Unwrap Them First: Operando Potential- induced Activation Is Required when Using PVP-Capped Ag Nanocubes as Catalysts of CO2 Electroreduction

Metallic nanoparticles of different shape can be used as efficient electrocatalysts for many technologically and environmentally relevant processes, like the electroreduction of CO2. Intense research is thus targeted at finding the morphology of nanosized features that best suits catalytic needs. In order to control the shape and size distribution of the designed nanoobjects, and to prevent their aggregation, synthesis routes often rely on the use of organic capping agents (surfactants). It is known, however, that these agents tend to remain adsorbed on the surface of the synthesized nanoparticles and may significantly impair their catalytic performance, both in terms of overall yield and of product selectivity. It thus became a standard procedure to apply certain methods (e.g. involving UV-ozone or plasma treatments) for the removal of capping agents from the surface of nanoparticles, before they are used as catalysts. Proper design of the operating procedure of the electrocatalysis process may, however, render such cleaning steps unnecessary. In this paper we use poly-vinylpyrrolidone (PVP) capped Ag nanocubes to demonstrate a mere electrochemical, operando activation method. The proposed method is based on an observed hysteresis of the catalytic yield of CO (the desired product of CO2 electroreduction) as a function of the applied potential. When as-synthesized nanocubes were directly used for CO2 electroreduction, the CO yield was rather low at moderate overpotentials. However, following a potential excursion to more negative potentials, most of the (blocking) PVP was irreversibly removed from the catalyst surface, allowing a significantly higher catalytic yield even under less harsh operating conditions. The described hysteresis of the product distribution is shown to be of transient nature, and following operando activation by a single 'break-in' cycle, a truly efficient catalyst was obtained that retained its stability during long hours of operation

Non-conventional fluorescent biogenic and synthetic polymers without aromatic rings

Non-conventional fluorescent materials without aromatic structures have attracted much research attention in recent years. However, the working mechanism responsible for their fluorescence remains mysterious. Here we decipher the origin of fluorescence by studying the photophysical properties of a series of non-aromatic biogenic and synthetic peptides. An experimental study suggests that the turn-on fluorescence in the aggregation state/condensed phase is associated with the communication of amide groups, where hydrogen bonds are playing a critical role in bringing these functionalities into close proximity. This explanation is further justified by the study of the hierarchical influence on fluorescence and applied to biomimetic polymers in a more general content. This discovery provides a more comprehensive insight into the bioluminescence system. It may stimulate future development of new fluorescent materials, and inspire research on disease diagnostics, biomechanics measurements, etc. that are associated with protein morphology

The Crest Phenotype in Chicken Is Associated with Ectopic Expression of HOXC8 in Cranial Skin

The Crest phenotype is characterised by a tuft of elongated feathers atop the head. A similar phenotype is also seen in several wild bird species. Crest shows an autosomal incompletely dominant mode of inheritance and is associated with cerebral hernia. Here we show, using linkage analysis and genome-wide association, that Crest is located on the E22C19W28 linkage group and that it shows complete association to the HOXC-cluster on this chromosome. Expression analysis of tissues from Crested and non-crested chickens, representing 26 different breeds, revealed that HOXC8, but not HOXC12 or HOXC13, showed ectopic expression in cranial skin during embryonic development. We propose that Crest is caused by a cis-acting regulatory mutation underlying the ectopic expression of HOXC8. However, the identification of the causative mutation(s) has to await until a method becomes available for assembling this chromosomal region. Crest is unfortunately located in a genomic region that has so far defied all attempts to establish a contiguous sequence

Regional CO emission estimated from ground-based remote sensing at Hefei site, China

Carbon monoxide (CO) is regarded as a useful tracer of biomass burning and anthropogenic pollution, so CO measurements can provide valuable information about the intensity of various anthropogenic activities. However, the emission estimates of CO based on inventories are associated with high uncertainties, especially in China. As CO is co-emitted with CO 2 in the combustion of carbonaceous fuels, the relationship between CO and CO 2 is often used to estimate regional CO emissions. Hefei is located in the area of eastern central China, which is one of the most industrialized regions in China, with severe regional air pollution. The enhancement slopes of ∆CO to ∆CO 2 were calculated and compared from ground-based remote sensing observations, surface in-situ measurements, satellite and emission inventory data at the Hefei site during the period from September 2015 to August 2017. Both inventory based ratios of ΔCO to ΔCO 2 are significantly larger than the ratios based on the observation data, including Fourier Transform Spectrometer (FTS) data, in-situ data, and satellite data. Further the CO emissions in the central China were estimated from the enhancement slopes of ∆CO/∆CO 2 combined with the CO 2 emission inventory. The CO emission estimated from the ground-based FTS observations and the Peking University (PKU) inventory based CO 2 emission is about 10.96 ± 0.88 and 11.95 ± 0.71 Tg CO yr −1 during the 2015–2016 and the 2016–2017 period, respectively. The CO emission estimated from the ground-based FTS observations and the Emission Database for Global Atmospheric Research (EDGAR) inventory based CO 2 emission is about 11.27 ± 0.91 and 12.35 ± 0.74 Tg CO yr −1 , respectively. So the CO emissions estimated from the ground-based FTS data and the different inventory based CO 2 emission show a good agreement. However, CO emissions derived from FTS data are substantially lower than those calculated directly from the inventories, i.e. there is a large difference between CO emissions derived from FTS and CO emissions directly derived from the two inventories. The phenomenon suggests that the emission inventories greatly overestimate the actual CO emission in the study area. This study estimates the regional CO emissions from ground-based remote sensing observations and investigates how much the difference is between the emissions from inventories and ground-based measurements

Controlled synthesis of highly stable lead-free bismuth halide perovskite nanocrystals : tructures and photophysics

Recently, cesium bismuth halide perovskites have emerged as potential substitutes to their counterparts, cesium lead halide perovskites, owing to their low toxicity. However, the photophysics of cesium-bismuth halides nanocrystals (NCs) have not yet been fully rationalized because their structures remain highly debated. The ultraviolet-visible (UV-vis) absorption along with other photophysical properties such as the nature and lifetime of the excited states vary considerably across the previous reports. Here, we successfully synthesize pure Cs3BiBr6 and Cs3Bi2Br9 NCs via a modified hot-injection method, where the structure can be easily controlled by tuning the reaction temperature. The UV-vis absorption spectrum of the pure Cs3Bi2Br9 NCs features two characteristic peaks originating from the absorption of the first exciton and second exciton, respectively, which ultimately clarifies the debate in the previous reports. Using femtosecond transient absorption spectroscopy, we systematically investigate the excited state dynamics of the Cs3Bi2Br9 NCs and reveal that the photoexcited carriers undergo a self-trapping process within 3 ps after excitation. More intriguingly, the Cs3Bi2Br9 NCs prepared by this method show much better photostability than those prepared by the ligand-assisted reprecipitation process. Photodetectors based on these Cs3Bi2Br9 NCs show a sensitive light response, demonstrating the definite potential for breakthrough optoelectronic applications. [Figure not available: see fulltext.]