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Li–S batteries can meet the demand of market development in terms of high energy density, but the notorious 'shuttle effect' and lithium dendrites pose a great threat to their cycling and safety performance, and greatly hinder their commercialization process. Under high sulfur loadings and high current densities, unsatisfactory cycling performances are also headache issues. Here, modified separators (SPLFPPD) with LiFePO4 (LFP) and Super P coating on the original separators (DKJ-14) are prepared to solve the above problems. The SPLFPPD has the advantages of a physical barrier to the polysulfides and promoting the catalytic conversion of polysulfides (S2− and sulfides). Besides, the SPLFPPD can enable the uniform deposition of lithium ions, increase ionic conductivities, and fully utilize active S substances. The capacity attenuation of the assembled Li–S batteries with the SPLFPPD is 0.062% per cycle at 1C after 800 cycles, and 0.045% per cycle at 5C after 1000 cycles. The specific capacity can be stable up to about 500 mA h g−1 after 400 cycles at 0.2C with a high S loading of 4.0 mg cm−2. After 100 cycles, no signs of corrosion or lithium dendrites were observed. This work provides a feasible way to prepare commercial separators for high-performance Li–S batteries. [ABSTRACT FROM AUTHOR]

A facile and practical silver-mediated radical cascade cyclization of N-allylamides with sodium sulfinates is developed, giving a series of sulfonated oxazolines in moderate to good yields. This transformation involves a radical process via intermolecular sulfonylation of alkenes and intramolecular cyclization. This reaction system could be also applied to access sulfonated dihydrofurans. [ABSTRACT FROM AUTHOR]

Herein, the origin and evolution mechanism of N2O formation over the MnFeOx spherical catalyst were investigated in detail, accompanied by a comparison analysis of pristine MnOx and FeOx catalysts. The results showed that the MnFeOx catalyst possessed higher catalytic activity but poorer N2 selectivity than the sole oxide catalysts, and the N2O concentration could even reach 300 ppm over 175 °C. Further activation tests under separate NH3/NO oxidation conditions revealed the N2O accumulation of the MnFeOx catalyst that was primarily derived from the NSCR pathway below 150 °C and then gradually turned to NH3 over-oxidation with temperature. The coupling of Mn and Fe cations induced electron migration and released more Mn4+ and Os, contributing to the upgraded redox capacity, which served as the inherent motivation of high activity but poor N2 selectivity over the MnFeOx catalyst. For the NH3 over-oxidation pathway, both gaseous O and catalyst oxygen acted as the oxidizers, and the double –NH2/NH species with the assistance of O was deemed as the restricted step for N2O generation. For the NSCR pathway, the byproduct N2O was generated through both E–R and L–H mechanisms, and the former contributed to more N2O. In addition, the kinetic analysis further verified the obtained conclusions. Finally, a possible mechanism model of N2O origins over the MnFeOx catalyst was proposed. [ABSTRACT FROM AUTHOR]

State-to-state photodissociation of CO2(v2 = 0 and 1) at 157 nm via the O(1D) + CO(X1Σ+) channel was studied by using the sliced velocity map imaging technique. Both the O(1D) and CO(X1Σ+) products were detected by (2 + 1) resonance enhanced multiphoton ionization (REMPI). Detection of CO via the B1Σ+ ←← X1Σ+ transition allowed ro-vibrational state-selective detection, and combined with imaging, the fragment energy and angular distributions have been derived. For CO(v = 0 and 1‖j) products from the CO2(v2 = 0) molecule, the angular distributions of low-j CO display positive anisotropic parameters (about 0.8); with j increasing, the product anisotropic parameters gradually reduce to zero. While for CO(v = 0 and 1‖j) products from the vibrational excited CO2(v2 = 1) molecule, the angular distributions of low-j CO also display positive anisotropic parameters; with j increasing, the product anisotropic parameters first decrease to zero and then become negative (about −0.5). Experimental results show that the observed variation of the product angular distribution with the rotational quantum number of CO is consistent with trends predicted by a classical model for non-axial fragment recoil. The results support advanced theoretical predictions of a predominantly parallel transition to the bent 21A′ excited state of CO2, where bending introduces torque during the direct dissociation process. [ABSTRACT FROM AUTHOR]

The excited-state decay dynamics of 2-ethylpyrrole following UV excitation in the wavelength range of 254.8–218.0 nm is investigated in detail using the femtosecond time-resolved photoelectron imaging method. The time-resolved photoelectron spectra and photoelectron angular distributions at all pump wavelengths are carefully analysed and the following picture is derived: at the longest pump wavelengths (254.8, 248.3 and 246.1 nm), 2-ethylpyrrole is excited to the S1(1πσ*) state having a lifetime of about 50 fs. At 248.3, 246.1 and 237.4 nm, another excited state of Rydberg character is excited. The lifetime of this state is ∼570 fs at 237.4 nm and becomes slightly longer at other two pump wavelengths. At the shortest pump wavelengths (230.8 and 218.0 nm), 2-ethylpyrrole is excited to a state which is tentatively assigned to the 11ππ* state, having a lifetime of 75 ± 15 and 48 ± 10 fs for the longer and shorter pump wavelengths, respectively. Internal conversion to the S1(1πσ*) state might be one of the decay mechanisms of the 11ππ* state. [ABSTRACT FROM AUTHOR]

State-to-state photodissociation of carbon dioxide (CO2) via the 3p1Πu Rydberg state was investigated by the time-sliced velocity map ion imaging technique (TSVMI) using a tunable vacuum ultraviolet free electron laser (VUV FEL) source. Raw images of the O(1S) products resulting from the O(1S) + CO(X1Σ+) channel were acquired at the photolysis wavelengths between 107.37 and 108.84 nm. From the vibrational resolved O(1S) images, the product total kinetic energy releases and the vibrational state distributions of the CO(X1Σ+) co-products were obtained, respectively. It is found that vibrationally excited CO co-products populate at as high as v = 6 or 7 while peaking at v = 1 and v = 4, and most of the individual vibrational peaks present a bimodal rotational structure. Furthermore, the angular distributions at all studied photolysis wavelengths have also been determined. The associated vibrational-state specific anisotropy parameters (β) exhibit a photolysis wavelength-dependent feature, in which the β-values observed at 108.01 nm and 108.27 nm are more positive than those at 107.37 nm and 107.52 nm, while the β-values have almost isotropic behaviour at 108.84 nm. These experimental results indicate that the initially prepared CO2 molecules around 108 nm should decay to the 41A′ state via non-adiabatic coupling, and dissociate in the 41A′ state to produce O(1S) + CO(X1Σ+) products with different dissociation time scales. [ABSTRACT FROM AUTHOR]

Photodissociation dynamics of H2O and D2O via the D~; state by one-photon excitation have been investigated using the H/D atom Rydberg tagging time-of-flight technique. The TOF spectra of the H/D-atom product in both parallel and perpendicular polarizations have been measured. Product translational energy distributions and angular distributions have been derived from TOF spectra. By simulating these distributions, quantum state distributions of the OH/OD product as well as the state-resolved angular anisotropy parameters were determined. The most important pathway of H2O/D2O dissociation via the D~; state leads to highly rotationally excited OH/OD(X, v = 0) products, while vibrationally excited OH/OD products with v ≥ 1 comprise only one third of the total OH/OD(X) population. The branching ratios of OH(A)/OH(X) and OD(A)/OD(X) have also been determined, 1.0/3.0 for H2O at 122.12 nm and 1.0/2.2 for D2O at 121.95 nm, which are reasonably consistent with the values predicted by the previous theory. [ABSTRACT FROM AUTHOR]

The ultrafast decay dynamics of water molecules excited to D˜′1B1 and D˜′′1A2 states is studied by combining two-photon excitation and time-resolved photoelectron imaging methods. The lifetime of the D˜′1B1(000) state of H2O (D2O) is determined to be 1.54 ± 0.1 (22.6 ± 1.6) ps, consistent with a previous high-resolution spectroscopic study. The H2O D˜′′1A2(000) state decays with a lifetime of 4.1 ± 0.2 ps, while in the D2O D˜′′1A2(000) state, two independent decay pathways are observed, with time constants of 0.55 ± 0.1 and 13 ± 1 ps, respectively. The former is proposed to be associated with a hitherto undocumented D˜′′→ C˜ pathway, induced by Coriolis interaction. [ABSTRACT FROM AUTHOR]

A novel peroxidase-mimicking DNAzyme-based colorimetric homogenous bioassay is developed for kanamycin detection. Aptamer biorecognition triggers DNAzyme liberation from DNA duplexes for “off–on” signal transduction. The special hairpin structure of the aptamer–kanamycin biocomposite enables Exo III-assisted target recycling for signal amplification. [ABSTRACT FROM AUTHOR]

Elaborate design of highly active catalysts from earth-abundant elements is important for the development of water-splitting devices. We have synthesized {2̅ 1 1} high index-faceted Ni12P5 nanoplates and Ni12P5 spherical nanoparticles (SNPs) by the one-step solvothermal method. The Ni12P5 nanoplates show enhanced hydrogen evolution reaction activity with a lower overpotential of −128 mV and a smaller Tafel slope of 60.6 mV dec−1 compared to Ni12P5 SNPs. Stability tests reveal exceptional durability of the catalyst. This study offers an attractive catalytic material for large-scale hydrogen production technology. [ABSTRACT FROM AUTHOR]

The ultrafast excited-state dynamics of 2,5-dimethylpyrrole following excitation at wavelengths in the range of 265.7–216.7 nm is studied using the time-resolved photoelectron imaging method. It is found that excitation at longer wavelengths (265.7–250.2 nm) results in the population of the S1(1πσ*) state, which decays out of the photoionization window in about 90 fs. At shorter pump wavelengths (242.1–216.7 nm), the assignments are less clear-cut. We tentatively assign the initially photoexcited state(s) to the 1π3p Rydberg state(s) which has lifetimes of 159 ± 20, 125 ± 15, 102 ± 10 and 88 ± 10 fs for the pump wavelengths of 242.1, 238.1, 232.6 and 216.7 nm, respectively. Internal conversion to the S1(1πσ*) state represents at most a minor decay channel. The methyl substitution effects on the decay dynamics of the excited states of pyrrole are also discussed. Methyl substitution on the pyrrole ring seems to enhance the direct internal conversion from the 1π3p Rydberg state to the ground state, while methyl substitution on the N atom has less influence and the internal conversion to the S1(πσ*) state represents a main channel. [ABSTRACT FROM AUTHOR]

The predissociation dynamics of water molecules in the electronic C˜ state were studied using the time-resolved photoelectron imaging method. Both vibrationless and vibrationally excited states in the C˜ electronic state were studied, with an emphasis on the vibrational excitation effects on the predissociation dynamics of the C˜ state. Besides the well-known rotationally and non-rotationally mediated predissociation pathways (Proc. Natl. Acad. Sci. U. S. A., 2008, 105, 19148), an accidental resonance mediated predissociation pathway for the first bending mode excited state in the C˜ electronic state of H2O is revealed, providing an excellent example of competition between non-adiabatic decay pathways involving at least five electronic states. [ABSTRACT FROM AUTHOR]

The ultrafast excited-state dynamics of 2,4-dimethylpyrrole following excitation at wavelengths in the range of 255.8–199.7 nm are studied using the time-resolved photoelectron imaging method. It is found that excitation at longer wavelengths (255.8, 250.0, 246.0 and 242.0 nm) results in population of the S1(1πσ*) state, which decays out of the photoionization window in less than 30 fs. At 237.7 nm, the second 1πσ* state is excited, which decays in about 130 fs. At shorter pump wavelengths (231.8, 224.8, 217.5 and 199.7 nm), the assignments are less clear-cut. We tentatively assign the initially photoexcited states to the 1π3p Rydberg states, which decay in about 60 fs, with internal conversion to the S1(1πσ*) state as one of the decay channels. The lifetimes of these 1π3p Rydberg states vary little with the pump wavelengths in this wavelength range. [ABSTRACT FROM AUTHOR]

Silver nanosized particles were grown on the surface and in the channels of mesoporous silica (MCM-41) by stirring a mixture of AgNO3 and polyvinylpyrrolidone (PVP) in ethylene glycol in a 1 : 20 weight ratio with MCM-41 for 1 h. The heterogeneous product was analysed by BET surface area and X-ray powder diffraction measurements, as well as TEM images which indicated that 5 to 20 nm sized Ag particles were on the surface of MCM-41. The dried material, suspended in a mixture of 1,2-dichloroethane and acetonitrile and in the presence of tBuOOH held at 80 °C for 24 h, was capable of the oxidation of the olefins (Z)-cyclooctene, cyclohexene, styrene and indene resulting in a variety of oxidized products. Comparable oxidation was also accomplished in a green solvent mixture consisting of 3% NaCl dissolved in H2O and tBuOH (1 : 1 by volume). The catalyst was active for five sequential cycles. After the first cycle, H2O2 instead of tBuOOH could be used as the radical initiator as the Ag nanoparticles were passivated by the formation of AgCl on the surface. This research illustrates a method of oxygen activation allowing for the transfer of an oxygen atom from the atmosphere onto an olefin, presumably via the formation of a peroxide radical. [ABSTRACT FROM AUTHOR]

Monodispersed NiPt hollow nanospheres with citric acid as surfactant were synthesized by a one-pot wet chemical method in water at room temperature. The diameter is adjustable from 13 to 100 nm with the shell thickness of 2-3 nm, roughly the size of nanocrystallites. The composition is also tunable with the ratio of Ni : Pt from 1: 9 to 9 : 1. A phase formation mechanism is proposed for the controllability of the diameter from the sacrificial templates of intermediate Ni--B amorphous nanocompounds. Molecular dynamic calculations show that 2 nm is the lower-bound shell thickness for a stable hollow spherical structure to avoid distortion or collapse. Electrocatalytic properties for the oxidation of ethylene glycol are measured for 35 nm Ni50Pt50 hollow nanospheres. Its performance is apparently better than that using commercial Pt/C catalyst. This makes it a potential application as a fuel cell catalyst. [ABSTRACT FROM AUTHOR]