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1.
Modulated charge separation across (MO)/CH3NH3PbI3 and (MO)/PbI2/CH3NH3PbI3 (MO = TiO2, MoO3) interfaces was investigated by surface photovoltage (SPV) spectroscopy. Perovskite layers were deposited by solution‐based one‐step preparation and two‐step preparation methods. An unreacted PbI2 layer remained at the interface between the metal oxide and CH3NH3PbI3 for two‐step preparation. For the two‐step preparation on TiO2, the SPV signal related to absorption in CH3NH3PbI3 increased in comparison to the one‐step preparation due to electron transfer from CH3NH3PbI3 via PbI2 into TiO2 whereas the SPV signal related to defect transitions decreased. For the one‐step preparation on MoO3, holes photogenerated in CH3NH3PbI3 recombined with electrons in MoO3. In contrast, a hole transfer from CH3NH3PbI3 towards MoO3 was blocked by the PbI2 interlayer for the two‐step preparation on MoO3. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)  相似文献   

2.
Photocatalytic experiment results under visible light demonstrate that both TiO2 and Cu2O have low activity for brilliant red X-3B degradation and neither can produce H2 from water splitting. In comparison, TiO2/Cu2O composite can do the both efficiently. Further investigation shows that the formation of Ti3+ under visible light has great contribution. The mechanism of photocatalytic reaction is proposed based on energy band theory and experimental results. The photogenerated electrons from Cu2O were captured by Ti4+ ions in TiO2 and Ti4+ ions were further reduced to Ti3+ ions. Thus, the photogenerated electrons were stored in Ti3+ ions as the form of energy. These electrons trapped in Ti3+ can be released if a suitable electron acceptor is present. So, the electrons can be transferred to the interface between the composite and solution to participate in photocatalytic reaction. XPS spectra of TiO2/Cu2O composite before and after visible light irradiation were carried out and provided evidence for the presence of Ti3+. The image of high-resolution transmission electron microscopy demonstrates that TiO2 combines with Cu2O tightly. So, the photogenerated electrons can be transferred from Cu2O to TiO2.  相似文献   

3.
The aminoxyl radical 6‐trifluoromethyl‐benzotriazol‐N‐oxyl (TFNO) has been generated from the parent hydroxylamine 6‐CF3‐1‐hydroxy‐benzotriazole (TFBT) by one‐electron oxidation with a CeIV salt and characterized by spectrophotometry and cyclic voltammetry (CV). Rate constants of H‐abstraction (kH) by TFNO from a number of H‐donor benzylic substrates have been determined spectrophotometrically in MeCN solution at 25 °C. A radical H‐atom transfer (HAT) route of oxidation is substantiated for TFNO by several pieces of evidence. The kinetic data also testify the relevance of stereoelectronic effects upon the HAT reactivity of TFNO. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

4.
Oxidation of acetonitrile has been studied in a flow reactor in the absence and presence of nitric oxide. The experiments were conducted at atmospheric pressure in the temperature range 1150–1450 K, varying the excess air ratio from slightly fuel-lean to very lean. Oxidation of CH3CN was slow below 1300 K. Nitric oxide, hydrogen cyanide and nitrous oxide were detected as important products. A detailed chemical kinetic model for oxidation of acetonitrile was developed, based on a critical evaluation of data from literature. The rate coefficients for the reactions of CH3CN and CH2CN with O2 were calculated from ab initio theory. Modeling predictions were in satisfactory agreement with experiments. Calculations were sensitive to thermal dissociation of CH3CN and to the branching fraction for CH3CN + OH to CH2CN + H2O and HOCN + CH3, respectively. More work is desirable for these steps, as well as for reactions of CH2CN and HCCN.  相似文献   

5.
In a TiO2–perovskite heterojunction solar cell (TiO2–PHSC), besides the perovskite CH3NH3PbX3, TiO2 as one side of the TiO2/CH3NH3PbX3 heterojunction also plays an important role in the photovoltaic effect. In order to improve the performance of the TiO2–PHSC with the structure of glass/FTO/compact TiO2/mesoporous TiO2/CH3NH3PbI3–xClx /poly‐TPD (poly(N,N ′‐bis(4‐butylphenyl)‐N,N ′‐bis(phenyl)benzidine))/Au, a 2 nanometer thick Cs2CO3 layer is thermally evaporated on the mesoporous TiO2 layer. The short‐circuit current density (Jsc) raises from 17.7 mA cm–2 to 18.9 mA cm–2, the open‐circuit voltage (Voc) from 0.81 V to 0.87 V, and the fill factor (FF) from 55.2% to 67.3%; as a result, the power conservation efficiency (PCE) increases from 8.0% to 11.1% under AM 1.5G solar illumination (100 mW cm–2). Moreover, in a TiO2–PHSC free of mesoporous TiO2, where Cs2CO3 is evaporated on the compact TiO2 layer, the Jsc, Voc, FF and PCE values increase from 16.0 mA cm–2, 0.83 V, 50.8% and 6.7% to 17.9 mA cm–2, 0.90 V, 59.3%, and 9.5%, respectively. The reasons of the PCE increase for either the first kind of TiO2–PHSC or the mesoporous‐TiO2‐free TiO2–PHSC with a nanometer‐thick Cs2CO3 layer on mesoporous TiO2 or compact TiO2 are discussed. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)  相似文献   

6.
Naphthalene and biphenyl dianions are interesting compounds that can be obtained by double reduction of the corresponding arenes in solution with certain alkali metals. These dianions are highly reactive and rather elusive species with very high laying and highly delocalized electrons. They share many aspects of the reactivity of the alkali metal they originated from and consequently behave primarily as strong electron transfer (ET) reagents. We report here kinetic evidence for a different type of reactivity in their alkylation reactions with alkyl fluorides. By using cyclopropylmethyl fluoride (c‐C3H5CH2F) as a very fast radical probe, we were able to settle that this alkylation does not involve the classical electron transfer reaction followed by radical coupling between diffusing radicals, but supports the alternative SN2 concerted mechanism, discerning thus this mechanistic SN2‐ET dichotomy. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

7.
Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids' polarity. This is accomplished by investigating the Raman bandshape of the ν (CN) band, corresponding to the CN stretching mode of CH3CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH3CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1‐alkyl‐3‐methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the ν (CN) band of CH3CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the ν (CN) band were corroborated by the analysis of the symmetric ν1 (CD3 ) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
Sulfide alkoxy radicals are important intermediates during the partial oxidation of alkyl sulfides in atmospheric chemistry and in combustion. The atmospheric reaction sequence to formation of the alkoxy radicals includes (1) initial reaction with OH to create a radical on a carbon site, (2) the carbon radical then associates with 3O2 to form a peroxy radical, and (3) an NO radical reacts with the peroxy radical to form an alkoxy radical (RO?) plus NO2. This study determines structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (ΔfH°, S°, and Cp(T)) of 3 corresponding alcohols HOCH2SCH2CH3, CH3SCH(OH)CH3, and CH3SCH2CH2OH of methyl ethyl sulfides studied in order to characterize the thermochemistry of the respective alkoxy radicals. The lowest energy molecular structures were calculated using the B3LYP density functional level of theory with the 6‐311G(2d,d,p) basis set. Standard enthalpies of formation (Δf298) for the radicals and their parent molecules were calculated using B3LYP/6‐31 + G(2d,p), CBS‐QB3, M062x/6‐311 + g(2d,p), and G3MP2B3 methods. Isodesmic reactions were used to determine ?fH° values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31 + G(d,p) level theory. The contributions for S°298 and Cp(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by CBS‐QB3 calculations, with contributions from torsion frequencies replaced by internal rotor contributions. Group additivity and hydrogen bond increment values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxide molecules and their radicals.  相似文献   

9.
The redundancy-free internal valence force field (RFIVFF) of acetonitrile is reported using CNDO/force method. The initial force field is set up by taking the interaction and bending force constants from CNDO force field and transferring stretching force constants from the force fields of chemically related molecules. The final force field is obtained by refining the initial force field using vibrational harmonic frequencies of CH3CN,13CH3CN, CH3 13CN, CH3C15N, CD3CN and CD3 13CN. The final force field thus obtained is found to be excellent on the basis of frequency fit and potential energy distribution.  相似文献   

10.
In this work, we demonstrate nano‐structured silver particles photo‐reduced from silver nitride (AgNO3) solution using visible‐light‐activated titanium dioxide (TiO2), which can be a convenient and effective substrate for surface enhanced Raman spectroscopy (SERS) observation. Visible‐light‐activated carbon‐containing TiO2 nanoparticles are applied to photo‐reduce and form nano‐structured silver from AgNO3 upon visible‐light illumination. Photo‐reduced nano‐structured silver is used as an active substrate for SERS studies of TiO2 as well as nano diamond and TiO2. The photo reduction of AgNO3 and SERS observation can be obtained by simultaneously using the same visible laser excitation. The coexistence of the anatase phase with small admixture of the rutile phase in the TiO2 can be observed using SERS. The carbon structure in the carbon‐containing TiO2 was determined to be sp2 type carbon bonding by SERS. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

11.
In this paper, pure and Zn‐doped TiO2 nanoparticles (NPs) with various content of Zn were prepared by a sol–hydrothermal method and were employed as active substrates for surface‐enhanced Raman scattering (SERS). On the 3% Zn‐doped TiO2 substrate, 4‐mercaptobenzoic acid(4‐MBA) molecules exhibit a higher SERS intensity by a factor of 6, as compared with the native enhancement of 4‐MBA adsorbed on undoped TiO2 NPs. Moreover, the higher SERS activity was still observed on the 3% Zn‐doped TiO2 NPs at temperature even up to 125 °C. These results indicate that an appropriate amount of Zn doping can improve the SERS performances of TiO2 SERS‐active substrates. The introduction of Zn dopant can enrich the surface states (defects) of TiO2 and improve the separation efficiency of photo‐generated charge carriers (electrons and holes) in TiO2, according to measurements of X‐ray diffraction, UV‐visible diffuse reflectance spectroscopy, and photoluminescence, which are responsible for the influence of Zn dopant on the improved SERS performances of TiO2 NPs. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

12.
The B‐band resonance Raman spectra of 2(1H)‐pyridinone (NHP) in water and acetonitrile were obtained, and their intensity patterns were found to be significantly different. To explore the underlying excited state tautomeric reaction mechanisms of NHP in water and acetonitrile, the vibrational analysis was carried out for NHP, 2(1D)‐pyridinone (NDP), NHP–(H2O)n (n = 1, 2) clusters, and NDP–(D2O)n (n = 1, 2) clusters on the basis of the FT‐Raman experiments, the B3LYP/6‐311++G(d,p) computations using PCM solvent model, and the normal mode analysis. Good agreements between experimental and theoretically predicted frequencies and intensities in different surrounding environments enabled reliable assignments of Raman bands in both the FT‐Raman and the resonance Raman spectra. The results indicated that most of the B‐band resonance Raman spectra in H2O was assignable to the fundamental, overtones, and combination bands of about ten vibration modes of ring‐type NHP–(H2O)2 cluster, while most of the B‐band resonance Raman spectra in CH3CN was assigned to the fundamental, overtones, and combination bands of about eight vibration modes of linear‐type NHP–CH3CN. The solvent effect of the excited state enol‐keto tautomeric reaction mechanisms was explored on the basis of the significant difference in the short‐time structural dynamics of NHP in H2O and CH3CN. The inter‐molecular and intra‐molecular ESPT reaction mechanisms were proposed respectively to explain the Franck–Condon region structural dynamics of NHP in H2O and CH3CN.Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

13.
Au nanoparticles deposited on mesoporous TiO2-B nanofibers have been prepared, characterized, and used to catalyze photoreactions of iodomethane. High-density gold-particle deposition on TiO2-B is obtained by electrostatic and/or chemical force between the particles of TiO2-B and Au capped with -SC(H)(CO2H)(CH2CO2H) through pH control. The capping groups on the gold particles can be removed after 400 °C calcination. It is found that the nature of the inorganic acids used for pH adjustment has effects on particle morphology and deposition. Two other methods, i.e., preparation of TiO2-B nanofibers in the presence of gold particles and preparation of gold nanoparticles in the presence of TiO2-B particles (deposition-precipitation method), are also investigated. However, the former method produces a low-density deposition and the latter one induces a morphology change of the TiO2-B and an increase of the Au in size. Fourier transform infrared spectroscopy has been employed to study and to compare the photoreactions of CH3I on TiO2-B and Au/TiO2-B and the effect of O2. The presence of gold particles on TiO2-B increases the efficiency of CH3I photodegradation, forming adsorbed methoxy and formate. The role of gold is also discussed.  相似文献   

14.
The reaction channels of di‐tert‐butylcarbene ( 2 ), its radical anion, ( 3 ) and its radical cation ( 4 ) were investigated theoretically by using DFT/B3LYP with 6‐31+G(d) basis set and 6‐311+G(2d,p) for single point energy calculations. Conversion of the neutral carbene 2 to the charged species 3 and 4 results in significant geometric changes. In cation 4 two different types of C? (CH3)3 bonds are observed: one elongated sigma bond called “axial” with 1.61 Å and two normal sigma bonds with a bond length of 1.55 Å. Species 2 and 4 have an electron deficient carbon center; therefore, migration of CH3 and H is observed from adjacent tert‐butyl groups with low activation energies in the range of 6–9 kcal/mol like similar Wagner–Meerwein rearrangements in the neopentyl‐cation system. Neutral carbene 2 shows C? H insertion to give a cyclopropane derivative with an activation energy of 6.1 kcal/mol in agreement with former calculations. Contrary to species 2 and 4 , the radical anion 3 has an electron rich carbon center which results in much higher calculated activation energies of 26.3 and 42.1 kcal/mol for H and CH3 migrations, respectively. NBO charge distribution indicates that the hydrogen migrates as a proton. The central issue of this work is the question: how can tetra‐tert‐butylethylene ( 1 ) be prepared from reaction of either species 2 , 3 , or 4 as precursors? The ion–ion reaction between 3 and 4 to give alkene 1 with a calculated reaction enthalpy of 203.5 kcal/mol is extremely exothermic. This high energy decomposes alkene 1 after its formation into two molecules of carbene 2 spontaneously. Ion–molecule reaction of radical anion 3 with the neutral carbene 2 is a much better choice: via a proper oriented charge–transfer complex the radical anion of tetra‐tert‐butylethylene (11) is formed. The electron affinity of 1 was calculated to be negligible. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

15.
A new kind of continuous-wave (CW) cold molecular beam, methyl cyanide (CH3CN) beam, is generated by a bent electrostatic quadrupole guiding. The Stark shift of rotational energy levels of CH3CN molecule and its population distribution are calculated, and the dynamic processes of electrostatic guiding and energy filtering of CH3CN molecules from a gas source with room temperature (300 K) are simulated by Monte Carlo Method. The study showed that the longitudinal and transversal temperatures of output cold CH3CN beam could be about ~2 K and ~ 420 mK, and the corresponding guiding efficiency was about 10?5 as the guiding voltage was 3 kV. Furthermore, the temperature of the guided molecules and its guiding efficiency can be controlled by adjusting the guiding voltages applied on electrodes.  相似文献   

16.
A new kind of continuous-wave (CW) cold molecular beam, methyl cyanide (CH3CN) beam, is generated by a bent electrostatic quadrupole guiding. The Stark shift of rotational energy levels of CH3CN molecule and its population distribution are calculated, and the dynamic processes of electrostatic guiding and energy filtering of CH3CN molecules from a gas source with room temperature (300 K) are simulated by Monte Carlo Method. The study showed that the longitudinal and transversal temperatures of output cold CH3CN beam could be about ∼2 K and ∼ 420 mK, and the corresponding guiding efficiency was about 10−5 as the guiding voltage was 3 kV. Furthermore, the temperature of the guided molecules and its guiding efficiency can be controlled by adjusting the guiding voltages applied on electrodes.   相似文献   

17.
Photocatalyst‐assisted degradation of organic pollutants, which exhibits a novel strategy for solar‐energy utilization, possesses enormous potential in various applications. Extending the light‐absorption range in the spectrum of sunlight and improving light‐conversion efficiency are always primary issues to enhance the catalytic performance of these photocatalysts. Herein, a new structure of gold‐nanorod‐decorated TiO2 rambutan‐like microspheres is designed, which exhibits superior photocatalytic ability toward Rhodamine B in the range of visible light due to the 3D distribution of the TiO2 branches on the surface of the microspheres, which prompts the multireflection of photons. The absorption rate of photons is thereby tremendously enhanced. This is beneficial for the generation of hot electrons originating from the localized surface plasmonic resonance of Au nanorods, which can be used to both initiate the reaction and produce the photothermal effect. Hot electrons generated by a single Au nanorod in microspheres to initiate the degradation reaction can be as high as 2.5 times of those in the nanowires' counterpart. Moreover, the heating power of a single Au nanorod in microspheres reaches up to 4.4 times higher than that in nanowires, which further accelerates the degradation rate. The reaction pathway of visible‐light‐assisted RhB degradation catalyzed by Au/TiO2 microspheres goes through an initial N‐deethylation process instead of the complete cycloreversion catalyzed by pure TiO2 microspheres under UV irradiation. This strategy of structure design for improved photon absorption, which achieves high degradation rate and photothermal effect, is promising for the development of novel photocatalysts.  相似文献   

18.
《Current Applied Physics》2019,19(11):1266-1270
Large-grain-size and void-free CH3NH3PbI3 films with bilayer structure are fabricated by spin-coating a PbI2 layer onto a mesoporous TiO2 layer and sequentially spraying CH3NH3I (methylammonium iodide, MAI) multilayers. The sprayer is controlled by a homemade three-axis computer numerical control machine; thus, the substrates are coated by successive parallel passes achieved by moving the nozzle. Spray deposition at the optimal spray rate and substrate temperature produces a large-grain-size and void-free methylammonium lead iodide (MAPbI3) bilayer structure. The mesoporous TiO2 layer plays an important role in electron transport by preventing the return of electrons to the perovskite layer and decreasing the contact resistance at the perovskite/compact TiO2/fluorine tin oxide interface. When the films are incorporated into a solar cell device with a conductive carbon counter electrode, a maximum power conversion efficiency of 10.58% is realised.  相似文献   

19.
4‐Stilbenecarboxaldehyde (4SCA) at pH 3 was added to TiO2 anatase to form a new catalyst where the aldehyde carbonyl group reacts with the TiO2‐OH to form the corresponding acetal (4SCA‐TiO2). 4SCA‐TiO2 significantly retards the electron recombination when it is illuminated with ultraviolet B light because of the formation of a stable radical anion·?4SCA‐TiO2 that we have detected spectroelectrochemically. The light excited electron on the catalysis is transferred relatively slow to solution. Therefore, the electron transfer to solution is the rate‐limiting step for water‐dissolved organic compound degradation when 4SCA‐TiO2 is used as photocatalyst. For instance, degradation rate constants using naphthalene (Naph) and p‐nitrophenol (PNP) in an ample pH range support the proposal. Accordingly, rate constants are faster when the standard redox potential of the involved electron acceptor in the solution increases. In fact, this condition can be tuned to promote reactivity. The affinity between the organics being degraded and 4SCA‐TiO2 also influences on the degradation rate constants.  相似文献   

20.
《Surface science》1986,175(3):445-464
The adsorption and reaction of acetonitrile (CH3CN) on clean and oxygen covered Ag(110) surfaces has been studied using temperature programmed reaction spectroscopy (TPRS), isotope exchange, chemical displacement reactions and high resolution electron energy loss spectroscopy (EELS). On the clean Ag(110) surface, CH3CN was reversibly adsorbed, desorbing with an activation energy of 10 kcal mol-1 at 166 K from a monolayer state and at 158 K from a multilayer state. Vibrational spectra of multilayer, monolayer and sub-monolayer CH3CN were in excellent agreement with that of gas phase CH3CN indicating that CH3CN is only weakly bonded to the clean Ag(110) surface. On the partially oxidized surface CH3CN reacts with atomic oxygen to form adsorbed CH2CN, OH and H2O in addition to forming another molecular adsorption state with a desorption peak at 240 K. This molecular state shows a CN stretching frequency of 1840 cm-1, which is indicative of substantial rehybridization of the CN bond and is associated with side-on coordination via the π system. The CH2CN species is stable up to 430 K, where C-H bond breaking and reformation begins, leading to the formation of CH3CN at 480 K and HCN at 510 K and leaving only carbon on the surface. In the presence of excess oxygen atoms C-H bond breaking and reformation is more facile leading to additional desorption peaks for CH3CN and H2O at 420 K. This destabilizing effect of O(a) on Ch2CN(a) is explained in terms of an anionic (CH2CN-1) species. Comparison of the vibrational spectra from CH2CN(a) and CD2CN(a) supports the following assignment for the modes of adsorbed CH2CN: ν(Ag-C) 215: δ(CCN) 545; ϱt(CH2) 695; ϱw(CH2) 850; ν(C-C) 960; ϱr(CH2) 1060; δ(CH2) 1375; ν(CN) 2075; and ν(CH2) 2940 cm-1. These results serve to further indicate the wide applicability of the acid-base reaction concept for reactions between gas phase Brönsted acids and adsorbed oxygen atoms on solver surfaces.  相似文献   

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