Surface charge accumulation on the spacers is one of the key issues restraining the development of HVDC GIS/GIL. The precise measurement of surface charge properties provides the basis for further ...study of the surface charge transport mechanism as well as the charge-induced flashover mechanism under DC voltage. In this study, the authors discuss their perspective on the current status, development needs and potential developing orientation of surface charge characterisation techniques. Different surface potential measurement methods and charge inversion algorithms are reviewed regarding the previous studies and future research needs. Drawbacks and outlooks of surface charge measurement techniques are also discussed with the background of laboratory experiment results and on-site measurements. It is hopefully that this study can serve as a useful guide reference for researchers within the same research field. More importantly, it is authors’ hope that this study can inspire some novel ideas for readers into developing of more accurate and scientific interface charge characterisation techniques.
As an important property of porous membranes, the surface charge property determines many ionic behaviors of nanopores, such as ionic conductance and selectivity. Based on the dependence of electric ...double layers on bulk concentrations, ionic conductance through nanopores at high and low concentrations is governed by the bulk conductance and surface charge density, respectively. Here, through the investigation of ionic conductance inside track‐etched single polyethylene terephthalate (PET) nanopores under various concentrations, the surface charge density of PET membranes is extracted as ∼−0.021 C/m2 at pH 10 over measurements with 40 PET nanopores. Simulations show that surface roughness can cause underestimation in surface charge density due to the inhibited electroosmotic flow. Then, the averaged pore size and porosity of track‐etched multipore PET membranes are characterized by the developed ionic conductance method. Through coupled theoretical predictions in ionic conductance under high and low concentrations, the averaged pore size and porosity of porous membranes can be obtained simultaneously. Our method provides a simple and precise way to characterize the pore size and porosity of multipore membranes, especially for those with sub‐100 nm pores and low porosities.
High, stable, and modulatable ionic conductivity is important for many nanofluidic applications of layered two-dimensional (2D) membranes. In this study, we demonstrate a proton and ionic ...conductivity of the Ti
C
T
membrane that is orders of magnitude higher than that of bulk solution at low concentrations. Importantly, the membrane is highly stable in aqueous solution without any modification, due to the strong and attractive interlayer van der Waals interaction and weak electrostatic repulsive interaction. Furthermore, by exploiting the intrinsic photothermal property of MXene, we demonstrate that the ionic conductivity can be reversely, rapidly, and completely switched on or off with laser light. This study should prove MXene membrane as a suitable platform to study and utilize nanofluidic ion transport. It should also inspire future studies to manipulate the mass transport through 2D membranes using their inherent physicochemical properties.
Semiconductor‐based photocatalysis as a productive technology furnishes a prospective solution to environmental and renewable energy issues, but its efficiency greatly relies on the effective bulk ...and surface separation of photoexcited charge carriers. Exploitation of atomic‐level strategies allows in‐depth understanding on the related mechanisms and enables bottom‐up precise design of photocatalysts, significantly enhancing photocatalytic activity. Herein, the advances on atomic‐level charge separation strategies toward developing robust photocatalysts are highlighted, elucidating the fundamentals of charge separation and transfer processes and advanced probing techniques. The atomic‐level bulk charge separation strategies, embodied by regulation of charge movement pathway and migration dynamic, boil down to shortening the charge diffusion distance to the atomic‐scale, establishing atomic‐level charge transfer channels, and enhancing the charge separation driving force. Meanwhile, regulating the in‐plane surface structure and spatial surface structure are summarized as atomic‐level surface charge separation strategies. Moreover, collaborative strategies for simultaneous manipulation of bulk and surface photocharges are also introduced. Finally, the existing challenges and future prospects for fabrication of state‐of‐the‐art photocatalysts are discussed on the basis of a thorough comprehension of atomic‐level charge separation strategies.
Semiconductor photocatalytic efficiency greatly relies on effective charge separation. The recent progress of atomic‐level strategies for promoting charge separation and migration in the bulk, on the surface, and both bulk and surface of a photocatalyst are highlighted and a guideline for the bottom‐up design of high‐performance photocatalysts suggested.
The physiochemical properties of nanoparticles (NPs), including surface charge, will affect their uptake, transformation, translocation, and final fate in the environment. In this study, we compared ...the phytoxoxicity and transport behaviors of nano CeO
(nCeO
) functionalized with positively charged (Cs-nCeO
) and negatively charged (PAA-nCeO
) coatings. Cucumber seedlings were hydroponically exposed to 0-1000 mg/L of Cs-nCeO
and PAA-nCeO
for 14 days and the contents, distribution, translocation, and transformation of Ce in plants were analyzed using inductively coupled plasma mass spectrometry, micro X-ray fluorescence (μ-XRF), and X-ray absorption near-edge spectroscopy (XANES), respectively. Results showed that the seedling growth and Ce contents in plant tissues were functions of exposure concentrations and surface charge. Cs-nCeO
was adsorbed strongly on a negatively charged root surface, which led to significantly higher Ce contents in the roots and lower translocation factors of Ce from the roots to shoots in Cs-nCeO
group than in PAA-nCeO
group. The results of μ-XRF showed that Ce elements were mainly accumulated at the root tips and lateral roots, as well as in the veins and at the edge of leaves. XANES results revealed that the proportion of Ce(III) was comparable in the plant tissues of the two groups. We speculated that Cs-nCeO
and PAA-nCeO
were partially dissolved under the effect of root exudates, releasing Ce
ions as a result. Then, the Ce
ions were transported upward in the form of Ce(III) complexes along the vascular bundles and eventually accumulated in the veins. The other portion of Cs-nCeO
and PAA-nCeO
entered the roots through the gap of a Casparian strip at root tips/lateral roots and was transported upward as intact NPs and finally accumulated at the edge of the blade. This study will greatly advance our information on how the properties of NPs influence their phytotoxicity, uptake, and subsequent trophic transfer in terrestrial food webs.
Nanoparticles (NPs) are commonly defined as particles with size <100 nm and are currently of considerable technological and academic interest, since they are often the starting materials for ...nanotechnology. Novel properties develop as a bulk material is reduced to nanodimensions and is reflected in new chemistry, physics and biology. With reduction in size, a greater function of the atoms is at the surface, and promote different interaction with its environment, as compared to the bulk material. In addition, the reduction in size alters the electronic structure of the material, resulting in novel quantum effects. Size also influences mobility, primarily controlled by Brownian motion for NPs, and relevant in biological and environmental processes. However, the small size also leads to high surface energy, and NPs tend to aggregate, thereby lowering the surface energy. In all applications, the uncontrolled aggregation of NPs can have negative effects and needs to be avoided. There are however examples of controlled aggregation of NPs which give rise to novel effects. This review article is focused on the NP features that influences aggregation. Common strategies for synthesis of NPs from the gas and liquid phases are discussed with emphasis on aggregation during and after synthesis. The theory involving Van der Waals attractive force and electrical repulsive force as the controlling features of the stability of NPs is discussed, followed by examples of how repulsive and attractive forces can be manipulated experimentally to control NP aggregation. In some applications, NPs prepared by liquid methods need to be isolated for further applications. The process of solvent removal introduces new forces such as capillary forces that promote aggregation, in many cases, irreversibly. Strategies for controlling aggregation upon drying are discussed. There are also many methods for redispersing aggregated NPs, which involve mechanical forces, as well as manipulating capillary forces and surface characteristics. We conclude this review with a discussion of aggregation relevant real-world applications of NPs. This review should be relevant for scientists and technologists interested in NPs, since emphasis has been on the practical aspects of NP-based technology, and especially, strategies relevant to controlling NP aggregation.
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•Aggregation of nanoparticles influences their technological application.•Gas phase and liquid phase synthesis have different effects on aggregation.•Difficult to control aggregation during the drying process•Many strategies for nanoparticle dispersion are available.•Examples of nanoparticle use in the real world demonstrate the relevance of aggregation.
Solvents are widely used in chemical processes. The use of efficient model‐based solvent selection techniques is an option worth considering for rapid identification of candidates with better ...economic, environment and human health properties. In this paper, an optimization‐based MLAC‐CAMD framework is established for solvent design, where a novel machine learning‐based atom contribution method is developed to predict molecular surface charge density profiles (σ‐profiles). In this method, weighted atom‐centered symmetry functions are associated with atomic σ‐profiles using a high‐dimensional neural network model, successfully leading to a higher prediction accuracy in molecular σ‐profiles and better isomer identifications compared with group contribution methods. The new method is integrated with the computer‐aided molecular design technique by formulating and solving a mixed‐integer nonlinear programming model, where model complexities are managed with a decomposition‐based strategy. Finally, two case studies involving crystallization and reaction are presented to highlight the wide applicability and effectiveness of the MLAC‐CAMD framework.
Carbon‐based cathodes for aqueous zinc ion hybrid supercapacitors (ZHSCs) typically undergo low Zn ion storage capability due to their electric double layer capacitance (EDLC) energy storage ...mechanism that is restricted by specific surface area and thickness of electric double layer (EDL). Here, we report a universal surface charge modulation strategy to effectively enhance the capacitance of carbon materials by decreasing the thickness of EDL. Amino groups with lone pair electrons were chosen to increase the surface charge density and enhanced the interaction between carbon electrode and Zn ions, thus effectively compacting the EDL. Consequently, amino functionalized porous carbon based ZHSCs can deliver an ultrahigh capacity of 255.2 mAh g−1 along with excellent cycling stability (95.5 % capacity retention after 50 000 cycles) in 1 M ZnCl2 electrolyte. This study demonstrates the feasibility of EDL modified carbon as Zn2+ storage cathode and great prospect for constructing high performance ZHSCs.
The electrical double layer (EDL) of carbon electrode can be compacted via surface charge modulation strategy to boost Zn ion storage capability. Zn//amino functionalized carbon Zn ion hybrid supercapacitor can deliver an ultrahigh capacity of 255.2 mAh g−1 as well as excellent cycling stability.
In an HVDC gas-insulated system, the surface of the insulator accumulates electric charges that distort the surface electric field and reduce the flashover voltage. Therefore, it is crucial to find a ...material that can effectively suppress the surface charge accumulation. In this work, MXene, a two-dimensional nanomaterial, is doped into an epoxy resin at different concentrations. By doping a small amount of MXene (30ppm), the resistivity of the composite is improved by about 4 times compared to pure epoxy resin. At the same time, the trap level of deep traps increases to 1.07 from 1.04 eV of pure epoxy. Measuring the surface potential of the insulator and using an inversion algorithm to calculate the surface charge establishes that a doping level of 30 ppm of MXene effectively suppresses the accumulation of the surface charge of the insulator, which is only about 1/3 of that of the pure epoxy resin. The surface flashover voltage is also increased by 10%. However, when the doping amount of MXene is increased to 100 or 150 ppm, the insulation performance is lowered. We used a potential barrier model to explain the effect of MXene doping in the epoxy resin. This work presents a possible way to suppress the charge accumulation on the surface of insulators in HVDC gas-insulated systems and provides a link between the microstructure and the macroscopic properties in the material.
As a promising energy harvesters, triboelectric nanogenerators (TENG) can be utilized to convert distributed energy into electric power, but the slow charge accumulation incorporated with the ...inevitable charge decay/leakage of conventional TENGs result in a low surface charge density and an inferior output performance, limiting their practical applications. Here, an effective strategy is proposed to realize high charge density by using a fast charge accumulation process on dielectric material with high relative permittivity. As a result, the charge density is tremendously improved to 2.20 mC m−2 on the poly(vinylidene fluoride‐trifluoroethylene) film. Meanwhile, the fast charge accumulation is highly conducive to reach a high charge density of 1.30 mC m−2 in a 90% relative humidity environment, which is ≈260 times that of a TENG with slow charge accumulation. This work not only provides a new insight into charge accumulation and equilibrium state, but also provides significant guidance on the performance optimization of TENG.
A fast charge accumulation process on a dielectric material with high relative permittivity is demonstrated to be extremely conducive to improve the charge density of a triboelectric nanogenerator. This work not only raises the equilibrium state of surface charges, but also provides significant guidance on the performance optimization of triboelectric nanogenerators.
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