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Rare-earth elements (REEs) are critical to modern industry but difficult to separate due to their subtle and monotonic changes in physicochemical properties. MoS2-based two-dimensional (2D) materials offer novel opportunities for enhancing REE separation, exhibiting a distinct volcano-shaped transport performance distribution that peaks at Sm3+. However, the specific contributions of thermodynamic and kinetic factors to ion transport within 2D confinement remain unclear. In this study, we conducted a series of non-equilibrium all-atom molecular dynamics (MD) simulations to explore the effects of interlayer spacing and external pressure on the transport of lanthanide ions in Å-scale acetate functionalized 2D MoS2 (MoS2-COOH) channels. We examined ion entry and permeation rates, water flux, dehydration, and binding modes. The simulation results reveal that the transport trends of lanthanide ions are jointly driven by the dehydration degree and the relative-binding strengths of ions to water and to the acetate within the 2D channels. Notably, the dehydration pattern of lanthanide ions during permeation is closely linked to kinetic factors. Overall, this study provides a detailed atomistic understanding of the mechanisms underlying lanthanide ion transport under confinement. These findings point to the significant potential for tuning confinement and chemical functionalization within Å-scale channels for more efficient REE separation.

Abstract Two-dimensional (2D) materials have attracted attention for quantum information science due to their ability to host single-photon emitters (SPEs). Although the properties of atomically thin materials are highly sensitive to surface modification, chemical functionalization remains unexplored in the design and control of 2D material SPEs. Here, we report a chemomechanical approach to modify SPEs in monolayer WSe2 through the synergistic combination of localized mechanical strain and noncovalent surface functionalization with aryl diazonium chemistry. Following the deposition of an aryl oligomer adlayer, the spectrally complex defect-related emission of strained monolayer WSe2 is simplified into spectrally isolated SPEs with high single-photon purity. Density functional theory calculations reveal energetic alignment between WSe2 defect states and adsorbed aryl oligomer energy levels, thus providing insight into the observed chemomechanically modified quantum emission. By revealing conditions under which chemical functionalization tunes SPEs, this work broadens the parameter space for controlling quantum emission in 2D materials.

Eco-friendly, efficient, and selective gold recovery technologies are urgently desired to satisfy the increasing demand for gold. Here, the authors report one such technology based on the supramolecular polymerization of second-sphere coordinated adducts formed between β-cyclodextrin and tetrabromoaurate anions.

Encapsulating large and contorted nanographenes inside artificial receptors remain challenging. This work reports the synthesis, characterization and binding properties of a trigonal prismatic cage compound that can serve as a receptor for contorted nanographene derivatives.

Two-photon excited near-infrared fluorescence materials have garnered considerable attention because of their superior optical properties compared with other optical materials. Here, the authors use a convenient and efficient supramolecular approach to synthesize a two-photon excited near-infrared emissive co-crystalline material.

Organic semiconductors are considered promising Surface Enhanced Raman Spectroscopy platforms. Here the authors demonstrate that metal-free films based on a π-conjugated molecule containing a fully π-conjugated backbone provides an enhancement factor of 105 and detection limit of 10−9 M for methylene blue.

In this paper, we develop a hybrid QM/MM-MD direct dynamics method for the study of Ar and O scattering from room-temperature ionic liquids (RTIL) at hyperthermal energies, with the goal of providing an understanding of the reactivity of ionic liquids as potential hypergolic fuels. The RTIL is chosen to be 1-ethyl-3-methylimidazolium nitrate ([emim][NO3]) as the bulk properties of this have been analyzed experimentally and theoretically, and a force field has been developed. Within our simulation time of 7.3 ps, Ar collisions with the liquid surface cause 2−3 proton transfers to occur from the imidazolium ring to the anion, and a small fraction of these events leads to the desorption of neutral “emim” or HNO3species. These charge-transfer processes also occur for O(3P) collisions, but in addition, there is a rich amount of chemical change at the surface leading to four main collision types, reaction with NO3to form species like [NO2] and O2, O addition to the imidazolium ring causing ring scission, H abstractions from the hydrocarbon chains (ethyl or methyl) or imidazolium ring generating OH, and O atom inelastic scattering. Within the MSINDO model, the major scattered products (all are neutral) from the O collisions, with their probabilities in parentheses, are O (0.13), emim (0.12), HNO2(0.05), HNO3(0.04), and OH (0.04). Of these products, only OH is unique to O atom collisions; the HNO2and HNO3products also arise when the incident atom is Ar or O. [ABSTRACT FROM AUTHOR]

Plasmonic silver nanoparticles have unique properties that lend themselves to unusual optical applications, potentially including use as absorption amplifiers in dye-sensitized solar cells (DSSCs). However, these particles are easily damaged under oxidizing conditions. Atomic layer deposition of TiO2onto transparent-conductive-oxide-supported silver particles was examined as a means of protecting particles while simultaneously incorporating them into DSSC-functional photoelectrodes. The resulting assemblies were exposed to corrosive I−/I3−solutions, and the degree of silver etching was determined via scanning electron microscopy and ultraviolet−visible spectroscopy. To form a pinhole-free (i.e., fully protective) crystalline TiO2layer, 7.7 nm (300 cycles) must be deposited. If, however, a 0.2 nm (2 cycles) Al2O3adhesion layer is included, only 5.8 nm (211 cycles) of TiO2are necessary for the formation of a pinhole-free coating. [ABSTRACT FROM AUTHOR]

This critical review highlights recent advances in using electronic structure methods to study surface-enhanced Raman scattering. Examples showing how electronic structure methods, in particular time-dependent density functional theory, can be used to gain microscopic insights into the enhancement mechanism are presented (150 references). [ABSTRACT FROM AUTHOR]

To deal with inhomogeneous diffusion coefficients of ions without altering the lattice spacing in the kinetic lattice grand canonical Monte Carlo (KLGCMC) simulation, an algorithm that incorporates diffusion coefficient variation into move probabilities is proposed and implemented into KLGCMC calculations. Using this algorithm, the KLGCMC simulation method is applied to the calculation of ion currents in a simple model ion channel system. Comparisons of ion currents and ion concentrations from these simulations with Poisson−Nernst−Planck (PNP) results show good agreement between the two methods for parameters where the latter method is expected to be accurate. [ABSTRACT FROM AUTHOR]

Hyperthermal collisions (5 eV) of ground-state atomic oxygen O (3P) with a liquid-saturated hydrocarbon, squalane (C30H62), have been studied using QM/MM hybrid “on-the-fly” direct dynamics. The surface structure of the liquid squalane is obtained from a classical molecular dynamics simulation using the OPLS-AA force field. The MSINDO semiempirical Hamiltonian is combined with OPLS-AA for the QM/MM calculations. In order to achieve a more consistent and efficient simulation of the collisions, we implemented a dynamic partitioning of the QM and MM atoms in which atoms are assigned to QM or MM regions based on their proximity to “seed” (open-shell) atoms that determine where bond making/breaking can occur. In addition, the number of seed atoms is allowed to increase or decrease as time evolves so that multiple reactive events can be described. The results show that H abstraction is the most important process for all incident angles, with H elimination, double H abstraction, and C−C bond cleavage also being important. A number of properties of these reactive channels, as well as inelastic nonreactive scattering, are investigated, including angular and translational energy distributions, the effect of incident collision angle, variation with depth of the reactive event within the liquid, with the reaction site on the hydrocarbon, and the effect of dynamics before and after reaction (direct reaction versus trapping reaction−desorption). [ABSTRACT FROM AUTHOR]

Potential of mean force (PMF) profiles of a single Naor Kion passing through a cyclic peptide nanotube, cyclo-(d-Ala-Glu-d-Ala-Gln)2-, in water are calculated to provide insight into ion transport and to understand the conductance difference between these two ions. The PMF profiles are obtained by performing steered molecular dynamics (SMD) simulations that are based on the Jarzynski equality. The computed PMF profiles for both ions show barriers of around 2.4 kcal/mol at the channel entrances and exits and energy wells in the middle of the tube. The energy barriers, so-called dielectric energy barriers, arise due to the desolvation of water molecules when ions move across the nanotube, and the energy wells appear as a result of attractive interactions between the cations and negatively charged carbonyl oxygens on the backbone of the tube. We find more and deeper energy wells in the PMF profile for Nathan for K, which suggests that Naions have a longer residence time inside the nanotube and that permeation of Naions is reduced compared to Kions. Calculations of the radial distribution functions (RDF) between the ions and oxygens in the water molecules and in carbonyl groups on the tube and an investigation of the orientations of the carbonyl groups show that, in contrast with the dynamic carbonyl groups observed in the selectivity filter of the KcsA ion channel, the carbonyl groups in the cyclic peptide nanotube are relatively rigid, with only slight reorientation of the carbonyl groups as the cations pass through. The rigidity of the carbonyl groups in the cyclic peptide nanotube can be attributed to their role in hydrogen bonding, which is responsible for the tube structure. Comparison of the PMF profiles with the electrostatic energy profiles calculated from the Poisson-Boltzmann (PB) equation, a dielectric continuum model, reveals that the dielectric continuum model breaks down in the confined region within the tube that governs ion transport. [ABSTRACT FROM AUTHOR]

We present time dependent density functional theory (TDDFT) calculations for a tetrahedral Au20complex interacting with pyridine for the purpose of modeling absorption and surface enhanced Raman scattering, with emphasis on chemical and electrodynamic enhancement effects. These calculations are done using the ADF code with the BP86 functional, the zeroth-order regular approximation and with the resonant electronic response modeled using a short time approximation expression for the perturbed density matrix, with a damping factor that is empirically chosen. The absorption spectrum of bare Au20shows strong intraband (sp-sp) and interband (sp-d) coupling with a low-energy peak at 2.89 eV that is mostly intraband and other peaks at 3.94 and 4.70 eV that have mixed intra- and interband character. SERS spectra are calculated for pyridine/Au20for both vertex (V) and surface (S) configurations at their respective lowest energy absorption maxima (near 2.89 eV), and we find that the V configuration has higher intensities that correspond to SERS enhancements of 103-104, whereas S has an enhancement of 102-103. These enhancement values are significantly lower than the analogous results for pyridine/Ag20primarily because of reduced oscillator strength associated with the intraband transition in Au20. Decomposition of the pyridine/Au20enhancement factor into chemical and electromagnetic contributions (through an analysis of the static SERS intensities) shows enhanced chemical enhancements compared to Ag20but reduced electromagnetic enhancements. [ABSTRACT FROM AUTHOR]

In this work, we present the first calculation of the resonance Raman scattering (RRS) spectrum of rhodamine 6G (R6G) which is a prototype molecule in surface-enhanced Raman scattering (SERS). The calculation is done using a recently developed time-dependent density functional theory (TDDFT) method, which uses a short-time approximation to evaluate the Raman scattering cross section. The normal Raman spectrum calculated with this method is in good agreement with experimental results. The calculated RRS spectrum shows qualitative agreement with SERS results at a wavelength that corresponds to excitation of the S1 state, but there are significant differences with the measured RRS spectrum at wavelengths that correspond to excitation of the vibronic sideband of S1. Although the agreement with the experiments is not perfect, the results provide insight into the RRS spectrum of R6G at wavelengths close to the absorption maximum where experiments are hindered due to strong fluorescence. The calculated resonance enhancements are found to be on the order of 105. This indicates that a surface enhancement factor of about 1010 would be required in SERS in order to achieve single-molecule detection of R6G. [ABSTRACT FROM AUTHOR]

Ion current calculations based on Poisson−Nernst−Planck (PNP) theory are performed for a synthetic cyclic peptide nanotube that consists of eight or ten cyclo[(-l-Trp-d-Leu-)4] embedded in a lipid bilayer membrane to investigate the ion transport properties of the nanotube. To explore systems with arbitrary geometries, three-dimensional PNP theory is implemented using a finite difference method. The influence of dipolar lipid molecules on the ion currents is also examined by turning on or off the charges of the lipid dipoles in dipalmitoylphosphatidylcholine (DPPC). Comparisons between the calculated and experimentally measured ion currents show that the PNP approach agrees well with the measurements at low ion concentrations but overestimates the currents at higher concentrations. Concentration profiles reveal the selectivity of the peptide nanotube to cations, which is attributed to the negatively charged carbonyl oxygens inside the nanotube. The dominant cation and the minimum anion concentrations inside the cyclic peptide nanotube suggest that these cyclic peptide nanotubes can be employed as ion sensors. In the case of the polar DPPC bilayer, smaller currents are obtained in the calculation. The variation of current with polarity of the lipids implies that both polar and nonpolar lipid bilayer membranes can be utilized to regulate ion currents in the peptide nanotube and other ion channels. Strengths and limitations of the PNP theory are also discussed. [ABSTRACT FROM AUTHOR]

In this paper we overview our recent studies of anisotropic noble metal (e.g. gold and silver) nanoparticles, in which a combination of theory and experiment has been used to elucidate the extinction spectra of the particles, as well as information related to their surface enhanced Raman spectroscopy. We used wet-chemical methods to generate several structurally well-defined nanostructures other than solid spheres, including silver nanodisks and triangular nanoprisms, and gold nanoshells and multipods. When solid spheres are transformed into one of these shapes, the surface plasmon resonances in these particles are strongly affected, typically red-shifting and even splitting into distinctive dipole and quadrupole plasmon modes. In parallel, we have developed computational electrodynamics methods based on the discrete dipole approximation (DDA) method to determine the origins of these intriguing optical features. This has resulted in considerable insight concerning the variation of plasmon wavelength with nanoparticle size, shape and dielectric environment, as well as the use of these particles for optical sensing applications. [ABSTRACT FROM AUTHOR]