Magnetic Nanotubes Research Articles

Magnetic nickel chrysotile nanotubes tethered with pH-sensitive poly(methacrylic acid) brushes for Cu(II) adsorption

Magnetic nickel chrysotile nanotubes (NCNTs) tailored with poly(methacrylic acid) (PMAA) brushes have been synthesized by surface-initiated atom transfer radical polymerization as a novel canonic nanosorbent for Cu(II) ions removal in aqueous solutions. Batch adsorption experiments are conducted to determine the effect of solution pH and coexisted ions on the adsorption capacity, sorption kinetics, adsorption isotherms, thermodynamics of Cu(II) adsorption of the as-synthesized magnetic PMAA-grafted NCNTs. Adsorption kinetics of magnetic nanosorbents are verified to be consistent with a pseudo-second-order (PSO) kinetic model and to be evidently affected by mass transfer process. The Langmuir-fitted maximum adsorption capacity of Cu(II) ions is as high as 1.40 mmol·g−1 (circa 89.0 mg·g−1) at solution pH 5.0 and 25 °C with the initial Cu(II) concentration of 20–100 mg·L−1. The desorption results demonstrate good regenerability, stability and easy separation of the magnetic PMAA-grafted NCNTs for repeated use.

Magnetic nanotubes obtained from atomic layer deposition coated electrospun nanofibers

High-aspect ratio Al2O3/Ni/Al2O3 core–shell hollow nanotubes were prepared by combining electrospinning, atomic layer deposition, and a subsequent chemical reduction process. Electrospun poly(vinyl alcohol) (PVOH) nanofibers were obtained by electrospinning. Then, these fibers were coated with atomic layer deposition to obtain PVOH/Al2O3/NiO/Al2O3 core–shell nanowires. Since the NiO must be deposited at 200 °C, the PVOH nanofibers must first be coated with Al2O3 at 80 °C, which act as a protective layer of the fibers so that they can withstand higher temperatures. Once PVOH/Al2O3/NiO/Al2O3 core–shell nanowires are obtained, they are subjected to a chemical reduction process that generates Al2O3/Ni/Al2O3 core–shell hollow nanotubes. Their morphologies were studied by scanning and transmission electron microscopies, the thickness was determined by ellipsometry, and all magnetic measurements were performed in an alternating-gradient force magnetometer. Finally, assuming that the nanostructures exhibit a curling reversal process, the authors have analytically calculated the coercivity of the nanotubes.

FeCo nanotubes: possible tool for targeted delivery of drugs and proteins

Progress in biomedicine leads to the appearance of novel methods of treatment at both the molecular and cellular scales. This treatment requires the nanoscale materials, capable to affect locally being manipulated from outside. Magnetic nanotubes (NTs) are the promising tool for a variety of bioapplications, including targeted delivery driven by a magnetic field, magnetic resonance imaging, magnetic separation. In this work, the Fe- and Co-doped NTs were synthesized by a template synthesis method in pores of polyethylene terephthalate membranes. The structural and magnetic properties of the obtained FeCo NTs were investigated. In comparison with well-established nanowires, the FeCo NTs demonstrated some advantages such as the homogeneous magnetic field, lower density, and larger specific surface area. A simple way for functionalization of the FeCo NTs with polymethylmethacrylate for targeted delivery of drugs is proposed. The model scheme of drugs attachment to the surface of NTs has been developed and the binding process was illustrated with cyclodipeptide.

Novel mixed hemimicelles based on nonionic surfactant-imidazolium ionic liquid and magnetic halloysite nanotubes as efficient approach for analytical determination.

The co-adsorption of mixed nonionic surfactant and imidazolium-based ionic liquid, Triton X100 (TX100), with 1-cetyl-3-methylimidazolium bromide (C16mimBr) adsorbed onto the surface of magnetic halloysite nanotubes (MHNTs) was used as an efficient adsorbent for simultaneous determination of amlodipine and nimodipine in urine. The designed adsorbent was characterized by TEM, TGA, FTIR, and DLS analysis methods. All the parameters that influence the extraction efficiency are optimized with the aid of response surface methodology (RSM). The effects of nonionic surfactant TX100 with different structures of ionic-liquid-coated MHNTs were investigated. Under optimum conditions, extraction recoveries of amlodipine and nimodipine were in the range of 73.8-81.2 and 94.3-96.1%, with RSDs (n = 3) of 2.6-5.5% in spiked urine samples, respectively. The adsorption mechanism principal of mixed hemimicelles was discussed in this study. The limit of detection obtained for analytes was < 0.002μg·mL-1. To our knowledge, this was the first attempt using a mixed hemimicelle solid-phase extraction (SPE) based on MHNTs and nonionic surfactant and imidazolium-based ionic liquid for the simultaneous determination of amlodipine and nimodipine in biological samples. Graphical abstract ᅟ.

Poly(ethylene imine)-modified magnetic halloysite nanotubes: A novel, efficient and recyclable catalyst for the synthesis of dihydropyrano[2,3-c]pyrazole derivatives

In this study, a green magnetic nanocatalyst based on natural clay was fabricated. Magnetic nanoparticles were loaded on halloysite nanotubes (HNTs) and poly(ethylene imine) (PEI) was covalently grafted onto the surface of HNTs. The morphology and chemistry of the Fe3O4@HNTs-PEI nanocomposite was fully characterized by Fourier transform infrared (FT-IR) spectroscopy spectra, field-emission scanning electron micrograph (FE-SEM) images, thermogravimetric analysis (TGA), energy-dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) pattern and vibrating sample magnetometer (VSM) curve analyses. These characteristics confirmed the successful synthesis of the nanocomposite. The catalytic performance of Fe3O4@HNTs-PEI was utilized for the synthesis of pyranopyrazole derivatives. This heterogeneous catalyst exhibited high efficiency in green media under mild reaction conditions at room temperature and can be easily recovered from the reaction mixture by using an external magnet and reused for at least eight times without any significant decrease in catalytic activity.

Immobilization of carborane derivatives on Ni/Fe nanotubes for BNCT

The most important limitation for boron neutron capture therapy of cancer is the selective accumulation of boron compounds in tumor tissues in significant quantities. In this paper, we describe the possibility to use magnetic Ni/Fe nanotubes as carriers for boron delivery. Carborane derivatives containing 10 and 21 boron atoms per molecule were immobilized on Ni/Fe nanotubes by covalent and ionic interactions. Magnetic properties of NTs were investigated by Mossbauer spectroscopy. Structure, element, chemical composition, and morphology of obtained magnetic nanotubes were studied by XRD, SEM-EDA, and FTIR spectroscopy. Results indicate success immobilization of carborane derivatives on Ni/Fe nanotubes and great potential to use them as carriers for boron neutron cancer therapy of cancer.

Magnetic Dendritic Halloysite Nanotube for Highly Selective Recovery of Heparin Digested from Porcine Intestinal Mucosa

Heparin, as a sulfated polysaccharide found in animal tissues, is a commonly employed clinical anticoagulant. However, the heparin concentration in digested raw materials is very low and difficult to recover at high concentrations. To address this issue and enrich the heparin content that can be purified, we have fabricated novel polyamidoamine (PAMAM) dendrimers functionalized on halloysite nanotubes (HNTs), which were also decorated and magnetized with iron oxide (Fe3O4) nanoparticles to enable magnetic separation for selective, scalable recovery of heparin. Using absorption spectroscopy, the heparin recovery efficiency of HNTs and PAMAM-Fe3O4/HNTs was evaluated and compared the results to Amberlite FPA98 Cl, a commercially accessible resin used in heparin extraction. Our results showed that the PAMAM-Fe3O4/HNTs demonstrated higher efficiency of heparin recovery, both in terms of the capacity and rate of adsorption. We also studied the adsorption mechanism of heparin onto the functional amino groups of ...

Bifunctional monomer molecularly imprinted sol-gel polymers based on the surface of magnetic halloysite nanotubes as an effective extraction approach for norfloxacin

Abstract An effective magnetic surface imprinted polymer with high adsorption ability and selectivity has been designed. Three magnetic halloysite nanotubes combined with molecularly imprinted polymer (MMIP) composites were fabricated. Halloysite nanotubes (Hal nanotubes) were us as supporting matrix, norfloxacin (NOR) as template molecules, Aminopropyltriethoxysilane (3-APTES) and Methacryloxypropyltrimethoxysilane (MTEOS) used as monomers and tetramethyl orthosilicate (TEOS) as cross linker through a one-pot sol-gel polymerization. The resulting MMIP were characterized by various techniques. The adsorption isotherms, adsorption kinetics and selective recognition of MMIP were investigated in detail. The imprinted polymers with bifunctional monomer possess the highest adsorption capacity (312.08 μg·mg−1) and the best select factor (5.41). After optimization of solid phase extraction (SPE) condition, imprinted polymer with bifunctional monomer possess the best extraction ability and can be successfully applied into the extraction of norfloxacin in lake water. In addition, the SPE-ultraviolet method established possesses good accuracy and precision. Hydrochloric acid (9:1/v:v) could be used as the best elution and the magnetic imprinted polymer could be reused for at least seven times.

Domain wall dynamics in magnetic nanotubes driven by an external magnetic field**Project supported by the National Natural Science Foundation of China (Grant No. 61774001), the National Social Science Foundation of China (Grant No. 17BJY103), the Key Project of Scientific and Technological Research in Hebei Province, China (Grant No. ZD2015133), and the Construction Project of Graduate Demonstration Course in Hebei Province,

We use the Landau–Lifshitz–Gilbert equation to investigate field-driven domain wall propagation in magnetic nanotubes. We find that the distortion is maximum as the time becomes infinite and the exact rigid-body solutions are obtained analytically. We also find that the velocity increases with increasing the ratio of inner radius and outer radius. That is to say, we can accelerate domain wall motion not only by increasing the magnetic field, but also by reducing the thickness of the nanotubes.

Folic acid-conjugated chitosan oligosaccharide-magnetic halloysite nanotubes as a delivery system for camptothecin

In this research, to achieve enhanced intracellular uptake of anticancer drug carriers for efficient chemotherapy, folic acid conjugated chitosan oligosaccharides assembled magnetic halloysite nanotubes (FA-COS/MHNTs) have been tailored as multitask drug delivery system towards camptothecin (CPT). Besides magnetic targeting, the nanocomposites have been reacted with folate complex in order to selectively target cancer cells over expressing the folic acid receptor. HNTs showed to have a high storage capacity of CPT. In vitro, the release results indicated that CPT outflow from the nanocarriers at pH 5 was much greater than that at both pH 6.8 and 7.4. MTT assays showed that the CPT-loaded nanocarriers exhibited stronger cell growth inhibitory against colon cancer cell. Furthermore, nanocarriers gained specificity to target cancer cells because of the enhanced cell uptake mediated by FA moiety and presence of COS. Therefore, the rational designed HNTs nanocarrier for chemotherapy drug showed great potential as tumor-targeted drug delivery carrier.

RETRACTED ARTICLE: FeNi nanotubes: perspective tool for targeted delivery

Targeted delivery of drugs and proteins by magnetic field is a promising method to treat cancer that reduces undesired systemic toxicity of drugs. In this method, the therapeutic agent is attached through links to functional groups with magnetic nanostructure and injected into the blood to be transported to the problem area. To provide a local effect of drug treatment, nanostructures are concentrated and fixed in the selected area by the external magnetic field (magnet). After the exposure, carriers are removed from the circulatory system by magnetic field. In this study, Fe20Ni80 nanotubes are considered as carriers for targeted delivery of drugs and proteins. A simple synthesis method is proposed to form these structures by electrodeposition in PET template pores, and structural and magnetic properties are studied in detail. Nanotubes have polycrystalline walls providing mechanical strength of carriers and magnetic anisotropy that allow controlling the nanostructure movement under the exposure of by magnetic field. Moreover, potential advantages of magnetic nanotubes are discussed in comparison with other carrier types. Most sufficient of them is predictable behavior in magnetic field due to the absence of magnetic core, low specific density that allows floating in biological media, and large specific surface area providing the attachment of a larger number of payloads for the targeted delivery. A method of coating nanotube surfaces with PMMA is proposed to exclude possible negative impact of the carrier material and to form functional bonds for the payload connection. Cytotoxicity studies of coated and uncoated nanotubes are carried out to understand their influence on the biological media.

Determination of perchlorate from tea leaves using quaternary ammonium modified magnetic carboxyl-carbon nanotubes followed by liquid chromatography-tandem quadrupole mass spectrometry

The novel quaternary ammonium modified magnetic carboxyl-carbon nanotubes (QA-Mag-CCNTs) have been synthesised and characterized. QA-Mag-CCNTs were applied in magnetic dispersive solid phase extraction (Mag-dSPE) for preconcentration of perchlorate from tea leaves prior to liquid chromatography-tandem quadrupole mass spectrometry (LC-MS/MS) analysis. The Mag-dSPE procedure for preconcentration of perchlorate succeed in overcoming the flaw (containing target analyte randomly) of commercially available SPE cartridge. Under optimal conditions, the results showed higher extraction efficiency of QA-Mag-CCNTs, with recoveries between 85.2% and 107%. And the satisfactory precision with inter-day and intra-day RSD values were lower than 8.0%. Furthermore, QA-Mag-CCNTs were evaluated for reuse up to 20 times. The limit of quantification (LOQ) for perchlorate was 8.21 ng kg−1. The developed method was successfully applied in tea leaves for food-safety risk monitoring in Zhejiang province, China. The results showed the concentrations of perchlorate in 229 out of 240 collected samples were in the range of 0.082–988 μg kg−1. It was confirmed that QA-Mag-CCNTs were highly effective materials used for preconcentration of perchlorate.

Compensation behaviors and magnetic properties in a cylindrical ferrimagnetic nanotube with core-shell structure: A Monte Carlo study

Compensation temperature Tcomp and transition temperature TC have significant applications for the experimental realization of magnetic nanotube structure in the field of thermal magnetic recording. In this work, we use the Monte Carlo simulation to investigate the phase diagrams, magnetizations, susceptibilities, internal energies, specific heats and hysteresis behaviors of a cylindrical ferrimagnetic nanotube with core-shell structure. The effects of the single-ion anisotropies (DC, DS) and the exchange couplings (Jint, JS) on the magnetic and thermodynamic properties of the system are examined. A number of characteristic behaviors are discovered in the thermal variations, depending on different physical parameters. In particular, the triple hysteresis loops behavior has been found for appropriate physical parameters. These findings are qualitatively in good agreement with related experimental and the other theoretical results.

Mixed hemimicelle solid-phase extraction based on magnetic halloysite nanotubes and ionic liquids for the determination and extraction of azo dyes in environmental water samples

An effective and greener mixed hemimicelles magnetic solid phase extraction (MHMSPE) based on magnetic halloysite nanotubes (MHNTs) and ionic liquid (IL) is developed for the simultaneous enrichment and determination of anionic azo dyes in a spiked environmental water sample. In this MHMSPE, the formation of C16mimBr with mixed hemimicelles on the surface of MHNTs leads to the retention of analytes by strong hydrophobic, p-p and electrostatic interactions. This MHMSPE technique combines the advantages of MHNTs and mixed hemimicelles. Zeta potential data demonstrated that mixed hemimicelles were formed in [C16mimBr]/[MHNTs] ratios of the range from 0.15 to 1.33. Different important factors affecting the preconcentration of analytes were investigated and optimized by response surface methodology and one variable at a time. Under the optimum conditions, the limits of detection (LOD) for methyl red and methyl orange (MR and MO) were 0.042 and 0.050 μg L−1 in samples, respectively. The accuracy of the method was assessed by recovery measurements on a spiked sample, and good recoveries 85–87% for MR and 89–93% for MO, with preconcentration factors of 481 and 524, respectively. The low relative standard deviations from 1.6–3.1% for tap water and 2.5–5.4% for lake water was achieved. So far as we know, this is the first development of a mixed hemimicelles SPE based on MHNTs and IL for the extraction of trace anionic azo dyes in environment water samples.

Efficient extraction of uranium from aqueous solution using an amino-functionalized magnetic titanate nanotubes

In this paper, titanate nanotubes/cobalt ferrite/tetraethylenepentamine (TNTs/CoFe2O4/TEPA) adsorbents were prepared for the adsorption of uranium (VI) from the solution. Its morphology was observed by transmission electron microscopy (TEM) and exhibited the uniform well tubular structure. TNTs/CoFe2O4/TEPA composites were easily separated from solution by an external magnetic field. The removal of uranium (VI) from aqueous solution (ppm level) and simulated seawater (ppb level) were investigated by the TNTs/CoFe2O4/TEPA composites. Batch adsorption experiments were conducted to determine the effect of varying pH, contact time, and reaction temperature. The best fit for uranium (VI) adsorption was obtained with the Langmuir model, and the highest adsorption of TNTs/CoFe2O4/TEPA composites reached 509.89 mg-U/g-adsorbent at pH 6. From an investigation of the adsorption by XRD, FTIR and XPS, it is suggested that the surface complexation and cation exchange were the main adsorption mechanism. In addition, TNTs/CoFe2O4/TEPA composites maintained good adsorption properties after five sorption-desorption cycles. Therefore, we conclude that the adsorbents are promising materials for the removal of uranium (VI) from aqueous solutions.

QbD approach by computer aided design and response surface methodology for molecularly imprinted polymer based on magnetic halloysite nanotubes for extraction of norfloxacin from real samples

This article describes the development, optimization, and evaluation of a novel composite imprinted polymer, on the basis of magnetic halloysite nanotubes (MHNTs-MIPs) using “Quality by Design (QbD)” approach combining computer simulation and response surface methodology. Norfloxacin, methacrylic acid, and ethylene glycol dimethacrylate were used as template, functional monomer and cross-linker, respectively. As a comparison, two MHNTs-MIPs have been prepared with the most suitable functional monomer methacrylic acid (MAA) along with acrylamide (AM). To explain the adsorption behavior, adsorption kinetics and isotherms were studied. Magnetic halloysite nanotubes molecularly imprinted polymers prepared from MAA (MHNTs-MIP1) displayed a high adsorption capacity (349 µg mg−1) toward NOR. A magnetic imprinting solid phase extraction method coupled with high performance liquid chromatography (MHNTs-MISPE-HPLC-UV) was developed for the determination of NOR in serum and water samples, by applying MHNTs-MIP as a sorbent. The recoveries from 83.76% to 103.30% in water and from 90.46% to 99.78% in serum were obtained. Besides remarquable mechanical properties and specific recognition of MHNTs-MIP toward template molecule. It could be also collected and separated fastly by external magnetic field. Moreover, MHNTs-MIPs could be reused for several cycles with the recovery range from 83.25% to 100.96% for water sample and from 85.65% to 100.33% for serum sample. These analytical results of serum and water samples showed that the proposed method based on MHNTs-MIPs is applicable for fast and selective extraction of therapeutic agents from biological fluids and environmental water.

Magnetization Reversal Modes in Short Nanotubes with Chiral Vortex Domain Walls.

Micromagnetic simulations of magnetization reversal were performed for magnetic nanotubes of a finite length, L, equal to 1 and 2 μm, 50 and 100 nm radii, R, and uniaxial anisotropy with “easy axis” parallel to the tube length. I.e., we considered relatively short nanotubes with the aspect ratio L/R in the range 10–40. The non-uniform curling magnetization states on both ends of the nanotubes can be treated as vortex domain walls (DW). The domain wall length, Lc, depends on the tube geometric parameters and the anisotropy constant Ku, and determines the magnetization reversal mode, as well as the switching field value. For nanotubes with relative small values of Lc (Lc/L < 0.2) the magnetization reversal process is characterized by flipping of the magnetization in the middle uniform state. Whereas, for relative large values of Lc, in the reverse magnetic field, coupling of two vortex domain walls with opposite magnetization rotation directions results in the formation of a specific narrow Néel type DW in the middle of the nanotube. The nanotube magnetization suddenly aligns to the applied field at the switching field, collapsing the central DW.

Highly water-dispersible and antibacterial magnetic clay nanotubes functionalized with polyelectrolyte brushes: high adsorption capacity and selectivity toward heparin in batch and continuous system

Heparin sodium, a widely used anticoagulant is extracted from porcine intestinal mucosa by a nanotubular macromolecule.

Initial concentrations of adsorbate influence on synergistic effect between a magnetic field and graphene oxide-carbon nanotube composite for Pb2+ and phenol adsorption

Initial concentrations of adsorbate influence on synergistic effect between a magnetic field and graphene oxide-carbon nanotube composite for Pb2+ and phenol adsorption

Theoretical Studies on Magnetic Structures, Hysteresis Loops and Size Effects of a Pair of Frustrated Double-Walled Nanotubes

We propose a theoretical quantum model and derive a set of analytic formulas to study the physical properties of a pair of double-walled magnetic nanotubes. The Heisenberg exchange parameters between the two walls of the nanotubes are assumed to differ only in sign. Thus, in the absence of external magnetic field, our calculated macroscopic properties of this pair of nanotubes are almost precisely identical, exhibiting fascinating duality of the nanosystems and demonstrating the correctness of our theoretical model. The two spin systems are all frustrated, so that sudden changes in the macroscopic properties are observed around T M2 that is well below the transition temperature T M1. However, only the inner shell consisting of smaller A-type spins has been obviously affected. In the temperature range T M2 < T < T M1, this shell becomes semi-antiferromagnetic and its magnetization is considerably suppressed, whereas as temperature falls below T M2 the shell gradually restores its ferromagnetic nature. The longitudinal hysteresis behavior of such a double-waled nanotube is ferromagnetic-like below T M2, but antiferromagnetic-like in the temperature interval T M2 < T < T M1. Moreover, we find that the diameter of the nanotube has seemly no effects on its physical properties, whereas its length does affects the two temperatures slightly, and also its spin configuration at very low temperatures if the tube is sufficiently long. More importantly, the theoretical results presented in this paper can be precisely reproduced with the quantum computational method we develop in recent years, justifying the validity of the numerical approach once again.