Electronic and local structures of Pt-based bimetallic alloy and core-shell systems

This thesis investigates the electronic structure of Pt for catalysis applications. The importance of the Pt 5d band is discussed in terms of the bonding capability of Pt. The oxygen reduction reaction in proton exchange membrane fuel cells is chosen as the catalytic reaction model to illustrate the effect of Pt 5d states on Pt-O interaction. Pt-based bimetallic systems are introduced as a solution for the high price and limited resources of Pt. Despite lower usage of Pt, the tuning capability to optimize the Pt 5d band in bimetallic catalysts is supposed to provide superior catalytic activity. Advanced synchrotron X-ray techniques including normal X-ray absorption fine structure (XAFS), X-ray ptychography, and high energy resolution fluorescence detected (HERFD) X-ray absorption/emission spectroscopy (XAS/XES) are combined with laboratory characterization techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) to study the behavior of Pt upon alloying or forming core-shell structures with 3d transition metals. Three Pt-based bimetallic systems are studied, including Pt-Ni bulk alloys, Pt-Ni nanoparticles (NPs), and Pt-Cu NPs. Pt-Ni bulk alloys are synthesized as model compounds to study the many-body effect, charge redistribution, and local structure of Pt upon alloying. It is found that Pt gains 5d electrons, resulting in more symmetric Pt 4f XPS peaks when diluted in Ni, while Ni loses 4p and 4d electrons, resulting in an increase of K-edge XAS whiteline (WL) intensity, more symmetric Ni 2p XPS peaks, and stronger shake-up satellites. The downshifting of the Pt valence states and upshifting of Ni valence states are also observed with ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) calculations. Pt-Ni NPs, as the Pt-Ni systems in nanoscale, are used to track the evolution process including the alloying and de-alloying of Pt during the synthesis of the bimetallic systems. It is found that Pt goes through five distinct stages, i.e. core frame, tight network, outer frame, thin skin, and particulate shell. The electronic and local structures at each stage are tracked with XAS. Pt-Cu NPs are in the form of core-shell or alloy NPs, with a very low amount of Pt either on the surface or in the bulk. For the 8-nm Cu@Pt core-shell NPs, several monolayers of Pt are deposited on the Cu core, exhibiting good controllability by the polyol reduction method. The advantages of HERFD-XAS/XES are demonstrated in studying the Pt 5d band of Pt-Ni and Pt-Cu bimetallic systems. In the valence-to-core (VTC) XES experiments, the widths of the VTC emission lines and energy transfers show the shrinking and downshifting of the Pt valence band upon alloying with Ni. For HERFD-XAS, significantly narrowed WLs, enhanced near-edge XAS features, and easily removable background have enabled detailed analysis of the WL peaks with high accuracy. Combining the HERFD-XAS results for Pt-Ni and Pt-Cu bimetallic systems, Pt foil, and Pt NPs, a general linear relationship between the WL areas of Pt L3- and L2-edges is established. Physically, this linear relationship indicates that the unoccupied Pt 5d5/2 and 5d3/2 states also have a linear relationship. Experimentally, this finding suggests that measuring the Pt L3-edge alone will provide enough information to study the unoccupied Pt 5d states of Pt-based metallic systems

Silicon-Incorporated Carbon Spheres As Anode Material for Lithium-ion Batteries

In this study, a porous silicon-incorporated carbon material is studied as anode material in Lithium-ion batteries. This material is synthesized with carbonization, spray-pyrolysis and magnesiothermic reduction, from sucrose and silica as carbon and silicon precursors. Carbonization of sucrose was conducted in 0.125 M sulfuric acid with addition of colloidal silica at 90 ℃ for 48 hours. The C/SiO2 spheres obtained from subsequent spray-pyrolysis were reduced by magnesium at 750 ℃ for 2 hours in a home-made Swagelok-type stainless steel reactor. The carbon was sacrificed to maintain the spherical structure of the composite during magnesiothermic reduction while silicon formed a highly porous sponge-like structure inside the spheres. C/Si (1:8) showed high recovery (85%) of specific capacity at the second cycle. However, the rapid capacity loss of porous silicon spheres was found to be caused by fracture the of thin silicon structure. Without the carbon shell, the debris dissolved into the electrolyte easily, leading to a lower availability of the silicon material

The safety and efficacy of transluminal injection of foam sclerotherapy after endovenous thermal ablation in varicose veins with large trunk: A retrospective cohort study

CONTEXT: Closure rate of endovenous thermal ablation is limited by the trunk diameter of great saphenous vein. AIMS: This study aimed to investigate the safety and efficacy of transluminal injection of foam sclerotherapy (TLFS) after thermal ablation in improving the closure rate of primary varicose veins with large trunk. SUBJECTS AND METHODS: In this retrospective cohort study with 170 patients (189 legs), the outcomes of varicose veins patients treated with thermal ablation plus injection of sclerotherapy were compared with those treated with thermal ablation only. The primary outcome of this study was the rate of ablated segment closure after surgery and during patient follow-up. Propensity score matching model was used to eliminate the bias. RESULTS: After matching, 75 legs (65 patients) from the thermal ablation plus sclerotherapy group and 71 legs (66 patients) from the thermal ablation only group were further analyzed. The closure rate of the thermal ablation plus sclerotherapy group was 97.3%, which was significantly higher than that of the thermal ablation only group (87.3%, P = 0.048), and the closure rate of the thermal ablation plus sclerotherapy group remained higher during 1-year follow-up. No serious complications were observed in groups. CONCLUSIONS: TLFS can improve the efficacy of thermal ablation, increasing the closure rate of the ablation segment, and thus improving the symptoms

Spatiotemporal variations and controlling mechanism of low dissolved oxygen in a highly urbanized complex river system

Study region: Dongjiang River Network (DJRN), a complex urbanized river network in the Pearl River Basin, China. Study focus: Low-oxygen conditions have been expanding in urbanized river systems, whereas a clear and quantitative understanding on the deoxygenation processes is still lacking. This study utilized a well-validated physical-biogeochemical model to investigate the oxygen dynamics combined with river ecosystem metabolisms over an annual cycle and explicitly quantify the contribution of major oxygen-depleting substances from different sources to low-oxygen conditions. New hydrological insight for the region: Our results showed significant spatiotemporal variations in low-oxygen extents and oxygen source-sink patterns in the DJRN, where the underlying control mechanisms varied across stream order due to the intricate geographic and hydrological regime shifts in conjunction with diverse pollution stressors. Ascribed to the seasonal variations in anthropogenic pollution and water temperature, the entire DJRN shifted to a completely heterotrophic system with severe oxygen deficits during the late summer and early autumn. Scenario simulations indicated that in line with the substantial wastewater control in the DJRN region, local pollutant loads played a trivial role in the low-oxygen generation, which instead was primarily fueled by organic matter from transboundary delivery and in-situ primary production. Our findings underscored the necessity of co-regional collaborative management on pollutant emissions and the importance of eutrophication mitigation for the sake of oxygen recovery in the urbanized river network

Machine learning-based models for predicting mortality and acute kidney injury in critical pulmonary embolism

Abstract Objectives We aimed to use machine learning (ML) algorithms to risk stratify the prognosis of critical pulmonary embolism (PE). Material and methods In total, 1229 patients were obtained from MIMIC-IV database. Main outcomes were set as all-cause mortality within 30 days. Logistic regression (LR) and simplified eXtreme gradient boosting (XGBoost) were applied for model constructions. We chose the final models based on their matching degree with data. To simplify the model and increase its usefulness, finally simplified models were built based on the most important 8 variables. Discrimination and calibration were exploited to evaluate the prediction ability. We stratified the risk groups based on risk estimate deciles. Results The simplified XGB model performed better in model discrimination, which AUC were 0.82 (95% CI: 0.78–0.87) in the validation cohort, compared with the AUC of simplified LR model (0.75 [95% CI: 0.69—0.80]). And XGB performed better than sPESI in the validation cohort. A new risk-classification based on XGB could accurately predict low-risk of mortality, and had high consistency with acknowledged risk scores. Conclusions ML models can accurately predict the 30-day mortality of critical PE patients, which could further be used to reduce the burden of ICU stay, decrease the mortality and improve the quality of life for critical PE patients

Engineering Coexposed {001} and {101} Facets in Oxygen-Deficient TiO₂ Nanocrystals for Enhanced CO₂ Photoreduction under Visible Light

This work for the first time reports engineered oxygen-deficient, blue TiO₂ nanocrystals with coexposed {101}-{001} facets (TiO_2–<i>x</i>{001}-{101}) to enhance CO₂ photoreduction under visible light. The TiO_2–<i>x</i>{001}-{101} material demonstrated a relatively high quantum yield (0.31% under UV–vis light and 0.134% under visible light) for CO₂ reduction to CO by water vapor and more than 4 times higher visible light activity in comparison with TiO₂ with a single {001} plane or {101} plane and TiO₂(P25). Possible reasons are the exposure of more active sites (e.g., undercoordinated Ti atoms and oxygen vacancies), the facilitated electron transfer between {001} and {101} planes, and the formation of a new energy state (Ti³⁺) within the TiO₂ band gap to extend the visible light response. An in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study was applied to understand the roles of coexposed {001}-{101} facets and Ti³⁺ sites in activating surface intermediates. The in situ DRIFTS analysis suggested that the coexposed {001}-{101} facets increased the capacity of reversible CO₂ adsorption and that the combination of {001}-{101} and Ti³⁺ enhanced the activation and conversion kinetics of adsorbed species. The visible light responsive TiO_2–<i>x</i>{001}-{101} material is not oxidized after long-term exposure to an air environment. This work is a significant contribution to the design of efficient and stable solar fuel catalysts

A family of oxychloride amorphous solid electrolytes for long-cycling all-solid-state lithium batteries

Abstract Solid electrolyte is vital to ensure all-solid-state batteries with improved safety, long cyclability, and feasibility at different temperatures. Herein, we report a new family of amorphous solid electrolytes, xLi2O-MCly (M = Ta or Hf, 0.8 ≤ x ≤ 2, y = 5 or 4). xLi2O-MCly amorphous solid electrolytes can achieve desirable ionic conductivities up to 6.6 × 10−3 S cm−1 at 25 °C, which is one of the highest values among all the reported amorphous solid electrolytes and comparable to those of the popular crystalline ones. The mixed-anion structural models of xLi2O-MCly amorphous SEs are well established and correlated to the ionic conductivities. It is found that the oxygen-jointed anion networks with abundant terminal chlorines in xLi2O-MCly amorphous solid electrolytes play an important role for the fast Li-ion conduction. More importantly, all-solid-state batteries using the amorphous solid electrolytes show excellent electrochemical performance at both 25 °C and −10 °C. Long cycle life (more than 2400 times of charging and discharging) can be achieved for all-solid-state batteries using the xLi2O-TaCl5 amorphous solid electrolyte at 400 mA g−1, demonstrating vast application prospects of the oxychloride amorphous solid electrolytes