Beyond the Charge Transfer Mechanism for 2D Materials-Assisted Surface Enhanced Raman Scattering.

Two-dimensional (2D) materials have been extensively implemented as surface-enhanced Raman scattering (SERS) substrates, enabling trace-molecule detection for broad applications. However, the accurate understanding of the mechanism remains elusive because most theoretical explanations are still phenomenological or qualitative based on simplified models and rough assumptions. To advance the development of 2D material-assisted SERS, it is vital to attain a comprehensive understanding of the enhancement mechanism and a quantitative assessment of the enhancement performance. Here, the microscopic chemical mechanism of 2D material-assisted SERS is quantitatively investigated. The frequency-dependent Raman scattering cross sections suggest that the 2D materials' SERS performance is strongly dependent on the excitation wavelengths and the molecule types. By analysis of the microscopic Raman scattering processes, the comprehensive contributions of SERS can be revealed. Beyond the widely postulated charge transfer mechanisms, the quantitative results conclusively demonstrate that the resonant transitions within 2D materials alone are also capable of enhancing the molecular Raman scattering through the diffusive scattering of phonons. Furthermore, all of these scattering routines will interfere with each other and determine the final SERS performance. Our results not only provide a complete picture of the SERS mechanisms but also demonstrate a systematic and quantitative approach to theoretically understand, predict, and promote the 2D materials SERS toward analytical applications.

Ionic Porous Aromatic Frameworks Embedding Polyoxometalates for Heterogeneous Catalysis.

Porous aromatic frameworks (PAFs) are highly promising functional porous solids known for their feasible amenability and extraordinary stability. When the framework was modified by ionic functional groups, these ionic PAFs (iPAFs) exhibited charged channels for adsorption, separation, and catalysis. However, the surface areas of ionic porous frameworks are usually lower than that of neutral frameworks, and their synthesis is limited by specific strategies and complex modification processes. To address these challenges, an intuitive route to construct ionic porous framework with high specific surface area was proposed. Herein, a multivariate ionic porous aromatic framework (MTV-iPAFs, named PAF-270) was synthesized using readily available building units with ionic functional groups through a multivariable synthesis strategy. PAF-270 exhibited hierarchical structure with the highest specific surface area among reported imidazolium-functionalized PAFs. Utilizing its physical and chemical properties, the availability for polyoxometalate loading and heterogeneous catalysis of PAF-270 were explored. PAF-270 exhibited a high adsorption capacity up to 50 % for both H3O40PW12 (HPW) and (NH4)5H6PV8Mo4O40 (V8). HPW@PAF-270 and V8@PAF-270 exhibited excellent catalytic abilities for oleic acid esterification and extractive oxidative desulfurization, respectively. Due to the stability of PAFs, these materials also showed remarkable resistance to temperature and pH changes. Overall, these results underscore the potential application of MTV-iPAFs as versatile functional porous materials.

L-shaped association between the GA/HbA1c ratio and all-cause mortality in U.S. adults with NAFLD: a cross-sectional study from the NHANES 1999-2004.

OBJECTIVE: It is currently unclear whether there is a relationship between the ratio of glycated albumin to hemoglobin A1c (GA/HbA1c) and mortality in individuals diagnosed with nonalcoholic fatty liver disease (NAFLD). The primary objective of the study was to investigate the relationship between the GA/HbA1c ratio and all-cause mortality in adults with NAFLD in the U.S. METHODS: The investigation included a total of 5,295 individuals aged ≥ 18 years who were diagnosed with NAFLD, these individuals were selected from the National Health and Nutrition Examination Survey conducted between 1999 and 2004. To evaluate the outcomes of death, the researchers relied on National Death Index (NDI) records up to December 31, 2019. To better understand the nonlinear relationship between the GA/HbA1c ratio and mortality among individuals with NAFLD, this study employed both subgroup and sensitivity analyses. Furthermore, Cox proportional hazards models and two-part Cox proportional hazards model were utilized. RESULTS: The study included a total of 5,295 adult patients with NAFLD in the U.S. During a median follow-up period of 16.9 years, there were 1,471 recorded deaths, including 419 cardiovascular deaths. After accounting for various factors, a higher GA/HbA1c ratio exhibited a positive and nonlinear association with an increased risk of all-cause mortality in patients with NAFLD. Furthermore, the study revealed an L-shaped relationship between the GA/HbA1c ratio and all-cause mortality, with the inflection point occurring at a GA/HbA1c ratio of 2.21. When the GA/HbA1c ratio exceeded 2.21, each 1-unit increase in the ratio was associated with a 33% increase in the adjusted hazard ratio (HR 1.33; 95% CI 1.14, 1.60) for all-cause mortality. CONCLUSIONS: A nonlinear correlation between the ratio of GA to HbA1c and all-cause mortality was observed in U.S. adults with NAFLD. In addition, an elevated GA/HbA1c ratio was linked to an increased risk of all-cause mortality in these patients.

A Feasible Strategy for Identifying Single-Atom Catalysts Toward Electrochemical NO-to-NH3 Conversion.

Combining NO removal and NH3 synthesis, electrochemical NO reduction reaction (NORR) toward NH3 is considered as a novel and attractive approach. However, exploring suitable catalysts for NO-to-NH3 conversion is still a formidable task due to the lack of a feasible method. Herein, utilizing systematic first-principles calculations, a rational strategy for screening efficient single-atom catalysts (SACs) for NO-to-NH3 conversion is reported. This strategy runs the gamut of stability, NO adsorbability, NORR activity, and NH3 selectivity. Taking transition metal atom embedded in C2 N (TM-C2 N) as an example, its validity is demonstrated and Zr-C2 N is selected as a stable NO-adsorbable NORR catalyst with high NH3 selectivity. Therefore, this work has established a theoretical landscape for screening SACs toward NO-to-NH3 conversion, which will contribute to the application of SACs for NORR and other electrochemical reactions.

Production of Piperidine and δ-Lactam Chemicals from Biomass-Derived Triacetic Acid Lactone.

Piperidine and δ-Lactam chemicals have wide application, which are currently produced from fossil resource in industry. Production of this kind of chemicals from lignocellulosic biomass is of great importance, but is challenging and the reported routes give low yield. Herein, we demonstrate the strategy to synthesize 2-methyl piperidine (MP) and 6-methylpiperidin-2-one (MPO) from biomass-derived triacetic acid lactone (TAL) that is produced microbially from glucose. In this route, TAL was firstly converted into 4-hydroxy-6-methylpyridin-2(1H)-one (HMPO) through facile aminolysis, subsequently HMPO was selectively transformed into MP or MPO over Ru catalysts supported on beta zeolite (Ru/BEA-X, X is the molar ratio of Si to Al) via the tandem reaction. It was found that the yield of MP could reach 76.5 % over Ru/BEA-60 in t-BuOH, and the yield of MPO could be 78.5 % in dioxane. Systematic studies reveal that the excellent catalytic performance of Ru/BEA-60 was closely correlated with the cooperative effects between active metal and acidic zeolite with large pore geometries. The related reaction pathway was studied on the basis of control experiments.

Thermal transport properties of novel two-dimensional CSe.

Recently, as a novel member of the IV-VI group compounds, two-dimensional (2D) buckled monolayer CSe has been discovered for use in high-performance light-emitting devices (Q. Zhang, Y. Feng, X. Chen, W. Zhang, L. Wu and Y. Wang, Nanomaterials, 2019, 9, 598). However, to date, the heat transport properties of this novel CSe is still lacking, which would hinder its potential application in electronic devices and thermoelectric materials that can generate electricity from waste heat. Here we systematically study the heat transport properties of monolayer CSe based on ab initio calculations and phonon Boltzmann transport theory. We find that the lattice thermal conductivity κlat of monolayer CSe is around 42 W m-1 K-1 at room temperature, which is much lower than those of black phosphorene, buckled phosphorene, MoS2, and buckled arsenene. Moreover, the longitudinal acoustic phonon mode contributes the most to the κlat, which is much larger than those of the out-of-plane phonon mode and transverse acoustic branches. The calculated size-dependent κlat shows that the sample size can significantly reduce the κlat of monolayer CSe and can persist up to 10 µm. These discoveries provide new insight into the size-dependent thermal transport in nanomaterials and guide the design of CSe-based low-dimensional quantum devices, such as thermoelectric devices.

Ultra-low lattice thermal conductivity of monolayer penta-silicene and penta-germanene.

We study the lattice thermal conductivity of two-dimensional (2D) pentagonal systems, such as penta-silicene and penta-germanene. Penta-silicene has been recently reported, while the stable penta-germanene, made up of another group IV element, is first revealed by our ab initio calculations. We find that both penta-silicene and penta-germanene at room temperature have ultra-low lattice thermal conductivities, κ, of 1.29 W m-1 K-1 and 0.30 W m-1 K-1, respectively. To the best of our knowledge, penta-germanene may have the lowest κ in 2D crystal materials. We attribute the ultra-low κ to the weak phonon harmonic interaction and strong anharmonic scattering. A small phonon group velocity, a small Debye frequency, a large Grüneisen parameter, and a large number of modes available for phonon-phonon interplay together lead to the ultra-low κ of penta-silicene and penta-germanene. These discoveries provide new insight into the manipulation of ultra-low κ in 2D materials and highlight the potential applications of silicon and germanium based high thermoelectric materials.

In Situ Resonant Raman Spectroscopy to Monitor the Surface Functionalization of MoS2 and WSe2 for High-k Integration: A First-Principles Study.

Surface functionalization of the dangling-bond-free MoS2, WSe2, and other TMDs (transition metal dichalcogenides) is of large practical importance, for example, in providing nucleation sites for the subsequent high-k dielectric integration. Of the surface functionalization methods, the reversible O or N atom adsorption on top of the chalcogen atoms is most promising. However, hazards such as severe oxidation or nitridation persist when the adsorption coverage is high. An in situ characterization technique, which can be integrated with the surface functionalization and dielectric deposition chamber, becomes valuable to enable the real-time monitoring of surface adsorption conditions. Raman spectroscopy, as a nondestructive characterization method without vacuum requirement, is a strong candidate. By utilizing first-principles calculations, Raman spectra of single-layer MoS2 and WSe2 with various O/N adsorption coverages are studied. The calculations suggest that the low-coverage O/N adsorbates will act as perturbations to the periodic lattice and activate the acoustic-phonon Raman scatterings. While high-coverage adsorptions will further activate and intensify the optical-phonon Raman scatterings of previously silent A2u and E1g modes, due to the breaking of reflection symmetry in the z direction, new phonon modes associated with the adatom oscillations are also introduced. All these pieces of evidence, together with the peak shifts of previously active A1g and E2g1 modes, suggest that in situ resonant Raman spectroscopy is capable of providing important information to quantify the O/N adsorption coverage and can be used as a valuable real-time characterization technique to monitor and control the surface functionalization conditions of MoS2 and WSe2.

Enhanced dielectric deposition on single-layer MoS2 with low damage using remote N2 plasma treatment.

Using remote N2 plasma treatment to promote dielectric deposition on the dangling-bond free MoS2 is explored for the first time. The N2 plasma induced damages are systematically studied by the defect-sensitive acoustic-phonon Raman of single-layer MoS2, with samples undergoing O2 plasma treatment as a comparison. O2 plasma treatment causes defects in MoS2 mainly by oxidizing MoS2 along the already defective sites (most likely the flake edges), which results in the layer oxidation of MoS2. In contrast, N2 plasma causes defects in MoS2 mainly by straining and mechanically distorting the MoS2 layers first. Owing to the relatively strong MoS2-substrate interaction and chemical inertness of MoS2 in N2 plasma, single-layer MoS2 shows great stability in N2 plasma and only stable point defects are introduced after long-duration N2 plasma exposure. Considering the enormous vulnerability of single-layer MoS2 in O2 plasma and the excellent stability of single-layer MoS2 in N2 plasma, the remote N2 plasma treatment shows great advantage as surface functionalization to promote dielectric deposition on single-layer MoS2.

Synthesis of Supported Ultrafine Non-noble Subnanometer-Scale Metal Particles Derived from Metal-Organic Frameworks as Highly Efficient Heterogeneous Catalysts.

The properties of supported non-noble metal particles with a size of less than 1 nm are unknown because their synthesis is a challenge. A strategy has now been created to immobilize ultrafine non-noble metal particles on supports using metal-organic frameworks (MOFs) as metal precursors. Ni/SiO2 and Co/SiO2 catalysts were synthesized with an average metal particle size of 0.9 nm. The metal nanoparticles were immobilized uniformly on the support with a metal loading of about 20 wt%. Interestingly, the ultrafine non-noble metal particles exhibited very high activity for liquid-phase hydrogenation of benzene to cyclohexane even at 80 °C, while Ni/SiO2 with larger Ni particles fabricated by a conventional method was not active under the same conditions.

Molybdenum-Bismuth Bimetallic Chalcogenide Nanosheets for Highly Efficient Electrocatalytic Reduction of Carbon Dioxide to Methanol.

Methanol is a very useful platform molecule and liquid fuel. Electrocatalytic reduction of CO2 to methanol is a promising route, which currently suffers from low efficiency and poor selectivity. Herein we report the first work to use a Mo-Bi bimetallic chalcogenide (BMC) as an electrocatalyst for CO2 reduction. By using the Mo-Bi BMC on carbon paper as the electrode and 1-butyl-3-methylimidazolium tetrafluoroborate in MeCN as the electrolyte, the Faradaic efficiency of methanol could reach 71.2 % with a current density of 12.1 mA cm(-2) , which is much higher than the best result reported to date. The superior performance of the electrode resulted from the excellent synergistic effect of Mo and Bi for producing methanol. The reaction mechanism was proposed and the reason for the synergistic effect of Mo and Bi was discussed on the basis of some control experiments. This work opens a way to produce methanol efficiently by electrochemical reduction of CO2 .

Palladium-catalyzed Cs2CO3-promoted arylation of unactivated C(sp(3))-H bonds by (diacetoxyiodo)arenes: shifting the reactivity of (diacetoxyiodo)arenes from acetoxylation to arylation.

PdCl2(CH3CN)2-catalyzed arylation of unactivated C(sp(3))-H bonds using (diacetoxyiodo)arenes as arylation reagents is reported. The reactivity of (diacetoxyiodo)arenes as arylation reagents is enabled in the presence of Cs2CO3 under the reaction conditions. This arylation method is highly efficient and occurs without the use of silver salt. The reaction tolerates a broad substrate scope that was not demonstrated by other silver salt-free C(sp(3))-H bond arylation conditions. The synthetic utility of the method is further illustrated in the synthesis of the psychotropic drug phenibut. A detailed mechanism study has been conducted to understand the reaction pathway.

Synthesis of higher alcohols from CO2 hydrogenation over a PtRu/Fe2O3 catalyst under supercritical condition.

Hydrogenation of CO(2) to alcohols is of great importance, especially when producing higher alcohols. In this work, we synthesized heterogeneous PtRu/Fe(2)O(3), in which the Pt and Ru bimetallic catalysts were supported on Fe(2)O(3). The catalyst was used to catalyse CO(2) hydrogenation to alcohols. It was demonstrated that the activity and selectivity could be tuned by the bimetallic composition, and the catalyst with a Pt to Ru molar ratio of 1:2 (Pt(1)Ru(2)/Fe(2)O(3)) had high activity and selectivity at 200°C, which is very low for heterogeneous hydrogenation of CO(2) to produce higher alcohols. The conversion and the selectivity increased with increasing pressures of CO(2) and/or H(2). The catalyst could be reused at least five times without any obvious change in activity or selectivity.

Transformation of atmospheric CO2 catalyzed by protic ionic liquids: efficient synthesis of 2-oxazolidinones.

Protic ionic liquids (PILs), such as 1,8-diazabicyclo[5.4.0]-7-undecenium 2-methylimidazolide [DBUH][MIm], can catalyze the reaction of atmospheric CO2 with a broad range of propargylic amines to form the corresponding 2-oxazolidinones. The products are formed in high yields under mild, metal-free conditions. The cheaper and greener PILs can be easily recycled and reused at least five times without a decrease in the catalytic activity and selectivity. A reaction mechanism was proposed on the basis of a detailed DFT study which indicates that both the cation and anion of the PIL play key synergistic roles in accelerating the reaction.

Porous Aromatic Frameworks Enabling Polyiodide Confinement toward High Capacity and Long Lifespan Zinc-Iodine Batteries.

Aqueous zinc-iodine batteries (AZIBs) are attracting increasing attention because of their high safety and abundance of resources. However, the performance of AZIBs is compromised by inadequate confinement of soluble polyiodides, the undesired shuttle effect, and slow reaction kinetics. In this study, a porous aromatic framework (PAF) with abundant benzene motifs and a well-organized pore structure is adopted as the iodine host, which exhibits high iodine adsorption capacity and robust polyiodide confinement. Both experimental characterizations and theoretical simulations indicate that the interactions between iodine species and the PAF-1 facilitate the redox reaction by coupling the electronic structures of the active species in the framework. A comparison of PAF-1, PAF-5, and PAF-11 also emphasizes the structural advantages of the high surface area and interconnected three-dimensional channels of PAF-1. Consequently, the I2@PAF-1 cathode can deliver a high capacity of 328 mAh g-1 at 0.5 C, outstanding rate performance, and a stable cycling life of 20 000 cycles (86 % retention at 10 C). The robust polyiodide confinement and superb electrochemical performance of Zn-I2@PAF-1 provide insights into the practical application of PAFs as excellent electrode materials for AZIBs.

Unveiling Atomic-Scale Product Selectivity at the Cocatalyst-TiO2 Interface Using X-Ray Techniques: Insights into Interface Reactivity.

The microstructure at the interface between the cocatalyst and semiconductor plays a vital role in concentrating photo-induced carriers and reactants. However, observing the atomic arrangement of this interface directly using an electron microscope is challenging due to the coverings of the semiconductor and cocatalyst. To address this, multiple metal-semiconductor interfaces on three TiO2 crystal facets (M/TiO2 ─N, where M represents Ag, Au, and Pt, and N represents the 001, 010, and 101 single crystal facets). The identical surface atomic configuration of the TiO2 facets allowed us to investigate the evolution of the microstructure within these constructs using spectroscopies and DFT calculations. For the first time, they observed the transformation of saturated Ti6c ─O bonds into unsaturated Ti5c ─O and Ti6c ─O─Pt bonds on the TiO2 ─010 facet after loading Pt. This transformation have a direct impact on the selectivity of the resulting products, leading to the generation of CO and CH4 at the Ti6c ─O─Pt and Pt sites, respectively. These findings pinpoint the pivotal roles played by the atomic arrangement at the M/TiO2 ─N interfaces and provide valuable insights for the development of new methodologies using conventional lab-grade equipment.

Theoretical Insight into the Band Alignment at High-κ Oxide XO2/Diamond (X = Hf and Zr) Interfaces with a SiO2 Interlayer for MOS Devices.

Diamond has become a promising candidate for high-power devices based on its ultrawide bandgap and excellent thermoelectric properties, where an appropriate gate dielectric has been a bottleneck hindering the development of diamond devices. Herein, we have systematically investigated the structural arrangement and electronic properties of diamond/high-κ oxide (HfO2, ZrO2) heterojunctions by first-principles calculations with a SiO2 interlayer. Charge analysis reveals that the C-Si bonding interface attracts a large amount of charge concentrated at the diamond interface, indicating the potential for the formation of a 2D hole gas (2DHG). The diamond/HfO2 and diamond/ZrO2 heterostructures exhibit similar "Type II" band alignments with VBOs of 2.47 and 2.21 eV, respectively, which is consistent with experimental predictions. The introduction of a SiO2 dielectric layer into the diamond/SiO2/high-κ stacks exhibits the typical "Type I″ straddling band offsets (BOs). In addition, the wide bandgap SiO2 interlayer keeps the valence band maximum (VBM) and conduction band minimum (CBM) in the stacks away from those of diamond, effectively confining the electrons and holes in MOS devices. This work exhibits the potential of SiO2/high-κ oxide gate dielectrics for diamond devices and provides theoretical insights into the rational design of high-quality gate dielectrics for diamond-based MOS device applications.

Theoretical study on the reaction of CO2 and 2-aminobenzonitrile to form quinazoline-2,4(1H,3H)-dione in water without any catalyst.

Development of efficient and green routes to convert CO2 into value-added products is of great importance. Recently, we found that quinazoline-2,4(1H,3H)-diones and their derivatives could be synthesized from CO2 and 2-aminobenzonitriles in water efficiently without a catalyst and excellent yields were obtained, while the reactions did not occur in organic solvents. In this work, using density functional theory (DFT) we conduct the first theoretical work to study the mechanism of the reactions in water. It is revealed that CO2 reacts via carbonic acid (H2CO3) with 2-aminobenzonitrile to form the product. Formation of H2CO3 from CO2 and water is the key for the reactions to proceed smoothly in water without a catalyst because of two reasons. First, H2CO3 reacts with 2-aminobenzonitriles more easily than CO2 itself; second, H2CO3 can effectively promote the reaction by the synergistic action of its carbonyl O atom and one of the hydroxyl O atoms.

High-Accuracy Neural Network Interatomic Potential for Silicon Nitride.

In the field of machine learning (ML) and data science, it is meaningful to use the advantages of ML to create reliable interatomic potentials. Deep potential molecular dynamics (DEEPMD) are one of the most useful methods to create interatomic potentials. Among ceramic materials, amorphous silicon nitride (SiNx) features good electrical insulation, abrasion resistance, and mechanical strength, which is widely applied in industries. In our work, a neural network potential (NNP) for SiNx was created based on DEEPMD, and the NNP is confirmed to be applicable to the SiNx model. The tensile tests were simulated to compare the mechanical properties of SiNx with different compositions based on the molecular dynamic method coupled with NNP. Among these SiNx, Si3N4 has the largest elastic modulus (E) and yield stress (σs), showing the desired mechanical strength owing to the largest coordination numbers (CN) and radial distribution function (RDF). The RDFs and CNs decrease with the increase of x; meanwhile, E and σs of SiNx decrease when the proportion of Si increases. It can be concluded that the ratio of nitrogen to silicon can reflect the RDFs and CNs in micro level and macro mechanical properties of SiNx to a large extent.

High-Throughput Screening of Gas Sensor Materials for Decomposition Products of Eco-Friendly Insulation Medium by Machine Learning.

Nowadays, trifluoromethyl sulfonyl fluoride (CF3SO2F) has shown great potential to replace SF6 as an eco-friendly insulation medium in the power industry. In this work, an effective and low-cost design strategy toward ideal gas sensors for the decomposed gas products of CF3SO2F was proposed. The strategy achieved high-throughput screening from a large candidate space based on first-principle calculation and machine learning (ML). The candidate space is made up of different transition metal-embedded graphic carbon nitrides (TM/g-C3N4) owing to their high surface area and subtle electronic structure. Four main noteworthy decomposition gases of CF3SO2F, namely, CF4, SO2, SO2F2, and HF, as well as their initial stable structure on TM/g-C3N4 were determined. The best-performing ML model was established and implemented to predict the interaction strength between gas products and TM/g-C3N4, thus determining the promising gas-sensing materials for target gases with the requirements of interaction strength, recovery time, sensitivity, and selectivity. Further analysis guarantees their stability and reveals the origin of excellent properties as a gas sensor. The high-throughput strategy opens a new avenue of rational and low-cost design principles of desirable gas-sensing materials in an interdisciplinary view.