FCF-LDH/BiVO4 with synergistic effect of physical enrichment and chemical adsorption for efficient reduction of nitrate. - In: Green energy & environment, ISSN 2468-0257, Bd. 9 (2024), 7, S. 1112-1121
Photoelectrochemical NO3− reduction (PEC NITRR) not only provides a promising solution for promoting the global nitrogen cycle, but also converts NO3− to the important chemicals (NH3). However, it is still a great challenge to prepare catalysts with excellent NO3− adsorption/activation capacity to achieve high NITRR. Herein, we designed a novel Fe2+Cu2+Fe3+LDH/BiVO4 (FCF-LDH/BVO) catalyst with synergistic effect of chemical adsorption and physical enrichment. Fe2+ in FCF-LDH/BVO provides the rich Lewis acid sites for the adsorption of NO3−, and the appropriate layer spacing of FCF-LDH further promotes the physical enrichment of NO3− in its interior, thus realizing the effective contact between NO3− and active sites (Fe2+). FCF-LDH/BVO showed excellent NH3 production performance (FENH3 = 66.1%, rNH3 = 13.8 μg h−1 cm−2) and selectivity (FENO2- = 2.5%, rNO2- = 4.9 μg h−1 cm−2) in 0.5 mol L−1 Na2SO4 electrolyte. In addition, FCF-LDH/BVO maintains the desirable PEC stability for six cycle experiments, showing great potential for practical application. The 14NO3− and 15NO3− isotope test provides strong evidence for further verification of the origin of N in the generated NH3. This LDH catalyst has a great potential in PEC removal of NO3− from groundwater.
https://doi.org/10.1016/j.gee.2023.05.011
Effect of orbital symmetry on probing the single-molecule Kondo effect. - In: Physical review, ISSN 2469-9969, Bd. 109 (2024), 24, L241401, S. L241401-1-L241401-6
The low-energy excitation spectrum of a metal-free phthalocyanine molecule on Ag(111) is probed in scanning tunneling spectroscopy experiments. The use of functionalized p-orbital and s-orbital tips leads to markedly different results. While CO-terminated p-wave tips probe the zero-energy Abrikosov-Suhl resonance induced by the molecular Kondo effect, Ag-coated s-wave tips - in strong contrast - feign the absence of the Kondo effect due to a missing Abrikosov-Suhl resonance. Reducing the vertical distance between the s-orbital tip and the molecule progressively unveils the resonance, compatible with findings for the p-orbital tip in the far tunneling range. A mechanism based on orbital overlap is suggested as the tentative origin of the observations. The CO-functionalized tip is then used to explore the altered Kondo effect of the tautomerized phthalocyanine.
https://doi.org/10.1103/PhysRevB.109.L241401
Investigation of Tl-doped silicon by low-temperature photoluminescence during light-induced degradation treatments. - In: Physica status solidi, ISSN 1862-6319, Bd. n/a (2024), n/a, 2400287, S. 1-6
Scientific progress is made in understanding photoluminescence (PL) lines in thallium-doped silicon. Two PL lines called A and P, which appear after quenching, are found to exhibit irreversible as well as reversible behavior under the application of light-induced degradation (LID) treatments. The reversible behavior is similar to changes of a P line in indium-doped silicon due to LID treatments, which have led to the identification of this P line to be caused by an InSi-Sii-defect. By exploiting the metastability of defects from the ASi-Sii category, the experimental findings of this study indicate that the underlying defect for the A and P line in thallium-doped silicon is the TlSi-Sii-defect.
https://doi.org/10.1002/pssa.202400287
Graphitic carbons: preparation, characterization, and application on K-ion batteries. - In: Rare metals, ISSN 1867-7185, Bd. 0 (2024), 0, insges. 20 S.
K-ion batteries (KIBs) have drawn much attention due to the abundant potassium reserves and wide accessibility as well as high energy density, which can be designed for large-scale energy storage systems. As the most promising anode materials for KIBs, graphitic carbons, especially those with an intermediate structure between the crystalline graphite and amorphous carbons become a hot research focus because of the improved rate capability and enhanced diffusion-controlled capacity at low voltage regions. Herein, we first review the structures of graphitic carbons in the view of graphitic domains and the structure changes in their K-ion intercalation compounds. Then, we summarize the preparation mechanisms and characterizations of graphitic carbons and the influence factors in their degree of graphitization. Furtherly, we illustrate the strategies to optimize their K-ion storage properties from four aspects, namely graphitic domain design, microstructure engineering, electrochemical active component regulation, and defect engineering. Finally, we propose the issues that urgently need to be solved in graphitic carbons and the possible solutions. We hope that this view could offer some inspiration for the further designing and optimizing of graphitic carbons for practical KIBs.
https://doi.org/10.1007/s12598-024-02764-z
Impact of single-melamine tautomerization on the excitation of molecular vibrations in inelastic electron tunneling spectroscopy. - In: Nano letters, ISSN 1530-6992, Bd. 24 (2024), 24, S. 7195-7201
Vibrational quanta of melamine and its tautomer are analyzed at the single-molecule level on Cu(100) with inelastic electron tunneling spectroscopy. The on-surface tautomerization gives rise to markedly different low-energy vibrational spectra of the isomers, as evidenced by a shift in mode energies and a variation in inelastic cross sections. Spatially resolved spectroscopy reveals the maximum signal strength on an orbital nodal plane, excluding resonant inelastic tunneling as the mechanism underlying the quantum excitations. Decreasing the probe-molecule separation down to the formation of a chemical bond between the melamine amino group and the Cu apex atom of the tip leads to a quenched vibrational spectrum with different excitation energies. Density functional and electron transport calculations reproduce the experimental findings and show that the shift in the quantum energies applies to internal molecular bending modes. The simulations moreover suggest that the bond formation represents an efficient manner of tautomerizing the molecule.
https://doi.org/10.1021/acs.nanolett.4c00904
NMR relaxation dispersion of liquids adsorbed on modified surfaces of SBA-15 mesoporous silica. - In: The journal of physical chemistry, ISSN 1932-7455, Bd. 128 (2024), 21, S. 8785-8796
The NMR relaxation dispersion of 1H and 2H nuclei in water and alkanes was studied in mesoporous SBA-15 silica in its native state and with modified internal surfaces. By comparison with silica gel of comparable characteristic pore size, a qualitative agreement of the relaxation dispersion was found. In the absence of detectable amounts of paramagnetic centers, intramolecular relaxation is approximated by the model of Reorientations Mediated by Translational Displacements (RMTD), which assumes rigid molecules diffusing along curved surfaces and experiencing long-term memory of their relative orientation due to their polarity. For all liquids, significant relaxation dispersion is found so that the vanishing polarity of alkanes does not allow the assumption of a negligible surface interaction. The difference in dispersion shape between 1H and 2H nuclei, relaxing by dipolar and quadrupolar mechanisms, respectively, allows the reconstruction of the intermolecular contribution to relaxation, which has not yet been studied systematically in porous media. A model based on the relative contributions of intra- and intermolecular interactions as well as hydrogen exchange with OH- and NH2-groups is presented.
https://doi.org/10.1021/acs.jpcc.4c00645
Unveiling the nature of atomic defects in graphene on a metal surface. - In: Beilstein journal of nanotechnology, ISSN 2190-4286, Bd. 15 (2024), S. 416-425
Low-energy argon ion bombardment of graphene on Ir(111) induces atomic-scale defects at the surface. Using a scanning tunneling microscope, the two smallest defects appear as a depression without discernible interior structure suggesting the presence of vacancy sites in the graphene lattice. With an atomic force microscope, however, only one kind can be identified as a vacancy defect with four missing carbon atoms, while the other kind reveals an intact graphene sheet. Spatially resolved spectroscopy of the differential conductance and the measurement of total-force variations as a function of the lateral and vertical probe–defect distance corroborate the different character of the defects. The tendency of the vacancy defect to form a chemical bond with the microscope probe is reflected by the strongest attraction at the vacancy center as well as by hysteresis effects in force traces recorded for tip approach to and retraction from the Pauli repulsion range of vertical distances.
https://doi.org/10.3762/bjnano.15.37
Chip-integrated non-mechanical microfluidic pump driven by electrowetting on dielectrics. - In: Lab on a chip, ISSN 1473-0189, Bd. 24 (2024), 11, S. 2893-2905
A microfluidic pump is presented that generates its pumping action via the EWOD (electrowetting-on-dielectric) effect. The flow is generated by the periodic movement of liquid-vapor interfaces in a large number (≈10^6) of microcavities resulting in a volume change of approx. 0.5 pl per cavity per pump stroke. The total flow resulting from all microcavities adds up to a few hundred nanolitres per cycle. Passive, topologically optimized, non-mechanical Tesla valves are used to rectify the flow. As a result, the micropump operates without any moving components. The dimensioning, fabrication, and characterization process of the micropump are described. Device fabrication is done using conventional manufacturing processes from microsystems technology, enabling cost-effective mass production on wafer-level without additional assembly steps like piezo chip-level bonding, etc. This allows for direct integration into wafer-based microfluidic or lab-on-a-chip applications. Furthermore, first measurement results obtained with prototypes of the micropump are presented. The voltage- and frequency-dependent pump performance is determined. The measurements show that a continuous flow rate larger than 0.2 ml min^−1 can be achieved at a maximum pump pressure larger than 12 mbar.
https://doi.org/10.1039/D4LC00178H
Yu-Shiba-Rusinov states induced by single Fe atoms on reconstructed compound superconductor V3Si. - In: Surface science, ISSN 1879-2758, Bd. 746 (2024), 122504, S. 1-10
Reconstructed surfaces of the A15-compound superconductor V3Si(100) that are possibly induced by the segregation of bulk impurities serve as platforms to study the dependence of Yu-Shiba-Rusinov states induced by a single Fe atom on the adsorption site. Their number, energy and electron-hole asymmetry vary strongly with the atomic environment of the Fe atom. These variations are indicative of different Fe d-orbitals being active in the site-dependent exchange coupling with the substrate Cooper pairs. Spatially resolved spectroscopy gives rise to a short decay length of the Yu-Shiba-Rusinov states and thereby suggests the three-dimensional character of the scattering process underlying the bound states.
https://doi.org/10.1016/j.susc.2024.122504
Exploring crystal-phase molecular dynamics of the low-viscous mesogen 6CHBT: a combined FFC and high-field NMR relaxometry investigation. - In: The journal of physical chemistry, ISSN 1520-5207, Bd. 128 (2024), 16, S. 3997-4007
The molecular dynamics study of thermotropic mesogens exhibiting the crystal phases is valuable in unraveling the complex global (collective) and local (noncollective) motions executed by liquid crystal molecules, which would further advance the existing knowledge on orientationally disordered crystalline (ODIC) phases. Toward the fulfillment of such a task, a combined nuclear magnetic resonance (NMR) relaxometry approach employing the fast field cycling (FFC) NMR (10 kHz-30 MHz) and high-field pulsed NMR (400 MHz) techniques is utilized to sample the broad frequency range offered by molecular motions in the crystal phase of 4-(trans-4′-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The validity of the observed relaxation data is tested and interpreted by the Bloembergen-Purcell-Pound (BPP) model involving the superposition of four mutually independent Lorentzian spectral densities, reflecting molecular dynamical processes on different time scales. The salient feature of the detailed analysis reveals that the lengthening of temporal dynamics in the crystal phase due to molecular rotations by jumps, which are of intermolecular origin, is evident and further supports the presence of collective-like local dynamics. The analysis does permit decoupling of the molecular reorientations about their short axes (∼100 ns) as well as long axes (∼50 ns) and methyl group rotations (∼0.5 ns) on distinct time scales. The activation energies for reorientations about the short axes and methyl group rotations are found to be 27.3 ± 2.7 and 15.8 ± 1.1 kJ/mol, respectively. The fast methyl rotations in the crystal phase of 6CHBT obtained from FFC NMR are further well complemented by high-field NMR, where 1H NMR line shapes are relatively narrow when compared to those of the nematic phase.
https://doi.org/10.1021/acs.jpcb.3c08259