Nm For TiO2 Research Articles

Photocatalytic Oxidation Based on Modified Titanium Dioxide with Reduced Graphene Oxide and CdSe/CdS as Nanohybrid Materials

Photocatalytic activity of TiO2 nanoparticles in the visible light region was enhanced. TiO2–CdSe and TiO2–CdSe/CdS nanohybrids were supported on the reduced graphene oxide. These nanohybrid materials were applied as photocatalyst toward oxidation of aromatic alcohols under a mild condition and the molecular oxygen as oxidant. A plausible mechanism for the photocatalytic oxidation was also proposed. Desired nanohybrids were obtained via in situ fixation of CdSe/CdS on the surface of nanosheets of reduced graphene oxide (rGO). Finally, it was modified by TiO2 sol nanoparticles through a hydrothermal method. The obtained nanomaterials, were characterized by SEM, TEM imaging, XRD, EDAX, DRS and XPS analyses. The size of nanohybrids materials were distributed mostly in a narrow range of 50–65 and 60–75 nm for TiO2–rGO–CdSe and TiO2–rGO–CdSe/CdS, respectively. These photocatalysts showed high catalytic activity under visible light irradiation in a short reaction time and even higher selectivity rather than UV irradiation. The yield of catalytic oxidation increased at least 25–30% for TiO2–CdSe/CdS on rGO, which could be related to its higher light sensitivity and lower energy band gap. The photocatalysts were recycled and reused 8 times without significant loss of their activities due to their stability under visible light.

Hydrogen peroxide-assisted photocatalytic degradation of textile wastewater using titanium dioxide and zinc oxide

ABSTRACTThe present work investigated the degradation of a dyeing factory effluent by advanced oxidative process under UV irradiation. TiO2 and ZnO were used as catalysts and the influence of different concentrations of H2O2 added to the system was studied. The catalysts were characterized in terms of crystal structure (X-ray diffraction), textural properties (Brunauer–Emmett–Teller area and pore volume) and point of zero charge, which indicated the semiconductors had a positively charged surface in an acidic medium. After 8 h of irradiation at pH 3.0 and catalyst concentration of 0.0625 g L−1, the effect of H2O2 was evaluated by means of kinetic efficiency (rate constants), absorbance reduction (at 284, 621 e 669 nm), total organic carbon reduction and mineralization (in terms of the formation of ions such as and ). Adding H2O2 to the photocatalytic system significantly increased pollutants’ removal, highlighting tests with 1.0 × 10−2 mol L−1, showing higher absorbance reduction and rate constants at 621 and 669 nm for TiO2 and best mineralization rates for ZnO. Ecotoxicity bioassays using Artemia salina L confirmed the treatment efficacy, with effluent lethal concentration (LC50) increasing from 65.68% (in natura) to over 100% after photocatalysis treatment.

(Invited) Hot-Electron Driven Photocatalysis and Photoexcited Charge Carrier Dynamics in TiO2-Passivated Photocatalysts

We report enhanced photocatalysis for H2 evolution and CO2 reduction using TiO2-passivated InP and GaAs photocathodes.1-3 The TiO2 layer makes the InP semiconductor photochemically stable. This represents a major step forward in photocatalysis, which has typically been limited to metal oxide materials. In addition to making these surfaces stable, the TiO2 film, deposited by atomic layer deposition (ALD), also provides a substantial enhancement in the efficiency of H2 evolution. We find that passivating GaAs with just a few nm of TiO2 produces a shift in the onset potential of H2 evolution by +0.35 V at 1 mA/cm2 and enhances the photocurrent by 32-fold over bare GaAs (at 0 V vs. RHE). Here, thinner TiO2 films produce a larger enhancement than thicker films, which correlates with the higher density of O-vacancies (i.e., Ti3+ surface states) observed in these thinner films using X-ray photoemission spectroscopy (XPS). While TiO2 films 1-5nm thick produce large enhancements, no enhancement is observed for TiO2 thicknesses above 10 nm, which are crystalline and, therefore, considerably more insulating than thinner amorphous TiO2films. We also report photocatalytic CO2 reduction with water to produce methanol using TiO2-passivated InP nanopillar photocathodes under visible wavelength illumination.2 Again, the TiO2 passivation layer provides a stable photocatalytic surface and substantial enhancement in the photoconversion efficiency and selectivity through the introduction of O-vacancies associated with the nonstoichiometric growth of TiO2 by ALD. Plane wave-density functional theory (PW-DFT) calculations confirm the role of oxygen vacancies in the TiO2 surface, which serve as catalytically active sites in the CO2 reduction process. PW-DFT shows that CO2 binds stably to these oxygen vacancies and CO2 gains an electron (−0.897e) spontaneously from the TiO2 support. The TiO2 film increases the Faraday efficiency of methanol production by a factor 5.7X under an applied potential of −0.6 V vs NHE, which is 1.3 V below the E o (CO2/CO2 −) = −1.9 eV standard redox potential. In order to further understand the strong dependence of these photocatalysts on TiO2 thickness over the range of 0−15 nm, we performed cross-sectional high resolution transmission electron microscopy (HRTEM) of GaAs/TiO2 heterojunctions.3 Thinner films (1−10 nm) are amorphous and show enhanced catalytic performance with respect to bare GaAs. HRTEM images and electron energy loss spectroscopy (EELS) maps show that the native oxide of GaAs is removed by the TiCl4 ALD precursor, which is corrosive. Thicker TiO2 films (15 nm) are crystalline and have poor charge transfer due to their insulating nature, while thinner amorphous TiO2films are conducting. We also report measurements of hot electron-driven photocatalytic water splitting using Au films with and without TiO2 coatings.4 In these structures, a thin (3-10nm) film of TiO2is deposited using atomic layer deposition (ALD) on top of a 100nm thick Au film. We utilize an AC lock-in technique, which enables us to detect the relatively small photocurrents (~µA) produced by the short-lived hot electrons that are photoexcited in the metal. Under illumination, the bare Au film produces a small AC photocurrent (<1 µA) for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) due to hot electrons and hot holes, respectively, that are photoexcited in the Au film.

Electrochemical Impedance Spectroscopy (EIS) Analysis of TiO2 Nanoparticles for Hydrogen Production in Photoelectrochemical Cells

In recent years, public awareness regarding the carbon dioxide emissions and the depletion of fossil fuel reserves has been increased. This motivates the development of the alternative energy sources based technology [1]. The Photoelectrochemical cell (PEC) is a capable clean and renewable way to convert sunlight into a storable chemical energy form. This technology enables the water to be split into hydrogen and oxygen by light-induced electrochemical processes [2]. One of the most studied and promising photocatalysts using in PEC is TiO2, which is relatively inexpensive and stable against photo irradiation while non-toxic [3]. In order to evaluate the PEC performances, the difference between various types of photocatalysts is usually attributed to the difference in their corresponding band gap energies, while the semiconductor particle size has not been taken into account as the main parameter. Having smaller particle size, particularly in the lower nanometer range, can give materials unique properties that could increase photoactivity [4]. There are some basic requirements for materials used as photo-electrodes such as optical function required to obtain maximal absorption of solar energy, the band gap of semiconductor which should be small enough to absorb a significant portion of the solar spectrum, the band edge potentials at the surfaces which must include the hydrogen and oxygen redox potentials, and especially sufficient charge transfer processes as well as the reaction kinetics at the semiconductor/electrolyte interface [5]. The present work reports the study of the kinetic aspects of photo electrochemical cells based on different nanoparticle sizes ranging from 50 nm down to 5 nm of TiO2, by using the electrochemical impedance spectroscopy (EIS) under illumination. The EIS is a useful method for the analysis of kinetic aspects such as charge transfer process that influences the cell performance. To measure the current response to the application of an AC voltage as a function of the frequency, EIS is considered as an electrochemical measurement [6]. Running the EIS is comparatively easy, but the interpretation of the results is often complicated and requires the application of suitable theoretical models. The equivalent electrical circuit is required to fit EIS data to identify the charge transfer phenomenon occurring in the PEC cell under 1 sun simulated illumination [5]. In our analysis, the three different electrode configurations were applied. The three semicircles are attributed to the redox reaction at the platinum counter electrode (Z1), the electron transfer at the TiO2 /electrolyte interface (Z2), and charge carrier transport in the electrolyte (Z3) (Figure 1a). The resistance elements R1, R2, and R3 are labeled as the real part of Z1, Z2, and Z3, respectively (Figure 1b). Therefore, it would be a powerful technique to recognize the internal resistance and the electron transportation of each photoelectrode in various particle size of the TiO2. A decrement of the internal resistance related to the electron transportation in the TiO2 /electrolyte interface causes an improvement in the electron transportation in the TiO2 thin film, which leads to the improvement of the cell efficiency. Furthermore, the exchange current density of each photoelectrode can be calculated when Rct (Charge Transfer Resistance) is known. This study is trying to reveal the effect of TiO2particle size on kinetic aspects of the Photoelectrochemical cell (PEC) for hydrogen production. Nanoparticle sizes ranging from 50 nm down to 5 nm were tested using EIS measurements. It was our prediction that by increasing particle size the internal resistance of electron transportation decreases, as per other literature [7]. The process of putting together the working electrode, as well as procedure and results of experiments, will be discussed.

Effect of constructional features of the insulating gap of open TiN–SiO2–W and Si–SiO2–W “sandwich” structures on the process of their electroforming

It is experimentally shown that the introduction of an additional dielectrical layer several nanometers thick (more than 2.5 and 1.3 nm for TiO2 and SiO2, respectively) into open TiN–SiO2–W and Si–SiO2–W “sandwich”-structures on their anode (lower electrode, i.e., TiN and Si, respectively) in series with respect to the conducting medium formed in the insulating gap during electroformation appreciably decreases the probability of an electrical breakdown. This effect is produced by the limitation of the current by the resistance of an additional dielectrical layer at the prebreakdown level. Some experimental dependences of the probability of successfully electroforming on the thickness of an additional dielectrical layer (TiO2) are obtained for the TiN–SiO2–W structure.

Single-Site, Heterogeneous Electrocatalytic Reduction of CO2 in Water as the Solvent

Creating stable surface-bound molecular catalysts for CO2 reduction in aqueous solutions for either electrochemical or photoelectrochemical reduction is a continuing challenge. We report here the preparation and characterization of thin oxide/carbon nanotube electrodes on fluorine-doped tin oxide (FTO) electrodes. The electrodes were prepared by atomic layer deposition (ALD) of ∼15 nm of TiO2 followed by a layer of carbon nanotubes and a thin (2 nm) overlayer of TiO2 for surface stabilization and binding. The phosphonate-derivatized version of the known aqueous solution catalyst for H2/CO reduction, [RuII(tpy-Ph–CH2–PO3H2)(Mebim-py)(H2O)](PF6)2 (tpy-Ph–CH2–PO3H2 = (4-([2, 2′:6′,2″-terpyridin]-4′-yl)benzyl)phosphonic acid; Mebim-py = 3-methyl-1-pyridyl-benzimidazol-2-ylidene), was added to the surface and stabilized by addition of a thin overlayer of TiO2 by ALD. In the derivatized electrodes, the catalyst maintains its reactivity toward CO2 reduction in the short-term, giving mixtures of H2/CO that vary f...

Low-cost synthesis of titanium dioxide anatase nanoclusters as advanced materials for hydrogen photoproduction

Sub-nm titanium dioxide (TiO2) clusters are synthesized via the hydrolysis of TiCl4 in order to produce clean and surfactant-free oxide surfaces. By controlling the synthesis, stable TiO2 nanoclusters with well-defined size distributions are obtained. The prepared clusters are characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman spectroscopy in order to gain information about the size and morphology of the material. Photoresponsive methylene blue dye monitoring and hydrogen production under UV irradiation are described in detail and performed. The rate order of photodegradation and hydrogen photoproduction under UV light irradiation of the samples is increased by decreasing the size of TiO2 nanoparticles from 47 nm to 3 nm. The hydrogen evolution rate of TiO2 nanoclusters with size lower than 5 nm is about 3.03 times and 1.96 times faster than that of 47 nm of TiO2 and 12 nm of TiO2, respectively. The enhanced photocatalytic performance suggests that the ternary TiO2 nanoclusters can serve as a highly efficient catalyst for photodegradation of organic pollutants in aquatic environments and hydrogen production from water splitting.

The influence of adding modified zirconium oxide-titanium dioxide nano-particles on mechanical properties of orthodontic adhesive: an in vitro study

BackgroundThe purpose of this in-vitro study was to examine the effect of incorporating different concentrations of Zirconium oxide-Titanium dioxide (ZrO2-TiO2) nanoparticles, which can have antibacterial properties, on the mechanical properties of an orthodontic adhesive.MethodsZrO2-TiO2 (Zirconium oxide, HWNANO, Hongwu International Group Ltd, China) -Titanium dioxide, Nanoshell, USA) nanopowder were incorporated into orthodontic adhesive (Transbond XT, 3 M Unitek, Monrovia, USA) with different concentrations (0.5% weight nonofiller and 1% weight nanofiller). The size of nanoparticle was 70–80 nm for ZrO2 and less than 50 nm for TiO2. For measuring the shear bond strength of the three groups of orthodontic adhesives [Transbond (control), Transbond mixed with 0.5% weight ZrO2-TiO2, and Transbond mixed with 1% weight ZrO2-TiO2], 30 freshly extracted human first premolars were used and bonded with stainless steel metal brackets (Dentaurum®, Discovery®, Deutschland), using the 3 orthodontic adhesives and 3 M Unitek; Transbond TM Plus Self-Etching Primer (10 samples in each group). The recorded values of compressive strength and tensile strength (measured separately on 10 samples of orthodontic adhesives (add the 3 D size of sample, light cured for 40 s on both sides) of each orthodontic adhesives), as well as the shear bond strength in Mega Pascal unit (MPa) were collected and exposed to one-way analysis of variance (ANOVA) and Tukey’s post-hoc tests.Resultsorthodontic adhesive with 1% weight ZrO2-TiO2 showed the highest mean compressive (73.42 ± 1.55 MPa, p: 0.003, F: 12.74), tensile strength (8.65 ± 0.74 MPa, p: 0.001, F: 68.20), and shear bond strength (20.05 ± 0.2 MPa, p: 0.001, F: 0.17).ConclusionsAdding ZrO2-TiO2 nanoparticle to orthodontic adhesive increased compressive strength, tensile strength, and shear bond strength in vitro, but in vivo studies and randomized clinical trials are needed to validate the present findings.

Photodegradation of Methyl Orange in Aqueous Solution by the Visible Light Active Co:La:TiO2 Nanocomposite

In this study, the Co:La:TiO2 nanocomposite was prepared by the wet chemical method. Synthesized TiO2 and Co:La:TiO2 were characterized by X-Ray Diffractometer, SEM, TEM, UV- vis, FT-IR, Band gap energy and BET. The TiO2 and Co:La:TiO2 were used as photocatalyst for the degradation of Methyl Blue. The XRD pattern confirmed the presence of anatase and rutile phase in the catalyst. The particle size was estimated by the Scherrer’s and found 68 and 32 nm for TiO2 and Co:La:TiO2 respectively. The particle morphology of the photocatalysts was found in nanodiamension. The surface area of the photocatalysts was found 37.52 and 106.68 m2/g for TiO2 and Co:La:TiO2 respectively. The band gap energy of TiO2 and Co:La:TiO2 were 3.2 and 3.0 eV. The photodegradation of Methyl Orange has been found 18% and 88% at 5 pH for TiO2 and Co:La:TiO2 respectively. The photodegradation of Methyl Orange has been found 19% and 98.9% at 25 ppm concentration of dye. The photodegradation of Methyl Orange has been found 25% and 96% at 800 mg/L amount of photocatalyst and 180 min illumination of visible light. The photodegradation was following the first order kinetics.

Molybdenum-Loaded Anatase TiO2 Nanoparticles With Enhanced Optoelectronics Properties

The structural, optical and electrical properties of molybdenum nanoparticles (Mo-NPs)-loaded anatase TiO2 were investigated using x-ray diffraction, UV–Vis diffuse reflectance, and Fourier transform infrared and complex impedance spectroscopy. x-ray diffraction showed that Mo-NPs incorporation induced a decrease in particle size from 30 nm to 21 nm of TiO2 and TiO2-Mo, respectively, producing a slight structure expansion. Mo-NPs dispersion resulted in a slight decrease in the optical band gap energy from 3.85 eV to 3.51 eV. Slight shifts towards higher wavelengths were attributed to the change in the acceptor capacity level induced by Mo-NPs. In addition, the ac impedance studies show the effect of Mo-NPs incorporation that appeared to be responsible for conductance of enhancement. The conduction mechanism is based on space charge-limited current via deep levels with different energy positions in the band gap. The temperature dependence of electrical properties showed that both capacitance and conductance of TiO2-Mo samples increased with increasing temperature. At low frequency, the relaxation phenomenon is related to the surface effect. The results will be beneficial to further developing titanium dioxide photo-catalysts.

(Invited) Enhanced Photocatalysis on TiO2-Passivated III-V Compounds for Water Splitting and CO2 Reduction

We report enhanced photocatalysis for H2 evolution and CO2 reduction using TiO2-passivated InP and GaAs photocathodes.1-3 The TiO2 layer makes the InP semiconductor photochemically stable. This represents a major step forward in photocatalysis, which has typically been limited to metal oxide materials. In addition to making these surfaces stable, the TiO2 film, deposited by atomic layer deposition (ALD), also provides a substantial enhancement in the efficiency of H2 evolution. We find that passivating GaAs with just a few nm of TiO2 produces a shift in the onset potential of H2 evolution by +0.35 V at 1 mA/cm2 and enhances the photocurrent by 32-fold over bare GaAs (at 0 V vs. RHE). Here, thinner TiO2 films produce a larger enhancement than thicker films, which correlates with the higher density of O-vacancies (i.e., Ti3+ surface states) observed in these thinner films using X-ray photoemission spectroscopy (XPS). While TiO2 films 1-5nm thick produce large enhancements, no enhancement is observed for TiO2 thicknesses above 10 nm, which are crystalline and, therefore, considerably more insulating than thinner amorphous TiO2 films. We also report photocatalytic CO2 reduction with water to produce methanol using TiO2-passivated InP nanopillar photocathodes under visible wavelength illumination.2 Again, the TiO2 passivation layer provides a stable photocatalytic surface and substantial enhancement in the photoconversion efficiency and selectivity through the introduction of O-vacancies associated with the nonstoichiometric growth of TiO2 by ALD. Plane wave-density functional theory (PW-DFT) calculations confirm the role of oxygen vacancies in the TiO2 surface, which serve as catalytically active sites in the CO2 reduction process. PW-DFT shows that CO2 binds stably to these oxygen vacancies and CO2 gains an electron (−0.897e) spontaneously from the TiO2 support. The TiO2 film increases the Faraday efficiency of methanol production by a factor 5.7X under an applied potential of −0.6 V vs NHE, which is 1.3 V below the E o (CO2/CO2 −) = −1.9 eV standard redox potential. In order to further understand the strong dependence of these photocatalysts on TiO2 thickness over the range of 0−15 nm, we performed cross-sectional high resolution transmission electron microscopy (HRTEM) of GaAs/TiO2 heterojunctions.3 Thinner films (1−10 nm) are amorphous and show enhanced catalytic performance with respect to bare GaAs. HRTEM images and electron energy loss spectroscopy (EELS) maps show that the native oxide of GaAs is removed by the TiCl4 ALD precursor, which is corrosive. Thicker TiO2 films (15 nm) are crystalline and have poor charge transfer due to their insulating nature, while thinner amorphous TiO2 films are conducting.

A Study of Metal@Graphene Core–Shell Spherical Nano-Geometry to Enhance the SPR Tunability: Influence of Graphene Monolayer Shell Thickness

Graphene, new generation advance material of two dimensional hexagonal lattice having extraordinary optical signatures, is used as coating material to enhance the surface plasmon resonance (SPR) effect of core@shell metal nanospheres. In a core@shell nanosphere, we have chosen metal as a core and graphene monolayer (GML) as a shell. We have analysed optical signature of coated and non-coated nanospheres in terms of extinction efficiency (Q ext) and tunabilty of surface plasmon resonances using electrostatic model, where particle size is much smaller than the wavelength of incident light. We analysed this model over different metals (silver, gold and aluminium) core, coated with different thickness of GML (d = 0.1 to 0.5 nm). These core@shell nanospheres are embedded in refractive index media of air (n em = 1), SiO2 (n em = 1.47) and TiO2 (n em = 2.79). The Q ext has been calculated by varying both the core radii as well as the GML shell thickness. Graphene-coated metal nanosphere exhibits SPRs that have wide range tunability from 300 to 1500 nm. In the presenting work, we also analysed that extinction efficiency for metal@GML is higher in TiO2 than others. The optimum value of GML shell thickness is 0.4 nm for TiO2, the magnitude of extinction efficiency is maximum for the optimum thickness. The tunability of these plasmonic resonances is highly dependent on the core@shell material, thickness of Graphene shell and surrounding environment while non-coated metal nano-spheres do not show appropriate SPR tunability.

Efficiency enhancement of dye-sensitized solar cells by use of ZrO2-doped TiO2 nanofibers photoanode

Due to the good stability and convenient optical properties, TiO2 nanostructures still the prominent photoanode materials in the Dye Sensitized Solar Cells (DSCs). However, the well-known low bandgap energy and weak adsorption affinity for the dye distinctly constrain the wide application. This work discusses the impact of Zr-doping and nanofibrous morphology on the performance and physicochemical properties of TiO2. Zr-doped TiO2 nanofibers (NFs), with various zirconia content (0, 0.5, 1, 1.5 and 2wt%) were prepared by calcination of electrospun mats composed of polyvinyl acetate, titanium isopropoxyl and zirconium n-propoxyl. For all formulations, the results have shown that the prepared materials are continuous, randomly oriented, and good morphology nanofibers. The average diameter decreased from 353.85nm to 210.78nm after calcination without a considerable influence on the nanofibrous structure regardless the zirconia content. XRD result shows that there is no Rutile nor Brookite phases in the obtained material and the average crystallite size of the sample is affected by the presence of Zr-doping and changed from 23.01nm to 37.63nm for TiO2 and Zr-doped TiO2, respectively. Optical studies have shown Zr-doped TiO2 NFs have more absorbance in the visible region than that of pristine TiO2 NFs; the maximum absorbance is corresponding to the NFs having 1wt% zirconia. The improved spectra of Zr-doped TiO2 in the visible region is attributed to the heterostructure composition resulting from Zr-doping. The absorption bandgaps were calculated using Tauc model as 3.202 and 3.217 for pristine and Zr (1wt%)-doped TiO2 NFs, respectively. Furthermore, in Dye-sensitized Solar Cells, utilizing Zr (1wt%)-doped TiO2 nanofibers achieved higher efficiency of 4.51% compared to the 1.61% obtained from the pristine TiO2 NFs.

Fabrication and Characterization of Metal Oxide-Coated Long-Period Fiber Gratings

Sensors based on long-period fiber gratings (LPFGs) over coated with metal oxide were fabricated and characterized for refractive index (RI) sensing. Oxidation of Ni, Ti, Al, and Cr was monitored in real time by following the features of the LPFG attenuation band. The metals were deposited simultaneously on top of Si substrates for further chemical and morphological analysis. Wavelength sensitivities (nm/RIU) of about 10 437 at 1.432, 1150 at 1.400, 20 125 at 1.448, and 875 at 1.420 were achieved for LPFGs coated, with 68 nm of Ni, 60 nm of TiO 2, 50 nm of Al2O3, and 62 nm of Cr2O3, respectively. For surrounding RI higher than the cladding RI, the wavelength sensitivities are 1937, 6801, 5762, and 3051 nm/RIU at 1.457 for the Ni, Ti, Al, and Cr oxides, respectively. Working as intensity sensing devices sensitivities up to 167 dB/RIU were measured. Metal oxide coated LPFGs leads to wavelength sensitivity enhancement comparing to bare LPFGs and may be used in systems with RI higher than the fiber cladding, a region where bare LPFGs are insensitive.

Inherent substrate-dependent growth initiation and selective-area atomic layer deposition of TiO2 using “water-free” metal-halide/metal alkoxide reactants

Titanium dioxide atomic layer deposition (ALD) is shown to proceed selectively on oxidized surfaces with minimal deposition on hydrogen-terminated silicon using titanium tetrachloride (TiCl4) and titanium tetra-isopropoxide [Ti(OCH(CH3)2)4, TTIP] precursors. Ex situ x-ray photoelectron spectroscopy shows a more rapid ALD nucleation rate on both Si–OH and Si–H surfaces when water is the oxygen source. Eliminating water delays the oxidation of the hydrogen-terminated silicon, thereby impeding TiO2 film growth. For deposition at 170 °C, the authors achieve ∼2 nm of TiO2 on SiO2 before substantial growth takes place on Si–H. On both Si–H and Si–OH, the surface reactions proceed during the first few TiCl4/TTIP ALD exposure steps where the resulting products act to impede subsequent growth, especially on Si–H surfaces. Insight from this work helps expand understanding of “inherent” substrate selective ALD, where native differences in substrate surface reaction chemistry are used to promote desired selective-area growth.

Direct Light-Driven Water Oxidation by a Ladder-Type Conjugated Polymer Photoanode.

A conjugated polymer known for high stability (poly[benzimidazobenzophenanthroline], coded as BBL) is examined as a photoanode for direct solar water oxidation. In aqueous electrolyte with a sacrificial hole acceptor (SO32–), photoelectrodes show a morphology-dependent performance. Films prepared by a dispersion-spray method with a nanostructured surface (feature size of ∼20 nm) gave photocurrents up to 0.23 ± 0.02 mA cm–2 at 1.23 VRHE under standard simulated solar illumination. Electrochemical impedance spectroscopy reveals a constant flat-band potential over a wide pH range at +0.31 VNHE. The solar water oxidation photocurrent with bare BBL electrodes is found to increase with increasing pH, and no evidence of semiconductor oxidation was observed over a 30 min testing time. Characterization of the photo-oxidation reaction suggests H2O2 or •OH production with the bare film, while functionalization of the interface with 1 nm of TiO2 followed by a nickel–cobalt catalyst gave solar photocurrents of 20–30 μA cm–2, corresponding with O2 evolution. Limitations to photocurrent production are discussed.

Transmission Electron Microscopy and Scanning Transmission X-Ray Microscopy Studies on the Bioaccumulation and Tissue Level Absorption of TiO2 Nanoparticles in Daphnia magna.

In this study, bioaccumulation and tissue-level absorption of TiO2 nanoparticles (NPs) in freshwater invertebrates were investigated using transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM). The TiO2 NPs were used to test impacts of core sizes (i.e., 5 ± 2 nm and 23 ± 7 nm for TiO2(SYN) and TiO2(P25), respectively) and agglomerations (i.e., well dispersed vs. highly agglomerated) on the uptake of TiO2 NPs in Daphnia magna (D. magna). Highly agglomerated TiO2 NPs, regardless of their core sizes, were heavily taken up into the digestive tract of D. magna and no detectable penetration of both TiO2 NPs into the gut epithelial cells of D. magna was observed in TEM and STXM images. However, significant damages involving morphological changes in the microvilli and gut epithelial cells (e.g., irregular shaped microvilli, epithelial cell protrusion, and dilatation of cytoplasmic inclusion) were observed only with the commercial TiO2 NPs (TiO2(P25)) with larger core size and mixed crystalline phase, while the laboratory synthesized TiO2 NPs (TiO2(Syn)) with smaller core size and single crystalline phase showed slight morphological changes in the gut microvilli and epithelial cells. In the case of D. magna exposed to the well dispersed synthetic TiO2 NP ((Cit)TiO2(Syn)), only a negligible amount of TiO2 NPs were found within the digestive tract of the D. magna without any significant damages in the gut microvilli and epithelial cells and any detectable penetrations of TiO2 NPs into epithelial cells of D. magna gut. These TEM and STXM observations confirmed us that uptake of NP into D. magna are strongly dependent on their agglomeration (i.e., hydrodynamic sizes), rather than their core sizes, while direct penetration of NPs into tissues of digestive tract seems unlikely without significant morphological changes (e.g., collapse of the epithelial tissue) caused by high toxicity of NPs or released metal ions.

Shape Control Synthesis, Characterizations, Mechanisms And Optical Properties Of Larg Scaled Metal oxide Nanostructures Of ZnO And TiO2

In the present study, ZnO and TiO2 nanostructures of different size have been synthesized in high yield with excellent repeatability by simple, economical and environmentally benign chemical route. ZnO quantum dots and nanorods of tuned aspect ratio were evolved by optimising the reaction conditions such as by varying solvent composition, precursor concentration and by using different additives. On the other hand, the synthesis of brookite, the rare phase, anatase and rutile, the stable phases of TiO2 were also achieved by just varying the annealing temperature from 400 to 615 °C. The obtained nanostructures were rationalized by various characterization techniques such as XRD, FTIR, Raman, SEM, HR- TEM, UV-Vis and PL. The Phase formation and structure determination were identified by using XRD, FTIR and Raman Spectra, SEM and HR-TEM were performed to determine the morphology and particle size. The aspect ratio was calculated to be in the range of 3.2-9.4 in case of ZnO NRs, and particle size was found to be 2-5 nm for ZnO QDs of wurtzite phase and ~ 10 nm for TiO2 (anatase phase) NPs, respectively. The UV-Vis optical absorption spectrum demonstrates the band gap value of 3.60, 4.02 and 3.40 eV for ZnO NRs, QDs and TiO2 NPs respectively. The UV-Vis optical absorption spectrum demonstrates the band gap and room temperature PL spectra illustrates about the various defects present in the sample. Various chemical reactions and mechanism involved in producing these nanostructures are dealt in detail. The future prospective of these metal oxide nanostructures lie in photocatalysis, sensors and biomedical applications. Copyright © 2015 VBRI press.

Control of crystallographic texture and surface morphology of Pt/Tio2 templates for enhanced PZT thin film texture.

Optimized processing conditions for Pt/TiO2/SiO2/Si templating electrodes were investigated. These electrodes are used to obtain [111] textured thin film lead zirconate titanate (Pb[ZrxTi1-x ]O3 0 ≤ x ≤ 1) (PZT). Titanium deposited by dc magnetron sputtering yields [0001] texture on a thermally oxidized Si wafer. It was found that by optimizing deposition time, pressure, power, and the chamber pre-conditioning, the Ti texture could be maximized while maintaining low surface roughness. When oxidized, titanium yields [100]-oriented rutile. This seed layer has as low as a 4.6% lattice mismatch with [111] Pt; thus, it is possible to achieve strongly oriented [111] Pt. The quality of the orientation and surface roughness of the TiO2 and the Ti directly affect the achievable Pt texture and surface morphology. A transition between optimal crystallographic texture and the smoothest templating surface occurs at approximately 30 nm of original Ti thickness (45 nm TiO2). This corresponds to 0.5 nm (2 nm for TiO2) rms roughness as determined by atomic force microscopy and a full-width at half-maximum (FWHM) of the rocking curve 0002 (200) peak of 5.5/spl degrees/ (3.1/spl degrees/ for TiO2). A Pb[Zr0.52Ti 0.48]O3 layer was deposited and shown to template from the textured Pt electrode, with a maximum [111] Lotgering factor of 87% and a minimum 111 FWHM of 2.4/spl degrees/ at approximately 30 nm of original Ti.

Plasmon-enhanced photoelectrochemical water splitting with size-controllable gold nanodot arrays.

Size-controllable Au nanodot arrays (50, 63, and 83 nm dot size) with a narrow size distribution (± 5%) were prepared by a direct contact printing method on an indium tin oxide (ITO) substrate. Titania was added to the Au nanodots using TiO(2) sols of 2-3 nm in size. This created a precisely controlled Au nanodot with 110 nm of TiO(2) overcoats. Using these precisely controlled nanodot arrays, the effects of Au nanodot size and TiO(2) overcoats were investigated for photoelectrochemical water splitting using a three-electrode system with a fiber-optic visible light source. From UV-vis measurement, the localized surface plasmon resonance (LSPR) peak energy (ELSPR) increased and the LSPR line width (Γ) decreased with decreasing Au nanodot size. The generated plasmonic enhancement for the photoelectrochemical water splitting reaction increased with decreasing Au particle size. The measured plasmonic enhancement for light on/off experiments was 25 times for the 50 nm Au size and 10 times for the 83 nm Au nanodot size. The activity of each catalyst increased by a factor of 6 when TiO2 was added to the Au nanodots for all the samples. The activity of the catalyst was proportional to the quality factor (defined as Q = E(LSPR)/Γ) of the plasmonic metal nanostructure. The enhanced water splitting performance with the decreased Au nanodot size is probably due to more generated charge carriers (electron/hole pair) by local field enhancement as the quality factor increases.