Microtubes Research Articles

Developing highly reliable Ag@NaYF4 hybrid structures for efficiently improving optical property

Here, we report a rational method for constructing a composite functional surface-enhanced Raman scattering (SERS) substrate, which is prepared by modifying the surfaces of β-NaYF4:Yb3+/Er3+ microtubes (MTs) with Ag nanoparticles (NPs). A single Ag@NaYF4 MT hybrid structure (Ag@NaYF4 MTHS) improves SERS activity compared to a typical substrate consisting of pure Ag NPs deposited on glass slide and exhibits excellent Raman signal response to various probe molecules (4-nitrothiophenol (4-NTP), crystal violet (CV), and Rhodamine 6G (Rh6G)). Furthermore, the Ag@NaYF4 MTHS substrate presents good catalytic performance and the plasmon-driven catalytic kinetics process is successfully monitored by using in situ SERS spectroscopy technique. This study provides valuable insights for designing multifunctional hybrid structures that incorporate containing noble metallic and lanthanide-based materials. These composite structures hold significant potential for advancing applications in photocatalysis, sensor, and in situ bio/chemical-analysis.

Volatile Memristive Devices with Analog Resistance Switching Based on Self-Assembled Squaraine Microtubes as Synaptic Emulators.

In this work, the discovery of volatile memristive devices that exhibit analog resistive switching (RS) and synaptic emulation based on squaraine materials is presented. Specifically, organic microtubes (MTs) based on 2,4-bis[(4-(N,N-diisobutyl)-2-6-hydroxyphenyl]squaraine (SQ) are prepared by evaporation-induced self-assembly (EISA). The MTs are ca. 2 μm in diameter (aspect ratio: 10-130). While powder X-ray diffraction data for MTs identify monoclinic and orthorhombic polymorphs, optical data report the monoclinic phase with energetic disorder. By favorable energetic alignment of the Au work function with the SQ HOMO energy, unipolar (hole-only) symmetric metal-insulator-metal devices are formed by EISA of MT meshes on interdigitated electrodes. The DC I-V characteristics acquired exhibit pinched hysteretic I-V loops, indicative of memristive behavior. Analysis indicates Ohmic transport at low bias with carrier extraction by thermionic emission. At high bias, space-charge-limited conduction in the presence of traps distributed in energy, enhanced by a Poole-Frenkel effect and with carrier extraction by Fowler-Nordheim tunneling, is observed. These data indicate purely electronic conduction. I-V hysteresis attenuates at smaller voltage windows, suggesting that carrier trapping/detrapping underpins the hysteresis. By applying triangular voltage waveforms, device conductance gradually increases sweep-on-sweep, with wait-time-erase or voltage-erase options. Using square waveforms, repeated erase-write-read of multiple distinct conductance states is achieved. Such analog RS behavior is consistent with trap filling/emptying effects. By waveform design, volatile conductance states may also be written so that successive conductance states exhibit identical current levels, indicating forgetting of previously written states and mimicking the forgetting curve. Finally, advanced synaptic functions, i.e., excitatory postsynaptic current, paired-pulse facilitation, pulse-dependent plasticity, and a transition from short- to long-term memory driven by post-tetanic potentiation, are demonstrated.

Effect of copper doping on the photocatalytic performance of Ni2O3@PC membrane composites in norfloxacin degradation.

In this study, copper (Cu) and nickel oxide (Ni2O3) microtubes (MTs) were synthesized using an electroless template deposition technique within porous polycarbonate (PC) track-etched membranes (TeMs) to obtain Cu@PC and Ni2O3@PC composite membranes, respectively. The pristine PC TeMs featured nanochannels with a pore density of 4 × 107 pores per cm2 and an average pore diameter of 400 ± 13 nm. The synthesis of a mixed composite, combining Cu and Ni2O3 within the PC matrix, was achieved through a two-step deposition process using a Ni2O3@PC template. An analysis of the resultant composite structure (Cu/Ni2O3@PC) confirmed the existence of CuNi (97.3%) and CuO (2.7%) crystalline phases. The synthesized catalysts were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) analysis, and atomic force microscopy (AFM). In photodegradation assessments, the Cu/Ni2O3@PC mixed composite demonstrated higher photocatalytic activity, achieving a substantial 59% degradation of norfloxacin (NOR) under UV light irradiation. This performance surpassed that of both Ni2O3@PC and Cu@PC composites. The optimal pH for maximum NOR removal from the aqueous solution was determined to be pH 5, with a reaction time of 180 min. The degradation of NOR in the presence of these composites adhered to the Langmuir-Hinshelwood mechanism and a pseudo-first order kinetic model. The reusability of the catalysts was also investigated for 10 consecutive runs, without any activation or regeneration treatments. The Cu@PC membrane catalyst demonstrated a marked decline in degradation efficiency after the 2nd test cycle, ultimately catalyzing only 10% of NOR after the 10th cycle. In contrast, the Ni2O3@PC based catalyst demonstrated a more stable NOR degradation efficiency throughout all 10 runs, with 27% NOR removal observed during the final test. Remarkably, the catalytic performance of the Cu/Ni2O3@PC mixed composite remained highly active even after being recycled 4 times. The degradation efficiency exhibited a gradual reduction, with a 17% decrease after the 6th run and a cumulative 35% removal of NOR achieved by the 10th cycle. Overall, the findings indicate that Cu/Ni2O3@PC mixed composite membranes may represent an advancement in the quest to mitigate the adverse effects of antibiotic pollution in aquatic environments and hold significant promise for sustainable water treatment practices.

Template-free synthesis of novel TiO2 microtube (MT) and N-doped MT and their photocatalytic properties decomposing organic compounds

Novel TiO2 microtubes (MTs) with a pore size of ∼1.6 µm, a wall thickness of ∼200 nm, and lengths of 15–30 µm were synthesized by solvothermal reaction without templates. TiO2 MTs, self-assembled with highly crystallized anatase particles, were obtained at the specific concentration ranges of titanium tetraisopropoxide (TTIP) and tetrabutyl ammonium hydroxide (TBAH) (0.32–0.45 M TTIP and 0.32–0.38 M TBAH). We also prepared nitrogen-doped TiO2 (N-TiO2) MTs by flowing gaseous ammonia to the bare TiO2 MTs at 550 °C and analyzed the photocatalytic properties of TiO2 MT and N-TiO2 MT in decomposing gaseous isopropanol (IPA) and aqueous salicylic acid (SA). Under UV–visible light illumination TiO2 MT showed slightly lower photocatalytic activities than commercial TiO2 NP (Aeroxide P25), but under visible light N-TiO2 MT demonstrated 2.2–3.4 times higher activities than N-TiO2 NP, presumably due to its effective structure for space-charge separation of the photogenerated electron/hole pairs.

Vertex protein PduN tunes encapsulated pathway performance by dictating bacterial metabolosome morphology

Engineering subcellular organization in microbes shows great promise in addressing bottlenecks in metabolic engineering efforts; however, rules guiding selection of an organization strategy or platform are lacking. Here, we study compartment morphology as a factor in mediating encapsulated pathway performance. Using the 1,2-propanediol utilization microcompartment (Pdu MCP) system from Salmonella enterica serovar Typhimurium LT2, we find that we can shift the morphology of this protein nanoreactor from polyhedral to tubular by removing vertex protein PduN. Analysis of the metabolic function between these Pdu microtubes (MTs) shows that they provide a diffusional barrier capable of shielding the cytosol from a toxic pathway intermediate, similar to native MCPs. However, kinetic modeling suggests that the different surface area to volume ratios of MCP and MT structures alters encapsulated pathway performance. Finally, we report a microscopy-based assay that permits rapid assessment of Pdu MT formation to enable future engineering efforts on these structures.

A Novel Cu2O/ZnO@PET Composite Membrane for the Photocatalytic Degradation of Carbendazim.

The extremely high levels of water pollution caused by various industrial activities represent one of the most important environmental problems. Efficient techniques and advanced materials have been extensively developed for the removal of highly toxic organic pollutants, including pesticides. This study investigated the photocatalytic degradation of the fungicide carbendazim (Czm) using composite track-etched membranes (TeMs) in an aqueous solution. Copper(I) oxide (Cu2O) and zinc oxide (ZnO) microtubes (MTs) were prepared using an electroless template deposition technique in porous poly(ethylene terephthalate) (PET) TeMs with nanochannels with a density of 4 × 107 pores/cm−2 and diameter of 385 ± 9 nm to yield Cu2O@PET and ZnO@PET composite membranes, respectively. A mixed Cu2O/ZnO@PET composite was prepared via a two-step deposition process, containing ZnO (87%) and CuZ (13%) as crystalline phases. The structure and composition of all composite membranes were elucidated using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. Under UV–visible light irradiation, the Cu2O/ZnO@PET composite displayed enhanced photocatalytic activity, reaching 98% Czm degradation, higher than Cu2O@PET and ZnO@PET composites. The maximum Czm degradation efficiency from aqueous solution was obtained at an optimal pH of 6 and contact time of 140 min. The effects of various parameters such as temperature, catalyst dosage and sample exposure time on the photocatalytic degradation process were studied. The degradation reaction of Czm was found to follow the Langmuir–Hinshelwood mechanism and a pseudo-first order kinetic model. The degradation kinetics of Czm accelerated with increasing temperature, and the activation energy (Ea) levels were calculated as 11.9 kJ/mol, 14.22 kJ/mol and 15.82 kJ/mol for Cu2O/ZnO@PET, ZnO@PET and Cu2O@PET composite membranes, respectively. The reusability of the Cu2O/ZnO@PET catalyst was also investigated at different temperatures for 10 consecutive runs, without any activation or regeneration processes. The Cu2O/ZnO@PET composite exhibited degradation efficiency levels of over 50% at 14 °C and over 30% at 52 °C after 5 consecutive uses.

A Selective Etching Route for Large-Scale Fabrication of β-Ga2O3 Micro-/Nanotube Arrays.

In this paper, based on the different etching characteristics between GaN and Ga2O3, large-scale and vertically aligned β-Ga2O3 nanotube (NT) and microtube (MT) arrays were fabricated on the GaN template by a facile and feasible selective etching method. GaN micro-/nanowire arrays were prepared first by inductively coupled plasma (ICP) etching using self-organized or patterning nickel masks as the etching masks, and then the Ga2O3 shell layer converted from GaN was formed by thermal oxidation, resulting in GaN@Ga2O3 micro-/nanowire arrays. After the GaN core of GaN@Ga2O3 micro-/nanowire arrays was removed by ICP etching, hollow Ga2O3 tubes were obtained successfully. The micro-/nanotubes have uniform morphology and controllable size, and the wall thickness can also be controlled with the thermal oxidation conditions. These vertical β-Ga2O3 micro-/nanotube arrays could be used as new materials for novel optoelectronic devices.

Application of Silver-Loaded Composite Track-Etched Membranes for Photocatalytic Decomposition of Methylene Blue under Visible Light.

In this study, the use of composite track-etched membranes (TeMs) based on polyethylene terephthalate (PET) and electrolessly deposited silver microtubes (MTs) for the decomposition of toxic phenothiazine cationic dye, methylene blue (MB), under visible light was investigated. The structure and composition of the composite membranes were elucidated by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction technique. Under visible light irradiation, composite membrane with embedded silver MTs (Ag/PET) displayed high photocatalytic efficiency. The effects of various parameters such as initial dye concentration, temperature, and sample exposure time on the photocatalytic degradation process were studied. The decomposition reaction of MB was found to follow the Langmuir–Hinshelwood mechanism and a pseudo-first-order kinetic model. The degradation kinetics of MB accelerated with increasing temperature and activation energy, Ea, was calculated to be 20.6 kJ/mol. The reusability of the catalyst was also investigated for 11 consecutive runs without any activation and regeneration procedures. The Ag/PET composite performed at high degradation efficiency of over 68% after 11 consecutive uses.

Tunable synthesis of mesoporous titania with different morphologies for dye-sensitized solar cells

Different TiO2 mesoporous structures, including core-shell spheres (CCSs) and micro-tubes (MTs), are synthesized through adjusting the pH of the solution using TiOSO4 as titanium source in a hydrothermal route. TiO2 CSSs with an average diameter of 1.3–3.5 μm exhibit excellent light scattering property and high specific surface area (177.63 m2 g−1). TiO2 MTs show ultrahigh specific surface area of 276.03 m2 g−1. Dye-sensitized solar cell is fabricated using TiO2 CSSs as the light scattering layer and TiO2 nanoparticles (NPs) layer as the bottom layer. The efficiency of Cell-NPs + CSSs is up to 9.24% due to the good light scattering effect and excellent dye loading capacity. Furthermore, TiO2 MTs are introduced to form the NPs/MTs bottom layer. The Cell-NPs/MTs + CSSs achieves an outstanding efficiency of 9.60% due to the further optimized electron transport path.

Protein-based Smart Microtubes and Nanotubes as Ultrasmall Biomaterials

This review highlights the latest research on protein-based smart microtubes (MTs) and nanotubes (NTs) as ultrasmall biomaterials that are designed for use in biochemical and biomedical application...

Synthesis, radical scavenging, and antimicrobial activities of core–shell Au/Ni microtubes

Highly ordered Ni/Au core–shell microtube (MT) arrays with the inner diameters of 110 ± 13 nm and the wall thickness of 118 ± 5 nm were synthesized by a two-step template deposition approach in pores of the track-etched membranes. First, the Au MTs were obtained by electroless plating. On the second stage, Ni MTs were electrochemically deposited inside gold MTs. The dimensions, chemical composition, and crystal structure of the synthesized samples have been analyzed using scanning electron microscopy, energy dispersive analysis as well as X-ray diffraction technique. The in vitro antioxidant activity of synthesized single component and core–shell MTs was evaluated by scavenging of 2.2-diphenyl-1-picrylhydrazyl hydrate (DPPH) radical and the effective rate of inhibition IC50 for DPPH radical was found to be 0.49 for Au/Ni MTs and 3.22 and 2.73 for Ni and Au MTs, respectively. The antibacterial activity was elucidated against the strains such as: Staphylococcus aureus, Bacillus subtilis, Escherichia coli and the yeast-like fungus Candida albicans P. by the agar diffusion method. The core–shell Au/Ni MTs possess the highest activity against the tested Gram-negative bacteria E. Coli (zone of inhibition of 37 ± 1.0 mm). Gram-positive bacteria S. Aureus showed resistance to the Au/Ni MTs; however, single component of Au and Ni MTs showed a pronounced antimicrobial activity as compared to Penicillin G sodium (control).

Fabrication of CuO nanosheets-built microtubes via Kirkendall effect for non-enzymatic glucose sensor

Reliable and accurate detection of blood glucose level is extremely important to monitor and prevent diabetic complications. Transition metal oxides, especially copper oxide (CuO), hold great potential for glucose sensor due to their good electrochemical activity and controllable structure. Herein, we fabricated a facile non-enzymatic sensor using CuO microtubes (MTs) as electrocatalytic active materials for electrochemical detection of glucose. The CuO MTs were hydrothermally prepared via the Kirkendall effect of KCu7S4 microwires. The obtained CuO shows unique tubular structure with abundant nanosheets on the surface and exhibits good crystallinity. The developed CuO based sensor exhibits a wide linear range up to 5.664 mM, with a satisfactory sensitivity of 992.073 μAcm−2 mM−1 and a short response time within 2 s. The detection limit for glucose is as low as 307 nM. In addition, the sensor also displays superior anti-interference performance, excellent reproducibility and long-term stability owing to its special tubular structure. All these excellent results show that the prepared CuO MTs can be a promising electrode material for glucose sensing.

Construction of Hierarchical Co-Fe Oxyphosphide Microtubes for Electrocatalytic Overall Water Splitting.

Development of efficient electrocatalysts is a crucial requirement to build water splitting systems for the production of clean and sustainable fuels. This goal could be achieved by fine‐tuning the composition and structure of the electrocatalytic materials. Here, a facile self‐templated synthetic strategy is developed for the fabrication of hierarchical Co–Fe oxyphosphide microtubes (MTs). Fe‐based metal–organic compound microrods are first synthesized as the self‐sacrificing template. Afterward, the Fe‐based precursors are converted into hierarchical Co–Fe layered double hydroxide MTs through a hydrothermal approach, which are then transformed into the hierarchical Co–Fe oxyphosphide MTs by a phosphidation treatment. Benefiting from the synergistic effect of the compositions and the advantages of the hierarchical hollow structure, the obtained electrocatalyst exhibits enhanced performance for overall water splitting.

Design of TiO2eC hierarchical tubular heterostructures for high performance potassium ion batteries

Potassium-ion battery (PIB) has been considered as a promising alternative to lithium-ion battery for large-scale energy storage owing to the natural abundance of potassium resources. The lack of suitable anode material is one of the bottlenecks for developing high performance PIBs. In this work, hierarchical HeTiO2eC micro-tubes (MTs) composed of heterostructured TiO2eC nanosheets (NSs) have been fabricated through a facile wet-chemical method. HeTiO2eC MTs demonstrate an enhance K+ accommodation capability, exhibit a high specific capacity (240.8 mAh g−1 at 100 mA g−1), exceptional rate capability (208.5, 180.1, 114.6 and 97.3 mAh g−1 at 200, 400, 1000, and 2000 mA g−1, respectively), good cycling stability (132.8 mA g−1 at 500 mA g−1 after 1200 cycles). The TiO2/C heterointerface plays a vital role in achieving the excellent electrochemical performance by enhancing affinity between TiO2 and carbon, stabilizing TiO2 and reaction products, providing improved electronic and K+ ions diffusion mobility.

Construction of MoS2/C Hierarchical Tubular Heterostructures for High-Performance Sodium Ion Batteries.

Molybdenum disulfide (MoS2) has been considered to be a promising anode material for sodium ion batteries (SIBs), because of its high capacity and graphene-like layered structure. However, irreversible conversion reaction during the sodiation/desodiation process is a major problem that must be overcome before its practical applications. In this work, MoS2/amorphous carbon (C) microtubes (MTs) composed of heterostructured MoS2/C nanosheets have been developed via a simple template method. The existence of MoS2/C heterointerface plays a key role in achieving high and stable performance by stabilizing the reaction products Mo and sulfide phases, providing fast electronic and Na+ ions diffusion mobility, and alleviating the volume change. MoS2/C MTs exhibit a high reversible specific capacity of 563.5 mA h g-1 at 0.2 A g-1, good rate performance (520.5, 489.4, 452.9, 425.1, and 401.3 mA h g-1 at 0.5, 1.0, 2.0, 5.0, and 10.0 A g-1, respectively), and excellent cycling stability (484.9 mA h g-1 at 2.0 A g-1 after 1500 cycles).

Ultra-light h-BCN architectures derived from new organic monomers with tunable electromagnetic wave absorption

Hexagonal BCN (h-BCN) has been identified as a promising class of electromagnetic wave (EMW) absorption material for critical Mach number aerocraft due to its exceptional thermal and chemical stabilities as well as adjustable dielectric property. Herein, we report a facile precursor synthesis-pyrolysis method to obtain ultra-light h-BCN bulk ceramics and microtubes (MTs) using commercially available BCl3, ethylenediamine and aniline as the monomers. The h-BCN bulk with a density of 15 mg/cm3 can be in situ synthesized derived from the precursor located in a tube furnace, while h-BCN MTs are simultaneously obtained on the downstream graphite sheets by controlling the pyrolysis temperature at the wide range of 800–1200 °C. For the h-BCN bulk ceramics, the minimum reflection loss (RL) can be tailored by controlling the N dopants, ranging from −52.7 dB at 5.44 GHz (the band width below −10 dB is achieved in a wide frequency range from 2.8 to 18 GHz) to −20.6 dB at 14.8 GHz (the band width below −10 dB is narrowed from 13.4 to 18 GHz). The excellent and frequency-controllable microwave absorption properties are due to the combination of tunable complex permittivity and lattice polarization resulting from B and N dopants in carbon networks.

Facile One-Step Synthesis of Silica Micro- and Nanotubes and Their Functionalization

Rectangular silica nanotubes (NTs) and microtubes (MTs) were synthesized by a simple one-step sol-gel hydrolysis reaction. Although silica nanotubes are usually prepared in the presence of a template (e.g. metal rods), the proposed procedure eliminates the need for such template insertion and, subsequently, no further etching step is required.The Stöber silica nanoparticles (NPs) synthesis employs ammonium hydroxide solution as the base for tetraethyl orthosilicate (TEOS) hydrolysis, leading to the formation of discreet uniform NPs. Replacing ammonium hydroxide with sodium bicarbonate resulted in the formation of silica NTs with unique rectangular shape, both for the tube (external) and the lumen (internal cavity). On the other hand, replacing ammonium hydroxide with ammonium carbonate led to the formation of larger silica MTs with similar geometry. The influence of parameters such as: monomer concentration, base concentration, base:monomer ratio, temperature and solvent, on tube formation was investigated. This procedure was also utilized to prepare mesoporous and functionalized NTs and MTs with unique characteristics as omniphobic coatings.A proposed mechanism for the production of silica rectangular NTs and MTs via sheet folding is offered, based on our findings.

Dispersing upconversion nanocrystals in a single silicon microtube.

Nanocrystals of Ln3+ (Ln = Yb, Tm and Ho) doped β-NaLuF4 with average diameter about 200 nm are dispersed in silica-based microtube (MT) by a simple flame heating method. The fabricated microtube has a diameter range from 2 μm to 30 μm and lengths up to hundreds microns. The fluorescence of upconversion nanocrystals (UCNCs) can propagate along a single MT and couple into another MT through evanescent field. The guiding performance of the single UCNCs doped MT is measured to prove that it can be used as an active waveguide. Moreover, optical temperature sensing based on the single UCNCs-MT is also demonstrated, and the sensitivity of UCNCs-MT is significantly enough for thermometry applications in the range of 298–383 K.

ZnO nanorods assisted Ni1.1Pt and Co3.9Pt alloy microtube counter electrodes for efficient dye-sensitized solar cells

Pt counter electrode (CE) has been a burden for the commercialization of liquid-junction dye-sensitized solar cells (DSSCs). In searching for cost-effective CEs without sacrificing electrochemical activities, here we report the experimental realization of ZnO nanorods assisted Ni1.1Pt and Co3.9Pt alloy microtube (MT) CEs by combining a simple electrodeposition deposition on aligned ZnO nanorods and a galvanic displacement reaction. On behalf of the good charge-transfer ability along one-dimensional alloy electrocatalyst and electrocatalytic activity toward liquid electrolyte, the resultant DSSCs with Ni1.1Pt and Co3.9Pt MT CEs display promising power conversion efficiencies of 8.29% and 7.73%, yielding 30.6% and 21.7% enhancements, respectively. Similarly importantly, the alloyed CEs are still scalable, other alloyed low-Pt or non-Pt nano/microstructures can also be realized using the method reported here.

Growth of Ultra-Long ZnO Microtubes Using a Modified Vapor-Solid Setup

In this work, we have modified the experimental setup for a vapor-solid (VS) process to synthesize Zinc oxide (ZnO) microtubes (MTs) with lengths up to 3 mm during a 90-min growth period. The critical idea behind this modification is to control the distribution of Zn vapor along the Si substrates. The morphology evolution of ZnO structures with the increasing reaction time was particularly explored. We found that, within the 90-min growth period, four different types of ZnO microstructures appeared in this synthesis process: microrods (MRs), short MTs, two-tier structures, and long MTs. Growth mechanisms were proposed to interpret the formation of these structures.