Magnetic Nanotubes Research Articles

Analytical magnetostatic model for 2D arrays of interacting magnetic nanowires and nanotubes.

A fully analytical model to describe the magnetostatic properties of these 2D nanocylinder arrays (tubes and wires) is presented. The model allows calculating the components of the effective demagnetizing field as a function of the cylinder height, inner and outer diameters, and the center-to-center distance. From these components, it is possible to calculate the shape anisotropy of the cylinder, the dipolar interaction between them, and the total magnetostatic energy. The model allows performing calculations very simply, using a simple spreadsheet or open-access software such as Geogebra. This allows analyzing the effect of each geometrical parameter in the different contributions to the magnetostatic energy. Amongst the most interesting findings is that the model describes naturally the magnetization easy-axis reorientation transition induced by the dipolar interaction, for which a general phase diagram has been calculated for both tubes and wires. For the case of nanowires, our results show a very good agreement with previously published results. While for nanotubes, the model predicts that the magnetization easy-axis reorientation transition is frustrated as the tube wall thickness decreases and reaches a critical value even when the distance between tubes is reduced to its lowest possible value.

Thiol–Yne Click Synthesis of Polyamide–Amine Dendritic Magnetic Halloysite Nanotubes for the Efficient Removal of Pb(II)

Heavy metals such as Pb(II) pollutions in wastewater have been a serious environmental problem. In this study, we loaded polyamide–amine (PAMAM) on the surface of magnetic halloysite nanotubes (MHN...

Cellulase Immobilization onto Magnetic Halloysite Nanotubes: Enhanced Enzyme Activity and Stability with High Cellulose Saccharification

A quest for efficient biotransformation of cellulosic material into sustainable biochemical products for recent biotechnological interventions is currently under way. Herein, we report the fabricat...

Synthesis of magnetic halloysite nanotube-based molecularly imprinted polymers for sensitive spectrophotometric detection of metoclopramide in urine samples.

A novel molecularly imprinted polymer was synthesized on magnetic halloysite nanotube via surface initiated reversible addition-fragmentation chain transfer polymerization in the presence of 2-aminoethylmethacrylamide, 2-Cyano-2-propyl benzodithioate, ethylene glycol dimethacrylate (EGDMA) and azobis(isobutyronitrile) for sensitive and selective spectrophotometric determination of metoclopramide in urine samples. The synthesized imprinted polymer was characterized by several surface characterization techniques and the results indicated there was a thin polymer network on the magnetic halloysite nanotube. The rebinding properties of the molecularly imprinted magnetic halloysite nanotube were also investigated in detail and the maximum adsorption capacity and imprinting factor were found to be 37.8 mg/g and 4.51, respectively. The application of the proposed method was carried out by enrichment and spectrophotometric determination of metoclopramide via formation of a charge transfer complex between picric acid and eluted metoclopramide. Under the optimized conditions, the calibration curve was linear in the concentration range of 5.0-150.0 ng/mL and the limit of detection and the limit of quantification were calculated to be 1.5 ng/mL and 4.95 ng/mL, respectively. The inter-day and intra-day precisions were below 5% and recoveries were between 92.8% and 99.2%. The results showed that the proposed method increased the sensitivity and selectivity for spectrophotometric determination of metoclopramide.

Wave reversal mode: A new magnetization reversal mechanism in magnetic nanotubes

We have investigated the magnetic properties of 14 nm thick and 1 μm long nickel and permalloy nanotubes with external diameters of 40 and 100 nm as a function of the angle θ at which the external magnetic field is applied. Our results show that the coercivity of 40 nm diameter nickel nanotubes follows a non-monotonic behavior from θ = 0° up to θ = 60°, while that corresponding to permalloy displays an increasing monotonic trend at the same angular range. At θ = 90°, both materials evidence a sharp drop of the coercivity to zero, indicating that the reversal mechanism has changed to a pseudo-coherent rotation. On the other hand, nickel and permalloy nanotubes with 100 nm in diameter exhibit a similar angular dependence of the coercivity, reversing their magnetization through the nucleation and propagation of vortex domain walls for angles lower than 75°. For θ = 90°, a novel striking mechanism, the wave reversal mode (W), arises. This phenomenon leads to an unusual S-type shape in the hysteresis curves at those given parameters, which is until now an effect that has not been reported for these nanostructures.

Synthesis and characterization of magnetic halloysite–chitosan nanocomposites: use in the removal of methylene blue in wastewaters

Magnetic halloysite–chitosan (MHNT-CTN) nanocomposites were synthesized by turning magnetic halloysite nanotubes (MHNTs) into nanocomposites using biopolymeric chitosan (CTN). The magnetic properties of pure halloysite nanotubes (HNTs) were achieved using the co-precipitation method, and MHNTs were synthesized. The characterization of the MHNT-CTN nanocomposite and the pure states of the components forming the nanocomposite was performed by FTIR, TGA, TEM, and VSM. Methylene blue (MB) adsorption on MHNT-CTN nanocomposites was investigated as a function of medium pH, the mass ratio of the components forming the nanocomposite material, and the initial MB concentration. The optimum conditions for MB adsorption on MHNT-CTN were determined as pH 8.0, in a solution volume of 25 mL, 25 mg MHNT-CTN, and the MHNT-to-CTN mass ratio of 2:1. The highest adsorption efficiency for MB adsorption on MHNT2-CTN1 was reached at an initial MB concentration of 20 mg/L, and it was found to be 83.9%. The adsorption equilibrium data obtained from the studies on MB adsorption on MHNT-CTN were used to investigate compatibility with the Langmuir, Freundlich, and Redlich–Peterson adsorption models. It was found out that the MB adsorption kinetics was compatible with the pseudo-second-order model.

Anodic Titanium Dioxide Nanotubes for Magnetically Guided Therapeutic Delivery

Hollow titanium dioxide (TiO2) nanotubes offer substantially higher drug loading capacity and slower drug release kinetics compared to solid drug nanocarriers of comparable size. In this report, we load TiO2 nanotubes with iron oxide nanoparticles to facilitate site-specific magnetic guidance and drug delivery. We generate magnetic TiO2 nanotubes (TiO2NTs) by incorporating a ferrofluid containing Ø ≈ 10 nm iron oxide nanoparticles in planar sheets of weakly connected TiO2 nanotubes. After thermal annealing, the magnetic tubular arrays are loaded with therapeutic drugs and then sonicated to separate the nanotubes. We demonstrate that magnetic TiO2NTs are non-toxic for HeLa cells at therapeutic concentrations (≤200 µg/mL). Adhesion and endocytosis of magnetic nanotubes to a layer of HeLa cells are increased in the presence of a magnetic gradient field. As a proof-of-concept, we load the nanotubes with the topoisomerase inhibitor camptothecin and achieve a 90% killing efficiency. We also load the nanotubes with oligonucleotides for cell transfection and achieve 100% cellular uptake efficiency. Our results demonstrate the potential of magnetic TiO2NTs for a wide range of biomedical applications, including site-specific delivery of therapeutic drugs.

Magnetic switching field distribution and morphology in electrodeposited Ni@Cu coaxial nanotubes

Using magnetic measurements structural irregularities in electrodeposited nanotubes are inferred. The correlation between morphology and magnetic properties is very useful for studying materials. Through the use of the magnetic switching field distribution, the association with the surface irregularities imperfections of the magnetic nanotubes was performed. The distribution of magnetic switching field presents well behaved in smooth-surface nanotubes and, for nanotubes with irregularities, the distribution of switching fields has a noisy behavior, added to that smoothed signal. This noise is due to the superficial irregularities on the tubes surface because the magnetic barriers occurring in imperfect structures. Pinning centers due to irregularities are the principal aspect to observe in this situation. Magnetic measurements were associated directly to the morphology obtained by scanning electron microscopy.

Magnetic hydroxyapatite nanotubes on micro-arc oxidized titanium for drug loading

A novel coating which comprised magnetic hydroxyapatite (HA) nanotubes as an outer layer and porous TiO2 as the inner layer was fabricated on Ti by a hybrid process of micro arc oxidation (MAO), hydrothermal treatment (HT) and electrochemical treatment (ET). The microstructure of HA nanorods after HT was investigated, and their morphology evolution from nanorods to nanotubes by prolonging ET was observed. The formation mechanism of HA nanotubes was explored, and magnetism property of the composite coating was evaluated. Monocrystallized HA nanorods doped with 1.19 At% Fe were initially formed on microporous TiO2 by MAO and HT, and they had a mean diameter of 300 nm. The mismatching between Ca and Fe ions induced some lattice distortions on the basal-faceted surfaces of HA. During ET process, Na+ and H+ ions should concentrate on the negatively charged basal planes of HA inducing further lattice distortion and local dissolution. By prolonging the ET process, dissolution of basal planes increased, resulting in the formation of HA nanotubes with an average outer diameter of about 300 nm, and wall thickness of about 30 nm. The composite coating showed magnetism behavior with a value of 0.3 emu g−1 at applied field of 4 T. A strategy to fabricate a magnetic HA nanotube coating on Ti was given, and the unique nanostructure should have a potential application in drug loading.

Synthesis and Characterization of Magnetic Halloysite–Alginate Beads for the Removal of Lead(II) Ions from Aqueous Solutions

In this study, alginate (ALG) hybrid spheres supported with magnetic halloysite nanotubes (MHNTs) were synthesized and used effectively in the removal of Pb(II) ions from aqueous solutions. MHNTs were prepared using the “co-precipitation” method. Afterward, magnetic halloysite–alginate (MHNT–ALG) hybrid beads were formed using ALG and MHNTs by the “extrusion dripping” method. The characterization of halloysite nanotubes (HNTs), ALG, MHNTs, and MHNT–ALG hydrogels was performed using FTIR, TGA, particle size analysis, SEM–EDX, TEM, VSM, and BET. According to VSM measurements, the saturation magnetization values of MHNTs and MHNT–ALG hybrid beads at a mass ratio of 1:2 were determined to be 22.7 emu/g and 8.17 emu/g, respectively. The BET surface area of MHNT–ALG hybrid beads was measured to be 81.3 m2/g. The adsorption of Pb(II) ions on MHNT–ALG hydrogels was investigated as a function of the pH of the medium, amount of MHNT–ALG, the mass ratio of MHNT to ALG in the composite, and initial Pb(II) concentration in batch stirred vessels. The fit of the adsorption equilibrium of Pb(II) ions on MHNT–ALG hydrogels to the Langmuir type-I and type-II models, Freundlich model, and Redlich–Peterson model was investigated. The fit of the adsorption kinetics to the pseudo-second-order kinetics model was evaluated. Using the Weber and Morris model, the effect of internal and external diffusion limitations was discussed.

β-Cyclodextrin coated and folic acid conjugated magnetic halloysite nanotubes for targeting and isolating of cancer cells

The study developed a simple, effective and inexpensive strategy for capturing, enriching and detecting circulating tumor cells (CTCs) by using folic acid (FA) as the targeting molecule instead of antibodies. This work constructed magnetic halloysite nanotubes (MHNTs) coated with biocompatible β-cyclodextrin (CD), and conjugated to FA via a PEG-Ad linker, to specifically capture the FA receptor (FR)-overexpressing cancer cells. The capture efficiencies of MHNTs@β-CD@Ad-PEG-FA for the Skov3, Hela and A549 cancer cells were 96.3%, 97.0% and 95.6% respectively. In addition, the nanoparticles were able to capture very low numbers of the cancer cells (25–500 cells/mL) from PBS and whole blood, as well as selectively capture the cancer cells over normal HEK 293 T cells. Furthermore, the captured cells were viable and grew normally in vitro, indicating the future potential of downstream analyses. This approach can be adapted for different CTCs, once the tumor-specific surface markers are identified and the efficacy of targeting ligands is established. Taken together, FA-conjugated MHNTs nanoparticles are a highly promising tool for isolating CTCs for the diagnosis and treatment of cancer.

Novel materials for Cr(VI) adsorption by magnetic titanium nanotubes coated phosphorene

The accumulation of Cr(VI) will cause mutagenic and carcinogenic effects on humans. Therefore, the standard regulations have been governed by the EPA to control the chromium content in the effluent and drinking water and have made it mandatory [1]. For the better recovery of the adsorbent; Magnetic nano particle based phosphorene titanium nano tubes were used for the first time in action which has been proven to be superior for the Chormium pollutants. MNP-PN-TNT (Magnetic nanoparticle-Phosphorene-Titanium nano tubes) was synthesized from hydrothermal method in this study. The prepared material is used for effective removal of Cr(VI) from the water by adsorption technique in acidic environment. The adsorption capacity was found to be 35 mg g−1 at the initial concentration of 50 mg L−1maintainingthe temperature under 45 °C. The optimal operation condition is under pH 9, temperature of 25 °C, and dosage of 0.8 g L−1 obtained from RSM (Response Surface Methdology). The adsorption process of MNP-PN-TNT is conformed with a pseudo-second-order kinetic model. Cr(VI) adsorption behavior with MNP-PN-TNT, is spontaneous from the results of thermodynamics analysis. The adsorption mechanism of Cr(VI) with MNP-PN-TNT was evident by O1s, C1s, Cr 2p, Ti 2p, Fe 2p and P 2p of XPS. Cr(VI) is adsorbed with MNP-PN-TNT, in randomness during the adsorption process.

Current-induced skyrmion motion on magnetic nanotubes

Magnetic skyrmions are believed to be the promising candidate of information carriers in spintronics. However, the skyrmion Hall effect, due to the nontrivial topology of skyrmions, can induce a skyrmion accumulation or even annihilation at the edge of the devices, which hinders the real-world applications of skyrmions. In this work, we theoretically investigate the current-driven skyrmion motion on magnetic nanotubes which can be regarded as ‘edgeless’ in the tangential direction. By performing micromagnetic simulations, we find that the skyrmion motion exhibits a helical trajectory on the nanotube, with its axial propagation velocity proportional to the current density. Interestingly, the skyrmion’s angular speed increases with the increase of the thickness of the nanotube. A simple explanation is presented. Since the tube is edgeless for the tangential skyrmion motion, a stable skyrmion propagation can survive in the presence of a very large current density without any annihilation or accumulation. Our results provide a new route to overcome the edge effect in planar geometries.

Magnetic ZnFe2O4 nanotubes for dispersive micro solid-phase extraction of trace rare earth elements prior to their determination by ICP-MS.

Magnetic ZnFe2O4 nanotubes (ZFONTs) with numerous pores on their walls were synthesized and characterized. They are shown to be a viable sorbent for dispersive micro-solid phase extraction of the trivalent ions of rare earth elements (REEs), specifically of lanthanum, praseodymium, europium, gadolinium, holmium and ytterbium. The specific surface area of ZFONTs is large (57m2⋅g-1) and much bigger than that of ZnFeO4 nanoparticles (16m2⋅g-1). It is shown that REEs are quantitatively retained on ZFONTs in the pH range of 7.0-9.0. The separation of the sorbent from the aqueous phase was achieved by an external magnetic field. Following elution with 0.5mol⋅L-1 HNO3, REEs were quantified by inductively coupled plasma mass spectrometry. The main parameters influencing preconcentration and determination of the REEs were studied. Under optimum conditions, detection limits for REEs range from 0.01(Ho) to 0.75(La) pg⋅mL-1. Relative standard deviations are less than 6.5% (for n = 9; at 1.0ng⋅mL-1). The method was applied to the determination of trace REEs in spiked biological and environmental samples and gave satisfactory results. Graphical abstract Schematic presentation of a new adsorbent for dispersive micro-solid phase extraction (DMSPE) combined with ICP-MS. Magnetic ZnFe2O4 nanotubes with many pores on their walls were used for preconcentration and determination of rare earth elements (REEs) in environmental and biological samples.

Magnetically tunable iron oxide nanotubes for multifunctional biomedical applications

Design of a multifunctional magnetic bionanosystem has become increasingly important towards advancing the future of clinical medicine. While hollow iron oxide nanoparticles with enhanced surface areas allow for more drug molecules to be attached to the particles, their relatively low saturation magnetization (MS) hinders their practicality in medicinal applications such as drug delivery and hyperthermia therapy. We demonstrate that this limitation can be overcome by utilizing 1D magnetic nanotubes that possess both enhanced surface areas and high MS. In this study, highly crystalline, tunable aspect ratio Fe3O4 nanotubes have been successfully synthesized using a hydrothermal method. Magnetic measurements showed a clear Verwey transition (∼120 K) and high MS (∼75 emu/g) at 300 K, confirming the high quality of the synthesized Fe3O4 nanotubes. Calorimetric experiments on randomly dispersed Fe3O4 nanotubes in water with concentration of 1 mg/mL showed a large Specific Absorption Rate (SAR) value of 400 W/g for an AC magnetic field of 800 Oe, which increased to 500 W/g when the nanotubes were aligned parallel to the DC magnetic field and suspended in a 2% agar solution. Our study shows the possibility of using the Fe3O4 nanotubes as a highly effective multifunctional nanoscale tool for targeted hyperthermia and on-demand drug delivery.

Potential Contamination Sources on Fresh Produce Associated with Food Safety

The health benefits associated with consumption of fresh produce have been clearly demonstrated and encouraged by international nutrition and health authorities. However, since fresh produce is usually minimally processed, increased consumption of fresh fruits and vegetables has also led to a simultaneous escalation of foodborne illness cases. According to the report by the World Health Organization (WHO), 1 in 10 people suffer from foodborne diseases and 420,000 die every year globally. In comparison to other processed foods, fresh produce can be easily contaminated by various routes at different points in the supply chain from farm to fork. This review is focused on the identification and characterization of possible sources of foodborne illnesses from chemical, biological, and physical hazards and the applicable methodologies to detect potential contaminants. Agro-chemicals (pesticides, fungicides and herbicides), natural toxins (mycotoxins and plant toxins), and heavy metals (mercury and cadmium) are the main sources of chemical hazards, which can be detected by several methods including chromatography and nano-techniques based on nanostructured materials such as noble metal nanoparticles (NMPs), quantum dots (QDs) and magnetic nanoparticles or nanotube. However, the diversity of chemical structures complicates the establishment of one standard method to differentiate the variety of chemical compounds. In addition, fresh fruits and vegetables contain high nutrient contents and moisture, which promote the growth of unwanted microorganisms including bacterial pathogens (Salmonella, E. coli O157: H7, Shigella, Listeria monocytogenes, and Bacillus cereus) and non-bacterial pathogens (norovirus and parasites). In order to detect specific pathogens in fresh produce, methods based on molecular biology such as PCR and immunology are commonly used. Finally, physical hazards including contamination by glass, metal, and gravel in food can cause serious injuries to customers. In order to decrease physical hazards, vision systems such as X-ray inspection have been adopted to detect physical contaminants in food, while exceptional handling skills by food production employees are required to prevent additional contamination.

Dispersive micro-solid phase extraction using magnetic ZnFe2O4 nanotubes as adsorbent for preconcentration of Co(II), Ni(II), Mn(II) and Cd(II) followed by ICP-MS determination

In this work, magnetic ZnFe2O4 nanotubes (ZFONTs) were synthesized, characterized and used as adsorbent for dispersive micro-solid phase extraction of Co(II), Ni(II), Mn(II) and Cd(II) before their determination by inductively coupled plasma mass spectrometry. Adsorption behaviors of target ions on ZFONTs were investigated. The results showed that the analytes were quantitatively retained on ZFONTs in the pH range of 6.0–8.0, and eluted completely with 1.0 mL of 0.4 mol L−1 HNO3. The separation of sorbent from aqueous phase was performed by an external magnet to avoid tedious centrifugation or filtration steps. Main parameters affecting preconcentration and determination of the analytes were studied in detail. Under optimum conditions, detection limits for Co(II), Ni(II), Mn(II) and Cd(II) were 0.10, 1.2, 3.7 and 0.09 pg mL−1, respectively. Relative standard deviations were <4.5% (n = 9, c = 1.0 ng mL−1). This method was verified by analysis of Co(II), Ni(II), Mn(II) and Cd(II) in environmental and biological samples, including water samples and certified reference materials of mussel (GBW 08571) and human hair (GBW 09101).

Quantification of the local magnetized nanotube domains accelerating the photocatalytic removal of the emerging pollutant tetracycline

Evidence is presented for the enhanced photodegradation of tetracycline (TC) by AgxO/FeOx/ZnO nanotubes (NTs) compared to AgxO/ZnO nanotubes under low-intensity solar light irradiation. A higher amount of the local magnetic domains with random orientation in the AgxO/FeOx/ZnO NTs lead to a faster TC-degradation. Fe introduces intra-gap states in the ZnO NTs facilitating the e-transport under light. The AgxO/FeOx/ZnO nanotubes were observed to present predominantly semiconductor behavior during the light induced TC-degradation. The nature of the interaction between non-polarized photos with the local domains due the addition of Fe is discussed. By X-ray photoelectron spectroscopy (XPS) redox reactions were observed on the nanotube surface NTs leading to the reactive oxygen radical species (ROS). The ROS-intermediates were identified by appropriate scavengers. Fast TC-degradation kinetics was attained by a catalyst with a composition AgOx(5.8%)FeOx(21.9%)ZnO (72.3%) as determined by X-ray fluorescence (XRF). A scheme for the interfacial charge transfer (IFCT) between the oxides on the nanotube surface is presented. Magnetized nanotubes present a practical potential in environmental cleaning avoiding the high cost separation of the catalyst from the reaction media at the end of the process

Biopolymer-Grafted, Magnetically Tuned Halloysite Nanotubes as Efficient and Recyclable Spongelike Adsorbents for Anionic Azo Dye Removal.

The quest for sustainable development and green chemistry had led to the design and synthesis of advanced adsorbent materials for efficient removal of pollutants in industrial effluents. Magnetic halloysite nanotubes with chitosan nanocomposite sponges were prepared by combining solution-mixing and freeze-drying. Magnetic@chitosan/halloysite (Fe3O4–HNT/CS) and spongelike chitosan/halloysite (HNT/CS) were used as adsorbents for the removal of Congo red dye in aqueous solution in a batch process. The as-prepared composites were characterized using scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction, vibrating-sample magnetometry, thermal gravimetry–differential scanning calorimetry, and Fourier transform infrared spectroscopy. Data from kinetic study were analyzed with pseudo-first-order and pseudo-second-order models, whereas the mechanism was analyzed using Bangham’s, Elovich’s, intraparticle, and double-exponential diffusion models. The equilibrium data were evaluated using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models. The adsorption kinetics of dye removal followed the pseudo-first-order model with average rate constants of 0.260 and 0.196 min–1 for Fe3O4–HNT/CS and HNT/CS, respectively. The Langmuir adsorption isotherm best fitted the equilibrium data with R2 > 0.9 with maximum adsorption capacities of 41.54 and 54.49 mg g–1 obtained for HNT/CS and Fe3O4–HNT/CS, respectively. Negative values of ΔG° obtained from thermodynamic studies revealed that the adsorption process was spontaneous. The values of ΔH° and ΔS° obtained for Congo red dye removal were 69.46 and 39.54 kJ mol–1 and 240.5 and 145.1 J mol–1 K–1 for HNT/CS and Fe3O4–HNT/CS, respectively. The results indicated that CS–HNT is an excellent adsorbent; however, its magnetic modification further improved its recyclability and enhanced the performance for the removal of Congo red dye from aqueous solution.

Novel magnetic standpoints in Na2Ti3O7 nanotubes

Abstract The preparation of magnetic nanotubes opens new avenues in nanobiotechnology as a consequence of their multiple properties embedded within the same moiety. Here, we report on synthesis and characterization of titanate nanotubes and their Fe-/Co-doped by means of X-ray diffraction, high-resolution transmission electron microscopy, and magnetic studies. Although the absence of 3d elements in Na2Ti3O7 nanotubes, our data for the first time, exhibits room temperature M−H hysteresis. Furthermore, our results show that the magnetization increased with Fe doping, while Co doping enhanced the coercivity. This behaviour was expected from the magnetic character of Fe and the positive magnetocrystalline anisotropy of Co. These results give access to the doping effect on tuning the properties of Na2Ti3O7 nanotubes.