Complex nanomineral formation utilizing kinetic control by PLAL.

We used pulsed-laser ablation in liquids (PLAL) of Cu or Zn foil targets in water or in aqueous Cu or Zn salt solutions. PLAL in neat water generated mixtures of metal and (thermodynamically preferred) metal oxide nanomaterials, whereas the availability of select dissolved anions predictably led to the fabrication of more complex phase-pure nanominerals. PLAL of Cu foil in aqueous CuCl2 solution produced nano-paratacamite, Cu2Cl(OH)3, whereas nano-rouaite, Cu2(NO3)(OH)3, was formed in aqueous Cu(NO3)2 and NH4OH solution. Likewise, we synthesized simonkolleite, Zn5(OH)8Cl2·H2O, or layered zinc hydroxide nitrate, Zn5(OH)8(NO3)2·2H2O, nanoparticles by PLAL of Zn targets in aqueous ablation liquids with added ZnCl2 and NH4OH or Zn(NO3)2, respectively. Bimetallic zincian paratacamite resulted from PLAL of Cu foil in aqueous Cu and Zn chloride solution. Our results show that kinetic control exceeded thermodynamic product formation during nanosecond ultraviolet PLAL.

Lightly Fluorinated Graphene as a Protective Layer for n-Type Si(111) Photoanodes in Aqueous Electrolytes.

The behavior of n-Si(111) photoanodes covered by monolayer sheets of fluorinated graphene (F-Gr) was investigated under a range of chemical and electrochemical conditions. The electrochemical behavior of n-Si/F-Gr and np(+)-Si/F-Gr photoanodes was compared to hydride-terminated n-Si (n-Si-H) and np(+)-Si-H electrodes in contact with aqueous Fe(CN)6(3-/4-) and Br2/HBr electrolytes as well as in contact with a series of outer-sphere, one-electron redox couples in nonaqueous electrolytes. Illuminated n-Si/F-Gr and np(+)-Si/F-Gr electrodes in contact with an aqueous K3(Fe(CN)6/K4(Fe(CN)6 solutions exhibited stable short-circuit photocurrent densities of ∼10 mA cm(-2) for 100,000 s (>24 h), in comparison to bare Si electrodes, which yielded nearly a complete photocurrent decay over ∼100 s. X-ray photoelectron spectra collected before and after exposure to aqueous anodic conditions showed that oxide formation at the Si surface was significantly inhibited for Si electrodes coated with F-Gr relative to bare Si electrodes exposed to the same conditions. The variation of the open-circuit potential for n-Si/F-Gr in contact with a series of nonaqueous electrolytes of varying reduction potential indicated that the n-Si/F-Gr did not form a buried junction with respect to the solution contact. Further, illuminated n-Si/F-Gr electrodes in contact with Br2/HBr(aq) were significantly more electrochemically stable than n-Si-H electrodes, and n-Si/F-Gr electrodes coupled to a Pt catalyst exhibited ideal regenerative cell efficiencies of up to 5% for the oxidation of Br(-) to Br2.

Use of Mixed CH3-/HC(O)CH2CH2-Si(111) Functionality to Control Interfacial Chemical and Electronic Properties During the Atomic-Layer Deposition of Ultrathin Oxides on Si(111).

Silicon surfaces terminated with a mixed monolayer containing both a propyl aldehyde functionality and methyl groups were prepared and used to control the interfacial chemical and electronic properties of Si(111) surfaces during atomic-layer deposition (ALD) of Al2O3 or MnO. Si(111) surfaces functionalized only with the aldehyde moiety exhibited surface recombination velocities, S, of 2500 ± 600 cm s(-1) whereas the mixed CH3-/HC(O)CH2CH2-Si(111) surfaces displayed S = 25 ± 7 cm s(-1). During the ALD growth of either Al2O3 or MnO, both the HC(O)CH2CH2-Si(111) and CH3-/HC(O)CH2CH2-Si(111) surfaces produced increased metal oxide deposition at low cycle number, relative to H-Si(111) or CH3-Si(111) surfaces. As detected by X-ray photoelectron spectroscopy after the ALD process, the CH3- and mixed CH3-/HC(O)CH2CH2- functionalized Si(111) surfaces exhibited less interfacial SiOx than was observed for ALD of metal oxides on H-Si(111) substrates.

Comparison of the Performance of CoP-Coated and Pt-Coated Radial Junction n(+)p-Silicon Microwire-Array Photocathodes for the Sunlight-Driven Reduction of Water to H2(g).

The electrocatalytic performance for hydrogen evolution has been evaluated for radial-junction n(+)p-Si microwire (MW) arrays with Pt or cobalt phosphide, CoP, nanoparticulate catalysts in contact with 0.50 M H2SO4(aq). The CoP-coated (2.0 mg cm(-2)) n(+)p-Si MW photocathodes were stable for over 12 h of continuous operation and produced an open-circuit photovoltage (Voc) of 0.48 V, a light-limited photocurrent density (Jph) of 17 mA cm(-2), a fill factor (ff) of 0.24, and an ideal regenerative cell efficiency (ηIRC) of 1.9% under simulated 1 Sun illumination. Pt-coated (0.5 mg cm(-2)) n(+)p-Si MW-array photocathodes produced Voc = 0.44 V, Jph = 14 mA cm(-2), ff = 0.46, and η = 2.9% under identical conditions. Thus, the MW geometry allows the fabrication of photocathodes entirely comprised of earth-abundant materials that exhibit performance comparable to that of devices that contain Pt.

Highly active electrocatalysis of the hydrogen evolution reaction by cobalt phosphide nanoparticles.

Nanoparticles of cobalt phosphide, CoP, have been prepared and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50 M H2SO4, pH 0.3). Uniform, multi-faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm(-2) mass loading) produced a cathodic current density of 20 mA cm(-2) at an overpotential of -85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen production in 0.50 M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long-term viability under operating conditions. CoP is therefore amongst the most active, acid-stable, earth-abundant HER electrocatalysts reported to date.

Stopped-flow ultra-rapid-scanning Fourier transform infrared spectroscopy on the millisecond time scale.

Full-range mid-infrared spectra were measured during the reaction of CpCo(CO)(2) with nitrosyl chloride by interfacing a rapid-mixing stopped-flow device with an ultra-rapid-scanning Fourier transform infrared (FT-IR) spectrometer having a temporal resolution of 5 ms. Changes to the data acquisition hardware of this spectrometer now allow a sequence of well over 2000 spectra to be collected without interruption. Two transient species were observed spectroscopically during the first 500 ms of the reaction of CpCo(CO)(2) with nitrosyl chloride. The shortest-lived species that was observed, [CpCo(CO)(2)(NO)](+), had a half-life of approximately 20 ms at 25 degrees C and approximately 70 ms at 10 degrees C. This intermediate transformed into a longer-lived (approximately 0.5 s) intermediate, CpCo(NO)Cl. Potential intermediate species with one CO and one NO ligand, such as [CpCo(CO)(NO)](+) and CpCo(CO)(NO)Cl, were not observed, although the possibility that they exist cannot be ruled out.

Detection of chemical agents in the atmosphere by open-path FT-IR spectroscopy under conditions of background interference: II. Fog and rain.

Open-path FT-IR spectra of low-concentration releases of diethyl ether were measured both when a glycol fog was passed into the infrared beam and when large water droplets from a lawn sprinkler were sprayed into the beam. It was shown that the glycol fog, for which the droplet size was much less than the wavelength of the infrared radiation, gave rise to a significant interference such that partial least squares (PLS) regression would only yield reasonable values for the ether concentration if background spectra in which the glycol fog was present were included in the calibration set. On the other hand, target factor analysis (TFA) allowed the presence of the ether to be recognized without precalibration. When large water droplets were present in the beam, any infrared radiation entering the droplet was completely absorbed, so that both PLS and TFA would yield accurate results.

Detection of chemical agents in the atmosphere by open-path FT-IR spectroscopy under conditions of background interference: I. High-frequency flashes.

Open-path FT-IR spectra were measured while fireworks were emitting smoke and incandescent particles into the infrared beam. These conditions were designed to simulate the appearance of smoke and explosions in a battlefield. Diethyl ether was used to simulate the vapor-phase spectra of G agents such as sarin. The measured interferograms were corrected by a high-pass filter and were rejected when interfering features were of such high frequency that they could not be removed by application of this filter. The concentration of diethyl ether was calculated correctly by partial least squares regression in the absence of fireworks but significant errors were encountered when the spectra of the oxide particles were not included in the calibration set. Target factor analysis allowed the presence of the analyte to be detected even when the incandescent particles were present in the beam.

Electrochemical detection of triacetone triperoxide employing the electrocatalytic reaction of iron(II/III)-ethylenediaminetetraacetate and hydrogen peroxide.

An electrochemical method for the detection of triacetone triperoxide (TATP) is proposed and examined. In this method, TATP solutions were treated with 1.08 M HCl for 10min releasing H2O2 and/or hydroperoxides. Subsequently, these peroxides undergo an electrocatalytic reduction through the Fe(II/III)ethylenediaminetetraacetate (EDTA) complex at a glassy carbon electrode. Cyclic voltammetric results indicate that no redox reaction was observed between Fe(II)EDTA and TATP. Acid treated TATP yielded voltammograms indicative of electrocatalysis of ROOH/HOOH reduction via Fe(II/III)EDTA redox cycling. Chronoamperometric results yielded a detection limit of 0.89 microM for TATP and a sensitivity of 0.025 mAmM(-1). The influence of pH and O2 interference on the analytical signal is briefly discussed.