First-principle calculations study of the ORR/OER electrocatalytic activity of ruthenium polyphthalocyanine axially modified with aliphatic thiol groups.

In this study, the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activity of ruthenium polyphthalocyanine axially modified with different aliphatic thiol groups, RuPPc-SR (SR = -SCH3, -SC2H5, -SC3H7, -SC4H9, -SC5H11, and -SC6H13), in an acidic medium were simulated using DFT. All -SR groups can effectively enhance the ORR and OER catalytic activities of RuPPc. The ORR and OER overpotentials of RuPPc-SC4H9 are 0.237 V and 0.436 V, respectively, which are far lower than those of RuPPc (0.960 V and 0.903 V). For RuPPc-SC4H9, the four C and S atoms of the -SC4H9 chain and Ru atom are coplanar, and thus, conjugate effects and inductive effects exist between the -SC4H9 chain and Ru atom. This makes the Ru atom exhibit the least positive Bader charge and smallest spin density, and the anti-bonding orbitals of dxz, dyz, and dz2 of the Ru atom shift below the Fermi level (Ef). This makes the adsorption strength of RuPPc-SC4H9 toward ORR and OER intermediates the weakest, which accelerates the reaction process, thus resulting in better ORR and OER catalytic activity. Therefore, the introduction of the aliphatic thiol groups might effectively improve the OER/ORR catalytic activity of RuPPc.

Structural and Chemical Bonding Properties of AuS2H0/-: A Photoelectron Velocity-Map Imaging Spectroscopic and Theoretical Study.

Mass-selected photoelectron velocity-map imaging spectroscopy was employed to investigate the geometrical and electronic properties of AuS2H-/0. The comprehensive comparison between the experiment and theoretical calculations establishes that the ground-state AuS2H- anion has a mixed-ligand structure [SAuSH]- with an unsymmetrical S-Au-S unit. Further chemical bonding analyses on AuS2H and comparison with the isoelectronic AuS2- suggest that the unique S-Au-S unit in these species features two three-center, three-electron π-bonding, and one three-center, two-electron σ-bonding. The isoelectronic replacement of the extra electron in AuS2- by the H atom can lead to σ bonding evolution from the electron-sharing bond to the dative bond. These findings are conducive to the fundamental understanding of the intrinsic stability of thiolate-protected gold nanoclusters and their delicate ligand design to achieve desirable properties.

Controlled Growth of Pd Nanocrystals by Interface Interaction on Monolayer MoS2: An Atom-Resolved in Situ Study.

The crystal growth kinetics is crucial for the controllable preparation and performance modulation of metal nanocrystals (NCs). However, the study of growth mechanisms is significantly limited by characterization techniques, and it is still challenging to in situ capture the growth process. Real-time and real-space imaging techniques at the atomic scale can promote the understanding of microdynamics for NC growth. Herein, the growth of Pd NCs on monolayer MoS2 under different atmospheres was in situ studied by environmental transmission electron microscopy. Introducing carbon monoxide can modulate the diffusion of Pd monomers, resulting in the epitaxial growth of Pd NCs with a uniform orientation. The electron energy loss spectroscopy and theoretical calculations showed that the CO adsorption assured the specific exposed facets and good uniformity of Pd NCs. The insight into the gas-solid interface interaction and the microscopic growth mechanism of NCs may shed light on the precise synthesis of NCs on two-dimensional (2D) materials.

Fabrication of a Molybdenum Dioxide/Multi-Walled Carbon Nanotubes Nanocomposite as an Anodic Modification Material for High-Performance Microbial Fuel Cells.

A nanocomposite of multi-walled carbon nanotubes (MWCNTs) decorated with molybdenum dioxide (MoO2) nanoparticles is fabricated through the reduction of phosphomolybdic acid hydrate on functionalized MWCNTs in a hydrogen-argon (10%) atmosphere in a tube furnace. The MoO2/MWCNTs composite is proposed as an anodic modification material for microbial fuel cells (MFCs). MWCNTs have outstanding physical and chemical peculiarities, with functionalized MWCNTs having substantially large electroactive areas. In addition, combined with the exceptional properties of MoO2 nanoparticles, the synergistic advantages of functionalized MWCNTs and MoO2 nanoparticles give a MoO2/MWCNTs anode a large electroactive area, excellent electronic conductivity, enhanced extracellular electron transfer capacity, and improved nutrient transfer capability. Finally, the power harvesting of an MFC with the MoO2/MWCNTs anode is improved, with the MFC showing long-term repeatability of voltage and current density outputs. This exploratory research advances the fundamental application of anodic modification to MFCs, simultaneously providing valuable guidance for the use of carbon-based transition metal oxide nanomaterials in high-performance MFCs.

A Universal Approach for Sustainable Urea Synthesis via Intermediate Assembly at the Electrode/Electrolyte Interface.

Electrocatalytic C-N coupling process is indeed a sustainable alternative for direct urea synthesis and co-upgrading of carbon dioxide and nitrate wastes. However, the main challenge lies in the unactivated C-N coupling process. Here, we proposed a strategy of intermediate assembly with alkali metal cations to activate C-N coupling at the electrode/electrolyte interface. Urea synthesis activity follows the trend of Li+

A theoretical study on the ORR electrocatalytic activity of axial ligand modified cobalt polyphthalocyanine.

In this work, the catalytic activity in the oxygen reduction reaction (ORR) of cobalt polyphthalocyanine whose central Co atom is coordinated at the axial position by ligands (L = -F, -OH, -OCH3, -N3, -Cl, -Br, -I, -SCN, and -CN) (CoPPc-L) was investigated using theoretical calculations in alkaline medium. Among all CoPPc-L, CoPPc-N3 exhibited the lowest ORR overpotential of 0.23 V vs. a standard hydrogen electrode, which is significantly lower than those of CoPPc (0.48 V) and Pt(111) (0.43 V). There is a good linear relationship between ΔG*OOH and the electronegativity of ligating atoms in axial ligands of CoPPc-L. The greater the electronegativity, the stronger the adsorption of the catalyst to the intermediate. Additionally, the adsorption strength of CoPPc to the intermediate is modified by the axial ligands, which adjust the distribution of anti-bonding electronic states of dz2, dxz, and dyz orbitals near the Fermi level, Ef. A larger Mayer bond order of the Co-L bond resulted in a smaller bond order of the Co-O bond. CoPPc-N3 exhibited a moderate Co-O bond order of 0.737, corresponding to moderate adsorption energy to the OOH intermediate. This study demonstrates that the interaction strength between CoPPc and ORR intermediates can be adjusted by selecting appropriate axial ligands, which can modulate the ORR catalytic activity.

Engineering topological states in a two-dimensional honeycomb lattice.

In this work, we use first-principles calculations to determine the interplay between spin-orbit coupling (SOC) and magnetism which can not only generate a quantum anomalous Hall state but can also result in topologically trivial states although some honeycomb systems host large band gaps. By employing tight-binding model analysis, we have summarized two types of topologically trivial states: one is due to the coexistence of quadratic non-Dirac and linear Dirac bands in the same spin channel that act together destructively in magnetic materials (such as, CrBr3, CrCl3, and VBr3 monolayers); the other one is caused by the destructive coupling effect between two different spin channels due to small magnetic spin splitting in heavy-metal-based materials, such as, BaTe(111)-supported plumbene. Further investigations reveal that topologically nontrivial states can be realized by removing the Dirac band dispersion of the magnetic monolayers for the former case (such as in alkali metal doped CrBr3), while separating the two different spin channels from each other by enhancing the magnetic spin splitting for the latter case (such as in half-iodinated silicene). Thus, our work provides a theoretical guideline to manipulate the topological states in a two-dimensional honeycomb lattice.

Strain-tunable magnetism and topological states in layered VBi2Te4.

Similar to the magnetic topological insulator of MnBi2Te4, recent studies have demonstrated that VBi2Te4 is also an ideal candidate to explore many intriguing quantum states. Different from the strong interlayer antiferromagnetic (AFM) coupling in layered MnBi2Te4, based on first-principles calculations, we find that the energy difference between AFM and ferromagnetic (FM) orders in layered VBi2Te4 is much smaller than that of MnBi2Te4. Specifically, it is found that the interlayer FM coupling can be readily achieved by applying strain. Further electronic band structures reveal that the VBi2Te4 bilayer is a time-reversal symmetry broken quantum spin Hall insulator with a spin Chern number of CS = 1, which is essentially different from the QAH state with a Chern number of C = 1 in the MnBi2Te4 bilayer. Most strikingly, the topological states of the magnetic VBi2Te4 bilayer can be well tuned by strain, whose topological phase diagram is mapped out as a function of strain by employing continuum model analyses. All of these results indicate that the layered VBi2Te4 not only enriches the family of magnetic topological materials, but also provides a promising platform to explore more exotic quantum phenomena.

Immobilized triatomic CuB2 clusters on 2D carbon nitride: highly selective conversion of CO to ethanol at low potentials.

A promising pathway for carbon usage and energy storage is electrocatalytic reduction of CO to form high-value multi-carbon products. Herein, the d-p coupled triatomic catalyst CuB2@g-C3N4 with significant activity and selectivity for ethanol is presented for the first time. Density functional theory calculations elucidate that these spatially confined triatomic centers are capable of immobilizing multiple CO molecules, providing an exclusive reaction channel for direct C-C coupling. The CuB2@g-C3N4 catalyst can effectively reduce the energy barrier of CO dimerization to 0.46 eV. The limiting potential is only -0.19 V, which is much smaller than that of other Cu-based catalysts. Additionally, the CuB2@g-C3N4 catalyst can effectively inhibit the generation of competing C1 products and hydrogen evolution reactions. Excitingly, CuB2 loading makes g-C3N4 more optically active in visible and even infrared light. This work provides important ideas for the atomically precise design of novel d-p coupled catalysts for the direct conversion of CO2/CO into energetic fuels and high-value chemicals.

Coordination-induced bond weakening in NiC3: An experimental and theoretical investigation.

Mass-selected photoelectron velocity-map imaging spectroscopy in conjunction with the density functional theory calculations was employed to investigate the geometrical and chemical bonding properties of NiC3-/0. Both the photoelectron spectrum and photoelectron angular distribution were measured from the spectra, yielding useful geometrical and electronic information about NiC3-/0. The complementary theoretical calculations suggest that the linear and fan-like structures were both populated experimentally in the cluster beam. Further comparative study on the synergistic donor-acceptor interactions in both isomers revealed the side-on coordination-induced bond weakening in the fan-like isomer as compared to the linear isomer. These findings will shed light on the structure-dependent reactivity of transition metal carbides.

A study on the rapid diagnosis of chronic heart failure by measuring the difference in pulse oxygen saturation before and after arm compression.

BACKGROUND: Clinically, the pulse oxygen saturation of patients with chronic heart failure does not decrease significantly, and the clinical manifestations of labor-related dyspnea are not typical. As such, it is difficult to make a rapid diagnosis. OBJECTIVE: To investigate changes in pulse oxygen saturation in patients with chronic heart failure and examine the relationship between B-type natriuretic peptide (BNP) and normal pulse oxygen saturation. METHODS: A total of 80 hospitalized patients with chronic heart failure and increased BNP were randomly selected as the study group; the family members of 60 patients without dyspnea were randomly selected as the control group. The researchers measured the value of pulse oxygen saturation before and after upper arm compression, calculating the difference and analyzing the correlation between this difference and BNP values. The data were statistically analyzed using the SPSS Statistics 17.0 program. RESULTS: The decrease in pulse oxygen saturation in the study group was greater than in the control group; the decrease in pulse oxygen saturation of patients with chronic heart failure positively correlated with BNP. CONCLUSION: The value of pulse oxygen saturation in patients with chronic heart failure decreased more than in the control group, and this difference positively correlated with BNP. The measurement of pulse oxygen saturation before and after upper arm compression is a simple and effective method for diagnosing and evaluating chronic heart failure.

Tuning the Site-to-Site Interaction of Heteronuclear Diatom Catalysts MoTM/C2N (TM = 3d Transition Metal) for Electrochemical Ammonia Synthesis.

Ammonia (NH3) synthesis is one of the most important catalytic reactions in energy and chemical fertilizer production, which is of great significance to the sustainable development of society and the economy. The electrochemical nitrogen reduction reaction (eNRR), especially when driven by renewable energy, is generally regarded as an energy-efficient and sustainable process to synthesize NH3 in ambient conditions. However, the performance of the electrocatalyst is far below expectations, with the lack of a high-efficiency catalyst being the main obstacle. Herein, by means of comprehensive spin-polarized density functional theory (DFT) computations, the catalytic performance of MoTM/C2N (TM = 3d transition metal) for use in eNRR was systematically evaluated. Among the results, MoFe/C2N can be considered the most promising catalyst due to its having the lowest limiting potential (-0.26 V) and high selectivity in the context of eNRR. Compared with its homonuclear counterparts, MoMo/C2N and FeFe/C2N, MoFe/C2N can balance the first protonation step and the sixth protonation step synergistically, showing outstanding activity regarding eNRR. Our work not only opens a new door to advancing sustainable NH3 production by tailoring the active sites of heteronuclear diatom catalysts but also promotes the design and production of novel low-cost and efficient nanocatalysts.

Theoretical Study on ORR/OER Bifunctional Catalytic Activity of Axial Functionalized Iron Polyphthalocyanine.

Designing efficient ORR/OER bifunctional electrocatalysts is very significant for reducing energy consumption and environmental protection. Hence, we studied the ORR/OER bifunctional catalytic activity of iron polyphthalocyanine (FePPc) coordinated by a series of axial ligands which has different electronegative coordination atom (FePPc-L) (L = -CN, -SH, -SCH3, -SC2H5, -I, -Br, -NH2, -Cl, -OCH3, -OH, and -F) in alkaline medium by DFT calculations. Among all FePPc-L, FePPc-CN, FePPc-SH, FePPc-SCH3, and FePPc-SC2H5 exhibit excellent ORR/OER bifunctional catalytic activities. Their ORR/OER overpotential is 0.256 V/0.234 V, 0.278 V/0.256 V, 0.280 V/0.329 V, and 0.290 V/0.316 V, respectively, which are much lower than that of the FePPc (0.483 V/0.834 V). The analysis of the electronic structure of the above catalysts shows that the electronegativity of the coordination atoms in the axial ligand is small, resulting in less distribution of dz2, dyz, and dxz orbitals near Ef, weak orbital polarization, small charge and magnetic moment of the central Fe atom, and weak adsorption strength for *OH. All these prove that the introduction of axial ligands with appropriate electronegativity coordinating atoms can adjust the adsorption of catalyst to intermediates and modify the ORR/OER bifunctional catalytic activities. This is an effective strategy for designing efficient ORR/OER bifunctional electrocatalysts.

Carbonaceous Material Modified MoO2 Nanospheres with Oxygen Vacancies for Enhanced Visible-Light Photocatalytic Oxidative Coupling of Benzylamine.

Surface oxygen vacancy (OV) plays a pivotal role in the activation of molecular oxygen and separation of electrons and holes in photocatalysis. Herein, carbonaceous materials-modified MoO2 nanospheres with abundant surface OVs (MoO2/C-OV) were successfully synthesized via glucose hydrothermal processes. In situ introduction of carbonaceous materials triggered a reconstruction of the MoO2 surface, which introduced abundant surface OVs on the MoO2/C composites. The surface oxygen vacancies on the obtained MoO2/C-OV were confirmed via electron spin resonance spectroscopy (ESR) and X-ray photoelectron spectroscopy (XPS). The surface OVs and carbonaceous materials boosted the activation of molecular oxygen to singlet oxygen (1O2) and superoxide anion radical (•O2-) in selectively photocatalytic oxidation of benzylamine to imine. The conversion of benzylamine was 10 times that of pristine MoO2 nanospheres with a high selectivity under visible light irradiation at 1 atm air pressure. These results open an avenue to modify Mo-based materials for visible light-driven photocatalysis.

Plasmonic Silver-Nanoparticle-Catalysed Hydrogen Abstraction from the C(sp3 )-H Bond of the Benzylic Cα atom for Cleavage of Alkyl Aryl Ether Bonds.

Selective activation of the C(sp3 )-H bond is an important process in organic synthesis, where efficiently activating a specific C(sp3 )-H bond without causing side reactions remains one of chemistry's great challenges. Here we report that illuminated plasmonic silver metal nanoparticles (NPs) can abstract hydrogen from the C(sp3 )-H bond of the Cα atom of an alkyl aryl ether ß-O-4 linkage. The intense electromagnetic near-field generated at the illuminated plasmonic NPs promotes chemisorption of the ß-O-4 compound and the transfer of photo-generated hot electrons from the NPs to the adsorbed molecules leads to hydrogen abstraction and direct cleavage of the unreactive ether Cß -O bond under moderate reaction conditions (≈90 °C). The plasmon-driven process has certain exceptional features: enabling hydrogen abstraction from a specific C(sp3 )-H bond, along with precise scission of the targeted C-O bond to form aromatic compounds containing unsaturated, substituted groups in excellent yields.

Oxygen Vacancy-Mediated Selective C-N Coupling toward Electrocatalytic Urea Synthesis.

The electrocatalytic C-N coupling for one-step urea synthesis under ambient conditions serves as the promising alternative to the traditional urea synthetic protocol. However, the hydrogenation of intermediate species hinders the efficient urea synthesis. Herein, the oxygen vacancy-enriched CeO2 was demonstrated as the efficient electrocatalyst with the stabilization of the crucial intermediate of *NO via inserting into vacant sites, which is conducive to the subsequent C-N coupling process rather than protonation, whereas the poor selectivity of C-N coupling with protonation was observed on the vacancy-deficient catalyst. The oxygen vacancy-mediated selective C-N coupling was distinguished and validated by the in situ sum frequency generation spectroscopy. The introduction of oxygen vacancies tailors the common catalyst carrier into an efficient electrocatalyst with a high urea yield rate of 943.6 mg h-1 g-1, superior than that of partial noble-metal-based electrocatalysts. This work provides novel insights into the catalyst design and developments of coupling systems.

A density functional theory study of a water gas shift reaction on Ag(111): potassium effect.

Density functional theory (DFT) calculations are executed to investigate the effect of a potassium (K) promoter on the activity of the water gas shift reaction (WGSR) over an Ag(111) surface. It is found that the WGSR proceeds mainly through the OH(O)-assisted carboxy pathway in which H2O dehydrogenation is the rate-controlling step on both Ag(111) and K/Ag(111) surfaces. Energetic span model analysis shows that K addition can enhance the activity of the WGSR by reducing the apparent activation energy of the whole reaction since it can promote H2O dissociation and stabilize the adsorption of the reactants (CO and H2O). Importantly, the K adatom can stabilize the binding of all oxygenates by direct K-O bonding and the stabilizing effect of K on OH adsorption of the transition state (TS) plays a leading role in promoting H2O dissociation. Moreover, the K-O distance and K coverage are two key factors affecting H2O activation, that is, the shorter the K-O distance (2-3 Å) the more the K coverage (25%) contributes to the stronger promotion effect. For various metals catalyzing the WGSR, K promotes H2O dissociation on inert metals like Ag, Au and Cu better than those on reactive metals (Pd and Ni) since the more inert metal surfaces would weaken the K and O binding and accordingly strengthen the interaction between them, resulting in a higher promotion effect.

Adsorption Characteristics of Gas Molecules Adsorbed on Graphene Doped with Mn: A First Principle Study.

Herein, the adsorption characteristics of graphene substrates modified through a combined single manganese atom with a vacancy or four nitrogen to CH2O, H2S and HCN, are thoroughly investigated via the density functional theory (DFT) method. The adsorption structural, electronic structures, magnetic properties and adsorption energies of the adsorption system have been completely analyzed. It is found that the adsorption activity of a single vacancy graphene-embedded Mn atom (MnSV-GN) is the largest in the three graphene supports. The adsorption energies have a good correlation with the integrated projected crystal overlap Hamilton population (-IpCOHP) and Fermi softness. The rising height of the Mn atom and Fermi softness could well describe the adsorption activity of the Mn-modified graphene catalyst. Moreover, the projected crystal overlap Hamilton population (-pCOHP) curves were studied and they can be used as the descriptors of the magnetic field. These results can provide guidance for the development and design of graphene-based single-atom catalysts, especially for the support effect.

Binary Solvent Regulated Architecture of Ultra-Microporous Hydrogen-Bonded Organic Frameworks with Tunable Polarization for Highly-Selective Gas Separation.

A binary solvent synthetic strategy is proposed for the construction of C2 -symmetric molecule-based hydrogen-bonded organic frameworks (HOFs) with permanent ultra-micropores and surface polarization derived from tunable coplanar open oxygen atoms. The activated HOFs BTBA-1 a and PTBA-1 a show highly selective separation of CO2 /N2 with a record high ideal adsorbed solution theory (IAST) selectivity >2000 under ambient temperature and pressure.

A label-free electrochemical aptasensor based on the core-shell Cu-MOF@TpBD hybrid nanoarchitecture for the sensitive detection of PDGF-BB.

As one of the significant serum cytokines, platelet-derived growth factor-BB (PDGF-BB) is a crucial protein biomarker overexpressed in human life-threatening tumors, the sensitive identification and quantification of which are urgently desired but challenging. Herein we report a novel core-shell nanoarchitecture consisting of Cu-based metal-organic frameworks (Cu-MOFs) and covalent organic frameworks (denoted as TpBD-COFs), which was used to prepare an aptasensor for the detection of platelet-derived growth factor-BB (PDGF-BB). The central Cu-MOFs function as signal labels with no need for extra redox media, whereas the porous TpBD serves as the shell to immobilize the PDGF-BB-targeted aptamer strands in abundance via strong interactions involving π-π stacking, electrostatic, and hydrogen bonding interactions. The proposed aptasensor based on Cu-MOF@TpBD can achieve a detection limit as low as 0.034 pg mL-1 within the dynamic detection range from 0.0001 to 60 ng mL-1. The hybridization of MOFs and COFs, together with the immobilization with the specific analyte targeted aptamer, provides a promising and propagable approach to prepare an aptasensor for the simple, sensitive, and selective detection of a specific biomarker in clinical diagnosis.