Plasmonic Au nanobipyramid assembly covalent organic framework for boosting photocatalytic hydrogen evolution through strong local electric field

BackgroundCellular biomechanics can be manipulated by strong electric fields, manifested by the field-induced membrane deformation and migration (galvanotaxis), which significantly impacts normal cellular physiology. Artificial giant vesicles that mimic the phospholipid bilayer of the cell membrane have been used to investigate the membrane biomechanics subjected to electric fields. Under a strong direct current (DC) electric field, the vesicle membrane demonstrates various patterns of deformation, which depends on the conductivity ratio between the medium and the cytoplasm. The vesicle exhibits prolate elongation along the direction of the electric field if the cytoplasm is more conductive than the medium. Conversely, the vesicle exhibits an oblate deformation if the medium is more conductive. Unlike a biological cell, artificial vesicles do not migrate in the strong DC electric field.To reconcile the kinematic difference between a cell and a vesicle under a strong DC electric field, we proposed a structure that represents a low-conductive, “shell-like” membrane. This membrane separates the extracellular medium from the cytoplasm. We computed the electric field, induced surface charge and mechanical pressure on the fixed membrane surface. We also computed the overall translational forces imposed on the structure for a vesicle and a cell.ResultsThe DC electric field generated a steady-state radial pressure due to the interaction between the local electric field and field-induced surface charges. The radial pressure switches its direction from “pulling” to “compressing” when the medium becomes more conductive than the cytoplasm. However, this switch can happen only if the membrane becomes extremely conductive under the strong electric field. The induced surface charges do not contribute to the net translational force imposed on the structure. Instead, the net translational force generated on the shell structure depends on its intrinsic charges. It is zero for the neutrally-charged, artificial vesicle membrane. In contrast, intrinsic charges in a biological cell could generate translational force for its movement in a DC electric field.ConclusionsThis work provides insights into factors that affect cellular/vesicle biomechanics inside a strong DC electric field. It provides a quantitative explanation for the distinct kinematics of a spherical cell verses a vesicle inside the field.

This Full Paper investigates a series of strongly fluorescent donor–acceptor‐substituted spirobifluorene compounds, red 2‐diphenylamino‐7‐(2,2‐dicyanovinyl)‐9,9′‐spirobifluorene (DCV), green 2‐diphenylamino‐9,9′‐spirobifluorene7‐carxoxaldehyde (CHO), and blue 2‐diphenylamino‐7‐(2,2‐diphenylvinyl)‐9,9′‐spirobifluorene (DPV), together with their spiro‐linked “dimeric” analogs, 2DCV, 2,2′‐bis(diphenylamino)‐9,9′‐spirobifluorene‐7,7′‐dicarboxaldehyde (2CHO), and 2,2′‐bis(diphenylamino)‐7,7′‐bis(2,2‐diphenylvinyl)‐9,9′‐spirobifluorene (2DPV), respectively. The emission optical density and, hence, the intensity of photoluminescence (PL) or electroluminescence (EL) of the “dimeric” analogs is presumed to increase, which is beneficial for organic light‐emitting diode (OLED) applications. The physical properties, including the dipole moments obtained from quantum chemistry calculations, emission solvatochromism, fluorescence quantum yield (Φf) as well as the EL of these six spirobifluorene compounds have been examined in detail. We found that Φf as well as OLED performance (EL efficiency and intensity) of the strongly dipolar DCV decrease significantly in the “dimeric” analog 2DCV, but less so in the moderately dipolar CHO and 2CHO, and only slightly in the weakly dipolar DPV and 2DPV. This is parallel to the intramolecular dipole moment, which is large for 2DCV, medium for 2CHO, and very small for 2DPV. Here, we show for the first time systematically that the luminescence intensity is closely correlated with the local electric field induced by the molecular dipole. A strong electric field may facilitate radiationless decay channels with a charge‐transfer nature, leading to a high quenching rate. Consistent with this conclusion, which is derived from the red DCV/2DCV and green CHO/2CHO, our new blue fluorophore DPV with an essentially zero dipole moment has successfully achieved one of the best electrofluorescent blue OLEDs. At the same time, by doping the highly dipolar DCV into an isolated environment with the low‐polarity Alq3 as the host matrix, we obtained a very high performance of saturated yellow OLEDs as well, This is possibly due to the reduction of emission‐quenching dipoles from the neighboring molecules. Our results have provided an important insight in designing luminescent materials, as follows: molecular dipole moments should be kept at a low magnitude to avoid quenching induced by a strong local electric field in the chromophore.

The results of a linear analysis for the stability of a homogeneous dielectric liquid with respect to density perturbations in a uniform electric field are presented. The electric field increases the instability increment for the stratification along the field and decreases this increment in the transverse direction. Thus, a strong electric field can induce anisotropic decay into liquid and vapor phases for a fluid that is initially both in a labile state and in a metastable or stable state. Theoretical calculations are confirmed by the results of numerical modeling of the fluid dynamics. The new regions of a low-density phase have the form of narrow cylindrical channels oriented along the field. This new mechanism of gas phase formation in strong local electric fields probably plays a key role in the inception and ultra-fast propagation of streamers during the breakdown in dielectric liquids in a nanosecond range.

Local electric field direct writing – Electron-beam lithography and mechanism

Enhanced electrocatalytic nitrogen reduction inspired by a lightning rod effect on urchin-like Co3O4 catalyst

Cadmium halides (CdCl2, CdBr2 and CdI2) crystallize in a layered structure in which a Cd2þ-ion plane is sandwiched between two halogen ion planes. The fundamental layers pile up along the crystal c-axis to make up cadmium halide crystals. When doping a small amount of metal cyanide into these cadmium halide crystals, cyanic ions are supposed to be substituted for the halogen ions. In the present work, polarized infrared (IR) absorption has been investigated on CN centers doped in CdI2 crystals. For interpretation of these IR absorption, interaction of the CN elastic dipole with the local electric field in the crystal must be taken into account: A strong local electric uniaxial crystal field along the c-axis could arrange the CN molecular axis along this axis of the crystal. On the other hand, IR absorption and luminescence on CN centers in alkali halide crystals have been studied extensively without any indication of such arrangement of the dipole centers. The crystals were grown from melt in a vacuum sealed quartz ampule filled with CdI2 powder containing impurity Hg(CN)2 of 0.1mol% as an impurity. The CN -ion would substitute for a host I -ion. The specimens were cleaved in the size of 10 10 5mm from the CdI2 crystal ingot. The concentration of Hg(CN)2 in the specimens was not determined in the present study. The values of concentration in the following are those in the melt. The crystal samples were mounted on a copper holder of a closed-cycle He refrigerator and were cooled down to 6K. The present experiments were performed at the absorption and reflection spectroscopy station on the beamline BL43IR of the synchrotron radiation facility SPring-8, Hyogo, Japan. Polarized IR absorption spectra were measured by using a FT-IR spectrometer (Bruker IFS 120HR). The spectral resolution of this spectrometer was set for 0.025 cm 1 at 2000 cm . An internal globar lamp of the FT-IR spectrometer was used as the light source. Figure 1 shows the IR absorption spectra of CdI2:Hg(CN)2 (0.1mol%) in the range of 2060–2160 cm 1 for the polarization parallel (E k c) and perpendicular (E ? c) to the c-axis. Polarized light with E k c or E ? c was led on the polished crystal surface along the direction perpendicular to the crystal c-axis (E is the electric field vector of polarized light). The interference pattern due to BaF2 windows of the cryostat appears on the background of both spectra. Dichroism between the E k c and E ? c spectra is remarkable: All absorption peaks are observed only in the polarization of E k c. As described above, the CdI2 crystal has the uniaxial crystal field in the direction along the c-axis. The dichroic absorption results show that the CN -ions in the I -ion planes are arranged with their electric dipole axes parallel to the crystal c-axis. In addition, the full width at half-maximum (0.07 cm ) of the absorption lines is much narrower than those ( 5 cm ) in alkali halides. The rotational motion of CN molecules is restrained by the local uniaxial electric field along the c-axis in the CdI2 crystal. The local uniaxial electric field at halogen ion sites comes from Cd2þ-ion planes with positive charge and I -ion planes with negative charge. The absorption peaks are classified into two groups. The one is of sharp doublet peaks (2082.1, 2084.8 cm ) in the low energy region. These peaks are attributed to CN -ions simply substituted for host I -ions, which are called Isolated-CN centers [see Figs. 2(a) and 2(a0)]. They correspond to the absorption peak due to substitutional CN ions for I -ions in alkali-iodides, e.g., the peak observed at Fig. 1. The IR absorption spectra of CdI2 doped CN measured at 6K. Upper and lower spectrum is E k c and E ? c, respectively.

The reactivity of the same molecular electrocatalyst under homogenous and heterogeneous conditions can be dramatically different, highlighting that the reaction environment plays an important role in catalysis. For catalysis on solid electrodes, reactions take place in the electric double layer (EDL) where a strong electric field is experienced. In this work, empirical valence bond molecular dynamics (EVB-MD) was used to explore CO2 binding in the EDL. It allows explicit descriptions of the solvent, electrolyte, catalyst-reactant, and the electrode surface material, as well as an unbiased description of the applied electric field. The strong local electric field concentrates cations at the interface, which in turn stabilises the bound CO2. Furthermore, controlled computational experiments suggest that neither the electric field nor the cations alone can produce significant stabilisation, but that the combination led to a dramatic stabilisation of the CO2 bound state.

Strong electric field at the sharp tips of Cu(OH)2 nanochrysanthemums for selective electrochemical CO2 conversion into ethylene

ABSTRACTThe effect of plasma-activated water (PAW) generated with a dielectric barrier discharge diffusor (DBDD) system on microbial load and organoleptic quality of cucamelons was investigated and compared to the established sanitizer, sodium hypochlorite (NaOCl). Pathogenic serotypes of Escherichia coli, Salmonella enterica, and Listeria monocytogenes were inoculated onto the surface of cucamelons (6.5 log CFU g−1) and into the wash water (6 log CFU mL−1). PAW treatment involved 2 min in situ with water activated at 1,500 Hz and 120 V and air as the feed gas; NaOCl treatment was a wash with 100 ppm total chlorine; control treatment was a wash with tap water. PAW treatment produced a 3-log CFU g−1 reduction of pathogens on the cucamelon surface without negatively impacting quality or shelf life. NaOCl treatment reduced the pathogenic bacteria on the cucamelon surface by 3 to 4 log CFU g−1; however, this treatment also reduced fruit shelf life and quality. Both systems reduced 6-log CFU mL−1 pathogens in the wash water to below detectable limits. The critical role of superoxide anion radical (·O2−) in the antimicrobial power of DBDD-PAW was demonstrated through a Tiron scavenger assay, and chemistry modeling confirmed that ·O2− generation readily occurs in DBDD-PAW generated with the employed settings. Modeling of the physical forces produced during plasma treatment showed that bacteria likely experience strong local electric fields and polarization. We hypothesize that these physical effects synergize with reactive chemical species to produce the acute antimicrobial activity seen with the in situ PAW system.IMPORTANCE Plasma-activated water (PAW) is an emerging sanitizer in the fresh food industry, where food safety must be achieved without a thermal kill step. Here, we demonstrate PAW generated in situ to be a competitive sanitizer technology, providing a significant reduction of pathogenic and spoilage microorganisms while maintaining the quality and shelf life of the produce item. Our experimental results are supported by modeling of the plasma chemistry and applied physical forces, which show that the system can generate highly reactive ·O2− and strong electric fields that combine to produce potent antimicrobial power. In situ PAW has promise in industrial applications as it requires only low power (12 W), tap water, and air. Moreover, it does not produce toxic by-products or hazardous effluent waste, making it a sustainable solution for fresh food safety.

Lattice-induced strong coupling and localized electric field enhancement in complementary diabolo metasurfaces

Effect of adsorbed polymers on electrophoresis of dispersed particles in strong electric fields

Light utilization largely governs the performance of CO2 photoconversion, whereas most of the materials that are implemented in such an application are restricted in a narrow spectral absorption range. Plasmonic metamaterials with a designable regular pattern and facile tunability are excellent candidates for maximizing light absorption to generate substantial hot electrons and thermal energy. Herein, a concept of coupling a Au-based stacked plasmonic metamaterial with single Cu atoms in alloy, as light absorber and catalytic sites, respectively, is reported for gas-phase light-driven catalytic CO2 hydrogenation. The metamaterial structure works in a broad spectral range (370-1040nm) to generate high surface temperature for photothermal catalysis, and also induces strong localized electric field in favor of transfer of hot electrons and reduced energy barrier in CO2 hydrogenation. This work unravels the significant role of a strong localized electric field in photothermal catalysis and demonstrates a scalable fabrication approach to light-driven catalysts based on plasmonic metamaterials.

The participation of high-energy hot electrons generated from the non-radiative decay of localized surface plasmons is an important mechanism for promoting catalytic processes. Herein, another vital mechanism associated with the localized surface plasmon resonance (LSPR) effect, significantly contributing to the nitrogen reduction reaction (NRR), is found. That is to say, the LSPR-induced strong localized electric fields can weaken the intermolecular hydrogen bonds and regulate the arrangement of water molecules at the solid-liquid interface. The AuCu pentacle nanoparticles with excellent light absorption ability and the capability to generate strong localized electric fields are chosen to demonstrate this effect. The in situ Raman spectra and theoretical calculations are employed to verify the mechanism at the molecular scale in a nitrogen fixation process. Meanwhile, due to the promoted electron transfer at the interface by the well-ordered interfacial water, as well as the participation of high-energy hot electrons, the optimal catalyst exhibits excellent performance with an NH3 yield of 52.09 µg h-1 cm-2 and Faradaic efficiency (FE) of 45.82% at ─0.20V versus RHE. The results are significant for understanding the LSPR effect in catalysis and provide a new approach for regulating the reaction process.

By examining the electric field induced processes in glasses and glass-metal nanocomposites (GMN) we propose mechanism of the electric field assisted dissolution (EFAD) of metal nanoparticles in glass. We show that in both glass poling and EFAD processes, the strong (up to 1 V/nm) local electric field in the subanodic region is due to the presence of “slow” hydrogen ions bonded to nonbridging oxygen atoms in glass matrix. However, the origin of these hydrogen ions in glass and GMN is different. Specifically, when we apply the electric field to a virgin glass, the enrichment of the glass with hydrogen species takes place in the course of the poling. In GMN, the hydrogen ions have been incorporated into the glass matrix during metal nanoparticles formation via reduction in a metal by hydrogen, i.e., before the electric field was applied. The EFAD of metal nanoparticles resembles the electric field stimulated diffusion of metal film in glass (the important difference however is that in GMN, there is no direct contact of dissolving metal entity with anodic electrode). This similarity makes it possible to estimate the energy of thermal activated transition of silver atoms from a nanoparticle to glass matrix as ∼1.3 eV. Electroneutrality of the GMN requires emission of electrons from nanoparticles. Photoconductivity spectra of soda-lime glasses and the results of numerical calculations of band structure of fused silica, sodium disilicate and sodium-calcium-silicate glass enable us to evaluate the bandgap and the position of electron mobility edge in soda-lime glass. The evaluated values are ∼6 eV and ∼1.2 eV below vacuum level, respectively. The bent of the glass band structure in strong electric field permits a direct tunneling of Fermi electrons from silver nanoparticle (4.6 eV below the vacuum level) to the glass conductivity band. Evaluated in accordance with the Fowler–Nordheim equation the magnitude of electric field necessary to establish comparable electron emission and ion ejection rates is ∼0.27 V/nm, although other phenomena including polarization of the nanoparticles and tunneling of electrons thermally distributed above Fermi level, decreases this magnitude. We believe that the different mechanisms of ejection for electrons and ions should result in charging nanoparticles in EFAD process. The electron tunneling to localized OH− states and glass matrix relaxation process are also discussed.

Space charge accumulation in the polypropylene will accelerate the aging of the material and lead to the degradation of its insulation performance. In the work, space charge distribution, current conduction characteristics, thermally stimulated depolarization current (TSDC) and surface potential decay (SPD) characteristics of polypropylene (PP) under strong electric field are measured and analyzed, and the bulk trap and surface trap parameters are extracted. Further, the charge transport model of PP is established to study the charge dynamic transport physical processes and characteristics under strong electric field. The experimental results show that the charge accumulation amount in PP under the action of negative polarity electric field is higher than that of positive polarity electric field, about one order of magnitude. and the corresponding trap energy levels are 0.84 eV and 0.81 eV, which both belong to deep traps. There are two obvious charge density peaks on the PP surface, which are 2.60 × 1020·eV−1·m−3 and 3.66 × 1020·eV−1·m−3, respectively, and the corresponding surface trap energy levels are 0.86 eV and 0.97 eV. The simulation results show that with the extension of the applied voltage time, the injected charges by the electrode gradually migrate to the bulk of the material and eventually the positive and negative charges are offset at the middle position. The local electric field caused by the accumulation of interfacial charges will weaken the original electric field, while the local electric field caused by the accumulation of the bulk charges will strengthen the original electric field, resulting in the distortion of the internal electric field.