Inside Nanotubes Research Articles

(Invited) One Dimensional Anodic TiO2 Nanotubes for Energy and Catalytic Applications

Self-organized TiO2 nanotube (TNT) layers, prepared by anodization of Ti have in suitable electrolytes, attracted considerable scientific and technological interest, especially due to their wide range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2].The advantages of anodic TNT layers compared to TiO2 nanotubes prepared by other methods (e.g. hydrothermal) are the tunability of dimensions, their directionality, the ability to absorb significant amount of incident light, and the possibility to utilize nanotube interiors and exteriors for decoration or coating with secondary materials [2].The presentation will review the recent advancements in TNT layer synthesis for their use for the photocatalytic degradation of pollutants in the liquid and in the gas phase. This will include the upscaling of TNT layers from the laboratory scale to several dozens of cm2 [3-6], with a strong focus on the anodization of 3D Ti substrates by bipolar electrochemistry, which cannot be directly connected to the potentiostat (such as Ti meshes) [5-6]. The application of these large scale TiO2 nanotube layers in flow-through photocatalytic reactors will be discussed [3-6]. Additionally, the selective etching of double wall TiO2 nanotube layers towards single wall TiO2 nanotube layers [7] and single nanotube powders [8, 9] will be presented, showing the possibility of preparing magnetically guidable single nanotube photocatalysts by a decoration with Fe3O4.The presentation will also summarize recent advancements in the utilization of TNT layers in energy conversion and energy storage applications [10], in particular Li-ion microbatteries. Experimental details and photocatalytic and battery results will be presented and discussed.

Comparative studies on Fenton-like reactions catalyzed by Fe3O4 loaded inside and outside halloysite nanotubes for the removal of organic pollutants

Comparative studies on Fenton-like reactions catalyzed by Fe3O4 loaded inside and outside halloysite nanotubes for the removal of organic pollutants

Enhanced fluidity of water in superhydrophobic nanotubes: estimating viscosity using jump-corrected confined Stokes-Einstein approach.

Accurately predicting the viscosity of water confined within nanotubes is vital for various technological applications. Traditional methods have failed in this regard, necessitating a novel approach. We introduced the jump-corrected confined Stokes-Einstein (JCSE) method and now employ the same to estimate the viscosity and diffusion in superhydrophobic nanotubes. Our study covers a temperature range of 230-300 K and considers three nanotube diameters. Results show that water inside superhydrophobic nanotubes exhibits a significantly lower viscosity and higher diffusion than those inside hydrophobic nanotubes. Narrower nanotubes and lower temperatures accentuate these effects. Furthermore, water inside superhydrophobic nanotubes display a lower viscosity than bulk water, with the difference increasing at lower temperatures. This reduction is attributed to weaker water-water interactions caused by a lower water density in the interfacial region. These findings highlight the importance of interfacial water density and its influence on nanotube viscosity, shedding light on nanoscale fluid dynamics and opening avenues for diverse applications.

Thermal Degradation Kinetics of Vacuum Residues in the Presence of Chrysotile Supported Ni-Ti Catalyst

For the first time, thermal decomposition of vacuum residue and a mixture of vacuum residue with binary nanocatalysts based on leached and non-leached chrysotile with applied active metals was studied using the thermogravimetry method. It is shown that the thermokinetic parameters of decomposition of vacuum residue and its mixture with binary nanocatalyst are different. The phase composition of the binary nanocatalyst was established through X-ray phase analysis (XRD): (Mg3Si2O5 (OH), NiO and Ti (SO4)2). The quantitative content of elements on the chrysotile surface was determined using X-ray fluorescence analysis: (Ni (4.88%), Ti (7.29%), Si (24.93%), Mg (7.83%), Fe (0.69%) and S (3.89%)). Using atomic emission spectral analysis, the gross quantitative content of supported metals on chrysotile was determined: Ni (4.85%) and Ti (4.86%). A transmission electron microscope showed the presence of finely dispersed particles adsorbed on the surface of and possibly inside chrysotile nanotubes with sizes ranging from 5 to 70 nm. The acidity of the nanocatalyst obtained from the leached active-metal-supported chrysotile was 267 μmol/g and the specific surface area of the nanocatalyst was 54 m2/g. The Ozawa–Flynn–Wall (OFW) method was used to calculate the kinetic parameters of the thermal degradation of vacuum residue and the mixture of vacuum residue with nanocatalysts. Using the isoconversion method, the average values of activation energies and the pre-exponential factor were calculated: 147.55 kJ/mol and 3.37·1016 min−1 for the initial vacuum residue; 118.69 kJ/mol and 1.54·1018 min−1 for the mixture of vacuum residue with nanocatalyst obtained from non-leached chrysotile with applied metals; 82.83 kJ/mol and 2.15·1019 min−1 for the mixture of vacuum residue with nanocatalyst obtained from leached chrysotile with applied metals. The kinetic parameters obtained can be used in modeling and designing the processes of thermal degradation and hydroforming of heavy hydrocarbon raw materials.

Dynamic behavior of lysozyme enzyme inside titania nanotubes: a continuum approach

Dynamic behavior of lysozyme enzyme inside titania nanotubes: a continuum approach

Regulation of water access, storage, separation and release of drugs from the carbon nanotube functionalized by cytosine rich DNA fragments.

We found that carmustine can be stored in the carbon nanotube (CNT) interior for a long time due to hydrophobic interactions. The access of water to carmustine phase in the CNT interior can be controlled by the state of cytosine rich DNA fragments covalently bound to the CNT tips and to the presence of doxorubicin molecules intercalated within bundles of DNA fragments. More effective control of water access and subsequent decomposition of carmustine due to the contact with water was observed when some small amount of doxorubicin molecules cork the CNT ends. Our analysis shows that carmustine decomposition products naturally separate when decomposition occurs within the CNT. The alkylating agent, chloroethyl carbonium cation, spontaneously escapes from the CNT but the carbamylation agent, chloroethyl isocyanate, is still kept within the nanotube interior. The separation process and release of the alkylating agent needs uncorking the nanotube by doxorubicin molecules. The latter process is likely to occur spontaneously at acidic pH when intercalation of doxorubicin within the DNA fragments becomes ineffective. The features of the proposed molecular model, obtained from molecular dynamics simulations, can be beneficial in design of novel smart drugs carriers to a tumor microenvironment revealing the reduced extracellular pH.

"Missing" One-Dimensional Red-Phosphorus Chains Encapsulated within Single-Walled Carbon Nanotubes.

We identify the "missing" 1D-phosphorus allotrope, red phosphorus chains, formed in the interior of tip-opened single-walled carbon nanotubes (SWCNTs). Via a comprehensive experimental and theoretical study we show that in intermediate diameter cavities (1.6-2.9 nm), phosphorus vapor condenses into linear P8]P2 chains and fibrous red-phosphorus type cross-linked double-chains. Thermogravimetric and X-ray photoelectron spectroscopy analysis estimates ∼7 atom % of elemental phosphorus in the sample, while high-resolution energy dispersive X-ray spectroscopy mapping reveals that phosphorus fills the SWCNTs. High-resolution transmission electron microscopy (HRTEM) shows long chains inside the nanotubes with varying arrangement and packing density. A detailed match is obtained between density functional theory (DFT) simulations, HRTEM, and low-frequency Raman spectroscopy. Notably, a signature spectroscopic signal for phosphorus chain cross-linking is identified. When coupled with reinterpretation of literature data and wide-ranging DFT calculations, these results reveal a comprehensive picture of the diameter dependence of confined 1D-phosphorus allotropes.

Polymerizable channel-like stacks derived from cyclic tetrameric diacetylenes

A small series of cyclic diacetylenes has been synthesized and tested by scanning electron microscopy (SEM), single crystal X-ray diffraction, and atomic force microscopy (AFM) to examine their ability to form arrangements of discrete molecules in the solid state. Examining solid state structures clearly demonstrated propensity of diacetylene tetramers to form channel-like stacks. Remarkably, cyclotetradiyne DA-4 monomer tends to produce two types of nano-tubular motifs ( i.e ., the channel-like arrangement with solvent matrix inside and unprecedented flattened nano-tube incorporated no solvent guest molecules) which is indicative of the weak C–H/π interactions dominating and directing the stacking in such simplistic diacetylene cyclic systems. Noteworthy, DA-4 molecules may be crystallized from organic solvents into birefringent branchy patterns revealed by Polarized Optical Microscopy (POM) and twisted ribbons of both handedness as evidenced by SEM data. We hypothesize that all these secondary structures may arise from the bundling the individual stacks discovered by single crystal X-ray analysis. Overall, engineering the elongated motifs may open up new opportunities for the future applications such as a rational design of synthetic ion channels and carriers, synthesis of the covalent polymeric nanotubes, etc .

Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 15 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet.Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials.One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4].The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will also show that various secondary materials have a positive influence on photo-electrochemical properties of nanotube layers [8, 9]. Experimental details and some recent photocatalytic results will be presented and discussed.

Lithium-Conducting Self-Assembled Organic Nanotubes.

Supramolecular polymers are compelling platforms for the design of stimuli-responsive materials with emergent functions. Here, we report the assembly of an amphiphilic nanotube for Li-ion conduction that exhibits high ionic conductivity, mechanical integrity, electrochemical stability, and solution processability. Imine condensation of a pyridine-containing diamine with a triethylene glycol functionalized isophthalaldehyde yields pore-functionalized macrocycles. Atomic force microscopy, scanning electron microscopy, and in solvo X-ray diffraction reveal that macrocycle protonation during their mild synthesis drives assembly into high-aspect ratio (>103) nanotubes with three interior triethylene glycol groups. Electrochemical impedance spectroscopy demonstrates that lithiated nanotubes are efficient Li+ conductors, with an activation energy of 0.42 eV and a peak room temperature conductivity of 3.91 ± 0.38 × 10-5 S cm-1. 7Li NMR and Raman spectroscopy show that lithiation occurs exclusively within the nanotube interior and implicates the glycol groups in facilitating efficient Li+ transduction. Linear sweep voltammetry and galvanostatic lithium plating-stripping tests reveal that this nanotube-based electrolyte is stable over a wide potential range and supports long-term cyclability. These findings demonstrate how the coupling of synthetic design and supramolecular structural control can yield high-performance ionic transporters that are amenable to device-relevant fabrication, as well as the technological potential of chemically designed self-assembled nanotubes.

Cytosine-Rich DNA Fragments Covalently Bound to Carbon Nanotube as Factors Triggering Doxorubicin Release at Acidic pH. A Molecular Dynamics Study.

This works deals with analysis of properties of a carbon nanotube, the tips of which were functionalized by short cytosine-rich fragments of ssDNA. That object is aimed to work as a platform for storage and controlled release of doxorubicin in response to pH changes. We found that at neutral pH, doxorubicin molecules can be intercalated between the ssDNA fragments, and formation of such knots can effectively block other doxorubicin molecules, encapsulated in the nanotube interior, against release to the bulk. Because at the neutral pH, the ssDNA fragments are in form of random coils, the intercalation of doxorubicin is strong. At acidic pH, the ssDNA fragments undergo folding into i-motifs, and this leads to significant reduction of the interaction strength between doxorubicin and other components of the system. Thus, the drug molecules can be released to the bulk at acidic pH. The above conclusions concerning the storage/release mechanism of doxorubicin were drawn from the observation of molecular dynamics trajectories of the systems as well as from analysis of various components of pair interaction energies.

(Invited) Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 15 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet.Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials.One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4].The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will demonstrate the photocatalytic performance of recently developed single-wall TiO2 nanotubes and single-tube TiO2 powders [8]. We will also show that various modifications of nanotube ssecondary materials have a positive influence on photo-electrochemical properties of nanotube layers [9,10]. Experimental details and some recent photocatalytic results will be presented and discussed.

Nanotechnology: an approach for water purification-review

Clean water is the global need and need of life for all the human kinds. But the clean water resources are being contaminated in present time. Nanotechnology is an easy and practical approach to clean waste water by using different methods. Different types of bacteria, toxic chemicals like arsenic, mercury etc., and sediments can be removed by using nanotechnology. Nanomaterial based devices are being used for water purification. Nano filtration method has advantages over other conventional method as low pressure is required to pass the water through filters and these filters can be cleaned easily by back flushing. Smooth interior of carbon nanotubes make them convenient for the removal of almost all types of water contaminants. Because of larger surface area nanostructured materials have advantages over conventional micro structured materials.

Diameter Dependence of Water Filling in Lithographically Segmented Isolated Carbon Nanotubes.

Although the structure and properties of water under conditions of extreme confinement are fundamentally important for a variety of applications, they remain poorly understood, especially for dimensions less than 2 nm. This problem is confounded by the difficulty in controlling surface roughness and dimensionality in fabricated nanochannels, contributing to a dearth of experimental platforms capable of carrying out the necessary precision measurements. In this work, we utilize an experimental platform based on the interior of lithographically segmented, isolated single-walled carbon nanotubes to study water under extreme nanoscale confinement. This platform generates multiple copies of nanotubes with identical chirality, of diameters from 0.8 to 2.5 nm and lengths spanning 6 to 160 μm, that can be studied individually in real time before and after opening, exposure to water, and subsequent water filling. We demonstrate that, under controlled conditions, the diameter-dependent blue shift of the Raman radial breathing mode (RBM) between 1 and 8 cm-1 measures an increase in the interior mechanical modulus associated with liquid water filling, with no response from exterior water exposure. The observed RBM shift with filling demonstrates a non-monotonic trend with diameter, supporting the assignment of a minimum of 1.81 ± 0.09 cm-1 at 0.93 ± 0.08 nm with a nearly linear increase at larger diameters. We find that a simple hard-sphere model of water in the confined nanotube interior describes key features of the diameter-dependent modulus change of the carbon nanotube and supports previous observations in the literature. Longer segments of 160 μm show partial filling from their ends, consistent with pore clogging. These devices provide an opportunity to study fluid behavior under extreme confinement with high precision and repeatability.

Термофорез одноатомных частиц в открытых нанотрубках

Using the method of molecular dynamics, it is shown that thermophoresis of particles (atoms) inside single-walled carbon nanotubes (CNTs) is highly efficient. Placing a particle inside the CNT involved in heat transfer causes it to move in the direction of the heat flow at a constant speed, the value of which weakly depends on the length of the nanotube. The heat flow along the CNT leads to the formation of a constant thermophoresis force for the particles inside. The direction of this force coincides with the direction of heat transfer. The monatomic nature of the particle allowed us to numerically calculate this force and to determine the contribution to this force of interaction with each thermal phonon of the nanotube. It is shown that the magnitude of the force is almost completely determined by the interaction of the particle with long-wave bending phonons of the nanotube, which have a long free run path. Therefore, the speed of the particle movement and the value of the thermophoresis force depend weakly on the length of the nanotube, but are determined by the temperature difference at its ends. Because of this, the mode of thermophoresis of particles inside nanotubes is ballistic, not diffusive.

Optical Property Tuning of Single-Wall Carbon Nanotubes by Endohedral Encapsulation of a Wide Variety of Dielectric Molecules.

Specific and tunable modification to the optical properties of single-wall carbon nanotubes (SWCNTs) is demonstrated through direct encapsulation into the nanotube interior of guest molecules with widely varying static dielectric constants. Filled through simple ingestion of the guest molecule, each SWCNT population is demonstrated to display a robust modification to absorbance, fluorescence, and Raman spectra. Over 30 distinct compounds, covering static dielectric constants from 1.8 to 109, are inserted in large diameter SWCNTs (d = 1.104-1.524 nm) and more than 10 compounds in small diameter SWCNTs (d = 0.747-1.153 nm), demonstrating that the general effect of filler dielectric on the nanotube optical properties is a monotonic energy reduction (red-shifting) of the optical transitions with increased magnitude of the dielectric constant. Systematic fitting of the two-dimensional fluorescence-excitation and Raman spectra additionally enables determination of the critical filling diameter for each molecule and distinguishing of overall trends from specific guest-host interactions. Comparisons to predictions from existing theory are presented, and specific guest molecule/SWCNT chirality combinations that disobey the general trend and theory are identified. A general increase of the fluorescence intensity and line narrowing is observed for low dielectric constants, with long linear alkane filled SWCNTs exhibiting emission intensities approaching those of empty SWCNTs. These results demonstrate an exploitable modulation in the optical properties of SWCNTs and provide a foundation for examining higher-order effects, such as due to nonbulk-like molecule stacking, in host-guest interactions in well-controlled nanopore size materials.

Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 13 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet.Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials.One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4].The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will also show that various secondary materials have a positive influence on photo-electrochemical properties of nanotube layers [8, 9]. Experimental details and some recent photocatalytic results will be presented and discussed.

Recent Progress in Anodic TiO2 Nanotube Layer Synthesis

Over the past 15 years, self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest due to their wide possible range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of the 1D TiO2 nanotube layers is usually carried out by electrochemical anodization of valve Ti metal sheets in various electrolytes.The advantage of anodic TiO2 nanotube layers compared to TiO2 nanotubes prepared by other methods (e.g. hydrothermal) are the tunability of dimensions, their directionality, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials [2]. However, by now most publications report on the nanotube layer production on the laboratory scale, i.e. on Ti substrates of a few cm2.The presentation will focus on the recent progress in the TiO2 nanotube layer synthesis. We will show and discuss a possible upscaling of the nanotube layers towards areas of dozens of cm2 [3], taking into account the control of the anodization parameters. Furthermore, we will discuss the use of bipolar electrochemistry for the preparation of TiO2 nanotube layers on small Ti objects which cannot be connected to the potentiostat [4], as well as the selective etching of anodic TiO2 nanotube layers towards single-wall nanotube layers [5] and single nanotubes [6], where nanotubes are separated from one another into tube powders.

Magnetic Properties of 1D Iron–Sulfur Compounds Formed Inside Single‐Walled Carbon Nanotubes

Herein, the filling of single‐walled carbon nanotubes (SWCNTs) with sulfur is performed, and the magnetic properties of the formed nanomaterials are studied. Encapsulation of sulfur species results in the appearance of a specific magnetic ordering in the system due to the formation of nanoscopic grains composed of sulfur and residual catalytic Fe nanoparticles contained in the SWCNTs. The magnetic character of the obtained 1D nanostructures is studied using superconducting quantum interference device (SQUID) magnetometer and a sequential ferromagnetic–antiferromagnetic ordering in the material is revealed. Magnetic and optical properties are strongly dependent on the synthesis protocols. A significant Raman intensity increase related to the encapsulated nanostructures is obtained when filling is performed at high‐pressure high‐temperature conditions. Simultaneously, the magnetic susceptibility gets strongly reduced for high‐pressure filling, which is related to the escape of iron particles from the nanotube interior, and the magnetic properties of the material are governed by a weak ferromagnetic ordering of Fe–S structures remained inside SWCNTs. Sulfur encapsulation provides the new route for controlling the magnetic properties in 1D nanomaterials that pave the way for advanced magneto‐optical applications.

Carbon Nanotubes and Short Cytosine-Rich Telomeric DNA Oligomeres as Platforms for Controlled Release of Doxorubicin-A Molecular Dynamics Study.

This work deals with molecular dynamics analysis of properties of systems composed of carbon nanotubes and short telomeric DNA strands able to fold into i-motif structures at slightly acidic pH conditions. The studies are focused on possible application of such constructs as pH-controlled drug delivery and release systems. We study two different approaches. The first assumes that folding/unfolding property of these DNA strands might realize a gate closing/opening mechanism with carbon nanotube as a container for drug molecules. The second approach assumes that these DNA strands can modulate the drug intercalating property as a function of pH. As a model drug molecule we used doxorubicin. We found that the first approach is impossible to realize because doxorubicin is not effectively locked in the nanotube interior by DNA oligonuceotides. The second approach is more promising though direct drug release was not observed in unbiased molecular dynamics simulations. However, by applying detailed analysis of pair interaction energies, mobilities and potential of mean force we can show that doxorubicin can be released when the DNA strands fold into i-motifs. Carbon nanotube in that latter case acts mainly as a carrier for active phase which is composed of DNA fragments able to fold into noncanonical tetraplexes (i-motif).