Nanochannel Network Research Articles

Brain-inspired computing with fluidic iontronic nanochannels

The brain's remarkable and efficient information processing capability is driving research into brain-inspired (neuromorphic) computing paradigms. Artificial aqueous ion channels are emerging as an exciting platform for neuromorphic computing, representing a departure from conventional solid-state devices by directly mimicking the brain's fluidic ion transport. Supported by a quantitative theoretical model, we present easy-to-fabricate tapered microchannels that embed a conducting network of fluidic nanochannels between a colloidal structure. Due to transient salt concentration polarization, our devices are volatile memristors (memory resistors) that are remarkably stable. The voltage-driven net salt flux and accumulation, that underpin the concentration polarization, surprisingly combine into a diffusionlike quadratic dependence of the memory retention time on the channel length, allowing channel design for a specific timescale. We implement our device as a synaptic element for neuromorphic reservoir computing. Individual channels distinguish various time series, that together represent (handwritten) numbers, for subsequent in silico classification with a simple readout function. Our results represent a significant step toward realizing the promise of fluidic ion channels as a platform to emulate the rich aqueous dynamics of the brain.

Fabrication of a hybrid device for the integration of light-triggered proton pumps

Biological ion pumps, such as bacteriorhodopsin (bR), utilize photons to move ions against concentration gradients, offering energy harvesting and spatiotemporal control of chemical gradients. This capability goes far beyond the capabilities of today's synthetic devices, suggesting a hybrid approach to embed bRs in synthetic devices in order to direct the proton flow towards useful system applications. In this study, a hybrid silicon-based nanochannel network with integrated purple membranes (PM) containing bR was fabricated. The fabrication method combines thermal scanning probe lithography, etching techniques, atomic layer deposition, plasma-enhanced chemical vapor deposition, and photolithography to create devices with buried nanochannels on silicon substrates. PM patches were deposited onto specified sites by a tunable nanofluidic confinement apparatus. The resulting device holds the potential for locally controlling directed ion transport in micrometer scale devices, a first step towards applications, such as locally affected proton catalyzed chemical reaction networks. Furthermore, this fabrication strategy, employing a maskless overlay, is a tool for constructing intricate nanofluidic network designs which are mechanically robust and straightforward to fabricate.

Focused ion beam-SEM 3D study of osteodentin in the teeth of the Atlantic wolfish Anarhichas lupus

The palette of mineralized tissues in fish is wide, and this is particularly apparent in fish dentin. While the teeth of all vertebrates except fish contain a single dentinal tissue type, called orthodentin, dentin in the teeth of fish can be one of several different tissue types. The most common dentin type in fish is orthodentin. Orthodentin is characterized by several key structural features that are fundamentally different from those of bone and from those of osteodentin. Osteodentin, the second-most common dentin type in fish (based on the tiny fraction of fish species out of ∼30,000 extant fish species in which tooth structure was so far studied), is found in most Selachians (sharks and rays) as well as in several teleost species, and is structurally different from orthodentin.Here we examine the hypothesis that osteodentin is similar to anosteocytic bone tissue in terms of its micro- and nano-structure. We use Focused Ion Beam-Scanning Electron Microscopy (FIB/SEM), as well as several other high-resolution imaging techniques, to characterize the 3D architecture of the three main components of osteodentin (denteons, inter-denteonal matrix, and the transition zone between them). We show that the matrix of osteodentin, although acellular, is extremely similar to mammalian osteonal bone matrix, both in general morphology and in the three-dimensional nano-arrangement of its mineralized collagen fibrils. We also document the presence of a complex network of nano-channels, similar to such networks recently described in bone. Finally, we document the presence of strings of hyper-mineralized small ‘pearls’ which surround the denteonal canals, and characterize their structure.

Exceptionally Fast Temperature-Responsive, Mechanically Strong and Extensible Monolithic Non-Porous Hydrogels: Poly(N-isopropylacrylamide) Intercalated with Hydroxypropyl Methylcellulose.

Exceptionally fast temperature-responsive, mechanically strong, tough and extensible monolithic non-porous hydrogels were synthesized. They are based on divinyl-crosslinked poly(N-isopropyl-acrylamide) (PNIPAm) intercalated by hydroxypropyl methylcellulose (HPMC). HPMC was largely extracted after polymerization, thus yielding a 'template-modified' PNIPAm network intercalated with a modest residue of HPMC. High contents of divinyl crosslinker and of HPMC caused a varying degree of micro-phase-separation in some products, but without detriment to mechanical or tensile properties. After extraction of non-fixed HPMC, the micro-phase-separated products combine superior mechanical properties with ultra-fast T-response (in 30 s). Their PNIPAm network was highly regular and extensible (intercalation effect), toughened by hydrogen bonds to HPMC, and interpenetrated by a network of nano-channels (left behind by extracted HPMC), which ensured the water transport rates needed for ultra-fast deswelling. Moreover, the T-response rate could be widely tuned by the degree of heterogeneity during synthesis. The fastest-responsive among our hydrogels could be of practical interest as soft actuators with very good mechanical properties (soft robotics), while the slower ones offer applications in drug delivery systems (as tested on the example of Theophylline), or in related biomedical engineering applications.

Mxene-based ceramic nanofiltration membranes for selective separation of primary contaminants in semiconductor wastewater

Ceramic membranes, known for their exceptional chemical stability, have found practical applications in the treatment of semiconductor wastewater. In this study, we have developed an innovative ceramic nanofiltration membrane featuring a nanochannel network created by two-dimensional (2D) nanomaterials, enabling high-performance separation and permeation. This accomplishment is realized through precise control of the size and thickness of MXene nanomaterials, which can be tailored using various coating conditions. The repeated stacking of MXene nanosheets onto the ceramic membrane substrate resulted in the formation of additional nanochannels and surface chemistry modifications, leading to significant enhancements in pollutant removal. These MXene-coated ceramic nanofiltration (NF) membranes significantly improved the removal efficiency of representative organic contaminants in semiconductor wastewater when compared to the pristine ceramic membrane. It enhanced the removal efficiencies by 4.2 times for dissolved silica, 3.7 times for dimethyl sulfoxide (DMSO), and 2.5 times for isopropyl alcohol (IPA). Furthermore, the MXene ceramic NF membrane exhibited exceptional fluoride removal capability, achieving approximately 99.1% removal, in addition to organic solvents. These findings not only help meet regulatory standards for wastewater discharge but also provide valuable insights into the transport behaviors of contaminants and their separation mechanisms. This innovative approach brings us one step closer to efficient and sustainable solutions for semiconductor wastewater treatment.

Efficient degradation capability of the FePCB amorphous alloy in acid orange 7 dye solution

The degradation ability of the Fe85P11C2B2 amorphous alloy in the acid orange 7 (AO7) solution was compared to that of Fe80B13C7. The results show that the Fe85P11C2B2 amorphous ribbon exhibits a higher degradation efficiency and lower reaction activation energy than Fe80B13C7. This is due to the fact that Fe85P11C2B2 is prone to form 3D nanochannel and porous nanosheet network structures, which improves adsorption capacity and increases the number of active reaction sites. On the other hand, the weakly bonded Fe–B and Fe–P can form more complex galvanic cells with strongly bonded Fe–C to accelerate dye degradation. The analysis of electron paramagnetic resonance and liquid chromatography-mass spectrometry reveals that the generation of the reactive species [H] plays a key role in the degradation of AO7. In addition, the degradation pathway and environmental applicability were studied. The results confirm that the low-cost Fe85P11C2B2 alloy is a potential material for wastewater treatment.

Multi-Layered Bipolar Ionic Diode Working in Broad Range Ion Concentration.

Ion current rectification (ICR) is the ratio of ion current by forward bias to backward bias and is a critical indicator of diode performance. In previous studies, there have been many attempts to improve the performance of this ICR, but there is the intrinsic problem for geometric changes that induce ionic rectification due to fabrication problems. Additionally, the high ICR could be achieved in the narrow salt concentration range only. Here, we propose a multi-layered bipolar ionic diode based on an asymmetric nanochannel network membrane (NCNM), which is realized by soft lithography and self-assembly of homogenous-sized nanoparticles. Owing to the freely changeable geometry based on soft lithography, the ICR performance can be explored according to the variation of microchannel shape. The presented diode with multi-layered configuration shows strong ICR performance, and in a broad range of salt concentrations (0.1 mM~100 mM), steady ICR performance. It is interesting to note that when each anion-selective (AS) and cation-selective (CS) NCNM volume was similar to each optimized volume in a single-layered device, the maximum ICR was obtained. Multi-physics simulation, which reveals greater ionic concentration at the bipolar diode junction under forward bias and less depletion under backward in comparison to the single-layer scenario, supports this tendency as well. Additionally, under different frequencies and salt concentrations, a large-area hysteresis loop emerges, which indicates fascinating potential for electroosmotic pumps, memristors, biosensors, etc.

Continuous Electrophoretic Separation of Charged Dyes in Liquid Foam

A novel electrophoretic separation technique is presented, where continuous electrophoretic separation is demonstrated using free flowing liquid foams. Continuous foam electrophoresis combines the principle of capillary electrophoresis and interactions between analytes and the electrical double layer, with the ability of Free Flow Electrophoresis to continuously separate and recover analytes automatically. A liquid foam is used to provide a network of deformable micro and nano channels with a high surface area, presenting a novel platform for electrophoresis, where interfacial phenomena could be exploited to modify analyte migration. The main purpose of this paper is to present a proof-of-concept study and provide fundamental understanding of a complex foam system in continuous separation mode, i.e., flowing liquid foam under an external electric field with electrophoresis and chemical reactions at the electrodes continuously changing the system. Liquid foam is generated using a mixture of anionic and non-ionic surfactants and pumped through a microfluidic separation chamber between two electrodes. The effectiveness of the device is demonstrated using a dye mixture containing a neutral dye and an anionic dye. At the outlet, the foam is separated and collected into five fractions which are individually probed for the concentration of the two dyes used. The anionic dye was concentrated up to 1.75 (±0.05) times the initial concentration in a select outlet, while the neutral dye concentration remained unchanged in all outlets, demonstrating the potential for electrophoretic foam separations.

A perpendicular micro-hole array for efficient ion transport in a thick, dense MoS2-based capacitive electrode

Two-dimensional (2D) nanosheets with a high electrochemical capacitance, density, and electrical conductivity are promising for assembling thick and dense films for supercapacitors with a high volumetric energy density. However, 2D nanosheet-based films with cascading nanochannel networks are not ideal for efficient ion transport due to the tortuous pathways. We used a micro-stamping method to create a perpendicular micro-hole array in a thick, dense MoS2-based electrode without lowering its density. Our nuclear magnetic resonance measurement and computational simulations reveal that the micro-hole array can serve as ion reservoirs and provide shortcuts in the cascading nanochannel network, greatly improving the ion accessibility to MoS2-based electrodes in both the adsorption and charging processes. A MoS2-based film electrode with 2-3 times the density of a conventional carbon electrode, shows almost thickness independent capacitance performance with a mass loading up to 18.6 mg cm−2. The electrode has a volumetric capacitance of 469.5 F cm−3 and the assembled device a volumetric energy density of 80.5 Wh L−1 in an ionic liquid electrolyte. This micro-stamping strategy is easy to scale up and may pave the way for the development of 2D materials-based compact energy storage systems.

Interfacial Super-Assembly of Intertwined Nanofibers toward Hybrid Nanochannels for Synergistic Salinity Gradient Power Conversion.

Capturing the abundant salinity gradient power into electric power by nanofluidic systems has attracted increasing attention and has shown huge potential to alleviate the energy crisis and environmental pollution problems. However, not only the imbalance between permeability and selectivity but also the poor stability and high cost of traditional membranes limit their scale-up realistic applications. Here, intertwined "soft-hard" nanofibers/tubes are densely super-assembled on the surface of anodic aluminum oxide (AAO) to construct a heterogeneous nanochannel membrane, which exhibits smart ion transport and improved salinity gradient power conversion. In this process, one-dimensional (1D) "soft" TEMPO-oxidized cellulose nanofibers (CNFs) are wrapped around "hard" carbon nanotubes (CNTs) to form three-dimensional (3D) dense nanochannel networks, subsequently forming a CNF-CNT/AAO hybrid membrane. The 3D nanochannel networks constructed by this intertwined "soft-hard" nanofiber/tube method can significantly enhance the membrane stability while maintaining the ion selectivity and permeability. Furthermore, benefiting from the asymmetric structure and charge polarity, the hybrid nanofluidic membrane displays a low membrane inner resistance, directional ionic rectification characteristics, outstanding cation selectivity, and excellent salinity gradient power conversion performance with an output power density of 3.3 W/m2. Besides, a pH sensitive property of the hybrid membrane is exhibited, and a higher power density of 4.2 W/m2 can be achieved at a pH of 11, which is approximately 2 times more compared to that of pure 1D nanomaterial based homogeneous membranes. These results indicate that this interfacial super-assembly strategy can provide a way for large-scale production of nanofluidic devices for various fields including salinity gradient energy harvesting.

High‐Performance Integrated Iontronic Circuits Based on Single Nano/Microchannels

Recently, artificial channel-based ionic diodes and transistors are extensively studied to mimic biological systems. Most of them are constructed vertically and are challenging to be further integrated. Several examples of ionic circuits with horizontal ionic diodes are reported. However, they generally require nanoscale channel sizes to meet the demand for ion-selectivity, resulting in low current output and restricting potential applications. In this paper, a novel ionic diode is developed based on multiple-layer polyelectrolyte nanochannel network membranes. Both bipolar and unipolar ionic diodes can be achieved by simply switching the modification solution. Ionic diodes with a high rectification ratio of ≈226 are achieved in single channels with the largest channel size of 2.5µm. This design can significantly reduce the channel size requirement and improve the output current level of ionic devices. The high-performance ionic diode with a horizontal structure enables the integration of advanced iontronic circuits. Ionic transistors, logic gates, and rectifiers are fabricated on a single chip and demonstrated for current rectification. Furthermore, the excellent current rectification ratio and the high output current of the on-chip ionic devices highlight the promise of the ionic diode as a component of complex iontronic systems for practical applications.

Porous gold nanomesh films electrodeposited in toluene-based dynamic soft template

Two-dimensional (2D) metallic nanomaterials have received much attention as next-generation materials. The creation of the characteristic pores into 2D metallic materials is expected to improve performance in sensing, surface-enhanced Raman spectroscopy, electrocatalytic activity, and so on. Here, we report that gold electrodeposition in a toluene-based bicontinuous microemulsion (BME), called a dynamic soft template, provides porous gold nanomesh (PGNM) film. The selective toluene adsorption onto Au{111} surfaces induces anisotropic 2D growth of gold in the aqueous phase of BME, and an intertwined network of water and toluene nanochannels in BME resulted in the formation of abundant in-plane nanopores. Toluene adsorption during Au electrodeposition makes the {111}-oriented Au surfaces more lipophilic, i.e., a structural change in BME is induced to expose the organic phase solution selectively to the toluene-adsorbed {111} Au surfaces. This dynamic change in the BME solution structure during electrodeposition might enhance the anisotropic growth of gold (dynamic soft templating). Electrochemical behaviors of low-index planes of Au electrode supported the growth mechanism of PGNM film.

Polyamide thin films with nanochannel networks synthesized at the liquid–gas interface for water purification

An important challenge concerning thin-film composite (TFC) membranes in brine treatment is to increase their water permeance while maintaining salt rejection for desalination performance. Structural control of polyamide (PA) thin films is a key factor in improving the desalination performance. In this study, we employed a Langmuir–Schaefer technique to fabricate PA Langmuir monolayers by interfacial polymerization of m-phenylenediamine and trimesoyl chloride at the liquid–gas interface and deposition on polysulfone supports. This technique allows the fabrication of nanoscale-controlled PA multilayers (2.3 nm per layer) with a nano-channeled structure through repeated deposition. The nanochannels of PA thin-film multilayers were clarified using the neutron reflectivity technique. UV treatment facilitates the maintenance of water-permeable sites in the nanochannels, which increases the water permeance up to 203% without loss of salt rejection performance.

A 3D Network of Nanochannels for Possible Ion and Molecule Transit in Mineralizing Bone and Cartilage

During crucial growth stages of vertebrate long bones, calcified cartilage beneath the growth plate is anchored to bone by a third mineralized component, the cement line. Proper skeletal development is contingent on the interplay of these three constituents, yet their mineralization processes and structural interactions are incompletely understood, in part from limited knowledge of their meso‐ and nanoscale features. Herein, focused ion beam‐scanning electron microscopy (FIB‐SEM) with serial surface imaging is applied to examine the cartilage–bone interface of mouse femoral heads at an unprecedented scale: FIB‐SEM provides 3D, nanometer resolution of structural details for volumes encompassing metaphyseal calcified cartilage, bone, and the intervening cement line. A novel and complex structural network is revealed, comprising densely packed nanochannels smaller than bone canaliculi (≈10–50 nm diameter) within the calcified cartilage and bone extracellular matrices, but absent in the cement line. A structural correlation is demonstrated between the nanochannels and ellipsoidal mineral domains, which appear to coalesce during mineralization in a process analogous to powder sintering in metallurgy. A mineralization process is proposed, supported by energy‐dispersive X‐Ray spectroscopy of nanochannel contents, in which these unreported structures offer ion and molecule conduits to access the extracellular matrices of calcified cartilage and bone.

Asymmetric Nanochannel Network-Based Bipolar Ionic Diode for Enhanced Heavy Metal Ion Detection

A higher rectification degree in ionic diodes is required to achieve better performance in applications. Nonetheless, the active geometrical change that is critical for inducing electrical potential asymmetry is difficult to realize in typical ionic diodes because of the intrinsic limitation of the fabrication method. Here, we propose a nanochannel-network-based bipolar diode with a high rectification degree of ∼1600─the highest value realized until now, to the best of our knowledge. Such a high rectification is obtained based on the synergetic effect of the bipolar surface charge and the optimization of the microchannel through experimental studies and multiphysics numerical simulations. It induces ion concentrations at the heterogeneous junction based on the accumulation effect under the forward potential bias. In particular, this proposed molecular concentration occurs in the ohmic region without vortex and instability that is inevitable at the conventional nano-electrokinetic concentration. Combining this accumulation with the horizontally aligned configuration of the nanochannel network membrane (NCNM), a highly sensitive and quantitative mercury ion (Hg2+) sensor based on a fluorescent signal is fabricated that allows direct measurement using a general fluorescent microscope. The detection limit of Hg2+ is 10 pM, which is ∼10 times lower than the best detection limit realized so far (∼100 pM) in fluorescent dye-based detection. This demonstrates the potential of asymmetric NCNM for high-performance ion transport in applications such as energy conversion, based on its design and material flexibility.

New Structural Insights into Densely Assembled Reduced Graphene Oxide Membranes

AbstractDensely assembled graphene‐based membranes have attracted substantial interest for their widespread applications, such as compact capacitive energy storage, ion/molecular separation, gas barrier films, and flexible electronics. However, the multiscale structure of densely packed graphene membranes remains ambiguously understood. This article combines X‐ray and light scattering techniques as well as dynamic electrosorption analysis to uncover the stacking structure of the densely stacked reduced graphene oxide (rGO) membranes. The membranes are produced by reducing graphene oxide (GO) membranes with hydrazine, during which the colloidal interactions between GO sheets are modulated by the electrolyte solution. In contrast to the common notion that direct reduction of densely assembled GO sheets in parallel tends to result in significant “graphitization”, this article unexpectedly discovers that the resultant densely packed rGO membrane can still retain the interconnected network nanochannels and show good capacitive performances. This inspires the development of a hierarchical structural model to describe the densely packed rGO membranes. This article further shows that the nanochannel network can be fine‐tuned at the sub‐nanometer level by tailoring the salt concentration and the reduction temperature to render exceptional volumetric capacitance and good rate performance for rGO membranes even with increased packing density.

Membranes based on porous hexagonal boron nitride nanorods for ultrafast and effective molecular separation

Effective and ultrafast molecular separation capable of exclusively transporting target molecules is highly desirable for the sustainable development of the ecosystem. Ensuring both high permeability and selective rejection is particularly challenging, especially, for long-term service in a harsh environment. Herein, we demonstrate the simultaneously functionalized hexagonal boron nitride nanorods (BNNDs) with ultrahigh porosity (specific surface area 1437 m2 g−1) that can be assembled into supported membranes for high-performance molecular separation. The BNNDs membranes with controllable thicknesses exhibit abundant nanochannel network and superhydrophilic that render ultrafast water permeance (326 L m−2 h−1) without pressure drive and efficiently selective molecular screening in both aqueous and organic solutions. In addition, the membranes possess the flexibility and high tolerance to acidic, alkaline media for over one month. Such fast permeability and excellent separation performance offer these porous BNNDs membranes promising opportunities for practical molecular separation and purification applications.

Highly stretchable van der Waals thin films for adaptable and breathable electronic membranes.

The conformal integration of electronic systems with irregular, soft objects is essential for many emerging technologies. We report the design of van der Waals thin films consisting of staggered two-dimensional nanosheets with bond-free van der Waals interfaces. The films feature sliding and rotation degrees of freedom among the staggered nanosheets to ensure mechanical stretchability and malleability, as well as a percolating network of nanochannels to endow permeability and breathability. With an excellent mechanical match to soft biological tissues, the freestanding films can naturally adapt to local surface topographies and seamlessly merge with living organisms with highly conformal interfaces, rendering living organisms with electronic functions, including leaf-gate and skin-gate transistors. On-skin transistors allow high-fidelity monitoring and local amplification of skin potentials and electrophysiological signals.

Ultrahigh-permeance functionalized boron nitride membrane for nanoconfined heterogeneous catalysis

Practical applications of heterogeneous advanced oxidation processes for organic pollutant destruction remain elusive due to poor yield of reactive oxygen species (ROS) as well as their ultrashort lifetimes and mass transfer limitations. To address these issues, nanoconfined catalysis, whereby improved reaction efficiency is attained due to rapid mass transfer, has recently gained traction in environmental remediation. Here, we introduce a simple concept of functionalizing the boron nitride nanosheet (BNNS) membrane, involving nucleation of cobalt nanocatalysts within the membrane intralayer network of water transport nanochannels. Membrane-confined crystalline reactive species with multiple exposed active sites spontaneously activate peroxymonosulfate, producing ROS for ultrafast (∼80 ms) destruction of organic pollutants at a fast flow rate of 548 L m −2 h −1 . Co-BNNS membrane showed good stability and outperformed previously developed membrane-confined catalysis systems (up to 26-fold higher permeance). Co-BNNS membrane enabled ultrafast destruction of several organic pollutants, offering an attractive alternative for membrane-based catalysis applications. • Cobalt nanocatalysts are grown in boron nitride membrane for heterogeneous catalysis • Analyses confirmed the membrane-confined growth of α-Co(OH) 2 and Co 3 O 4 crystals • Catalysis performance of membrane is explained both theoretically and experimentally • Functionalized membrane can achieve rapid destruction of organic pollutants in 80 ms Water pollution is mainly caused by anthropogenic activities and could disrupt the smooth functioning of economic activities and human health. In this context, detection of persistent organic pollutants, such as pharmaceutical and pesticides, in freshwater bodies is alarming due to their well-documented harmful impacts on human health (e.g., genetic malformations) after prolonged exposure. Due to these severe consequences, clean water (SDG6) and good health (SDG3) are included in the UN sustainable development goals. Herein, we developed a compact platform by combining a membrane separation process and advanced oxidation process in a single step for nanoconfined heterogeneous catalysis of persistent organic pollutants to produce clean water. The in situ functionalization strategy presented here is convenient and allows nucleation of nanocatalysts within the water transport nanochannels of boron nitride membrane, opening a promising avenue for the construction of catalytic membranes. We present an in situ approach of functionalizing the intralayer nanochannels of 2D boron nitride membrane, which allows simultaneous confinement of nanocatalysts, ROS species, and fluids within the intralayer for ultrafast organic pollutant destruction. Compared with conventional AOP reactors, the functionalized boron nitride membrane can be operated in a continuous-flow mode at an ultrahigh water permeance, which would allow its widespread application in water treatment.

Polyamide Thin Films with Nanochannel Networks Synthesized at the Liquid–Gas Interface for Water Purification

Polyamide Thin Films with Nanochannel Networks Synthesized at the Liquid–Gas Interface for Water Purification