Synergetic Electrostatic and Steric Effects in α-FAPbI3 Single Crystals For X-Ray Detection and Imaging.

It is still challenging to stabilize α-FAPbI3 perovskite for high performance optoelectrical devices. Herein, a novel strategy is proposed utilizing the synergetic electrostatic and steric effect to stabilize the α-FAPbI3 phase and suppress the ion migration. Dimethylamine (DMA+) cations are chosen as the dopant to fabricate FA0.96DMA0.04PbI3 single crystals (SCs). DFT calculations reveal that DMA+ cations can improve the stability of α-FAPbI3 phase in both thermodynamics (lower Gibbs free energy) and kinetics (higher defect formation and migration energy). The resulting SCs exhibit an environmental stability over 100 days and an extraordinary low dark current drift of 3.7 × 10-7 nA cm-1 s-1 V-1, comparable to 2D perovskite SCs. The X-ray detectors have also achieved the-state-of-the-art performance in X-ray detection and imaging. This work demonstrates the significance of electrostatic and steric effects in improving the phase and operational stability of perovskites.

Insight into the Catalytic Oxidation Mechanism of Hydrogen Isotopes by Pt Clusters Confined by Silicalite-1.

Highly efficient removal of low concentrations of hydrogen isotope gas in air is crucial for the safe operation of nuclear energy plants. Herein, silicalite-1-confined Pt cluster catalysts were used for the catalytic oxidation of hydrogen isotopes, and the related catalytic mechanism was revealed. Increased temperature in direct hydrogen reduction treatment slightly increased the size of Pt clusters from 1.6 nm at 400 °C to 1.8 nm at 600 °C. The catalyst reduced at 600 °C exhibited excellent performance (99%) in hydrogen isotope oxidation at 75 °C, as well as high stability and catalytic efficiency in continuous and intermittent operation for 7200 min. X-ray absorbance spectroscopy confirmed the existence of Pt clusters in the catalysts, and the theoretical results showed that the total net charge was -0.07 e, indicating a slight charge transfer from the zeolite to the Pt atoms. The metal-support interaction thermally stabilized Pt clusters and altered the metal electronic structure, which enhanced the catalytic activity following a hydroperoxyl (OOH)-mediated route. Based on the low reaction temperature, efficient hydrogen conversion rate, and high stability, the silicalite-1-confined Pt cluster catalyst is expected to be used in hydrogen isotope oxidation treatment to achieve nuclear safety.

Unraveling CO adsorption behaviors and its poisoning effects on ZrCo surface.

Theoretical calculations are performed to elucidate the adsorption behaviors and poisoning effects of CO gas on the ZrCo surface, which drastically limits its application in hydrogen isotopic storage. Specifically, the ionic Zr-Co bond on the surface leads to unique CO adsorption structures on different sites. The CO molecule tends to prefer a tilted adsorption configuration on the Co-Co bridge site. The electronic structures, charge distributions, and bonding characteristics are further explored to study the CO adsorption properties, which obey the electron density donation and back-donation mechanism. For different CO coverages, the stepwise adsorption energies of CO increase with the increasing of coverage, reaching the saturated coverage at nCO = 11. Then, the effects of temperature and partial pressure on CO coverage are evaluated using atomic thermodynamics. The computed phase diagram shows that the ZrCo(110) surface has a stable coverage of nCO = 6 at ambient temperature under ultrahigh vacuum conditions. The pre-adsorbed CO molecules lead to the charge redistribution and the d-band center downshift on the surface, which significantly affect hydrogen adsorption and dissociation. Our results provide insights into the poisoning mechanisms of the impurity gas on ZrCo alloys, which can be beneficial for designing high-performance ZrCo-based alloys with improved poisoning tolerance.

Isotope Effects on State-to-State Photodissociation Dynamics of D2S in Its First Absorption Band.

State-to-state photodissociation dynamics of D2S in its first absorption band were explored by utilizing recently developed diabatic potential energy surfaces (PESs). Quantum dynamics calculations, involving the first two strongly coupled 1A″ states, were executed employing a Chebyshev real wavepacket method. The nonadiabatic channel via the conical intersection (CI) is facile, direct, and fast, leading to the production of rotationally and vibrationally cold SD(X̃2Π). The calculated absorption spectrum, product state distributions, and angular distributions are in reasonable agreement with the experimental results, although some discrepancies exist at 193.3 nm. Compared with H2S, there are obvious isotope effects on rotational state distributions for D2S photodissociation in its first absorption band. Moreover, we scrutinize the variation of product state distributions as a function of photon energy and the vibrational mediated photodissociation of the parent molecule. Due to the diverse shapes of the three fundamental vibrational wave functions, photoexcited wavepackets access distinct segments of the upper-state PES, resulting in a disparate absorption spectrum and ro-vibrational distributions via the nonadiabatic transition. This study provides a comprehensive figure of the isotopic effect and wavelength dependence on the photofragmentation behaviors from D2S photodissociation, which should attract more experimental and theoretical attention to this prototypical system.

New accurate diabatic potential energy surfaces for the two lowest 1A'' states of H2S and photodissociation dynamics in its first absorption band.

In this work, state-to-state photodissociation dynamics of H2S in its first absorption band has been studied quantum mechanically with a new set of coupled potential energy surfaces (PESs) for the first two 1A'' excited states, which were developed at the explicitly correlated internally contracted multi-reference configuration interaction level with the cc-pVQZ-F12 basis set and a large active space. The calculated absorption spectrum, product state distributions, and angular distributions are in excellent agreement with available experimental data, validating the accuracy of the PESs and the non-adiabatic couplings. Detailed analysis of the dynamics reveals that there are strong non-adiabatic couplings between the bound 11B1 and dissociative 11A2 states around the Franck-Condon region, leading to very fast predissociation to ro-vibrationally cold SH(X̃) fragments, during which marginal angular anisotropy of the PESs is involved. This study provides quantitatively accurate characterization of the electronic structure and detailed fragmentation dynamics of this prototypical photodissociation system, which is desirable for improving astrochemical modelling.

Overexpression of DAPK1-mediated inhibition of IKKß/CSN5/PD-L1 axis enhances natural killer cell killing ability and inhibits tumor immune evasion in gastric cancer.

Gastric cancer (GC) originates from the stomach and is a prevalent human malignancy. Dysfunction of death associated protein kinase 1 (DAPK1) has been identified as a major regulator involved in the development and progression of GC. However, there's limited data regarding the regulatory mechanism of GC. Herein, we investigated role of DAPK1 in natural killer (NK) cell killing ability and immune evasion of GC cells and mediated pathway. Samples from GC-related gene expression profile and clinical samples from 67 patients with GC were collected to determine the expression of DAPK1, IκB kinase ß (IKKß), programmed death receptor-ligand 1 (PD-L1), and photomorphogenesis 9 (COP9) signalosome 5 (CSN5). The binding affinity among DAPK1, IKKß, CSN5, and PD-L1 was characterized to verify the underlying mechanism. GC lines were transfected with overexpressed plasmid or siRNA to determine the effect of DAPK1/IKKß/CSN5/PD-L1 axis on NK cell killing ability and immune evasion of GC cells. GC cells and tissues presented low expression of DAPK1 and high expression of IKKß, CSN5 and PD-L1. IKKß, negatively regulated by DAPK1, was capable of activating CSN5 and upregulating PD-L1 expression. Overexpression of DAPK1 promoted NK cell killing ability and reduced immune evasion, coupled with reduction of NK cell apoptosis and increases in levels of TNF-α, IFN-γ, CD107a, and Granzyme B cytokines. The tumor-suppressing properties of DAPK1 through downregulation of IKKß/CSN5/PD-L1 axis in GC were further confirmed in vivo. In summary, overexpression of DAPK1 promoted the NK cell killing ability and restrained immune evasion of GC cells, providing a potential therapeutic strategy for GC treatment by modulating immune evasion.

Mechanistic Insights into Photocatalyzed H2 Dissociation on Au Clusters.

Localized surface plasmon resonances (LSPRs) have attracted much recent attention for their potential in promoting chemical reactions with light. However, the mechanism of LSPR-induced chemical reactions is still not clear, even for H2 dissociation on metal nanoparticles. In this work, we investigate the mechanism for photoinduced H2 dissociation using a simple H2@Au6 model. Our time-dependent density functional theory calculations indicate that the initial excitation is largely restricted to the metal cluster, involving intraband excitation that produces hot electrons (HEs). However, diabatization via overlapping orbitals reveals two types of nested electronic states, one involving excitations of the metallic electrons, namely, the HE states, and the other concerned with charge transfer (CT) to the adsorbate antibonding σ* orbital. Dissociation of H2 thus takes place by transitions from the former to the latter. Quantum dynamics simulations on the diabatic CT states suggest rapid dissociation of H2, while no such dissociation occurs on diabatic HE states. Our research provides a clear physical picture of photoinduced H2 dissociation on Au clusters, which has important implications in plasmonic facilitated photocatalysis.

Highly Localized SERS Measurements Using Single Silicon Nanowires Decorated with DNA Origami-Based SERS Probe.

Surface enhanced Raman spectroscopy (SERS) measurements are conventionally performed using assemblies of metal nanostructures on a macro- to micro-sized substrate or by dispersing colloidal metal nanoparticles directly onto the sample of interest. Despite intense use, these methods allow neither the removal of the nanoparticles after a measurement nor a defined confinement of the SERS measurement position. So far, tip enhanced Raman spectroscopy is still the key technique in this regard but not adequate for various samples mainly due to diminished signal enhancement compared to other techniques, poor device fabrication reproducibility, and cumbersome experimental setup requirements. Here, we demonstrate that a rational combination of only four gold nanoparticles (AuNPs) on a DNA origami template, and single silicon nanowires (SiNWs) yield functional optical amplifier nanoprobes for SERS. These nanoscale SERS devices offer a spatial resolution below the diffraction limit of light and still a high electric field intensity enhancement factor ( EF) of about 105 despite of miniaturization.

Origin of Thermal and Hyperthermal CO2 from CO Oxidation on Pt Surfaces: The Role of Post-Transition-State Dynamics, Active Sites, and Chemisorbed CO2.

The post-transition-state dynamics in CO oxidation on Pt surfaces are investigated using DFT-based ab initio molecular dynamics simulations. While the initial CO2 formed on a terrace site on Pt(111) desorbs directly, it is temporarily trapped in a chemisorption well on a Pt(332) step site. These two reaction channels thus produce CO2 with hyperthermal and thermal velocities with drastically different angular distributions, in agreement with recent experiments (Nature, 2018, 558, 280-283). The chemisorbed CO2 is formed by electron transfer from the metal to the adsorbate, resulting in a bent geometry. While chemisorbed CO2 on Pt(111) is unstable, it is stable by 0.2 eV on a Pt(332) step site. This helps explain why newly formed CO2 produced at step sites desorbs with far lower translational energies than those formed at terraces. This work shows that steps and other defects could be potentially important in finding optimal conditions for the chemical activation and dissociation of CO2 .

Communication: Fingerprints of reaction mechanisms in product distributions: Eley-Rideal-type reactions between D and CD3/Cu(111).

Through extensive direct dynamics studies of a prototypical Eley-Rideal type process, we demonstrate that fingerprints of microscopic reaction mechanisms can be identified in product distributions. Specifically, the umbrella vibration of CD4 formed by reacting gaseous D atoms with CD3 adsorbed on Cu(111) is highly excited if the reaction is initiated by a direct collision between the reactants due to the necessary inversion of the CD3 moiety. On the other hand, an indirect collision via a hot atom mechanism leads to much lower excitation in this product vibrational mode, and as such, an inversion is unnecessary. This fingerprint suggests an experimentally verifiable means to disentangle different mechanistic pathways.

Ab initio molecular dynamics study of the Eley-Rideal reaction of H + Cl-Au(111) → HCl + Au(111): Impact of energy dissipation to surface phonons and electron-hole pairs.

The reaction between an impinging H atom and a Cl atom adsorbed on Au(111), which is a prototype for the Eley-Rideal mechanism, is investigated using ab initio molecular dynamics at different incidence angles. The reaction yielding gaseous HCl with large internal excitation proceeds via both direct and hot-atom mechanisms. Significant energy exchange with both surface phonons and electron-hole pairs has been observed. However, their impact on the reactivity and final state distributions was found to be limited, thanks to the large exothermicity and small barrier of the reaction.

Adsorption of methylene blue and its N-demethylated derivatives on the (111) face of coinage metals: The importance of dispersion interactions.

The adsorption of methylene blue and its N-demethylated derivatives on the (111) surface of three coinage metals is investigated using density functional theory with and without the inclusion of dispersion interactions. It is shown that the adsorption of these dye molecules on the metal surfaces can be largely classified as physisorption as the adsorption energy is dominated by dispersion interactions. While the molecules are found to adsorb on Au and Ag parallel to the surface with molecular geometries basically unaltered, the adsorption on Cu(111) features a butterfly configuration, accompanied by the largest adsorption energies among the three metal surfaces. The significant covalent character on Cu(111) is analyzed from the perspective of electronic structure.

Experimental and theoretical studies of the reactions of ground-state sulfur atoms with hydrogen and deuterium.

The gas-phase kinetics of S(3P) atoms with H2 and D2 have been studied via the laser flash photolysis-resonance fluorescence technique. S atoms were generated by pulsed photolysis of CS2 at 193 nm and monitored by time-resolved fluorescence at 181 nm. The rate coefficients for H2 (k1) and D2 (k2), respectively, are summarized as k1(600-1110 K) = 3.0 × 10-9 exp-1.317×105-2.703×107K/T8.314 T/K cm3 molecule-1 s-1 and k2(770-1110 K) = 2.2 × 10-14 (T/298 K)3.55 exp(-5420 K/T) cm3 molecule-1 s-1. Error limits are discussed in the text. The rate coefficients for formation of SH(SD) + H(D) on a newly developed triplet potential energy surface were characterized via ring polymer molecular dynamics and canonical variational transition-state theory. There is excellent agreement above about 1000 K between theory and experiment. At lower temperatures, the experimental rate coefficient is substantially larger than the results computed for the adiabatic reaction, suggesting a significant role for intersystem crossing to the singlet potential energy surface at lower temperatures.

Full-Dimensional Quantum Dynamics of Vibrational Mediated Photodissociation of HOD in Its B Band.

The photodissociation dynamics for the ground and three fundamental vibrational states of HOD were explored from quantum dynamical calculations including the electronic X̃, Ã, and B̃ states. The calculations were based on a Chebyshev real wave packet method. Due to the different shapes of the initial vibrational wave functions and isotopic effect, the calculated absorption spectra, product state distributions, and branching ratios show different dynamic features. The initial bending excited vibtaional state (0, 1, 0) generates a bimodal behavior on the absorption spectrum and an inverted vibrational population of OD(X̃) fragment at some total energies. The rotational state distributions from four vibrational states have two different behaviors. One has a single broad peak, whereas the other one has a bimodal structure. Large OD(Ã)/OD(X̃) ratios are found for photodissociation from four vibrational states at high total energies, which indicate that the H atom dissociates mainly via the adiabatic pathway. We also calculated the OD/OH isotopic branching ratios from four vibrational states and found that the OD + H production channel is dominant over the OH + D channel in the energy range considered. The calculated results are consistent with the available observed ones.

Signatures of non-adiabatic dynamics in the fine-structure state distributions of the OH(X̃/Ã) products in the B-band photodissociation of H2O.

A detailed quantum mechanical characterization of the photodissociation dynamics of H2O at 121.6 nm is presented. The calculations were performed using a full-dimensional wave packet method on coupled potential energy surfaces of all relevant electronic states. Our state-to-state model permits a detailed analysis of the OH(X̃/Ã) product fine-structure populations as a probe of the non-adiabatic dissociation dynamics. The calculated rotational state distributions of the two Λ-doublet levels of OH(X̃, v = 0) exhibit very different characteristics. The A' states, produced mostly via the B̃→X̃ conical intersection pathway, have significantly higher populations than the A″ counterparts, which are primarily from the B̃→à Renner-Teller pathway. The former features a highly inverted and oscillatory rotational state distribution, while the latter has a smooth distribution with much less rotational excitation. In good agreement with experiment, the calculated total OH(X̃) rotational state distribution and anisotropy parameters show clear even-odd oscillations, which can be attributed to a quantum mechanical interference between waves emanating from the HOH and HHO conical intersections in the B̃→X̃ non-adiabatic pathway. On the other hand, the experiment-theory agreement for the OH(Ã) fragment is also satisfactory, although some small quantitative differences suggest remaining imperfections of the ab initio based potential energy surfaces.

Theoretical study of the state-to-state photodissociation dynamics of the vibrationally excited water molecule in the B band.

The state-to-state photodissociation dynamics for the vibrationally excited H2O in its second absorption band has been investigated on the recent three-dimensional potential energy surfaces based on a large number of high-level ab initio points. The photodissociassion dynamics from three fundamental vibrational states of H2O were explored from quantum dynamical calculations including the electronic X̃ and B̃ states on the basis of a Chebyshev real wave packet method. Because of the different shapes of various initial vibrational wave functions, the photoexcited wavepackets access different portions of the upper-state potential energy surface, which yields different absorption spectra, ro-vibrational distributions, and branching ratios. The bending excited vibrational state (0,1,0) generates two lobes with a shallow minimum on the absorption spectrum, a dominant vibrational inverted population OH(X̃, ν = 1) fragment at higher energy, and a nearly single rotational product propensity. The bond-stretching vibrational states (0,0,1) and (1,0,0) show a high OH(Ã)/OH(X̃) ratio at short photon wavelength, which indicates that dissociation proceeds mainly via the adiabatic channel.

Product fine-structure resolved photodissociation dynamics: the A band of H2O.

The photodissociation dynamics of H2O in its first absorption band is investigated on an accurate potential energy surface based on a large number of high-level ab initio points. Several ro-vibrational states of the parent molecule are considered. Different from most previous theoretical studies, the spin-orbit and Λ-doublet populations of the open-shell OH fragment are reported from full-dimensional wave packet calculations. The populations of the two spin-orbit manifolds are in most cases close to the statistical limit, but the Λ-doublet is dominated by the A(") component, thanks largely to the fast in-plane dissociation of H2O(Ã(1)A('')). Comparisons with experimental data and a Franck-Condon model are generally very good, although some discrepancies exist.

Exploring the Interfacial Hydrogen Transfer between Pt and the Siliceous Framework and Its Promotional Effect on the Isotope Catalytic Exchange.

Interfacial hydrogen transfer between metal particles and catalyst supports is a ubiquitous phenomenon in heterogeneous catalysis, and this occurrence on reducible supports has been established, yet controversies remain about how hydrogen transfer can take place on nonreducible supports, such as silica. Herein, highly dispersed Pt clusters supported on a series of porous silica materials with zeolitic or/and amorphous frameworks were prepared to interrogate the nature of hydrogen transfer and its promotional effect on H2-HDO isotope catalytic exchange. The formation of zeolitic frameworks upon these porous silica supports by hydrothermal crystallization greatly promotes the interfacial hydrogen bidirectional migration between metal clusters and supports. Benefiting from this transfer effect, the isotope exchange rate is enhanced by 10 times compared to that on the amorphous counterpart (e.g., Pt/SBA-15). In situ spectroscopic and theoretical studies suggest that the defective silanols formed within the zeolite framework serve as the reactive sites to bind HDO or H2O by hydrogen bonds. Under the electrostatic attraction interaction, the D of hydrogen-bonded HDO scrambles to the Pt site and the dissociated H on Pt simultaneously spills back to the electronegative oxygen atom of adsorbed water to attain H-D isotope exchange with an energy barrier of 0.43 eV. The reverse spillover D on Pt combines with the other H on Pt to form HD in the effluent. We anticipate that these findings are able to improve our understanding of hydrogen transfer between metal and silica supports and favor the catalyst design for the hydrogen-involving reaction.

Rational design and construction of hierarchical porous quasi-hexagonal Co2P nanosheets/Co heterostructures as highly efficient bifunctional electrocatalysts for overall water splitting.

Constructing heterostructured electrocatalysts has proven effective in enhancing intrinsic catalytic activity. Herein, under guidance of theoretical calculations, hierarchical porous quasi-hexagonal Co2P nanosheets/Co heterostructures supported on carbon cloth (Co2P/Co/CC) with a high surface area were rationally designed and elaborately constructed through electroless Co plating, electrochemical oxidation, and phosphidation process, which showed significant electrocatalytic performance toward water electrolysis. Specifically, theoretical calculations revealed that the Co2P/Co heterostructure adjusted the electronic structure of Co2P and Co, reducing the energy barrier for target reactions and thereby boosting electrocatalytic activities for the hydrogen evolution reaction (HER). Notably, the typical Co2P/Co/CC catalyst demonstrated impressive HER performance, with low overpotentials of only 52 and 48 mV to achieve a current density of 10 mA/cm2 in 0.5 M H2SO4 and 1.0 M KOH solutions, respectively. The remarkable electrocatalytic performance of the catalyst can be attributed to the improved intrinsic activity resulting from the Co2P/Co heterostructures and the highly exposed active sites provided by the hierarchical porous structures. Furthermore, the Co2P/Co/CC catalyst exhibited excellent oxygen evolution reaction (OER) performance in alkaline electrolyte, requiring a low overpotential of only 306 mV to achieve a current density of 100 mA/cm2. Additionally, a two-electrode electrolyzer assembled with the Co2P/Co/CC electrodes achieved a current density of 10 mA/cm2 at a low cell voltage of 1.54 V and demonstrated excellent long-term stability. This work presents a novel and feasible strategy for constructing hierarchical heterostructured electrocatalysts that enable efficient water electrolysis. By combining rational design and theoretical guidance, our approach offers promising prospects for advancing the field of electrocatalysis and facilitating sustainable energy conversion.

State-to-state photodissociation dynamics of H2O in the B-band: competition between two coexisting nonadiabatic pathways.

The photodissociation of H2O in its B band is a prototype for nonadiabatic reaction dynamics. In addition to dissociation via the adiabatic pathway to the OH(Ã(2)Σ(+)) + H fragments, it also produces the OH(X̃(2)Π) + H fragments through two nonadiabatic pathways: the B̃ → X̃ transition via two conical intersections and the B̃ → à transition via a Renner-Teller pair. In this work, the state-to-state dissociation dynamics in all three channels are investigated with a full-dimensional quantum mechanical model using a set of coupled diabatic potential energy surfaces determined at the internally contracted multireference configuration interaction level with the aug-cc-pVQZ basis set. The inclusion of all relevant electronic states not only results in an improved agreement with the latest experimental data but also sheds valuable insights into the competition between the two coexisting nonadiabatic pathways.