Space confinement and rotation stress induced self-organization of double-helix nanostructure: a nanotube twist with a moving catalyst head

Fluidization and Application of Carbon Nano Agglomerations

Carbon nanomaterials are unique with excellent functionality and diverse structures. However, agglomerated structures are commonly formed because of small-size effects and surface effects. Their hierarchical assembly into micro particles enables carbon nanomaterials to break the boundaries of classical Geldart particle classification before stable fluidization under gas-solid interactions. Currently, there are few systematic reports regarding the structural evolution and fluidization mechanism of carbon nano agglomerations. Based on existing research on carbon nanomaterials, this article reviews the fluidized structure control and fluidization principles of prototypical carbon nanotubes (CNTs) as well as their nanocomposites. The controlled agglomerate fluidization technology leads to the successful mass production of agglomerated and aligned CNTs. In addition, the self-similar agglomeration of individual ultralong CNTs and nanocomposites with silicon as model systems further exemplify the important role of surface structure and particle-fluid interactions. These emerging nano agglomerations have endowed classical fluidization technology with more innovations in advanced applications like energy storage, biomedical, and electronics. This review aims to provide insights into the connections between fluidization and carbon nanomaterials by highlighting their hierarchical structural evolution and the principle of agglomerated fluidization, expecting to showcase the vitality and connotation of fluidization science and technology in the new era.

High-value utilization of bamboo pulp black liquor lignin: Preparation of silicon-carbide derived materials and its application

The black liquor of bamboo pulp contains a large amount of silicon, which makes it difficult to separate industrial lignin, thus hindering its high-value utilization. Herein, this paper dedicates to exploring the high-value use of silica-containing lignin. Tetraethyl silicate (TEOS) was added to the above silicon-containing lignin for crosslinking with the lignin to prevent disintegration during carbonization and provide an additional source of silica. The carbonization is carried out at 600 °C (LT-6), 900 °C (LT-9) and 1200 °C (LT-12), and the structural evolution of SiO_xC_y is innovatively analyzed. The results show that LT-9 is dominated by the SiO₃C structure and has a specific surface area of 269 m² g^-1. The specific capacitance of LT-9 and LT-12 as supercapacitors electrodes is 78.6 F g^-1 and 74.8 F g^-1 at a current density of 1 A g^-1, and remains 95 % and 91.7 % after 10,000 cycles. Moreover, LT-9 has a high yield of 54 %. In this work, silicon-containing lignin is exploratively prepared as a silicon-carbide-derived material. Furthermore, the potential relationship between different SiO_xC_y molecular structures and electrochemical performance is evaluated, which is instructive for the high-value utilization of black liquor in bamboo pulp.

Carbon nanofibers derived from cellulose via molten-salt method as supercapacitor electrode

Carbon nanofibers (CNFs) have been paid much attention as supercapacitor electrode due to outstanding chemical stability, high electron transfer rate and large specific surface area. However, the preparation process of CNFs is always stalemated in electrospinning, heat stabilization and carbonization. The problems of solvent pollution in the electrospinning process, complex process and high energy consumption in conventional carbonization process can't be solved. Herein, CNFs have been innovatively prepared from nanofibrillated cellulose by the molten-salt method (NaCl/NaOH). Molten salt penetrates between the fibers, separates and activates the fibers. The obtained carbon nanofibers remain developed branching structures and have a large specific surface area (899 m² g^-1). The electrical properties are tested in a symmetrical two-electrode system. The specific capacitance is 150 F g^-1 at the current density of 1 A g^-1. Low equivalent series resistance (1.13 Ω) indicates that it has high electrode conductivity. This study has taken into account energy conservation, environmental protection, recyclability and simplified preparation process, which has a very far-reaching significance for the industrial production of CNFs.

Braiding Ultrathin Au Nanowires into Ropes

Braiding is a common skill in daily life but rare at the nanoscale. Most of the current nanohelices are directly grown or assembled without involving mechanical interactions, and they are thus distinctively different from ropes in terms of functions and mechanisms. Here, by coaxially twisting multiple ultrathin Au nanowires, nanoropes are synthesized with elegant helical patterns that are consistent with the macroscopic equivalents. The strain relaxation of lattice transformation causes the nanowires to pursue the maximum degree of twisting, while the mutual packing interactions in a bundle prevent sideways emergence of U-turns. The consistent chirality of the seemingly independent strands can only arise when a first twisting strand causes morphological deformation in its neighbors, which induces the collective uni-directional twisting. The spontaneous braiding and the "remote" control of the nanowires involve mechanical interactions and possibly energy transmission, thus opening doors to chiral assembly and future smart nanodevices.

Solution synthesis of helical gold nanowire bundles

Helical nanostructures are important nanoscale building blocks. While only a few methods are available for synthesizing helical metal nanostructures, those involving collective twisting behaviour are even fewer. Here, we report a solution synthesis of Au nanowire bundles with hierarchical helical constructions. Ultrathin nanowires with diameters of only about 10 nm formed huge ribbon bundles that have a width of 0.5-1 μm and thickness of a few hundreds of nanometres. These bundles extended to hundreds of micrometres and curled into helices. Mechanism studies revealed that the white floccules formed by Au(i) and a thiol ligand are of critical importance for both the nanowire growth and helical bundle formation. The nanowire growth took place in the floccules following the previously reported active surface growth mode, and the bundle formation was due to the splitting of the active surface. Most importantly, the floccules assisted the strain-induced curling process that yielded helices. As the length of the bundles keeps increasing and they break out from the surrounding floccules, they would have to pass through the pores of the floccules. The imbalanced squeezing at the pore caused the bundles to curl into helices.

Twisting Ultrathin Au Nanowires into Double Helices

Previously, double helix nanowire was reported by coating Pd/Pt/Au onto Au-Ag alloy nanowire. Here, straight oleylamine-stabilized ultrathin Au nanowires with single crystalline fcc lattice are surprisingly converted into double helix helices upon reacting with Ag in tetrahydrofuran (THF). The obtained Au-Ag helical nanowires contain lattice distinctively different from the fcc lattice and are different in many aspects with the previous system. The discovery may expand the scope of nanoscale double helix formation and the understanding of lattice transformation among ultrafine nanostructures.

Branched artificial nanofinger arrays by mesoporous interfacial atomic rearrangement

The direct production of branched semiconductor arrays with highly ordered orientation has proven to be a considerable challenge over the last two decades. Here we report a mesoporous interfacial atomic rearrangement (MIAR) method to directly produce highly crystalline, finger-like branched iron oxide nanoarrays from the mesoporous nanopyramids. This method has excellent versatility and flexibility for heteroatom doping of metallic elements, including Sn, Bi, Mn, Fe, Co, Ni, Cu, Zn, and W, in which the mesoporous nanopyramids first absorb guest-doping molecules into the mesoporous channels and then convert the mesoporous pyramids into branching artificial nanofingers. The crystalline structure can provide more optoelectronic active sites of the nanofingers by interfacial atomic rearrangements of doping molecules and mesopore channels at the porous solid-solid interface. As a proof-of-concept, the Sn-doped Fe2O3 artificial nanofingers (ANFs) exhibit a high photocurrent density of ∼1.26 mA/cm(2), ∼5.25-fold of the pristine mesoporous Fe2O3 nanopyramid arrays. Furthermore, with surface chemical functionalization, the Sn-doped ANF biointerfaces allow nanomolar level recognition of metabolism-related biomolecules (∼5 nm for glutathione). This MIAR method suggests a new growth means of branched mesostructures, with enhanced optoelectronic applications.

Hierarchical vine-tree-like carbon nanotube architectures: In-situ CVD self-assembly and their use as robust scaffolds for lithium-sulfur batteries

Hierarchical vine-tree-like carbon nanotube architectures composed of vine-like single-walled carbon nanotubes wrapping around the tree-like multi-walled carbon nanotubes are fabricated through in-situ chemical vapor deposition self-assembly. The vine-tree-like nanoarchitectures exhibit excellent cycling stability and rate performance when employed as the cathode scaffolds for lithium-sulfur batteries.

A review of helical nanostructures: growth theories, synthesis strategies and properties

Helical nanomaterials represent an emerging group of nanostructures with unique spiral geometry as well as multiple functionalities owing to their enriched physical and chemical properties. With the novel properties enabled by their nanoscale dimension and unique geometry, the helical nanostructures may open opportunities to develop our understanding of new physics, chemistry and biology, and enable new nanodevice design and fabrication. This review article presents a comprehensive and in-depth overview of the latest progress in helical nanostructures synthesis, properties and potential applications. Specific attention is concentrated on the crystal growth theory for helical nanostructures, summary of the helical nanomaterials obtained so far, and their fabrication techniques as well as typical physical properties that can be potentially utilized for various applications.

Emerging double helical nanostructures

As one of the most important and land-mark structures found in nature, a double helix consists of two congruent single helices with the same axis or a translation along the axis. This double helical structure renders the deoxyribonucleic acid (DNA) the crucial biomolecule in evolution and metabolism. DNA-like double helical nanostructures are probably the most fantastic yet ubiquitous geometry at the nanoscale level, which are expected to exhibit exceptional and even rather different properties due to the unique organization of the two single helices and their synergistic effect. The organization of nanomaterials into double helical structures is an emerging hot topic for nanomaterials science due to their promising exceptional unique properties and applications. This review focuses on the state-of-the-art research progress for the fabrication of double-helical nanostructures based on 'bottom-up' and 'top-down' strategies. The relevant nanoscale, mesoscale, and macroscopic scale fabrication methods, as well as the properties of the double helical nanostructures are included. Critical perspectives are devoted to the synthesis principles and potential applications in this emerging research area. A multidisciplinary approach from the scope of nanoscience, physics, chemistry, materials, engineering, and other application areas is still required to the well-controlled and large-scale synthesis, mechanism, property, and application exploration of double helical nanostructures.

Electrochemical immunosensor based on hydrophilic polydopamine-coated prussian blue-mesoporous carbon for the rapid screening of 3-bromobiphenyl

A sensitive electrochemical immunosensor for 3-bromobiphenyl (3-BBP) detection was constructed by employing a new polydopamine coated prussian blue-mesoporous carbon (PDOP/PB/CMK-3) nanocomposite as the substrate platform and multi-horseradish peroxidase-double helix carbon nanotubes-secondary antibody (multi-HRP-DHCNTs-Ab2) as the signal label. PB/CMK-3 was firstly successfully in-situ synthesized with the aid of the CMK-3 reduction, which was characterized by transmission electron microscope (TEM), infrared spectroscopy (IR), X-ray diffraction (XRD) and N2 adsorption-desorption analysis. By using PDOP/PB/CMK-3 as the substrate, it can effectively enhance the specific surface for antigen loading due to the three-dimensional structure of the nanocomposites, while large amount of PB that fixed inside or outside the pore of CMK-3 successfully improved the electrochemical response and the PDOP film can provide a biocompatible environment to maintain the activity of antigen availability. Under the optimized conditions, the proposed immunosensor shows a good current response to 3-BBP in a linear range from 5 pM to 2 nM with a detection limit of 2.25 pM. In addition, the specificity, reproducibility and stability of the immunosensor were also proved to be acceptable, indicating its potential application in environmental monitoring.

Emerging chirality in nanoscience

Chirality in nanoscience may offer new opportunities for applications beyond the traditional fields of chirality, such as the asymmetric catalysts in the molecular world and the chiral propellers in the macroscopic world. In the last two decades, there has been an amazing array of chiral nanostructures reported in the literature. This review aims to explore and categorize the common mechanisms underlying these systems. We start by analyzing the origin of chirality in simple systems such as the helical spring and hair vortex. Then, the chiral nanostructures in the literature were categorized according to their material composition and underlying mechanism. Special attention is paid to highlight systems with original discoveries, exceptional structural characteristics, or unique mechanisms.

The road for nanomaterials industry: a review of carbon nanotube production, post-treatment, and bulk applications for composites and energy storage

The innovation on the low dimensional nanomaterials brings the rapid growth of nano community. Developing the controllable production and commercial applications of nanomaterials for sustainable society is highly concerned. Herein, carbon nanotubes (CNTs) with sp(2) carbon bonding, excellent mechanical, electrical, thermal, as well as transport properties are selected as model nanomaterials to demonstrate the road of nanomaterials towards industry. The engineering principles of the mass production and recent progress in the area of CNT purification and dispersion are described, as well as its bulk application for nanocomposites and energy storage. The environmental, health, and safety considerations of CNTs, and recent progress in CNT commercialization are also included. With the effort from the CNT industry during the past 10 years, the price of multi-walled CNTs have decreased from 45 000 to 100 $ kg(-1) and the productivity increased to several hundred tons per year for commercial applications in Li ion battery and nanocomposites. When the prices of CNTs decrease to 10 $ kg(-1) , their applications as composites and conductive fillers at a million ton scale can be anticipated, replacing conventional carbon black fillers. Compared with traditional bulk chemicals, the controllable synthesis and applications of CNTs on a million ton scale are still far from being achieved due to the challenges in production, purification, dispersion, and commercial application. The basic knowledge of growth mechanisms, efficient and controllable routes for CNT production, the environmental and safety issues, and the commercialization models are still inadequate. The gap between the basic scientific research and industrial development should be bridged by multidisciplinary research for the rapid growth of CNT nano-industry.

Coke- and sintering-resistant monolithic catalysts derived from in situ supported hydrotalcite-like films on Al wires for dry reforming of methane

Monolithic catalysts derived from in situ supported hydrotalcite-like films on Al wires display high resistance to coke formation and sintering in the dry reforming of methane due to their hierarchical porous structure, well dispersed metallic nickel species, more basic sites and strong metal-support interaction effect.

Highly twisted double-helix carbon nanotube yarns

The strength and flexibility of carbon nanotubes (CNTs) allow them to be constructed into a variety of innovated architectures with fascinating properties. Here, we show that CNTs can be made into a highly twisted yarn-derived double-helix structure by a conventional twist-spinning process. The double-helix is a stable and hierarchical configuration consisting of two single-helical yarn segments, with controlled pitch and unique mechanical properties. While one of the yarn components breaks early under tension due to the highly twisted state, the second yarn produces much larger tensile strain and significantly prolongs the process until ultimate fracture. In addition, these elastic and conductive double-helix yarns show simultaneous and reversible resistance change in response to a wide range of input sources (mechanical, photo, and thermal) such as applied strains or stresses, light illumination, and environmental temperature. Our results indicate that it is possible to create higher-level, more complex architectures from CNT yarns and fabricate multifunctional nanomaterials with potential applications in many areas.

Graphene/single-walled carbon nanotube hybrids: one-step catalytic growth and applications for high-rate Li-S batteries

The theoretically proposed graphene/single-walled carbon nanotube (G/SWCNT) hybrids by placing SWCNTs among graphene planes through covalent C-C bonding are expected to have extraordinary physical properties and promising engineering applications. However, the G/CNT hybrids that have been fabricated differ greatly from the proposed G/SWCNT hybrids because either the covalent C-C bonding is not well constructed or only multiwalled CNTs/carbon nanofibers rather than SWCNTs are available in the hybrids. Herein, a novel G/SWCNT hybrid was successfully fabricated by a facile catalytic growth on layered double hydroxide (LDH) at a high temperature over 950 °C. The thermally stable Fe nanoparticles and the uniform structure of the calcined LDH flakes are essential for the simultaneously catalytic deposition of SWCNTs and graphene. The SWCNTs and the CVD-grown graphene, as well as the robust connection between the SWCNTs and graphene, facilitated the construction of a high electrical conductive pathway. The internal spaces between the two stacked graphene layers and among SWCNTs offer room for sulfur storage. Therefore, the as obtained G/SWCNT-S cathode exhibited excellent performance in Li-S batteries with a capacity as high as 650 mAh g(-1) after 100 cycles even at a high current rate of 5 C. Such a novel G/SWCNT hybrid can serve not only as a prototype to shed light on the chemical principle of G/CNT synthesis but also as a platform for their further applications in the area of nanocomposites, heterogeneous catalysis, drug delivery, electrochemical energy storage, and so on.

Gas-induced formation of Cu nanoparticle as catalyst for high-purity straight and helical carbon nanofibers

The facile preparation of high-purity carbon nanofibers (CNFs) remains challenging due to the high complexity and low controllability in reaction. A novel approach using gas-induced formation of Cu crystals to control the growth of CNFs is developed in this study. By adjusting the atmospheric composition, controllable preparation of Cu nanoparticles (NPs) with specific size and shape is achieved, and they are further used as a catalyst for the growth of straight or helical CNFs with good selectivity and high yield. The preparation of Cu NPs and the formation of CNFs are completed by a one-step process. The inducing effect of N(2), Ar, H(2), and C(2)H(2) on the formation of Cu NPs is systematically investigated through a combined experimental and computational approach. The morphology of CNFs obtained under different conditions is rationalized in terms of Cu NP and CNF growth models. The results suggest that the shapes of CNFs, namely, straight or helical, depend closely on the size, shape, and facet activity of Cu NPs, while such a gas-inducing method offers a simple way to control the formation of Cu NPs.