Showing papers in "Journal of Physical Chemistry C in 2007"
TL;DR: In this paper, the capacitive effects of nanostructured materials for electrochemical energy storage have been investigated over a dimensional regime where both capacitive and lithium intercalation processes contribute to the total stored charge.
Abstract: The advantages in using nanostructured materials for electrochemical energy storage have largely focused on the benefits associated with short path lengths. In this paper, we consider another contribution, that of the capacitive effects, which become increasingly important at nanoscale dimensions. Nanocrystalline TiO2 (anatase) was studied over a dimensional regime where both capacitive and lithium intercalation processes contribute to the total stored charge. An analysis of the voltammetric sweep data was used to distinguish between the amount of charge stored by these two processes. At particle sizes below 10 nm, capacitive contributions became increasingly important, leading to greater amounts of total stored charge (gravimetrically normalized) with decreasing TiO2 particle size. The area normalized capacitance was determined to be well above 100 μF/cm2, confirming that the capacitive contribution was pseudocapacitive in nature. Moreover, reducing the particle size to the nanoscale regime led to faster...
3,572 citations
TL;DR: In this article, the authors present an in-depth study of surface enhanced Raman scattering (SERS) enhancement factors and cross-sections, including several issues often overlooked, and demonstrate that SERS EFs as low as 107, as opposed to the figure of 1014 often claimed in the literature, are sufficient for SERS applications.
Abstract: This paper presents an in-depth study of Surface Enhanced Raman Scattering (SERS) enhancement factors (EFs) and cross-sections, including several issues often overlooked. In particular, various possible rigorous definitions of the SERS EFs are introduced and discussed in the context of SERS applications, such as analytical chemistry and single molecule SERS. These definitions highlight the importance of a careful characterization of the non-SERS cross-sections of the probes under consideration. This aspect is illustrated by experimental results for the non-SERS cross-sections of representative SERS probes along with average SERS EFs for the same probes. In addition, the accurate experimental determination of single molecule enhancement factors is tackled with two recently developed techniques, namely: bi-analyte SERS (BiASERS) and temperature-dependent SERS vibrational pumping. We demonstrate that SERS EFs as low as 107, as opposed to the figure of 1014 often claimed in the literature, are sufficient for...
2,298 citations
TL;DR: In this article, three major ways to utilize nanostructures for the design of solar energy conversion devices are discussed: (i) mimicking photosynthesis with donor−acceptor molecular assemblies or clusters, (ii) semiconductor assisted photocatalysis to produce fuels such as hydrogen, and (iii) nanostructure semiconductor based solar cells.
Abstract: The increasing energy demand in the near future will force us to seek environmentally clean alternative energy resources. The emergence of nanomaterials as the new building blocks to construct light energy harvesting assemblies has opened up new ways to utilize renewable energy sources. This article discusses three major ways to utilize nanostructures for the design of solar energy conversion devices: (i) Mimicking photosynthesis with donor−acceptor molecular assemblies or clusters, (ii) semiconductor assisted photocatalysis to produce fuels such as hydrogen, and (iii) nanostructure semiconductor based solar cells. This account further highlights some of the recent developments in these areas and points out the factors that limit the efficiency optimization. Strategies to employ ordered assemblies of semiconductor and metal nanoparticles, inorganic-organic hybrid assemblies, and carbon nanostructures in the energy conversion schemes are also discussed. Directing the future research efforts toward utiliza...
2,119 citations
TL;DR: In this paper, the surface plasmon response of metal nanoparticles is studied for different shapes and physical environments, and the modification of these surface plasmons by different surrounding media and the presence of a substrate or other nanoparticles are also discussed.
Abstract: The surface plasmon response of metal nanoparticles is studied for different shapes and physical environments. For polyhedral nanoparticles, the surface plasmon resonances are studied as a function of the number of faces and vertices. The modification of these surface plasmons by different surrounding media and the presence of a substrate or other nanoparticles is also discussed. We found that polyhedral nanoparticles composed with less faces show more surface plasmon resonances, and as the nanoparticle becomes more symmetric, the main surface plasmon resonance is blue-shifted. It is also found that the corners induce more surface plasmons in a wider energy range. In the presence of a substrate, multipolar plasmon resonances are induced, and as the nanoparticle approaches the substrate, such resonances are red-shifted. The interaction among nanoparticles also induces multipolar resonances, but they can be red or blue-shifted depending on the polarization of the external field.
1,574 citations
TL;DR: In this article, the development of visible-light-driven photocatalysts focusing on the refinement of non-oxide-type photocatalyst such as (oxy)nitrides and oxysulfides is discussed.
Abstract: Overall water splitting to form hydrogen and oxygen over a heterogeneous photocatalyst using solar energy is a promising process for clean and recyclable hydrogen production in large-scale. In recent years, numerous attempts have been made for the development of photocatalysts that work under visible-light irradiation to efficiently utilize solar energy. This article presents recent research progress in the development of visible-light-driven photocatalysts, focusing on the refinement of non-oxide-type photocatalysts such as (oxy)nitrides and oxysulfides.
1,341 citations
TL;DR: Temperature in
Abstract: Visible radiation at resonant frequencies is transduced to thermal energy by surface plasmons on gold nanoparticles. Temperature in ≤10-microliter aqueous suspensions of 20-nanometer gold particles irradiated by a continuous wave Ar+ ion laser at 514 nm increased to a maximum equilibrium value. This value increased in proportion to incident laser power and in proportion to nanoparticle content at low concentration. Heat input to the system by nanoparticle transduction of resonant irradiation equaled heat flux outward by conduction and radiation at thermal equilibrium. The efficiency of transducing incident resonant light to heat by microvolume suspensions of gold nanoparticles was determined by applying an energy balance to obtain a microscale heat-transfer time constant from the transient temperature profile. Measured values of transduction efficiency were increased from 3.4% to 9.9% by modulating the incident continuous wave irradiation.
1,216 citations
TL;DR: In this article, the performance of a few graphene layer n ∼ 4, with a thickness of ∼ 2 nm, was investigated for epoxy composites and it was shown that the G4 GNPs provide a thermal conductivity enhancement of more than 3000% (loading of ∼25 vol %).
Abstract: Natural graphite was intercalated, thermally exfoliated, and dispersed in acetone to prepare graphite nanoplatelets (GNPs, Gn) of controlled aspect ratio. Thermal conductivity measurements indicate that few graphene layer Gn, where n ∼ 4, with a thickness of ∼2 nm function as a very efficient filler for epoxy composites. When embedded in an epoxy matrix, the G4 GNPs provide a thermal conductivity enhancement of more than 3000% (loading of ∼25 vol %), and a thermal conductivity κ = 6.44 W/mK, which surpasses the performance of conventional fillers that require a loading of ∼70 vol % to achieve these values. We attribute the outstanding thermal properties of this material to a favorable combination of the high aspect ratio, two-dimensional geometry, stiffness, and low thermal interface resistance of the GNPs.
981 citations
TL;DR: In this article, Nitrogen-doped TiO2 nanocatalysts with a homogeneous anatase structure were successfully synthesized through a microemulsion−hydrothermal method by using some organic compounds such as triethylamine, urea, thiourea, and hydrazine hydrate.
Abstract: Nitrogen-doped TiO2 nanocatalysts with a homogeneous anatase structure were successfully synthesized through a microemulsion−hydrothermal method by using some organic compounds such as triethylamine, urea, thiourea, and hydrazine hydrate. Analysis by Raman and X-ray photoemission spectroscopy indicated that nitrogen was doped effectively and most nitrogen dopants might be present in the chemical environment of Ti−O−N and O−Ti−N. A shift of the absorption edge to a lower energy and a stronger absorption in the visible light region were observed. The results of photodegradation or the organic pollutant rhodamine B in the visible light irradiation (λ > 420 nm) suggested that the TiO2 photocatalysts after nitrogen doping were greatly improved compared with the undoped TiO2 photocatalysts and Degussa P-25; especially the nitrogen-doped TiO2 using triathylamine as the nitrogen source showed the highest photocatalytic activity, which also showed a higher efficiency for photodecomposition of 2,4-dichlorophenol. T...
961 citations
TL;DR: In this paper, the characteristics of dye-sensitized solar cells using an ionic liquid as the electrolyte and compare them with the response of a solvent-containing electrolyte cell were analyzed.
Abstract: In this work, we study the characteristics of dye-sensitized solar cells using an ionic liquid as the electrolyte and compare them with the response of a solvent-containing electrolyte cell. Impedance spectroscopy is used to derive the key circuit elements determining the photovoltaic performance of the cell. On the basis of this data, photocurrent voltage curves are calculated and compared with experimental results.
881 citations
TL;DR: In this article, a core-shell nanocomposites (R−Au) bearing well-defined gold nanoparticles as surface atoms of variable sizes (8−55 nm) have been synthesized exploiting polystyrene-based commercial anion exchangers.
Abstract: Core−shell nanocomposites (R−Au) bearing well-defined gold nanoparticles as surface atoms of variable sizes (8−55 nm) have been synthesized exploiting polystyrene-based commercial anion exchangers. Immobilization of gold nanoparticles, prepared by the Frens method, onto the resin beads in the chloride form is possible by the ready exchange of the citrate-capped negatively charged gold particles. The difficulty of nanoparticle loading, avoiding aggregation, has been solved by stepwise operation. Analysis of the gold particles after immobilization and successive elution confirm the unaltered particle morphology while compared to those of the citrate-capped gold particles in colloidal dispersion. It was observed that the rate of the reaction increases with the increase in catalyst loading, which suggests the catalytic behavior of the gold nanoparticles for the reduction of the aromatic nitrocompounds. The rate constant, k, was found to be proportional to the total surface area of the nanoparticles in the sys...
739 citations
TL;DR: In this article, the state-of-the-art synthesis and improved luminescence properties of thiol-capped CdTe nanocrystals (NCs) synthesized in water were reported.
Abstract: We report on the state-of-the art synthesis and improved luminescence properties of thiol-capped CdTe nanocrystals (NCs) synthesized in water. The optimized pH (12) and molar ratio of thiol to Cd ions (1.3:1) increases the room-temperature photoluminescence quantum efficiency of as-synthesized CdTe NCs capped by thioglycolic acid (TGA) to values of 40−60%. By employing mercaptopropionic acid (MPA) as a stabilizer, we have synthesized large (up to 6.0 nm in diameter) NCs so that the spectral range of the NCs' emission currently available within this synthetic route extends from 500 to 800 nm. Sizing curve for thiol-capped CdTe NCs is provided. In contrast to CdTe NCs capped by TGA, MPA-capped CdTe NCs show up to 1 order of magnitude longer (up to 145 ns) emission decay times, which become monoexponential for larger particles. This phenomenon is explained by considering the energetics of the Te-related traps in respect to the valence-band position of CdTe NCs. The correlation between luminescence quantum ef...
TL;DR: In this article, the synthesis, electronic, and photovoltaic properties of green porphyrin sensitizers were reported, and the best performing dye under standard global AM 1.5 solar conditions gives a short circuit photocurrent density (jsc) of 14.0 ± 0.20 mA/cm2, an open circuit voltage of 680 ± 30 mV, and a fill factor of 0.74, corresponding to an overall conversion efficiency of 7.1%.
Abstract: In TiO2-based dye-sensitized nanocrystalline solar cells, efficiencies of up to 11% have been obtained using Ru dyes, but the limited availability of these dyes together with their undesirable environmental impact have led to the search for cheaper and safer organic-based dyes. In this Letter, we report the synthesis, electronic, and photovoltaic properties of novel green porphyrin sensitizers. All six porphyrin dyes give solar cell efficiencies of ≥5%, but the best performing dye under standard global AM 1.5 solar conditions gives a short circuit photocurrent density (jsc) of 14.0 ± 0.20 mA/cm2, an open circuit voltage of 680 ± 30 mV, and a fill factor of 0.74, corresponding to an overall conversion efficiency of 7.1%, which, for porphyrin-based sensitizers, is unprecedented. This same dye gives an efficiency of 3.6% in a solid-state cell with spiro-MeOTAD as the hole transporting component, comparable to solid-state cells incorporating the best performing ruthenium dyes.
TL;DR: In this article, a first principle, theoretical study of MoS2 nanoparticles is presented, which provides a unified explanation of measured photoluminescence spectra and recent STM measurements as a function of size.
Abstract: We present a first principle, theoretical study of MoS2 nanoparticles that provides a unified explanation of measured photoluminescence spectra and recent STM measurements as a function of size. In addition, our calculations suggest ways to engineer the electronic properties of these systems so as to obtain direct band gap 3D layered nanoparticles or Mo doped metallic nanowires. In particular, we show that single sheet MoS2 nanoparticles up to ∼3.4 nm show no appreciable quantum confinement effects. Instead, their electronic structure is entirely dominated by surface states near the Fermi level. In 3D nanoparticles, we found a strong dependence of their electronic properties on layer stacking and distance, and we suggest that the observed photoluminescence variation as a function of size originates from the number of planes composing the system. The number of these planes and their distance can be tuned to engineer clusters with direct band gaps, at variance with the bulk. Our results also suggest ways to...
TL;DR: In this article, the authors have focused on the mechanisms of the one-electron redox reactions of organic compounds during the TiO2 photocatalytic reactions and on the development of TiO 2-based materials.
Abstract: Titanium dioxide (TiO2) has been extensively investigated for the photocatalytic purification of air and water. In this article, we have focused on the mechanisms of the one-electron redox reactions of organic compounds during the TiO2 photocatalytic reactions and on the development of TiO2-based materials. It was clearly demonstrated that the adsorption dynamics of substrates and intermediates, the electronic interaction between TiO2 and adsorbates, and the band structure and morphology of TiO2 nanomaterials are crucial factors for establishing efficient photocatalytic reaction systems. The TiO2-based hybrid nanoparticles with various functional materials, such as polyoxometalates (POMs) and cyclodextrins (CDs), have been fabricated on the basis of the mechanistic aspects. New experimental methods, such as two-color two-laser flash photolysis and single-molecule fluorescence techniques, for the investigation of the TiO2 photocatalytic reactions have been demonstrated.
TL;DR: In this article, a self-standing 720 μm-thick TiO2 nanotubular membrane was constructed by double-sided electrochemical oxidation of titanium in an electrolyte comprised of water, NH4F, and ethylene glycol.
Abstract: We report on the anodic formation of a self-standing 720 μm thick TiO2 nanotubular membrane by complete consumption of a 250 μm thick titanium foil sample. By employing double sided electrochemical oxidation of titanium in an electrolyte comprised of water, NH4F, and ethylene glycol, we obtain two highly ordered, hexagonal close-packed titania nanotube arrays 360 μm in length that are separated by a thin compact oxide layer; the individual nanotubes in each array have an aspect ratio of ∼2200. The potentiostatic anodization of titanium in an ethylene glycol, NH4F, and water electrolyte dramatically increases the rate of nanotube array growth to approximately 15 μm/h, representing a growth rate ∼750−6000% greater than that seen, respectively, in other polar organic or aqueous based electrolytes previously used to form TiO2 nanotube arrays. We consider the effects of electrolyte composition, applied potential, and anodization duration on the length and diameter of the resulting nanotubes in terms of a growt...
TL;DR: In this paper, the authors comprehensively present the highly efficient multicolor up-conversion (UC) emissions and related mechanisms of monodisperse NaYF4:Yb,Er core (α- and β-NaYF 4,Er) and core/shell.
Abstract: This paper comprehensively presents the highly efficient multicolor up-conversion (UC) emissions and related mechanisms of monodisperse NaYF4:Yb,Er core (α- and β-NaYF4:Yb,Er) and core/shell (α-NaYF4:Yb,Er@α-NaYF4 and β-NaYF4:Yb,Er@α-NaYF4) nanocrystals with controlled size (5−14 nm for α-phase nanocrystals and 20−300 nm for β-phase nanocrystals), chemical composition, and surface state. These nanoparticles were synthesized via a unique delayed nucleation pathway using trifluoroacetates as precursors in hot solutions of oleic acid/oleylamine/1-octadecene. With the naked eye and natural light the intense multicolor UC emissions (red, yellow, or green, without filters) can be observed in cyclohexane dispersions of as-prepared nanocrystals (1 wt %) excited by a 980 nm laser source (power density 1.22 W cm-2). On the basis of compositional optimization for β-NaYF4:Yb,Er nanocrystals, the intensity ratio of green to red emission (fg/r) reaches ca. 30, the highest value to our knowledge. The highly efficient mu...
TL;DR: In this paper, applications of nanoscale zerovalent iron (nZVI) for removal of metal cations in water are investigated with the result that nZVI has much larger capacity than conventional materials for the seques.
Abstract: Applications of nanoscale zerovalent iron (nZVI) for removal of metal cations in water are investigated with the result that nZVI has much larger capacity than conventional materials for the seques...
TL;DR: In this paper, the authors determined the kinetics of the ORR on the surfaces of single crystals of Au(111), Ag(111, Pd, Rh, Ir, and R...
Abstract: We determined, by the rotating disk electrode technique, the kinetics of the oxygen-reduction reaction (ORR) on the surfaces of single crystals of Au(111), Ag(111), Pd(111), Rh(111), Ir(111), and R...
TL;DR: In this paper, a correlation of the particle size with the surface plasmon (SP) resonance band properties and the surface-enhanced Raman scattering (SERS) spectroscopic properties was found for nanoparticles with diameters ranging from 10 to 100 nm in aqueous solutions.
Abstract: While the optical and spectroscopic properties of gold nanoparticles are widely used for chemical, bioanalytical, and biomedical applications, the study of the size correlation with these properties for nanoparticles in solutions is rather limited. This paper describes the results of a systematic study of such a correlation for gold nanoparticles with diameters ranging from 10 to 100 nm in aqueous solutions. The high monodispersity of these nanoparticles permitted a meaningful correlation of the particle size with the surface plasmon (SP) resonance band properties and the surface-enhanced Raman scattering (SERS) spectroscopic properties. This correlation is compared to the results from the simulation based on Mie theory. The close agreement between the experimental and the theoretical results provides insight into the validity of determining the wavelength of the SP resonance band as a measure of the particle size. The size correlation with the SERS intensity from the adsorption of 4-mercaptobenzoic acid ...
TL;DR: In this paper, nanocrystalline particles of ZnO and TiO2 of approximately equal size (∼15 nm) were used to prepare mesoporous electrodes for dye-sensitized solar cells.
Abstract: Nanocrystalline particles of ZnO and TiO2 of approximately equal size (∼15 nm) were used to prepare mesoporous electrodes for dye-sensitized solar cells. Electron transport in the solar cells was studied using intensity-modulated photocurrent spectroscopy and revealed very similar results for ZnO and TiO2. Apparent activation energies for electron transport in nanostructured ZnO of ≤0.1 eV were calculated from the temperature dependence of transport times under short-circuit conditions. The lifetime of electrons in the nanostructured semiconductors was evaluated from open-circuit voltage decay and intensity-modulated photovoltage spectroscopy. Significantly longer lifetimes were obtained with ZnO. Despite the reduced recombination, ZnO-based solar cells performed worse than TiO2 cells, which was attributed to a lower electron injection efficiency from excited dye molecules and/or a lower dye regeneration efficiency. The internal voltage in the nanostructured ZnO film under short-circuit conditions was abo...
TL;DR: In this paper, the authors show that the surface area calculated in a geometric fashion from the crystal structure is a useful tool for characterizing metal-organic frameworks (MOFs) for adsorption applications.
Abstract: Metal−organic frameworks (MOFs) synthesized in a building-block approach from organic linkers and metal corner units offer the opportunity to design materials with high surface areas for adsorption applications by assembling the appropriate building blocks. In this paper, we show that the surface area calculated in a geometric fashion from the crystal structure is a useful tool for characterizing MOFs. We argue that the accessible surface area rather than the widely used Connolly surface area is the appropriate surface area to characterize crystalline solids for adsorption applications. The accessible surface area calculated with a probe diameter corresponding to the adsorbate of interest provides a simple way to screen and compare adsorbents. We investigate the effects of the probe molecule diameter on the accessible surface area and discuss the implications for increasing the surface area of metal−organic frameworks by the use of catenated structures. We also demonstrate that the accessible surface area...
TL;DR: In this article, a new coumarin dye, 2-cyano-3-(5-{2-[5-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6)-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen -9-yl]-vinyl}-thiophen-2-yl)-acrylic acid (NKX-2700), and its application in dye
Abstract: This paper reports a new coumarin dye, 2-cyano-3-(5-{2-[5-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen -9-yl)-thiophen-2-yl]-vinyl}-thiophen-2-yl)-acrylic acid (NKX-2700), and its application in dye-sensitized solar cells (DSSCs). Under illumination of simulated AM1.5G solar light (100 mW cm-2) with an aperture black mask, 5.0% of power conversion efficiency [short-circuit photocurrent density (Jsc) = 12.0 mA cm-2, open-circuit photovoltage (Voc) = 0.59 V, and fill factor (FF) = 0.71] was obtained for NKX-2700 based DSSC, which was significantly improved to 8.2% (Jsc = 15.9 mA cm-2, Voc = 0.69 V, FF = 0.75) upon addition of 120 mM deoxycholic acid (DCA) to the dye solution for TiO2 sensitization. Coadsorption of DCA decreased dye coverage by ∼50% but significantly improved the Jsc by 33%. The breakup of π-stacked aggregates might improve electron injection yield and thus Jsc. Electrochemical impedance data indicate that the electron lifetime was improved by coa...
TL;DR: In this paper, the performance of carbon materials in a neutral electrolyte for the first time has been studied, and the structural and surface properties of the prepared carbon materials were studied using scanning electron microscopy and N2 adsorption/desorption studies.
Abstract: Carbon materials were synthesized from banana fibers by treating the fibers with pore-forming substances such as ZnCl2 and KOH with an intention to improve the surface area and their electrochemical performance as electrical double-layer capacitor electrodes. The performance of these materials was studied in a neutral electrolyte for the first time. There has been a substantive increase in the specific surface area of the treated carbon material because of the effective pore generations. The structural and surface properties of the prepared carbon materials were studied using scanning electron microscopy and N2 adsorption/desorption studies. The surface area of the 10% ZnCl2 treated sample was found to be 1097 m2/g. The electrochemical properties of untreated and porogen treated carbons were evaluated by using cyclic voltammetry and galvanostatic charge−discharge studies, and the specific capacitance as high as 74 F/g in 1 M Na2SO4 neutral electrolyte was obtained for 10% ZnCl2 treated carbon as determine...
TL;DR: In this paper, the structure and properties of the co-doped particles were studied by XRD, XPS, Raman, FL, and UV-diffuse reflectance spectra.
Abstract: Nanoparticles of titanium dioxide co-doped with nitrogen and iron (III) were first prepared using the homogeneous precipitation-hydrothermal method. The structure and properties of the co-doped were studied by XRD, XPS, Raman, FL, and UV-diffuse reflectance spectra. By analyzing the structures and photocatalytic activities of the undoped and nitrogen and/or Fe3+-doped TiO2 under ultraviolet and visible light irradiation, the probable mechanism of co-doped particles was investigated. It is presumed that the nitrogen and Fe3+ ion doping induced the formation of new states closed to the valence band and conduction band, respectively. The co-operation of the nitrogen and Fe3+ ion leads to the much narrowing of the band gap and greatly improves the photocatalytic activity in the visible light region. Meanwhile, the co-doping can also promote the separation of the photogenerated electrons and holes to accelerate the transmission of photocurrent carrier. The photocatalyst co-doped with nitrogen and 0.5% Fe3+ sho...
TL;DR: In this paper, charge density and kinetic data are used to show that the main effects of this treatment are an 80 mV downward shift in the TiO2 conduction band edge potential and a 20-fold decrease in the electron/electrolyte recombination rate constant.
Abstract: Chemical bath deposition of TiO2 from TiCl4 is an often used treatment that improves the photocurrent from dye-sensitized TiO2 solar cells. In this paper, charge density and kinetic data are used to show that the main effects of this treatment are an 80 mV downward shift in the TiO2 conduction band edge potential and a 20-fold decrease in the electron/electrolyte recombination rate constant. Together, these changes increase the quantum efficiency of charge separation at the interface, thus providing the observed increase in the photocurrent. The reduction in the recombination rate constant allows a greater concentration of electrons to accumulate at Voc, thus offsetting the Voc loss otherwise expected from the conduction band edge shift. Photocurrent transients and charge extraction data are used to show that the TiCl4 treatment has little effect on the transport of electrons at short circuit. The electron/electrolyte recombination rate constant at short circuit has been measured with the CCTPV (Constant ...
TL;DR: In this article, a self-aligned hexagonally closed-packed titania nanotube arrays of over 1000 μm in length and aspect ratio ≈10,000 by potentiostatic anodization of titanium were fabricated.
Abstract: We report for the first time fabrication of self-aligned hexagonally closed-packed titania nanotube arrays of over 1000 μm in length and aspect ratio ≈10 000 by potentiostatic anodization of titanium. We describe a process by which such thick nanotube array films can be transformed into self-standing, flat or cylindrical, mechanically robust, polycrystalline TiO2 membranes of precisely controlled nanoscale porosity. The self-standing membranes are characterized using Brunauer−Emmett−Teller surface area measurements, glancing angle X-ray diffraction, and transmission electron microscopy. In initial application, such membranes are used to control the diffusion of phenol red.
TL;DR: In this paper, α-MnO2 hollow spheres and hollow urchins are synthesized via a simple hydrothermal process without using any template or organic surfactant.
Abstract: In this work, α-MnO2 hollow spheres and hollow urchins are synthesized via a simple hydrothermal process without using any template or organic surfactant. The effect of the reaction time on the mic...
TL;DR: In this paper, the solvation force profiles for three room-temperature ionic liquids (ILs), EAN, propylammonium nitrate (PAN), and 1-ethyl-3-methylimidazolium acetate (C2mimAc) confined between Si3N4 tips and mica, silica, and graphite have been measured using an atomic force microscope.
Abstract: Solvation force profiles for three room-temperature ionic liquids (ILs), ethylammonium nitrate (EAN), propylammonium nitrate (PAN), and 1-ethyl-3-methylimidazolium acetate (C2mimAc) confined between Si3N4 tips and mica, silica, and graphite have been measured using an atomic force microscope. The measurements reveal oscillatory behavior in all cases, with the size of the oscillations corresponding to the physical dimension of the ion pair. The surface charge and roughness and the orientation of cations at the interface are critical determinants of solvation layer formation in ILs. The greatest number of solvation layers is observed for EAN on highly charged, atomically smooth mica. Fewer and more compressible layers are observed for PAN due to its increased molecular flexibility. The lower surface charge and increased roughness of silica produces fewer solvation layers for both EAN and PAN compared to mica. For the EAN− and PAN−graphite systems, any attractive interaction with the substrate is due to the ...
TL;DR: In this paper, the effects of hydrothermal time on the phase composition, porosity, and photocatalytic activity of hierarchically porous titania were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and high-resolution HRTEM and N2 adsorption−desorption measurements.
Abstract: Trimodally sponge-like macro-/mesoporous titania was prepared by hydrothermal treatment of precipitates of tetrabutyl titanate (Ti(OC4H9)4) in pure water. Effects of hydrothermal time on the phase composition, porosity, and photocatalytic activity of hierarchically porous titania were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) and N2 adsorption−desorption measurements. All TiO2 powders prepared at 180 °C showed trimodal pore-size distributions in the macro-/mesoporous region: fine intraparticle mesopores with peak pore diameters of ca. 3.7−6.9 nm, larger interparticle mesopores with peak pore diameters of ca. 23−39 nm, and macropore with pore diameter of ca. 0.5−3 μm. With increasing hydrothermal time, crystallinity, and average anatase crystallite size, pore size and pore volume increased, while specific surface area decreased. The hierarchically porous titania prepared ...
TL;DR: In this article, an ordered organic−inorganic solar cell architecture based on ZnO−TiO2 core−shell nanorod arrays encased in the hole-conducting polymer P3HT was evaluated.
Abstract: We evaluate an ordered organic−inorganic solar cell architecture based on ZnO−TiO2 core−shell nanorod arrays encased in the hole-conducting polymer P3HT. Thin shells of TiO2 grown on the ZnO nanorods by atomic layer deposition significantly increase the voltage and fill factor relative to devices without shells. We find that the core−shell cells must be exposed to air to reproducibly attain efficiencies higher than 0.05%. Cells stored in air for 1 month are 0.29% efficient.