Dipole Polarization Effects Research Articles

Surface-iodine-grafting-induced local electric field drives charge separation of CdBiO2Br for excellent photocatalytic antibiotic degradation

Photocatalytic technology has demonstrated immense potential in environmental purification, particularly in the degradation of antibiotics that pose serious health risks. However, the rapid recombination of photogenerated charge carriers and the limited light absorption capacity, which are major obstacles, severely hinder the photocatalytic degradation activity. Herein, the surface halogen-grafting strategy is introduced to address these issues in a Sillén-related layer-structured photocatalyst, CdBiO2Br (CBOB). The iodine-grafted CBOB nanosheets deliver a superb tetracycline hydrochloride photodegradation efficiency of 72.36 % within one hour, which is 2.44 times higher than that of the original CBOB. Additionally, they demonstrated a broad-spectrum degradation capability against various antibiotics and phenolic pollutants, such as ciprofloxacin, chloramphenicol hydrochloride, bisphenol A, highlighting their practical and industrial value. Mechanistic studies indicated that the high electronegativity of iodine could induce a surface dipole polarization effect to form localized electric fields that efficiently drive the separation of photogenerated electrons and holes, and, on the other hand, improve light absorption, which profoundly boosts the photocatalytic degradation process, as corroborated by experimental and theoretical results collectively. This work provides a foundation for understanding the highly electronegative halogen grafting-induced surface local electric field and offers new insights for the future design of high-performance environmental purification materials.

Proton conductivity and dielectric studies on chitosan/polyvinyl alcohol blend electrolytes: Synergistic improvements with ionic liquid and graphene oxide

This study investigates the impact of ionic liquid, 1-methylimidazolium tetrafluoroborate (IL) and graphene oxide (GO) on the performance of chitosan/polyvinyl alcohol (CS/PVA)-based composite electrolytes. Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) confirm the successful incorporation of IL and GO, affecting the structural and morphological properties of the electrolytes. Thermogravimetric analysis (TGA) reveals enhanced thermal stability in GO-doped samples, with increased residual weight at high temperatures, while IL addition leads to higher initial weight loss due to its hygroscopic nature. Ionic conductivity measurements demonstrate that the CS/PVA/IL-GO(4.0) composite achieves the highest proton conductivity of 1.76 × 10−3 S/m at 300 K and 1 MHz, surpassing other samples and aligning with top values reported in literature. Dielectric studies show a significant increase in dielectric constant to 9.55 × 104 at 300 K and 20 Hz for CS/PVA/IL-GO(4.0), attributed to enhanced dipole alignment and polarization effects. The loss tangent analysis indicates the shortest relaxation time of 2.07 × 10−4 s for CS/PVA/IL-GO(4.0), correlating with its superior proton conductivity. These findings highlight the potential of CS/PVA/IL-GO electrolytes for advanced energy storage and conversion applications, suggesting further research into GO dispersion and long-term stability for optimized performance in practical devices.

Construction of spherical heterogeneous interface on ZnFe2O4@C composite nanofibers for highly efficient microwave absorption

Enriching the electromagnetic wave loss mechanism and improving the impedance matching are the keys to improve the electromagnetic wave absorption performance of carbon fibers. In this study, beaded ZnFe2O4@C absorbing composite fibers (ZFCF) with synergistic effects of magnetic loss and dielectric loss was prepared by electrospinning and heat treatment. ZnFe2O4 magnetic particles effectively improve the impedance matching and increase the loss mechanism of carbon nanofibers. The optimal ZFCF composite has excellent absorption performance, with a minimum reflection loss of −53.6 dB at 2.64 mm and the widest effective absorption bandwidth of 4.32 GHz. The excellent absorption performance is attributed to significant magnetic losses from eddy currents and magnetic resonance generated by ZnFe2O4, and strong interfacial polarization from the numerous heterogeneous interfaces. Additionally, the one-dimensional carbon nanofibers create a conductive network and structural defects that enhance conductive loss and dipole polarization effects. Moreover, the RCS of ZFCF composite was significantly reduced by −32.85 dBm2. The combination of simulation technology and material design is of great significance for the study of electromagnetic wave absorption mechanism and the rational design of electromagnetic wave absorbing coatings.

Asymmetric aggregation enables red-light CO2 reduction with tunable activity and selectivity by intermolecular electronic coupling

Photocatalytic CO2 reduction to value-added chemicals is a promising way to simultaneously mitigate environmental and energy issues. Integrating low-energy red light harvesting, fast charge separation, and robust CO2 activation in a photosystem is a crucial prerequisite for highly efficient CO2 photoreduction but remains a huge challenge. Herein, we constructed an aggregated [Ru(2, 2'-bipyridine)3]Cl2 (denoted as Ru(bpy)3Cl2) photosystem. Various characterizations combining molecular dynamic simulations and theoretical calculations confirm that the electronic coupling between adjacent Ru(bpy)3Cl2 molecules can induce orbital hybridization, thus broadening the light absorption edge to the red light region. Meanwhile, the asymmetric aggregation of Ru(bpy)3Cl2 enables exciton dissociation and charge transfer through a dipole polarization effect. Significantly, this dipole polarization can also upshift the d-orbital of Ni catalytic centers, greatly strengthening the activation of CO2 and lowering the formation energy barrier of COOH* intermediates. Consequently, the apparent quantum yield (AQY) of aggregates for CO2-to-CO reduction reaches 4.2% at 610 nm, significantly higher than the AQYs of other reported photosystems at wavelengths ≥ 600 nm. More importantly, the catalytic efficiency and selectivity of CO2 reduction can be rationally tuned by controlling the aggregated degrees of Ru(bpy)3Cl2. This work highlights the key role of Ru(bpy)3Cl2 aggregation in prompting red-light harvesting and CO2 activation, which may help boost CO2 photoreduction efficiency from a fresh perspective.

Construction of the N, S co-doped C/FeS2 materials for low thickness and high-efficiency microwave absorption

Research into electromagnetic wave-absorbing materials is essential to tackle the growing impact of electromagnetic wave pollution on human health and social advancement. Therefore, a method for synthesizing N,S co-doped C/FeS2 porous carbon composite absorbers (N,S@APCs) with low thickness, low filler content, and high performance is reported. The porous carbon structures were prepared by a high-temperature-hydrothermal two-step method using directly liquefied coal pitch as the carbon source. The successful doping of diatomic N and S at optimal concentrations enhances their impedance matching capacity. At the same time, forming FeS2 through the reaction between S and Fe3+ in the raw material efficiently improves the dielectric loss effect and enhances interfacial and dipole polarization effects. These factors together contribute to the strong absorption performance and low matching thickness of the fabricated N, S@APCs. At a thickness of 1.5 mm, 10 wt% of absorber filling resulted in a strong absorption performance with RLmin=-51.05 dB. Meanwhile, at a thickness of 1.7 mm, an effective absorption bandwidth of 4.76 GHz was achieved. This research offers a novel viewpoint on investigating porous carbon absorbers at low thicknesses. It serves as a reference for later investigations into polyatomic co-doped porous carbon absorbers.

Regulating N-doping strategies to construct 3D interconnected abundant porous N-doped carbon for polarization loss-enhanced microwave absorbers: Theory, design, and experiments

The widespread proliferation of modern portable electronic devices has necessitated the development of functional materials with high-efficiency microwave absorption properties. In this study, we utilized biomass-derived jujube shells as a carbon source and employed a nitrogen-doping process to modify carbon materials, resulting in the fabrication of outstanding microwave-absorbing biomass-based nitrogen-doped porous carbon. Additionally, we discussed the influence of different nitrogen sources on material structure and microwave absorption performance. These N-doped porous carbon materials exhibited excellent specific surface areas, particularly Org-N, which facilitated the formation of conductive networks and the multi-stage reflection and scattering of microwave. Moreover, N-doping created numerous defect sites and heterogeneous structures, improving impedance matching, thus promoting dipole polarization and interface polarization effects, which accelerated electron migration and interlayer hopping, contributing to the attenuation of microwave energy. The lowest reflection loss for Org-N, Inorg-N, and Mixed-N reached −27.3 dB, −40.9 dB, and −45.6 dB, respectively. Mixed-N exhibited optimal microwave absorption performance at 9.9 GHz with d = 2.4 mm and achieved an effective absorption bandwidth (EAB10) of 3.0 GHz (11.0 GHz–14.0 GHz) at d = 2.0 mm. Additionally, the enhancement of polarization relaxation effects was elucidated by examining the charge density distribution in molecular models featuring various N-doping forms. Consequently, biomass-derived N-doped porous carbon materials emerge as lightweight and highly efficient functional materials for microwave absorption purposes.

Synergetic dielectric and magnetic losses of melamine sponge-loaded puffed-rice biomass carbon and Ni3ZnC0.7 for optimal effective microwave absorption

Multi-dimensional design and the combination of multiple phases can effectively enhance the dielectric loss properties and multiple reflection effects of absorbers. Herein, a novel multi-dimensional microporous nanostructured composite, melamine sponge (MS) loaded puffed-rice biomass carbon (C) together with bimetallic carbide material Ni3ZnC0.7 (Ni3ZnC0.7-MS/C) was synthesized by simple vacuum filtration and hydrothermal calcination. The result indicates that small Ni3ZnC0.7 particles with little Ni doping uniformly decorated on the surfaces of the three-dimensional (3D) melamine sponge and puffed rice carbons. The Ni3ZnC0.7-MS/C composite mixed with paraffin (weight ratio of 1:2) exhibited the best electromagnetic wave (EMW) absorption performance, and the minimum reflection loss (RLmin) value of the Ni3ZnC0.7-MS/C composite reaches −107.7 dB with a matching thickness of 2.78 mm and the maximum effective absorption bandwidth for RL below −10 dB (EABmax) is adjusted to 9.2 GHz at a matching thickness of 4.0 mm. The dipole polarization effect of the N doping and the different interfaces provided by the 3D structure of the MS carbon enhance the conduction loss and interface polarization, while the positive effects of eddy current and resonance caused by Ni3ZnC0.7 effectively improve the microwave absorption performances. This melamine sponge–loaded bimetallic carbon composite exhibited a magnetic/dielectric loss combination, resulting in a high-performance absorber with lightweight, cost-effective and efficient properties.

Preparation and performance of self-cleaning photothermal-induced self-healing flexible sensors

Flexible conductive materials for wearable applications have seen remarkable advancements in recent years. However, a significant challenge that must be addressed is their susceptibility to accidental mechanical damage. In this study, a self-healing superhydrophobic flexible fabric sensor by incorporating fluorinated polyurethane with fluorinated side chains and graphene modified with Fe3O4 nanoparticles. The fabric composite coating exhibited excellent hydrophobicity and self-cleaning ability, allowing easy removal of dirt and dust by rainwater or other liquids. Due to its excellent conductivity and stretch recovery properties, the composite coating can be applied as a wearable fabric sensor. The sensor demonstrates remarkable sensitivity to strain and can be used to monitor the movements of fingers, wrists, elbows, and other joints. Most importantly, the damaged fabric coating could restore surface integrity, repair conductivity, and maintain superhydrophobicity, which is attributed to the dynamic reversible nature of disulfide bonds and the induced dipole polarization effect of fluorinated side chains. Moreover, the fabric sensor exhibits stable photothermal conversion performance based on the joint effect of graphene and Fe3O4. This property provides a foundation for light-induced self-healing. The combination of a fluorine-modified self-healing polyurethane, Fe3O4 nanoparticles-modified graphene (FFNs-iaG), and an elastic fabric creates a self-healing superhydrophobic conductive fabric coating. This coating has excellent properties for various applications, enhancing the longevity and reliability of the fabric sensor. The combination of these materials greatly improves the performance of the fabric composite coating, resulting in a versatile fabric sensor with unique characteristics suitable for a wide range of applications.

Field dipole interaction and polarization effects in light-sheet optical fluorescence microscopy

Polarization plays a crucial role in understanding the interaction of fluorescent molecules in a light field. We report the study on the effect of a field–dipole interaction under polarization light-sheet fluorescence microscopy using the vectorial theory of light. The molecule is suitably modeled as a radiating electric dipole in a polarized electric field (both linear and random), and the system point spread function (PSF) is determined for different orientations of the dipole (both fixed and random). PSF analysis and contour plots suggest distinct nature of a field distribution in each case, indicating the importance of a field–dipole interaction for high-quality fluorescence imaging. The analysis suggests that the field spreads gradually along the polarization axis at a high numerical aperture (NA) of the objective lens, whereas it is more isotropic and homogeneous at low NA. Moreover, fast changes are not observed at low NA (i.e., far from the central lobe in the field contour plots), suggesting the absence of high-frequency components. However, sidelobes are prominent for linear polarized (along x) light. On the other hand, rapid variations are evident for randomly polarized light, depicting the presence of high spatial frequencies in the system optical transfer function. The other significant observation is the distinct frequency spectrum (both kx and ky) for random and fixed dipoles, indicating the significance of dipole orientation in a light-sheet field. Compared to the point-illumination-based fluorescence microscopy, sheet based polarization technique provides a high signal-to-noise ratio, a uniform field, an order large field of view, and critical information (related to the micro-environment of a dipole and its short-range interactions). The study is expected to facilitate polarization-sensitive investigation of large biological specimens (both fixed and live).

N-plasma modulation for boosting electromagnetic wave absorption behavior of MoO3 ceramic based on non-metallic doping

Rational design and fabrication of MoO3 ceramic with controllable electronic structure is expected to deliver favorable magnetic moments, leading to excellent electromagnetic behavior. However, achieving large-scale precise modulation of the MoO3 electronic structure is still a challenge. Here, a low-temperature, high-efficiency nitrogen radio frequency (RF) plasma treatment method was adopted to modify the surface of MoO3 with N doping and investigate its electromagnetic wave absorption (EMA) mechanism in depth. After MoO3 powder treating with N2 plasma for 30 s, at the doping ratio is 70%, the minimum reflection loss (RLmin) is –43.35 dB and the maximum effective absorption bandwidth (EAB) could reach 6.16 GHz at a low thickness (2.1 mm). The significant improvements in dielectric loss and permeability loss of N-doped MoO3 are because the doping of N atoms reduces the bandgap of MoO3, promotes electron jumping, dramatically improves electrical conductivity of semiconductors, and introduces interfacial polarization and dipole polarization effects. The presence of magnetic moments renders the N-doped MoO3 with weak magnetic properties and significant eddy current losses. This study provides an explicit EMA mechanism for non-metal doped transition metal oxidation.

Resonances close to the first ionization threshold of selenium

Relativistic multichannel theory has been used to calculate the even-parity Rydberg states and odd-parity autoionizing (AI) Rydberg spectrum converging to the limit of second and third excited core states of selenium (Se), taking into account the ionic core dipole polarization effect caused by the Rydberg electron. Six even-parity Rydberg series and are calculated, along with AI Rydberg states converging to or in or symmetry. In general, there is less than a 0.05 difference between calculated and experimental quantum defects. The influence of the perturbers on quantum defects and peak profiles has all been investigated. The accuracy of our calculations allows us to provide a reliable the assignment of the measured AI Rydberg states and the accompanying total angular momentum.

Old molybdenum blue for new application: {Mo 72X 30}/PANI/MWCNTs (X = Fe, V) ternary coaxial cable-like fibers for superior electromagnetic wave absorption

The systematic design of heterointerfaces has been a topic of considerable attention in electromagnetic absorption applications. For the first time, molybdenum blue/polyaniline/multiwalled carbon nanotubes ({Mo₇₂X₃₀}/PANI/MWCNTs, X = Fe, V) ternary coaxial cable-like fibers are systematically designed and synthesized via host–guest electrostatic and synergistic effect and employed as exceptional electromagnetic wave absorbers. The coaxial cable-like structure features an abundance of heterointerfaces between layers, which improves dipole polarization and interface polarization effect, and regulates conductive loss. In addition, the inclusion of polyoxometalates boosts magnetic losses dominated by eddy current losses and improves impedance matching. The optimal {Mo₇₂V₃₀}/PANI/MWCNTs exhibit higher electromagnetic wave absorption (−48.12 dB) at a thinner thickness (2.3 mm). At a thickness of 2.5 mm, {Mo₇₂Fe₃₀}/PANI/MWCNTs exhibit the maximum effective absorption bandwidth (6.16 GHz). In addition to expanding our understanding of the effect of heterointerfaces on electromagnetic absorption, this study demonstrates the potential utilization of polyoxometalate functional molecules in the electromagnetic wave absorption field.

Ultra-large dynamic range synaptic indium gallium zinc oxide transistors

Three-terminal neuromorphic transistors have garnered considerable attention owing to their superior learning and recognition capabilities in neural computing. For efficient and rapid computing of parallel arithmetic and unstructured large-sized data, a high-synaptic channel conductance (G) (i.e., synaptic weight) and large dynamic range (DR) (i.e., weight update) are necessary. In this study, we successfully fabricated high-performance and all-solution-processed synaptic transistors by employing a thiol–ene photoclick chemistry-based, cross-linked vinyl addition polynorbornene copolymer dielectric layer, poly(norbornene-co-5-vinyl-2-norbornene) (P(NB/VNB)) and sol-gel-derived indium gallium zinc oxide (IGZO) semiconducting channel layer. The molecular behaviors of free hydroxyl group in the dielectric layer formed via ultraviolet photo-induced thiol–ene click reactions of the polar cross-linker pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) allows slow dipole polarization effects on the IGZO channel layer. An exhaustive and systemic investigation of the surface physicochemical and electrical properties confirmed that the mutual interface coupling between the cross-linked P(NB/VNB) dielectric and IGZO semiconductor exhibited remarkable synaptic functionality with a high G (∼540 μS), large DR (∼6213), and long-term operational stability following excitation with 104 successive pulses that resulted in neural recognition accuracy of 87.11% based on the use of MNIST database set which is close to ideal value of 88%. This high-performance synaptic transistor based on all-solution-derived functional organic–inorganic hybrid stack layers can serve as a basis for the successful implementation of novel neuromorphic computing systems that satisfy the requirements for strong neuronal signal transmission and distinguishable multi-level data states.

Three-dimensional reduction graphene oxide (rGO) supported ScFeO3 for enhancing microwave absorption properties

Magnetic-dielectric composites with multiple dissipation mediums are extensively applied in microwave absorption fields. However, it still remains bottleneck problem to combine magnetic and dielectric components in a rational way to achieve significant microwave absorption performance. In this study, rGO/ScFeO 3 composites were synthesized by freeze-drying and heat treatment methods. The ScFeO 3 particles decorated the rGO sheet notably improves microwave absorption performance, owing to the suitable impedance matching and abundant dissipation capabilities induced by the effective complementarities between ScFeO 3 particles and carbon sheet. These results show that the electromagnetic parameters and microwave absorption properties of rGO/ScFeO 3 composites are controlled by ScFeO 3 content. In particular, the prepared rGO/ScFeO 3 composites (content of 2%wt) exhibit the minimum reflection loss (RL min ) of −19 dB. The effective absorption bandwidth (EAB) is 4.2 GHz at thickness ranging from 3.05 to 3.55 mm. The microwave dissipation abilities probably benefit from multiple reflections and scattering, interface and dipole polarization and natural resonance effect. Therefore, the composites prepared by embedding ScFeO 3 particles into rGO can improve the microwave absorption performance. More importantly, the microwave absorption mechanism of the composites is explored and analyzed, which provides a reliable reference for the construction of magnetic dielectric composites. • The rGO/ScFeO 3 composites were synthesized by freeze-drying and heat treatment methods. • The rGO/ScFeO 3 composites possessed the magnetic-dielectric property withRL min of −19 dB. • The microwave dissipation abilities benefited from dielectric and magnetic losses.

Elastic scattering and boron, lithium, and α -particle production in the Be9 + V51 reaction

Background: Experimental and theoretical investigation of breakup coupling effects due to different cluster structures ($^{8}\mathrm{Be}+n$ and $^{5}\mathrm{He}+\ensuremath{\alpha}$), relative importance of neutron or $^{5}\mathrm{He}/\ensuremath{\alpha}$ transfer, and their contribution to $\ensuremath{\alpha}$ production are important to understand reaction mechanism in a weakly bound projectile ($^{9}\mathrm{Be}$) near the Coulomb barrier.Purpose: Breakup coupling effect on elastic scattering and measurement of angular distributions and energy spectra of $\ensuremath{\alpha}$ particles produced through breakup, transfer, and complete fusion processes to disentangle their relative contributions and to investigate the relative importance of breakup followed by fusion (breakup-fusion) are compared to transfer.Methods: Elastic scattering, inclusive $\ensuremath{\alpha}$ production, lithium, and boron production cross sections have been measured for the $^{9}\mathrm{Be}+^{51}\mathrm{V}$ system above Coulomb barrier energies. Continuum-discretized-coupled-channels (CDCC) breakup coupling effect using $^{8}\mathrm{Be}+n$ and $^{5}\mathrm{He}+\ensuremath{\alpha}$ cluster configurations have been investigated. Coupled reaction channels (CRC) calculations for $1\mathit{p}, 1\mathit{d}$, and $1\mathit{n}$ stripping and $1\mathit{p}, 1\mathit{d}$ pickup leading to $^{8}\mathrm{Li}+^{52}\mathrm{Cr}, ^{7}\mathrm{Li}+^{53}\mathrm{Cr}, ^{8}\mathrm{Be}+^{52}\mathrm{V}$, and $^{10}\mathrm{B}+^{50}\mathrm{Ti}, ^{11}\mathrm{B}+^{49}\mathrm{Ti}$, respectively, were performed and compared with the experimental data. Theoretical calculations for the estimation of various reaction channels contributing to $\ensuremath{\alpha}$ production have been performed with CDCC and CRC methods using the fresco code.Results: Global optical model parameters for the $^{9}\mathrm{Be}$ projectile describe the elastic scattering data very well and the optical model fit improves the ${\ensuremath{\chi}}^{2}$ slightly. CRC calculations show a major contribution in the production of lithium through $1\mathit{p}, 1\mathit{d}$ stripping and boron through $1\mathit{p}, 1\mathit{d}$ pickup reactions. $\ensuremath{\alpha}$ production angular and energy distributions are obtained, and direct $\ensuremath{\alpha}$ production is described with contributions from noncapture breakup, breakup-fusion, and transfer reactions.Conclusions: Breakup coupling for $^{5}\mathrm{He}+\ensuremath{\alpha}$ and $^{8}\mathrm{Be}+n$ cluster structures shows a repulsive and attractive coupling effect on elastic scattering, respectively. The $^{8}\mathrm{Be}+n$ cluster structure also shows a dipole polarization effect by suppressing the Coulomb rainbow compared to the $^{5}\mathrm{He}+\ensuremath{\alpha}$ cluster structure. Kinematic analysis of the $\ensuremath{\alpha}$ particles energy spectra suggest that $\ensuremath{\alpha}$ production is dominated by breakup-fusion over cluster transfer. CRC calculations suggest that $1\mathit{p}, 1\mathit{d}$ stripping and pickup reactions are a major contributor to lithium and boron production cross sections.

A comprehensive theoretical study of positron binding and annihilation properties of hydrogen bonded binary molecular clusters.

We studied the positron binding and annihilation of hydrogen bonded binary molecular clusters containing small inorganic molecules such as water, hydrogen fluoride, ammonia, hydrogen sulfide, hydrogen chloride, and phosphine, using first-principles calculation. While unimolecular systems of these species mostly exhibit no or very small positron binding energies (positron affinities), we found that all of their hydrogen bonding clusters have greater positive positron affinities. The permanent dipole moment enhanced by the formation of the intermolecular hydrogen bond acts as a dominant parameter to bind a positron for a given proton donor, whereas it is insufficient for reproducing the dependence of the positron affinity on substitutions of the proton donor. By multiple regression analyses with inherent properties of the clusters, we found a reasonable model with additional effective parameters represented by, particularly, the number of hydrogen atoms free from the hydrogen bond. By density analyses for the single-particle and electron-positron collision probabilities, we revealed that these effective parameters are associated with the electronic structure changes induced by the hydrogen bond and positron binding, which have important roles to enhance the electron-positron contact densities due to the proton-screening effect.

Resonances close to the first ionization threshold of antimony

Even-parity Rydberg and autoionizing Rydberg spectrum of antimony have been calculated by relativistic multichannel theory, in which the ionic core dipole polarization effect due to the Rydberg electron has been included. Combining reanalysis of the experimental spectra via different intermediate states, and some perturbers below the first ionization threshold which are corresponding to the lower-lying members of Rydberg series converging to higher thresholds are found and identified as well as these reported perturbers. Some Rydberg states are reclassified and all observed autoionizing resonances are identified. Moreover, the reason why linewidths of autoionizing peaks span one orders of magnitude is because two closely spaced autoionizing states result in the apparent isolated broad peak while autoionizing resonances associated with orbitals have narrow linewidths.

Nanostructured Lateral Boryl Substitution Conjugated Donor-Acceptor Oligomers for Visible-Light-Driven Hydrogen Production.

Poor charge separation is the main factor that limits the photocatalytic hydrogen generation efficiency of organic conjugated polymers. In this work, a series of linear donor-acceptor (D-A) type oligomers are synthesized by a palladium-catalyzed Sonogashira-Hagihara coupling of electron-deficient diborane unit and different dihalide substitution sulfur functionalized monomers. Such diborane-based A unit exerts great impact on the resulting oligomers, including distinct semiconductor characters with isolated lowest unoccupied molecular orbital (LUMO) orbits locating in diborane-containing fragment, and elevated LUMO level higher than water reduction potential. Relative to A-A type counterpart, the enhanced dipole polarization effect in D-A oligomers facilitates separation of photogenerated charge carriers, as evidenced by notably prolonged electron lifetime. Owing to π-π stacking of rigid backbone, the oligomers can aggregate into an interesting 2D semicrystalline nanosheet (≈2.74nm), which is rarely reported in linear polymeric photocatalysts prepared by similar carbon-carbon coupling reaction. Despite low surface area (30.3 m2 g-1 ), such ultrathin nanosheet D-A oligomer offers outstanding visible light (λ> 420nm) hydrogen evolution rate of 833 µmol g-1 h-1 , 14 times greater than its A-A analogue (61 µmol g-1 h-1 ). The study highlights the great potential of using boron element to construct D-A type oligomers for efficient photocatalytic hydrogen generation.

Used dye adsorbent derived N-doped magnetic carbon foam with enhanced electromagnetic wave absorption performance

The increasing excess electromagnetic wave (EMW) radiations induce a serious pollution problem. The social requests urgently for EMW absorbing materials. Herein, as-prepared magnetic carbon foam (MCF) adsorbed RhB from the dye pollutant solutions. The used adsorbent was heat-treated at high temperature. Then, magnetic particle-decorated N-doped carbon foams (N-MCFs) were fabricated. N-doping content is determined by mass ratio of adsorbed RhB vs MCF. Excellent EMW absorption performance is achieved by optimizing impedance matching of N-MCFs. N-MCF-2 with a loading rate of 15% exhibits a lowest RLmin value of −60.46 dB with a Tm value as thin as only 1.70 mm. The corresponding effective bandwidth is 14.29 GHz and 13.79 GHz for −10 dB and −20 dB, covering the whole C band, X band and Ku band. For the absorbers with higher conductivities, the corresponding EMW absorption capacity can be further improved by reducing the loading rate. The distorted skeletons caused by N-doping induce the graphite lattice distortion and local density change of the carbon atomic state, significantly contributing to the magnetic moment. The enhanced dielectric loss by both defect polarization and dipole polarization effects, as well as the activated complex permeability by α-Fe/Fe3C/Fe2O3 composites decoration, are beneficial to EMW absorption.

Microwave absorption and infrared stealth performance of reduced graphene oxide-wrapped Al flake

A novel Al@reduced graphene oxide (Al@RGO) composite was designed and synthesized by a one-step hydrothermal method. We investigated the effect of the graphene on the microwave absorbing properties and infrared emissivity of composites. The crystal structure, microscopic morphology, infrared emissivity and electromagnetic parameters of the prepared samples were characterized by XRD, FESEM, TEM, XPS, dual band infrared emissometer and vector network analyzer. TEM and SEM show that the thin Al sheet is uniformly wrapped by RGO with a crumpled surface. Functionalized RGO and surface cation-modified Al sheets are tightly compounded through an electrostatic interaction. The oxygen content and defect from RGO as polarization center endows the material with enhanced molecular polarization and dipole polarization effect. The Al sheet is well coated with RGO, enhancing interface polarization and impedance matching. The minimum reflection loss (RL) of optimized Al@RGO composites is − 46.11 dB at 13.68 GHz under the coating thickness of only 2 mm. The bandwidth below − 10 dB can reach 4.88 GHz (11.52–16.4 GHz). Al sheet is a suitable base material for both microwave absorption and infrared stealth. The Al@RGO composites exhibit excellent infrared stealth ability, and their lowest infrared emissivity is 0.62. Thus, Al@RGO composites show potential application for both electromagnetic wave absorption and infrared stealth.