Correcting flaws in the assignment of nitrogen chemical environments in N-doped graphene

X-ray Photoelectron Spectroscopy (XPS) applied to N-doped graphene leads to a rather broad N(1s) core level signal that, based on different sources available in the literature, is most often interpreted by fitting the experimental spectra to three peaks. The resulting N(1s) features are assigned to graphitic, pyrrolic, and pyridinic nitrogen, even if these are far from being uniquely defined in the literature. This broadly accepted interpretation has been questioned by recent accurate Hartree-Fock calculations concluding that graphitic and pyrrolic N(1s) core level binding energies are too close to be distinguished. Consideration of models with N in other so far unexplored environments such as N dimers or N at defects show some variations in the calculated core level binding energies. However, these are not large enough to justify a third peak and suggest that the usual three peaks interpretation of the N(1s) XPS in N-doped graphene may be an artefact caused by the fitting procedure. New measurements have been carried out for samples of N-doped graphene and the obtained N(1s) spectra fitted to two or three peaks. It turns out that the spectra can be equally fitted using two or three peaks but only the former is consistent with the results of the unbiased ab initio calculations which calls for a revision of the usual assignment

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Nanostructuration Effect of Carbon‐Based Phenylene Vinylene Conjugated Porous Polymers on TiO2 Hybrid Materials for Artificial Photosynthesis

This work examines the role of polymer nanostructuration of phenylene vinylene (PV) conjugated porous polymers (PV‐CPPs) as highly active photocatalysts for both hydrogen production and CO2 photoreduction reactions. It is found that nanostructured PV‐CPP hybrids with TiO2 show a high increase in H2 production being the most active example, the n‐IEP‐20@T‐10 sample with an evolution rate of 3.24 mmol g−1 h−1 (ξ = 1.20%), that is, 8 times higher than that of its non‐nanostructured and 65‐fold higher than TiO2. In contrast, CO2 photoreduction in both nanostructured polymers shows a significant improvement in CH4 production compared with bare TiO2, and a clear change of selectivity toward C2+ products. In particular, C2+/C1 ratios are obtained with n‐IEP‐20‐based hybrids increased by one order of magnitude that obtained for TiO2. The beneficial effect of this synthetic strategy is associated with an increase of the dispersion on nanostructured CPPs over TiO2 leading to an improvement on the surface interaction between them that favors longer‐lived photogenerated carriers in spatially separated redox active sites, which favor the production and selectivity to highly electron demanding products. The use of these nanostructuration strategies opens new opportunities for the production of more processable polymers for different energy technologies

Correlating the electronic structure of perovskite La1−Sr CoO3 with activity for the oxygen evolution reaction: The critical role of Co 3d hole state

Perovskite LaCoO3 is being increasingly explored as an effective low-cost electrocatalyst for the oxygen evolution reaction (OER). Sr doping in LaCoO3 (La1xSrxCoO3) has been found to substantially increase its catalytic activity. In this work, we report a detailed study on the evolution of the electronic structure of La1xSrxCoO3 with 0 x 1 and its correlation with electrocatalytic activity for the OER. A combination of X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) was used to unravel the electronic density of states (DOS) near the Fermi level (EF), which provide insights into the key electronic structure features for the enhanced OER catalytic activity. Detailed analysis on the Co L-edge XAS suggest that LaCoO3 has a low spin state with t2g 6 eg 0 configuration at room temperature. This implies that the high OER catalytic activity of LaCoO3 should not be rationalized by the occupancy of eg = 1 descriptor. Substituting Sr2+ for La3+ in LaCoO3 induces Co4+ oxidation states and effectively dopes hole states into the top of valence band. A semiconductor-to-metal transition is observed for 0.2, due to the holeinduced electronic DOS at the EF and increased hybridization between Co 3d and O 2p. Such an electronic modulation enhances the surface adsorption of the *OH intermediate and reduces the energy barrier for interfacial charge transfer, thus improving the OER catalytic activity in La1xSrxCoO3. In addition, we found that the La1xSrxCoO3 surface undergoes amorphization after certain period of OER measurement, leading to a partial deactivation of the electrocatalyst. High Sr doping levels accelerated the amorphization process.K.H.L. Zhang is grateful for funding support by the National Natural Science Foundation of China (Grant No. 21872116). J.C. gratefully acknowledges the financial support by the National Natural Science Foundation of China (Grant No. 21621091 and 21373166). Freddy E. Oropeza and Victor A. de la Peña O'Shea are grateful for the funding supported by the Spanish AEI (NyMPhA PID2019-106315RB-I00). Victor A. de la Peña O'Shea also wishes to thank ''Comunidad de Madrid" and European Structural Funds for their financial support to FotoArt-CM project (S2018/NMT-4367) and the Fundación Ramón Areces. C. M. Tian gratefully acknowledges financial support by the China Scholarship Council (CSC). K.H.L. Zhang and Jan P. Hofmann also ackonwledge the Sino-German Mobility Program (Grant No. M-0377). Preliminar spectroscopic measurements were performed at the CLAESS beamline at the ALBA synchrotron

Au@AuPd Core-Alloyed Shell Nanoparticles for Enhanced Electrocatalytic Activity and Selectivity under Visible Light Excitation

Plasmonic catalysis has been employed to enhance molecular transformations under visible light excitation, leveraging the localized surface plasmon resonance (LSPR) in plasmonic nanoparticles. While plasmonic catalysis has been employed for accelerating reaction rates, achieving control over the reaction selectivity has remained a challenge. In addition, the incorporation of catalytic components into traditional plasmonic-catalytic antenna-reactor nanoparticles often leads to a decrease in optical absorption. To address these issues, this study focuses on the synthesis of bimetallic core@shell Au@AuPd nanoparticles (NPs) with ultralow loadings of palladium (Pd) into gold (Au) NPs. The goal is to achieve NPs with an Au core and a dilute alloyed shell containing both Au and Pd, with a low Pd content of around 10 atom %. By employing the (photo)electrocatalytic nitrite reduction reaction (NO2RR) as a model transformation, experimental and theoretical analyses show that this design enables enhanced catalytic activity and selectivity under visible light illumination. We found that the optimized Pd distribution in the alloyed shell allowed for stronger interaction with key adsorbed species, leading to improved catalytic activity and selectivity, both under no illumination and under visible light excitation conditions. The findings provide valuable insights for the rational design of antenna-reactor plasmonic-catalytic NPs with controlled activities and selectivity under visible light irradiation, addressing critical challenges to enable sustainable molecular transformations

Surgical site infection after gastrointestinal surgery in children : an international, multicentre, prospective cohort study

Introduction Surgical site infection (SSI) is one of the most common healthcare-associated infections (HAIs). However, there is a lack of data available about SSI in children worldwide, especially from low-income and middle-income countries. This study aimed to estimate the incidence of SSI in children and associations between SSI and morbidity across human development settings. Methods A multicentre, international, prospective, validated cohort study of children aged under 16 years undergoing clean-contaminated, contaminated or dirty gastrointestinal surgery. Any hospital in the world providing paediatric surgery was eligible to contribute data between January and July 2016. The primary outcome was the incidence of SSI by 30 days. Relationships between explanatory variables and SSI were examined using multilevel logistic regression. Countries were stratified into high development, middle development and low development groups using the United Nations Human Development Index (HDI). Results Of 1159 children across 181 hospitals in 51 countries, 523 (45 center dot 1%) children were from high HDI, 397 (34 center dot 2%) from middle HDI and 239 (20 center dot 6%) from low HDI countries. The 30-day SSI rate was 6.3% (33/523) in high HDI, 12 center dot 8% (51/397) in middle HDI and 24 center dot 7% (59/239) in low HDI countries. SSI was associated with higher incidence of 30-day mortality, intervention, organ-space infection and other HAIs, with the highest rates seen in low HDI countries. Median length of stay in patients who had an SSI was longer (7.0 days), compared with 3.0 days in patients who did not have an SSI. Use of laparoscopy was associated with significantly lower SSI rates, even after accounting for HDI. Conclusion The odds of SSI in children is nearly four times greater in low HDI compared with high HDI countries. Policies to reduce SSI should be prioritised as part of the wider global agenda.Peer reviewe

Search for intermediate-mass black hole binaries in the third observing run of Advanced LIGO and Advanced Virgo

International audienceIntermediate-mass black holes (IMBHs) span the approximate mass range 100−105 M⊙, between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass ∼150 M⊙ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the individual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200 M⊙ and effective aligned spin 0.8 at 0.056 Gpc−3 yr−1 (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpc−3 yr−1.Key words: gravitational waves / stars: black holes / black hole physicsCorresponding author: W. Del Pozzo, e-mail: [email protected]† Deceased, August 2020