Latest ArticlesA novel atmospheric pressure matrix-assisted laser desorption ionization mass spectrometry (AP-MALDI-MS) method was established for the facile detection of pesticides in ambient environment. Four kinds of multi-walled carbon nanotubes (MWCNTs)-based matrix were synthesized and utilized to enhance the ionization efficiency of pesticides. Organophosphorus, anilinopyrimidine, carbamate, triazine, triazole and benzimidazole pesticides were directly desorbed and ionized from MWCNTs-based matrix in ambient environment, showing clear background and good sensitivity. In a comparison, Fe3O4-doped MWCNTs improved the intensity of pesticide ions more than the other three matrices. Moreover, MWCNTs-based matrix exhibited better performance than organic matrix. Quantitative analysis of pesticides using AP-MALDI-MS was validated to be adequate linearity, repeatability and sensitivity. Overall, AP-MALDI-MS combined with MWCNTs-based matrix enables the directly qualitative and quantitative analysis of pesticides in ambient environment.
Lithium–sulfur (Li-S) batteries are regarded as one of the most promising energy storage devices because of their low cost, high energy density, and environmental friendliness. However, Li-S batteries suffer from sluggish reaction kinetics and serious "shuttle effect" of lithium polysulfides (LiPSs), which causes rapid decay of battery capacity and prevent their practical application. To address these problems, introducing single-atom catalysts (SACs) is an effective method to improve the electrochemical performance of Li-S batteries, due to their high catalytic efficiency and definite active sites for LiPSs. In this paper, we summarized the latest developments in enhancing the electrochemical performance of cathode for Li-S batteries through introducing different SACs. Furthermore, we briefly introduced the catalytic mechanism of SACs and discussed the strategies of synthesizing SACs, including the spatial confinement strategy and the coordination design strategy. Finally, the challenges and prospects in this field are proposed. We believe that this review would help to design and fabricate high-performance Li-S batteries via introducing SACs and boost their practical application.
Sluggish kinetics of lithium/sulfur (Li/S) conversion chemistry and the ion channels formation in the cathode is still a bottleneck for developing future Li/S batteries with high-rate, long-cycling and high-energy. Here, a rational cathode structure design of an oxygen (O) and nitrogen (N) tailoring carbon fiber aerogel (OCNF) as a host material integrated with platinum (Pt) electrocatalysis interface is employed to regulate Li/S conversion chemistry and ion channel. The Pt nanoparticles were uniformly sprayed onto the S surface to construct the electrocatalysis interface (Pt/S/OCNF) for generating ion channels to promote the effective penetration of electrolyte into the cathode. This Pt/S/OCNF gives the cathode a high sulfur utilization of 77.5%, an excellent rate capacity of 813.2 mAh/g (2 C), and an outstanding long-cycling performance with a capacitance retention of 82.6% and a decay of 0.086% per cycle after 200 cycles at 0.5 C. Density functional theory (DFT) calculations reveal that the Pt electrocatalysis interface makes the cathode a high density of state (DOS) at Fermi level to facilitate the electrical conductivity, charge transfer kinetics and electrocatalysis to accelerate the lithium polysulfides (LiPSs) electrochemical conversion. Furthermore, the unique chemisorption structure and adsorption ability of Li2Sn (n = 1, 2, 4, 6, 8) and S8 on OCNF are attributed to the bridging effects of interfacial Pt and the bonding of N-Li. The Pt electrocatalysis interface combined with the unique 3D hierarchical porous structure and abundant functional active sites at OCNF guarantee strong adsorption confinement, fast Li/S electrocatalytic conversion and unblocked ion channels for electrolyte permeation in cathode.
Derivative-extremum analysis (DEA) of j-E curves is a newly proposed method of half wave potential (E1/2) and activation feature extraction from steady-state voltammetry. Here, the DEA is demonstrated to be valid in the full range of reversibility using numerical simulations with a derived universal electrode equation, providing a novel perspective of electrochemical kinetics in the reversibility domain. The results reveal that E1/2 is a better choice of the reference potential instead of equilibrium potential (Eeq) in electrode equations, especially since Eeq is meaningless in an irreversible case. The equations referenced with standard potential, E1/2 and Eeq, are summarized in three tables, and their applications in parameter determinations are specified. Finally, reversibility is proved to be a relative measure between kinetic slowness and mass transport of electroactive species, and the reversibility classifications are proposed according to the DEA feature in the reversibility domain. This work, based on the DEA principle, refines the electrode equation forms and generalizes their applicability in the full range of reversibility.
Development of adsorbent materials for highly efficient iodine capture is high demand from the perspective of ecological environment and human health. Herein, the two kinds of thiophene-based covalent organic frameworks (COFs) with different morphologies were synthesized by solvothermal reaction using thieno[3, 2-b]thiophene-2, 5-dicarbaldehyde (TT) as the aldehyde monomer and tri(4-aminophenyl)benzene (PB) or tris(4-aminophenyl)amine (PA) as the amino monomer (denoted as PB-TT COF and PA-TT COF) and the as-prepared two heteroatoms-rich COFs possessed many excellent properties, including high thermal stability and abundant binding sites. Among them, PB-TT COF exhibited ultra-high iodine uptake up to 5.97 g/g in vapor, surpassing most of adsorbents previously reported, which was ascribed to its high specific surface (1305.3 m2/g). Interestingly, PA-TT COF with low specific surface (48.6 m2/g) showed good adsorption ability for iodine in cyclohexane solution with uptake value of 750 mg/g, which was 2.38 times higher than that obtained with PB-TT COF due to its unique sheet-like morphology. Besides, the two COFs possessed good reusability, high selectivity and iodine retention ability. Based on experimental results, the adsorption mechanisms of both COFs were studied, revealing that iodine was captured by the physical-chemical adsorption. Furthermore, the both COFs showed excellent adsorption ability in real radioactive seawater treated safely, demonstrating their great potential in real environment.
Nickel cobalt bimetallic heterogeneous sulfides are attractive battery-type materials for electrochemical energy storage. However, the precise synthesis of electrode materials that integrate highly efficient ions/electrons diffusion with abundant charge transfer channels has always been challenging. Herein, an effective and concise controllable hydrothermal approach is reported for tuning the crystalline and integrated structures of MOF-derived bimetallic sulfides to accelerate the charge transfer kinetics, and thus enabling rich Faradaic redox reaction. The as-obtained low-crystalline heterogeneous NiCo2S4/Co3S4 nanocages exhibit a high specific capacity (1023 C/g at 1 A/g), remarkable rate performance (560 C/g at 10 A/g), and outstanding cycling stability (89.6% retention after 5000 cycles). Furthermore, hybrid supercapacitors fabricated with NiCo2S4/Co3S4 and nitrogen-doped reduced graphene oxide display an outstanding energy density of 40.8 Wh/kg at a power density of 806.3 W/kg, with an excellent capacity retention of 88.3% after 10000 charge-discharge cycles.
In this study, through direct pyrolysis of a nitrogen-rich metal-organic framework of Fe-BTT at different temperatures and followed by acid treatment, we prepared a series of Fe–N–CT (T = 800–1000 ℃) composite catalysts with uniform cubic morphology and homogeneously distributed active sites. Acid leaching leads to the removal of excess Fe NPs and the exposure of more pyridinic N and porphyrin-like Fe–Nx sites and creates a higher specific surface area. Structural and electrochemical performance test results showed that Fe–N–C900 catalyst exhibited the highest selectivity for CO product at –1.2 V vs. Ag/AgCl, with 496 mV of overpotential and 86.8% of Faraday efficiency, as well as excellent long-term stability, due to the good inheritance from rich-N Fe–BTT precursor.
A dual-readout sensing platform based on two signal transduction channels can integrate the unique advantages of each sensing pattern, compensate for the deficiency in the adaptive capacity, and enable a more convincing performance in analytical applications. Here, we introduce a responsive molecule dye, xylenol orange (XO), to combine with lanthanide terbium ions (Tb3+). The resultant Tb3+-XO complex exhibited tunable optical properties and was used as a novel colorimetric and luminometric dual-readout sensing platform for assaying the anthrax biomarker, dipicolinic acid (DPA). In the presence of Tb3+, the XO solution underwent a color change from yellow to magenta; however, upon adding DPA, the color changed back to yellow immediately, accompanied by the characteristic luminescence emission of Tb3+. Considering the strong affinity between DPA/XO and metal ions, the proposed sensing platform was further employed for the determination and differentiation of certain metal ions using linear discriminant analysis. This convenient dual-readout sensing platform offers several notable features and significantly promotes the application and development of lanthanide-based materials.
Although converting the greenhouse gasses carbon dioxide (CO2) into solar fuels is regarded as a convenient means of solar energy storage, the intrinsic mechanism on how the high chemical inertness linear CO2 molecules is activated and converted on a semiconductor oxide is still elusive. Herein, by creating the oxygen vacancies on the typical hexagonal tungsten oxide (WO3), we realize the continuous photo-induced CO2 reduction to selectively produce CO under light irradiation, which was verified by isotope labeling experiment. Detailed oxygen vacancies evolution investigation indicates that light irradiation can simultaneously induce the in-situ formation of oxygen vacancies on hexagonal WO3, and the oxygen vacancies promote the adsorption and activation of CO2 molecules, leading to the CO2 reduction to CO on the hexagonal WO3 via an oxygen vacancies-involved process. Besides, the existence of water further promotes the formation of CO2 reduction intermediate, further promote the CO2 photoreduction. Our work provides insight on the mechanism for converting CO2 into CO under light irradiation.
Simulating the structures and behaviors of living organisms are of great significance to develop novel multi-functional intelligent devices. However, the development of biomimetic devices with complex deformable structures and synergistic properties is still on the way. Herein, we propose a simple and effective approach to create the multi-functional stimuli-responsive biomimetic devices with independently pre-programmable colorful visual patterns, complex geometries and morphable modes. The metal organic framework (MOF)-based composite film acts as a rigidity actuation substrate to support and mechanically guide the spatial configuration of the soft chiral nematic liquid crystal elastomer (CLCE) sheet. We can directly program the structural color of the CLCE sheet by adjusting the thickness distribution without tedious chemical modification. By using this coordination strategy, we fabricate an artificial flower, which exhibits a synergistic effect of both shape transformation and color change like paeonia 'Coral Sunset' at different flowering stages, and can even perform different flowering behaviors by bending, twisting and curling petals. The assembled bionic flower is innovatively demonstrated to respond to local stimuli of humidity, heat or ultraviolet irradiation. Therefore, the spatial assembly of CLCE combined with functional MOF materials has a wide range of potential application in multi-functional integrated artificial systems.
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