Mechanochemically synthesized Pb-free halide perovskite-based Cs2AgBiBr6–Cu–RGO nanocomposite for photocatalytic CO2 reduction

Pb-based halide perovskites have recently showed great potential in various applications such as solar cells, optoelectronics and photocatalysis. Despite their high performance, the Pb2+ toxicity along with poor stability hinders long term applications in photocatalysis. Herein, we report mechanochemically prepared Pb-free Cs2AgBiBr6 double perovskite nanoplates and their heterostructure with Cu-loaded reduced graphene oxide (Cu–RGO) for gas-phase photocatalytic CO2 reduction using water vapor as the proton source in the absence of a hole scavenger. The resulting Cs2AgBiBr6–Cu–RGO nanocomposite shows significant photocatalytic activity of 10.7 (±0.6) μmol CH4 g−1 h−1, 1.9 (±0.3) μmol CO g−1 h−1 and 1.0 (±0.2) μmol H2 g−1 h−1, with a CH4 selectivity of 93.0 (±0.5)% on an electron basis with 1 sun and a remarkable apparent quantum efficiency of 0.89 (±0.21)% at 590 nm. A further 32% enhancement in photocatalytic activity on an electron basis is achieved when the light intensity is doubled (2 suns). The high performance was attributed to their improved charge separation and suppressed electron–hole recombination, along with extended visible light absorption, better stability in a humid environment and improved CO2 adsorption. These findings support Cs2AgBiBr6 as a potential Pb-free alternative to conventional halide perovskites for photocatalytic solar-to-fuel conversion and CO2 utilization

Pancreatic islet chromatin accessibility and conformation reveals distal enhancer networks of type 2 diabetes risk

Genetic variants affecting pancreatic islet enhancers are central to T2D risk, but the gene targets of islet enhancer activity are largely unknown. We generate a high-resolution map of islet chromatin loops using Hi-C assays in three islet samples and use loops to annotate target genes of islet enhancers defined using ATAC-seq and published ChIP-seq data. We identify candidate target genes for thousands of islet enhancers, and find that enhancer looping is correlated with islet-specific gene expression. We fine-map T2D risk variants affecting islet enhancers, and find that candidate target genes of these variants defined using chromatin looping and eQTL mapping are enriched in protein transport and secretion pathways. At IGF2BP2, a fine-mapped T2D variant reduces islet enhancer activity and IGF2BP2 expression, and conditional inactivation of IGF2BP2 in mouse islets impairs glucose-stimulated insulin secretion. Our findings provide a resource for studying islet enhancer function and identifying genes involved in T2D risk

PCR-Based Identification of Klebsiella pneumoniae subsp. rhinoscleromatis, the Agent of Rhinoscleroma

Rhinoscleroma is a chronic granulomatous infection of the upper airways caused by the bacterium Klebsiella pneumoniae subsp. rhinoscleromatis. The disease is endemic in tropical and subtropical areas, but its diagnosis remains difficult. As a consequence, and despite available antibiotherapy, some patients evolve advanced stages that can lead to disfiguration, severe respiratory impairment and death by anoxia. Because identification of the etiologic agent is crucial for the definitive diagnosis of the disease, the aim of this study was to develop two simple PCR assays. We took advantage of the fact that all Klebsiella pneumoniae subsp. rhinoscleromatis isolates are (i) of capsular serotype K3; and (ii) belong to a single clone with diagnostic single nucleotide polymorphisms (SNP). The complete sequence of the genomic region comprising the capsular polysaccharide synthesis (cps) gene cluster was determined. Putative functions of the 21 genes identified were consistent with the structure of the K3 antigen. The K3-specific sequence of gene Kr11509 (wzy) was exploited to set up a PCR test, which was positive for 40 K3 strains but negative when assayed on the 76 other Klebsiella capsular types. Further, to discriminate Klebsiella pneumoniae subsp. rhinoscleromatis from other K3 Klebsiella strains, a specific PCR assay was developed based on diagnostic SNPs in the phosphate porin gene phoE. This work provides rapid and simple molecular tools to confirm the diagnostic of rhinoscleroma, which should improve patient care as well as knowledge on the prevalence and epidemiology of rhinoscleroma

The Major Surface-Associated Saccharides of Klebsiella pneumoniae Contribute to Host Cell Association

Analysing the pathogenic mechanisms of a bacterium requires an understanding of the composition of the bacterial cell surface. The bacterial surface provides the first barrier against innate immune mechanisms as well as mediating attachment to cells/surfaces to resist clearance. We utilised a series of Klebsiella pneumoniae mutants in which the two major polysaccharide layers, capsule and lipopolysaccharide (LPS), were absent or truncated, to investigate the ability of these layers to protect against innate immune mechanisms and to associate with eukaryotic cells. The capsule alone was found to be essential for resistance to complement mediated killing while both capsule and LPS were involved in cell-association, albeit through different mechanisms. The capsule impeded cell-association while the LPS saccharides increased cell-association in a non-specific manner. The electrohydrodynamic characteristics of the strains suggested the differing interaction of each bacterial strain with eukaryotic cells could be partly explained by the charge density displayed by the outermost polysaccharide layer. This highlights the importance of considering not only specific adhesin:ligand interactions commonly studied in adherence assays but also the initial non-specific interactions governed largely by the electrostatic interaction forces

Graphite-protected CsPbBr3 perovskite photoanodes functionalised with water oxidation catalyst for oxygen evolution in water

Metal-halide perovskites have been widely investigated in the photovoltaic sector due to their promising optoelectronic properties and inexpensive fabrication techniques based on solution processing. Here we report the development of inorganic CsPbBr3-based photoanodes for direct photoelectrochemical oxygen evolution from aqueous electrolytes. We use a commercial thermal graphite sheet and a mesoporous carbon scaffold to encapsulate CsPbBr3 as an inexpensive and efficient protection strategy. We achieve a record stability of 30 h in aqueous electrolyte under constant simulated solar illumination, with currents above 2 mA cm−2 at 1.23 VRHE. We further demonstrate the versatility of our approach by grafting a molecular Ir-based water oxidation catalyst on the electrolyte-facing surface of the sealing graphite sheet, which cathodically shifts the onset potential of the composite photoanode due to accelerated charge transfer. These results suggest an efficient route to develop stable halide perovskite based electrodes for photoelectrochemical solar fuel generation

All-Inorganic CsPbBr3 nanocrystals: gram-scale mechanochemical synthesis and selective photocatalytic CO2 reduction to methane

Halide perovskite CsPbBr3 has recently gained wide interest for its application in solar cells, optoelectronics and artificial photosynthesis, but further progress is needed to develop greener and more scalable synthesis procedures and for their application in humid environments. Herein, we report a fast and convenient mechanochemical synthesis of CsPbBr3 perovskite nanocrystals with scale-up capability and control over crystal size and morphology. These perovskite nanocrystals show excellent crystallinity and tunable morphologies, from nanorods to nanospheres and nanosheets, simply changing the mechanochemical reaction conditions such as ball milling time, ball size and Cs precursor. Furthermore, we explore their use for gas-phase photocatalytic CO2 reduction using water vapor as proton source. A photocatalytic conversion of CO2 and H2O(g) to 0.43 (0.03) μmol CH4 g-1 h-1, 2.25 (0.09) μmol CO g-1 h-1 and 0.08 (0.02) μmol H2 g-1 h-1 was for example achieved with CsPbBr3 nanosheets and simulated sunlight, keeping 30% of this activity over three consecutive cycles. When these CsPbBr3 nanosheets were mechanochemically prepared together with Cu-loaded reduced graphene oxide (Cu-RGO), the photocatalytic activity significantly improved to 12.7 (0.95) μmol CH4 g-1 h-1, 0.46 (0.11) μmol CO g-1 h-1 and 0.27 (0.02) μmol H2 g-1 h-1, and a 90% of this activity was retained over three consecutive cycles. The selectivity for CH4 increased to 98.5(0.93)% on an electron basis and a remarkable apparent quantum efficiency of 1.10(0.15)% at 523 nm was achieved. This enhanced activity, selectivity and stability were assigned to the better charge separation, visible light absorption, CO2 adsorption & activation, and hydrophobic character of the obtained composites. These results will contribute to the rational design and application of halide perovskites for CO2 photocatalytic reduction