Ultrathin Nanotubes Research Articles

Electronic structure of ultrathin single-walled platinum nanotubes

Using Density Functional Theory based on the plane wave method and linearized augmented cylindrical wave method, and taking into account the spin–orbit interaction, the structural, electronic and spin properties of ultrathin single-walled nanotubes consisting of six platinum rows are obtained. The nanotubes are found to possess metallic electronic mobility, including the nonchiral Pt(6,0) with the largest number (15G0) of ballistic channels. Analysis of the density of electronic states at Fermi level revealed that the chiral Pt(5,1) has a difference in concentration of mobile electrons with opposite spins of 1.42 times, and up to 3–4 times under a weak torsional strain.

Novel discrete architecture for quantum dots modified ultrathin hollow nanotube Bi2Sn2O7/Bi4O5I2 S-scheme heterojunction for ultra-efficient photocatalytic degradation of bisphenol A

Designing and constructing novel discrete architecture for quantum dots modified ultrathin hollow nanotube Bi2Sn2O7/Bi4O5I2 S-scheme heterojunctions for the first time in this work is an ideal strategy to improve the photocatalytic activity. As expected, the Bi2Sn2O7/Bi4O5I2 heterojunction exhibited outstanding performance of degradation bisphenol A (BPA), the rate constant of Bi2Sn2O7/Bi4O5I2 heterojunction was 1.7 and 41.8 times higher than that of Bi4O5I2 and Bi2Sn2O7, respectively. The promoted activity could be attributed to the spatial separation of photogenerated carriers as well as redox reaction sites due to the discrete structure, and the enhanced charge separation due to the S-scheme mechanism via Bi-O channels as derived from DFT calculations. Furthermore, Bi2Sn2O7/Bi4O5I2 heterojunction exhibited unprecedented ultra-efficient in BPA degradation compared to other published Bi-based catalysts, and excellent performance under actual sunlight contributes to its prospective practical application. This strategy affords a novel approach for fabricating discrete S-scheme heterojunctions photocatalysts with high-efficiency, strong-stable, and sustainable.

Engineering FeCo Dual Sites on Tube-on-Plate Hollow Structure for Efficient Oxygen Electroreduction.

Atomically dispersed single-atom catalysts are intriguing catalysts in the field of electrocatalysis for nearly 100% exploitation of metal atoms. However, they are still far from practical usage due to the scaling relationship limit and metal loading limit. Generation of a diatomic complex would offer superior catalytic performance through the cooperation of two neighboring atoms as active sites. Herein, Fe/Co dual atomic sites embedded in a tube-on-plate hollow structure are designed and fabricated for an efficient electrochemical oxygen reduction reaction (ORR). The unique structure composed of ultrathin nanotube building blocks dramatically maximizes the surface area for copious active site exposure. Thanks to the synergetic interaction between Fe/Co pairs, the obtained FeCo/NC exhibits outstanding ORR activity and stability in alkaline media. Furthermore, density functional theory calculations have revealed that the remarkable activity is attributed to the electron-deficient Fe sites in FeCoN6. This work may pave the way for the innovative design of highly dispersed dual-site catalysts for broader applications in the realm of electrochemical catalysis.

Low-temperature and high-sensitivity Au-decorated thin-walled SnO2 nanotubes sensor for ethanol detection

The nanostructures of oxides decorated with noble metals have been used to detect ethanol at low temperature with high sensitivity. Instead of traditional thick ones, this work explored the ultrathin SnO2 nanotubes (NTs) decorated with Au nanoparticles (NPs) for chemical gas sensors. The field-emission scanning electron microscopy and field-emission transmission electron microscopy characterized the SnO2 NTs and Au NPs with uniform structures. After that, the X-ray diffraction, X-ray photoelectron spectroscopy and base resistance test proved the existence of the Schottky junction. Then, the gas-sensing test results show that the gold-modified SnO2 NTs sensor has excellent sensing properties such as low operating temperature (25 ℃), high sensitivity (Response value of 192 at 160 °C), low detection limit (1 ppm), good selectivity for ethanol, and high stability. This study presents a novel approach for gas sensing using ultrathin SnO2 NTs decorated with Au NPs, which has demonstrated excellent sensing properties. The results of this study provide a foundation for further research and development of highly efficient gas sensors for various applications.

Confinement effect induced efficient electro-catalytic reduction of dinitrogen in transition metal atom endohedral ultra-thin C4N3 nanotubes

The confinement effect could effectively enhance the catalytic activity of electro-catalysts by modulating the micro-environment around active center. Herein, the transition metal endohedral (3,3) C4N3 nanotubes (TM-CNNTs) were computationally proposed as promising electro-catalysts for reduction of dinitrogen into NH3. Using binding energy, adsorption energy of N2 and free energy difference between adsorbed *N2H and *N2 as the indicators, Cr-CNNT and Mo-CNNT (prefers end-on configuration of *N2), as well as Mn-CNNT, Fe-CNNT and W-CNNT (prefers side-on configuration of *N2) were screened out as the potential candidates. Then the optimal reaction paths and the changes in the free energy for nitrogen reduction reaction (NRR) were determined. Among the potential candidates, the Mn-CNNT was determined as the most efficient NRR electro-catalyst, with good conductivity and stability, as well as the lowest limiting potential (UL) of −0.32 V. After comparisons with other C4N3-based nanomaterials, the confinement effect in the ultra-thin (3,3) CNNT was elucidated to stabilize the adsorption of N2 by side-on configuration, thus facilitates the enzymatic pathway during NRR catalysis. Our research shed light on the mechanism of enhanced NRR electro-catalytic activity induced by confinement effect within the ultra-thin nanotubes.

Confining Co-Based Nanocatalysts by Ultrathin Nanotubes for Efficient Transfer Hydrogenation of Biomass Derivatives.

Catalytic transfer hydrogenation (CTH) based on non-noble-metal catalysts has emerged as an environmentally friendly way for the utilization of biomass resources. However, the development of efficient and stable non-noble-metal catalysts is crucially challenging due to their inherent inactivity. Herein, a metal-organic framework (MOF)-transformed CoAl nanotube catalyst (CoAl NT160-H) with unique confinement effect was developed via a "MOF transformation and reduction" strategy, which exhibited excellent catalytic activity for the CTH reaction of levulinic acid (LA) to γ-valerolactone (GVL) with isopropanol (2-PrOH) as the H donor. Comprehensive characterizations and experimental investigations uncovered that the confined effect of the ultrathin amorphous Al2O3 nanotubes could modulate the electronic structure and enhance the Lewis acidity of Co nanoparticles (NPs), thus contributing to the adsorption and activation of LA and 2-PrOH. The synergy between the electropositive Co NPs and Lewis acid-base sites of the CoAl NT160-H catalyst facilitated the transfer of α-H in 2-PrOH to the C atom of carbonyl in LA during the CTH process via a Meerwein-Ponndorf-Verley mechanism. Moreover, the confined Co NPs embedded on am-Al2O3 nanotubes endowed the CoAl NT160-H catalyst with superior stability and the catalytic activity was nearly unchanged for at least ten cycles, far surpassing that of the Co/am-Al2O3 catalyst prepared by the traditional impregnation method.

Manganese, Fluorine, and Nitrogen Co-Doped Bronze Titanium Dioxide Nanotubes with Improved Lithium-Ion Storage Properties

Because of the unique crystal framework, bronze TiO2 (or TiO2(B)) is considered the prospective choice for high-performance lithium-ion battery anodes. Nevertheless, TiO2(B) requires efficient modification, e.g., suitable doping with other elements, to improve the electronic properties and enhance the stability upon insertion/extraction of guest ions. However, due to the metastability of TiO2(B), doping is challenging. Herein, for the first time, TiO2(B) co-doped with Mn, F, and N were synthesized through a successive method based on a hydrothermal technique. The prepared doped TiO2(B) consists of ultrathin nanotubes (outer diameter of 10 nm, wall thickness of 2–3 nm) and exhibits a highly porous structure (pore volume of up to 1 cm3 g−1) with a large specific surface area near 200 m2 g−1. The incorporation of Mn, F, and N into TiO2(B) expands its crystal lattice and modifies its electronic structure. The band gap of TiO2(B) narrows from 3.14 to 2.18 eV upon Mn- and N-doping and electronic conductivity improves more than 40 times. Doping with fluorine improves the thermal stability of TiO2(B) and prevents its temperature-induced transformation into anatase. It was found that the diffusivity of Li is about two times faster in doped TiO2(B). These properties make Mn, F, and N co-doped TiO2(B) nanotubes promising for application as high-performance anodes in advanced lithium-ion batteries. In particular, it possesses a good reversible capacity (231.5 mAh g−1 after 100 cycles at 70 mA g−1) and prominent rate capability (134 mAh g−1 at 1500 mA g−1) in the half-cell configuration. The (Mn, F, N)-doped TiO2(B) possesses a remarkable low-temperature Li storage performance, keeping 70% of capacity at −20 °C and demonstrating potentialities to be employed in full-cell configuration with LiMn2O4 cathode delivering a reversible capacity of 123 and 79 mAh g−1 at 35 and 1500 mA g−1, respectively, at a voltage of ~2.5 V. This research underlies that regulation of electronic and crystal structure is desired to uncover capabilities of nanoparticulate TiO2(B) for electrochemical energy storage and conversion.

Unlocking nanotubular bismuth oxyiodide toward carbon-neutral electrosynthesis

Defective ultrathin Bi5O7I nanotubes are designed by the combination of structure and defect engineering strategies to achieve highly active, selective, and stable performance for electrocatalytic reduction of CO2 to formate.

Ultrathin Nanotube Structure for Mass-Efficient and Durable Oxygen Reduction Reaction Catalysts in PEM Fuel Cells.

It remains a challenge for platinum-based oxygen reduction reaction catalysts to simultaneously possess high mass activity and high durability in proton-exchange-membrane fuel cells. Herein, we report ultrathin holey nanotube (UHT)-structured Pt-M (M = Ni, Co) alloy catalysts that achieve unprecedented comprehensive performance. The nanotubes have ultrathin walls of 2-3 nm and construct self-supporting network-like catalyst layers with thicknesses of less than 1 μm, which have efficient mass transfer and 100% surface exposure, thus enabling high utilization of Pt atoms. Combined with the high intrinsic activity produced by the alloying effect, the catalysts achieve high mass activity. Moreover, the nanotube structure not only avoids the agglomeration problem of nanoparticles, but the low curvature of the tube wall also gives UHT a low surface energy (less than 1/3 of that of the same size nanoparticle), so UHT is more resistant to the Ostwald ripening and is stable. For the first time, the U.S. DOE mass activity target and dual durability targets for load and start-stop cycles are achieved on one catalyst. This study provides an effective structural strategy for the preparation of electrocatalysts with high atomic efficiency and excellent durability.

Oxygen-vacancy-induced charge localization and atomic site activation in ultrathin Bi4O5Br2 nanotubes for boosted CO2 photoreduction

Solar CO2 reduction into value-added carbon fuels emerges as a sustainable and significant approach for CO2 conversion. However, poor photoabsorption, sluggish dynamics of multi-electrons transfer and high CO2 activation barrier substantially hamper CO2 photoreduction efficiency. Herein, freestanding ultrathin Bi4O5Br2 nanotubes with abundant oxygen vacancies were initially fabricated for optimizing these crucial processes. The ultrathin-shelled topologies of open tubular scaffolds and abundant surface oxygen vacancies endow the Bi4O5Br2 nanotubes with extended photo-response region and boosted charge separation. Furthermore, the presence of oxygen vacancies alters charge density distribution and affords abundant localized electrons on the catalysts’ surface. These not only reinforce covalent interactions, electron exchange and transfer between CO2 and oxygen vacancies, but also lower the CO2 reaction energy barriers and stabilize the rate-limiting COOH* intermediate. As a result, the OV-rich Bi4O5Br2 ultrathin nanotubes exhibit an outstanding CO production rate of 19.56 µmol g−1h−1 without using any cocatalyst or sacrificial agent, approximately 11.2 times higher than the Bi4O5Br2 nanoplates counterpart. This work provides insights into the future design of ultrathin hollow scaffolds for solar fuel photosynthesis and other applications.

Moss-like Hierarchical Architecture Self-Assembled by Ultrathin Na2Ti3O7 Nanotubes: Synthesis, Electrical Conductivity, and Electrochemical Performance in Sodium-Ion Batteries.

Nanocrystalline layer-structured monoclinic Na2Ti3O7 is currently under consideration for usage in solid state electrolyte applications or electrochemical devices, including sodium-ion batteries, fuel cells, and sensors. Herein, a facile one-pot hydrothermal synthetic procedure is developed to prepare self-assembled moss-like hierarchical porous structure constructed by ultrathin Na2Ti3O7 nanotubes with an outer diameter of 6–9 nm, a wall thickness of 2–3 nm, and a length of several hundred nanometers. The phase and chemical transformations, optoelectronic, conductive, and electrochemical properties of as-prepared hierarchically-organized Na2Ti3O7 nanotubes have been studied. It is established that the obtained substance possesses an electrical conductivity of 3.34 × 10−4 S/cm at room temperature allowing faster motion of charge carriers. Besides, the unique hierarchical Na2Ti3O7 architecture exhibits promising cycling and rate performance as an anode material for sodium-ion batteries. In particular, after 50 charge/discharge cycles at the current loads of 50, 150, 350, and 800 mA/g, the reversible capacities of about 145, 120, 100, and 80 mA∙h/g, respectively, were achieved. Upon prolonged cycling at 350 mA/g, the capacity of approximately 95 mA∙h/g at the 200th cycle was observed with a Coulombic efficiency of almost 100% showing the retention as high as 95.0% initial storage. At last, it is found that residual water in the un-annealed nanotubular Na2Ti3O7 affects its electrochemical properties.

Eco-Friendly, Highly Efficient Ethanol-Assisted Supercritical Preparation of an Ultrathin ZnO Nanotube

Eco-Friendly, Highly Efficient Ethanol-Assisted Supercritical Preparation of an Ultrathin ZnO Nanotube

Self-doped Br in Bi5O7Br ultrathin nanotubes: Efficient photocatalytic NO purification and mechanism investigation

Bismuth-rich Bi5O7Br is a promising photocatalyst for pollutant removal owing to its stability and appropriate band structure in comparison with bismuth oxybromide. However, bulk-phase Bi5O7Br suffers from poor light absorption and high charge recombination rates resulting in poor activity. Elemental doping is a powerful strategy to enhance photocatalytic activity. In this study, we prepared a series of Br auto-doped ultrathin Bi5O7Br nanotubes and explored the effect of Br doping on photocatalytic NO removal. The optimal doping content was determined via a photocatalytic NO removal experiment, which revealed the optimal ratio of Bi and Br was approximately 3:1. In situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFT) and density functional theory (DFT) studies revealed that NO removal mechanism catalyzed by Br doped Bi5O7Br. Our work presents a new strategy for the enhancement of photocatalytic pollutant degradation by bismuth oxyhalide photocatalysts.

Structural and Optical Properties of Ultra-thin g-C3N4 nanotubes based g-C3N4/Ag/Ag2CrO4 ternary composite photocatalyst with Z-scheme carrier transfer mechanism

Ultra-thin g-C3N4 nanotubes with a wall thickness of about 10 nm were prepared by calcining a supramolecular precursor synthesized from cyanuric acid, melamine and urea. After Ag nanoparticles were deposited on the surface of g-C3N4 nanotubes and partially oxidized to Ag2CrO4, a g-C3N4/Ag/Ag2CrO4 ternary nanocomposite was obtained. The structural, optical and electronic properties of the composite were investigated. Compared with pure g-C3N4 nanotubes and g-C3N4 nanotubes decorated with Ag nanoparticles, the photocatalytic performance of the ternary composite is much improved due to its large specific surface area and effective separation efficiency of photo-generated electron-hole pairs. Furthermore, the composite not only promotes the effective separation of photo-generated carriers, but also inhibits the photocorrosion of its Ag2CrO4 component. A Z-scheme photo-generated carrier transfer mechanism with strong redox ability between the components in the g-C3N4/Ag/Ag2CrO4 ternary composite is confirmed by constructing the band structure of the composite. The high photocatalytic degradation performance of organic pollutants after several cycle tests makes it possible to be applied in practice.

Combining Cu7S4 ultrathin nanosheets and nanotubes for efficient and selective absorption of anionic dyes

The growth of unique two-dimensional nanosheets on hollow and porous metal sulfides has received significant attention in adsorption and catalysis applications. Herein, we report a facile strategy to grow ultrathin nanosheets (NSs) on Cu7S4 nanotubes (NTs) via a two-step process (Cu7S4-NS-T). First, the obtained Cu nanowires (NWs) are oxidized in a hydrogen peroxide solution to form Cu@CuO composite nanowires decorated with ultrathin CuO NSs. Then, Cu7S4-NS-T composed of Cu7S4 NTs and Cu7S4 NSs is obtained from Cu@CuO NWs via a sulfurization process with the Kirkendall effect, in which anion-exchange reaction between Cu@CuO and S2‐− anions resulted in the formation of hollow structure. Due to fuse porous nanotubes and ultrathin nanosheets with abundant exposed copper centers, the obtained Cu7S4-NS-T shows extraordinary adsorption ability for the removal of anionic dyes, such as Congo red (CR) with a maximum adsorption capacity of 1166.07 mg/g, much superior to that of commercial activated carbon. Adsorption equilibrium and kinetic studies indicate that chemisorption is the main control process for the enrichment of the anionic dyes. The Cu7S4-NS-T can be used as a novel effective adsorbent for rapidly and efficiently removing dyes contaminants in water.

A trace ppb-level electrochemical H2S sensor based on ultrathin Pt nanotubes

An amperometric sensor has been developed with high sensitivity for real-time measurement of H2S gas at room temperature (25 °C ± 2 °C). In order to enhance the utilization of platinum and improve its catalytic performance, an ultrathin and one-dimensional (1D) Pt nanotubes (Pt NTs, ~3.5 nm in wall thickness) were designed and used as sensing electrode materials. Different concentrations of H2S gas were tested to evaluate the sensitivity of the sensor and to obtain the relationship between the electricity response signal and H2S gas concentration. At room temperature, the sensor based on Pt NTs shows better sensing performance than that based on Pt nanoparticles, which is mainly attributed to two factors, namely, the inherent characteristic of the hollow 1D Pt NTs. The Pt NTs-based sensor shows a detection limit as low as 0.025 ppb, which are the lowest among H2S gas sensors reported in the literatures. The response and recovery times are 0.75 s and 0.86 s for 0.8 ppb H2S, respectively. In addition, the sensor shows a wide range (100 ppm-0.025 ppb), high selectivity compared to other gases (including CO, NH3, CH2O, NO and NO2), good reproducibility, and satisfactory long-term stability. Thus, the ultrathin Pt NTs-based gas sensor would be a great potential to the real-time and online monitoring of the trace ppb-level H2S gas at room temperature.

Electronic Structures, Stabilities, and Magnetism of SrTiO3 Monolayer and Ultrathin Nanotubes

Electronic Structures, Stabilities, and Magnetism of SrTiO3 Monolayer and Ultrathin Nanotubes

Modeling the threshold voltage of core-and-outer gates of ultra-thin nanotube Junctionless-double gate-all-around (NJL-DGAA) MOSFETs

The present article deals with the analytical modeling of threshold voltage of an ultra-thin nanotube Junctionless double-gate-all-around (NJL-DGAA) metal-oxide-semiconductor field-effect-transistor (MOSFET). Under the condition of full depletion, the modeling of the surface potential relating to inner and outer gates of the device has been performed by solving three-dimensional Poisson's equation in cylindrical coordinates with appropriate boundary conditions. Corresponding to inner and outer channel potential expressions, the two different threshold voltages of the device are obtained. Moreover, the connection between the source-to-drain subthreshold current and threshold voltage is investigated. The drain-induced-barrier-lowering (DIBL) as an indicator of short-channel effects has been studied. Further, the quantum confinement effects have been explored through quantum mechanical correction in the threshold voltage model. The model outcomes are compared with data extracted from ATLAS™ TCAD simulations, and good acceptances have been observed.

Ultra-thin dark amorphous TiOx hollow nanotubes for full spectrum solar energy harvesting and conversion‡

Dark titania (TiOx) have been widely used for solar energy harvesting and conversion applications due to its excellent light absorbing performance throughout the ultraviolet to near infrared wavelength band, low cost, and non-toxic nature. However, the synthesis methods of dark TiOx are usually complicated and time-consuming. Here we report a facile and rapid method to fabricate dark amorphous TiOx (am-TiOx) hollow nanotube arrays on nanoporous anodic alumina oxide (AAO) templates using atomic layer deposition. Systematic investigation was performed to demonstrate that Ti3+ and O- species in the am-TiOx ultra-thin films, as well as the spatial distribution of these am-TiOx ultra-thin films on the vertical side walls of AAO templates are two major mechanisms of the black color. Importantly, the film deposition took ~18 min only to produce the optimized ~4‐nm‐thick am-TiOx film. Representative applications were demonstrated using photocatalytic reduction of silver nitrate and photothermal solar vapor generation, revealing the potential of these ultra-thin dark am-TiOx/AAO structures for full spectrum solar energy harvesting and conversion.

Focused Electric-Field Polymer Writing: Toward Ultralarge, Multistimuli-Responsive Membranes.

The cost-effective direct writing of polymer nanofibers (NFs) has garnered considerable research attention as a compelling one-pot strategy for obtaining key building blocks of electrochemical and optical devices. Among the promising applications, the changes in optical response from external stimuli such as mechanical deformation and changes in the thermal environment are of great significance for emerging applications in smart windows, privacy protection, aesthetics, artificial skin, and camouflage. Herein, we propose a rational design for the mass production of customized NFs through the development of focused electric-field polymer writing (FEPW) coupled with the roll-to-roll technique. As a proof of key applications, we demonstrate multistimuli-responsive (mechano- and thermochromism) membranes with an exceptional production scale (over 300 cm2). Specifically, the membranes consist of periodically aligned ultrathin (∼60 nm) alumina nanotubes inserted in the elastomers. We performed a two-phase finite element analysis of the unit cells to verify the underlying physics of light scattering at heterogeneous interfaces of the strain-induced air gaps. By adding thermochromic dye during the FEPW, the optical modulation of transmittance change (∼83% to 37% at visible wavelength) was successfully extended to high-contrast thermal-dependent coloration.