Experimental and theoretical studies of the kinetics of the reactions of OH and OD with 2-methyl-3-buten-2-ol between 300 and 415 K at low pressure

The rate constants for the reactions of OH and OD with 2-methyl-3-buten-2-ol (MBO) have been measured at 2, 3, and 5 Torr total pressure over the temperature range 300-415 K using a discharge-flow system coupled with laser induced fluorescence detection of OH. The measured rate constants at room temperature and 5 Torr for the OH + MBO reaction in the presence of O2 and the OD + MBO reaction are (6.32 +/- 0.27) and (6.61 +/- 0.66) x 10(-11) cm3 molecule(-1) s(-1), respectively, in agreement with previous measurements at higher pressures. However, the rate constants begin to show a pressure dependence at temperatures above 335 K. An Arrhenius expression of k0 = (2.5 +/- 7.4) x 10(-32) exp[(4150 +/- 1150)/T] cm6 molecule(-2) s(-1) was obtained for the low-pressure-limiting rate constant for the OH + MBO reaction in the presence of oxygen. Theoretical calculations of the energetics of the OH + MBO reaction suggest that the stability of the different HO-MBO adducts are similar, with predicted stabilization energies between 27.0 and 33.4 kcal mol(-1) relative to the reactants, with OH addition to the internal carbon predicted to be 1-4 kcal mol(-1) more stable than addition to the terminal carbon. These stabilization energies result in estimated termolecular rate constants for the OH + MBO reaction using simplified calculations based on RRKM theory that are in reasonable agreement with the experimental values.     

Electrocatalytic Activity of a 2D Phosphorene‐Based Heteroelectrocatalyst for Photoelectrochemical Cells

Research into efficient synthesis, fundamental properties, and potential applications of phosphorene is currently the subject of intense investigation. Herein, solution‐processed phosphorene or few‐layer black phosphorus (FL‐BP) sheets are prepared using a microwave exfoliation method and used in photoelectrochemical cells. Based on experimental and theoretical (DFT) studies, the FL‐BP sheets are found to act as catalytically active sites and show excellent electrocatalytic activity for triiodide reduction in dye‐sensitized solar cells. Importantly, the device fabricated based on the newly designed cobalt sulfide (CoS_x) decorated nitrogen and sulfur co‐doped carbon nanotube heteroelectrocatalyst coated with FL‐BP (FL‐BP@N,S‐doped CNTs‐CoS_x) displayed an impressive photovoltaic efficiency of 8.31 %, outperforming expensive platinum based cells. This work paves the way for using phosphorene‐based electrocatalysts for next‐generation energy‐storage systems.     

Near‐Infrared Active Lead Chalcogenide Quantum Dots: Preparation,Post‐Synthesis Ligand Exchange,and Applications in Solar Cells

Quantum dots (QDs) of lead chalcogenides (e.g. PbS, PbSe, and PbTe) are attractive near‐infrared (NIR) active materials that show great potential in a wide range of applications, such as, photovoltaics (PV), optoelectronics, sensors, and bio‐electronics. The surface ligand plays an essential role in the production of QDs, post‐synthesis modification, and their integration to practical applications. Therefore, it is critically important that the influence of surface ligands on the synthesis and properties of QDs is well understood for their applications in various devices. In this Review we elaborate the application of colloidal synthesis techniques for the preparation of lead chalcogenide based QDs. We specifically focus on the influence of surface ligands on the synthesis of QDs and their solution‐phase ligand exchange. Given the importance of lead chalcogenide QDs as potential light harvesters, we also pay particular attention to the current progress of these QDs in photovoltaic applications.     

Gate‐controlled metal–insulator transition in the LaAlO3/SrTiO3 system with sub‐critical LaAlO3 thickness

We studied the electrical conduction in the LaAlO₃/SrTiO₃ (LAO/STO) interface electron system with a sub‐critical LAO layer thickness of ～3.5 unit cells (uc). It was found that the true dividing point between metallic and insulating behaviour without gating lies near the LAO thickness of 3.5 uc. Our marginally metallic 3.5 uc sample showed a sharp transition to insulating state at temperatures which strongly depended on the applied negative back‐gate voltage. The superior gate‐controllability of the sample was attributed to its sheet carrier density which was an order of magnitude lower than those of conducting LAO/STO samples with 4 uc or more of LAO layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rate coefficients and ClO radical yields in the reaction of O(1D) with CClF2CCl2F,CCl3CF3, CClF2CClF2, and CCl2FCF3

Rate coefficients, k, and ClO radical product yields, Y, for the gas‐phase reaction of O(¹D) with CClF₂CCl₂F (CFC‐113) (k₂), CCl₃CF₃ (CFC‐113a) (k₃), CClF₂CClF₂ (CFC‐114) (k₄), and CCl₂FCF₃ (CFC‐114a) (k₅) at 296 K are reported. Rate coefficients for the loss of O(¹D) were measured using a competitive reaction technique, with n‐butane (n‐C₄H₁₀) as the reference reactant, employing pulsed laser photolysis production of O(¹D) combined with laser‐induced fluorescence detection of the OH radical temporal profile. Rate coefficients were measured to be k₂ = (2.33 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₃ = (2.61 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₄ = (1.42 ± 0.25) × 10^?10 cm³ molecule^?1 s^?1, and k₅ = (1.62 ± 0.30) × 10^?10 cm³ molecule^?1 s^?1. ClO radical product yields for reactions (2)–(5) were measured using pulsed laser photolysis combined with cavity ring‐down spectroscopy to be 0.80 ± 0.10, 0.79 ± 0.10, 0.85 ± 0.12, and 0.79 ± 0.10, respectively. The quoted errors in k and Y are at the 2σ (95% confidence) level and include estimated systematic errors. © 2011 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America

Int J Chem Kinet 43: 393–401, 2011     

Rate Coefficient for the Gas‐Phase OH + CHF=CF2 Reaction between 212 and 375 K

Rate coefficients, k(T), for the OH + CHF=CF₂ (trifluoroethylene, HFO‐1123) gas‐phase reaction were measured under pseudo–first‐order conditions using pulsed laser photolysis to produce OH radicals and pulsed laser induced fluorescence to measure the OH radical temporal profile. Rate coefficients were measured over the temperature range 212–375 K at total pressures between 20 and 500 Torr (He, N₂ bath gas). The rate coefficient was found to be independent of pressure over this range of pressure with a temperature dependence that is described by the Arrhenius expression (3.04 ± 0.30) × 10^–12 exp[(312 ± 25)/T] cm³ molecule^–1 s^–1 with k(296 K) measured to be (8.77 ± 0.80) × 10^–12 cm³ molecule^–1 s^–1 (quoted uncertainties are 2σ and include estimated systematic errors). Rate coefficients for the reaction of CHF=CF₂ with ¹⁸OH and OD were also measured as part of this study at 296 and 373 K and a total pressure of ～25 Torr (He). The isotope measurements were used to evaluate the observed OH radical regeneration. CHF=CF₂ is a very short‐lived substance with an atmospheric lifetime of ～1 day with respect to OH reactive loss, whereas the actual lifetime of CHF=CF₂ will depend on the time and location of its emission. The global warming potential for CHF=CF₂ on the 100‐year time horizon (GWP₁₀₀) was estimated using the present results and a lifetime correction factor to be 3.9 × 10^?3.     

Atmospheric chemistry of (Z)-CF3CH═CHCF3: OH radical reaction rate coefficient and global warming potential

Rate coefficients, k, for the gas-phase reaction of the OH radical with (Z)-CF(3)CH═CHCF(3) (cis-1,1,1,4,4,4-hexafluoro-2-butene) were measured under pseudo-first-order conditions in OH using pulsed laser photolysis (PLP) to produce OH and laser-induced fluorescence (LIF) to detect it. Rate coefficients were measured over a range of temperatures (212-374 K) and bath gas pressures (20-200 Torr; He, N(2)) and found to be independent of pressure over this range of conditions. The rate coefficient has a non-Arrhenius behavior that is well-described by the expression k(1)(T) = (5.73 ± 0.60) × 10(-19) × T(2) × exp[(678 ± 10)/T] cm(3) molecule(-1) s(-1) where k(1)(296 K) was measured to be (4.91 ± 0.50) × 10(-13) cm(3) molecule(-1) s(-1) and the uncertainties are at the 2σ level and include estimated systematic errors. Rate coefficients for the analogous OD radical reaction were determined over a range of temperatures (262-374 K) at 100 Torr (He) to be k(2)(T) = (4.81 ± 0.20) × 10(-19) × T(2) × exp[(776 ± 15)/T], with k(2)(296 K) = (5.73 ± 0.50) × 10(-13) cm(3) molecule(-1) s(-1). OH radical rate coefficients were also measured at 296, 345, and 375 K using a relative rate technique and found to be in good agreement with the PLP-LIF results. A room-temperature rate coefficient for the O(3) + (Z)-CF(3)CH═CHCF(3) reaction was measured using an absolute method with O(3) in excess to be <6 × 10(-21) cm(3) molecule(-1) s(-1). The atmospheric lifetime of (Z)-CF(3)CH═CHCF(3) due to loss by OH reaction was estimated to be ~20 days. Infrared absorption spectra of (Z)-CF(3)CH═CHCF(3) measured in this work were used to determine a (Z)-CF(3)CH═CHCF(3) global warming potential (GWP) of ~9 for the 100 year time horizon. A comparison of the OH reactivity of (Z)-CF(3)CH═CHCF(3) with other unsaturated fluorinated compounds is presented.