Changes In Charge Distribution Research Articles

Photo-induced tunable luminescence from an aggregated amphiphilic ethylene-pyrene derivative in aqueous media

An amphiphilic derivative with a large Stokes shift by introducing flexible hydrophilic long chains into a rigid ethylene-pyrene compound have been successfully synthesized. The alkylated compound exhibited a notable change in charge distribution, facilitating cation-π interactions. Through the process of amphiphilic self-assembly, the formation of highly ordered aggregates enabled effective photo-dimerization under 449 nm LED irradiation. Notably, this photo-responsive technology not only exhibited advanced multi-color emission effects, including white light emission but also exhibited environmentally friendly behavior in the aqueous phase.

An impedance flow cytometry with integrated dual microneedle for electrical properties characterization of single cell

Electrical characteristics of living cells have been proven to reveal important details about their internal structure, charge distribution and composition changes in the cell membrane, as well as the extracellular context. An impedance flow cytometry is a common approach to determine the electrical properties of a cell, having the advantage of label-free and high throughput. However, the current techniques are complex and costly for the fabrication process. For that reason, we introduce an integrated dual microneedle-microchannel for single-cell detection and electrical properties extraction. The dual microneedles utilized a commercially available tungsten needle coated with parylene. When a single cell flows through the parallel-facing electrode configuration of the dual microneedle, the electrical impedance at multiple frequencies is measured. The impedance measurement demonstrated the differential of normal red blood cells (RBCs) with three different sizes of microbeads at low and high frequencies, 100 kHz and 2 MHz, respectively. An electrical equivalent circuit model (ECM) was used to determine the unique membrane capacitance of individual cells. The proposed technique demonstrated that the specific membrane capacitance of an RBC is 9.42 mF/m−2, with the regression coefficients, at 0.9895. As a result, this device may potentially be used in developing countries for low-cost single-cell screening and detection.

Research on detection technology of sulfur hexafluoride decomposition products of GIL based on carbon nanotubes

Sulfur hexafluoride (SF6) gas is a stable gas that is widely used in gas insulated lines (GILs) in power systems. However, in GIL, SF6 gas is in the environment of high temperature, high pressure and high voltage for a long time, SF6 gas will decompose into toxic gas, damage electrical equipment, and pose a huge threat to human body and ecological environment. In addition, SF6 gas is a greenhouse gas that is strictly forbidden to leak. Once leaked, it will cause great harm to the environment. Therefore, it is necessary to recover and purify the SF6 gas in the power system GIL. In this paper, a molecular model of carbon nanotubes is constructed, and the density functional theory is used to analyze the changes of charge distribution, density of states and molecular orbitals after adsorption of SF6 decomposition products by carbon nanotubes, and determine the gas-sensing response of carbon nanotubes to gas molecules characteristic.

In Situ Visualization of the Pinning Effect of Planar Defects on Li Ion Insertion.

Longevity of Li ion batteries strongly depends on the interaction of transporting Li ions in electrode crystals with defects. However, detailed interactions between the Li ion flux and structural defects in the host crystal remain obscure due to the transient nature of such interactions. Here, by in situ transmission electron microscopy and density function theory calculations, we reveal how the diffusion pathways and transport kinetics of a Li ion can be affected by planar defects in a tungsten trioxide lattice. We uncover that changes in charge distribution and lattice spacing along the planar defects disrupt the continuity of ion conduction channels and dramatically increase the energy barrier of Li diffusion, thus, arresting Li ions at the defect sites and twisting the lithiation front. The atomic-scale understanding holds critical implications for rational interface design in solid-state batteries and solid oxide fuel cells.

Not So Innocent After All: Interfacial Chemistry Determines Charge-Transport Efficiency in Single-Molecule Junctions.

Most studies in molecular electronics focus on altering the molecular wire backbone to tune the electrical properties of the whole junction. However, it is often overlooked that the chemical structure of the groups anchoring the molecule to the metallic electrodes influences the electronic structure of the whole system and, therefore, its conductance. We synthesised electron-accepting dithienophosphole oxide derivatives and fabricated their single-molecule junctions. We found that the anchor group has a dramatic effect on charge-transport efficiency: in our case, electron-deficient 4-pyridyl contacts suppress conductance, while electron-rich 4-thioanisole termini promote efficient transport. Our calculations show that this is due to minute changes in charge distribution, probed at the electrode interface. Our findings provide a framework for efficient molecular junction design, especially valuable for compounds with strong electron withdrawing/donating backbones.

Not So Innocent After All: Interfacial Chemistry Determines Charge‐Transport Efficiency in Single‐Molecule Junctions

AbstractMost studies in molecular electronics focus on altering the molecular wire backbone to tune the electrical properties of the whole junction. However, it is often overlooked that the chemical structure of the groups anchoring the molecule to the metallic electrodes influences the electronic structure of the whole system and, therefore, its conductance. We synthesised electron‐accepting dithienophosphole oxide derivatives and fabricated their single‐molecule junctions. We found that the anchor group has a dramatic effect on charge‐transport efficiency: in our case, electron‐deficient 4‐pyridyl contacts suppress conductance, while electron‐rich 4‐thioanisole termini promote efficient transport. Our calculations show that this is due to minute changes in charge distribution, probed at the electrode interface. Our findings provide a framework for efficient molecular junction design, especially valuable for compounds with strong electron withdrawing/donating backbones.

Symmetry Analysis of Zero-Field Antiferroquadrupole Order in CeB6: Extremely Low-Frequency 11B-NQR Study

The zero-field state in the antiferroquadrupole (AFQ) ordered phase of CeB6 has been investigated by a 11B-nuclear quadrupole resonance (NQR) measurement that is sensitive to changes in local charge distribution. In order to achieve this experiment, we have improved our low-frequency NQR techniques, so that the 11B-NQR spectrum has been successfully observed at an NQR frequency νQ ∼ 560 kHz, exceptionally low frequency among direct NQR measurements on strongly correlated electron systems. The temperature dependence of the NQR spectrum reveals that νQ rapidly decreases just below AFQ ordering temperature TQ = 3.3 K, while the spectral shape does not show any sign of site splitting below TQ. The latter is incompatible with the theoretical prediction based on the Oxy-type AFQ order, suggesting that the ordered state in the zero-field region differs from that in the nonzero-field region. Some new possible interpretations to explain the obtained results are proposed.

Investigation of salinity and ion effects on low salinity water flooding efficiency in a tight sandstone reservoir

Low salinity water flooding (LSW) has been proven to be a low-cost and accessible enhanced oil recovery method in conventional reservoirs. However, its applications and potentials in tight reservoirs are mysterious in tight sandstone reservoirs due to the low porosity and low permeability.A series of laboratory experiments were designed to investigate ionic composition and salinity on the performance of LSW in a tight oil formation. More specifically, zeta potential and contact angle were measured to examine rock surface charge distribution and wettability changes. Pressure-controlled mercury injection (PMI) and permeability tests were conducted to analyze the pore & throat and permeability changes during LSW injection. Thereafter, displacement experiments were implemented to analyze oil recovery under different LSW injection schemes.The experimental observation demonstrates that LSW injection expands the double electric layer on the oil/brine and rock/brine interfaces, resulting in the expected wettability modification. However, the presence of divalent ions in the LSW undermines this effect. On the other hand, the permeability reduction resulting from salinity decrease can be alleviated by introducing divalent ions into LSW. The coreflooding experiments reveal that continuous injection of monovalent brine would reduce the ultimate oil recovery. Alternatively, a mixture of monovalent and divalent ions in LSW is utilized to revive the permeability and maintain the wettability modification. Furthermore, an optimized lower divalent ion concentration is found to be conducive to refining the cutoff throat radius and achieving a higher oil recovery from tight oil reservoirs.

"Electron Complementation"-Induced Molybdenum Nitride/Co-Anchored Graphitic Carbon Nitride Porous Nanoparticles for Efficient Overall Water Splitting.

Maximizing the usable space of electrocatalysts and fine-tuning the interface geometry as well as the electronic structure to facilitate hydrogen and oxygen evolution reactions (HER and OER) have always been the focus of research. Herein, a homogeneous porous nanoparticle construction strategy was proposed, in which molybdenum nitride (Mo2N) particles were prepared by controlled heat treatment of the precursor nanoparticle induced by polyethylene glycol, and the Mo2N/Co-C3N4 heterostructure with a pore size of about 1.13 nm was obtained by compounding Co-anchored graphitic carbon nitride. In particular, exploring the change of charge distribution at the interface based on the principle of "electron complementation" shows that under the regulation of nitrogen with high electronegativity, the affinity of active site Co to oxygenated species in the OER process and the adsorption as well as cleavage ability of HER reactants in the active site were effectively optimized. Thus, Mo2N/Co-C3N4 not only inherits the functions of each component, but also provides an ideal heterogeneous interface for exhibiting impressive bifunctional activity, which only needs 100 and 210 mV to deliver 10 mA cm-2 for the HER and OER, respectively. In addition, the Mo2N/Co-C3N4 catalyst also demonstrates high overall water splitting stability with a slight current decrease after 95 h. Manipulating the electronic structure of multiple sites by constructing electronically complementary interfaces may provide another avenue to develop highly active catalysts for overall water splitting and other applications.

Hydroxide Chemoselectivity Changes with Water Microsolvation.

Solvent molecules are known to affect chemical reactions, especially if they interact with one or more of the reactants or catalysts. In ion microsolvation, i.e., solvent molecules in the first solvation sphere, strong electronic interactions are created, leading to significant changes in charge distribution and consequently on their nucleophilicity/electrophilicity and acidity/basicity. Despite a long history of research in the field, fundamental issues regarding the effects of ion microsolvation are still open, especially in the condensed phase. Using reactions between hydroxide and relatively stable quaternary ammonium salts as an example, we show that water microsolvation can change hydroxide's chemoselectivity by differently affecting its basicity and nucleophilicity. In this example, the hydroxide reactivity as a nucleophile is less affected by water microsolvation than its reactivity as a base. These disparities are discussed by calculating and comparing oxidation potentials and polarizabilities of the different water-hydroxide clusters.

Effects of a far-infrared photon cavity field on the magnetization of a square quantum dot array

The orbital and spin magnetization of a cavity-embedded quantum dot array defined in a GaAs heterostructure are calculated within quantum-electrodynamical density-functional theory. To this end, a gradient-based exchange-correlation functional recently employed for atomic systems is adapted to the hosting two-dimensional electron gas submitted to an external perpendicular homogeneous magnetic field. Numerical results reveal the polarizing effects of the cavity photon field on the electron charge distribution and nontrivial changes of the orbital magnetization. We discuss its intertwined dependence on the electron number in each dot, and on the electron-photon coupling strength. In particular, the calculated dispersion of the photon-dressed electron states around the Fermi energy as a function of the electron-photon coupling strength indicates the formation of magnetoplasmon-polaritons in the dots.

High-throughput screening of dual-atom doped PC6 electrocatalysts for efficient CO2 electrochemical reduction to CH4 by breaking scaling relations

The catalytic activity of the CO2 electrochemical reduction reaction (CO2RR), which is regarded as one of the most promising approach to tackle the current excess carbon emissions problem, is significantly restricted by the scaling relationship between adsorption energy of reaction intermediates. Here, inspired by the concept of multiple active centers, we designed 36 dual-atom catalysts in PC6 monolayer, including 8 homonuclear (M2@PC6, M=Cr, Mn, Fe, Co, Ni, Cu, Pd, and Ag) and 28 heteronuclear (M1M2@PC6) catalysts, to obtain efficient CO2RR catalysts by breaking the inherent limitation of linear scaling relations. After several rounds of screening for catalysts with stability, activity, selectivity through density functional theory (DFT) study, Mn2@PC6 was identified as a promising candidate for deep reduction of CO2 to CH4 with a low limiting potential of -0.31V (vs RHE). The projected density of states analysis demonstrates that the candidates break the linear scaling relationship stemming from the apparent mixing of the O-2p states and metal-3d states. The apparent change of spin polarization and asymmetric charge distribution on the active site of Mn2@PC6 play a crucial role in its superior CO2RR catalytic performance. This work provides a potential strategy from the theoretical perspective for rational design of efficient electrocatalyst by introduction of dual active centers to break the scaling relationship of intermediates.

Bio‐Imaging quorum sensing signal molecules in a soil‐mimic gel

Rhizosphere, the narrow region surrounding plant roots directly influenced by root exudates and the root associated microbiome, plays an important role in plant productivity and the rhizosphere is well known for stimulating microbial metabolic activities. How microbial communities interact to form stable, metabolically interconnected functional communities is an area of intense interest. The question remains on how microbially produced secreted molecules that function as intercellular communication signals shape the structure and function of microbial communities. Our goal is to detect and quantify signal molecules produced by microbes or plants in the root‐soil environment, spatially and temporarily. As a proof‐of‐concept, we are imaging diffusible extracellular microbial metabolites involved in a bacteria‐bacteria communication process called quorum‐sensing. Quorum‐sensing relies on the accumulation of high concentrations of signal molecules in the environment to control bacterial gene expression, influencing rhizosphere colonization and plant health. Local concentration of quorum sensing molecules are determined using aptamer based sensors. Aptamers that can specifically bind the desired signal molecules are selected through SELEX and immobilized on the surface of nano‐porous membranes. Binding of the signal molecules and aptamer covered surface results in changes in surface charge distribution and steric hinderance and thus modifying the transmembrane ionic transport. Changes in transmembrane impedance can be measured through electrochemical impedance spectroscopy methods to monitor local concentrations of signal molecules. Sensor responses were determined for different concentrations of signal molecules and results showed detection of C4‐HSL in a soil‐mimic solution with KD of 10 nM. We demonstrate that the quorum‐sensing signal molecule C4‐homoserine lactone and (C4‐HSL) can rapidly diffuse in a soil‐mimic gel, providing evidence for our use of a soil‐mimic for further aptasensor development and validation. The sensors were then inserted into soil mimic gel for monitoring C4‐HSL diffusion and the resulted impedance changes were used to determine the C4‐HSL concentration at different positions in the gel. Measurements of local C4‐HSL concentrations variation and numerical solution of diffusion equation were used to create 4D images of C4‐HSL molecule diffusion in the soil‐mimic gel.

The peculiarities of charge distribution and spatiotemporal changes in electronic and atomic structure of bone tissue

X-ray diffraction and inner-shell photoemission studies of rat cortical bone were performed.

Designing asymmetrically modified nanochannel sensors using virtual EIS

Monitoring electrochemical impedance changes across an asymmetrically functionalized nanochannel array provides an attractive mechanism for chemical and biological sensors. Specific binding of the receptor molecules with their analyte leads to changes in charge distribution on the nanochannel surfaces modifying the ionic transport across them. The magnitude of impedance change due to receptor/ligand binding or sensor sensitivity depends on a large number of parameters and consequently, identification of parameters that result in sensitive and specific sensing performance is extremely tedious and cost-intensive. We rely on a ’virtual EIS’ procedure that models the transient ionic current due to a step-change in voltage to determine the frequency-dependent impedance of an asymmetrically functionalized nanochannel. This procedure is used to predict the impedance changes due to the specific binding of thrombin on nanochannel surfaces. Surface charge changes associated with the binding of thrombin protein on the aptamer coated surface result in a decrease of the membrane impedance and computational results suggest that a reduction in the ionic strength of the electrolyte leads to an increase in the magnitude of binding induced impedance reduction. Sensing experiments with thrombin binding aptamer are performed to evaluate the trends from the high-throughput computations. The agreement between model predictions and experimental observations suggests that the present modeling approach may be utilized to computationally evaluate sensor performance for a range of parameters and rapidly identify sensor configurations that enable point-of-care diagnostic devices with improved sensitivities.

Non-Arrhenian Temperature-Dependent Viscosity of Alkali(ne) Carbonate Melts at Mantle Pressures

The viscosity of carbonate melts is a fundamental parameter to constrain their migration and ascent rates through the mantle and ultimately, their role as carbon conveyors within the deep carbon cycle. Yet, data on the viscosity of carbonate melts have remained scarce due to experimental limitations and the lack of appropriate theoretical descriptions for molten carbonates. Here, we report the viscosity of K2Mg(CO3)2 and K2Ca(CO3)2 melts up to 13 GPa and 2,000 K by means of classical molecular dynamics (MD) simulations using optimized force fields and provide first evidence for non-Arrhenian temperature-dependent viscosity of molten carbonates at mantle pressures. The viscosity of K2Mg(CO3)2 and K2Ca(CO3)2 melts ranges respectively between 0.0056–0.0875 Pa s and 0.0046–0.0650 Pa s in the investigated pressure-temperature interval. Alkali(ne) carbonate melts, i.e. mixed alkali and alkaline earth carbonate melts -K2Mg(CO3)2 and K2Ca(CO3)2− display higher viscosity than alkaline earth carbonate melts -CaCO3 and MgCO3− at similar conditions, possibly reflecting the change in charge distribution upon addition of potassium. The non-Arrhenian temperature-dependence of the viscosity is accurately described by the Vogel-Fulcher-Tammann model with activation energies Ea for viscous flow that decrease with temperature at all investigated pressures, e.g. from ∼100 kJ/mol to ∼30 kJ/mol between 1,300 and 2,000 K at 3 GPa. Pressure is found to have a much more moderate effect on the viscosity of alkali(ne) carbonate melts, with activation volumes Va that decrease from 4.5 to 1.9 cm3/mol between 1,300 and 2,000 K. The non-Arrhenian temperature-viscosity relationship reported here could be exhibited by other carbonate melt compositions as observed for a broad range of silicate melt compositions and it should be thus considered when modeling the mobility of carbonate melts in the upper mantle.

Permanent Dipole Moments Enhance Electronic Coupling and Singlet Fission in Pentacene.

Singlet fission (SF), the photophysical process in which one singlet exciton is transformed into two triplets, depends inter alia on the coupling of electronic states. Here, we use fluorination and the resulting changes in partial charge distribution across the chromophore backbone as a particularly powerful tool to control this parameter in pentacene. We find that the introduction of a permanent dipole moment leads to an enhanced coupling of Frenkel exciton and charge transfer states and to an increased SF rate which we probed using ultrafast transient absorption spectroscopy. These findings are contrasted with H-aggregate formation and a significantly reduced triplet-pair state lifetime in a fluorinated pentacene for which the different partial charge distribution leads to a negligible dipole moment.

Influence of surfactants in improving degradation of polluting dyes photocatalyzed by TiO2 in aqueous dispersion

The role of tetraalkylammonium bromide surfactants on the TiO2 photocatalyzed degradation of Alizarin, Purpurin and Bromothymol Blue has been studied in air-equilibrated aqueous medium under UV light irradiation. Alizarin has also been investigated by carrying out the photodegradation in TiO2/surfactant dispersions irradiated by natural solar light. Absorption spectral analysis showed that the photodegradation efficiency of the dyes was significantly enhanced by the addition of the cationic surfactants. The effect of pre-micellar, micellar and post-micellar concentrations of the surfactants was analyzed to gain insight into the mechanism of the surfactant-assisted TiO2-photocatalytic degradation of the three dyes. The findings revealed that various parameters, such as initial pH, dye pK’s, type of water and light source exerted their influence on the photocatalytic degradation. The results were explained on the basis of hydrophobic and electrostatic interactions between dye and surfactant/TiO2 in the various forms of aggregation. Density functional theory (DFT) calculations of charge distribution and Gibbs free energy changes of solvation of the species involved were used as a support in rationalizing the surfactant effect on the photodegradation process.

Density functional theory study on the enhanced adsorption mechanism of gaseous pollutants on Al-doped Ti2CO2 monolayer

Inorganic toxic gases (ITGs) and volatile organic compounds (VOCs) are two kinds of typical hazardous gaseous pollutants harming human health. The removal of them is still an enormous challenge. Based on density functional theory (DFT) calculations in this work, Al-doped Ti2CO2 (ATCO), a single-atom-decorated MXene, is expected to be a more effective adsorbent for these gases than pristine Ti2CO2 (TCO) due to the outstanding adsorption capacity and superb electrical properties. We then shed light on the mechanism of enhanced adsorption by ATCO. The results of Mulliken charge analysis, partial density of states (PDOS) and deformation charge density (DCD) confirm the change of charge distribution on ATCO surface after the decoration of Al atom. Obviously, Al atom can act as a bridge to promote the formation of chemical bonds between the adsorbed gases and ATCO substrate. This work not only provides a promising material for the adsorption of gaseous pollutants, but also explores a new avenue for designing and fabricating MXene-based non-noble metal materials in the area of gas adsorbents.

Determining Excited-State Structures and Photophysical Properties in Phenylphosphine Rhenium(I) Diimine Biscarbonyl Complexes Using Time-Resolved Infrared and X-ray Absorption Spectroscopies.

We have explored the structural factors on the photophysical properties in two rhenium(I) diimine complexes in acetonitrile solution, cis,trans-[Re(dmb)(CO)2(PPh2Et)2]+ (Et(2,2)) and cis,trans-[Re(dmb)(CO)2(PPh3)2]+ ((3,3)) (dmb = 4,4'-dimethyl-2,2'-bipyridine, Ph = phenyl, Et = ethyl) using the combination method of time-resolved infrared spectroscopy, time-resolved extended X-ray absorption fine structure, and quantum chemical calculations. The difference between these complexes is the number of phenyl groups in the phosphine ligand, and this only indirectly affects the central Re(I). Despite this minor difference, the complexes exhibit large differences in emission wavelength and excited-state lifetime. Upon photoexcitation, the bond length of Re-P and angle of P-Re-P are significantly changed in both complexes, while the phenyl groups are largely rotated by ∼20° only in (3,3). In contrast, there is little change in charge distribution on the phenyl groups when Re to dmb charge transfer occurs upon photoexcitation. We concluded that the instability from steric effects of phenyl groups and diimine leads to a smaller Stokes shift of the lowest excited triplet state (T1) in (3,3). The large structural change between the ground and excited states causes the longer lifetime of T1 in (3,3).