Open Tubular Structure Research Articles

Design of bifunctional 1D nanostructures for the catalytic conversion of carbon dioxide into cyclic carbonates

One dimensional silica-based nanotubes represent an innovative and promising morphology in the context of heterogeneous catalysis. Here these nanostructures were prepared for the first time as bifunctional materials, with hafnium or tin atoms inserted as single sites in the silica structure and imidazolium moieties anchored at the surface. The low dimensional solids thus present both acid sites owing to the presence of metal cations in tetrahedral coordination (co-catalyst) and nucleophilic species coming from the counterion of the imidazolium moieties (catalyst). The design of the catalysts consisted of two main steps. The Hf- or Sn-doped silica solids were initially prepared using a straightforward sol-gel method including a pH adjustment step allowing a quantitative insertion of the metal cations in the silica framework. These materials were post-functionalized with imidazolium moieties. The solids were extensively characterized thus confirming the presence of well-defined and open tubular structure, high specific surface area, successful insertion of Hf and Sn in the silica framework, and a correct functionalization with imidazolium salts. The different catalysts were tested in the valorization of CO2 with styrene oxide to give the corresponding cyclic carbonate. The bifunctional solids were stable and recyclable. The versatility of the best catalyst, represented by the Hf-based material, was confirmed using different epoxides. Finally, by tuning the reaction conditions or changing the imidazolium salt, a further boost of the catalytic performances was achieved.

Stimulus-Responsive Ultrathin Films for Bioapplications: A Concise Review.

The term "nanosheets" has been coined recently to describe supported and free-standing "ultrathin film" materials, with thicknesses ranging from a single atomic layer to a few tens of nanometers. Owing to their physicochemical properties and their large surface area with abundant accessible active sites, nanosheets (NSHs) of inorganic materials such as Au, amorphous carbon, graphene, and boron nitride (BN) are considered ideal building blocks or scaffolds for a wide range of applications encompassing electronic and optical devices, membranes, drug delivery systems, and multimodal contrast agents, among others. A wide variety of synthetic methods are employed for the manufacturing of these NSHs, and they can be categorized into (1) top-down approaches involving exfoliation of layered materials, or (2) bottom-up approaches where crystal growth of nanocomposites takes place in a liquid or gas phase. Of note, polymer template liquid exfoliation (PTLE) methods are the most suitable as they lead to the fabrication of high-performance and stable hybrid NSHs and NSH composites with the appropriate quality, solubility, and properties. Moreover, PTLE methods allow for the production of stimulus-responsive NSHs, whose response is commonly driven by a favorable growth in the appropriate polymer chains onto one side of the NSHs, resulting in the ability of the NSHs to roll up to form nanoscrolls (NSCs), i.e., open tubular structures with tunable interlayer gaps between their walls. On the other hand, this review gives insight into the potential of the stimulus-responsive nanostructures for biosensing and controlled drug release systems, illustrating the last advances in the PTLE methods of synthesis of these nanostructures and their applications.

Engineering NiMoP nanosheets on hollow Cu3P nanotube arrays as efficient electrocatalyst for hydrogen evolution reaction

By virtue of its unique core–shell open tubular structure, NiMoP@Cu3P/CF shows large specific surface area and short diffusion paths, which facilitates mass transport and easy accessibility of water, resulting in a superior HER activity in 1 M KOH.

Wood-based carbon tubes with low-tortuosity and open tubular structure for energy storage application

Wood-based carbon tubes with low-tortuosity and open tubular structure for energy storage application

Wettability and reactivity between molten aluminum and randomly aligned carbon nanotubes

The wettability and reactivity between molten aluminum (Al) and carbon nanotubes (CNTs) are a key issue in the preparation of CNTs-reinforced Al-matrix composites using a solidification route. In this work, we measured the wettability of randomly aligned multi-walled carbon nanotubes (buckypaper) by molten Al at 973–1173 K in a high vacuum using a modified sessile-drop method and examined their interactions using a droplet-sucking technique. The wettability between Al and CNTs is even worse than that of the Al/graphite system. The contact angles are basically larger than 140° and show only a sluggish decrease with time during isothermal dwelling. The chemical stability of CNTs in contact with Al is closely related to their structural integrity. The CNTs with good crystallinity and structural integrity have relatively high chemical stability and exhibit only a weak interfacial reaction with Al at 973 K. However, the stability of structural defective parts is much lower. They are readily eroded by molten Al, leading to the fragmentation of the CNTs. These CNT fragments having an open tubular structure are then rapidly dissolved in molten Al along the axial and radial directions. Simultaneously, a large amount of Al4C3 is formed at the interfaces.

Efficient Synthesis of Graphene Nanoscrolls for Fabricating Sulfur-Loaded Cathode and Flexible Hybrid Interlayer Toward High Performance Li−S Batteries

Graphene oxide; Sulfur/carbon composite; Graphene nanoscroll; Metal oxides nanowires; Interlayer; Li−S batteries Nowadays, the growing grievous environmental problems together with the exhaustion of energy resources put urgent demands for developing high energy density devices, whereas traditional lithium-ion batteries (LIBs) are getting close to their energy density. Consideration of the factors including capacity, resource and environment, lithium sulfur (Li-S) batteries are the most potential lithium secondary batteries.[1] However, many drawbacks need to be overcome before its industrial application, such as low electronic conductivity of sulfur, serious shuttling effects of dissolution polysulfides, volume change of electrode during charging-discharging process and problems such as lithium dendrites, passivation and corrosion of lithium anode. This work aims to improve the properties of Li-S batteries by preparation of sulfur/carbon composite cathode materials and building high-efficiency interlayer .[2-4] Firstly, a modified lyophilization approach is developed and used for highly efficient transformation of 2D graphene oxide sheet into 1D graphene nanoscroll (GNS) with high topological transforming efficiency (94%). Because of the unique open tubular structure and large specific surface area (545 m2 g−1), GNS is utilized for the first time as a porous cathode scaffold for encapsulating sulfur with a high loading (81 wt%). The interlayer space and pores of obtained GNS provide large sites for sulfur loading, and this unique structure can accommodate volume expansion and prevent the dissolution of polysulfides. As a result, the composite deliver good rate performance and cycling stability (the capacity decay is only 0.04% per cycle after 400 cylces at 2C).[5] Furthermore, a flexible self-standing hybrid interlayer is engineered by intertwining one-dimensional (1D) metal oxides nanowires (NWs) with GNS into a robust interconnected 3D network to be used as both an upper current collector and physical/chemical polysulfide-trapper. Combining GNS with MnO2, V2O5 and MoO3 respectively, free-standing membranes are obtained to serve as interlayers for Li-S battery (namely, GNSMn, GNSV and GNSMo). The highly conductive and open GNS framework provides bicontinuous transfer channels for rapid electron and ion transport across the cathode/separator interface. Meanwhile, the metal oxides nanowires act as ideal redox mediators to dynamically block polysulfide dissolution and facilitate their conversion into sulfides via formation of active intermediate polythionate complexes. Even though GNSV is used as an interlayer for lithium sulfur battery with bare sulfur as cathodethese cells with 70 wt% sulfur content in the whole cathode have significantly improved performance with a long cycling life (1000 cycles), low capacity decay (0.041% per cycle), and considerable areal capacity (>4 mA h cm- 2), even at a high sulfur loading of 5.5 mg cm- 2. This novel interlayer design strategy has great potential for promoting the practical use of Li–S batteries.[6] In summary, the work described here shows a potential of GNS as a promising functional carbon material to realize high sulfur loading and electrochemically stable electrode configuration aimed toward developing high-performance Li−S batteries. Figure 1 (a) SEM images and (b) TEM images of GNS, (c) schematic illustration on the advantages in entrapping polysulfides of the S@GNS (insert: typical colors of the cycled S@GNS and Gs-S cathodes after soaking in a mixture of DOL/DME for 24 h), (d) schematic model of the cell (insert: photos of the free-standing and flexible GNSM interlayer).

Controllable Microfluidic Fabrication of Magnetic Hybrid Microswimmers with Hollow Helical Structures

Controllable magnetic hybrid microswimmers with hollow helical structures are fabricated, by a facile strategy based on microfluidic template synthesis and biosilicification, to achieve enhanced rotation-based locomotion for cargo transport. The magnetic hybrid microswimmers are fabricated by first synthesizing Fe3O4-nanoparticles-containing helical Ca-alginate microfibers from microfluidics, followed with biosilicification and controllable dicing to engineer their rigid hollow helical structures. The microswimmers show hollow helical structures consisting of a rigid, biocompatible alginate/protamine/silica shell embedded with Fe3O4 nanoparticles. Their helical structures can be engineered into open tubular structures or closed compartmental structures by using microfibers or diced microfibers as templates for biosilicification. Powered by a simple rotating magnet, the microswimmers can achieve enhanced rotation-based locomotion and provide good mechanical strength for supporting cargo for transportation....

Condensing Vapor Phase Polymerization (CVPP) of Electrochemically Capacitive and Stable Polypyrrole Microtubes.

We introduce a novel condensing vapor phase polymerization (CVPP) strategy for depositing microtubes of the conducting polymer polypyrrole; these serve as one-dimensional hollow microstructures for storing electrochemical energy. In CVPP, water droplets are structure-directing templates for polypyrrole microtubes. Water vapor condensation and polymerization occur simultaneously-conformal coatings of microtubes deposit on porous substrates such as hard carbon fiber paper or glass fiber filter paper. A mechanistic evolution of the microtubular morphology is proposed and tested based on the mass transport of water and monomer vapors as well as on the reaction stoichiometry. A coating of PPy microtubes is characterized by a high reversible capacitance of 342 F g-1 at 5 mV s-1 throughout 5000 cycles of cyclic voltammetry and a low sheet resistance of 70.2 Ω □-1. The open tubular structure is controlled in situ during synthesis and leads to electrodes that exhibit electrochemical stability at high scanning rates up to 250 mV s-1 retaining all stored charge, even after extensive cycling at 25 mV s-1.

Efficient Synthesis of Graphene Nanoscrolls for Fabricating Sulfur-Loaded Cathode and Flexible Hybrid Interlayer toward High-Performance Li-S Batteries.

A modified lyophilization approach is developed and used for highly efficient transformation of 2D graphene oxide sheet into 1D graphene nanoscroll (GNS) with high topological transforming efficiency (∼94%). Because of the unique open tubular structure and large specific surface area (545 m2 g-1), GNS is utilized for the first time as a porous cathode scaffold for encapsulating sulfur with a high loading (81 wt %), and also as a conductive skeleton for assembling MnO2 nanowires into a flexible free-standing hybrid interlayer, both enabling high-rate and long-life Li-S battery.

Initial stage of growth of single-walled carbon nanotubes: modeling and simulations

Because there are different pathways to grow carbon nanotubes (CNTs), a common mechanism for the synthesis of CNTs does not likely exist. However, after carbon atoms are liberated from carbon-containing precursors by catalysts or from pure carbon systems, a common feature, the nucleation of CNTs by electron mediation, does appear. We studied this feature using the initial stage of growth of single wall CNTs (SWCNTs) by transition metal nano-particle catalysts as the working example. To circumvent the bottleneck due to the size and simulation time, we used a model in which the metal droplet is represented by a jellium, and the effect of collisions between the carbon atoms and atoms of the catalyst is captured by charge transfers between the jellium and the carbon. The simulations were performed using a transferable semi-empirical Hamiltonian to model the interactions between carbon atoms in jellium. We annealed different initial configurations of carbon clusters in jellium as well as in a vacuum. We found that in jellium, elongated open tubular structures, precursors to the growth of SWCNTs, are formed. Our model was also shown to be capable of mimicking the continued growth when more atoms were placed near the open end of the tubular structure.

Thin‐Wall Assembled SnO2 Fibers Functionalized by Catalytic Pt Nanoparticles and their Superior Exhaled‐Breath‐Sensing Properties for the Diagnosis of Diabetes

AbstractHierarchical SnO2 fibers assembled from wrinkled thin tubes are synthesized by controlling the microphase separation between tin precursors and polymers, by varying flow rates during electrospinning and a subsequent heat treatment. The inner and outer SnO2 tubes have a number of elongated open pores ranging from 10 nm to 500 nm in length along the fiber direction, enabling fast transport of gas molecules to the entire thin‐walled sensing layers. These features admit exhaled gases such as acetone and toluene, which are markers used for the diagnosis of diabetes and lung cancer. The open tubular structures facilitated the uniform coating of catalytic Pt nanoparticles onto the inner SnO2 layers. Highly porous SnO2 fibers synthesized at a high flow rate show five‐fold higher acetone responses than densely packed SnO2 fibers synthesized at a low flow rate. Interestingly, thin‐wall assembled SnO2 fibers functionalized by Pt particles exhibit a dramatically shortened gas response time compared to that of un‐doped SnO2 fibers, even at low acetone concentrations. Moreover, Pt‐decorated SnO2 fibers significantly enhance toluene response. These results demonstrate the novel and practical feasibility of thin‐wall assembled metal oxide based breath sensors for the accurate diagnosis of diabetes and potential detection of lung cancer.

Studies on the properties of surface and edges of N-layer graphenes

Graphene, a new two-dimensional carbon material, is a rising star of physics, chemistry and materials science. In this work, we report the recent experimental researches on the Raman spectra and the temperature-dependent features of graphenes and carbon nanoscrolls, which are evolved from graphene and have an open tubular structure. The layer-dependent Raman enhancing characteristics of n-layer graphenes for crystal violet, and the thickness-dependent morphologies of gold on n-layer graphenes are also systematically investigated. Meanwhile, the aggregations of ferromagnetic and paramagnetic atoms at edges of graphenes and graphite are observed and the mechanisms are discussed.

Robust open tubular layer of S‐ketoprofen imprinted polymer for chiral LC separation

This study is about the preparation of an open tubular capillary column of molecularly imprinted polymer (MIP) and its application to chiral separation by microLC. A non-covalent in-situ molecular imprinting polymerization protocol was used to synthesize the S-ketoprofen MIP. A special procedure was employed to secure formation of an open tubular and rigid MIP layer in a silica capillary of 100 microm id. The capillary was filled with the reaction mixture, sealed, and placed in a water bath at 50 degrees C for 3 h. Then it was flushed with a 0.5 MPa nitrogen flow for 5 min, and was again placed in the water bath for 2 h to complete MIP formation. Methacrylic acid (MAA) has been known to be an inefficient functional monomer in preparation of MIP of an acid molecule. However, MAA was used with ethylene glycol dimethacrylate in preparation of the S-ketoprofen MIP in this study. The open tubular structure and the microLC mode of separation enabled free optimization without any restriction, thus a very good resolution (R=4.7) of ketoprofen enantiomers was achieved when a mobile phase composed of 30% acetonitrile and 70% acetate buffer at pH 4.5 was used with 5 mbar inlet pressure. This may be partially attributed to the open tubular structure of our MIP, enabling low column back-pressure and free optimization of eluent composition, as well as to the small capillary dimensions. Our MIP capillary column also showed some versatility in chiral separation, thus a good chiral separation was observed for naproxen, ibuprofen, and fenoprofen enantiomers.