1D Nanotubes Research Articles

Synthesis and characterization of 3D carbon nanotubes

ABSTRACTA nanomaterial that attracts the attention in a variety of research areas is multiwall carbon nanotubes (MWCNTs), due to their good mechanical proprieties, and high electrical and thermal conductivity. For this reason, the preparation of three-dimensional (3D) structures from them draws interest because it opens new horizons to produce materials with novel properties and useful applications. In this investigation the synthesis of 3D nanotube carbon (nanoforest type) functionalized with nanoparticles of silver, aluminum, and iron was studied. A 3D structure was produced in the form of aligned microchannels. The functionalization of carbon nanotubes with nanoparticles of silver, aluminum or iron during the synthesis process of carbon nanotubes, was carried out through spray-pyrolysis with different synthesis time and solution concentration. The results were characterized through microscopy SEM, TEM and Raman’s spectroscopy.

Modeling of percolation phenomena in 3D nanotube system

Modeling of percolation phenomena in 3D nanotube system

Growth and microstructural evolution of WS2 nanostructures with tunable field and light modulated electrical transport

We report CVD growth of WS2 nanostructures with the ability to control the evolution of 1D to 2D microstructural changes for light and field effect transistor applications. Detailed mechanistic growth sequences from WO3 nanorod to nanotube, monolayer and pyramidal structures of WS2 has been achieved using atmospheric pressure chemical vapor deposition (APCVD). Electron microscopy and Raman spectroscopy analysis showed the growth evolution of different nanostructures and their formation mechanism. Location specific growth of different WS2 nanostructures can be achieved by drop casting dispersed WO3 nanorods on required substrate. Layer dependent photoluminescence (PL) properties of WS2 indicate the effect of quantum confinement induced radiative recombination and enhanced PL intensity in monolayer WS2 provides suitability for nanoscale photodetector application. The fabricated device shows light as well as field modulated switching at ultra-low biased voltage in hybrid WS2 nanostructure that contains 1D (nanotube)-2D (flake) interface. The demonstrated aspects of CVD growth and hybrid device characteristics provide opportunities to tune electrical transport of WS2 nanostructures at low active power.

Application of 3D gold nanotube ensembles in electrochemical sensing of ultra-trace Hg (II) in drinkable water

As a novel and highly sensitive sensor, three-dimensional gold nanoelectrode ensembles (3D GNE) prepared by gold deposition inside the parallel pores of a porous template have been successfully applied in electrochemical determination experiments. In this study, we report on the fabrication of 3D gold nanotubes (GNT) and their application in determination of Hg (II) in water. The morphology and crystal structure of the 3D GNT were characterized by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD), respectively. The sensitivity of the fabricated electrode towards Hg (II) was examined using anodic stripping voltammetry (ASV) as a powerful technique in determination experiments. Under the optimized conditions, a linear response was achieved over a wide range (0.1–50 nM) for Hg (II) with a sensitivity of 0.247 µA/nM. The 3D GNT electrode exhibited good repeatability and reproducibility and a detection limit of 0.06 nM (S/N = 3) was achieved which is much lower than the limit set by the Environmental Protection Agency (EPA) for Hg (II) in drinkable water.

Impact of Interconnections, Dynamic Conductivity, Pore Size on the Performance of V2O5 Cathode for Lithium Ion Batteries

It is well known that a nanostructured electrodes have superior performance over their bulk counter parts. It has been pursued by the battery community to explore different nanostructures to discover critical parameters for designing next generation batteries. Here, we describe a systematic study from 1D array electrode to 3D electrode enabled by nanostructured scaffolds and atomic layer deposition. Nanostructured scaffolds have been used as templates for the fabrication of nanostructured materials for wide range of applications. One of the commonly used scaffolding material is porous anodized aluminum oxide films (AAO). AAO are used for their hexagonally ordered nanoporous structures and the ease of controlling the structural parameters such as the pore diameter and the pore length by altering the anodization conditions. Here we use voltage control to fabricate not only the traditional straight porous AAO templates, for 1D nanotube array, but also interconnected porous AAO templates, 3D interconnected nanotube array. From previous work, by deviating from a constant voltage, which results in straight pores, to lower voltage and back to the initial voltage cause the pores to deviate from their straight structure to interconnecting layer and back to their straight structure allowing controllable insertion of the interconnecting layers throughout the film. Using atomic layer deposition, V2O5 was conformally coated along the walls of these high aspect ratio AAO with sputtering of gold current collector at the top. Using AAO as a template which can be tuned systematically, the resulting nanostructured V2O5 electrodes were examined for Li ion batteries as it is one of the well characterized cathode material. V2O5 can reversibly accommodate up to two Li ions. From the previous study, when V2O5 was cycled within the one Li insertion window, the 3D interconnected nanotubular structure showed superior power capabilities over the 1D nanotubular array. This was due to the interconnections allowed more of the materials closer to the top current collector. As faradaic reactions are much more sensitive to the ohmic loss, this close proximity to the current collector allowed more efficient utilization of the overall electrode. With the two Li ion insertion window, an opposite trend was observed, with interconnected electrode performing worse. As the structure between the one and two Li insertion windows were kept constant, we hypothesized two possibilities. One, because we have more material within the interconnected electrodes, it will require more Li ions than the straight electrodes. However the pore opening is the same which could lead to ion starvation in the interconnected electrodes because the diffusion of the Li ions into these interconnected electrodes could not keep up with the demand. Two, V2O5 with the second lithiation causes a dramatic change the electrochemical properties more severely in the interconnected electrode. To test these hypothesis, different pore diameter electrodes were used. With the larger pores, the electrodes overall performed better but the difference between the interconnected and the straight electrodes could not be explained. Literatures show the electronic conductivity of V2O5 varies dramatically depending on the degree of lithiation. Up to one lithiation, the conductivity of the material slightly increases whereas with the second lithiation the conductivity dramatically drops by two orders of magnitude due to the disruption in the electron conduction mechanism. This could explain the performance difference between the straight and the interconnected electrodes. When the current density is low, the electrons have enough time to travel through the electrode regardless of the structure. When the current density is high, now the conductivity matters. In the interconnected electrode, with one Li insertion, the conductivity of the electrode near the current collector increases with the degree of lithiation allowing better usage of the material farther away from the current collector due to lower ohmic loss of the overpotential needed. However, with two Li insertion the conductivity drops near the current collector which prevents the utilization of the material farther away resulting in lower power performance. Comsol simulations are in progress to better understand the overpotentials and ion depletion in these straight and interconnected electrodes. This work is able to show the need to match the properties of the electroactive material with the properties of the nanostructure for high performance electrodes.

Novel 3D metallic boron nitride containing only sp2 bonds

As the closest isoelectronic analogue of carbon, boron nitride (BN) shares a similar structure with carbon from 1D nanotubes, 2D nanosheets, and 3D diamond structures. However, most BN structures are insulators, which limits their application. In this work, under the inspiration of the sp2 hybridized carbon honeycomb, we propose a hexagonal phase of BN consisting of only sp2 bonds, which exhibits intriguingly intrinsic metallicity. First-principles calculations confirm that this phase is both thermally and dynamically stable. Moreover, the calculations on the band structure, partial density states and electron localization function suggest that the metallic behavior is attributable to the delocalized B-2p electrons, leading to second-neighbor interaction between the pz states of sp2-bonded B atoms in adjacent layers. Our findings not only enrich the BN allotrope family with 3D structures but also stimulate further experimental interest in applications of metallic BN in electronic devices.

Fabrication and Modeling of an Ultrasensitive Label Free Impedimetric Immunosensor for Aflatoxin B1 based on Protein A Self-assembly Modified Gold 3D Nanotube Electrode ensembles

A novel label-free impedimetric immunosensor for the quantitative detection of aflatoxin B1 (AFB1) was developed based on orientated staphylococcus protein A (SPA) modified gold three dimensional nanotube ensembles (3DTNEEs) which consisted of gold nanotubes fabricated by combining the technologies of template synthesis and controlled chemical etching of track-etched polycarbonate membrane. The structure and morphology of 3DTNEEs were evaluated by scanning electron microscopy. The diffusion characteristic and local current distribution on 3DTNEEs were simulated via the COMSOL Multiphysics 4.4 simulative software. The SPA self-assembly modified 3DTNEEs (SPA/3DTNEEs) was assessed by X-ray photoelectron spectroscopy. Electrochemical impedance spectroscopy was employed to characterize the fabrication process and optimize working conditions. The model of the molecular recognition interface was constructed and analyzed. The detection limit of AFB1 was 1.0×10−12gmL−1 (S/N=3) with a linear AFB1 concentration range of 4.0×10−12 to 6.0×10−9gmL−1. The AFB1 recovery test in corn samples demonstrated one potential application of the immunosensor.

Pt nanoparticles supported on one-dimensional (1D) titanium silicon nitride with high performance and stability for methanol electrooxidation

A titanium silicon nitride nanotubes (Ti0.95Si0.05N NTs) support with a one-dimensional (1D) nanostructure is controllable prepared in a controlled manner by adjusting the molar ratio of the precursors, and the Ti0.95Si0.05N NTs support is further decorated with Pt nanoparticles to form an electrocatalyst for methanol electrooxidation. Transmission electron microscopy shows that the Ti0.95Si0.05N NTs are formed with nanocrystals, and the hollow structure is composed of mesoporous walls. The N2 adsorption–desorption results reveal that the novel 1D nanotube structure exhibits a large Brunauer–Emmett–Teller surface area, and the XPS patterns demonstrate the strong interaction between the Ti0.95Si0.05N NTs support and the Pt nanoparticles. Furthermore, the electrochemical measurements show that the Pt/Ti0.95Si0.05N NTs exhibit an enhanced performance and stability compared to the conventional Pt/C catalysts. The dramatically improved durability of the catalyst is confirmed by the accelerated durability test. The combination of facile preparation and remarkable electrochemical performance demonstrates that Ti0.95Si0.05N NTs are promising candidates as supports for direct methanol fuel cells.

H‐bonding Assisted Self‐Assembled One‐Dimensional Nanotubes of Redox Active Triphenylamine‐Benzothiadiazole Derivative

AbstractControl over the one‐dimensional (1D) nanotubular structures significant in organic electronics. Although, p‐ and n‐type derivatives have shown diverse nanostructures, however very few ambipolar derivatives reported until now because of constrained structural properties. By considering this issue, three triphenylamine‐benzothiadiazole based ambipolar derivatives (TBE, TBAc and TBAm) synthesized and TBAm forms 1D nanotubes exclusively. DFT and spectroelectrochemical studies displayed the formation of stable cation and anion radicals of TBAm under controlled potential of 1.30 V. UV‐vis, emission (steady‐state and TCSPC) and microscopic analyses revealed TBAm exists as J‐aggregates and further leads to nanotubes by utilizing directional amide H‐bonding, together with π‐π stacking and van der Waals interactions. Consequently, these properties aid to design novel materials, which pave the way towards efficient organic field effect transistors.

One Dimensional (1D) Nanotubular F Doped Transition Metal Oxide Arrayed Architectures - Robust Oxygen Evolution Electrocatalyst for PEM Water Electrolysis

There is an ever increasing demand for renewable and non-carbonaceous clean energy sources to fulfill massive global energy demand1. Hydrogen (H2) as a fuel is clearly the frontrunner due to its non-carbonaceous nature and superior energy density than the carbonaceous energy sources1. Acid assisted proton exchange membrane (PEM) based water electrolysis is promisingly at the forefront among all other conventional hydrogen production methods. Commercial development of PEM water electrolyzer has been stymied due to requirement of highly expensive and scarce noble metal based electro-catalysts such as Pt, RuO2, IrO2; which exhibit excellent oxygen evolution reaction (OER) activity in PEM water electrolysis2. Therefore, identification and development of ultra-low noble metal containing electro-catalyst system which can exhibit superior electrochemical performance than state of the art-noble metals based electro-catalysts in highly aggressive acidic media for OER, will indeed lead to significant reduction in capital costs of the water splitting process2. In the pursuit of this objective, based on theoretical first principles calculations of the total energies and electronic structures, the present authors have identified fluorine (F) doped transition metal oxide (TMO) based solid solution electro-catalyst with ultra-low noble metal for OER in PEM water electrolysis. The F-doped synthesized TMO in two dimensional (2D) thin film morphology exhibits electro-catalytic performance (i.e. overpotential and electro-catalytic activity) similar to that of IrO2 thin film electro-catalyst. Therefore, aiming to further improve the reaction kinetics and also achieve superior electro-catalytic activity, tailoring of the 2D material length scale to 1D vertically aligned nanotubular (VANT) architecture has been executed. Over the past few years, electro-catalysts with 1D nanostructured morphologies such as nanowires (NWs) as well as nanotubes (NTs) have garnered significant attention as a potentially effective materials for water splitting due their inherent benefits such as high electro-catalytic surface area, high aspect ratios (length-to-width ratio) and facile electron transport though 1D nanotubular arrays3. Therefore, in order to enhance the electrochemical performance of as prepared 2D thin film electro-catalyst i.e. F-doped TMO for OER, we have explored 1D nanotube (NT) structured-morphology; retaining similar electro-catalyst composition. In this study, a sacrificial template-assisted approach has been utilized to grow VANTs on titanium (Ti) substrate. Fig. 1 displays the SEM micrograph showing top view, cross-sectional view of F-doped TMO NTs. The electrochemical characterization of synthesized electro-catalysts has been carried out in three-electrode configuration using 1N sulfuric acid (H2SO4) solution as a proton source as well as the electrolyte, Pt wire as counter electrode and Hg/Hg2SO4 as the reference electrode (+0.65 V with respect to normal hydrogen electrode, NHE), with a scan rate of 10 mV/sec and at temperature of 40oC. 1D VANTs of F-doped TMO grown on Ti substrate showed onset potential of ~1.43 vs NHE, similar to that of IrO2 (total loading=0.3 mg/cm2) and lower charge transfer resistance (Rct) than 2D thin films of F-doped TMO. The 1D F-doped TMO VANTs also exhibit remarkable ~2.3 and ~ 2.6 fold higher electro-catalytic OER activity (current density) than that of 2D thin film architectures of F-doped TMO and IrO2 respectively. In addition, the chronoamperometry test conducted in 1N H2SO4 solution at ~1.5 V (vs NHE) for 24 hours shows minimal loss in current density demonstrating good electrochemical stability of the F-doped TMO VANTs, comparable to that of IrO22D thin films. In summary, we have synthesized high performance 1D vertically aligned nanotubes of F-doped TMO OER electro-catalyst. The superior electrocatalytic activity of the F-doped TMO VANTs is attributed to the presence of vertical channels in 1D morphology, exhibiting higher electrochemical surface area (ECSA) than 2D thin film architectures. These encouraging results of 1D-F-doped TMO VANTs with ultra-low noble metal content and superior OER kinetics show potential of these systems for water electrolysis. The results of this study will be presented and discussed.

SiO2 monomer-triggered self-assembly of hybrid CdTe quantum dots

The self-assembly activity of quantum dots (QDs) including thioglycolic acid (TGA)-capped CdTe and hybrid SiO2-coated CdTe QDs into one- to three-dimensional (3D) nanostructures was reported using a slow growth process. SiO2 monomers from a sol-gel process and TGA play vital roles for the self-assembly. The hybrid SiO2-coated QDs were assembled into 1D nanotube, 2D nanosheets, and 3D nanoflowers by adjusting QD concentrations. It is found that the assemblies actually are CdTe@Cd-TGA-SiO2 complex hybrid nanostructures in which many well-separated CdTe QDs are uniformly distributed. Such assembly also occurred in an initial CdTe QD solution or in PBS and NaCl solutions. The assembly in the initial CdTe QD solution is accompanied by a hybrid SiO2 layer which resulted in red-shifted photoluminescence (PL) from green to yellow. Because of the domain growth of NaCl to form fractal structures through tip splitting and side branching dynamics, the hybrid SiO2-coated QDs were assembled into leaf morphology. As a result, the CdTe QDs with their in effective protection by hybrid Cd-TGA-SiO2 complex, these nanostructures show visually bright PL and retain the size-quantized properties of the QDs. These QD-based assemblies may be suitable for subsequent processing into quantum-confined materials and devices.

Ultra‐Lightweight and Highly Adaptive All‐Carbon Elastic Conductors with Stable Electrical Resistance

The rapid development of wearable electronics needs flexible conductive materials that have stable electrical properties, good mechanical reliability, and broad environmental tolerance. Herein, ultralow‐density all‐carbon conductors that show excellent elasticity and high electrical stability when subjected to bending, stretching, and compression at high strains, which are superior to previously reported elastic conductors, are demonstrated. These all‐carbon conductors are fabricated from carbon nanotube forms, with their nanotube joints being selectively welded by amorphous carbon. The joint‐welded foams have a robust 3D nanotube network with fixed nodes and mobile nanotube segments, and thus have excellent electrical and mechanical stabilities. They can readily scale up, presenting a new type of nonmetal elastic conductor for many possible applications.

Nickel induced re-structuring of 2D graphene to 1D graphene nanotubes: Role of radical hydrogen in catalyst assisted growth

Here, we demonstrate for the first time the structural evolution of 1D graphene nanotubes (GNTs) by the cutting of two dimensional (2D) graphene oxide (GO) sheet in reducing environment at ambient conditions in presence of Ni metal in acidic environment. We observed that in-situ generated radical hydrogen (H) responsible for cutting of graphene sheets and re-structuring of 2D sheet structure to one 1D nanotubes. Structural evolution of GNTs was confirmed by using of transmission electron microscopy (TEM) technique. The current vs. voltage (I–V) characteristics of GNTs displayed room temperature (RT) negative differential resistance (NDR) effect which is typical in nanowires, suggested the applicability of nanomaterial for various kind of electronics applications such as memory devices and transistors fabrication.

Self-Assembled Fe-N-Doped Carbon Nanotube Aerogels with Single-Atom Catalyst Feature as High-Efficiency Oxygen Reduction Electrocatalysts.

Self-assembled M-N-doped carbon nanotube aerogels with single-atom catalyst feature are for the first time reported through one-step hydrothermal route and subsequent facile annealing treatment. By taking advantage of the porous nanostructures, 1D nanotubes as well as single-atom catalyst feature, the resultant Fe-N-doped carbon nanotube aerogels exhibit excellent oxygen reduction reaction electrocatalytic performance even better than commercial Pt/C in alkaline solution.

From Carbon-Based Nanotubes to Nanocages for Advanced Energy Conversion and Storage.

Carbon-based nanomaterials have been the focus of research interests in the past 30 years due to their abundant microstructures and morphologies, excellent properties, and wide potential applications, as landmarked by 0D fullerene, 1D nanotubes, and 2D graphene. With the availability of high specific surface area (SSA), well-balanced pore distribution, high conductivity, and tunable wettability, carbon-based nanomaterials are highly expected as advanced materials for energy conversion and storage to meet the increasing demands for clean and renewable energies. In this context, attention is usually attracted by the star material of graphene in recent years. In this Account, we overview our studies on carbon-based nanotubes to nanocages for energy conversion and storage, including their synthesis, performances, and related mechanisms. The two carbon nanostructures have the common features of interior cavity, high conductivity, and easy doping but much different SSAs and pore distributions, leading to different performances. We demonstrated a six-membered-ring-based growth mechanism of carbon nanotubes (CNTs) with benzene precursor based on the structural similarity of the benzene ring to the building unit of CNTs. By this mechanism, nitrogen-doped CNTs (NCNTs) with homogeneous N distribution and predominant pyridinic N were obtained with pyridine precursor, providing a new kind of support for convenient surface functionalization via N-participation. Accordingly, various transition-metal nanoparticles were directly immobilized onto NCNTs without premodification. The so-constructed catalysts featured high dispersion, narrow size distribution and tunable composition, which presented superior catalytic performances for energy conversions, for example, the oxygen reduction reaction (ORR) and methanol oxidation in fuel cells. With the advent of the new field of carbon-based metal-free electrocatalysts, we first extended ORR catalysts from the electron-rich N-doped to the electron-deficient B-doped sp2 carbon. The combined experimental and theoretical study indicated the ORR activity originated from the activation of carbon π electrons by breaking the integrity of π conjugation, despite the electron-rich or electron-deficient nature of the dopants. With this understanding, metal-free electrocatalysts were further extended to the dopant-free defective carbon nanomaterials. Moreover, we developed novel 3D hierarchical carbon-based nanocages by the in situ MgO template method, which featured coexisting micro-meso-macropores and much larger SSA than the nanotubes. The unique 3D architecture avoids the restacking generally faced by 2D graphene due to the intrinsic π-π interaction. Consequently, the hierarchical nanocages presented superior performances not only as new catalyst supports and metal-free electrocatalysts but also as electrode materials for energy storage. State-of-the-art supercapacitive performances were achieved with high energy density and power density, as well as excellent rate capability and cycling stability. The large interior space of the nanocages enabled the encapsulation of high-loading sulfur to alleviate polysulfide dissolution while greatly enhancing the electron conduction and Li-ion diffusion, leading to top level performance of lithium-sulfur battery. These results not only provide unique carbon-based nanomaterials but also lead to in-depth understanding of growth mechanisms, material design, and structure-performance relationships, which is significant to promote their energy applications and also to enrich the exciting field of carbon-based nanomaterials.

Enzyme-Triggered Defined Protein Nanoarrays: Efficient Light-Harvesting Systems to Mimic Chloroplasts.

The elegance and efficiency by which chloroplasts harvest solar energy and conduct energy transfer have been a source of inspiration for chemists to mimic such process. However, precise manipulation to obtain orderly arranged antenna chromophores in constructing artificial chloroplast mimics was a great challenge, especially from the structural similarity and bioaffinity standpoints. Here we reported a design strategy that combined covalent and noncovalent interactions to prepare a protein-based light-harvesting system to mimic chloroplasts. Cricoid stable protein one (SP1) was utilized as a building block model. Under enzyme-triggered covalent protein assembly, mutant SP1 with tyrosine (Tyr) residues at the designated sites can couple together to form nanostructures. Through controlling the Tyr sites on the protein surface, we can manipulate the assembly orientation to respectively generate 1D nanotubes and 2D nanosheets. The excellent stability endowed the self-assembled protein architectures with promising applications. We further integrated quantum dots (QDs) possessing optical and electronic properties with the 2D nanosheets to fabricate chloroplast mimics. By attaching different sized QDs as donor and acceptor chromophores to the negatively charged surface of SP1-based protein nanosheets via electrostatic interactions, we successfully developed an artificial light-harvesting system. The assembled protein nanosheets structurally resembled the natural thylakoids, and the QDs can achieve pronounced FRET phenomenon just like the chlorophylls. Therefore, the coassembled system was meaningful to explore the photosynthetic process in vitro, as it was designed to mimic the natural chloroplast.

Nanochimneys: Topology and Thermal Conductance of 3D Nanotube–Graphene Cone Junctions

Pillared 3D carbon architectures, with the graphene layers and carbon nanotubes connected by topological junctions, have been produced and observed, as reported recently. However, the atomistic details of such junctions are hard to discern in microscopy and remain presently unclear. The simplest junction contains six heptagons in the transition region between the nanotube and graphene. Although these junctions make the pillared architectures possible, they are susceptible to failure when the whole structure undergoes mechanical or thermal stress. In this work we consider “nanochimneys”, a variety of special junctions with cones in between the nanotube and graphene parts. We explore the structures of the nanochimneys (NCs) and determine their underlying topological requirements. We also study the thermal conductance of these pillared architectures and show that NCs conduct heat better than regular simple junctions.

Reconstruction of multidimensional carbon hosts with combined 0D, 1D and 2D networks for enhanced lithium-sulfur batteries

Abstract It is a core task to find solutions to suppress the “shuttle effect” of polysulfides and improve high rate capability at the sulfur cathode of lithium sulfur batteries. Herein we first time propose a concept of multileveled blocking “dams” to suppress the diffusion of polysulfides. We report a facile and effective strategy to construct multidimensional conductive carbon hosts for accommodation of active sulfur. Multidimensional ternary carbon networks (MTCNs) with 0D nanospheres, 1D nanotubes and 2D nanoflakes are organically combined together to provide multileveled conductive channels to reserve active sulfur and promote stable sustained reactions. In the light of enhanced conductivity and multileveled blocking “dams” for polysulfides, the designed MTCNs/S cathode has been demonstrated with noticeable improvement in discharge capacity (1472 mAh g −1 at 0.l C) and long-term cycling stability (65% retention at 5.0 C after 500 cycles). Our research may provide a new insight in the gradient blocking of polysulfides with the help of multidimensional carbon networks.

Reticular synthesis of porous molecular 1D nanotubes and 3D networks.

Synthetic control over pore size and pore connectivity is the crowning achievement for porous metal-organic frameworks (MOFs). The same level of control has not been achieved for molecular crystals, which are not defined by strong, directional intermolecular coordination bonds. Hence, molecular crystallization is inherently less controllable than framework crystallization, and there are fewer examples of 'reticular synthesis', in which multiple building blocks can be assembled according to a common assembly motif. Here we apply a chiral recognition strategy to a new family of tubular covalent cages to create both 1D porous nanotubes and 3D diamondoid pillared porous networks. The diamondoid networks are analogous to MOFs prepared from tetrahedral metal nodes and linear ditopic organic linkers. The crystal structures can be rationalized by computational lattice-energy searches, which provide an in silico screening method to evaluate candidate molecular building blocks. These results are a blueprint for applying the 'node and strut' principles of reticular synthesis to molecular crystals.

First‐principles Studies of the Electronic and Thermoelectric Properties of Misfit Layered Phases of Calcium Cobaltite

AbstractThe electronic and thermoelectric properties of two phases of calcium cobaltite, a misfit layered compound, are investigated and compared using first‐principles DFT calculations. The two phases considered here include the conventional bulk phase that consists of alternating layers of Ca2CoO3 and CoO2, and a new phase that consists of alternating layers of CaCoO2 and CoO2, which was recently discovered in nanotubes. Electronic structure calculations reveal that both phases are ferrimagnetic materials with one important difference: the bulk phase is metallic, whereas the nanotubular phase is semiconducting. The metal‐to‐semiconductor transition that accompanies the Ca2CoO3 to CaCoO2 structural transition is shown to arise from the depletion of free carriers from the donor Ca atoms. The implications of the difference in electronic structure for the thermoelectric performance of these two phases are further examined with Boltzmann transport calculations. Relative to the metallic phase, the semiconducting phase displays appreciably higher Seebeck coefficients at minimal doping levels; these increased Seebeck coefficients compensate for the reduced conductivity and result in large power factors. In conjunction with the fact that the semiconducting phase is peculiar to 1D nanotubes, it is expected that additional effects from quantum confinement could render these low‐dimensional materials as promising thermoelectric materials.