Showing papers in "Langmuir in 2002"
TL;DR: In this paper, reactive magnesium oxide nanoparticles and halogen (Cl2, Br2) adducts of these MgO particles were allowed to contact certain bacteria and spore cells, which yield insight into the biocidal action of these nanoscale materials.
Abstract: Reactive magnesium oxide nanoparticles and halogen (Cl2, Br2) adducts of these MgO particles were allowed to contact certain bacteria and spore cells. Bacteriological test data, atomic force microscopy (AFM) images, and electron microscopy (TEM) images are provided, which yield insight into the biocidal action of these nanoscale materials. The tests show that these materials are very effective against Gram-positive and Gram-negative bacteria as well as spores. ζ-Potential measurements show an attractive interaction between the MgO nanoparticles and bacteria and spore cells, which is confirmed by confocal microscopy images. The AFM studies illustrate considerable changes in the cell membranes upon treatment, resulting in the death of the cells. TEM micrographs confirm these results and supply additional information about the processes inside the cells. Overall, the results presented illustrate that dry powder nanoparticulate formulations as well as water slurries are effective. It is proposed that abrasive...
1,679 citations
TL;DR: In this article, the sliding behavior of water droplets over pillarlike and groove structures was investigated and a proper design of the surface with respect to shape and extent of the three-phase line is more effective than the increase of contact angles merely by decreasing the solid−water contact area.
Abstract: Hydrophobicity and sliding behavior of water droplets were investigated on various hydrophobic pillarlike and groove structures prepared on a silicon wafer by dicing and subsequently coating with fluoroalkylsilane. The dominant hydrophobicity mode was changed from Wenzel's mode to Cassie's mode at a smaller roughness than that expected from the calculation based on the sinusoidal surface by Johnson and Dettre. The effect of water intrusion on the microstructure due to droplet weight was revealed to be an important factor governing the water sliding angle on the surface. In a comparison of the sliding behavior of water droplets over pillarlike and groove structures, it was demonstrated that a proper design of the surface with respect to shape and extent of the three-phase line is more effective than the increase of contact angles merely by decreasing the solid−water contact area.
1,083 citations
TL;DR: In this article, the preparation of two-layer stamps was adapted from a procedure originally developed by Schmid et al. (Macromolecules 2000, 33, 3042) for microcontact printing.
Abstract: Composite stamps composed of two layersa stiff layer supported by a flexible layerextend the capabilities of soft lithography to the generation of 50−100-nm features. The preparation of these stamps was adapted from a procedure originally developed by Schmid et al. (Macromolecules 2000, 33, 3042) for microcontact printing. This paper demonstrates how pattern transfer using other soft lithographic techniquesmicromolding in capillaries, microtransfer molding, and phase-shifting lithographycan be improved using two-layer stamps relative to stamps made of Sylgard 184 poly(dimethylsiloxane).
734 citations
TL;DR: In this paper, the effect of H2O2 on the behavior of O2•- and OH• produced in photocatalysis of aqueous TiO2 suspensions by means of luminol chemiluminescence probing and terephthalic acid fluorescence probing, respectively.
Abstract: We have investigated the effect of H2O2 on the behavior of O2•- and OH• produced in photocatalysis of aqueous TiO2 suspensions by means of luminol chemiluminescence probing and terephthalic acid fluorescence probing, respectively. The reduction of O2 by photoinduced conduction band electrons (e-) was increased by the addition of H2O2, since the consumption of photoinduced valence band holes (h+) in the oxidation of H2O2 caused the repression of e-−h+ recombination. After the end of the light irradiation, the amount of O2•- decreased based on the fractal-like kinetics at the heterogeneous surface of the TiO2 particle. The decay process might be caused by trapped h+, which cannot react with water and then remains on the TiO2 particle after the irradiation. The energy level of the trapped h+ was estimated to be above the redox potential of SCN-, since it could react with the adsorbed H2O2 and I- ions but not with other ions such as SCN-, Br-, and Cl-. The formation rate of OH• was increased by the addition o...
705 citations
TL;DR: The concept of molecular packing parameter is widely invoked in the literature to explain, rationalize and even predict molecular self-assembly in surfactant solutions as discussed by the authors, where a particular value of the packing parameter can be translated via simple geometrical relations into specific shape and size of the equilibrium aggregate.
Abstract: The concept of molecular packing parameter is widely invoked in the literature to explain, rationalize and even predict molecular self-assembly in surfactant solutions. The molecular packing parameter is defined as vo/aelo, where vo is the surfactant tail volume, lo is the tail length, and ae is the equilibrium area per molecule at the aggregate surface. A particular value of the molecular packing parameter can be translated via simple geometrical relations into specific shape and size of the equilibrium aggregate. This is the predictive application of the concept of molecular packing parameter, as discussed in the literature. In calculating the packing parameter, the dominant notion in the literature is that the surfactant headgroup determines the surface area per molecule of equilibrium aggregates ae. It follows that, given a headgroup, the molecular packing parameter vo/aelo is fixed, because the volume-to-length ratio (vo/lo) of the tail is a constant independent of the tail length for common surfacta...
682 citations
TL;DR: In this article, concentrated colloidal gels with tailored visco-elastic properties were designed to form self-supporting periodic structures via directed assembly of colloidal inks.
Abstract: Mesoscale periodic structures have been fabricated via directed assembly of colloidal inks. Concentrated colloidal gels with tailored viscoelastic properties were designed to form self-supporting f...
633 citations
TL;DR: In this article, lead adsorption on chitosan/PVA beads was found to be strongly pH-dependent and displayed a maximum uptake capacity at pH around 4 and a minimum at pH about 6.4.
Abstract: Removal of lead from aqueous solution with chitosan/PVA (poly(vinyl alcohol)) hydrogel beads was studied in batch adsorption experiments at various solution pH values (2−7.6). Lead adsorption on chitosan/PVA beads was found to be strongly pH-dependent and displayed a maximum uptake capacity at pH around 4 and a minimum at pH about 6.4. ζ-Potential study indicated that chitosan/PVA beads possessed positive ζ-potentials at pH 6.3. Hence, adsorption occurred even though the interaction between lead and chitosan/PVA beads was electrostatically repulsive at pH < 6.3. Complexation, ion exchange, and electrostatic interaction are all believed to play a role in lead adsorption on chitosan/PVA beads, but the relative importance of each of these mechanisms varies with solution pH values. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy spectra suggested that lead adsorption was mainly through interactions with the N atoms in chitosan in the pH rang...
576 citations
TL;DR: In this article, a theoretical treatment for the wetting of a solid particle at an oil−water interface in terms of the components of the surface energies of all three phases was developed.
Abstract: A theoretical treatment is developed for the wetting of a solid particle at an oil−water interface in terms of the components of the surface energies of all three phases. Calculated oil−water contact angles for a solid of given hydrophobicity with a range of oils of different polarity show good agreement with experimental data. For a hydrophobically modified silica surface, oils of increasing polarity give higher oil−water contact angles measured through water. The results are in line with the effect of oil type on Pickering emulsion type where more polar oils preferentially give water-in-oil emulsions. The approach is also used to predict the type of solid particles that would be required to stabilize emulsions of two immiscible oils. For hydrocarbon−fluorocarbon pairs, it is predicted that perfluorinated particles would stabilize fluorocarbon-external emulsions while silica particles with a high coverage of hydrocarbon groups should stabilize hydrocarbon-external emulsions.
575 citations
TL;DR: In this article, a criterion based on contact line density is proposed for predicting the conditions that produce ultrahydrophobic surfaces, where, above a critical value, drops are suspended by asperities.
Abstract: Very rough surfaces can suspend small water drops, prevent wetting, and cause contact angles to approach 180°. A criterion based on contact line density is proposed for predicting the conditions that produce these ultrahydrophobic surfaces, where, above a critical value, drops are suspended by asperities. Critical values of the contact line density can be calculated from contact angles, asperity shape, and information about the contact liquid, such as density and surface tension. The criterion was found to correctly predict suspension for several model surfaces prepared by lithography techniques. Apparent contact angles from suspended and collapsed drops also were modeled by accounting for rough edges and employing a linear average of contact angle along the perimeter of the drop, rather than an area average of cosine. This linear model suggests that, for suspended drops, both advancing and receding angles should increase. Alternatively, for drops that have collapsed over surface asperities, advancing con...
568 citations
TL;DR: In this paper, a higher yield of functionalized carbon nanotubes (CNTs) was obtained by treatment of CNTs in HNO3 or H2SO4−K2Cr2O7.
Abstract: A higher yield of functionalized carbon nanotubes (CNTs) was obtained by treatment of CNTs in HNO3 or H2SO4−K2Cr2O7. The deposition of platinum nanoparticles and nanoclusters on these functionalized multiwalled carbon nanotubes by electroless plating was facilitated by a two-step sensitization-activation pretreatment. The deposition was sensitive to the aging time of the sensitizing solution and the pH of the plating solution. The resulting electrocatalysts were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry. XPS analysis showed that the Pt/CNT electrocatalysts contained 67.3% of Pt(0) and 32.7% of Pt(IV). Test runs on a single stack polymer electrolyte membrane fuel cell showed that these electrocatalysts are very promising for fuel cell applications.
532 citations
TL;DR: In this article, a new approach for the synthesis of colloidal gold shell particles with a dielectric core is described, and the optical properties of the particles made are in good agreement with theoretical calculations for core−shell particles.
Abstract: A new approach for the synthesis of colloidal gold shell particles with a dielectric core is described. Small gold nanoclusters were attached to the functionalized surface of colloidal silica particles. Reductive growth and coalescence of these clusters lead to the formation of a closed gold layer. By variation of the thickness of this gold layer and the radius of the shell it is possible to adjust the plasmon resonance of the gold shell particles over the whole visible and infrared region of the spectrum. The optical properties of the particles made are in good agreement with theoretical calculations for core−shell particles. Because of their low polydispersity, these gold shell particles form large crystals with submicron lattice constants. It is also possible to produce hollow gold shells by dissolution of the silica core. Further, a new method to coat the silica core gold shell particles with an additional outer silica shell is presented. This allows for a reduction in the van der Waals forces and fac...
TL;DR: Polyvinylpyrrolidone (PVP) is a polymer capable of complexing and stabilizing Ag and Au nanoparticles formed through the reduction of Ag+ or AuCl4- ions with N,N-dimethylformamide.
Abstract: Poly(vinylpyrrolidone) (PVP) is a polymer capable of complexing and stabilizing Ag and Au nanoparticles formed through the reduction of Ag+ or AuCl4- ions with N,N-dimethylformamide. The reduction can be efficiently performed both at reflux and under microwave irradiation, but each of these methods leads to different nanoparticle morphology and colloid stability. The use of microwave irradiation provides an extra degree of control of the reduction process. The use of PVP with different polymer chain lengths leads to particles with similar sizes though with a different degree of stability. The colloids are also stable in ethanol for months, but only marginally stable in water.
TL;DR: In this paper, the authors compared the performance of cavities with ordered nanoporous materials with cubic Pm3n (SBA-1, HMM-3), cubic Im3m (S BA-16), and 3D hexagonal P63/mmc cagelike structures, and showed that in sufficiently small cavities (pore diameters 3 ca. 6 nm), the condensation step corresponds to the theoretical limit of the metastable adsorption film.
Abstract: Adsorption in spherical cavities is studied by the nonlocal density functional theory (NLDFT). Theoretical results are compared with experimental data on ordered nanoporous materials with cubic Pm3n (SBA-1, HMM-3), cubic Im3m (SBA-16), and 3D hexagonal P63/mmc (SBA-2, SBA-12) cagelike structures. Quantitative comparison shows that capillary condensation of N2 at 77 K in sufficiently small cavities (pore diameters 3 ca. 6 nm, the capillary condensation step corresponds to the theoretical limit of stability of the metastable adsorption film. For pores wider than ca. 10 nm, this limit is approximated by the macroscopic Derjaguin−Broekhoff−de Boer equations. Desorption from cavities of >6 nm is controlled by the size of the windows that connect the cavity with the bulk fluid. If the diameter of the window is below ca. 4 nm, desorp...
TL;DR: In this article, self-assembled micro/nanotubes (650−76 nm in diameter) of polyaniline (PANI) were synthesized in the presence of β-naphthalene sulfonic acid (β-NSA) as a dopant.
Abstract: Self-assembled micro/nanotubes (650−76 nm in diameter) of polyaniline (PANI) were synthesized in the presence of β-naphthalene sulfonic acid (β-NSA) as a dopant. It was found that the diameter and room-temperature conductivity of the PANI−NSA tubes decreased with the decrease of the molar ratio of β-NSA to aniline. On the bases of the results obtained from X-ray diffraction (XRD) and dynamic lighting scattering (DLS), it was proposed that when the molar ratio of β-NSA to aniline was high (e. g. 2), the NSA−An salt precipitate formed by β-NSA and aniline played a “template-like” role in forming the PANI−NSA tubes, while the “template-like” role was played by the NSA−An micelle when the ratio is low (e.g., 1/2 or 1/4).
TL;DR: In this paper, a new classification of physical mechanisms of adsorption hysteresis in ink-bottle type pores confirmed by experimental studies of capillary condensation of N2, Ar, and Kr at 77.4 and 87.4 K in ordered 3D cage-like structures of FDU-1 and SBA-16 nanoporous templated silicas with narrow pore size distribution.
Abstract: We present a new classification of physical mechanisms of adsorption hysteresis in ink-bottle type pores confirmed by experimental studies of capillary condensation of N2, Ar, and Kr at 77.4 and 87.4 K in ordered 3D cage-like structures of FDU-1 and SBA-16 nanoporous templated silicas with narrow pore size distribution. An analysis of the hysteresis loops and scanning desorption isotherms on FDU-1 with ∼15 nm spherical pores reveals three mechanisms of evaporation: (1) evaporation from the blocked cavities controlled by the size of connecting pores (classical ink-bottle or pore blocking effect); (2) spontaneous evaporation caused by cavitation of the stretched metastable liquid; and, for the first time, (3) near-equilibrium evaporation in the region of hysteresis from unblocked cavities that have access to the vapor phase. Studies of the temperature dependence of the hysteresis loop showed a transition between the cavitation and the pore blocking regimes of evaporation, which opens up the possibility to ...
TL;DR: In this paper, the authors describe the functionalization of the surfaces of gold nanoshells with self-assembled monolayers derived from the adsorption of a series of alkanethiols.
Abstract: This paper describes the functionalization of the surfaces of gold nanoshells, which consist of silica nanoparticles coated with a continuous thin layer of gold. Previous studies have shown that gold nanoshells exhibit optical properties similar to those of metal colloids (e.g., strong optical absorptions and large third-order nonlinear optical polarizabilities). In contrast to metal colloids, however, the plasmon resonance of the nanoshells can be tuned to specific wavelengths across the visible and infrared range of the electromagnetic spectrum by adjusting the relative size of the dielectric core and the thickness of the gold overlayer. In efforts to develop new strategies for protecting and manipulating these nanoparticles, this paper describes the functionalization of the surfaces of gold nanoshells with self-assembled monolayers derived from the adsorption of a series of alkanethiols. The nanoshells are characterized by transmission electron microscopy, UV−vis spectroscopy, FTIR spectroscopy, Raman ...
TL;DR: In this article, the authors used mixed monolayers comprising of undecanethiol and ω-mercaptoundecyl bromoisobyrate (1) to initiate the controlled radical polymerization of methyl methacrylate (MMA) and glycidyl methacelate (GMA) from gold, and found that SAMs composed of 10% and 50% of initiator 1 grow PMMA brushes to approximately 1/10 and 1/2 the thickness of polymer brushes.
Abstract: We report the first systematic study of initiator density on surface-initiated polymerizations. We used mixed monolayers comprising of undecanethiol and ω-mercaptoundecyl bromoisobutyrate (1) to initiate the controlled radical polymerization of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) from gold. We found that SAMs composed of 10% and 50% of initiator 1 grow PMMA brushes to approximately 1/10 and 1/2 the thickness of polymer brushes grafted from SAMs comprising 100% 1. We did not find a clear maximum initiator density, beyond which no further increase in polymer brush thickness is observed. We show that the initiator density at the start of the polymerization determines the ultimate “footprint” and hence density of polymer molecules in polymer brushes.
TL;DR: In this paper, the impact of stamp deformation on the dimensional stability of the microcontact printing process is investigated. But the authors consider limitations imposed due to reversible deformation of a single stamp.
Abstract: Stamp deformation can affect the dimensional stability of the microcontact printing process. We consider limitations imposed due to reversible deformation of a single stamp. Detailed analyses of several modes of stamp deformation have been carried out. Stability criteria have been obtained for both vertical and lateral collapse of surface relief features, including buckling. The shape change of surface features imposed by surface tension has been analyzed, and the corresponding internal stresses are given in closed form. The residual stresses induced by chemical and thermal shrinkage when the elastomeric stamp is bonded to a stiff substrate are analyzed. In addition, the relation between applied load and displacement of a stamp supported by a stiff substrate is given in closed form. Contact stresses between the stamp and substrate have been analyzed both analytically and numerically by a finite element method. The role of adhesion in determining the contact area is clarified. The effect of surface roughne...
TL;DR: The binding affinity of deoxynucleosides (dA, dG, dC, and dT) to gold nanoparticles was studied using a colorimetric assay to determine if nucleobase sequence may play a role in binding alkanethiol-capped oligonucleotides togold nanoparticles, and data indicate that the dT has a much lower binding affinity to the gold nanoparticle surface.
Abstract: The binding affinity of deoxynucleosides (dA, dG, dC, and dT) to gold nanoparticles was studied using a colorimetric assay to determine if nucleobase sequence may play a role in binding alkanethiol-capped oligonucleotides to gold nanoparticles. These data indicate that the deoxynucleoside dT has a much lower binding affinity to the gold nanoparticle surface than the deoxynucleosides dG, dC, and dA. These data can be correlated with a previous study in our lab which indicated that alkanethiol-capped oligonucleotides containing (dT)20 spacers have a significantly higher surface coverage than oligonucleotides containing (dA)20 spacers. To probe the physical consequences of this phenomenon, gold nanoparticles were loaded with alkanethiol-capped poly dT, dA, and dC oligonucleotide sequences of 5−20 bases in length, and the stabilities of the particles in electrolytic media were measured by monitoring a colorimetric change associated with particle agglomeration. The gold nanoparticles loaded with alkanethiol-ca...
TL;DR: In this paper, the effects of polymer−particle and particle-particle interactions on viscoelastic properties of nanocomposite materials are investigated using narrow molecular weight distribution poly(ethylene oxide) (PEO) containing isotropic silica nanospheres.
Abstract: The effects of polymer−particle and particle−particle interactions on viscoelastic properties of nanocomposite materials are investigated using narrow molecular weight distribution poly(ethylene oxide) (PEO) containing isotropic silica nanospheres. Nanocomposites are prepared using a “freeze-drying” method to guarantee homogeneous dispersion of silica. The dispersion state of silica nanospheres is characterized by atomic force microscopy phase contrast imaging, and mechanical rheometry is used to study relaxation dynamics and viscoelastic properties of these materials in the melt state. Linear viscoelastic data indicate a transition to a solidlike response at low oscillation frequencies for particle volume fractions φ as low as 2%, dramatically lower than the theoretical percolation threshold (φ ∼ 30%). Nanoparticle volume fraction, surface chemistry, and PEO molecular weight are all found to strongly influence nanocomposite structure and dynamics. A filler networking mechanism, wherein nanosized silica p...
TL;DR: In this article, the phase inversion temperature emulsification method was used for the formation of O/W nano-emulsions in water/C12Ē4/oil systems.
Abstract: Formation of O/W nano-emulsions has been studied in water/C12Ē4/oil systems by the phase inversion temperature emulsification method. Emulsification was carried out at the corresponding HLB (hydrophilic−lipophilic balance) temperature, and then the emulsions were cooled fast to 25 °C. The influence of surfactant concentration and oil solubility on HLB temperature, nano-emulsion droplet size, and stability has also been studied. Droplet size was determined by dynamic light scattering, and nano-emulsion stability was assessed, measuring the variation of droplet size as a function of time. The results obtained showed that the breakdown process of nano-emulsions studied could be attributed to Ostwald ripening. An increase of nano-emulsion instability with the increase in surfactant concentration and oil solubility was also found.
TL;DR: In this paper, a slurry of silica submicrospheres, silver nitrate, and ammonia in an aqueous medium for 90 min under an atmosphere of argon to hydrogen (95:5) yielded a silver−silica nanocomposite.
Abstract: Silver nanoparticles with an average size of ∼5 nm were deposited on the surface of preformed silica submicrospheres with the aid of power ultrasound. Ultrasound irradiation of a slurry of silica submicrospheres, silver nitrate, and ammonia in an aqueous medium for 90 min under an atmosphere of argon to hydrogen (95:5) yielded a silver−silica nanocomposite. By controlling the atmospheric and reaction conditions, we could achieve the deposition of metallic silver on the surface of the silica spheres. The resulting silver-deposited silica submicrosphere samples were characterized with X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, energy-dispersive X-ray analysis, high-resolution transmission electron microscopy, high-resolution scanning electron microscopy, photoacoustic spectroscopy, and Fourier transform infrared, UV−visible, and X-ray photoelectron spectroscopy.
TL;DR: In this article, the surface chemistry of activated carbon samples was characterized by selective neutralization, temperature-programmed desorption, X-ray photoelectron spectroscopy, and pH of the point of zero charge.
Abstract: The combined use of ozone and activated carbon has recently started to be developed for the treatment of toxic effluents However, the effect of ozone on the properties of activated carbon is not fully elucidated A study was undertaken of modifications in the surface properties of a commercial activated carbon produced by its ozonation during different time periods Surface chemistry of the activated carbon samples was characterized by selective neutralization, temperature-programmed desorption, X-ray photoelectron spectroscopy, and pH of the point of zero charge Surface area and volume of micropores and mesopores were obtained from nitrogen adsorption isotherms at 77 K Adsorption properties were determined by methylene blue adsorption index Results show that the higher the ozone dose, the higher is the oxidation of the carbon and the greater is the number of acid groups present on the carbon surface, especially carboxylic groups, whereas the pH of the point of zero charge decreases The surface area,
TL;DR: In this article, the effect of particle size on the Suzuki reaction between phenylboronic acid and iodobenzene is investigated by the use of four Pd catalysts with mean particle sizes of 3.0, 3.9, 5.2, and 6.6 nm.
Abstract: A series of poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized Pd nanoparticles with varying particle size are prepared by using the stepwise growth reaction. The effect of Pd particle size on the Suzuki reaction between phenylboronic acid and iodobenzene is investigated by the use of four Pd catalysts with mean particle sizes of 3.0, 3.9, 5.2, and 6.6 nm, respectively. The catalytic activity of the Pd nanoparticles expressed in terms of the initial turnover frequency (moles of the biphenyl product per mole of total surface Pd atoms per min) is found to be in the order of Pd (3.9 nm) > Pd (3.0 nm) ≈ Pd (5.2 nm) > Pd (6.6 nm), indicating that surface Pd atoms do not all have the same reactivity in this reaction. The general trend of increased catalytic activity with the decrease in the particle size suggests that the low-coordination number vertex and edge atoms on the particle surface are active sites for the Suzuki reaction. The lower catalytic activity for the smallest Pd nanoparticles might be due to stronge...
TL;DR: In this paper, the surface plasmon bands at 540 and 860 nm associated with spherical and anisotropic triangular/hexagonal NPs, respectively, were found to have preferential adsorption of the flat particles on polyelectrolyte films.
Abstract: Gold nanoparticles (NPs) were prepared by reduction with salicylic acid in aqueous solution. The resulting dispersions were found to contain a mixture of flat triangular/hexagonal and smaller close-to-spherical NPs. As expected from theoretical considerations, such nanocolloids display two clearly differentiated surface plasmon bands at 540 and 860 nm associated with spherical and anisotropic triangular/hexagonal NPs, respectively. Layer-by-layer (LBL) assembly was used to deposit thin films of the Au colloids. UV−visible data indicate preferential adsorption of the flat particles on polyelectrolyte films. Importantly, a new band developed at 650 nm as the number of the Au NPs bilayers increased. This finding indicates that there exists a strong interaction between the NPs in adjacent layers, resulting in the surface plasmon absorption at a new wavelength. The insertion of extra polyelectrolyte or montmorillonite layers between the Au bilayers was shown to gradually reduce the interlayer interaction and r...
TL;DR: In this article, the voltammetric electrooxidation rates of formic acid, formaldehyde, and methanol in acidic electrolyte on carbon-supported platinum nanoparticle films with varying particle diameters (d) in the range of ca. 2−9 nm are examined with the objective of comparing the nanoparticle size sensitivity for these related yet distinct electrocatalytic processes.
Abstract: The voltammetric electrooxidation rates of formic acid, formaldehyde, and methanol in acidic electrolyte on carbon-supported platinum nanoparticle films with varying particle diameters (d) in the range of ca. 2−9 nm are examined with the objective of comparing the nanoparticle size sensitivity for these related yet distinct electrocatalytic processes. The reaction rates on the larger nanoparticles (d > 4 nm) are similar to those observed on polycrystalline Pt when normalized to the same microscopic Pt surface area. As noted previously, the rates of methanol electrooxidation decrease for Pt nanoparticle diameters below 4 nm. However, formic acid electrooxidation exhibits the opposite behavior, with rates increasing markedly for d < 4 nm, while formaldehyde electrooxidation displays little sensitivity to the Pt nanoparticle size. However, the extent of chemisorbed CO formation from all three reactants, as deduced from voltammetric and infrared spectral data, diminishes with decreasing d, the CO coverages fo...
TL;DR: In this article, the authors consider the thermodynamics of adsorption of gases in porous solids from both the perspective of absolute properties which appear naturally in theoretical studies and that of excess properties which are measured in experiments.
Abstract: We consider the thermodynamics of adsorption of gases in porous solids from both the perspective of absolute properties which appear naturally in theoretical studies and that of excess properties which are measured in experiments. Our thermodynamic description starts by treating the gas (or gas mixture) plus porous solid system as a mixture to which we can apply solution thermodynamics. We show that equations for the absolute thermodynamic properties for adsorption in rigid porous materials do not require an explicit reference to the pressure of the fluid confined in the porous material. We discuss how to relate absolute properties to excess properties by using an estimate of the helium void volume. We illustrate the thermodynamic formalism with calculations for a simple thermodynamic model in which the Langmuir equation is used to describe the absolute adsorption isotherm and the ideal gas equation of state is used for the bulk properties. The simplified model explains the apparently anomalous behavior o...
TL;DR: In this article, a monochromatic X-ray photoelectron spectroscopy (XPS) was used for surface characterization of indium−tin oxide (ITO) thin films.
Abstract: Surface characterization of indium−tin oxide (ITO) thin films has been carried out with monochromatic X-ray photoelectron spectroscopy (XPS) following various solution pretreatments, RF air plasma etching or high-vacuum argon-ion sputtering. Commercially available ITO films show high concentrations of hydrolyzed oxides and oxy-hydroxides in the near-surface region, along with stoichiometric oxide (In2O3, SnO2) and variable levels of oxygen defect sites. XPS revealed that solution and vacuum treatments changed both the relative surface coverage of the hydroxides and, to a lesser extent, the concentration of oxide defect sites in the near-surface region. These pretreatments have a significant effect on both the coverage and electron-transfer rates for chemisorbed ferrocene dicarboxylic acid (Fc(COOH)2), with the air-plasma-etched ITO showing the highest surface coverage of Fc(COOH)2 and an RCA treatment showing the highest electron-transfer rates.
TL;DR: In this article, it was shown that either an outward flow toward the contact line or an inward flow towards the center of the droplet can be induced, depending on the evaporative driving force.
Abstract: An emergent technique of patterning surfaces with solid particles utilizes the evaporation of colloidal droplets from a substrate. Upon complete evaporation of the liquid, the suspended particles remain adhered to the solid in a variety of patterns. Experimentally, the type of particle deposit has been correlated with the mode of liquid evaporation. It is expected that the manner in which the liquid evaporates from the droplet should significantly affect the flow of fluid inside the droplet. Therefore, the determination of the flow profiles in the droplet will aid in understanding the redistribution of particles under different experimental conditions. Using lubrication theory, this study shows that either an outward flow toward the contact line or an inward flow toward the center of the droplet can be induced, depending on the evaporative driving force. If an outward flow toward the contact line is generated inside the droplet, then a ringlike deposit remains on the substrate. Conversely, if the liquid i...
TL;DR: In this paper, the electrochemical and solvation properties of room-temperature ionic liquids (ILs) have been investigated for organic synthesis, separations, and electrochemical applications, and it is demonstrated that despite impurities, the cathodic limit at a Pt electrode is enhanced for the tetraalkylammonium-based IL.
Abstract: Room-temperature ionic liquids (ILs) have been proposed as alternative solvents for organic synthesis, separations, and electrochemical applications. Here, we report studies that probe the electrochemical and solvation properties of a tetraalkylammonium (methyltributylammonium bis(trifluoromethylsulfon)imide, M3BNIm) and an imidazolium (1-butyl-3-methylimidazolium hexafluorophosphate, BMIPF6) based ionic liquid. It is demonstrated that despite impurities, the cathodic limit at a Pt electrode is enhanced for the tetraalkylammonium-based IL. Electrogenerated chemiluminescence of tris(2,2‘-bipyrindinyl)ruthenium (Ru(bpy)32+) was observed in both ionic liquids, and differences in the response were interpreted in terms of the solvent reactivity and polarity. As ILs have been proposed as alternatives to organic solvents in extraction processes, an understanding of the relative lipophilicity of the IL ions and the equilibrium potential difference established across the IL/water interface is of fundamental releva...