Chemphyschem最新文献

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.

Broader adoption of 4D ultrafast electron microscopy (UEM) for the study of chemical, materials, and quantum systems is being driven by development of new instruments as well as continuous improvement and characterization of existing technologies. Perhaps owing to the still-high barrier to entry, the full range of capabilities of laser-driven 4D UEM instruments has yet to be established, particularly when operated at extremely low beam currents (~fA). Accordingly, with an eye on beam stability, we have conducted particle tracing simulations of unconventional off-axis photoemission geometries in a UEM equipped with a thermionic-emission gun. Specifically, we have explored the impact of experimentally adjustable parameters on the time-of-flight (TOF), the collection efficiency (CE), and the temporal width of ultrashort photoelectron packets. The adjustable parameters include the Wehnelt aperture diameter (D_W), the cathode set-back position (Z_tip), and the position of the femtosecond laser on the Wehnelt aperture surface relative to the optic axis (R_photo). Notable findings include significant sensitivity of TOF to D_W and Z_tip, as well as non-intuitive responses of CE and temporal width to varying R_photo. As a means to improve accessibility, practical implications and recommendations are emphasized wherever possible.

Two-dimensional layered double hydroxides (LDHs) are ideal candidates for a large number of (bio)catalytic applications due to their flexible composition and easy to tailor properties. Functionality can be achieved by intercalation of amino acids (as the basic units of peptides and proteins). To gain insight on the functionality, we apply resonant inelastic soft x-ray scattering and near edge x-ray absorption fine structure spectroscopy to CaFe LDH in its pristine form as well as intercalated with the amino acids proline and cysteine to probe the electronic structure and its changes upon intercalation. We observe the activation of pristine LDH defect states by soft x-rays and their passivation by the intercalated molecules. The nitrogen at the amino amino is found to form C=NH⁺ bonds and thus generating positive charge at the amino group, moving it away from the positively charged LDH layers. The carboxyl group in cysteine is deprotonated and thus in zwitterionic state after intercalation. This negative charge is used to compensate the positive layer charge. For intercalated proline the spectral signature of a protonated carboxyl group is observed, however, we find orbital overlap to defects at the layer surfaces indicating strong interaction with the carboxyl groups.

Indane-based molecules are effective scaffolds for different pharmaceutical products, so it is relevant to analyze the relation between structure and functionality in indane derivatives. Here, we have characterized the conformational landscape and molecular structure of 1-aminoindane in the gas phase using chirped-excitation Fourier-transform microwave spectroscopy and computational methods. The rotational spectrum confirmed the presence of two conformers, which were identified based on their rotational constants and ¹⁴N nuclear quadrupole coupling tensor elements. The observed conformers share the cyclopentane puckering and amino equatorial configuration but differ in the orientation of the amino group hydrogens. The spectral analysis further allowed the observation of all monosubstituted ¹³C and ¹⁵ N isotopologues in natural abundance for the most stable isomer, allowing a precise structural determination for this species. Structural information was derived using the substitution ( $r_s$ ) and effective vibrational ground state ( $r_0$ ) methods, revealing that the structure of 1-aminoindane is very similar to that of indane. A calculation of the potential energy surface along the pathway for the conversion between the most stable equatorial species permitted to rationalize the non-observation of additional conformers via molecular relaxation during the adiabatic expansion. The computational results include ab initio (MP2) and DFT methods (B3LYP, ωB97X-D and M06-2X).

For batteries to function effectively all active material must be accessible requiring both electron and ion transport to each particle. A common approach to generating the needed conductive network is the addition of carbon to create a composite electrode. An alternative approach is the electrochemically induced formation of conductive reaction products where the electrochemically generated materials are in intimate contact with the active material contributing to effective connection of each active particle. This study probes silver vanadium oxide (Ag₂V₄O₁₁, SVO), carbon monofluoride (CF_x), and hybrid SVO/CF_x electrodes in lithium batteries. Ex situ XRD identifies Ag⁰ as a reduction product from SVO and LiF from CF_x that can be followed as a function of depth-of-discharge (DOD). Spatially-resolved operando energy dispersive x-ray diffraction reveals that the presence of SVO alleviates reaction heterogeneity in the electrodes which are electron transfer limited in the absence of sufficient Ag⁰. Synchrotron X-ray tomography on discharged cathodes reveals the distribution of silver particles where the particles are more closely spaced near the current collector indicating multiple nucleation sites for their formation. Finally, operando isothermal microcalorimetry is used to determine the heat dissipation of the parent and hybrid battery types. Using material enthalpy potentials, we determine the current distribution between the two active materials for the discharging hybrid cathode adding further insight to the diffraction analysis. Taken together, these results provide a comprehensive understanding of hybrid SVO/CF_x cathodes and give guidance on optimal compositions that balance power and energy density considerations.

The reaction of terrylene in p-terphenyl with molecular oxygen is reinvestigated by TIRF-microscopy with λ_exc=488 nm or λ_exc=561 nm and 488 nm. A similar range of fluorescent products is obtained under both experimental conditions with a reaction quantum yield Φ_r>10^-7 for those molecules which undergo the photoreaction. The majority of these oxygen-susceptible molecules reacts via an electronically relaxed, dark intermediate, presumably an endoperoxide, with a lifetime of off>~20 s. From this time constant, an activation energy E_A<0.8 eV is estimated for the transition from the intermediate to the final product, the diepoxide, which nicely agrees with values calculated for the terrylene-derivative TDI. However, ~20 % of all reacting molecules at λ_exc=561 nm and even ~40 % at λ_exc=488 nm show an immediate change of the fluorescence colour within the time resolution of the experiment, bypassing any dark intermediate. Based on this experimentally observed impact of the excitation energy and the lack of relevant excited-state absorption, we hypothesize that oxygen forms a complex with ground-state terrylene which then undergoes a quasi-unimolecular reaction in the excited-state before vibrational relaxation takes place.

The design and development of particulate photocatalysts have been an attractive strategy to incorporate earth-abundant metal ions to water splitting devices. Herein, we synthesized CoFe-Prussian blue (PB) coated ZnO origami core-shell nanostructures (PB@ZnO) with different massratios of PB components and investigated their photocatalytic water oxidation activities in the presence of an electron scavenger. Photocatalytic experiments reveal that the integration of PB on ZnO boosts the oxygen evolution rate by a factor of ~2.4 compared to bare ZnO origami. We ascribe this increased photocatalytic rate to an improved charge carrier separation and transfer due to the formation of heterojunction at the interface between PB and ZnO. Long-term photocatalytic experiments indicate that the activity and stability of the catalyst was preserved up to 9 h. Our results indicate that the core-shell PB@ZnO particles possess a proper band energy alignment for the photocatalytic water oxidation process.

High entropy alloy (HEA) nanoparticles (NPs) have attracted much attention recently due to their unprecedented chemical properties. As such, HEA NPs have been used as materials with superior activity toward electrocatalytic applications. Specifically, solid solutions that form randomly mixed single-phased structures have received the most focus in the early stages of HEA NP development for their entropic-driven design and multifunctionality. Advances to non-colloidal and colloidal synthetic methods have allowed for the fabrication of solid solution HEA NPs with varying compositions and complexity to be applied to many practical applications such as fuel cells, energy storage and agriculture. In this review, the current colloidal methods and catalytic mechanisms for solid solution HEA NP synthesis are investigated from the physical chemistry perspective. A comprehensive discussion on the theory, techniques, and electrocatalytic applications of colloidal syntheses for successful solid solution HEA NP formation is presented. Finally, promising perspectives for the continued development of physical insights into structure-property relationships towards improved HEA NP synthesis and application are discussed.

Anode free concepts are gaining traction in battery research. To improve cyclability, a better understanding of the deposition processes and morphologies is necessary. Correlative experiments enable a link between a variety of properties obtained, such as chemical, mechanical or electrochemical data. Here, electron paramagnetic resonance imaging (EPRI) is correlated with atomic force microscopy (AFM) to gain a deeper understanding of the microscopic topography and local stiffness at different intensities of the lithium selective EPRI map. Experiments were carried out on a sample of lithium deposited on copper foil from standard battery electrolyte. The correlation of both methods reveals that EPRI has a high sensitivity towards small lithium structures, while bulk lithium was not detected. The results demonstrate that EPRI can be used for prescreening to identify regions with different properties, which can then be analysed individually by AFM.

This study investigates the modulations in the optical properties of cationic surfactant cetylpyridinium chloride (CPC) and hydrazine-mediated copper nanoclusters (CuNCs). By employing a bottom-up approach, we demonstrate the formation of blue-emitting CuNCs facilitated by CPC and hydrazine, where hydrazine acts both as a reducing and stabilizing agent. The optical properties of the CuNCs were systematically tuned by varying the chain length of the diamine, resulting in emissions ranging from blue to yellow. Comprehensive characterization using spectroscopic and microscopic techniques confirmed the successful formation of CuNCs and elucidated the roles of CPC and hydrazine in their preparation. Control experiments highlighted the critical role of the pyridinium moiety and hydrophobic chain of CPC in enhancing the photoluminescence properties of the CuNCs. This work provides new insights into the design of stable, highly luminescent CuNCs for potential applications in optoelectronics and bioimaging.