Solution‐pH‐Modulated Rectification of Ionic Current in Highly Ordered Nanochannel Arrays Patterned with Chemical Functional Groups at Designed Positions

A new ionic current rectification device responsive to a broad range of pH stimuli is established using highly ordered nanochannels of porous anodic alumina membrane with abrupt surface charge discontinuity. The asymmetric surface charge distribution is achieved by patterning the nanochannels with surface amine functional groups at designed positions using a two‐step anodization process. Due to the protonation/deprotonation of the patterned amine and the remaining intrinsic hydroxyl groups upon solution pH variation, the nanochannel‐array‐based device is able to regulate ion transport selectivity and has ionic current rectification properties. The rectification ratio of the device is mainly determined by the nanochannel size, and the rectification ratio is less sensitive to the patterned length of the amine groups when the nanochannels size is defined. Thus, the isoelectric point of nanochannels can be easily estimated to be the pH value with a unit rectification ratio. The present ionic device is promising for biosensing, molecular transport and separation, and drug delivery in confined environments.     

Light‐Gating Titania/Alumina Heterogeneous Nanochannels with Regulatable Ion Rectification Characteristic

Bioinspired artificial nanochannels exhibiting ion transport properties similar to biological ion channels have been attracting some attention for biosensors, separation technologies, and nanofluidic diodes. Herein, an easily available artificial heterogeneous nanochannel shows both ion gating and ion rectification characteristics when irradiated by ultraviolet light. The fabrication of heterogeneous nanochannels includes the coating of an anatase TiO₂ porous layer on an alumina porous supporter, followed by a chemical modification with octadecyltrimethoxysilane (OTS) molecules. The irreversible decomposition of OTS molecules by TiO₂ photocatalysis under ultraviolet light results in a change of surface wettability and an asymmetric distribution of surface negative charges simultaneously, which contributes to the ion gating and ion rectification. The asymmetric distribution of negative charges in the TiO₂ porous layer can be controlled by the irradiation time of ultraviolet light, which regulates the ion rectification characteristic.     

Synthetic Asymmetric‐Shaped Nanodevices with Symmetric pH‐Gating Characteristics

Synthetic stimuli‐gated nanodevices displaying intelligent ion transport properties similar to those observed in biological ion channels have attracted increasing interests for their wide potential applications in biosensors, nanofluidics, and energy conversions. Here, bioinspired asymmetric shaped nanodevices are reported that can exhibit symmetric and linear pH‐gating ion transport features based on polyelectrolyte‐asymmetric‐functionalized asymmetric hourglass‐shaped nanochannels. The pH‐responsive polymer brushes grafted on the inner channel surface are acted as a gate that open and close in response to external pH changing to linearly and symmetrically regulate transmembrane ionic currents of the channel. A complete experimental characterization of the pH‐dependent ion transport behaviors of the nanodevice and a comprehensive discussion of the experimental results in terms of theoretical simulation are also presented. Both experimental and theoretical data shown in this work demonstrate the feasibility of using the asymmetric chemical modification method to achieve symmetric pH gating behaviors inside the asymmetric nanochannels, and lay the foundation to build diverse stimuli‐gated artificial asymmetric shaped ion channels with symmetric gating ion transport features.     

Fabrication of Bio‐Inspired 2D MOFs/PAA Hybrid Membrane for Asymmetric Ion Transport

Biological ion channels are known as membrane proteins which can turn on and off under environmental stimulus to regulate ion transport and energy conversion. Rapid progress made in biological ion channels provides inspiration for developing artificial nanochannels to mimic the structures and functions of ion transport systems and energy conversion in biological ion channels. Due to the advantages of abundant pore channels, metal–organic frameworks (MOFs) have become competitive materials to control the nanofluidic transport. Herein, a facile in situ synthesis method is developed to prepare hybrid nanochannels constructed by 2D MOFs and porous anodic aluminum (PAA). The introduction of asymmetries in the chemical composition and surface charge properties gives the hybrid outstanding ion current rectification properties and excellent ion selectivity. A power density of 1.6 W m^?2 is achieved by integrating it into a salinity‐gradient‐driven device. With advantages of facile fabrication method and high ion selectivity, the prepared 2D MOFs/PAA hybrid membrane offers a promising candidate for power conversion and water desalination.     

Nanoengineered Polypyrrole‐Coated Fe2O3@C Multifunctional Composites with an Improved Cycle Stability as Lithium‐Ion Anodes

Novel multifunctional composites composed of highly dispersed nanosized Fe₂O₃ particles, a tubular mesoporous carbon host, and a conductive polypyrrole (PPy) sealing layer are hierarchically assembled via two facile processes, including bottom‐up introduction of Fe₂O₃ nanoparticles in tubular mesoporous carbons, followed by in situ surface sealing with the PPy coating. Fe₂O₃ particles are well‐dispersed within the carbon matrix and PPy is spatially and selectively coated onto the external surface and the pore entrances of the Fe₂O₃@C composite, thereby bridging the composite particles together into a larger unit. As an anode material for Li‐ion batteries (LIBs), the PPy‐coated Fe₂O₃@C composite exhibits stable cycle performance. Additionally, the PPy‐coated Fe₂O₃@C composite also possesses fast electrode reaction kinetics, high Fe₂O₃ use efficiency, and large volumetric capacity. The excellent electrochemical performance is associated with a synergistic effect of the highly porous carbon matrix and the conducting PPy sealing layer. Such multifunctional configuration prevents the aggregation of NPs and maintains the structural integrity of active materials, in addition to effectively enhancing the electronic conductivity and warranting the stability of as‐formed solid electrolyte interface (SEI) films. This nanoengineering strategy might open new avenues for the design of other multifunctional composite architectures as electrode materials in order to achieve high‐performance LIBs.     

Hybrid Templated Synthesis of Crack‐Free,Organized Mesoporous TiO2 Electrodes for High Efficiency Solid‐State Dye‐Sensitized Solar Cells

Organic/inorganic hybrid templates, i.e., aluminium oxide (Al₂O₃) nanoparticles grafted with poly(oxyethylene) methacrylate, Al₂O₃‐POEM, are synthesized via surface‐initiated atom transfer radical polymerization (ATRP), as confirmed by Fourier transform‐infrared spectroscopy (FT‐IR) and thermogravimetric analysis (TGA). Upon combining the Al₂O₃‐POEM with titanium(IV) isopropoxide (TTIP), hydrophilic TTIP is selectively confined in the hydrophilic POEM chains through hydrogen bonding interactions. Following the calcination at 450 °C and the selective etching of Al₂O₃ with NaOH, the OM‐TiO₂ films with high surface areas, good interconnectivity, and anatase phase are obtained. The solid‐state dye‐sensitized solar cells (ssDSSCs) fabricated with OM‐TiO₂ photoelectrodes and a polymerized ionic liquid (PIL) show a high energy conversion efficiency of 7.3% at 100 mW cm^?2, which is one of the highest values for ssDSSCs. The high cell performance is due to the well‐organized structure, resulting in improved dye loading, excellent pore filling of electrolyte, enhanced light harvesting, and reduced charge recombination.     

High‐Performance Mesostructured Organic Hybrid Pseudocapacitor Electrodes

The electrodes of a hybrid electrochemical capacitor which utilize the quinone (Q)‐hydroquinone (QH₂) couple, a prototypical organic redox system known to provide fast and reversible proton‐coupled electron‐transfer reactions, are deterministically mesostructured via a colloidal templating strategy to provide good ion and electron transport pathways, enabling a high rate performance. Specifically, a conducting polymer, polypyrrole (PPy), is functionalized with a pseudocapacitive material, a Q/QH₂‐containing catechol derivative, by noncovalent interactions. The mesostructure of this hybrid material is formed into an ordered 3D porous structure by a polystyrene colloidal crystal template‐assisted electrosynthesis. The catechol derivative is sufficiently bound to the PPy through noncovalent interactions to provide a volumetric capacitance as high as ≈130 F cm^?3 and a capacitance retention of ≈75% over 10 000 charging/discharging cycles. When compared with a randomly structured electrode, the deterministically structured electrode exhibits an improved rate performance due to the mesostructure facilitated electron and ion transport.     

A Flexible Dual‐Ion Battery Based on Sodium‐Ion Quasi‐Solid‐State Electrolyte with Long Cycling Life

Sodium‐based dual‐ion batteries (SDIBs) have attracted much attention for their advantages of high operating voltage, environmental friendliness, and especially low cost. However, the electrochemical performances of the reported SDIBs are still unsatisfied due to the decomposition problem of traditional liquid electrolyte under high working voltage. Development of quasi‐solid‐state electrolytes (QSSEs) with excellent electrochemical stability at high voltage is a possible means to improve their properties. In this work, a flexible SDIB based on a QSSE, consisting of poly(vinylidene ?uoride‐co‐hexa?uoropropylene) (PVDF‐HFP) three‐dimensionally cross‐linked with Al₂O₃ nanoparticles, which exhibits a porous 3D structure with dramatically enhanced ionic conductivity up to ≈1.3 × 10^?3 S cm^?1, facilitating fast ionic migration of both anions and cations, is reported. This quasi‐state SDIB exhibits a high specific capacity of 96.8 mAh g^?1 at a current rate of 5 C and excellent cycling stability with a capacity retention of 97.5% after 600 cycles at 5 C, which is the best performance of the SDIBs. Moreover, excellent flexibility and a wide working temperature range (?20 to 70 °C) have been realized for this battery, suggesting its potential for high‐performance flexible energy storage applications.     

In‐Plane Assembled Orthorhombic Nb2O5 Nanorod Films with High‐Rate Li+ Intercalation for High‐Performance Flexible Li‐Ion Capacitors

Organic hybrid supercapacitors that consist of a battery electrode and a capacitive electrode show greatly improved energy density, but their power density is generally limited by the poor rate capability of battery‐type electrodes. In addition, flexible organic hybrid supercapacitors are rarely reported. To address the above issues, herein an in‐plane assembled orthorhombic Nb₂O₅ nanorod film anode with high‐rate Li⁺ intercalation to develop a flexible Li‐ion hybrid capacitor (LIC) is reported. The binder‐/additive‐free film exhibits excellent rate capability (≈73% capacity retention with the rate increased from 0.5 to 20 C) and good cycling stability (>2500 times). Kinetic analyses reveal that the high rate performance is mainly attributed to the excellent in‐plane assembly of interconnected single‐crystalline Nb₂O₅ nanorods on the current collector, ensuring fast electron transport, facile Li‐ion migration in the porous film, and greatly reduced ion‐diffusion length. Using such a Nb₂O₅ film as anode and commercial activated carbon as cathode, a flexible LIC is designed. It delivers both high gravimetric and high volumetric energy/power densities (≈95.55 Wh kg^?1/5350.9 W kg^?1; 6.7 mW h cm^?3/374.63 mW cm^?3), surpassing previous typical Li‐intercalation electrode‐based LICs. Furthermore, this LIC device still keeps good electrochemical attributes even under serious bending states (30°–180°).     

Double Stimuli‐Responsive Isoporous Membranes via Post‐Modification of pH‐Sensitive Self‐Assembled Diblock Copolymer Membranes

Double stimuli‐responsive membranes are prepared by modification of pH‐sensitive integral asymmetric polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) diblock copolymer membranes with temperature‐responsive poly(N‐isopropylacrylamide) (pNIPAM) by a surface linking reaction. PS‐b‐P4VP membranes are first functionalized with a mild mussel‐inspired polydopamine coating and then reacted via Michael addition with an amine‐terminated pNIPAM‐NH₂ under slightly basic conditions. The membranes are thoroughly characterized by nuclear magnetic resonance (¹H‐NMR), Fourier transform infrared spectroscopy and X‐ray‐induced photoelectron spectroscopy. Additionally dynamic contact angle measurements are performed comparing the sinking rate of water droplets at different temperatures. The pH‐ and thermo‐double sensitivities of the modified membranes are proven by determining the water flux under different temperature and pH conditions.     

Ion‐Current Rectification in Nanopores and Nanotubes with Broken Symmetry

This article focuses on ion transport through nanoporous systems with special emphasis on rectification phenomena. The effect of ion‐current rectification is observed as asymmetric current–voltage (I–V) curves, with the current recorded for one voltage polarity higher than the current recorded for the same absolute value of voltage of opposite polarity. This diode‐like I–V curve indicates that there is a preferential direction for ion flow. Experimental evidence that ion‐current rectification is inherent to asymmetric, e.g., tapered, nanoporous systems with excess surface charge is provided and discussed. The fabrication and operation of asymmetric polymer nanopores, gold nanotubes, glass nanocapillaries, and silicon nanopores are presented. The possibility of tuning the direction and extent of rectification is discussed in detail. Theoretical models that have been developed to explain the ion‐current rectification effect are also presented.     

Nano Spray‐Dried Block Copolymer Nanoparticles and Their Transformation into Hybrid and Inorganic Nanoparticles

A novel combination of block copolymer (BCP) nano spray‐drying (NSD), solvent annealing, and selective metal oxide growth is utilized to create functional polymer nanoparticles, polymer‐metal‐oxide hybrid nanoparticles, and templated metal oxide nanoparticles with tunable composition, internal morphology, and porosity. NSD of BCPs from chloroform and toluene solutions results in porous and nonporous nanoparticles, respectively, with various degrees of phase separation. Further tuning of the nanoparticle internal morphology is performed by solvent annealing the spray‐dried particles with judicious choice of the nonsolvent dispersion medium and the surfactant, yielding assembly of both blocks at the surface of the nanoparticles. Finally, ZnO and Al₂O₃ are grown inside the polar blocks of phase‐ordered nanoparticles using a sequential infiltration synthesis method, in a post‐assembly process, resulting in hybrid BCP‐ZnO particles and BCP‐templated Al₂O₃ nanoparticles, as demonstrated by scanning transmission electron microscopy tomography. These structure engineering methods open new ways to direct and template functional nanoparticles.     

Optoelectronic In‐Ga‐Zn‐O Memtransistors for Artificial Vision System

An artificial vision system that can simulate the visual functions of human eyes is required for biological robots. Here, In‐Ga‐Zn‐O memtransistors using a naturally oxidized Al₂O₃ and an ion gel as a common gate stacking dielectric is proposed. Positive charge trapping in the Al₂O₃ layer can be induced by modulating the gate voltage, which causes the back sweep subthreshold swing (SS) of the device to break the physical limit (≥60 mV per decade at room temperature), and the minimum SS is as low as 26.4 mV per decade. In addition, photogenerated charges in the device are captured at the In‐Ga‐Zn‐O channel/ion gel interface due to the superposition of the additional electric field generated by positive charges trapped in the Al₂O₃ layer and the external gate electric field. Thus, persistent photoconductivity is observed in the In‐Ga‐Zn‐O memtransistors. Finally, by employing the optoelectronic memristive functions of In‐Ga‐Zn‐O memtransistors, an artificial vision system based on artificial retinal array (ARA) and artificial neural network is proposed. An obvious improvement in the recognition rate and efficiency with the use of ARA for the image preprocessing is achieved. This study provides a new strategy for the realization of artificial vision systems.     

Polypyrrole, α-Fe2O3 and their hybrid nanocomposite sensor: An impedance spectroscopy study

Polypyrrole (PPy), α-Fe₂O₃ and their hybrid nanocomposites have been successfully prepared using chemical polymerization, sol–gel and solid state synthesis method respectively. Films of PPy, α-Fe₂O₃ and PPy/α-Fe₂O₃ nanocomposites were deposited on glass substrates using spin coating technique and characterized using FTIR, XPS, FESEM, TEM techniques as well as their gas sensing performance were studied towards NO₂ gas. FTIR and XPS study confirms the formation of PPy, α-Fe₂O₃ and PPy/α-Fe₂O₃ hybrid nanocomposites. FESEM studies revealed that, the films consists of porous granular type of morphology. TEM analysis revealed that the hybrid composite is in nano range. Impedance spectroscopy studies in presence of air and after exposure of NO₂ gas were carried out on PPy, α-Fe₂O₃ and PPy/α-Fe₂O₃ hybrid nanocomposite films in the frequency range of 20 Hz–10 MHz. Impedance spectroscopy results demonstrate that, the impedance is mainly contributed by the potential barrier at grain boundaries of the films. With the help of impedance spectroscopy results, sensing mechanism between PPy, α-Fe₂O₃ and PPy/α-Fe₂O₃ hybrid nanocomposite films and NO₂ gas molecules was studied and explored.     

Flexible Films Derived from Electrospun Carbon Nanofibers Incorporated with Co3O4 Hollow Nanoparticles as Self‐Supported Electrodes for Electrochemical Capacitors

Flexible porous films are prepared from electrospun carbon nanofibers (CNFs) embedded with Co₃O₄ hollow nanoparticles (NPs) and are directly applied as self‐supported electrodes for high‐performance electrochemical capacitors. Uniform Co₃O₄ hollow NPs are well dispersed and/or embedded into each CNF with desirable electrical conductivity. These Co₃O₄‐CNFs intercross each other and form 3D hierarchical porous hybrid films. Benefiting from intriguing structural features, the unique binder‐free Co₃O₄ hollow NPs/CNF hybrid film electrodes exhibit high specific capacitance (SC), excellent rate capability and cycling stability. As an example, the flexible hybrid film with loading of 35.9 wt% Co₃O₄ delivers a SC of 556 F g^?1 at a current density of 1 A g^?1, and 403 F g^?1 even at a very high current density of 12 A g^?1. Remarkably, almost no decay in SC is found after continuous charge/discharge cycling for 2000 cycles at 4 A g^?1. This exceptional electrochemical performance makes such novel self‐supported Co₃O₄‐CNFs hybrid films attractive for high‐performance electrochemical capacitors.     

Superassembled Biocatalytic Porous Framework Micromotors with Reversible and Sensitive pH‐Speed Regulation at Ultralow Physiological H2O2 Concentration

Synthetic nano/micromotors are a burgeoning class of materials with vast promise for applications ranging from environmental remediation to nanomedicine. The motility of these motors is generally controlled by the concentration of accessible fuel, and therefore, engineering speed‐regulation mechanisms, particularly using biological triggers, remains a continuing challenge. Here, control over the movement of superassembled porous framework micromotors via a reversible, biological‐relevant pH‐responsive regulatory mechanism is demonstrated. Succinylated β‐lactoglobulin and catalase are superassembled in porous framework particles, where the β‐lactoglobulin is permeable at neutral pH. This permeability allows the fuel (H₂O₂) to access catalase, leading to autonomous movement of the micromotors. However, at mild acidic pH, succinylated β‐lactoglobulin undergoes a reversible gelation process, preventing the access of fuel into the micromotors where the catalase resides. To one's knowledge, this study represents the first example of chemically driven motors with rapid, reversible pH‐responsive motility. Furthermore, the porous framework significantly enhances the biocatalytic activity of catalase, allowing ultralow H₂O₂ concentrations to be exploited at physiological conditions. It is envisioned that the simultaneous exploitation of pH and chemical potential of such nanosystems could have potential applications as stimulus‐responsive drug delivery vehicles that benefit from the complex biological environment.     

Effect of Fluoride‐based Plasma Treatment on the Performance of AlGaN/GaN MISHFET

This paper demonstrates the effect of fluoride‐based plasma treatment on the performance of Al₂O₃/AlGaN/GaN metal‐insulator‐semiconductor heterostructure field effect transistors (MISHFETs) with a T‐shaped gate length of 0.20 μm. For the fabrication of the MISHFET, an Al₂O₃ layer as a gate dielectric was deposited using atomic layer deposition, which greatly decreases the gate leakage current, followed by the deposition of the silicon nitride layer. The silicon nitride layer on the gate foot region was then selectively removed through a reactive ion etching technique using CF₄ plasma. The etching process was continued for a longer period of time even after the complete removal of the silicon nitride layer to expose the Al₂O₃ gate dielectric layer to the plasma environment. The thickness of the Al₂O₃ gate dielectric layer was slowly reduced during the plasma exposure. Through this plasma treatment, the device exhibited a threshold voltage shift of 3.1 V in the positive direction, an increase of 50 mS/mm in trans conductance, a degraded off‐state performance and a larger gate leakage current compared with that of the reference device without a plasma treatment.     

A Bio‐inspired Potassium and pH Responsive Double‐gated Nanochannel

Bio‐inspired nanochannels have emerged as an interface to mimic the functionalities of biological nanochannels. One remaining challenge is to develop double‐gated nanochannels with dual response, which can regulate the ion transport direction by alternately opening and closing the two gates. In this work, a bio‐inspired potassium and pH responsive double‐gated nanosystem is presented, constructed through immobilizing C‐quadruplex and G‐quadruplex DNA molecules onto the top and bottom tip side of a cigar‐shaped nanochannel, respectively. It is demonstrated that the two gates of the nanochannel can be opened and closed alternately/simultaneously. This phenomenon results from the attached DNA conformational transition caused by adjusting the concentrations of potassium ion and proton. This design is believed to be the first example of dual‐responsive double‐gated nanosystem, and paves a new way to investigate more intelligent bio‐inspired nanofluidic system.     

Integrating Ionic Gate and Rectifier Within One Solid‐State Nanopore via Modification with Dual‐Responsive Copolymer Brushes

A dual‐functional nanofluidic device is demonstrated that integrates the ionic gate and the ionic rectifier within one solid‐state nanopore. The functionalities are realized by fabricating temperature‐ and pH‐responsive poly(N‐isopropyl acrylamide‐co‐acrylic acid) brushes onto the wall of a cone‐shaped nanopore. At ca. 25 °C, the nanopore works on a low ion conducting state. When the temperature is raised to ca. 40 °C, the nanopore switches to a high ion conducting state. The closing/opening of the nanopore results from the temperature‐triggered conformational transition of the attached copolymer brushes. Independently, in neutral and basic solutions, the conical nanopore rectifies the ionic current. While in acid solutions, no ion rectifying properties can be found. The charge properties of the copolymer brushes, combined with the asymmetrical pore geometry, render the nanopore a pH‐tunable ionic rectifier. The chemical modification strategy could be applied to incorporate other stimuli‐responsive materials for designing smart multi‐functional nanofluidic systems resembling the “live” creatures in nature.     

Multifunctional Graphene Oxide‐based Triple Stimuli‐Responsive Nanotheranostics

Construction of multifunctional stimuli‐responsive nanosystems intelligently responsive to inner physiological and/or external irradiations based on nanobiotechnology can enable the on‐demand drug release and improved diagnostic imaging to mitigate the side‐effects of anticancer drugs and enhance the diagnostic/therapeutic outcome simultaneously. Here, a triple‐functional stimuli‐responsive nanosystem based on the co‐integration of superparamagnetic Fe₃O₄ and paramagnetic MnO_x nanoparticles (NPs) onto exfoliated graphene oxide (GO) nanosheets by a novel and efficient double redox strategy (DRS) is reported. Aromatic anticancer drug molecules can interact with GO nanosheets through supramolecular π stacking to achieve high drug loading capacity and pH‐responsive drug releasing performance. The integrated MnO_x NPs can disintegrate in mild acidic and reduction environment to realize the highly efficient pH‐responsive and reduction‐triggered T₁‐weighted magnetic resonance imaging (MRI). Superparamagnetic Fe₃O₄ NPs can not only function as the T₂‐weighted contrast agents for MRI, but also response to the external magnetic field for magnetic hyperthermia against cancer. Importantly, the constructed biocompatible GO‐based nanoplatform can inhibit the metastasis of cancer cells by downregulating the expression of metastasis‐related proteins, and anticancer drug‐loaded carrier can significantly reverse the multidrug resistance (MDR) of cancer cells.