Porous Nanotubes Research Articles

Electrocatalytic production of ammonia: Biomimetic electrode–electrolyte design for efficient electrocatalytic nitrogen fixation under ambient conditions

Electrocatalytic nitrogen reduction offers a vital approach for nitrogen fixation in a green and sustainable way, but the low solubility of nitrogen and the competitive hydrogen evolution reaction still impede its further development. Inspired by the structure of gas-trapping hydrophobic hair on a subaquatic spider and the function of hemocyanin in its blood, in the present work, an aerophilic-hydrophilic heterostructured electrode is constructed by using aerophilic ultrathin porous Bi5O7I nanotubes and hydrophilic carbon spheres. Besides, the electrolyte is functionalized with suspended ultrathin porous Bi5O7I nanotubes. The Faradaic efficiency is increased from 5.19 % to 13.42 %, and the ammonia yield is boosted from 7.96 to 31.46 mg h−1m-2 by the new way at -0.4 V versus reversible hydrogen electrode under ambient conditions. Furthermore, the highest yield rate of 85.45 mg h−1 m-2 is achieved with a configured flow cell. This work presents a promising biomimetic strategy to boost electrocatalytic N2 fixation proceed from electrode and electrolyte.

Porous Silica Nanotube Thin Films as Thermally Insulating Barrier Coatings

The fabrication and examination of a porous silica thin film, potentially for use as an insulating thin film, were investigated. A vertically aligned carbon nanotube (CNT) forest, created by chemical vapor deposition (CVD), was used as scaffolding to construct the porous film. Silicon was deposited on the CNT forest using low-pressure CVD (LPCVD) and then oxidized to remove the CNTs and convert the silicon to silica for electrical or thermal passivation (e.g., thermal barrier). Thermal conductivity was determined using a 1D heat-transfer analysis that equated radiative heat loss in a vacuum with conduction through the substrate and thin film stack. A comparison of the surface temperature differences between a sample film and a reference of comparable thermal resistance enabled determination of the increase in the thermal resistance and of the thermal conductivity of the films. For film thicknesses of approximately 55 μm, the cross-plane thermal conductivity was found to be 0.054–0.071 W m–1 K–1 over 378–422 K. This thermal conductivity value is in the range of other silica aerogels and consistent with the low gravimetric density of 0.15 g cm–3 for the samples. The film is also relatively smooth and flat, with an average arithmetic mean roughness of 1.04 μm.

Torsional vibration of the porous nanotube with an arbitrary cross-section based on couple stress theory under magnetic field

This article presented a solution for torsion vibration a nanotube made of pores material. Based on the porosity distribution, the material properties are assumed to vary according to a function along radius of nanotube. Moreover, the cross-section area of nanotube varied in the longitudinal direction by nonlinear function. As for the torque effect of the axial magnetic field, the well-known Maxwell’s relation is used. Couple stress theory is employed to study the influence of small-scale on torsional vibration of nanotube. The Navier equation and boundary conditions of the size-dependent porous nanotube were derived by the Hamilton principle. These equations were solved by employing the generalized differential quadrature method. Comparison between the results of the present work with the other paper reveals the accuracy of this study. To the best of authors’ knowledge, so far all previous torsional vibration of nanotube address the case of ignoring porosity. The novelty of this work is to present a solution by taking into account the existence of porosity. Finally, numerical results are presented to study the small scale effect and porosity on the frequency of the porous nanotube.

Arrays of Ni/Co Nanoparticles within a Nanostructured Silicon Host

Herein, nanostructured silicon is fabricated with two different embedded magnetic nanostructures (Ni/Co) to exploit the magnetic properties of both metals and discern the behavior of the exchange coupling between the two—especially with respect to their volume ratio. A variation of the size as well as the volume ratio of the two metals modifies the exchange coupling and thus the energy product. Two templates are utilized: one involves the use of porous silicon (PSi) and the other entails porous silicon nanotubes (SiNTs). In the case of Psi, the bimetallic structures (Ni/Co) are electrodeposited, whereas in the case of SiNTs, Co is chemically grown within the tubes followed by the deposition of Ni on the outside. The magnetic properties of the systems strongly depend on the geometry of the deposits, on the volume ratio of the two metals, as well as on the proximity of the deposits. If the distance is small enough magnetic exchange coupling is present. Due to their size and the coupling of the bimetallic structures, the switching behavior of the hysteresis can be varied. Ultimately, nanocomposites with an energy product as high as possible is achieved to give rise to applications as permanent nanomagnets.

1D bamboo-like N-doped carbon nanotubes with encapsulated iron-based nanoparticles as an advanced Zn-air battery cathode electrocatalyst

Developing low-cost nonprecious metal catalysts with excellent activity and high durability for oxygen reduction reaction (ORR) is greatly imperative but challenging. Here, a high-performance ORR catalyst is designed based on in-situ grown bamboo-like N-doped carbon nanotubes with encapsulated Fe-based nanoparticles (Fe@B-NCNTs). The architecture of the 1D hierarchical porous nanotubes, large surface area with abundant defects and active sites, and strong coupling interactions between the enclosed metal-cluster core and the N-doped graphitic carbon shell synergistically enhance the electrocatalytic activity. As a result, Fe@B-NCNTs exhibit a more positive half-wave potential (0.898 V vs. the reversible hydrogen electrode, RHE), higher electrochemical stability and more superior resistance to methanol crossover than those of Pt/C in an alkaline electrolyte. Interestingly, when acting as a cathode electrocatalyst for a primary Zn-air battery (ZAB), Fe@B-NCNTs display a peak power density of ∼147 mW cm−2 and a first-class specific energy density of ∼921 Wh kgZn−1 at a discharge current density of 20 mA cm−2. Moreover, a proof-of-concept solid-state ZAB with bendable ability demonstrates the application potential in portable and wearable electronic devices.

Controllable synthesis of hollow porous silica nanotubes/CuS nanoplatform for targeted chemo-photothermal therapy

The design and synthesis of multifunctional nanocarriers for efficient synergistic cancer therapy have drawn great research interests in recent years. In this work, a nanoplatform for chemo-photothermal therapy with targeting ligand was developed. Hollow porous structured silica nanotubes (SNTs) with controllable lengths decorated with CuS nanoparticles (NPs) on the surface as photothermal agents were prepared and further conjugated with lactobionic acid groups as a cancer cell target. SNTs with average lengths of 40, 55 and 150 nm were obtained and further functionalized as drug carriers. The smallest bifunctional SNTs with targeting groups show good biocompatibility and highest cellular uptake for HepG2 cells. The release of doxorubicin hydrochloride (DOX) from the SNTs was dependent on the pH of the buffer solution and 808-nm near infrared (NIR) light irradiation. The integration of photothermal therapy (PTT) of CuS NPs and chemotherapy of anticancer drug leads to a better tumor inhibition effect than the individual therapy alone in vitro and in vivo. These results demonstrate potential applications of the nanocomposites as vector for efficient chemo-photothermal therapy.

Fabrication and characterization of Ni modified TiO2 electrode as anode material for direct methanol fuel cell

Highly ordered porous titanium dioxide nanotube (TiO2-NT) surfaces were prepared with anodization method to obtain a larger specific surface area that plays a very important role in methanol oxidation. In this regard, optimum conditions such as various anodization voltages and times were determined. The largest surface area of TiO2 occurred at anodization voltage and time of 60 V and 2 h, respectively. After obtaining the high specific surface area, very small amounts of Nickel (Ni) nanoparticles were deposited on TiO2-NT surface and their behaviors of methanol electro-oxidation were investigated by Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) methods. Characterizations of the TiO2-NT and Ni modified electrodes are exerted by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The average tube length and diameter are 36.32 μm and 93.6 nm according to SEM images. XRD results indicated the tetragonal structured anatase of TiO2 and Ni (111) and (200). While methanol oxidation peak does not observe on TiO2-NT surface, behaviors of methanol oxidation depend on the Ni content on TiO2-NT surface. Oxidation response increases by the increasing amount of Ni nano-particles in the deposits. High surface coverage (Γ) with 3.87 × 10−9 mol cm−2 and very low activation energy (Ea) with 11.0 kJ/mol are measured on Ni modified TiO2-NT with the highest Ni content. Charge transfer resistance either reduced or provided long stability and durability with the deposition of Ni on TiO2-NT. This may associate that TiO2-NTs with the large surface areas may play a significant role in the methanol oxidation efficiency. Modification of TiO2-NT surface with Ni particles is an effective plan for high-performance electrocatalysis. Besides, the strong electronic interaction between Ni and TiO2 may facilitate the adsorption of methanol through the bi-functional mechanism on the electrode surface.

Anodic hydrazine electrooxidation boosted overall water electrolysis by bifunctional porous nickel phosphide nanotubes on nickel foam.

Water electrolysis is an environmentally friendly and sustainable technique for ultra-pure hydrogen production, while expensive electrode materials and high driving voltage have seriously hindered its commercialization process. Here, Earth-abundant bifunctional porous Ni2P hollow nanotubes on nickel foam (Ni2P-HNTs/NF) electrocatalysts are synthesized through a facile self-template method and a phosphating process, which are perfectly combined with the hydrazine electrooxidation reaction (HzOR) boosted water electrolysis. Benefiting from the unique structural characteristic of open-framework and abundant step atoms, Ni2P-HNTs/NF achieves 10 mA cm-2 at 91 mV (vs. RHE) for the cathodic hydrogen evolution reaction and 18 mV (vs. RHE) for the anodic HzOR in a three electrode system, respectively. The corresponding two-electrode hydrazine electrolyzer produces 10 mA cm-2 with a total voltage of only 152 mV for ultra-pure hydrogen production, highlighting a cost-effective and energy-saving water electrolysis mode.

In situ formation of porous LiCuVO4/LiVO3/C nanotubes as a high-capacity anode material for lithium ion batteries

LiCuVO4/LiVO3/C porous nanotubes were fabricated by an efficient electrospinning method with subsequent calcination and exhibit excellent electrochemical performance as an anode material for lithium ion batteries.

Large-Scale Preparation of g-C3N4 Porous Nanotubes with Enhanced Photocatalytic Activity by Using Salicylic Acid and Melamine

Graphitic carbon nitride (g-C3N4) nanotubes were produced by using salicylic acid-mediated melamine successfully. The obtained long g-C3N4 nanotube possesses a large specific surface area and a par...

Oxygen vacancies-contained SnO2 nanotubes with enhanced ethanol gas sensing properties

[Formula: see text] porous nanotubes containing oxygen vacancies were prepared by electron spinning and H plasma treatment. The morphology and crystal structure of the samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The ethanol-sensing properties of the [Formula: see text] sensor were tested. The results show that the samples treated with H plasma for 20 min have the best performance. Its working temperature is [Formula: see text]C lower than [Formula: see text]C of the original sample, with a sensitivity of 17 at 100 ppm, which is seven times higher than the original sample. It also shows good selectivity to some common interfering gases. This enhancement can be ascribed to the introduced oxygen vacancy. This work provides an efficient way to design high-performance gas sensor materials.

In Situ Construction of Ag/TiO2/g-C3N4 Heterojunction Nanocomposite Based on Hierarchical Co-Assembly with Sustainable Hydrogen Evolution.

The construction of heterojunctions provides a promising strategy to improve photocatalytic hydrogen evolution. However, how to fabricate a nanoscale TiO2/g-C3N4 heterostructure and hinder the aggregation of bulk g-C3N4 using simple methods remains a challenge. In this work, we use a simple in situ construction method to design a heterojunction model based on molecular self-assembly, which uses a small molecule matrix for self-integration, including coordination donors (AgNO3), inorganic titanium source (Ti(SO4)2) and g-C3N4 precursor (melamine). The self-assembled porous g-C3N4 nanotube can hamper carrier aggregation and it provides numerous catalytic active sites, mainly via the coordination of Ag+ ions. Meanwhile, the TiO2 NPs are easily mineralized on the nanotube template in dispersive distribution to form a heterostructure via an N–Ti bond of protonation, which contributes to shortening the interfacial carrier transport, resulting in enhanced electron-hole pairs separation. Originating from all of the above synergistic effects, the obtained Ag/TiO2/g-C3N4 heterogenous photocatalysts exhibit an enhanced H2 evolution rate with excellent sustainability 20.6-fold-over pure g-C3N4. Our report provides a feasible and simple strategy to fabricate a nanoscale heterojunction incorporating g-C3N4, and has great potential in environmental protection and water splitting.

Three-Dimensional Hierarchical Porous Nanotubes Derived from Metal-Organic Frameworks for Highly Efficient Overall Water Splitting.

SummaryEffective design of bifunctional catalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is important but remains challenging. Herein, we report a three-dimensional (3D) hierarchical structure composed of homogeneously distributed Ni-Fe-P nanoparticles embedded in N-doped carbons on nickel foams (denoted as Ni-Fe-P@NC/NF) as an excellent bifunctional catalyst. This catalyst was fabricated by an anion exchange method and a low-temperature phosphidation of nanotubular Prussian blue analogue (PBA). The Ni-Fe-P@NC/NF displayed exceptional catalytic activity toward both HER and OER and delivered an ultralow cell voltage of 1.47 V to obtain 10 mA cm−2 with extremely excellent durability for 100 h when assembled as a practical electrolyser. The extraordinary performance of Ni-Fe-P@NC/NF is attributed to the abundance of unsaturated active sites, the well-defined hierarchical porous structure, and the synergistic effect between multiple components. Our work will inspire more rational designs of highly active non-noble electrocatalysts for industrial energy applications.

Formation of Platinum Nanocrystals on Silicon Nanotubes and Corresponding Anti-Cancer Activity in Vitro.

Biodegradable porous silicon nanotubes (pSiNTs), functionalized with primary amine moieties via the use of 3-aminopropyltriethoxysilane (APTES), is demonstrated as a template for formation of platinum nanocrystals (Pt NCs) (1-3 nm). Transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDX) indicates a relatively high and tunable concentration of Pt uniformly immobilized on a given nanotube (wt % Pt: 20-60%). In vitro viability and cellular uptake studies are consistent with a time-dependent toxicity of Pt NCs-pSiNTs against HeLa cells that is influenced by the degradation kinetics of the pSiNTs; internalization of the composites inside the cells exerts cellular damage in an apoptotic manner, therefore suggesting promising future applications in anticancer treatments.

A Versatile Solvent-Induced Polymerization Strategy To Synthesize Free-Standing Porous Polymer Nanosheets and Nanotubes for Fast Iodine Capture.

Two-dimensional (2D) porous polymers have demonstrated great potential in gas capture and surface catalysis as well as energy storage and conversion. Current synthesis of 2D porous polymers strongly depends on the usage of templates or an additional exfoliation process. The resultant products have uncontrollable morphology and structure, low structure integrity, and relatively low yield. Herein, a facile and high-throughput solvent-induced polymerization strategy to prepare ultrathin free-standing 2D porous hyper-cross-linked polymer nanosheets with large surface area and high sulfur content by cross-linking steric hexakis(benzylthio)benzene and thiophene is reported. Using this approach, the morphologies (nanosheets and nanotubes) and specific surface areas (658-1150 m2 g-1) of porous hyper-cross-linked polymers can be simply tailored by adjusting the cross-linking degree between monomers. The as-synthesized porous hyper-cross-linked polymer nanotubes exhibit promising iodine capture performance, including a superior iodine uptake capacity (∼270 wt %) and a rapid equilibrium adsorption (within 60 min). This method will pave a new avenue for the synthesis of advanced 2D porous polymers for various applications.

Double-walled hierarchical porous silica nanotubes loaded Au nanoparticles in the interlayer as a high-performance catalyst

Double-walled hierarchical porous silica nanotubes (NTs) loaded Au nanoparticles (Au NPs) in the interlayer (SiO2@Au@SiO2 NTs) are synthesized by using tetraethoxysilane as silica source and hollow polydivinylbenzene (PDVB) nanowires as the sacrificial templates. The mesopores on the walls and the hollow structure of NTs (macropores) construct the hierarchical porous structure. The SiO2@Au@SiO2 NTs possess a high surface area of 405 m2 g−1 and an average pores size of 4.7 nm. The double-walled structure protects the Au NPs from environmental attacks, which shows an excellent catalytic activity even after reusing 10 times. Meanwhile, the hierarchical porous structure shows excellent catalytic ability and allows the catalytic reaction process to be completed within 5 min. This result indicates that double-walled silica NTs have vast potential in catalysis application due to the special structure.

Development of nanotubes coated with platinum nanodendrites using a virus as a template

We developed a facile method to fabricate platinum (Pt) porous nanotubes coated with interconnected Pt dendrites using the tobacco mosaic virus (TMV) as a template. The surface-exposed arginine residues of the TMV induced the selective deposition of Pt seeds on the TMV outside surface, and poly(sodium-p-styrenesulfonate) (PSS) was chosen to stabilize the dispersity of TMV coated with Pt seeds (TMV/SPt). The limited space between the Pt seeds and their uniform distribution on the TMV exterior confined the growth of Pt dendrites, resulting in continuous dendritic platinum nanotubes (TMV/DPtNT). The synergistic effects of porous dendrites and anisotropic structures of the TMV/DPtNTs provided an increase in the active sites, the enhancement of transport efficiency and long-distance electron transfer, which greatly improved the catalytic activity. We also demonstrated that such nanotubes could be used in the detection of H2O2 with good sensitivity.

Design of highly porous SnO2-CuO nanotubes for enhancing H2S gas sensor performance

Highly porous SnO2-CuO hollow nanofiber mats were synthesized by electrospinning combined with thermal processing for high performance H2S gas sensing applications. The porous morphology generated in the one-dimensional (1-D) nanocomposite led to an improvement in surface-to-adsorbate molecule interactions. Our novel concept lies in fabrication of SnO2-CuO with a 1-D highly porous structure by electrospinning coupled with generation of hollow nanostructures drawing on nanofiber-to-nanotube transformation affected by Kirkendall effect during thermal processing. The fibrous structure was synthesized by electrospinning with mixed solution of Sn and Cu precursors, which then underwent heat treatment under various temperature conditions. The hollow structures were generated based on the different diffusion rates between SnO2-CuO and Sn/Cu. The SnO2-CuO nanotubes have low operating temperatures and high H2S sensing performance. The increased surface area for detecting H2S resulted in great enhancement of the response (Ra/Rg = 1395) and a very fast response time of 5.27 s with a stable recovery time to a low concentration of H2S to 5 ppm at 200 °C. The porous SnO2-CuO hollow nanofiber gas sensor proved to be a promising candidate for gas sensor systems due to increased surface area with metal oxide catalyst. The mechanisms involved in enhancement of gas response and extended applications are also discussed.

Rapid oxidation-etching synthesis of low-crystalline δ-MnO2 tubular nanostructures under ambient with high capacitance

The 1D low-crystalline and ultrathin MnO2-RT nanotubes consisted of tiny nanoflakes are rapid synthesized at ambient temperature through a facile oxidation-etching method, where Cu nanowires are served as sacrificial templates. Meanwhile, the MnO2-RT nanotubes can be undergone further nucleation and growth to generate 3D porous MnO2 nanotubes by calcination treatment and hydrothermal reaction, respectively. Importantly, the high specific capacitance of 384.6 F g−1 is obtained at the current density of 0.25 A g−1 for the low-crystalline MnO2-RT nanotubes, owing to its ultra-thin wall thickness, high surface area and highly disordered structure. Furthermore, the cycle stability of the low-crystalline MnO2 nanotubes can be improved by hydrothermal treatment, owing to the enhanced crystallinity.

Model for Formation of Self-Ordered Anodic Oxide Nanomaterials

Porous anodic films are self-organized porous oxides nanomaterials formed by electrochemical oxidation. Pores in porous alumina and nanotubes in TiO2nanotube layers initiate after an initial stage of barrier oxide growth. The porous film eventually evolves into a hexagonally-ordered array of parallel cylindrical pores or nanotubes of order 10-100 nm diameter with a characteristic spacing that scales directly with the cell voltage. We explore the roles of mechanical stress and oxide flow in self-ordering, through a modeling analysis of stress-driven viscous flow of oxide (1-3). The model is based on coupled viscous flow of oxide and stress- and electric field-driven migration of metal and oxygen ions (1). Stress at the film interfaces is generated by ion-transfer processes and relaxed by viscous flow, resulting in layers with elevated compressive or tensile stress within a few nm of the interfaces (2,3). Experimental evidence for these layers has been found from in situ stress measurements (2-4). We present linear stability analysis incorporating the surface stress boundary conditions in the coupled oxide flow-electrical migration model of Houser and Hebert (1). The calculations reveal self-organized pattern formation with steady-state pore spacing-voltage scaling ratios that compare favorably to those found experimentally, for both porous alumina and TiO2nanotube layers. The scaling ratios are independent of oxide viscosity or uncertainties in the values of any other model parameters. In the case of Al anodization, oxide flow resulting in pore patterns is driven by elevated stress near the oxide-solution interface, through a mechanism that has common features with the Marangoni instability in thin liquid films. Stress near the oxide surface is produced because strong electrolyte anion adsorption suppresses oxide growth on the surface. Such near-surface stress is not present in TiO2nanotube layers (5). Instead, compressive stress driving flow arises at the metal-oxide interface from the volume change upon conversion of metal to oxide. REFERENCES J. E. Houser and K. R. Hebert, Nature Mater., 8, 415 (2009).K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E737 (2018).K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E744 (2018).Ö. Ö. Çapraz, P. Shrotriya, P. Skeldon, G. E. Thompson, K. R. Hebert, Electrochim. Acta, 167, 404 (2015). Q. Dou, P. Shrotriya, W. F. Li, K. R. Hebert, Electrochim. Acta, 295, 418 (2019).