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Although progress has been made to improve photocatalytic CO2 reduction under visible light (λ>400 nm), the development of photocatalysts that can work under a longer wavelength (λ>600 nm) remains a challenge. Now, a heterogeneous photocatalyst system consisting of a ruthenium complex and a monolayer nickel-alumina layered double hydroxide (NiAl-LDH), which act as light-harvesting and catalytic units for selective photoreduction of CO2 and H2 O into CH4 and CO under irradiation with λ>400 nm. By precisely tuning the irradiation wavelength, the selectivity of CH4 can be improved to 70.3 %, and the H2 evolution reaction can be completely suppressed under irradiation with λ>600 nm. The photogenerated electrons matching the energy levels of photosensitizer and m-NiAl-LDH only localized at the defect state, providing a driving force of 0.313 eV to overcome the Gibbs free energy barrier of CO2 reduction to CH4 (0.127 eV), rather than that for H2 evolution (0.425 eV).

The electrochemical N2 fixation, which is far from practical application in aqueous solution under ambient conditions, is extremely challenging and requires a rational design of electrocatalytic centers. We observed that bismuth (Bi) might be a promising candidate for this task because of its weak binding with H adatoms, which increases the selectivity and production rate. Furthermore, we successfully synthesized defect-rich Bi nanoplates as an efficient noble-metal-free N2 reduction electrocatalyst via a low-temperature plasma bombardment approach. When exclusively using 1 H NMR measurements with N2 gas as a quantitative testing method, the defect-rich Bi(110) nanoplates achieved a 15 NH3 production rate of 5.453 μg mgBi -1 h-1 and a Faradaic efficiency of 11.68 % at -0.6 V vs. RHE in aqueous solution at ambient conditions.

The regulation of interfacial defects of nanocrystals aligned orderly in a superstructured photocatalyst is an effective approach to improve the photocatalytic performance. However, the synthesis of ordered self-assemblies with abundant interfacial defects and reactive sites is hard to achieve, and applications are limited due to the unclear physicochemical properties, which result from the unique mesocrystalline microstructures. It is reported herein that the photocatalytic properties depend on the interfacial defects of intergrains in anatase TiO2 mesocrystals (TMCs). Research reveals that the photocatalytic activity largely depends on defects, such as lattice distortion and oxygen vacancies, which are located at highly aligned interfaces of intergrains within TMCs. Moreover, the mesocrystalline TiO2 photocatalysts exhibit higher photocatalytic performance in organic degradation and hydrogen evolution, compared with single crystals and polycrystals; this can be ascribed to an appropriate amount of interfacial defects at the intergrains and improved carrier separation efficiency through the highly oriented interfaces. In addition, the photocatalytic performance of the TMCs could be further improved through regulation of defects by undergoing an annealing process under a redox atmosphere. This work can provide an avenue to defect engineering for improved photocatalytic performance.

Although oxygen vacancies (Ov s) play a critical role for many applications of metal oxides, a controllable synthetic strategy for anisotropic Ov s remains a great challenge. Here, a novel strategy is proposed to achieve the regional dual structure with anisotropic Ov s at both the surface and in the interior of TiO2 by constructing amorphous domains. The as-prepared black TiO2 with amorphous domains exhibits superior activity in degrading rhodamine B (RhB) solutions, which can instantly decompose RhB with just a shake. First-principle simulations reveal that subsurface Ov s in TiO2 are energetically favored, resulting in the formation of amorphous domains in the interior region via diffusion of surface-formed Ov s into the subsurface. The stable Ov -induced amorphous domains in TiO2 with enhanced catalytic performances provide a scalable strategy to practical Ov engineering in functional metal oxides.

In this paper, backscattering of 3 to 50-keV positrons on Al, Cu, Ag and Au metallic targets has been systematically investigated using GEANT4 code. The dependence of positron backscattering coefficients on atomic number Z, target thickness, incident energy and angles has been discussed comprehensively. Besides, positron backscattering spectra for those metallic targets at different discrete scattering angles were also studied to provide theoretical basis of the most appropriate scattering angle selected for simulation parameters and specified applied measurement techniques. The impact of atomic number Z of targets on positron backscattering spectra was investigated as well. Simulation results are in reasonable agreement with previous experiment data and theoretical work. Copyright © 2016 John Wiley & Sons, Ltd.

Polyethylene glycol (PEG) of three different molecular weights were used to prepared PEG/PVDF composite membranes for separating organosulphur compounds from n-heptane by pervaporation. All the composite membranes were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) X-ray diffraction (XRD) and positron annihilation spectroscopy (PAS). The effects of operating temperature, feed sulphur content and organosulphur species on performance of PEG/PVDF composite membranes with different molecular weights were investigated. When the feed organosulphur was thiophene, the fluxes decreased with an increase in PEG molecular weights, however, the enrichment factors were in the different order, PEG membrane with molecular weight of 35 000 exhibited highest enrichment factor of 12.59 for thiophene at 85 °C. When the feed organosulphur was 2-Methylthiophene or 2, 5-Dimethylthiophene, it was found that PEG membrane with molecular weight of 100 000 showed highest enrichment factor. The results showed that PEG molecular weights have a considerable effect on separation performance for pervaporation desulphurization. This article is protected by copyright. All rights reserved

An ultrafacile aluminum reduction method is reported herein for the preparation of blue TiO2 nanoparticles (donated as Al-TiO2 , anatase phase) with abundant oxygen deficiency for lithium-ion batteries. Under aluminum reduction, the morphology of the TiO2 nanosheets changes from well-defined rectangular into uniform round or oval nanoparticles and the particle size also decreases from 60 to 31 nm, which can aggressively accelerate the lithium-ion diffusion. Electron paramagnetic resonance (EPR) and positron annihilation lifetime spectroscopy (PALS) results reveal that plentiful oxygen deficiencies relative to the Ti(3+) species were generated in blue Al-TiO2 ; this effectively enhances the electron conductivity of the TiO2 . X-ray photoelectron spectrometry (XPS) analysis indicates that a small peak is observed for the Al-O bond, which probably plays a very important role in the stabilization of the oxygen deficiencies/Ti(3+) species. As a result, the blue Al-TiO2 possesses significantly higher capacity, better rate performance, and a longer cycle life than the white pure TiO2 . Such improvements can be attributed to the decreased particle size, as well as the existence of the oxygen deficiencies/Ti(3+) species.

Solar photocatalysis is a potential solution to satisfying energy demand and its resulting environmental impact. However, the low electron-hole separation efficiency in semiconductors has slowed the development of this technology. The effect of defects on electron-hole separation is not always clear. A model atomically thin structure of single-unit-cell Bi3 O4 Br nanosheets with surface defects is proposed to boost photocatalytic efficiency by simultaneously promoting bulk- and surface-charge separation. Defect-rich single-unit-cell Bi3 O4 Br displays 4.9 and 30.9 times enhanced photocatalytic hydrogen evolution and nitrogen fixation activity, respectively, than bulk Bi3 O4 Br. After the preparation of single-unit-cell structure, the bismuth defects are controlled to tune the oxygen defects. Benefiting from the unique single-unit-cell architecture and defects, the local atomic arrangement and electronic structure are tuned so as to greatly increase the charge separation efficiency and subsequently boost photocatalytic activity. This strategy provides an accessible pathway for next-generation photocatalysts.

As-annealed Fe–1.5 wt%Cu alloys were deformed by cold rolling. Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectra (DBS) were used to analyze the microdefects in the alloy induced by deformation. Cu precipitates were formed uniformly in the alloy after annealing at 1173 K. To investigate the effects of Cu precipitates on the formation and migration of defects, well-annealed pure Fe samples were prepared as a reference. PALS results show that the value of positron lifetime (both long lifetime τ2 and mean lifetime τm) in the alloy is smaller than in pure Fe during deformation. This indicates that Cu precipitates restrain the growth of vacancy clusters. Results of DBS show that the S parameter in pure Fe is larger than in the alloy, and more deformation is needed for the S parameter to be saturated in the alloy.

Diglycidyl ether of bisphenol A (DGEBA)/fluoro-terminated hyperbranched poly(phenylene oxide) (FHPPO) composites with improved mechanical and dielectric performances were prepared by blending a FHPPO with DGEBA. The low-polarity building blocks, abundant fluorinated terminal groups, and the inherent free volume brought by FHPPO efficiently lowered the dielectric constant and the dissipation factor. The free volumes of the cured DGEBA/FHPPO composites, which were quantified by positron annihilation lifetime spectroscopy, increased with the FHPPO loading. The moisture absorption of composites also decreased after the introduction of FHPPO due to the hydrophobicity of fluorinated substituents. Dynamic mechanical analysis tests and scanning electron morphology revealed that FHPPO phase separated from the composites during the curing process. The average diameter of dispersed FHPPO particles increased proportionally with the FHPPO loading. Composites with dispersed particle size of around 150 nm showed the best comprehensive mechanical performance. In addition, incorporation of FHPPO, which has lots of aromatic structures, into DGEBA also increased the thermal stabilities. POLYM. COMPOS., 34:1051-1060, 2013. (c) 2013 Society of Plastics Engineers

Poly(propylene carbonate) (PPC) modified with CBS-UFPR rubber particle was used as an example to explore the abnormal increase of glass transition temperature (Tg) of thermoplastics modified with rubber particle. TEM and AFM results showed that CBS-UFPR was dispersed well in PPC with diameter of about 100 nm. The concentration and size of free-volume in blends were measured by PALS, which indicated the existence of interfacial interaction between PPC and CBS-UFRP. A schematic two-layer model was proposed and the thickness of the interfacial layer was calculated. POLYM. COMPOS. 2012. (c) 2012 Society of Plastics Engineers

The purpose of the study detailed in this paper is to investigate the evolution of microstructural defects in the Fe-9Cr binary alloy induced by isochronal annealing from 373 to 1223 K. Positron annihilation lifetime spectroscopy (PALS), Doppler broadening spectroscopy (DBS), positron annihilation lifetime calculation, and transmission electron microscope (TEM) are used to analyze and characterize the change of defect concentration, defect type and the micro-morphology in the Fe-9Cr alloy as a function of the annealing temperature. The experimental results showed that, a large number of vacancies and dislocations were found to exist in the untreated Fe-9Cr alloy. The monovacancy (186.2 ps) in the Fe-9Cr alloy migrated during annealing from room temperature to 573 K. The annealing temperature at 773 K produce aggregation of dislocations and the formation of dislocation networks, as well as their heterogeneous distribution. When the temperature is further increased to 1073 K, most of the vacancies and dislocations are recovered and a bcc-fcc phase transmition occurred in Fe-9Cr model alloy. The dislocation density is continuous decreased with the increase of annealing temperature, the recovery is obvious from 773 K annealing to 1073 K annealing in Fe-9Cr alloy.

Transmission positron microscope projects in Japan are reviewed. Applications of imaging plates to obtain positron, electron and muon images are discussed and examples are shown. Characteristic features of positron, electron, and muon images are shown and compared. Quite interesting examples of crossed foils of copper and tungsten foils are shown and an explanation is given. Finally, a strong positron source at J-PARC (Japan Proton Accelerator Research Complex) is proposed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The formation of Cu precipitates in Cu containing steels is one of the key factors leading to embrittlement in reactor pressure vessel steels. Cu precipitates are formed by the migration of vacancies in steels and the behaviour of these vacancies is therefore important. In the present study, vacancies were introduced into Fe-Cu alloys by electron irradiation with 28 MeV at 100 K. The effects of Cu concentration and tiny Cu precipitates on the migration of vacancies and growth of precipitates in Fe-Cu alloys were investigated by positron annihilation lifetime measurements. The effect of Cu concentration between Fe-0.3 mass% Cu to Fe-0.6 mass% Cu on the migration of vacancies and the formation of Cu precipitates was negligible small. The formation of Cu precipitates was found to decrease the migration temperature of vacancies. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

MoSe2 is a promising earth-abundant electrocatalyst for the hydrogen-evolution reaction (HER), even though it has received much less attention among the layered dichalcogenide (MX2 ) materials than MoS2 so far. Here, a novel hydrothermal-synthesis strategy is presented to achieve simultaneous and synergistic modulation of crystal phase and disorder in partially crystallized 1T-MoSe2 nanosheets to dramatically enhance their HER catalytic activity. Careful structural characterization and defect characterization using positron annihilation lifetime spectroscopy correlated with electrochemical measurements show that the formation of the 1T phase under a large excess of the NaBH4 reductant during synthesis can effectively improve the intrinsic activity and conductivity, and the disordered structure from a lower reaction temperature can provide abundant unsaturated defects as active sites. Such synergistic effects lead to superior HER catalytic activity with an overpotential of 152 mV versus reversible hydrogen electrode (RHE) for the electrocatalytic current density of j = -10 mA cm-2 , and a Tafel slope of 52 mV dec-1 . This work paves a new pathway for improving the catalytic activity of MoSe2 and generally MX2 -based electrocatalysts via a synergistic modulation strategy.

The formation and stability of He bubbles in Fe irradiated with 2.5 MeV He to a dose of 1.0×1020 ions/m2 were investigated. The results of positron lifetime and coincidence Doppler broadening (CDB) measurements showed that He bubbles were formed in the He-ion-irradiated Fe. The growth of the He bubbles by the movement and coalescence of bubbles at temperatures higher than 773 K was detected. The He bubbles remained even at the high temperature of 1373 K. In addition, He atoms were also trapped by dislocation loops formed by the irradiation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The incubation period, a transient stage before the steady void swelling, in austenitic stainless steels is important, because it determines the duration of service under neutron irradiation in reactors. However, most of experimental studies have been performed after void formation by transmission electron microscopy, and point defects and their clusters under the resolution limits are impossible to detect. In this study, defect structures during the incubation period were studied by using positron annihilation lifetime measurement. The formations of small vacancy clusters below 363 K and precipitates above 563 K were detected by neutron irradiation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)