Chemphyschem最新文献

The major challenges in enhancing the cycle life of lithium-sulfur (Li-S) batteries are polysulfide (PS) shuttling and sluggish reaction kinetics (S to Li₂S, Li₂S to S). To alleviate the above issues, the use of heteroatom-doped carbon as a cathode host matrix is a low-cost and efficient approach, as it works as a dual-functional framework for PS anchoring as well as an electrocatalyst for faster redox kinetics. Here, the dual role of heteroatom-doped carbon sheets (CS) in the chemisorption of Li₂S₆ and catalysis of its faster conversion to Li₂S is established. To substantiate the catalytic effect, composite cathodes were prepared by encapsulating sulfur in CS which is further blended with carbon nanotubes (CNTs) to form a free-standing cathode. The electrochemical performances of the three cathodes (S@Fe-N-CS-CNT, S@Fe-S-CS-CNT, and S@Fe-NS-CS-CNT) were evaluated by constructing Li-S cells. The S@Fe-NS-CS-CNT delivers a high initial discharge capacity of 1017 mAh g^-1 at 0.5 C rate and sustains a capacity of 751 mAh g^-1 after 260 cycles with a capacity retention of 73.8 %. Even at a high S loading (12 mg cm^-2), it delivers an initial discharge capacity of 892 mAh g^-1 and retained 575 mAh g^-1 after 200 cycles.

The distinctive structure of MXene offers exceptional electron transport properties, abundant surface chemistry, and robust mechanical attributes, thereby bestowing it with remarkable advantages and promising prospects in the realm of surface-enhanced Raman scattering (SERS). This review comprehensively outlines the evolution, synthesis methodologies, and characterization techniques employed for MXene-based SERS substrates. It delves into the intricacies of its SERS enhancement mechanism, substrate variants, and performance metrics, alongside showcasing its diverse applications spanning molecular detection, biosensing, and environmental monitoring. Furthermore, it endeavors to pinpoint the research bottlenecks and chart the future research trajectories for MXene-based SERS substrates.

Carboxy groups on the edges of nanographene (NG) enable functionalization for realizing NG-organic hybrid materials. Therefore, assessment of the edge-functionalization of the electronic structures of NGs is valuable for the rational design of functional carbon materials. In this study, the structures of model NGs comprising 174 carbon atoms with armchair edges and various functional groups at the edges were computed. To achieve the greatest possible similarity between the computed structure and the real one, the carbon framework was designed based on experimental observations. The functional groups can be accessed via suitable chemical reactions. The computations predicted that although the conversion of carboxyl groups with electron-withdrawing/donating groups influences the orbital energies, the HOMO-LUMO (H-L) gap is not significantly affected, except in a few cases. Among the evaluated examples, π-extension had the greatest influence on the H-L gap. Interestingly, for the Pd2+-coordinated NG, the participation of the low-lying LUMO localized on Pd2+ in the surface-to-metal transitions seemingly narrowed the H-L gap, and a surface-to-ligand transition was observed.

Herein, we employed a combination of static electronic structure calculations and nonadiabatic dynamics simulations at linear-response time dependent density functional theory (LR-TDDFT) level with the optimally tuned range-separated hybrid (OT-RSH) functional to explore the ultrafast photoinduced dynamics of a zinc phthalocyanine-benzoperylenetriimide (ZnPc-BPTI) conjugate. Due to the flexibility of the linker, we identified two major conformations: the stacked conformation (ZnPc-BPTI-1) and the extended conformation (ZnPc-BPTI-2). Since the charge transfer states are much lower than the lowest local excitation in ZnPc-BPTI-1, which is contrary to ZnPc-BPTI-2, the ultrafast electron transfer (~3.6 ps) is only observed in the nonadiabatic simulations of ZnPc-BPTI-1 upon local excitation around the absorption maximum of ZnPc. However, when considering the solvent effects in benzonitrile: the lowest S₁ states are both charge transfer states from ZnPc to BPTI for different conformers. Subsequent nonadiabatic dynamics simulations indicate that both conformers experience ultrafast electron transfer in benzonitrile with two time constants of 90 [100] fs and 1.40 [1.43] ps. Our present work not only agrees well with previous experimental study, but also points out the important role of conformational changes and solvent effects in regulating the photodynamics of organic donor-acceptor conjugates.

Nuclear spins in small molecules dissolved in stretched hydrogels typically have population-averaged residual interactions. The nuclear magnetic resonance (NMR) spectra of these systems often show additional peaks and splittings compared with free solutions. Residual dipolar couplings (RDCs) and quadrupolar couplings (RQCs) are observed for guest 1H or 2H nuclear spins, respectively. Dimethyl sulfoxide (DMSO) is an exquisitely sensitive probe of such biologically relevant environments since it is prochiral and becomes effectively chiral when embedded in anisotropic gelatin-based hydrogels. Measured 1H RDCs and 2H RQCs were used to estimate bond order parameters over a wide range of stretching extents. At the largest extent of stretching, the 2H splittings were -73.0 and -9.4 Hz, similar to those found for guest molecules in liquid crystals. Inhomogeneous line broadening of the 2H resonances was related to the size of the RQC due to a spatial distribution of RQCs, which was revealed using a one-dimensional slice selective imaging experiment along the stretching direction. 1H NMR spectra exhibited homogeneous line broadening, with resonance integrals that indicated concealed multiplet structure. Understanding molecular bond ordering in mechanically oriented environments provides a conceptual framework for investigating more complex systems including zeolites and those found in vivo.

Herein, we synthesized a series of catalysts comprising iron (Fe), and nickel (Ni) supported on γ-Al₂O₃ nano-powder (Fe-Ni/γ-Al₂O₃) by controlling the stoichiometric ratio of the metals through the facile co-precipitation method. The ratio of Fe and Ni on the γ-Al₂O₃ support varied from 0 to 70 weight percent (wt %). The freshly prepared catalysts phase, structure, and crystallinity exhibited variability as the Fe and Ni stoichiometric ratios were altered. The catalyst demonstrated effective performance in methane cracking, producing turquoise hydrogen and carbon nanotubes (CNTs) using a temperature-programmed reactor coupled with mass spectrometry. It was observed that the Fe3Ni4 catalyst, comprising 30 % Fe and 40 % Ni, exhibited a maximum methane conversion rate of 85 % and a hydrogen yield of 72.55 %. Moreover, the values of turnover frequency (2.38 min^-1) indicated that the Fe3Ni4 had a better production rate and was consistent with the conversion process throughout the reaction. The structural attributes of the spent catalysts were examined, revealing variations in the lateral length, uniformity, and diameters (~33 to 56 nm) of the produced Carbon Nanotubes (CNTs) when transitioning from catalyst Fe0Ni7 to Fe7Ni0. The investigation underscored the significance of metal stoichiometrically controlled catalysts and their catalytic efficacy in methane cracking applications.

Advancing grid-scale energy storage technologies is crucial for realizing a fully renewable energy landscape, with non-aqueous redox flow batteries (NRFBs) presenting a promising solution. One of the current challenges in NRFBs stems from the low energy density of redox active materials, primarily due to their limited solubility in non-aqueous solvents. Herein, this study explores the solubility of vanadium(IV/V) bis-hydroxyiminodiacetate (VBH) crystals in acetonitrile, aiming to use them as anionic catholytes in NRFBs. We focused on enhancing VBH solubility by modifying the structure of the alkylammonium cation. Employing periodic density functional theory and a solvation model, we calculated the dissolution free energy ([[EQUATION]]), which includes sublimation ([[EQUATION]]) and solvation ([[EQUATION]]) energies. Our results indicate that neither elongating straight-chain alkyl groups beyond a tetrabutylammonium baseline nor introducing bulky substituents at the nitrogen center significantly enhances solubility. However, the introduction of carbon spacers combined with terminal bulky substituents markedly improves solubility by favorably altering both [[EQUATION]] and [[EQUATION]]. These findings underline the nuanced impact of cation structure on solubility and suggest a viable approach to optimize VBH-based anionic catholytes. This advancement promises to enhance NRFB efficiency and sustainability, marking a significant step forward in energy storage technology.

The red/green cyanobacteriochrome (CBCR) slr1393g3 exhibits a quantum yield of only 8% for its forward photoconversion significantly lower than other species from the same CBCR subfamily. The cause for this reduced photoconversion is not yet clear, although in the related NpR6012g4 dark-state structural heterogeneity of a paramount Trp residue has been proposed to cause the formation of nonproductive subpopulation. However, there is no such information on the equivalent residue in slr1393g3, W496. Here we use solid-state NMR to explore all possible sidechain rotamers of this Trp residue and their local interactions at the atomic level. The indole nitrogen (Nε1) is used as an NMR probe, achieved by site-specific 15N-indole labeling of a quadruply Trp-deleted variant and trehalose vitrification technique. The data reveal a set of seven indole rotamers of W496 with four distinct environments for the Nε1-H group. Only a minority population of 20% is found to retain the π-stacking and hydrogen-bonding interactions with the chromophore in the dark state that has been assigned to account for complete forward photoconversion. Our results demonstrate the direct role of W496 in modulating the forward quantum yield of slr1393g3 via rearrangement of its sidechain rotameric conformations.

Catalytic NO reduction by CO is imperative to satisfy the increasingly rigorous emission regulations. Identifying the structural characteristic of crucial intermediate that governs the selectivity of NO reduction is pivotal to having a fundamental understanding on real-life catalysis. Herein, benefiting from the state-of-the-art mass spectrometry, we demonstrated experimentally that the Cu₂VO_3-5 ^- clusters can mediate the catalysis of NO reduction by CO, and two competitive channels to generate N₂O and N₂ can co-exist. Quantum-chemical calculations were performed to rationalize this selectivity. The formation of the ONNO unit on the Cu₂ dimer was demonstrated to be a precursor from which two pathways of NO reduction start to emerge. In the pathway of N₂O generation, only the Cu₂ dimer was oxidized and the VO₃ moiety functions as a "support", while both moieties have to contribute to anchor oxygen atoms from the ONNO unit and then N₂ can be generated. This finding displays a clear picture to elucidate how and why the involvement of VO₃ "support" can regulate the selectivity of NO reduction.

Pyrolysis of carbonaceous waste material has become an attractive method of recycling to generate value added products. Alongside pyrolytic oil and gas fractions, the thermal degradation forms solid pyrolytic char, which can be further processed. Local waste materials, including birch wood residue (BW), Reynoutria japonica stems (KW), spent coffee grounds (CG), tire rubber (TR), and lobster shells (LS) we assessed to form pyrolytic char. Using a simple acid treatment step on the chars, this study has shown successfully incorporate many of them into the low-temperature synthesis of plasmonic TiC NPs. Each char was shown to display distinctive physical and chemical characteristics, which was exploited to synthesize TiC NPs with unique properties. To study the plasmonic behaviour of each TiC sample, solar driven desalination experiments were conducted. TiC formed from TR char achieved broadband absorbance of ~95 % of the solar spectrum, reaching a near-perfect solar-to-vapor generation efficiency of 95 %, or a water generation rate of 1.40±0.01 kg m^-2 h^-1 under one-sun illumination. This makes it the best performing of all chars tested, and among the top performers reported in the literature to date. The evaporators maintain activity over time and under strongly hypersaline conditions.