Nanostructured Network Research Articles

Robust, Flexible Thermoelectric Film for Energy Harvesting by a Simple and Eco-Friendly Method.

As for the self-supporting composite films, it is significant to develop a structural design that allows for excellent flexibility while reducing the negative effect on thermoelectric (TE) properties. Herein, a robust, flexible TE film was fabricated by in situ chemical transformation and vacuum-assisted filtration without any organic solvents involved. The performance of the films was further optimized by adjusting the Ag/Te ratio and post-treatment methods. Owing to the semi-interpenetrating nanonetwork structure formed by AgxTe nanowires and bacterial cellulose, the obtained TE film displayed a high tensile strength of ∼78.4 MPa and a high power factor of 48.9 μW m-1 K-2 at room temperature. A slight electrical conductivity decrement of the TE film in flexible test (∼2% after 1000 bending cycles) indicates an excellent flexibility. Finally, a TE bracelet was assembled to harvest body heat energy, and a steady current of ∼2.7 μA was generated when worn on the wrist indoors. This work provides a reference for the structural design and practical application of flexible TE films.

Stretchable Electrochemical Sensor Based on a Gold Nanowire and Carbon Nanotube Network for Real-Time Tracking Cell-Released H2S.

Hydrogen sulfide (H2S), as the third gas transporter in biological systems, plays a key role in the regulation of biological cells. Real-time detection of local H2S concentration in vivo is an important and challenging task. Herein, we explored a novel and facile strategy to develop a flexible and transparent H2S sensor based on gold nanowire (AuNW) and carbon nanotube (CNT) films embedded in poly(dimethylsiloxane) (PDMS) (AuNWs/CNTs/PDMS). Taking the advantage of the sandwich-like nanostructured network of AuNWs/CNTs, the prepared electrochemical sensing platform exhibited desirable electrocatalytic activity toward H2S oxidation with a wide linear range (5 nM to 24.9 μM) and a low dete ction limit (3 nM). Furthermore, thanks to the good biocompatibility and flexibility of the sensor, HeLa cells can be cultured directly on the electrode, allowing real-time monitoring of H2S released from cells under a stretched state. This work provides a versatile strategy for the construction of stretchable electrochemical sensors, which has potential applications in the study of H2S-related signal mechanotransduction and pathological processes.

The mechanism of nano-network structure formed by friction-induced pozzolanic silicate

Friction transfer film is one of the influencing factors in the evolution of the subsurface microstructure of frictional contact materials. An iron-poor friction transfer film of aluminum-based composites with silicon carbide and pozzolanic silicate particles as the reinforcing phase was investigated utilizing scanning electron microscope, focused ion beams, transmission electron microscopy and energy dispersive X-ray analysis. The results showed that the friction transfer film contained ultra-fine aluminum, nano-aluminum, broken silicon carbide and silicate particles, as well as in-situ generated andradite and gismondine, which self-assemble into a nano-network structure to support the formation of the friction transfer film. Thermodynamic calculations and high-resolution transmission electron microscopy clarified the formation mechanism of andradite and gismondine.

Zn‐Incorporated Titanium Substrates with High Antibacterial Activity and Consecutive Release of Zinc

AbstractIn this work, Zn‐incorporated titanium substrate with nano network structures was built, and its antibacterial activity against the gram positive and negative bacteria was tested. Ti plate was successively treated by hot alkaline, Zn2+ ion‐exchange, and ZnO nanoparticles deposit, where alkaline treated Ti plate (NTi), Zn2+ exchanged Ti plate (NZTi), Zn2+/ZnO incorporated Ti plate (NZZTi) were correspondingly generated. For Escherichia coli, the antibacterial percentage of NZTi and NZZTi after 24 h was 99.86 % and 99.98 %, while it was 99.95 % and 100 % for Staphylococcus aureus, respectively. The result disclosed that NZZTi have a bit better antibacterial activity than NZTi, which indicates that Zn2+ shows fabulous antibacteria activity and the presence of ZnOnps can contribute the antibacterial ability of Ti plates, which agrees with result of NZZTi‐Cup antibacterial effect. The release tests of Zn2+ after 8 days from NZZTi‐Cup disclosed that Zn‐incorporated Ti plate could consecutively release trace Zn ions.

Constructing a 3D interconnected network of Ag nanostructures for high-performance SERS detection of food coloring agents.

The design and preparation of various effective three-dimensional (3D) silver nanostructures is a frontier area of research in the field of surface-enhanced Raman scattering (SERS). This paper demonstrates a simple and novel method for the preparation of a substrate, whose surface was covered by a 3D interconnected network of Ag nanostructures, and the resulting network structure surface is free of organic contaminants. The EDS measurements confirm the metallic nature of the formed 3D Ag nanonetwork substrate. Additionally, the influence of experimental parameters on the morphology of the 3D Ag nanonetwork was also investigated, such as reaction time, hydrofluoric acid concentration, silver nitrate concentration and sodium citrate concentration. The 3D Ag nanonetwork has good uniformity. Importantly, the 3D Ag nanonetwork substrate was used to accurately and reliably detect amaranth (AR) and sunset yellow (SY) in beverages, with the lowest detection limit of 3 and 0.1 μg L-1, respectively. Therefore, this substrate is expected to be a promising candidate for SERS detection and offers attractive potential for a wider range of applications.

Analysis of the Performances of a New Type of Alumina Nanocomposite Structural Material Designed for the Thermal Insulation of High-Rise Buildings

The sol-gel method is used to prepare a new nano-alumina aerogel structure and the thermal properties of this nanomaterial are investigated comprehensively using electron microscope scanning, thermal analysis, X-ray and infrared spectrometer analysis methods. It is found that the composite aerogel alumina material has a multi-level porous nano-network structure. When employed for the thermal insulation of high-rise buildings, the alumina nanocomposite aerogel material can lead to effective energy savings in winter. However, it has almost no energy-saving effect on buildings where energy is consumed for cooling in summer.

Nanonet-/fiber-structured flexible ceramic membrane enabling dielectric energy storage

Ceramics are considered intrinsically brittle at macro scale due to the lack of slip mechanism and pre-existing defects, which greatly limits their potential applications in emerging fields including wearable electronic devices and flexible display. In this contribution, we developed BiFeO₃/SiO₂ dual-networks with exceptional flexibility through a coupled electronetting/electrospun method. The hybrid nanostructured networks endow the material with high tensile strength (2.7 MPa), excellent flexibility (80% recoverable deformation), and robust fatigue resistance performance (maintain flexibility after a 1000-cyclic compress test). After <i>in-situ</i> compounded with dielectric polymer via a layer-by-layer solution casting method, the resultant three-dimensional (3D) composite film exhibits a twice higher dielectric constant (<i>ε</i>_r) than polyether imide (PEI) film. More importantly, the breakdown strength of the 3D composite film is almost the same as that of the PEI film, resulting in an enhanced energy density of ~6.0 J/cm³ and a high efficiency of 80% at 4.58 MV/cm. The unique structure, combined with the excellent balance between mechanical and dielectric properties in flexible structures, is of critical significance to the design of flexible functional ceramics and broadening their applications in wearable electric devices.

Air-Conditioned Masks Using Nanofibrous Networks for Daytime Radiative Cooling.

Face masks, as effective measures for passive air pollution control, are of fundamental importance, especially with the outbreak of emerging infectious diseases. Most existing masks are dense or thick, resulting in a lack of thermal/humidity comfort level; despite being worn tightly, they show limited PM0.3/pathogen removal. Here, we use a facile strategy to create air-conditioned masks using heterogeneous nanofibrous networks, based on an electrospinning/netting technique. Manipulation of the phase separation and self-assembly of charged jet/droplets by control of humidity-induced double diffusion and Taylor cone instability allows for the generation of air-conditioned masks consisting of radiative cooling wrinkled nanofibers and 2D nanostructured networks. Our masks show desirable microenvironment with high-efficiency PM0.3 removal (>99.988%), low air resistance (0.07% of atmospheric pressure), and remarkable radiative cooling capacity (∼2.8 °C temperature and ∼10% humidity drop), making high-performance filtration and temperature/humidity management "always online". This work should make possible the development of high-performance, energy-saving, and scalable fiber textiles for various applications.

Electrochemical deposition of Ppy/Dex/ECM coatings and their regulation on cellular responses through electrical controlled drug release

Bone tissue engineering requires a material that can simultaneously promote osteogenic differentiation and anti-inflammatory effects at specific times in response to a series of problems after bone implantation. In this study, the porous network-like titanium matrix was constructed and polypyrrole/dexamethasone (Ppy/Dex) composite coatings with three-dimensional nano-network structure were prepared by electrochemical deposition. The biocompatibility of the composite coatings was further improved by the composite of the extracellular matrix (ECM). The Ppy/Dex/ECM composite coatings released Dex by changing the redox state of Ppy under the electrical stimulation of negative pulses, achieving a drug release controlled by electric field. In terms of osteogenic differentiation, the Ppy/Dex/ECM composite coatings exhibited the best osteogenic activity under electrical controlled release, indicating the synergistic effect of Dex and ECM on osteogenic differentiation. In terms of anti-inflammatory properties, ECM exhibited simultaneous inhibition of both pro- and anti-inflammatory process, while Dex demonstrated significant promotion of anti-inflammatory processes. In this work, the effect of electrical controlled drug release on osteogenic differentiation and inflammation in the ECM cell microenvironment was achieved by preparing Ppy/Dex/ECM composite coatings, which is of great significance for bone tissue engineering and regenerative medicine.

Combining thin-film microextraction and surface enhanced Raman spectroscopy to sensitively detect thiram based on 3D silver nanonetworks

By coupling thin-film microextraction (TFME) with surface enhanced Raman scattering (SERS), a facile method was developed for the determination of thiram in the complex matrix (orange juice or grape peel). The substrate of TFME was made by self-assembling silver sol on the silicon wafer to form a three-dimensional (3D) silver nanonetwork structure, without adding any template, which was used for TFME and SERS detection, respectively. The substrate exhibits high reproducibility with a relative standard deviation of about 7.32 % in spot and spot SERS intensity. The SERS signal intensity at a shift of 1384 cm−1 and the thiram concentration showed good linearity in the range of 0.01–5 µg/L and the linear correlation coefficient was 0.9912. The detection limit for thiram was found to be 0.01 µg/L. The TFME-SERS method was applied for the determination of thiram in fruit juice and the results were obtained very well. Therefore, this method is expected to play a role in the detection of trace pollutants.

Poly(p-phenylene vinylene) incorporated into carbon nanostructures

Composites of poly(p-phenylene vinylene) (PPV) and different carbon nanostructures, such as fullerene C60, multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes (SWCNTs), graphene oxide (GO), and graphene nanoplatelets (GNPLs), were produced by Wittig’s soluble precursor procedure in solutions containing dispersed particles of carbon nanomaterials. These composites were investigated using infrared and Raman spectroscopy, scanning and transmission electron microscopy, thermogravimetry analysis, adsorption/desorption of N2 measurement, and electrochemistry. Composites are produced in the form of nanostructural porous materials. A significant increase in the BET (Brunauer–Emmett–Teller) surface is observed for composites in comparison to unmodified PPV. The highest BET surface area of 125 m2·g−1 was obtained for the PPV/SWCNT composite. Compared to pristine PPV, composites also exhibit higher thermal stability. The effect of the content of composite components on their electrochemical properties was also investigated. The electronic interaction between components of composite significantly affects their electrochemical properties, particularly in the case of oxidation processes. PPV incorporated into network of carbon nanostructures exhibit two well separated oxidation steps. The carbon component is responsible for the shift of the PPV reduction and oxidation processes toward less negative and less positive potentials, respectively, significantly lowering the energy of the band gap.Graphical abstract

Hollow porous Co3O4/NC@rGO derived from reuleaux tetrahedral ZIF-67 as a promising anode material for Li-ion batteries

Constructing advanced nanostructures and combining various active materials are effective strategies to obtain high-performance anode materials for lithium-ion batteries (LIBs). Herein, we report a surface-coordinated polymerization method to synthesize ZIF-67 nanoparticles with a reuleaux tetrahedron morphology, and combine the electrostatic adsorption method and heat treatment, nitrogen-doped hollow porous Co3O4 (HP-Co3O4/NC) nanoparticles were anchored on reduced graphene oxide (rGO) to obtain HP-Co3O4/NC@rGO composites. This deliberate structural design can significantly improve the electrochemical performance of lithium (Li) storage. When applied as an anode material in LIBs, HP-Co3O4/NC@rGO nanocomposite renders a reversible capacity of 809 mAh g−1 after 200 charge/discharge cycles at a current density of 1000 mA g−1. The excellent electrochemical performance is mainly attributed to the synergistic effect of the hollow nanostructure and graphene network. A hollow nanostructure can provide abundant active sites and enhance structural stability. As a conductive network, graphene tightly wraps Co3O4, which can not only increase the electronic and ionic transport but also alleviates the volumetric changes of Co3O4 during the charge/discharge process, thereby improving the rate performance and cyclic stability.

Fabrication of charcoal-nickel (II)-poly(acrylic acid) nanocomposite hydrogels for photodegradation of rhodamine B under direct sunlight irradiation

The fabricated hydrogels charcoal-nickel-poly(acrylic acid) (char-Ni-PAA) synthesized by a free-radical polymerization technique was used for rhodamine B dye degradation under direct sunlight irradiation. Different Ni ions compositions were characterized using ATR-FTIR, TGA, EDAX, and SEM techniques. The shift and intensity change of the peaks in the ATR-FTIR spectrum indicated the binding of Ni ions and charcoal onto PAA chains in the hydrogel. EDAX also showed the incorporation of Ni ions into the composites. TGA results revealed the higher thermal stability of the nanocomposite hydrogel. SEM images revealed porous network nanostructures in the composite hydrogels. Ni ions adhered with charcoal provide an environment with high electron mobility to degrade targeted dye molecules under sunlight irradiation. In addition, different surface functional groups of charcoal enhanced the dye adsorption capacity of the composite hydrogel. Charcoal-nickel-poly(acrylic acid) hydrogel containing 1 g Ni ions showed a maximum of 75.56% rhodamine B degradation under direct sunlight irradiation for 8 h in an open atmosphere at a neutral pH solution. The photocatalytic capability of dispersed Ni ions and enhanced dye adsorption capacity of charcoal improved the photodegradation activity of the fabricated char-Ni-PAA nanocomposite hydrogels. The synthesized hydrogels containing a higher amount of Ni ions also showed promising antibacterial activity towards two microorganisms, B. cereus, and P. aeruginosa, as gram-positive and gram-negative bacteria under visible light illumination. The higher photodegradation activity and antibacterial properties of the synthesized char-Ni-PAA nanocomposite hydrogels demonstrate their efficacy in the treatment of textile wastewater under direct sunlight irradiation.

Double-interpenetrating nanostructured networks of marine polysaccharides possessing properties comparable to synthetic polymers

Sustainable circular economy requires materials that possess a property profile comparable to synthetic polymers and, additionally, processing and sourcing of raw materials that have a small environmental footprint. Here, we present a paradigm for processing marine biopolymers into materials that possess both elastic and plastic behavior within a single system involving a double-interpenetrating polymer network comprising the elastic phase of dynamic physical cross-links and stress-dissipating ionically cross-linked domains. As a proof of principle, films possessing more than twofold higher elastic modulus, ultimate tensile strength, and yield stress than those of polylactic acid were realized by blending two water-soluble marine polysaccharides, namely alginic acid (Alg) with physically cross-linkable carboxylated agarose (CA) followed by ionic cross-linking with a divalent cation. Dried CAAlg films showed homogeneous nano-micro-scale domains, with yield stress and size of the domains scaling inversely with calcium concentration. Through surface activation/cross-linking using calcium, CAAlg films could be further processed using wet bonding to yield laminated structures with interfacial failure loads (13.2 ± 0.81 N) similar to the ultimate loads of unlaminated films (10.09 ± 1.47 N). Toward the engineering of wood-marine biopolymer composites, an array of lines of CAAlg were printed on wood veneers (panels), dried, and then bonded following activation with calcium to yield fully bonded wood two-ply laminate. The system presented herein provides a blueprint for the adoption of marine algae-derived polysaccharides in the development of sustainable high-performance materials.

Green synthesis, characterization of SnO2 3D microbars with surface 2D nanostructures and evaluation of electrical properties of PMMA-SnO2 hybrid nanocomposites

SnO2 3D microbars (L ∼ 10 µm × B ∼ 1 µm x T ∼ 1 µm) distributed with 2D nanostructures (D ∼ 20 - 50 nm x l ∼ few nm) were synthesized by green approach using Plectranthus amboinicus plant extract. Effect of calcination treatments on the morphological changes of both primary microbars and secondary nanostructures were investigated. Dense corrugated networks of secondary particles were observed in the freshly synthesized material. When subjected to a temperature of 200 °C the densely covered particles on the surface, separate to distinct nanostructures. On further rise of temperature up to 400 °C, nanostructure networks break to complete individual nanoparticles, along with mild fragmental damage of particles. Presence of functional groups and bandgap energy levels of 3D/2D SnO2 material was studied using Fourier Transform Infra-Red (FTIR) and UV-Visible (UV-Vis) spectroscopy, respectively. Bandgap energy level of 3.05 eV was observed at 400 °C and 3.06 eV was observed at other two conditions. Structural, morphological and elemental characterization of the material was studied by X-ray diffraction (XRD), Field Emission-Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-ray Analysis (EDAX) spectroscopy. Using Polymethyl methacrylate (PMMA) as matrix and 3D/2D SnO2 as the dispersed filler phase nanocomposite films were prepared. Effect of 3D/2D SnO2 loading on the alternating current (AC) conductivity of the nanocomposite films was investigated. Effect of frequency on AC conductivity, permittivity and loss factor of the composites were reported. The composites exhibited frequency dependent conductivity at lower frequencies and frequency independent conductivity at higher frequencies.

Cyanogel-Induced Synthesis of RuPd Alloy Networks for High-Efficiency Formic Acid Oxidation

For direct formic acid fuel cells (DFAFC), palladium (Pd)-based alloy catalysts with competitive morphology and elemental composition are essential to boost the performance of the formic acid oxidation reaction (FAOR) in the anode zone. Herein, we design and synthesize RuPdx alloy nano-network structures (ANs) via the facile wet-chemical reduction of Pd-Ru cyanogel (Pdx [Ru(CN)6]y·aH2O) as an effective electrocatalyst for the FAOR. The formation of Pd-Ru cyanogel depends on the facile coordination of K2PdCl4 and K3 [Ru(CN)6]. The unique structure of cyanogel ensures the presentation of a three-dimensional mesoporous morphology and the homogeneity of the elemental components. The as-prepared RuPd3 ANs exhibit good electrocatalytic activity and stability for the FAOR. Notably, the RuPd3 ANs achieve a mass-specific activity of 2068.4 mA mg−1 in FAOR, which shows an improvement of approximately 16.9 times compared to Pd black. Such a competitive FAOR performance of RuPd3 ANs can be attributed to the advantages of structure and composition, which facilitate the exposure of more active sites, accelerate mass/electron transfer rates, and promote gas escape from the catalyst layer, as well as enhance chemical stability.

Non-Covalently Associated Streptavidin Multi-Arm Nanohubs Exhibit Mechanical and Thermal Stability in Cross-Linked Protein-Network Materials.

Constructing protein-network materials that exhibit physicochemical and mechanical properties of individual protein constituents requires molecular cross-linkers with specificity and stability. A well-known example involves specific chemical fusion of a four-arm polyethylene glycol (tetra-PEG) to desired proteins with secondary cross-linkers. However, it is necessary to investigate tetra-PEG-like biomolecular cross-linkers that are genetically fused to the proteins, simplifying synthesis by removing additional conjugation and purification steps. Non-covalently, self-associating, streptavidin homotetramer is a viable, biomolecular alternative to tetra-PEG. Here, a multi-arm streptavidin design is characterized as a protein-network material platform using various secondary, biomolecular cross-linkers, such as high-affinity physical (i.e., non-covalent), transient physical, spontaneous chemical (i.e., covalent), or stimuli-induced chemical cross-linkers. Stimuli-induced, chemical cross-linkers fused to multi-arm streptavidin nanohubs provide sufficient diffusion prior to initiating permanent covalent bonds, allowing proper characterization of streptavidin nanohubs. Surprisingly, non-covalently associated streptavidin nanohubs exhibit extreme stability, which translates into material properties that resemble hydrogels formed by chemical bonds even at high temperatures. Therefore, this study not only establishes that the streptavidin nanohub is an ideal multi-arm biopolymer precursor but also provides valuable guidance for designing self-assembling nanostructured molecular networks that can properly harness the extraordinary properties of protein-based building blocks.

Space-confined synthesis of a novel Ge@HCS-rGO yolk-shell nanostructure as anode materials for enhanced lithium storage

Germanium (Ge) is considered as a promising anode material due to its high lithium storage capability. However, the huge volume change during cycling cause serious structural degradation and poor cycling stability. Yolk-shell nanostructure design is an effective way to solve such problems for electrode materials such as Ge and Si. Herein, we proposed the design and synthesis of a novel Ge@hollow carbon sphere-reduced graphene oxide (Ge@HCS-rGO) yolk-shell nanostructure as anode via a space-confined strategy for the first time. Rational void space is engineered in the yolk-shell structure, offering a buffer zone for adapting the volume expansion of Ge core particles with protective carbon shells upon lithiation, while the 3D conductive network with hierarchical pores provides fast electron and Li-ion transport channels. Benefiting from the unique structural dual-protection of 3D conductive network and yolk-shell nanostructure, the as-synthesized Ge@HCS-rGO anode exhibits high discharge capacity (2117.3 mA h g−1 at 0.2 C), enhanced cycling stability (958.6 mA h g−1 up to 200 cycles at 0.2 C) and excellent rate capability (1010.0 mA h g−1 at 4 C). The electrochemical performance of Ge@HCS-rGO yolk-shell anode is greatly improved compared with bare Ge and Ge@HCS anode, suggesting its great potential to develop high performance electrode materials with large volume expansion.

Structural and Elastic Properties of Empty-Pore Metalattices Extracted via Nondestructive Coherent Extreme UV Scatterometry and Electron Tomography.

Semiconductor metalattices consisting of a linked network of three-dimensional nanostructures with periodicities on a length scale <100 nm can enable tailored functional properties due to their complex nanostructuring. For example, by controlling both the porosity and pore size, thermal transport in these phononic metalattices can be tuned, making them promising candidates for efficient thermoelectrics or thermal rectifiers. Thus, the ability to characterize the porosity, and other physical properties, of metalattices is critical but challenging, due to their nanoscale structure and thickness. To date, only metalattices with high porosities, close to the close-packing fraction of hard spheres, have been studied experimentally. Here, we characterize the porosity, thickness, and elastic properties of a low-porosity, empty-pore silicon metalattice film (∼500 nm thickness) with periodic spherical pores (∼tens of nanometers), for the first time. We use laser-driven nanoscale surface acoustic waves probed by extreme ultraviolet scatterometry to nondestructively measure the acoustic dispersion in these thin silicon metalattice layers. By comparing the data to finite element models of the metalattice sample, we can extract Young's modulus and porosity. Moreover, by controlling the acoustic wave penetration depth, we can also determine the metalattice layer thickness and verify the substrate properties. Additionally, we utilize electron tomography images of the metalattice to verify the geometry and validate the porosity extracted from scatterometry. These advanced characterization techniques are critical for informed and iterative fabrication of energy-efficient devices based on nanostructured metamaterials.

Hydroxide films on mica form charge-stabilized microphases that circumvent nucleation barriers.

Crystal nucleation is facilitated by transient, nanoscale fluctuations that are extraordinarily difficult to observe. Here, we use high-speed atomic force microscopy to directly observe the growth of an aluminum hydroxide film from an aqueous solution and characterize the dynamically fluctuating nanostructures that precede its formation. Nanoscale cluster distributions and fluctuation dynamics show many similarities to the predictions of classical nucleation theory, but the cluster energy landscape deviates from classical expectations. Kinetic Monte Carlo simulations show that these deviations can arise from electrostatic interactions between the clusters and the underlying substrate, which drive microphase separation to create a nanostructured surface phase. This phase can evolve seamlessly from a low-coverage state of fluctuating clusters into a high-coverage nanostructured network, allowing the film to grow without having to overcome classical nucleation barriers.