. Accordingly, small-sized TiO₂ nanoparticles have higher surface OH group concentrations and larger surface effects than large-sized TiO₂ nanoparticles. Larger surface effects result significant changes in their bond angles, bond distances, and coordination numbers. The simulation results of the surface properties reveal that the surface titanium atoms in the TiO2 nanoparticles have the capability of accommodating up to 5 hydroxyl groups. The mean surface hydroxyl group density of the amorphous TiO₂ spherical nanoparticles is estimated to be around 8.1/nm ², which lies in the range of 8–16/nm ², found by experimental and other simulation studies. Details of the modelling, simulations results and the study are presented in this paper.     

An investigation into ultra-thin pseudobinary oxide (TiO<Subscript>2</Subscript>)<Subscript>x</Subscript>(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>1-x</Subscript> films as high-<Emphasis Type="Italic">k</Emphasis> gate dielectrics

As potential gate dielectric materials, pseudobinary oxide (TiO₂)_x(Al₂O₃)_1-x (0.1≤x≤0.6) films (TAO) were deposited on Si (100) substrates by pulsed-laser deposition method and studied systematically via various measurements. By a special deposition process, including two separate steps, the TAO films were deposited in the form of two layers. The first layer was deposited at room temperature and the second layer was completed at the substrate temperature of 400 °C. Detailed data show that the properties of the TAO films are closely related to the ratio between TiO₂ and Al₂O₃. The existence of the first layer deposited at room temperature can effectively restrain the formation of the interfacial layer. And according to the results of X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy performed on the films, no other information belonging to the silicon oxide could be observed. For the (TiO₂)_0.4(Al₂O₃)_0.6 film, the best result has been achieved among all samples and its dielectric constant is evaluated to be about 38. It is valuable for the amorphous TAO film as one of the promising dielectric materials for high-k gate dielectric applications. PACS 77.55.+f; 73.40.Qv; 81.15.Fg     

Scalable synthesis and superior performance of TiO<Subscript>2</Subscript>-reduced graphene oxide composite anode for sodium-ion batteries

TiO₂-reduced graphene oxide (RGO) composite was synthesized via a sol-gel process and investigated as an anode material for sodium-ion batteries (SIBs). A remarkable improvement in sodium ion storage with a reversible capacity of 227 mAh g^?1 after 50 cycles at 50 mA g^?1 is achieved, compared to that (33 mAh g^?1) for TiO₂. The enhanced electrochemical performance of TiO₂-RGO composite is attributed to the larger specific surface area and better electrical conductivity of TiO₂-RGO composite. The excellent performance of TiO₂-RGO composite enables it a potential electrode material for SIBs.     

N+BF<Subscript>2</Subscript> and N+C+BF<Subscript>2</Subscript> high-dose co-implantation in silicon

Nitrogen and boron BF₂, and nitrogen, carbon, and boron BF₂ high-dose (6×10¹⁶–3×10¹⁷ cm^-2) co-implantation were performed at energies of about 21–77 keV. Subsequent high-temperature annealing processes (600, 850, and 1200 °C) lead to the formation of three and two surface layers respectively. The outer layer mainly consists of polycrystalline silicon and some amorphous material and Si₃N₄ inclusions. The inner layer is highly defective crystalline silicon, with some inclusions of Si₃N₄ too. In the N+B-implanted sample the intermediate layer is amorphous. Co-implantation of boron with nitrogen and with nitrogen and carbon prevents the excessive diffusivity of B and leads to a lattice-parameter reduction of 0.7–1.0%. Received: 10 January 2002 / Accepted: 30 May 2002 / Published online: 4 November 2002 RID="*" ID="*"Corresponding author. Fax: +34-91/3974895; E-mail: Lucia.Barbadillo@uam.es     

Efficient carbon-doped nanostructured TiO<Subscript>2</Subscript> (anatase) film for photoelectrochemical solar cells

In this paper, we have demonstrated that carbon-doped nanostructured TiO₂ (CD ns-TiO₂) films could be prepared simply and cheaply with oxalic acid and tetrabutylammonium bromide (Bu₄N·Br) as the carbon sources. The surface morphology of the films was a multiple-porous network structure.The average size of nanoparticle was about 40 nm. Carbon doped into substitutional sites of TiO₂ has also proven to be indispensable for band-gap narrowing and photovoltaic effect. Carbon doping lowered the band gap of n-TiO₂ to 1.98, 1.64, and 1.26 eV. The CD ns-TiO₂ film was first used as photoanode for solar cells, exhibiting high photocurrent densities (l.34 mA/cm²) and yielding an overall conversion efficiency (η) of 4.42 %.     

Preparation of TiO<Subscript>2</Subscript>-coated LiCo<Subscript>1/3</Subscript>Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by electrostatic self-assembly method and its properties

A precursor of TiO₂–LiCo_1/3Ni_1/3Mn_1/3O₂ was prepared by electrostatic self-assembly method. The final product was obtained by heating the precursor at 400–450 °C for 4–6 h in air. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical tests were used to examine the structural, morphology, elementary valence, and electrochemical characteristics. XRD indicated that the TiO₂-coated material can be indexed by α-NaFeO₂ layered structure, which belongs to hexagonal-type space group R3m. XPS results confirmed the existence of TiO₂ compound on the surface of the coated sample. The SEM image showed that the material had spherically porous morphology with the uniform size about 6 μm. The initial charge–discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ material was 168.8/160.0 mAh/g. After 60 cycles, the discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ sample was 147.0 mAh/g, and the coulombic efficiency was 94.0%. Compared with the uncoated sample, the electrochemical performance of TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ was improved.     

Nanocrystalline Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> electrodes for supercapattery application

Nanocrystalline Li₂TiO₃ was successfully synthesized using solid-state reaction method. The microstructural and electrochemical properties of the prepared material are systematically characterized. The X-ray diffraction pattern of the prepared material exhibits predominant (002) orientation related to the monoclinic structure with C2/c space group. HRTEM images and SAED analysis reveal the well-developed nanostructured particles with average size of ～40 nm. The electrochemical properties of the prepared sample are carried out using cyclic voltammetry (CV) and chronopotentiometry (CP) using Pt//Li₂TiO₃ cell in 1 mol L^?1 Li₂SO₄ aqueous electrolyte. The Li₂TiO₃ electrode exhibits a specific discharge capacity of 122 mAh g^?1; it can be used as anode in Li battery within the potential window 0.0–1.0 V, while investigated as a supercapacitor electrode, it delivers a specific capacitance of 317 F g^?1 at a current density of 1 mA g^?1 within the potential range ?0.4 to +0.4 V. The demonstration of both anodic and supercapacitor behavior concludes that the nanocrystalline Li₂TiO₃ is a suitable electrode material for supercapattery application.     

High-temperature complex impedance and modulus spectroscopic studies of doped Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> ferroelectric ceramics

Lead-free Na_0.5Bi_0.5TiO₃ (NBT) and (1 ? x)Na_0.5Bi_0.5TiO₃ + xBaTiO₃ with x = 0.1 and 0.2 (where x = 0.1 and 0.2 are named as NBT1 and NBT2, respectively), (1 ? y)Na_0.5Bi_0.5TiO₃ + yBa_0.925Nd_0.05TiO₃ with y = 0.1 and 0.2 (where y = 0.1 and 0.2 are named as NBT3 and NBT4, respectively)-based relaxor ferroelectric ceramics were prepared using the sol-gel method. The crystal structure was investigated by X-ray diffraction (XRD) at room temperature (RT). The XRD patterns confirmed the presence of the rhombohedral phase in all the samples. The electrical properties of the present NBT-based samples were investigated by complex impedance and the modulus spectroscopy technique in the temperature range of RT–600 °C. The AC conductivity was found to increase with the substitution of Ba²⁺ ions to the NBT sample whereas it significantly decreased with the addition of Nd³⁺ ions. The more anion vacancies in Ba-added samples and the lower anion vacancies in Nd-added samples were found to be responsible for higher and lower conductivities, respectively.     

Effects of LaNiO<Subscript>3</Subscript> on the structures and properties of SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> thin films

SrBi₂Ta₂O₉(SBT)/LaNiO₃(LNO)/Si and SBT/Pt/TiO₂/SiO₂/Si multilayers were fabricated by pulsed laser deposition. With Pt top electrodes, the measured remanent polarization (2P_r) of Pt/SBT/LNO/Si and Pt/SBT/Pt/TiO₂/SiO₂/Si capacitors was 6.5 C/cm² and 5.2 C/cm², respectively. Using LNO as both bottom electrodes and buffer layers, enhanced non-c-axis crystalline SBT films were induced, which resulted in a 2P_r greater than that of the Pt/SBT/Pt/TiO₂/SiO₂/Si capacitor. The hysteresis loop of the Pt/SBT/LNO/Si capacitor showed a great external-field-dependent horizontal shift. Using an electron-injection model, this dependence was addressed. The fatigue-free property of the Pt/SBT/LNO/Si capacitor was experimentally established, in that the non-volatile polarization decreased by less than 5% of the initial value after 1.44×10⁹ switching cycles . PACS 77.84.Dy; 68.65.+g     

CeO<Subscript>2</Subscript> coating to improve the performance of Li[Li<Subscript>0.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>]O<Subscript>2</Subscript>

The Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ coated with CeO₂ has been fabricated by an ionic interfusion method. Both the bare and the CeO₂-coated samples have a typical layered structure with R-3m and C2/m space group. The results of XRD and TEM images display that the CeO₂ coating layer on the precursor could enhance the growth of electrochemically active surface planes ((010), (110), and (100) planes) in the following ionic interfusion process. The results of galvanostatic cycling tests demonstrate that the CeO₂-coated sample has a discharge capacity of 261.81 mAh g^?1 with an increased initial Coulombic efficiency from 62.4 to 69.1% at 0.05 °C compared with that of bare sample and delivers an improved capacity retention from 71.7 to 83.4% after 100 cycles at 1 °C (1 °C?=?250 mA g^?1). The results of electrochemical performances confirm that the surface modification sample exhibits less capacity fading, lower voltage decay, and less polarization.     

Nanoparticles dispersion in processing functionalised PP/TiO<Subscript>2</Subscript> nanocomposites: distribution and properties

Future innovations in textiles and fibrous materials are likely to demand fibres with enhanced multifunctionality. The fibres can be functionalized by dispersing nanoadditives into the polymer during melt compounding/spinning. TiO₂ nanoparticles have the potential to improve UV resistance, antistatic, as well as impart self-cleaning by photocatalysis and thereby de-odour and antimicrobial effects. In this study, a micro-lab twin-screw extruder was used to produce samples of polypropylene (PP) nanocomposite monofilaments, doped with nano titanium oxide (TiO₂)/manganese oxide (MnO) compound having size ranging from 60 to 200 nm. As a control sample, PP filaments without additives were also extruded. Three samples were produced containing different concentrations (wt%) of the TiO₂ compound, i.e. 0.95, 1.24 and 1.79%. Nano metal-oxide distribution in the as-spun and drawn nanocomposite filaments was analysed. Although, there are small clusters of the nanoparticles, the characterizing techniques showed good dispersion and distribution of the modified TiO₂ along and across the processed filaments. From UV spectroscopy and TGA, a significant enhancement of polypropylene UV protection and thermal stability were observed: PP with higher percentage of TiO₂ absorbed UV wavelength of 387 nm and thermally decomposed at 320.16 °C accompanied by 95% weight loss.     

The Influence of Immersion of Porous Silicon in Aqueous Solutions of Fe(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> on Photoluminescence during Long Storage

The interaction of porous silicon (PS) with aqueous solutions of Fe(NO₃)₃ with different molar (M) concentrations causes introduction of iron ions into silicon pores (PS–Fe), formation of adsorbed iron coatings with different thicknesses, and an increase in the stability of PS layers, which is important for development of device structures based of PS. To treat PS layers with solutions by the immersion method, it is necessary to determine how this affects the spectral composition and intensity of photoluminescence (PL), as well as the kinetics of PL changes during long storage under atmospheric conditions. Upon treatment of freshly prepared PS by immersion into in a Fe(NO₃)₃ aqueous solution, it was found that, after short-term storage (up to 5 days) of the PS samples, the PL intensity increases by 7.5 and 3–3.6 times at low (0.2 M) and high (0.7–0.8 M) concentrations of Fe(NO₃)₃, respectively, compared to the PL intensity of an untreated PS layer. After long-term storage (4 months), the PL intensity of PS–Fe samples with concentrations of 0.1–0.2 and 0.7–0.8 M was observed to considerably increase (by 8–18 times) with unchanged position of the PL peak with respect to untreated PS. However, at the Fe(NO₃)₃ concentration of 0.3 М, the PL intensity decreases and the PL peak shifts to the blue, which is explained by incomplete coverage of the PS surface by an adsorbed iron layer. The kinetics of PL spectra during long-term storage is analyzed, and a model is proposed to explain the PL intensity and spectral composition.     

Film formation from TiO2-polystyrene latex composite: a fluorescence study

This work reports the use of the steady state fluorescence (SSF) technique for studying film formation from TiO₂ covered polystyrene (PS) latex particles. The composite films were prepared from pyrene (P)-labeled PS particles by covering them with TiO₂ at room temperature and then annealed at elevated temperatures in 10 min time interval above glass transition (T _g) temperature of polystyrene. Five different composite films were studied in various TiO₂ layer contents. Fluorescence intensities I _P from P were measured after each annealing step to monitor the stages of film formation. Films showed considerable increase in I _P above the certain onset temperature called minimum film forming temperature, T ₀. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 23.12 and 92.80 kJ mol^?1, respectively.     

A facile synthesis of heteroatom-doped carbon framework anchored with TiO<Subscript>2</Subscript> nanoparticles for high performance lithium ion battery anodes

Titanium dioxide (TiO₂)-based materials have been well studied because of the high safety and excellent cycling performance when employed as anode materials for lithium ion batteries (LIBs), whereas, the relatively low theoretical capacity (only 335 mAh g^?1) and serious kinetic problems such as poor electrical conductivity (~?10^?13S cm^?1) and low lithium diffusion coefficient (~?10^?9 to 10^?13 cm² s^?1) hinder the development of the TiO₂-based anode materials. To overcome these drawbacks, we present a facile strategy to synthesize N/S dual-doping carbon framework anchored with TiO₂ nanoparticles (NSC@TiO₂) as LIBs anode. Typically, TiO₂ nanoparticles are anchored into the porous graphene-based sheets with N, S dual doping feature, which is produced by carbonization and KOH activation process. The as-obtained NSC@TiO₂ electrode exhibits a high specific capacity of 250 mAh g^?1 with a coulombic efficiency of 99% after 500 cycles at 200 mA g^?1 and excellent rate performance, indicating its promising as anode material for LIBs.     

Sulfonated poly(phenylene oxide)/Ti<Superscript>3+</Superscript>/TiO<Subscript>2</Subscript> nanotube arrays membrane/electrode with high performances for lithium ion battery

Sulfonated poly(phenylene oxide) (SPPO) film was electrodeposited on Ti³⁺-doped TiO₂ nanotube arrays (Ti³⁺/TiO₂NT) electrode via the electropolymerization of sulfonated phenol. The as-synthesized SPPO/Ti³⁺/TiO₂NT membrane/electrode was investigated in terms of SEM, FESEM, EDX, FTIR, XPS, galvanostatic charge/discharge, and cycle voltammetry (CV). As expected, the porous SPPO film did form on the surface of Ti³⁺/TiO₂NT electrode; furthermore, the resultant SPPO/Ti³⁺/TiO₂NT membrane/electrode delivered higher electrochemical performances than PPO/Ti³⁺/TiO₂NT, mainly attributed to the contributions of the ionic conductivity induced by –SO₃H groups within SPPO.     

Thermostable photocatalytically active TiO<Subscript>2</Subscript> anatase nanoparticles

Anatase is the low-temperature (300–550 °C) crystalline polymorph of TiO₂ and it transforms to rutile upon heating. For applications utilizing the photocatalytic properties of nanoscale anatase at elevated temperatures (over 600 °C) the issue of phase stabilisation is of major interest. In this study, binary TiO₂/SiO₂ particles were synthesized by a flame aerosol process with TiCl₄ and SiCl₄ as precursors. The theoretical Si/Ti ratio was varied in the range of 0.7–1.3 mol/mol. The synthesized TiO₂/SiO₂ samples were heat treated at 900 and 1,000 °C for 3 h to determine the thermostability of anatase. Pyrogenic TiO₂ P25 (from Evonik/Degussa, Germany) widely applied as photocatalyst was used as non-thermostabilized reference material for comparison of photocatalytic activity of powders. Both the non-calcinated and calcinated powders were characterized by means of XRD, TEM and BET. Photocatalytic activity was examined with dichloroacetic acid (DCA) chosen as a model compound. It was found that SiO₂ stabilized the material retarding the collapse of catalyst surface area during calcination. The weighted anatase content of 85% remains completely unchanged even after calcination at 1,000 °C. The presence of SiO₂ layer/bridge as spacer between TiO₂ particles freezes the grain growth: the average crystallite size increased negligibly from 17 to 18 nm even during the calcination at 1,000 °C. Due to the stabilizing effect of SiO₂ the titania nanoparticles calcinated at 900 and 1,000 °C show significant photocatalytic activity. Furthermore, the increase in photocatalytic activity with calcination temperature indicates that the titania surface becomes more accessible either due to intensified cracking of the SiO₂ layer or due to enhanced transport of SiO₂ into the necks thus releasing additional titania surface.