Ultrathin Nanotubes Research Articles

Modified Nano-TiO2 Based Composites for Environmental Photocatalytic Applications

TiO2 probably plays the most important role in photocatalysis due to its excellent chemical and physical properties. However, the band gap of TiO2 corresponds to the Ultraviolet (UV) region, which is inactive under visible irradiation. At present, TiO2 has become activated in the visible light region by metal and nonmetal doping and the fabrication of composites. Recently, nano-TiO2 has attracted much attention due to its characteristics of larger specific surface area and more exposed surface active sites. nano-TiO2 has been obtained in many morphologies such as ultrathin nanosheets, nanotubes, and hollow nanospheres. This work focuses on the application of nano-TiO2 in efficient environmental photocatalysis such as hydrogen production, dye degradation, CO2 degradation, and nitrogen fixation, and discusses the methods to improve the activity of nano-TiO2 in the future.

A dual CoNi MOF nanosheet/nanotube assembled on carbon cloth for high performance hybrid supercapacitors

Layered-structure MOF is a promising material for electrochemical energy storage applications. However, low conductivity hinders their electrochemical performance. Herein, a hierarchical layered-structure CoNi-MOF with ultrathin nanosheets and nanotube arrays are directly grown on carbon cloth (CC) with Co(OH)2 as both template and Co source. The synthesized CC/CoNi-MOF shows high areal capacity of 1.01 C cm−2 at 2 mA cm−2, while keeps 61.4% capacity retention at 15 mA cm−2. A hybrid supercapacitor is successfully fabricated with CC/CoNi-MOF as positive electrode and reduced graphene oxide-carbon nanotube as negative electrode, possessing a maximum areal capacitance of 846 mF cm−2 at 1 mA cm−2, a high energy density of 55.5 Wh kg−1 at 175.5 W kg−1, and excellent cycling stability (96.5% after 10000 cycles). This work may pave a new way for designing MOF based materials with similar structure for high performance supercapacitors.

Ultrathin double-shell nanotubes of narrow band gap titanium oxide@carbon as efficient polysulfide inhibitors towards advanced lithium–sulfur batteries

“Double-shell” nanotubes of oxygen vacancy titanium oxide embedded nitrogen-doped carbon (OV-TiO2−x@NC) are designed as a robust host for Li–S batteries.

Influence of the reducing agent on the formation and morphology of the bismuth telluride nanostructures by using template assisted chemical process: From nanowires to ultrathin nanotubes

Abstract One-dimensional telluride based materials have recently attracted significant attention for development of the high-efficiency thermoelectric materials. Among one dimensional nanostructures, nanotubular structure has shown significant enhancement in the energy conversion efficiency due to higher reduction in the therml conductivity as compared to other one dimensional nanostructrues. Though some progress has already been establsihed to prepare nanotubes still synthesis of ultra-thin, smoother surface and stoichiometry Bi2Te3 nanotubes are still big challenges. Herein, we have reported that properly adjusting concentration of the reducing agent, different types of one-dimensional Bi2Te3 nanostructures such as nanowires to hollow nanostructures can be synthesized by using a template assisted chemical process. Furthermore, ultra-thin, smoother surface and close to stoichiometry Bi2Te3 nanotubes with a diameter of about 50 nm have been obtained by properly adjusting concentration of the reducing agent. Our experimental results evidenced that concentration of the reducing agent (hydrazine hydrate) plays a crucial role (morphology controlling agent) for synthesis of different types one-dimensional nanostructures from nanowires to ultrathin smooth surface nanotubes. A possible formation mechanism has been proposed to explain formation of the different one-dimensional Bi2Te3 nanostructures and the specific role of the reducing agent based on the experimental results.

Self-supported Ni2P nanotubes coated with FeP nanoparticles electrocatalyst (FeP@Ni2P/NF) for oxygen evolution reaction

Bimetallic phosphides have been widely investigated as electrocatalysts for oxygen evolution reaction (OER) due to their efficient activity and environmental friendliness. While the reasonable design and controllable synthesis of bimetallic phosphide with typical nanostructure is still a great challenge. Hence, we put forward a novel and straightforward way for constructing FeP nanoparticles coated Ni2P ultrathin nanotube arrays on the surface of Ni foil (FeP@Ni2P/NF), which is synthesized through two steps of electrodeposition and subsequent in-situ phosphorization process. The obtained FeP@Ni2P/NF shows excellent electrochemical activity for OER, and it only needs potential of 1.52 V vs. RHE to reach the current density of 50 mA cm−2 in an alkaline media. The excellent electrocatalytic activity of FeP@Ni2P/NF mainly benefits from: (i) the synergistic effect between FeP and Ni2P promoting electron transfer; (ii) the formation of the unique 3D ultrathin nanotube arrays increasing the quantity of active sites and avoiding the agglomeration of catalysts during testing. In addition, the influence of reaction condition on the electrochemical activity for OER has also been investigated through altering the phosphorization temperature of precursor.

Controllable synthesis of ultrathin WO3 nanotubes and nanowires with excellent gas sensing performance

Tungsten oxides (stoichiometric and non-stoichiometric) have gained extensive research interests because of promising physicochemical properties and diverse applications. Ultrathin walled tungsten oxide (WO3) nanotubes have been fabricated by hydrothermal route in the presence of both K2SO4 and citric acid under mild conditions. WO3 nanocrystals randomly assembled into ultrathin layered structures with highly peaked end which are then interwoven into nanotubes (diameter of 10−15 nm, wall thickness of 1−2 nm, width of 21 nm), because of Ostwald Ripening growth kinetics. Non-stoichiometric WO3-x nanowires (diameter 10−15 nm) were also synthesized using K2SO4 in the absence of organic ligand. The Brunauer–Emmett–Teller (BET) surface area for h-WO3 nanotubes was 71.95 m2 g−1 higher than WO3-x nanowires (51.83 m2 g−1), WO3 nanowires (42.70 m2 g−1) and nanorods (24.60 m2 g−1). Photoluminescence (PL) spectra show that the h-WO3 nanotubes and WO3-x nanowires have more crystal defects and oxygen vacancies. Time-dependent experiments were conducted and the plausible growth mechanism of h-WO3 nanotubes was proposed. The WO3 nanostructures with different morphologies were used as gas sensors that could detect acetone and ethanol with superior sensing performance (Ra/Rg for WO3 nanotubes = 32 & 26, respectively) under mild conditions, notably attributed to the ultrathin wall with high surface areas, crystal defects and oxygen vacancies.

Confined active species and effective charge separation in Bi4O5I2 ultrathin hollow nanotube with increased photocatalytic activity

Novel 1D Bi4O5I2 hollow nanotube (Bi4O5I2-HNT) material has been controlled synthesized via a facile PVP-assisted solvothermal method for the first time. Different parameters to control the formation of Bi4O5I2-HNT were tuned, such as usage amount of PVP, reaction temperature and mannitol concentration. Furthermore, structure, surface chemical composition, optical absorption ability and photogenerated charge separation efficiency of as-prepared Bi4O5I2 nanosheet and Bi4O5I2-HNT samples have been measured. Benefiting from the specific ultrathin hollow nanotube structure to produce confined highly concentrated active species and excellent electrical conductivity, Bi4O5I2-HNT material exhibited the increased photocatalytic degradation performance towards bisphenol A relative to Bi4O5I2 nanosheet. This work opens the door for designing other Bi-based photocatalysts via facile soft-template-assisted method to achieve a high-efficient photocatalytic performance.

Ni–Fe Phosphate/Ni Foam Electrode: Facile Hydrothermal Synthesis and Ultralong Oxygen Evolution Reaction Durability

Nickel–iron phosphate film with a porous surface formed by ultrathin nanotubes was successfully grown on Ni foam (NF) through a simple hydrothermal route at 150 °C for 90 min in the presence of HCl...

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

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

Correlation between microstructural defects and photoelectrochemical performance of 1D Ti–Nb composite oxide photoanodes for solar water splitting

We report on the optimized fabrication of ultrathin wall nanotubes grown on Ti–Nb alloy via anodization in organic-based electrolytes. The nanotubes are vertically aligned with wall thicknesses of 5–8 nm, diameters of 180–200 nm, and lengths of 2–2.8 μm. Raman spectroscopy and glancing angle x-ray diffraction (GAXRD) measurements indicated the formation of composite oxides of anatase TiO2 and monoclinic Nb2O5. The composite oxides showed better stability at elevated temperatures up to 650 ᵒC and with much smaller induced microstrain compared to the TiO2 counterpart. X-ray photoelectron spectroscopy (XPS) analysis confirmed the composition of the fabricated nanotubes as a mixed TiO2–Nb2O5 composite. Upon their use as photoanodes to split water, the composite TiO2–Nb2O5 NTs showed almost 2-fold increase in the obtained photocurrent compared to that of bare TiO2 NTs prepared under the same conditions. Moreover, the incident photon to current efficiency (IPCE) of the mixed oxide nanotubes was higher than that of bare TiO2 with a positive shift towards longer wavelengths, indicating improved electron mobility and charge collection. Hence, the addition of Nb resulted in the formation of thermally stable and photoactive photoanodes for solar fuel production.

Ultrathin Nanotubes of Bi5O7I with a Reduced Band Gap as a High-Performance Photocatalyst.

Bismuth oxyhalide (Bi-O-X) is a group of layered semiconductors, which are promising candidates for photocatalysis due to their inherent internal electric field and adjustable band gap through composition and morphology control. Bismuth-rich Bi-O-X has improved stability and advantageous band structure compared to those of Bi-O-X and hence has attracted an increasing amount of research interest. In this work, ultrathin nanotubes of Bi5O7I with a 5 nm diameter and a 1 nm wall are obtained through a hydrothermal method while the phase and morphology of the products are regulated by the pH values and polyvinylpyrrolidone (PVP) concentration of the reaction system, of which the products can be tuned from BiOI nanosheets to Bi5O7I nanobelts and ultrathin Bi5O7I nanotubes. PVP and pH control is important to the formation of the nanotubes as formation occurs via a PVP-guided oriented attachment from primary nanoparticles of Bi5O7I. The poorly crystalline and porous structure of the resultant bismuth-rich ultrathin nanotubes not only exposes more surface atoms but also exhibits a highly reduced conduction band minimum. The resultant band gap of 2.39 eV (as compared to 3.20 eV for the nanobelts) arises from the undercoordinated bismuth centers brought about by the rich oxygen vacancies in the nanotubes. The largely reduced band gap effectively enhances visible-light absorption, while the short charge-diffusion length of the nanotubes further reduces the charge-carrier loss in recombination.

Mechanical performance of lightweight polycrystalline Ni nanotubes

The mechanical properties of metallic nanowires and nanotubes were investigated using atomistic molecular dynamics simulations on Ni polycrystalline structures, similar to those experimentally obtained by Atomic Layer Deposition. We studied the response of nanostructures under uniaxial deformations with different thickness, geometry, and crystalline degree. Plastic deformation is due to stacking fault and coherent twin boundary formation, and to grain boundary activity. Different fracture processes are obtained from these systems, being the thin nanotubes failing thanks to a mix of brittle failure by grain boundary decohesion and ductile fracture due to significantly more twins than with a thicker nanotube and nanowire during the ductile fracture. The stress-strain curves, atomic displacements, and defects formation were analyzed, finding that nanotubes with a fraction of the volumetric mass have practically the same Young modulus and ultimate tensile stress, while fracture strain is slightly larger for nanowire. From all these studied cases, it is remarkable the result where ultra-thin nanotubes can withstand a 21% of tensile stress-strain with a similar yield strength than nanowires, but with a volumetric mass reduction of 60%, offering a lightweight alternative to design mechanical nanodevices with minimal loss of mechanical performance.

Ultrathin Pt–Ag Alloy Nanotubes with Regular Nanopores for Enhanced Electrocatalytic Activity

While creating open nanostructures represents a popular strategy for improving the utilization efficiency of Pt-based catalysts for electrochemical reactions, the exposed facets should be precisely controlled for further enhancement of the catalytic activity. Here, we report a novel strategy for creating regularly shaped nanopores in ultrathin nanotubes of bimetallic noble metals. By templating against Ag nanowires and then applying a thermal ripening process, we have successfully produced ultrathin (with a wall thickness of ∼1 nm) Pt–Ag alloy nanotubes containing high-density well-defined rectangular nanopores and a collapsed double-layer structure. The resulting porous nanotubes expose {100} facets at the basal sides and {110} facets with step sites at the edges of the rectangular nanopores. The particular surface structure and the bimetallic composition enable suppressed CO poisoning of the catalysts and consequently enhanced electrocatalytic activity in the methanol oxidation reaction. The typical spe...

Ultrathin, highly branched carbon nanotube cluster with outstanding oxygen electrocatalytic performance

Metal-free heteroatom-doped porous carbons such as N, P co-doped nanoporous carbon materials with designed properties are attracting increased attention for metal-air battery applications. Herein, we report a general approach to synthesizing highly branched N, P co-doped carbon nanotube cluster (NPCTC) derived from metal-organic frameworks as a bifunctional electrocatalyst. NPCTC were obtained by treating ZIF-8 with butyl methylphosphinate, followed by two-step pyrolysis. Benefiting from the cross-linking polymerization and self-aggregation between ZIF-8 and the monomer, the resulting NPCTC exhibited higher mechanical stability and strength. Although the wall thickness was <5 nm, no obvious shrinkage and collapse were observed after graphitization, thereby maximizing the exposure of the active sites. Studies of oxygen electrocatalysis demonstrate that the NPCTC can deliver outstanding bifunctional performance with a more positive half-wave potential, higher limiting current density for oxygen reduction reaction (ORR) than Pt/C, and lower onset potential for oxygen evolution reaction (OER) than IrO2. Homemade Zn-air battery exhibited stable charge-discharge durability over 180 cycles, with an overpotential increase of only 0.15 V. The improved electrochemical performance was mainly attributed to the synergistic effect of N, P co-doping and the distinct geometry of NPCTC, i.e., three-dimensionally interconnected hollow ultrathin nanotube branches facilitating electron and mass transfer.

Carbon-bonded, oxygen-deficient TiO2 nanotubes with hybridized phases for superior Na-ion storage

TiO2 shows great potential as anode materials for sodium-ion batteries (SIBs). However, its practical application has been deferred by the sluggish electronic/ionic transport. In this work, we report the controlled synthesis of ultrathin, carbon-bonded TiO2 nanotubes with oxygen vacancies (Vo) and hybridized amorphous/TiO2(B) phases via a hydrothermal reaction and heat-treatment. The introduction of Vo and carbon in TiO2 by C-Ti bonding effectively boosts its electron transport. Meantime, the ultrathin TiO2 nanotubes (with diameter of ∼10 nm and tube thickness of ∼3 nm) enable a large electrode/electrolyte contact interface with shortened Na+ diffusion distance. In addition, the formed coherent amorphous/TiO2(B) junctions further promote the charge transport and transfer at heterointerface. These synergic effects endow the resultant TiO2 material with superior Na+ storage capability in terms of high capacity (191 mA h/g at 0.2 C) and rate property (141 mA h/g at 10 C). Kinetics analysis further discloses a pseudocapacitive Na+ storage exerts a significant contribution to the total capacity. The proposed strategy based on synergic engineering of vacancy defects, chemical bonding and phase composition can pave the way for exploration of novel electrode materials for beyond lithium-ion batteries.

Electronic structure, stability, and magnetism of rutile-type ultrathin TiO2 nanotubes

In this study, based on density functional theory, we predicted the electronic structure, stability, and magnetism of ultrathin rutile-type TiO2 nanotubes (u-TiO2NTs) with different curvatures. The curvature energy calculations showed that the (m, 0) u-TiO2NTs follow the classical elasticity theory. As the diameter of the NTs increases, the wall thickness becomes thinner, and the binding energy and band gap increase until saturation. For the (10, 0) u-TiO2NT, the neutral Ti vacancies (VTi0) could induce a large magnetic moment and long-range ferromagnetic coupling, whereas the neutral O vacancies (VO0) cannot. In addition to calculations of the vacancy formation energy, we investigated the magnetism and magnetic coupling of the (10, 0) u-TiO2NT with VTi− or VO+. We found that the introduction of VTi− vacancies led to unstable ferromagnetic coupling in the NTs, whereas the VO+ vacancies preferred to couple in a stable ferromagnetic manner. Our results suggest a possible route for obtaining high Curie temperature ferromagnetism in TiO2 materials.

MoS2 quantum dots@TiO2 nanotube composites with enhanced photoexcited charge separation and high-efficiency visible-light driven photocatalysis

MoS2 quantum dots (QDs) that are 5 nm in size were deposited on the surface of ultrathin TiO2 nanotubes (TNTs) with 5 nm wall thickness by using an improved hydrothermal method to form a MoS2 QDs@TNT visible-light photocatalyst. The ultrathin TNTs with high percentage of photocatalytic reactive facets were fabricated by the commercially available TiO2 nanoparticles (P25) through an improved hydrothermal method, and the MoS2 QDs were acquired by using a surfactant-assisted technique. The novel MoS2 QDs@TNT photocatalysts showed excellent photocatalytic activity with a decolorization rate of 92% or approximately 3.5 times more than that of pure TNTs for the high initial concentration of methylene blue solution (20 mg l−1) within 40 min under visible-light irradiation. MoS2 as the co-catalysts favored the broadening of TNTs into the visible-light absorption scope. The quantum confinement and edge effects of the MoS2 QDs and the heterojunction formed between the MoS2 QDs and TNTs efficiently extended the lifetime of photoinduced charges, impeded the recombination of photoexcited electron–hole pairs, and improved the visible-light-driven high-efficiency photocatalysis.

Ultrathin dendritic IrTe nanotubes for an efficient oxygen evolution reaction in a wide pH range

The ultrathin and dendritic IrTe nanotubes, synthesized via galvanic replacement reaction, exhibited enhanced electrocatalytic performance toward OER with a wide pH range.

The Electronic and Magnetic Properties of Tetragonal Ultrathin BaTiO3 Nanotube

The unique structural, electronic and magnetic properties of intrinsic defect in tetragonal ultrathin BaTiO3 nanotube (u-BTONT) have been investigated by first-principle calculations. The zigzag (9,0) u-BTONTs with two different terminations (TiO2 and BaO) can be formed by rolling up one monolayer BTO along a certain crystallographic axis, and the BaO-terminated NT is more stable than TiO2 terminated due to its lower binding energy. The oxygen vacancies on the tube are more stable than cation vacancies, and their magnetic coupling is related not only to the kinds of oxygen vacancies but also to the distance of vacancies. Moreover, both Ba and Ti vacancies also can introduce the ferromagnetism in u-BTONT, which is different from the origin of magnetism in BTO bulk and (001) surface. It is indicated that one-dimensional structure with high surface area can make it easier to form more useful vacancies which prefer ferromagnetism. Our work offers a possible route to fabricate the multiferroic materials.

Optimal sidewall functionalization for the growth of ultrathin TiO2 nanotubes via atomic layer deposition

One of the most suitable approaches for the production of inorganic nanotubes is by means of carbon nanotube (CNT) templates coated by atomic layer deposition (ALD). This approach is attractive because it has the potential of controlling the wall thickness down to the Angstroms level. However, it is a recognized fact that the chemistry of the substrate surface can delay the full coverage at the initial stages of the ALD coating process, mainly due to nucleation issues. This is an important issue that might restrict laying down homogeneous coatings within the ultrathin range, which is the foundation for producing self-supported inorganic nanotubes. Here, we explore the early stage of the TiO2 nucleation on CNT templates systematically functionalized with different chemical groups (COOH, OH) or N-doped. The effects of the functionalization on the nucleation process from tetrakis (dimethylamino) titanium and water were meticulously studied by means of transmission electron microscopy. Observations revealed grain-like growth of TiO2 over pristine, purified and –OH-functionalized CNTs. In contrast, COOH functionalization yielded good conformality, which was improved on N-doped CNTs. Results were confirmed by X-rays photoelectron spectroscopy analysis. We recommend either COOH or N-doped CNTs for the production of ultrathin TiO2 nanotubes.