Latest ArticlesMicro-nano-level photonic waveguide regulation is essential for future on-chip photonic integrated systems and is still of great challenges. We report a molecular design strategy, changing the position of the methyl substituent makes the arrangement of the three isomer molecules different in their respective crystals. Based on this strategy, three sheet-like crystals with different polygonal morphologies were prepared via solution self-assembly approach. The in-depth optical measurements demonstrated that these three microsheet crystals have different 2D optical waveguide performances related to the shapes. Our work provides a feasible design strategy and material preparation method for realizing precise 2D optical waveguide modulation, which lays the foundation for complex photonic integrated systems in the future.
Silicon (Si) is regarded as the potential anode for lithium-ion batteries (LIBs), due to the remarkable theoretical specific capacity and low voltage plateau. However, the rapid capacity decay resulting from volume variation and slow electron/ion transportation of Si limit its practical application. Here, matryoshka-type carbon-stabilized hollow silicon spheres (Si/C/Si/C) are synthesized by an aluminothermic reduction and calcination process. The Si/C/Si/C anode materials prepared at 500 ℃ (Si/C/Si/C-500) exhibit unique structures, in which amorphous region and porous structure are preserved in the Si layers. The anode based on Si/C/Si/C-500 displays an initial specific capacity of 2792 mAh/g at a current density of 100 mA/g. At 1000 mA/g, this anode retains a reversible capacity of 1673 mAh/g, 86.9% of the initial capacity after 200 cycles. Such synthetic strategy can be employed to fabricate other high-capacity anode materials with large volume variation during charge/discharge process
The nitrogen-doped carbon derived from graphitic carbon nitride (g-C3N4) has been widely deployed in activating peroxymonosulfate (PMS) to remove organic pollutants. However, the instability of g-C3N4 at high temperature brings challenges to the preparation of materials. The nitrogen-doped graphitic carbon nanosheets (N-GC750) were synthesized by magnesium thermal denitrification. Magnesium undergoes the displacement reaction with small molecules produced by the pyrolysis of g-C3N4, thereby effectively fixing carbon on the in-situ template of Mg3N2 and avoiding direct product volatilization. N-GC750 exhibited excellent performance during the PMS activation process and bisphenol A (BPA, 0.2 g/L) could be thoroughly removed in 30 min. A wide range of pH (3–11), temperature (10–40 ℃) and common anions were employed in studying the impact on system. Additionally, N-GC750 showed satisfactory reusability in cycle tests and promising applicability in real water samples. Quenching experiments and electron paramagnetic resonance (EPR) measurements indicated that singlet oxygen was the main active species coupled with partial electron transfer in N-GC750/PMS system. Furtherly, the oxidation products were identified, and their ecotoxicity was evaluated. This work is expected to provide a reference for the feasibility of preparing g-C3N4 derived carbon materials and meaningful for PMS activation.
A hexafluoroisopropanol (HFIP)-catalyzed highly diastereoselective formal [4 + 2] cyclization between ortho-hydroxyphenyl para-quinone methides and difluoroenoxysilanes is developed. This tandem protocol provides a simple and straightforward approach to assemble diverse multiply functionalized difluorinated chromans with high to excellent diastereoselectivity by employing difluoroenoxysilane as a new C2 synthon.
Fabrication of selective adsorption coatings plays a crucial role in solid-phase microextraction (SPME). Herein, new strategies were developed for the in-situ fabrication of novel cobalt-based carbonaceous coatings on the nickel-titanium alloy (NiTi) fiber substrate using ZIF-67 as a precursor and template through the chemical reaction of ZIF-67 with glucose, dopamine (DA) and melamine, respectively. The adsorption performance of the resulting coatings was evaluated using representative aromatic compounds coupled to high-performance liquid chromatography (HPLC) with ultraviolet detection (HPLC-UV). The results clearly demonstrated that the adsorption selectivity was subject to the surface elemental composition of the fiber coatings. The cobalt and nitrogen co-doped carbonaceous coating showed better adsorption selectivity for ultraviolet filters. In contrast, the cobalt-doped carbonaceous coating exhibited higher adsorption selectivity for polycyclic aromatic hydrocarbons. The fabricated fibers present higher mechanical stability and higher adsorption capability for model analytes than the commercial polydimethylsiloxane and polyacrylate fibers. These new strategies will continue to expand the NiTi fibers as versatile fiber substrates for metal-organic frameworks (MOFs)-derived coating materials with controllable nanostructures and tunable properties.
Nicotine ingested from smoking exerts neuroprotection and developmental neurotoxicity in central nervous system. It can produce several changes of cognitive behaviors through regulating the release of different neurotransmitters in the brain. However, the effects of nicotine exposure or withdrawal on neurotransmitter metabolism of hippocampus are still unclear. In this study, we real-time evaluated the dynamic alterations in neurotransmitter metabolism of hippocampal neuronal (HT22) cells induced by nicotine exposure and withdrawal at relevant exposure levels of smoking and secondhand smoke by using a microfluidic chip-coupled with liquid chromatography-mass spectrometry (MC-LC-MS) system. We found HT22 cells mainly released related neurotransmitters of tryptophan and choline metabolism, both nicotine exposure and withdraw altered its neurotransmitters and their metabolites release. Exposure to nicotine mainly altered the secretion of serotonin, kynurenic acid, choline and acetylcholine of HT22 cells to improve hippocampal dependent cognition, and the change are closely related to the dose and duration of exposure. Moreover, the altered metabolites could rapidly recover after nicotine withdrawal, but picolinic acid was elevated. MC-LC-MS system used in present study showed a greater advantage to detect unstable metabolites than conventional method by using in vitro model, and the results of dynamic alterations of neurotransmitter metabolism induced by nicotine might provide a potential targets for drug development of neuroprotection or cognitive improvement.
Owing to the exorbitant overpotential and serious carrier recombination of graphitic carbon nitride (g-C3N4), noble metal (NM) is usually served as the H2 evolution co-catalyst. Although the NM (such as Pt) nanoparticles can reduce the H2 evolution overpotential, the weak van der Waals interaction between Pt and g-C3N4 makes against the charge transfer. Herein, the solvothermal method is developed to achieve semi-chemical interaction between Pt and g-C3N4 nanotube (Pt-CNNT) for fast charge transfer. Moreover, the generated in-plane homojunction of CNNT can accelerate charge separation and restrain recombination. Meanwhile, the metallic Pt is an excellent H2 evolution co-catalyst. Photo/electrochemical tests verify that the semi-chemical interaction can improve photogenerated charge separation and transferability of CNNT. As a result, the photocatalytic H2 evolution turnover frequency (TOF) of Pt-CNNT under visible light irradiation reaches up to 918 h−1, which is one of the highest in the g-C3N4-based photocatalysts. This work provides a new idea to improve the charge transfer for efficient photocatalytic H2 evolution.
Aprotic Li-CO2 batteries have attracted growing interest due to their high theoretical energy density and its ability to use green house gas CO2 for energy storage. However, the poor ability of activating CO2 in organic electrolyte often leads to the premature termination of CO2 reduction reaction (CO2RR) directly. Here in this work, cetyl trimethyl ammonium bromide (CTAB) was introduced into a dimethyl sulfoxide (DMSO) based Li-CO2 battery for the first time to enhance the CO2RR. Significantly improved electrochemical performances, including reduced discharge over-potential and increased discharge capacity, can be achieved with the addition of CTAB. Ab initio molecular dynamics (AIMD) simulations show that quaternary ammonium group CTA+ can accelerate CO2 reduction process by forming more stable contact ion pair (CIP) with CO2-, reducing the energy barrier for CO2RR, thus improving the CO2 reduction process. In addition, adding CTA+ is also favorable for the solution-phase growth of discharge products because of the improved migration ability of stable CTA+-CO2- CIP in the electrolyte, which is beneficial for improving the utilization ratio of cathode. This work could facilitate the development of CO2RR by providing a novel understanding of CO2RR mechanism in organic system.
Considering that cathode of microbial electrochemical system (MES) is a good electrons source for methane production via direct/indirect electron transfer to electroactive microorganisms, and that Fe(0) is also a confirmed electron donor for some electroactive microorganisms through metal-microbe direct electron transfer (DET), Fe(0)-cathode was equipped into an MES digester to enhance cathodic methane production. The results of this study indicated that the potential DET participator, Clostridium possibly obtained electrons directly from Fe(0)-cathode via metal-microbe electrons transfer, then transferred electrons directly to the definite DET participators, Methanosarcina/Methanothrix via microbe-microbe electrons transfer for CH4 production. In addition, Methanobacterium is another specially enriched methanogen on Fe(0)-cathode, which might obtain electrons directly from Fe(0)-cathode to produce CH4 via metal/electrode-microbe DET. The increment of conductivity of cathodic sludge in Fe(0)-cathode MES digester (R1) further confirmed the enrichment of electroactive microorganisms participating in DET process. As a consequence, a higher CH4 production (1205–1508 mL/d) and chemical oxygen demand (COD) removal (79.0%-93.8%) were achieved in R1 compared with graphite-cathode MES digester (R2, 720–1090 mL/d and 63.6%-85.6%) and the conventional anaerobic digester (R3, 384–428 mL/d and 35.2%-41.0%). In addition, energy efficiency calculated indicated that the output energy of CH4 production was 8.16 folds of electricity input in Fe(0)-cathode MES digester.
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