The high cost and poor durability of Pt nanoparticles (NPs) have always been great challenges to the commercialization of proton exchange membrane fuel cells (PEMFCs). Pt-based intermetallic NPs with ...a highly ordered structure are considered as promising catalysts for PEMFCs due to their high catalytic activity and stability. Here, we reported a facile method to synthesize N-doped carbon encapsulated PtZn intermetallic (PtZn@NC) NPs via the pyrolysis of Pt@Zn-based zeolitic imidazolate framework-8 (Pt@ZIF-8) composites. The catalyst obtained at 800 °C (10%-PtZn@NC-800) was found to exhibit a half-wave potential (
E
1/2
) up to 0.912 V versus reversible hydrogen electrode (RHE) for the cathodic oxygen reduction reaction in an acidic medium, which shifted by 26 mV positively compared to the benchmark Pt/C catalyst. Besides, the mass activity and specific activity of 10%-PtZn@NC-800 at 0.9 V versus RHE were nearly 3 and 5 times as great as that of commercial Pt/C, respectively. It is worth noting that the PtZn@NC showed excellent stability in ORR with just 1 mV of the
E
1/2
loss after 5,000 cycles, which is superior to that of most reported PtM catalysts (especially those disordered solid solutions). Furthermore, such N-doped carbon shell encapsulated PtZn intermetallic NPs showed significantly enhanced performances towards the anodic oxidation reaction of organic small molecules (such as methanol and formic acid). The synergistic effects of the N doped carbon encapsulation structure and intermetallic NPs are responsible for outstanding performances of the catalysts. This work provides us a new engineering strategy to acquire highly active and stable multifunctional catalysts for PEMFCs.
Fluorescent carbon nanodots (CNDs) have exhibited attractive potential for biomedical applications due to their intriguing luminescent properties and good biocompatibility. One interesting property ...of CNDs is that they typically show different emission colors upon optical excitation using different wavelengths. However, it is still a challenge to obtain emissions covering the entire visible spectrum with comparable intensity with only one type of CND. Herein, CNDs with tunable full-color luminescence are successful prepared by a solvothermal approach, show broad absorption (200–700 nm) and fluorescence emission (nearly cover the entire visible region: from 400 to 700 nm) with comparable fluorescence intensities. The oxidation (o-CNDs) and reduction (r-CNDs) of CNDs surface would lead to the shifting of photoluminescence band into blue/green and red-light region, respectively. Further spectroscopic analyses and structural characterizations of CNDs (pristine state), o-CNDs (oxidation state) and r-CNDs (reduction state) demonstrate that O-related defect states (CO) and N-related defect states (CN) on surface of CNDs should be responsible for blue/green and red fluorescence emissions, respectively. Moreover, the CNDs are found to be biocompatible, as verified by in vitro cells assay and in vivo histological analysis. In vivo fluorescence imaging assay demonstrates that CNDs can be excreted through intestine and bladder system. The tunable full-color emission, good biocompatibility and metabolism suggest that the CNDs are promising fluorescent probes for biomedical applications.
Carbon nanodots with tunable full-color luminescence can be controlled by oxygen/nitrogen-related surface state, and can serve as optical fluorescence nanoprobes in multicolor bio-imaging. Display omitted
In humans receiving intestinal transplantation (ITx), long-term multilineage blood chimerism often develops. Donor T cell macrochimerism (≥4%) frequently occurs without graft-versus-host disease ...(GVHD) and is associated with reduced rejection. Here we demonstrate that patients with macrochimerism had high graft-versus-host (GvH) to host-versus-graft (HvG) T cell clonal ratios in their allografts. These GvH clones entered the circulation, where their peak levels were associated with declines in HvG clones early after transplant, suggesting that GvH reactions may contribute to chimerism and control HvG responses without causing GVHD. Consistently, donor-derived T cells, including GvH clones, and CD34+ hematopoietic stem and progenitor cells (HSPCs) were simultaneously detected in the recipients' BM more than 100 days after transplant. Individual GvH clones appeared in ileal mucosa or PBMCs before detection in recipient BM, consistent with an intestinal mucosal origin, where donor GvH-reactive T cells expanded early upon entry of recipient APCs into the graft. These results, combined with cytotoxic single-cell transcriptional profiles of donor T cells in recipient BM, suggest that tissue-resident GvH-reactive donor T cells migrated into the recipient circulation and BM, where they destroyed recipient hematopoietic cells through cytolytic effector functions and promoted engraftment of graft-derived HSPCs that maintain chimerism. These mechanisms suggest an approach to achieving intestinal allograft tolerance.
The development of rechargeable aluminum batteries (RABs) has consistently relied on the logical selection and design of cathode materials. Se has a high electrical conductivity while S has a high ...theoretical specific capacity; yet, both materials are known to present lethal shuttle effects, space expansion, and slow reaction kinetics. The development of RABs will be accelerated if the synergistic properties of both materials can be utilized. Various ratios of SexSy as the cathode materials for RABs, and a series of electrochemical tests are shown in this work. The rise in the ratio of Se and S leads to the improvement of the cycling performance. However, the shuttle effect of Se and S has a fatal blow to the performance of the battery. To solve this problem, (mesostructured carbon materials) CMK3 modified separators were employed between the cathode and anode to further limit the dissolution of Se, considerably improving the utilization of the active materials. Therefore, initial capacity of Al/GF/C@CMK-3/SexSy is about 539.4 mAh g−1 and reversible capacity of 314.2 mAh g−1 was likewise maintained after 500 cycles at 1.0 A g−1. RABs based on Al/S and Al/Se batteries have promising research avenues opened up by Al/SexSy batteries based on CMK3 modified separators.
•SexSy composites are synthesized by simple calcination.•CMK-3 separator modification avoids dissolution of selenide and stabilizes its performance.•SexSy/CMK-3 still remain 314.2 mAh/g after 500 cycles at 1 A/g.
Nanoparticles (NPs) are widely used in polishing slurries for ensuring desired material removal and global planarization. Herein, novel multicomponent core–shell abrasive systems have been fabricated ...via an efficient chemical approach towards photochemical (photo-assisted chemical) mechanical polishing (PCMP) processes. The developed composite particles involved low-modulus mesoporous silica (mSiO2) cores and high-activity Gd-doped ceria (CeO2) shells. Compared to commercial CeO2 NPs, the mSiO2@CeGdO2 abrasives enabled superior fused silica surface quality in both CMP and PCMP tests. Furthermore, the as-proposed composites allowed an evident removal efficiency enhancement in the presence of ultraviolet light radiation. The improved polishing performance can be attributed to (i) the optimization of interfacial contact state and material removal behavior, (ii) the increasements of trivalent cerium and oxygen vacancy, and (iii) the enhancement of photochemical and tribochemical activities of the mSiO2@CeGdO2 heterostructured abrasive systems. The purpose of this work is to provide some contributions to the rational design and fabrication of functional abrasive systems for high-performance PCMP and other field-assisted finishing practices through abrasive structure regulation, surface chemistry, and defect engineering.
In recent years, inorganic perovskite solar cells (PSCs) based on CsPbI3 have made significant progress in stability compared to hybrid organic–inorganic PSCs by substituting the volatile organic ...component with Cs cations. However, the cubic perovskite structure of α-CsPbI3 changes to the orthorhombic non-perovskite phase at room temperature resulting in efficiency degradation. The partial substitution of an I ion with Br ion benefits for perovskite phase stability. Unfortunately, the substitution of Br ion would enlarge bandgap reducing the absorption spectrum range. To optimize the balance between band gap and stability, introducing and optimizing the spatial bandgap gradation configuration is an effective method to broaden the light absorption and benefit the perovskite phase stability. As the bandgap of the CsPb(I1–xBrx)3 perovskite layer can be adjusted by I-Br composition engineering, the performance of CsPb(I1–xBrx)3 based PSCs with three different spatial variation Br doping composition profiles were investigated. The effects of uniform doping and gradient doping on the performance of PSCs were investigated. The results show that bandgap (Eg) and electron affinity(χ) attributed to an appropriate energy band offset, have the most important effects on PSCs performance. With a positive conduction band offset (CBO) of 0.2 eV at the electron translate layer (ETL)/perovskite interface, and a positive valence band offset (VBO) of 0.24 eV at the hole translate layer (HTL)/perovskite interface, the highest power conversion efficiency (PCE) of 22.90% with open–circuit voltage (VOC) of 1.39 V, short–circuit current (JSC) of 20.22 mA/cm2 and filling factor (FF) of 81.61% was obtained in uniform doping CsPb(I1–xBrx)3 based PSCs with x = 0.09. By carrying out a further optimization of the uniform doping configuration, the evaluation of a single band gap gradation configuration was investigated. By introducing a back gradation of band gap directed towards the back contact, an optimized band offset (front interface CBO = 0.18 eV, back interface VBO = 0.15 eV) was obtained, increasing the efficiency to 23.03%. Finally, the double gradient doping structure was further evaluated. The highest PCE is 23.18% with VOC close to 1.44 V, JSC changes to 19.37 mA/cm2 and an FF of 83.31% was obtained.
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•Perfluorohexanoic acid (PFHxA) was the predominant PFASs in some cities.•PFOS represented a small proportion of ∑PFASs.•More than 4000kgyear−1 PFASs are discharged into the East ...China Sea.
Spatial distributions of perfluoroalkyl substances (PFASs) were investigated in surface waters in Shanghai, Jiangsu and Zhejiang Provinces of eastern China during 2011. A total of 39 samples of surface waters, including 29 rivers, 6 lakes and 4 reservoirs were collected. High performance liquid chromatography/negative electrospray ionization-tandem mass spectrometry (HPLC/(−)ESI-MS/MS) was used to identify and quantify PFASs. Concentrations of PFAS were greater in Shanghai than that in Zhejiang Province. Concentrations of the sum of PFASs (∑PFASs) in Shanghai and Kunshan ranged from 39 to 212ngL−1, while in Zhejiang Province, concentrations of ∑PFASs ranged from 0.68 to 146ngL−1. Perfluorooctanoic acid (PFOA) was the prevalent PFAS in Shanghai. In contrast, PFOA and perfluorohexanoic acid (PFHxA) were the prevalent PFASs in Zhejiang Province. Concentrations of perfluorooctane sulfonate (PFOS) ranged from <0.07 to 9.7ngL−1. Annual mass of ∑PFASs transported by rivers that flow into the East China Sea were calculated to be more than 4000kg PFASs. Correlation analyses between concentrations of individual PFASs showed the correlation between PFHxA and PFOA was positive, while the correlation between PFHxA and perfluorooctane sulfonamide (FOSA) was negative in Shanghai, which indicated that PFHxA and PFOA have common sources. Principal component analysis (PCA) was employed to identify important components or factors that explain different compounds, and results showed that PFHxA and FOSA dominated factor loadings.
The purpose of this study was to increase the dissolution of glycyrrhetinic acid (GA) by preparing ternary solid dispersion (TSD) systems containing alkalizers, and to explore the modulating ...mechanism of alkalizers in solid dispersion systems. GA TSDs were prepared by hot melt extrusion (HME) with Kollidon
VA64 as the carrier and L-arginine/meglumine as the alkalizers. The in vitro release of the TSD was investigated with a dissolution test, and the dissociation constant (pKa) was used to describe the ionization degree of the drug in different pH buffers. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectra, X-ray photoelectron spectroscopy (XPS), and a molecular model were used for solid-state characterizations and to study the dissolution mechanism of the TSDs. It was evident that the dissolution of GA significantly increased as a result of the TSD compared to the pure drug and binary solid dispersion. SEM, DSC, and XPRD data showed that GA transformed into an amorphous form in TSD. As illustrated by FTIR, Raman, XPS, and molecular docking, high binding energy ion-pair complexes formed between GA and the alkalizers during the process of HME. These can destroy the H-bond between GA molecules. Further, intermolecular H-bonds formed between the alkalizers and Kollidon
VA64, which can increase the wettability of the drug. Our results will significantly improve the solubility and dissolution of GA. In addition, the lower pKa value of TSD indicates that higher ionization is beneficial to the dissolution of the drug. This study should facilitate further developments of TSDs containing alkalizers to improve the dissolution of weakly acidic drugs and gain a richer understanding of the mechanism of dissolution.
Shale barrier distributes widely in heavy oil reservoirs. However, the influence mechanism of shale barrier on heavy oil recovery is still unclear. For this reason, the influence mechanism in physics ...was first proposed. Then, the influence mechanism in mechanics was concluded from the steam migration velocity decreasing and the heat conduction rate enhancing. Especially, it was obtained by theoretical analysis that shale barrier has a positive effect on heavy oil recovery under the reasobale condition. To validate the influence mechanism, a numerical model containing the shale barrier was established. The numerical results validated the influence mechanism in physics from two aspects of steam chamber shape and migration behaviors of steam and oil. In addition, the numerical results showed that it has the higher cumulative oil volume and the lower residual oil saturation for the heavy oil recovery when considering reasonable distribution of shale barrier, validating the conclusion that shale barrier has a positive effect on heavy oil recovery. Additionally, the reason behind positive effect caused by the shale barrier was analyzed, including the longer production period, the higher steam injection volume and the lower heat loss. Especially, economic feasibility for heavy oil recovery was evaluated by calculating net present value (NPV) and the ratio of the produced energy to the consumed energy. Finally, the parametric analysis was performed to investigate effects of geometric properties of shale barrier on heavy oil recovery, including the barrier location, the barrier length, the barrier thickness and the number of barrier. The results show that: (1) the reasonable distribution of barrier location far away from the injection well is advantageous for the heavy oil recovery; (2) the reasonable increasing of barrier length, thickness and number is beneficial for the heavy oil recovery.
►Influence mechanism of shale barrier on heavy oil recovery using SAGD was proposed.►Influence mechanism was validated by numerical model considering shale barrier.►Shale barrier has, to some extend, a positive effect on heavy oil recovery using SAGD.►Shale barrier induced potential benefits for the heavy oil recovery were concluded.
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