Nanochannel Diameter Research Articles

Solar-driven abnormal evaporation of nanoconfined water.

Intrinsic water evaporation demands a high energy input, which limits the efficacy of conventional interfacial solar evaporators. Here, we propose a nanoconfinement strategy altering inherent properties of water for solar-driven water evaporation using a highly uniform composite of vertically aligned Janus carbon nanotubes (CNTs). The water evaporation from the CNT shows the unexpected diameter-dependent evaporation rate, increasing abnormally with decreasing nanochannel diameter. The evaporation rate of CNT10@AAO evaporator thermodynamically exceeds the theoretical limit (1.47 kg m-2 hour-1 under one sun). A hybrid experimental, theoretical, and molecular simulation approach provided fundamental evidence of different nanoconfined water properties. The decreased number of H-bonds and lower interaction energy barrier of water molecules within CNT and formed water clusters may be one of the reasons for the less evaporative energy activating rapid nanoconfined water vaporization.

Hydrogen-Bonded Structures of Water Molecules in Hydroxy-Functionalized Nanochannels of Columnar Liquid Crystalline Nanostructured Membranes Studied by Soft X-ray Emission Spectroscopy.

Here, we report a synchrotron-based high-resolution soft X-ray emission spectroscopy study on hydrogen-bonded structures of water molecules in the self-organized, hydroxy-group-functionalized one-dimensional nanochannels of liquid crystalline nanostructured membranes. The water molecules confined in the uncharged hydroxy-functionalized nanochannels (which have a diameter of about 1.5 nm) exhibit hydrogen-bonded structures close to those of bulk liquid water, even directly interacting with diol groups. These hydrogen-bonded structures contrast with the more distorted hydrogen bonding of water molecules confined in self-organized channels with a diameter of 0.6 nm formed by an analogous nanostructured membrane with a cationic moiety, which was explained by the ability of the channel functional groups to donate and accept hydrogen bonds in a confined space and the nanochannel diameter.

Simple and direct electrochemical detection of rosmarinic acid in food samples based on nanochannel modified carbon electrode.

The detection of rosmarinic acid (Ros A) in food samples holds major significance. Simple and convenient electrochemical detection of Ros A with high performance remains a challenge. In this work, a nanochannel array-modified carbon electrode was constructed using a simple and convenient approach to achieve highly sensitive electrochemical detection of Ros A in food samples. Through simple electrochemical pre-activation of a glassy carbon electrode (GCE), oxygen-containing functional groups were introduced on the electrode surface (p-GCE). Vertically-ordered mesoporous silica film (VMSF) was stably grown on p-GCE through electrochemical-assisted self-assembly (EASA) without the introduction of another adhesive layer (VMSF/p-GCE). Transmission electron microscopy (TEM) characterization demonstrated the highly ordered structure of VMSF with a nanochannel diameter around 2.7 nm. Both p-GCE and the nanochannels significantly enhanced the electrochemical signals of Ros A on the electrode, exhibiting dual signal amplification. VMSF/p-GCE demonstrated sensitive detection of Ros A with a linear range of 500 nM to 1 μM and 1 μM to 35 μM. The detection limit (DL) was 26 nM. Combining the good anti-fouling and anti-interference properties of the nanochannels, VMSF/p-GCE can achieve direct electrochemical detection of Ros A in food samples. The sensor can be easily regenerated for repeated use. The simple fabrication, high detection sensitivity and selectivity of the sensor make it a new strategy for rapid preparation of high-performance electrochemical sensors.

Effect of Ni addition on CPP-GMR response in electrodeposited Co-Ni/Cu multilayered nanocylinders with an ultra-large aspect ratio

Effect of Co–Ni alloy composition on the current perpendicular-to-plane giant magnetoresistance (CPP-GMR) response of electrochemically synthesized Co–Ni/Cu multilayered nanocylinders was studied using anodized aluminum oxide membranes (AAOM) with nanochannel diameter D ∼67 nm and length L ∼70 μm. Co–Ni/Cu multilayered nanocylinders, which have an aspect ratio L/D of ∼1,045, were fabricated in the AAOM nanochannel templates by utilizing a pulse-current electrochemical growth process in an electrolytic bath with Co2+, Ni2+ and Cu2+ ions. Co–Ni/Cu alternating structure with Co84Ni16 alloy layer-thickness of 9.6 nm and Cu layer-thickness of 3.8 nm was clearly observed in a nanocylinder with a diameter of 63 nm. The alternating structure was composed from crystalline layers with preferential orientations in hcp-CoNi (002) and fcc-Cu (111). The Co–Ni/Cu multilayered nanocylinders were easily magnetized in the long axis direction because of the extremely large aspect ratio L/D. In Co84Ni16/Cu multilayered nanocylinders, the coercivity and squareness were ∼0.46 kOe and ∼0.5, respectively. The CPP-GMR value was achieved up to 22.5% (at room temperature) in Co84Ni16/Cu multilayered nanocylinders.

High-yield thermalized positronium at room temperature emitted by morphologically tuned nanochanneled silicon targets

Nanochanneled silicon targets with high positron/positronium (Ps) conversion rate and efficient Ps cooling were produced. Morphological parameters of the nanochannels, such as their diameter and length, were adjusted to get a large fraction of thermalized Ps at room temperature being emitted into vacuum. Ps cooling measurements were conducted combining single-shot positron annihilation lifetime spectroscopy and Doppler spectroscopy of the 13S → 23P transition. 2γ–3γ annihilation ratio measurements were also performed to estimate the positron/Ps conversion efficiency. In a converter with nanochannel diameter of 7–10 nm and depth of 3.89 μm, ∼28% of implanted positrons with an energy of 3.3 keV was found to be emitted as Ps with a transverse kinetic energy of 11 ± 2 meV. The reduction of the nanochannels depth to 1.13 μm, without changing the nanochannel diameter, was found to result in a less efficient cooling, highlighting the presence of Ps reflection from the bottom end of nanochannels.

Current-perpendicular-to-plane giant magnetoresistance in Co/Cu multilayered nanocylinders electrodeposited into anodized aluminum oxide nanochannels with ultra-large aspect ratio

An anodized aluminum oxide (AAO) thick film with numerous nanochannels was synthesized by a cathodic exfoliation technique from a metallic aluminum rod. The nanochannel diameter D and length L were about 60 nm and 60 µm, respectively. The aspect ratio L/D reached ~ 1000. A rectangular pulsed potential deposition technique was applied to electrochemically grow the multilayered nanocylinders with alternating Cu and Co thin layers in the AAO nanochannels. The Co/Cu bilayer thickness was decreased to around 7 nm at the minimum by controlling the pulsed potential and duty cycle during the electrodeposition process. An electrochemical in situ single contact process was demonstrated by monitoring the observed current until a Co/Cu multilayered nanocylinder reached the nanoporous Au film on the AAO thick film. The resistance of the Co/Cu multilayered nanocylinder was determined to range from 1 to 2 kΩ, which corresponded well with a theoretical estimation. Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of a Co/Cu multilayered nanocylinder with ~ 6000 bilayers (Cu = 2.4 nm, Co = 7.1 nm) reached up to 31.5% at room temperature. Valet–Fert model agreed well with the present study concerning the effect of Cu-layer thickness on CPP-GMR.

Towards explicit regulating-ion-transport: nanochannels with only function-elements at outer-surface

Function elements (FE) are vital components of nanochannel-systems for artificially regulating ion transport. Conventionally, the FE at inner wall (FEIW) of nanochannel−systems are of concern owing to their recognized effect on the compression of ionic passageways. However, their properties are inexplicit or generally presumed from the properties of the FE at outer surface (FEOS), which will bring potential errors. Here, we show that the FEOS independently regulate ion transport in a nanochannel−system without FEIW. The numerical simulations, assigned the measured parameters of FEOS to the Poisson and Nernst-Planck (PNP) equations, are well fitted with the experiments, indicating the generally explicit regulating-ion-transport accomplished by FEOS without FEIW. Meanwhile, the FEOS fulfill the key features of the pervious nanochannel systems on regulating-ion-transport in osmotic energy conversion devices and biosensors, and show advantages to (1) promote power density through concentrating FE at outer surface, bringing increase of ionic selectivity but no obvious change in internal resistance; (2) accommodate probes or targets with size beyond the diameter of nanochannels. Nanochannel-systems with only FEOS of explicit properties provide a quantitative platform for studying substrate transport phenomena through nanoconfined space, including nanopores, nanochannels, nanopipettes, porous membranes and two-dimensional channels.

CPP-GMR performance of electrodeposited metallic multilayered nanowires with a wide range of aspect ratios

Effect of the diameter on the CPP-GMR performance of electrodeposited Co/Cu multilayered nanowires was systematically investigated using our home-made anodized aluminum oxide (AAO) templates with the nanochannel diameter ranging from 35 to 130 nm. The nanochannel diameter was precisely controlled by tuning the anodization voltage ranging from 20 to 110 V. The Co/Cu multilayered nanowires with the aspect ratio of ~1000 were synthesized in the AAO nanochannels by applying a rectangular pulsed potential electrodeposition technique using an acidic aqueous solution containing Co2+ and Cu2+ ions. An ideal alternating Co/Cu multilayered structure with each layer thickness of several nanometers was clearly observed in the nanowires with the diameter ranging from 35 to 95 nm. The multilayered nanowires with the diameter ranging from 35 to 70 nm were spontaneously magnetized in the axial direction due to the preferential crystal orientation of hcp-Co (002) which was induced by the magnetic shape anisotropy. With decreasing the diameter down to 35 nm, the coercivity increased up to 1.37 kOe while the squareness reached 0.73 at the diameter of 50 nm. The CPP-GMR value reached 23.4% at room temperature in the Co/Cu multilayered nanowires with the diameter of 70 nm.

Ion sieving by a two-dimensional Ti3C2Tx alginate lamellar membrane with stable interlayer spacing

Two-dimensional membranes attract extensive interest due to the anomalous transport phenomena; however, the ion separation performance is below the theoretical prediction. The stabilization of d-spacing is a key step for enhancing ion selectivity. Here, we demonstrate a strategy for stabilizing the Ti3C2Tx laminar architecture by alginate hydrogel pillars. After pillared by Ca-alginate, the nanochannel diameters are effectively fixed at 7.4 ± 0.2 Å, and the membrane presents a permeation cutoff and an outstanding sieving property towards valent cations. When applied for acid recovery, the outstanding H+/Fe2+ selectivity makes the membrane a promising substitution for traditional ion-exchange membranes. Moreover, the ultrathin Mn-alginate pillared membrane with identical d-spacing exhibits 100% Na2SO4 rejection with high water permeance, which is superior to the state-of-the-art nanofiltration membranes. Building on these findings, we demonstrate an efficient method to tune the ion selectivity and introduce a new perspective for energy- and environment-related applications.

Confinement and Diffusion of Small Molecules in a Molecular-Scale Tunnel

Multi-step reaction cascades can be designed to include channeling mechanisms, which provide electrostatic or steric control over intermediate transport such that intermediates do not escape to the bulk between active sites. Physical confinement of the intermediate pathway between sites retains intermediate from bulk access and thus provides high transport efficiency. In this work, we use molecular dynamics to study the transport of intermediates (charged oxalate and neutral ethanol) inside a nanochannel represented by a single-walled carbon nanotube (SWCNT). This approach reveals that solvent orientation highly impacts intermediate transport. At small nanochannel diameter near 1 nm, highly structured solvent water and Knudsen diffusion decreases effective intermediate diffusivity. Finally, modified SWCNT termini with electrostatically-charged carboxylate groups are shown to increase intermediate retention for both charged and uncharged intermediates by up to five-fold. When catalyst sites are located within the nanochannel, decreased diffusion rate and increased retention time will enhance cascade efficiency.

Effects of water nanochannel diameter on proton transport in proton‐exchange membranes

ABSTRACTThe effects of water nanochannel diameter on proton transport pathways and properties have been studied using reactive molecular dynamics simulations. The proton distributions and diffusivities have been evaluated using the cylinder model of water domains at various diameters that is the most typical proposed morphological model in proton‐exchange membranes. The proton distributions are analyzed to clarify proton pathways by classifying the water channel into two regions in parallel: an inner channel (free water) and an outer channel (bound water). For all the water contents, the nonmonotonic trends that show a peak at a certain diameter are found to be observed in the proton diffusivity, which is dominated by the proton diffusivity in the free water region and has a strong correlation with the proton distribution that is controlled by the balance between the volume fraction of free water and the surface density of sulfonate groups. The electroosmotic drag coefficients are found to increase monotonically with increasing channel diameter as a result of the increase in the volume fraction of free water. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 867–878

Enhancing gas separation efficiency by surface functionalization of nanoporous membranes

Here we report evidence for substantial changes in the separation efficiency of nanoporous anodic alumina membranes with nanochannel diameters ranging from 10–100 nm modified with octadecylphosphonic acid in the transitional flow regime. Softening of surface by alkyl groups with a surface density ∼2 groups/nm2 leads to a general permeance decrease in 3–500 times, depending strongly on the penetrant gas nature and the channels diameter. The divergence of the permeance, for different gases, increases with the decreasing diameter of the pores. For a surface-functionalized membrane, with 10-nm channel diameters, it results in n-C4H10/CH4 ideal and mixed gas separation factors up to 32.3 and 9.0 respectively at a n-C4H10 permeance up to 3.5 m3/(m2·bar·h). The effect is related to the changes of the ratio of molecule travelling time to residence time in the adsorbed state, as well as a strong influence of surface saturation by the absorbed molecules on the tangential momentum accommodation coefficient, which is supported by the derived model. Synergetic contribution of these two factors allows to enhance the separation factor of permanent and condensable gases strongly beyond the Knudsen limit, while maintaining a high permeance of porous membranes.

Morphology of nanoporous anodic films formed on tin during anodic oxidation in less commonly used acidic and alkaline electrolytes

Porous anodic tin oxide layers were obtained by simple one-step potentiostatic anodic oxidation (anodization) of Sn foil in aqueous ammonia and citric acid in a transpassive region. Different anodizing conditions including electrolyte concentration, applied potential, and duration of the electrolysis have been examined in order to find the effect of process parameters on the morphology of anodic films. Layers with completely clogged surface and porous interior have been obtained at all studied conditions. Moreover, the synthesized samples exhibit a typical stacked morphology with a lot of internal cracks and discontinuities within the anodic film being a result of local accumulation and trapping of gaseous oxygen inside the pores. Diameters of nanochannels were found to be almost independent on the applied potential, and their formation was also attributed to the O2 co-evolution at the positive electrode during anodization. Increasing electrolyte concentration and anodizing potential usually result in higher rates of the oxide formation. However, no significant effect of anodizing conditions on the nanochannel diameter, and morphology of the compact outer layer was found. Anodic films with the almost identical morphology have been successfully obtained in other electrolytes such as tartaric acid and phosphoric acid solutions. It was proven that the as-obtained layers were amorphous in nature and composed mainly of tin and oxygen with a surface O/Sn ratio close to stoichiometric SnO2. Incorporation of phosphorous species to the anodic film during anodization in H3PO4 was also confirmed. Band gaps of all materials were found to be significantly lower (2.94–3.05 eV) than that typically observed for pure SnO2 (3.6 eV).

Selective enhancement of auxeticity through changing a diameter of nanochannels in Yukawa systems

A new effect of selective enhancement of auxeticity through the changes of nanochannels’ diameter in Yukawa systems is reported. Elastic properties of the model of Yukawa crystals with narrow nanochannels in the [001] crystallographic direction have been studied by Monte Carlo simulations in the isobaric–isothermal ensemble. It has been found that the choice of nanochannels’ diameter allows one to decrease the Poissons ratio value of the system in one of two selected crystallographic directions. The value of Poisson’s ratio in those directions can be changed in a wide range, e.g. from −0.061(9) to −0.625(44) in the -direction, depending on the nanochannels’ type and the Debye screening length.

Evaluating the potential of superhydrophobic nanoporous alumina membranes for direct contact membrane distillation

HypothesisDirect contact membrane distillation (DCMD) processes exploit water-repellant membranes to desalt warm seawaters by allowing only water vapor to transport across. While perfluorinated membranes/coatings are routinely used for DCMD, their vulnerability to abrasion, heat, and harsh chemicals necessitates alternatives, such as ceramics. Herein, we systematically assess the potential of ceramic membranes consisting of anodized aluminum oxide (AAO) for DCMD. ExperimentsWe rendered AAO membranes superhydrophobic to accomplish the separation of hot salty water (343 K, 0.7 M NaCl) and cold deionized water (292 K) and quantified vapor transport. We also developed a multiscale model based on computational fluid dynamics, conjugate heat transfer, and the kinetic theory of gases to gain insights into our experiments. FindingsThe average vapor fluxes, J, across three sets of AAO membranes with average nanochannel diameters (and porosities) centered at 80 nm (32%), 100 nm (37%), and 160 nm (57%) varied by < 25%, while we had expected them to scale with the porosities. Our multiscale simulations unveiled how the high thermal conductivity of the AAO membranes reduced the effective temperature drive for the mass transfer. Our results highlight the limitations of AAO membranes for DCMD and might advance the rational development of desalination membranes.

Effect of Nanochannel Size of Surface Treated Thru-Hole Alumina Membrane in Rejection of Polar Molecules

This paper presents the effect of nanochannel size of surface treated thru-hole alumina membrane in rejection of polar molecules. Polar molecules of methyl blue in a methyl blue aqueous solution were rejected by the equivalent charge of a surface-treated thru-hole alumina membrane. Thru-hole alumina membranes, having four different nanochannel diameters, were fabricated by the two-step aluminum anodic oxidation and wet-etching processes. Surface of the fabricated thru-hole alumina membrane was negatively charged using 3-(triethoxysilyl) propylsuccinic anhydride (TEPSA), which includes a carboxyl group. A methyl blue aqueous solution of 10 μM, which possessed negative charge, was injected through a negatively charged thru-hole alumina membrane to investigate its rejection ability. In the experiment using pristine thru-hole alumina membrane, it was observed that the methyl blue molecules passed through the nanochannel of the thru-hole alumina membrane, except for the molecules that were adsorbed to the surface of alumina membrane. In contrast, 95.2% of the methyl blue molecules were rejected by the electrical repulsive force of the surface-treated thru-hole alumina membrane. Also, efficient methyl blue rejection rate of nearly 96% was maintained in proper nanochannel diameter range of 150 to 200 nm.

Current-voltage characteristics influenced by the nanochannel diameter and surface charge density in a fluidic field-effect-transistor.

The nanochannel diameter and surface charge density have a significant impact on current-voltage characteristics in a nanofluidic transistor. We have simulated the effect of the channel diameter and surface charge density on current-voltage characteristics of a fluidic nanochannel with positive surface charge on its walls and a gate electrode on its surface. Anion depletion/enrichment leads to a decrease/increase in ion current with gate potential. The ion current tends to increase linearly with gate potential for narrow channels at high surface charge densities and narrow channels are more effective to control the ion current at high surface charge densities. The current-voltage characteristics are highly nonlinear for wide channels at low surface charge densities and they show different regions of current change with gate potential. The ion current decreases with gate potential after attaining a peak value for wide channels at low values of surface charge densities. At low surface charge densities, the ion current can be controlled by a narrow range of gate potentials for wide channels. The current change with source drain voltage shows ohmic, limiting and overlimiting regions.

The effect of electrolyte change on the morphology and degree of nanopore order of porous alumina formed by two-step anodization

The aim of this work was to verify if the quality, regularity and spacing of nanoconcaves formed on the Al surface during the first step of anodization (pre-texturing) have a significant effect on the morphology of AAO layers grown during the second anodization continued at the same potential but in different electrolytes. High purity (99.999%) aluminum substrates were anodized at 25V and 45V in sulfuric acid and oxalic acid, respectively. After chemical etching of initially formed oxide in a mixture of chromic and phosphoric acid, the samples were re-anodized under the same potentials, but in different electrolytes (sulfuric, oxalic, phosphoric acids). It was confirmed that the regular nanoporous structure formed on the Al surface during the first anodizing step is initially replicated at the beginning of the second anodization, independently of the electrolyte used. However, these initially formed oxide layers exhibit significantly different pore diameters but the same pore spacing, which is determined by the cell spacing on the Al surface. When phosphoric acid is used as an electrolyte, the prolonged anodization resulted in the formation of typical serrated nanochannels. However, we successfully obtained the almost ideally-ordered porous anodic alumina layer with a thickness of about 700nm, and the average diameter of nanochannels of ∼50nm after the second anodization carried out for 20min at 45V in 0.3M H3PO4, outside from the self-ordering regime for this electrolyte.

A capacitive-pulse model for nanoparticle sensing by single conical nanochannels.

Nanochannel based devices have been widely used for single-molecule detection. The detection usually relies on the resistive-pulse model, where the change of the monitored current depends on the physical volumetric blocking of the nanochannel by the analyte. However, this mechanism requires that the nanochannel diameter should not be much larger than the analyte size, because, otherwise, the resultant current change would be too small to detect, and therefore poses particular challenges for the fabrication of nanochannels. To circumvent this issue, in this report, we propose a different mechanism of capacitive-pulse model, where the transport signals can be significantly magnified by the capacitive effect of the nanochannel. We experimentally demonstrate that current pulses with an averaged peak height of 0.87 nA can be achieved for transporting 60 nm nanoparticles through a conical nanochannel device, whereas the traditional resistive-pulse model only predicts one-order-of-magnitude lowered value. With further comprehensive simulation, the dependence of this effect on the nanochannel geometry as well as the surface charge density for both the nanochannel and the analyte is predicted, which would provide important guidance for better designing of the nanochannel-based sensors.

How nanochannel confinement affects the DNA melting transition within the Poland-Scheraga model.

When double-stranded DNA molecules are heated, or exposed to denaturing agents, the two strands are separated. The statistical physics of this process has a long history and is commonly described in terms of the Poland-Scheraga (PS) model. Crucial to this model is the configurational entropy for a melted region (compared to the entropy of an intact region of the same size), quantified by the loop factor. In this study, we investigate how confinement affects the DNA melting transition, by using the loop factor for an ideal Gaussian chain. By subsequent numerical solutions of the PS model, we demonstrate that the melting temperature depends on the persistence lengths of single-stranded and double-stranded DNA. For realistic values of the persistence lengths, the melting temperature is predicted to decrease with decreasing channel diameter. We also demonstrate that confinement broadens the melting transition. These general findings hold for the three scenarios investigated: 1. homo-DNA, i.e., identical basepairs along the DNA molecule, 2. random sequence DNA, and 3. "real" DNA, here T4 phage DNA. We show that cases 2 and 3 in general give rise to broader transitions than case 1. Case 3 exhibits a similar phase transition as case 2 provided the random sequence DNA has the same ratio of AT to GC basepairs (A - adenine, T - thymine, G - guanine, C - cytosine). A simple analytical estimate for the shift in melting temperature is provided as a function of nanochannel diameter. For homo-DNA, we also present an analytical prediction of the melting probability as a function of temperature.