Physical Chemistry Chemical Physics最新文献

MXenes, a class of two-dimensional materials, have shown immense potential in various applications such as energy storage, electromagnetic shielding, solar cells, smart fabrics, optoelectronics, and plasmonics. In this study, we employ first-principles density functional theory (DFT) and time-dependent DFT calculations to investigate a semiconductor–metal heterostructure composed of a Cd₃₃Se₃₃ cluster and Ti₂C MXene monolayer flakes. Our research focuses on the formation and damping of localized surface plasmon resonances (LSPRs) within this heterostructure. We discover that the Cd₃₃Se₃₃/Ti₂C interface gives rise to a Schottky barrier. Importantly, this interface formation results in the damping of the Ti₂C LSPR, thereby facilitating the transfer of electrons into the Cd₃₃Se₃₃ cluster. By directly visualizing the LSPR damping phenomenon, our study enhances our understanding of the semiconductor-MXene interface and provides novel insights for the design of MXene-based photocatalysts.

Vertical van der Waals (vdW) heterostructures have shown potential for gas sensing owing to their remarkable sensitivity. However, the optimization process for achieving the best gas sensing performance is complicated by the heterostructure's reliance on both physical and electrical characteristics. This study employs density functional theory (DFT) to analyse the structural and electronic parameters of a MoTe₂/InN vdW heterostructure. The findings of this study indicate that the vdW heterostructure has a type-II band alignment with higher adsorption energy towards NH₃, NO₂, and SO₂ than the individual monolayers. In specific, the heterostructure is well suited for NO₂ detection but has limitations in reliably detecting NH₃ and SO₂ due to longer recovery times. We find significant hybridization between the adsorbate and interacting surfaces’ orbitals and a notable presence of NO₂ molecular orbitals in proximity to the Fermi level. Additionally, dielectric and work function modulations offer a viable means to develop optical-based gas sensors that can selectively detect NO₂. Our research provides valuable insights into vdW heterostructure design for high-performance gas sensors.

Three novel TADF (thermally activated delayed fluorescence) emitters based on the well-studied Qx-Ph-DMAC fluorophore are designed and synthesized. The photophysical properties of these materials are studied from a theoretical and experimental point of view, demonstrating the cumulative effects of multiple small modifications that combine to afford significantly improved TADF performance. First, an extra phenyl ring is added to the acceptor part of Qx-Ph-DMAC to increase the conjugation length, resulting in BQx-Ph-DMAC, which acts as an intermediate molecular structure. Next, an electron-deficient coumarin unit is incorporated to fortify the electron accepting ability, affording ChromPy-Ph-DMAC with red-shifted emission. Finally, the conjugated system is further enlarged by ‘locking’ the molecular structure, generating DBChromQx-DMAC with further red-shifted emission. The addition of the coumarin unit significantly impacts the charge-transfer excited state energy levels with little effect on the locally excited states, resulting in a decrease of the singlet–triplet energy gap. As a result, the two coumarin-based emitters show considerably improved TADF performance in 1 w/w% zeonex films when compared to the initial Qx-Ph-DMAC structure. ‘Locking’ the molecular structure further lowers the singlet–triplet energy gap, resulting in more efficient reverse intersystem crossing and increasing the contribution of TADF to the total emission.

The electrocatalytic properties of advanced metal-oxide catalysts are often related to a synergistic interplay between multiple active catalyst phases. The structure and chemical nature of these active phases are typically established under reaction conditions, i.e. upon interaction of the catalyst with the electrolyte. Here, we present a fundamental surface science (scanning tunneling microscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction) and electrochemical (cyclic voltammetry) study of CeO₂(111) nanoislands on Pt(111) in blank alkaline electrolyte (0.1 M KOH) in a potential window between −0.05 and 0.9 V_RHE. We observe a size- and preparation-dependent behavior. Large ceria nanoislands prepared at high temperatures exhibit stable redox behavior with Ce³⁺/Ce⁴⁺ electrooxidation/reduction limited to the surface only. In contrast, ceria nanoislands, smaller than ∼5 nm prepared at a lower temperature, undergo conversion into a fully hydrated phase with Ce³⁺/Ce⁴⁺ redox transitions, which are extended to the subsurface region. While the formation of adsorbed OH species on Pt depends strongly on the ceria coverage, the formation of adsorbed H_ads on Pt is independent of the ceria coverage. We assign this observation to intercalation of H_ads at the Pt/ceria interface. The intercalated H_ads cannot participate in the hydrogen evolution reaction, resulting in the moderation of this reaction by ceria nanoparticles on Pt.

Hydrogen energy is very important as a new clean energy source to combat the growing environmental problems. In this regard, novel photocatalyst materials for water splitting have a wide range of applications. Using first principles calculations, we theoretically studied three orthorhombic group-IVB nitride halide monolayers, Hf₂N₂Br₂, Janus HfZrN₂Br₂ and Janus Hf₂N₂ClBr. The energy, dynamic and thermal stabilities are demonstrated for all three monolayers. Using the HSE hybrid functional, the calculations reveal that they are direct band gap semiconductors with suitable band edge positions, good optical absorptions, and anisotropic carrier mobilities, which makes them promising for water splitting applications. Importantly, the photogenerated carriers provide enough driving force to trigger the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) within wide pH ranges, and then overall water splitting can be achieved spontaneously. We conclude that orthorhombic group-IVB nitride halide monolayers have potential applications in photocatalytic nanodevices.

Conventional mechanochemical synthetic tools, such as ball mills, offer no methodology to quantitatively link macroscale reaction parameters, such as shaking frequency or milling ball radius, to fundamental drivers of reactivity, namely the force vectors applied to the reactive molecules. As a result, although mechanochemistry has proven to be a valuable method to make a wide variety of products, the results are seldom reproduceable between reactors, difficult to rationally optimize, and hard to ascribe to a specific reaction pathway. Here we have developed a controlled force reactor, which is a mechanochemical ball mill reactor with integrated force measurement and control during each impact. We relate two macroscale reactor parameters—impact force and impact time—to thermodynamic and kinetic transition state theories of mechanochemistry utilizing continuum contact mechanics principles. We demonstrate force controlled particle fracture of NaCl to characterize particle size evolution during reactions, and force controlled reaction between anhydrous copper(II) chloride and (1, 10) phenanthroline. During the fracture of NaCl, we monitor the evolution of particle size as a function of impact force and find that particles quickly reach a particle size of ∼100 μm largely independent of impact force, and reach steady state 10–100× faster than reaction kinetics of typical mechanochemical reactions. We monitor the copper(II) chloride reactivity by measuring color change during reaction. Applying our transition state theory developed here to the reaction curves of copper(II) chloride and (1, 10) phenanthroline at multiple impact forces results in an activation energy barrier of 0.61 ± 0.07 eV, distinctly higher than barriers for hydrated metal salts and organic ligands and distinctly lower than the direct cleavage of the CuCl bond, indicating that the reaction may be mediated by the higher affinity of Fe in the stainless steel vessel to Cl. We further show that the results in the controlled force reactor match rudimentary estimations of impact force within a commercial ball mill reactor Retsch MM400. These results demonstrate the ability to quantitatively link macroscale reactor parameters to reaction properties, motivating further work to make mechanochemical synthesis quantitative, predictable, and fundamentally insightful.

Actinides are an important component of nuclear fuel for nuclear power and affect human health, and a key process in the transport of radionuclides in the environment is adsorption on mineral surfaces. In this work, we have used density functional theory (DFT) to investigate the microscopic adsorption and diffusion mechanisms of actinyls, U(V), U(VI), Np(V), Np(VI) Pu(V), and Pu(VI), on the gibbsite (001) surface. Actinyls(VI) are attached to the gibbsite surface through two An–O_s bonds, which results in a bidentate inner sphere mode, while actinyls(V) favor a monodentate inner sphere adsorption mode with the gibbsite (001) surface. The solvent effects were considered through an explicit water cluster model. All the actinyls studied can be efficiently adsorbed on the gibbsite (001) surface with binding energies ranging from −113.9 kJ mol⁻¹ to −341.2 kJ mol⁻¹. Electronic structure analyses indicate that the cooperation of the An–O_s bonds and hydrogen bonds leads to high adsorption stability of the actinyls with the gibbsite surface. The diffusion barriers of the actinyls on the gibbsite surface were determined, and the high energy barriers indicate that this type of gas-phase diffusion process is not likely to take place.

In noncentrosymmetric magnets, chiral Dzyaloshinskii–Moriya interactions (DMI) provide a distinctive mechanism for the stabilization of localized skyrmion states in two and three dimensions with a fixed sense of rotation. Near the ordering transition, the skyrmion strings develop attractive skyrmion–skyrmion interactions and ultimately become confined in extended clusters or textures [A. O. Leonov and U. K. Rößler, Nanomaterials, 2023, 13, 891], which is a consequence of the coupling between the magnitude and the angular part of the order parameter. Multi-skyrmionic states built from isolated skyrmions (IS) can form multiple modulated magnetic phases that may underlie the exotic magnetic phenomena of “partial order” or the field-driven “A-phase” observed in MnSi and other cubic helimagnets. Based on the standard phenomenological Dzyaloshinskii model, we obtain numerically exact solutions for skyrmion lattices (SkL), formulate their basic properties, and elucidate physical mechanisms of their formation and stability. Our detailed numerical studies show that the bound skyrmion states arise as hexagonal lattices of ±π-skyrmions (with the magnetization in the center along or opposite to the magnetic field) or square staggered lattices of π/2-skyrmions, which contain defect lines with zero modulus value and thus may form thermodynamically stable states only near the ordering temperature. In the simplest case of a two-dimensional (2D) skyrmionic texture, the structure is homogeneous in the third dimension (3D). The skyrmions preserve an ideal axisymmetric “double twist” core in condensed phases, while continuation into a space-filling texture is frustrated. The evolution of skyrmion lattices in an increasing magnetic field leads to a succession of phase transitions of first or second kind between diverse textures and finally ends due to the formation of isolated skyrmion-filaments with fixed radius and shape embedded in a homogeneously magnetized matrix. In the framework of the phenomenological model including only isotropic interactions (exchange, Zeeman, and DM energy contributions), the considered skyrmion lattices are only metastable states as the competing conical one-dimensional spiral forms the equilibrium state. But due to the weak couplings between skyrmions, secondary effects like anisotropies can stabilize skyrmionic textures as compared to simple helices. Also the topological nature of skyrmion condensates makes the magnetization processes in chiral magnets history-dependent and hysteretic.

The lifetime of blue organic light-emitting diodes (OLEDs) has always been a big challenge in practical applications. Blue OLEDs based on triplet–triplet annihilation (TTA) up-conversion materials have potential to achieve long lifetimes due to fusing two triplet excitons to one radiative singlet exciton, but there is a lack of an in-depth understanding of exciton dynamics on degradation mechanisms. In this work, we established a numerical model of exciton dynamics to study the impact factors in the stability of doped blue OLEDs based on TTA up-conversion hosts. By performing transient electroluminescence experiments, the intrinsic parameters related to the TTA up-conversion process of aging devices were determined. By combining the change of excess charge density in the emitting layer (EML) with aging time, it is concluded that the TTA materials are damaged by the excess electrons in the EML during ageing, which is the main degradation mechanism of OLEDs. This work provides a theoretical basis for preparing long-lifetime blue fluorescent OLEDs.

Biomembranes are a key component of all living systems. Most research on membranes is restricted to ambient physiological conditions. However, the influence of extreme conditions, such as the deep subsurface on Earth or extraterrestrial environments, is less well understood. The deep subsurface of Mars is thought to harbour high concentrations of chaotropic salts in brines, yet we know little about how these conditions would influence the habitability of such environments. Here, we investigated the combined effects of high concentrations of Mars-relevant salts, including sodium and magnesium perchlorate and sulphate, and high hydrostatic pressure on the stability, structure, and function of a bacterial model membrane. To this end, several biophysical techniques have been employed, including calorimetry, fluorescence and CD spectroscopy, confocal microscopy, and small-angle X-ray scattering. We demonstrate that sulphate and perchlorate salts affect the properties of the membrane differently, depending on the counterion present (Na⁺vs. Mg²⁺). We found that the perchlorates, which are believed to be abundant salts in the Martian environment, induce a more hydrated and less ordered membrane, strongly favouring the physiologically relevant fluid-like phase of the membrane even under high-pressure stress. Moreover, we show that the activity of the phospholipase A2 is strongly modulated by both high pressure and salt. Compellingly, in the presence of the chaotropic perchlorate, the enzymatic reaction proceeded at a reasonable rate even in the presence of condensing Mg²⁺ and at high pressure, suggesting that bacterial membranes could still persist when challenged to function in such a highly stressed Martian environment.