Latest ArticlesFe-N/C is a promising oxygen reduction reaction (ORR) catalyst to substitute the current widely used precious metal platinum. Cost-effectively fabricating the Fe-N/C material with high catalytic activity and getting in-depth insight into the responsible catalytic site are of great significance. In this work, we proposed to use biomass, tea leaves waste, as the precursor to prepare ORR catalyst. By adding 5% FeCl3 (wt%) into tea precursor, the pyrolysis product (i.e., 5%Fe-N/C) exhibited an excellent four-electron ORR activity, whose onset potential was only 10 mV lower than that of commercial Pt/C. The limiting current density of 5%Fe-N/C (5.75 mA/cm2) was even higher than Pt/C (5.44 mA/cm2). Compared with other biomass or metal organic frameworks derived catalysts, 5%Fe-N/C showed similar ORR activity. Also, both the methanol tolerance and material stability performances of as-prepared 5%Fe-N/C catalyst were superior to that of Pt/C. X-ray adsorption fine structure characterization revealed that the FeN4O2 might be the possible catalytic site. An appropriate amount of iron chloride addition not only facilitated catalytic site formation, but also enhanced material conductivity and reaction kinetics. The results of this work may be useful for the Fe based transition metal ORR catalyst design and application.
A lithium-sulfur (Li-S) system is an important candidate for future lithium-ion system due to its low cost and high specific theoretical capacity (1675 mAh/g, 2600 Wh/kg), which is greatly hindered by the poor conductivity of sulfur, large volume change and dissolution of lithium polysulfides. Two-dimensional (2D) materials with monolayers or few-layers usually have peculiar structures and physical/chemical properties, which can resolve the critical issues in Li-S batteries. Especially, the metal-based 2D nanomaterials, including ferrum, cobalt or other metal-based composites with various anions, can provide high conductivity, large surface area and abundant reaction sites for restraining the diffusion for lithium polysulfides. In this mini-review, we will present an overview of recent developments on metal-based 2D nanomaterials with various anions as the electrode materials for Li-S batteries. Since the main bottleneck for the Li-S system is the shuttle of polysulfides, emphasis is placed on the structure and components, physical/chemical interaction and interaction mechanisms of the 2D materials. Finally, the challenges and prospects of metal-based 2D nanomaterials for Li-S batteries are discussed and proposed.
Transition metal hydroxides/oxyhydroxides have recently emerged as highly active electrocatalysts for oxygen evolution reaction in alkaline water electrolysis, while have not yet been widely investigated for hydrogen evolution electrocatalysts owing to their unfavorable H*-adsorption, making it difficult to construct an overall-water-splitting cell for hydrogen production. In this work, we proposed a straightforward and effective approach to develop an efficient in-plane heterostructured CoOOH/Co(OH)2 catalyst via In-situ electrochemical dehydrogenation method, in which the dehydrogenated –CoOOH and Co(OH)2 at the surface synergistically boost the hydrogen evolution reaction (HER) kinetics in base as confirmed by high-resolution transmission electron microscope, synchrotron X-ray absorption spectroscopy, and electron energy loss spectroscopy. Due to the In-situ dehydrogenation of ultrathin Co(OH)2 nanosheets, the catalytic activity of the CoOOH/Co(OH)2 heterostructures is progressively improved, which exhibit outstanding hydrogen-evolving activity in base requiring a low overpotential of 132 mV to afford 10 mA/cm2 with very fast reaction kinetics after 60 h dehydrogenation. The gradually improved catalytic performance for the CoOOH/Co(OH)2 is probably due to the enhanced H*-adsorption induced by the synergistic effect of heterostructures and better conductivity of CoOOH relative to electrically insulating Co(OH)2. This work will open the opportunity for a new family of transition metal hydroxides/oxyhydroxides as active HER catalysts, and also highlight the importance of using in situ techniques to construct precious metal-free efficient catalysts for alkaline hydrogen evolution.
Lithium-sulfur batteries (LSBs) are among the most promising series of next-generation high density energy storage systems. However, the problem of "shuttle effect" caused by dissolution and migration of polysulfide intermediates has severely inhibited their practical applications. Herein, TiO2-carbon nanocomposites embedded hierarchical porous carbon (T-hPC) interlayers are fabricated via Ti3C2 MXene assisted phase separation and annealing method. The T-hPC processes micro- to macro-scale multi-pores along with highly adsorptive and catalytic carbon supported TiO2 nanoparticles, which significantly enhances the polysulfides immobilization and improves the redox reaction kinetics when applied as lithium-sulfur battery interlayers. An initial discharge specific capacity of 1551.1 mAh/g and a stable capacity of 893.8 mAh/g after 200 cycles at 0.5 C are obtained, corresponding to a capacity decay rate of only 0.04% per cycle. The investigations in this paper can provide a simple and effective strategy to enhance the electrochemical properties for lithium-sulfur batteries.
6-Thioguanine (6TG) is a widely used chemotherapeutic agent for the treatment of a variety of human diseases including acute lymphoblastic leukemia. After entry into cells, 6TG is metabolically converted into 6-thioguanosine (SG) nucleotide that can be incorporated into the genome during DNA replication. SG in genomic DNA could induce cell death by triggering the post-replicative mismatch repair (MMR) pathway. Meanwhile, incorporation of 6TG into the CpG sites could perturb the global DNA methylation and gene regulation. However, the effect of 6TG on RNA modifications is still unknown. Adenosine-to-inosine (A-to-I) editing in RNA is one of the most common post-transcriptional modifications in mammals and there is growing evidence showing the significant alteration of A-to-I RNA editing in tumor tissues compared to normal tissues. In the current study, we examined the incorporation of 6TG into RNA and investigated its effect on A-to-I editing of bladder cancer-associated protein (BLCAP) transcript in acute lymphoblastic leukemia cells. The results demonstrated that SG could be incorporated into various RNA species, with mRNA having the most abundant SG. In addition, the results showed 6TG treatment elevated A-to-I editing in BLCAP transcript through upregulating adenosine deaminase 2 acting on RNA (ADAR2), which eventually contributes to the decreased cell viability. This study highlights a new mechanism of the cytotoxicity of 6TG in inducing cell death.
The transformation of quantum dots (QDs) by organisms has attracted broad attention but remains unclear. Understanding of the metabolites helps to reveal the transformation pathway of QDs. Cd containing-metallothionein (MT) are the main species formed by Cd released from CdSe QDs in HepG2 cells, while speciation analysis of Cd containing MTs remains a challenge because MTs has several subisoforms and can bind with several metals. Herein, we built a hyphenated platform for speciation analysis of QDs in HepG2 cells after treatment with CdSe/ZnS QDs. The Cd-containing MTs were separated in reversed phase high performance liquid chromatography (RP-HPLC) and subsequently online detected by inductively coupled plasma mass spectrometry (ICP-MS) and electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-Q-TOF-MS) parallelly. Four groups of Cd-containing metabolites were found by detecting Cd in ICP-MS. Their structures were identified in ESI-Q-TOF-MS and further confirmed with standards of four subisoforms of MT, including N-terminal acetylation MT2a, N-terminal acetylation MT1e, N-terminal acetylation MT1g and MT1m. Each group of them contains various stoichiometry of Cd/Zn. The metabolites of QDs remain same while the concentrations of each metabolite and its stoichiometry of Cd/Zn vary for different incubation concentration/time. This work provides a new parallel hyphenation technique of HPLC-ICP-MS/ESI-MS with high separation resolution and powerful detection ability, and the obtained results provide detailed metabolism information of QDs in HepG2 cells after treatment of CdSe/ZnS QDs, contributing to deep exploration of the functional mechanisms of QDs in organisms.
Application of Li-oxygen (Li-O2) battery is in urgent need of bifunctional ORR/OER electrocatalyst. A surface-functionalization CoP/Ti3C2Tx composite was fabricated theoretically, with the optimized electronic structure and more active electron, which is beneficial to the electrochemical reaction. The accordion shaped Ti3C2Tx is featured with large specific surface area and outstanding electronic conductivity, which is beneficial for the adequate exposure of active sites and the deposition of Li2O2. Transition metal phosphides provide more electrocatalytic active sites and present good electrocatalytic effect. The CoP/Ti3C2Tx composite served as the electrocatalyst of Li-O2 battery reaches a high specific discharge capacity of 17, 413 mAh/g at 100 mA/g and the lower overpotential of 1.25 V, superior to those of the CoP and Ti3C2Tx individually. The composite of transition metal phosphides and MXene are applied in Li-O2 battery, not only demonstrating higher cycling stability of the prepared CoP/Ti3C2Tx composite, but pointing out the direction for their electrochemical performance improvement.
Heavy metals usually exist stably as the species of organic complexes in high-salinity wastewater. Therefore, their effective removal is challenging, especially when the initial pH is neutral. Herein, a novel nitrogen doped biomass-based composite (N-CMCS) was synthesized to remove the complexed heavy metal of Cr(Ⅲ)-carboxyl. The maximum adsorption capacity of Cr(Ⅲ)-Citrate (Cr-Cit) by N-CMCS under neutral pH (7.0) and high-salinity (200 mmol/L NaCl) condition was up to 2.50 mmol/g. And the removal performance remained stable after 6 times of regeneration. Combined with species and characterizations analysis, electrostatic attraction and hydrogen bonding were the main mechanisms for N-CMCS to remove Cr(Ⅲ)-carboxyl complexes. Dynamic adsorption indicated N-CMCS column could treat about 1300 BV simulated wastewater and 350 BV actual wastewater with the concentration of effluent lower than 1.0 mg/L. Furthermore, N-CMCS could remove a variety of complexed heavy metal ions under neutral pH, indicating the great potential in practical application.
A 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.
Separator is supposed to own outstanding thermal stability, superior wettability and electrolyte uptake, which is essential for developing high-rate and safe lithium metal batteries (LMBs). However, commercial polyolefin separators possess poor wettability and limited electrolyte uptake. For addressing this issue, we put forward a composite separator to implement above functions by doping layered-silicate (talcum) into polyvinylidene fluoride (PVDF). With significant improvement of electrolyte absorption benefiting from the strong adsorption energy values (-1.64 ~ -1.70 eV) between talcum and the electrolyte in lithium metal batteries, PVDF/Talcum (PVDF/TM) composite separator owns a small contact angle and superior electrolyte uptake. PVDF/TM composite separator with 10 wt% talcum (T-10) owns a tiny contact angle of 8°, while those of polypropylene (PP) and PVDF are 48° and 20° with commercial electrolyte. Moreover, the addition of thermotolerant talcum endows the T-10 composite separator with great thermostability, whose thermal shrinkage is only 5.39% at 150 ℃ for 0.5 h. The cell with LiFeO4 cathode and the T-10 composite separator reaches 91.7 mAh/g in discharge capacity at 4.8 mA/cm2 (10 C), far superior to that with pure PVDF separator (56.3 mAh/g) and PP (51.4 mAh/g).
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