Ligand removal of Au25 nanoclusters by thermal and electrochemical treatments for selective CO2 electroreduction to CO.

Undercoordinated metal nanoclusters have shown great promise for various catalytic applications. However, their activity is often limited by the covalently bonded ligands, which could block the active surface sites. Here, we investigate the ligand removal process for Au25 nanoclusters using both thermal and electrochemical treatments, as well as its impact on the electroreduction of CO2 to CO. The Au25 nanoclusters are synthesized with 2-phenylethanethiol as the capping agent and anchored on sulfur-doped graphene. The thiolate ligands can be readily removed under either thermal annealing at ≥180°C or electrochemical biasing at ≤-0.5 V vs reversible hydrogen electrode, as evidenced by the Cu underpotential deposition surface area measurement, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure spectroscopy. However, these ligand-removing treatments also trigger the structural evolution of Au25 nanoclusters concomitantly. The thermally and electrochemically treated Au25 nanoclusters show enhanced activity and selectivity for the electrochemical CO2-to-CO conversion than their pristine counterpart, which is attributed to the exposure of undercoordinated Au sites on the surface after ligand removal. This work provides facile strategies to strip away the staple ligands from metal nanoclusters and highlights its importance in promoting the catalytic performances.

High-Performance Pt-Co Nanoframes for Fuel-Cell Electrocatalysis.

Pt-based alloy catalysts are promising candidates for fuel-cell applications, especially for cathodic oxygen reduction reaction (ORR) and anodic methanol oxidation reaction (MOR). The rational design of composition and morphology is crucial to promoting catalytic performances. Here, we report the synthesis of Pt-Co nanoframes via chemical etching of Co from solid rhombic dodecahedra. The obtained Pt-Co nanoframes exhibit excellent ORR mass activity in acidic electrolyte, which is as high as 0.40 A mgPt-1 initially and 0.34 A mgPt-1 after 10 000 potential cycles at 0.95 VRHE. Furthermore, their MOR mass activity in alkaline media is up to 4.28 A mgPt-1 and is 4-fold higher than that of commercial Pt/C catalyst. Experimental studies indicate that the weakened binding of intermediate carbonaceous poison contributes to the enhanced MOR behavior. More impressively, the Pt-Co nanoframes also demonstrate remarkable stability under long-term testing, which could be attributed to the negligible electrochemical Co dissolution.

Size Transformation of the Au22(SG)18 Nanocluster and Its Surface-Sensitive Kinetics.

For many applications of well-defined gold nanoclusters, it is desirable to understand their structural evolution behavior under working conditions with molecular precision. Here we report the first systematic investigation of the size transformation products of the Au22(SG)18 nanocluster under representative working conditions and highlight the surface effect on the transformation kinetics. Under thermal and aerobic conditions, the consecutive and pH-dependent transformation from Au22 to both well-defined clusters and small Au(I)SR species was identified by ESI-MS and UV-vis spectroscopy. By introducing a perturbation onto the Au22 surface, significant changes in the activation parameters were determined from the kinetic study of the Au22 transformation. This indicates the sensitivity of the nanocluster transformation pathway to the cluster surface. The systematic study of cluster transformation and the sensitivity of cluster transformation to the surface revealed herein has significant implications for future attempts to design gold nanoparticles with adaptation to the working environment and the regeneration of active nanoparticles.

[Application of flexible bronchoscopy in children with respiratory diseases].

OBJECTIVE: To investigate the significance of flexible bronchoscopy in children with respiratory diseases. METHODS: A retrospective analysis was performed for the clinical data of 80 children who were hospitalized due to respiratory diseases (including severe pneumonia, Mycoplasma pneumoniae pneumonia with atelectasis/lung consolidation/local emphysema, protracted pneumonia, coughing and wheezing of unknown cause, chronic cough of unknown cause, and laryngeal stridor) and who underwent flexible bronchoscopy/alveolar lavage. RESULTS: Bronchoscopy found that all the 80 children had endobronchial inflammation, among whom 28 children had severe airway obstruction by secretion. Twenty-four children had congenital airway dysplasia besides endobronchial inflammation, and three children had bronchial foreign bodies. In the children with coughing and wheezing of unknown cause and laryngeal stridor, some had congenital airway dysplasia or bronchial foreign bodies. Among the 27 children with Mycoplasma pneumoniae pneumonia, 26 had severe airway obstruction/embolization by secretion; 25 children (93%) underwent chest imaging again at 2 weeks after alveolar lavage, and the results showed complete or partial lung recruitment. Among the 80 children who underwent bronchoscopy, 3 had severe hypoxemia during surgery, 1 had epistaxis, 1 had minor bleeding during alveolar lavage, 3 had transient bronchospasm, and 5 had postoperative fever; these children were all improved after symptomatic treatment. CONCLUSIONS: Flexible bronchoscopy is safe and reliable in children with respiratory diseases. Early alveolar lavage under a flexible bronchoscope is recommended for children with severe/refractory Mycoplasma pneumoniae pneumonia to improve prognosis. Flexible bronchoscopy is recommended for children with recurrent coughing and wheezing and persistent laryngeal stridor, in order to directly observe the throat and airway under an endoscope.

A Comprehensive Study on Epidemiology Case Studies Using Computational Analysis.

Health-related issues and occurrences with regard to a particular population are the subject of an epidemiology study. This paper presents the results of a retrospective epidemiological investigation on 15922 hospitalized hand trauma patients from Central China between 2011 and 2020. Gender, age, onset season, injury mechanism, injury environment, injury location, and clinical characteristics are among the characteristics of the data gathered. The study is using computational analysis to draw inferences from the case studies collected in the databases of the hospitals. The types and characteristics of occupational injuries at home and outdoor are compared and analyzed. The purpose of the study is to present the findings from recent case studies for future reference and to recommend useful roles for the industrial sector in the care of patients with hand trauma in order to lower occupational harm. The injuries of preschool children are also analyzed. The incidence rate of hand injuries in infants has been increasing year by year which is directly related to the inefficient growth of children in rural areas. The data are collected from hospitals, then the data analytical tools are applied to draw conclusions. The suggested model is intelligently learned through the application of computational techniques, which are also used to suggest treatments to trauma victims. According to this study, males are more likely than females to sustain hand trauma; occupational injuries are more common than living injuries; males between the ages of 20 and 50 are at an increased risk of suffering an occupational injury. This study showed that the proportion of hand trauma in preschool children was higher (12.27%), and the 2-3-year-old group was the main injury target of preschool children (45.70%). The accidental injuries of newborns and young children can be reduced by government assistance, social support, and tighter monitoring.

Effects of Catalyst Processing on the Activity and Stability of Pt-Ni Nanoframe Electrocatalysts.

Pt-based alloys have shown great promise as cathodic catalysts for cost-effective proton-exchange membrane fuel cells. Post-synthesis treatment has been recognized as a critical step to improve the catalytic performance of Pt-based alloys. Here, we present the effects of catalyst processing on the catalytic behavior of Pt-Ni nanoframe electrocatalysts in oxygen reduction reaction. The Pt-Ni nanoframes were made by corroding the Ni-rich phase from solid rhombic dodecahedral particles. A total of three different corrosion procedures were compared. Among them, electrochemical corrosion led to the highest initial specific activity (1.35 mA cm-2 at 0.95 V versus reversible hydrogen electrode) by retaining more Ni in the nanoframes. However, the high activity gradually went down in a subsequent stability test due to continuous Ni loss and concomitant surface reconstruction. On the other hand, the best stability was achieved by a more-aggressive corrosion using oxidative nitric acid. Although the initial activity was compromised, this procedure imparted a less-defective surface, and thus, the specific activity dropped by only 7% over 30 000 potential cycles. These results indicate a delicate trade-off between the activity and stability of Pt-Ni nanoframe electrocatalysts. The obtained understanding of how to balance the activity-stability trade-off via catalyst processing can be generalized to other Pt-based alloys.

Azo-Polymer Janus Particles Assembled by Solvent-Induced Microphase Separation and Their Photoresponsive Behavior.

We report the successful fabrication of photoresponsive Janus particles (JPs) composed of an epoxy-based azo polymer and poly(methyl methacrylate) (PMMA). Two representative azo polymers, of which one polymer (BP-AZ-CN) has cyano groups as electron-withdrawing substituents on the azobenzene moieties and the other polymer (BP-AZ-CA) has carboxyl groups as the electron-withdrawing substituents, were adopted for the investigation. The nanoscaled JPs, with a narrow size distribution and different azo polymer/PMMA ratios, were fabricated through self-assembly in solution and as dispersions. Upon irradiation with linearly polarized light (λ=488 nm), two types of photoresponsive behavior were observed for JPs in the solid state. For JPs composed of BP-AZ-CN and PMMA, the light irradiation caused the azo-polymer component to be stretched along the light polarization direction. Conversely, for JPs composed of BP-AZ-CA and PMMA, the azo-polymer component became separated from PMMA component under the same irradiation conditions. These observations are valuable for a deeper understanding of the nature of self-assembly and photoinduced mass-transport at the nanometer scale.