Magnetic Multi-walled Carbon Nanotubes Research Articles

Determination of multiclass contaminants in chilli powder based on magnetic multiwalled carbon nanotubes and UPLC-QTOF/MS

A multiclass analysis approach was developed using magnetic multiwalled carbon nanotubes sorbents and ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS) for the rapid screening and simultaneous determination of 216 contaminants including 15 mycotoxins, 9 synthetic colourants, and 192 pesticides in chilli powder. The sample preparation process was optimized. The optimal preparation procedure utilized NaCl and NaAc as the salting-out agents, and Fe3O4-MWCNTs as the sorbents, resulting in reduced chemical consumption, improved cleaning performance, and facilitated high-throughput analysis. The proposed method was validated, and satisfactory parameters were obtained. Approximately 85.6% of the target analytes exhibited a weak matrix effect, with the matrix effects falling within the range of 0.8 ∼ 1.2. The method demonstrated acceptable recoveries of the analytes, falling within the range of 62.14%∼119.76% at three fortified levels with relative standard deviations (RSDs) of less than 20%. Additionally, the method’s limit of quantification (LOQ) ranged from ranged from 0.50 μg·kg−1 to 49.56 μg·kg−1. The method was further applied for analysis of 27 chilli powder samples, demonstrating its potential for screening and quantification of multiclass contaminants for spices.

Optimization of Adsorption Conditions Using Response Surface Methodology for Tetracycline Removal by MnFe2O4/Multi-Wall Carbon Nanotubes

In this study, the optimal conditions and effects of external factors on tetracycline adsorption by magnetic multi-walled carbon nanotubes (MMWCNTs) were established by a response surface methodology for the first time. Batch adsorption experiments showed that increasing the dosage and contact time effectively promoted the adsorption of tetracycline and maximum removal of 97.93–99.13% was achieved at pH 3–7. The pseudo-second-order model and Fourier-transform infrared spectroscopy spectra indicated that the mechanism of adsorption may be π–π electron interaction and cation–π electron bonding. Design Expert was utilized to develop a response surface methodology for the analysis and optimization of tetracycline adsorption by magnetic multi-walled carbon nanotubes. The Box–Behnken design (BBD) results showed that the optimization exhibited high significance and reliability. The main effect plots and Pareto chart indicated that pH exerted a significant individual effect on the regulation of adsorption, while 3D response surface plots and interaction effect plots exhibited a significant antagonistic interaction between pH and contact time. A maximum tetracycline removal of 99.16% was achieved under the optimal conditions of 12 mg adsorbent dosage at pH 5.43, with an adsorption time of 120 min. Mathematical and experimental results confirmed the accuracy of the established optimal conditions.

Covalent immobilization of tyrosinase on magnetic multi-walled carbon nanotubes for inhibitor screening.

The inhibition of tyrosinase is considered to be a common therapeutic strategy for some hyperpigmentation disorders. Screening of tyrosinase inhibitors is of great significance to the treatment of pigmentation diseases. In this study, tyrosinase was covalently immobilized on magnetic multi-walled carbon nanotubes for the first time, and the immobilized tyrosinase was applied for ligand fishing of tyrosinase inhibitors from complex medicinal plants. The immobilized tyrosinase was characterized by transmission electron microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, vibratingsamplemagnetometry, and thermo-gravimetric analyzer, which indicated that tyrosinase was immobilized onto magnetic multi-walled carbon nanotubes. The immobilized tyrosinase showed better thermal stability and reusability than the free one. The ligand was fished out from Radix Paeoniae Alba and identified as 1,2,3,4,6-pentagalloylglucose by ultra-performance liquid chromatography-quadrupole time-of-flight high-resolution mass spectrometry. 1,2,3,4,6-pentagalloylglucose was found to be a tyrosinase inhibitor with similar half maximal inhibitory concentration values of 57.13±0.91μM compared to kojic acid (41.96±0.78μM). This work not only established a new method for screening tyrosinase inhibitors but also holds considerable potential for exploring the new medicinal value of medicinal plants.

Numerical study on the enhanced solidification process in ice thermal energy storage with magnetic carbon nanotubes

The ice thermal storage performance would be enhanced by nano-additives to improve thermal conductivity and reduce supercooling degree of water. In this work, the solidification heat transfer characteristics of the magnetic Multi-walled Carbon Nanotube (MWCNT) Phase Change Material (PCM) under the applied magnetic field were investigated numerically. The supercooling degree was considered by dividing the whole solidification process into two stages of supercooling and phase change regions in the simulation model. Furthermore, the simulation results were verified by the experimental data. Specifically, the temperature distribution influenced by MWCNT under magnetic field and the development features of convection in the supercooling region were discussed. The results indicated that the solidification characteristics were enhanced by adding magnetic MWCNT, and the heat transfer was further enhanced with the aligned MWCNT under extra applied magnetic field. Consequently, the stable flow field was advanced by 37 %, the time of vortices distribution was reduced by 69.4 % for MWCNT PCM under magnetic field. Besides, there was 68.6 % reduction in supercooling, 76.6 % shorten in nucleation time and 36.2 % shorten in total solidification time compared to pure water.

Preparation of Magnetic Superhydrophilic Imprinted Nanocomposite Resin and its Application in the Extraction of Chlorophenols in Water

AbstractFabricating hydrophilic imprinted materials with eminent aqueous recognition capacity is a bottleneck problem in imprinting field. Herein, a magnetic superhydrophilic imprinted nanocomposite resin (MWNTs@MIR) was first fabricated on magnetic multi walled carbon nanotube with 2,4,6‐trichlorophenol as virtual template, 3‐aminophenol as functional monomer and glyoxylic acid as crosslinking monomer. Via employing MWNTs@MIR as adsorbent and combining with magnetic solid‐phase extraction, the effective enrichment of chlorophenols (CPs) in water is realized. The SEM, TEM, FTIR, XRD and other characterizations confirm that the MWNTs@MIR has been successfully prepared and exhibits excellent magnetism (separated by external magnet within 30 s) and superhydrophilicity (water contact angle 0°). Under optimized extraction conditions, MWNTs@MIR can be directly employed for rapid and efficient extraction of four CPs in water (the extraction recoveries reach 78 %–92 %), and exhibits excellent selectivity (the extraction efficiency of MWNTs@MIR for the four CPs is evidently higher than that of the corresponding non‐imprinted material and reference compound) and stability (the recoveries of CPs did not significantly decrease after 5 cycles). The research provided a novel, easy and economical route for constructing hydrophilic imprinted materials to realize efficient extraction of CPs in water, and has potential application in the field of sample pretreatment and analytical chemistry.

Separation and Preconcentration of Atrazine on Magnetic Multiwalled Carbon Nanotubes before Determination in Food and Water Samples by High-Performance Liquid Chromatography with Diode Array Detection (HPLC-DAD)

This work focuses upon the easy and efficient synthesis of multi-walled carbon nanotubes (MWCNT) decorated with magnetite used in the vortex-assisted magnetic solid-phase microextraction (VA-m-µ-SPE) of atrazine in water and food samples. The nanocomposite was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and infrared spectroscopy. Parameters that influenced VA-m-µ-SPE (pH, mMWCNT mass, extraction time, eluent type and volume, and sample volume) were optimized. The presented technique provided a preconcentration factor of 10-fold with limits of detection and quantification of 2.1 μg L−1 and 6.4 μg L−1, respectively, and a linear range from 12.5 to 250 μg L−1. VA-m-µ-SPE has been applied in the preconcentration and determination of atrazine in the natural waters. In addition, atrazine was determined in ginger and fennel.

Sensitive and selective impedimetric determination of TNT using RSM-CCD optimization

Detection of trace amounts of 2,4,6-Trinitrotoluene as a widely used explosive in the military and industrial sectors is of vital importance due to security and environmental concerns. The sensitive and selective measurement characteristics of the compound still is considered a challenge for analytical chemists. Unlike conventional optical and electrochemical methods, the electrochemical impedance spectroscopy technique (EIS), has a very high sensitivity, but it faces a significant challenge in that it requires complex and expensive steps to modify the electrode surface with selective agents. We reported the design and construction of an inexpensive, simple, sensitive, and selective impedimetric electrochemical TNT sensor based on the formation of a Meisenheimer complex between magnetic multiwalled carbon nanotubes modified with aminopropyl triethoxysilane (MMWCNTs @ APTES) and TNT. The formation of the mentioned charge transfer complex at the electrode-solution interface blocks the electrode surface and disrupts the charge transfer in [(Fe (CN) 6)] 3−/4- redox probe system. Charge transfer resistance changes (ΔRCT) were used as an analytical response that corresponded to TNT concentration. To investigate the influence of effective parameters on the electrode response, such as pH, contact time, and modifier percentage, the response surface methodology based on central composite design (RSM-CCD) was used. The calibration curve was achieved in the range of 1–500 nM with a detection limit of 0.15 nM under optimal conditions, which included pH of 8.29, contact time of 479 s, and modifier percentage of 12.38% (w/w). The selectivity of the constructed electrode towards several nitroaromatic species was investigated, and no significant interference was found. Finally, the proposed sensor was able to successfully measure TNT in various water samples with satisfactory recovery percentages.

Improving the solidification performance of deionized water using magnetically oriented CNT by Fe3O4 nanoparticles as magnetic agents

In this work, directionally distributed Multi-walled Carbon Nanotube (MWCNT) were applied for supercooling suppression and improving the thermal conductivity of deionized water during the solidification. Specifically, Fe3O4 nanoparticles coated MWCNT are magnetized which would be directionally arranged along with the direction of extra magnetic field. A comparative study of solidification characteristics of the water based MWCNT nanofluids was carried out. The results indicated that 0.1% magnetic MWCNT nanofluid shows 31% enhancement in the thermal conductivity under the magnetic field intensity of 150 mT for fully display their axial thermal conductivity, and it exhibits ignorable reduction in the latent heat compared to the pure water. As a result, the magnetic MWCNT nanofluid has the optimal solidification characteristics under the magnetic field with 68% reduction in supercooling and 36% advance in the total solidification time. Moreover, the dynamic characteristics of solid/liquid interface were discussed, and then the growing velocity of ice crystal is obtained.

Dispersive magnetic solid-phase extraction for capsaicinoid compounds in human serum using LC-HRMS: targeted and non-targeted approaches

A new analytical method based on the use of dispersive magnetic solid-phase extraction (DMSPE) is described for the preconcentration of capsaicin (CAP), dihydrocapsaicin (DCAP), and N-vanillylnonanamide (PCAP) from human serum samples. The influence of several experimental factors affecting the adsorption (nature and amount of magnetic material, adsorption time, and pH) and desorption (nature of solvent, its volume and desorption time) steps was studied. Among seven different nanomaterials studied, the best results were obtained using magnetic multiwalled carbon nanotubes, which were characterized by means of spectrometry- and microscopy-based techniques. Analyses were performed by ultra-high-performance liquid chromatography with quadrupole-time-of-flight mass spectrometry using electrospray ionization in positive mode (UHPLC-ESI-Q-TOF-MS). The developed method was validated by obtaining several parameters, including linearity (0.3–300 μg L−1 range), and limits of detection which were 0.1, 0.15, and 0.17 μg L−1 for CAP, DCAP, and PCAP, respectively. The repeatability of the method, expressed as relative standard deviation (RSD, n = 7), varied from 3.4 to 11%. The serum samples were also studied through a non-targeted approach in a search for capsaicinoid metabolites and related compounds. With this objective, the fragmentation pathway of this family of compounds was initially studied and a strategy was established for the identification of novel or less studied capsaicinoid-derived compounds.Graphical abstract

Sulfonated magnetic multi-walled carbon nanotubes with enhanced bonding stability, high adsorption performance, and reusability for water remediation.

In view of the simple and rapid conveniency of magnetic separation, magnetic nanocomposites had notably gained attention from researchers for environmental field applications. In this work, carboxylated magnetic multi-walled carbon nanotubes (c-MMWCNTs) and novel sulfonated MMWCNTs (s-MMWCNTs) were synthesized by a facile solvent-free direct doping method. Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, energy dispersive X-ray, vibrating sample magnetometer, and point of zero charge analyses confirmed the successful doping of the Fe3O4 nanoparticles into the functionalized MWCNTs to form MMWCNTs. Besides, the bonding stabilities of both c-MMWCNTs and s-MMWCNTs were compared, and results showed that s-MMWCNTs possessed more substantial bonding stability than that of c-MMWCNTs with significantly less leaching amount of Fe3O4. The adsorption capacity of s-MMWCNTs was higher than that of c-MMWCNTs owing to the stronger electronegativity sulfonic group in s-MMWCNTs. Moreover, the reusability experiments proved that the adsorbent remained consistently excellent MB removal efficiency (R > 94%) even reused for twelve cycles of batch adsorption. The finding of the present work highlights the simple fabrication of novel s-MMWCNTs and its potential to be served as a promising and sustainable adsorbent for water remediation owing to its enhanced bonding stability, high adsorption performance, magnetic separability, and supreme recyclability.

Development of a Modified QuEChERS Method Based on Magnetic Multi-Walled Carbon Nanotubes as a Clean-Up Adsorbent for the Analysis of Heterocyclic Aromatic Amines in Braised Sauce Beef.

Heterocyclic aromatic amines (HAAs) generated during the cooking of meats cause adverse effects on human health. The purpose of the current research was to develop a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) method using magnetic multi-walled carbon nanotubes (Fe3O4-MWCNTs) as clean-up adsorbents for the rapid determination of HAAs in braised sauce beef. The significant parameters in extraction and clean-up processes were screened and optimized. Under optimal conditions, the LODs ranged from 3.0 ng/g to 4.2 ng/g. The recoveries (78.5−103.2%) and relative standard deviations RSDs (<4.6%) of five HAAs were obtained. These are in accordance with the validation criteria (recovery in the range of 70−120% with RSD less than 20%). Compared with conventional clean-up adsorbents (PSA or C18), Fe3O4-MWCNTs displayed equivalent or better matrix removal efficiency, while making the pretreatment process easier and more time-saving through magnetic separation. Less usage of adsorbent makes the method possess another advantage of being lower in cost per sample. The method developed was successfully applied to analyze real samples collected from local deli counters, demonstrating Fe3O4-MWCNTs could be considered as an effective alternative adsorbent with great potential in the QuEChERS process.

Gliclazide Removal Efficiency of Carbon‐Based Magnetic Materials: Isotherm and Kinetic Studies

AbstractGliclazide, one of the micropollutants that can be detected in water, is widely used in the treatment of type II diabetes patients. In this study, the removal of gliclazide from aqueous solutions with magnetic carbon‐based materials was investigated. Magnetic activated carbon (MAC) and magnetic multiwalled carbon nanotube (MMWCNT) adsorbents were prepared and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, and thermogravimetric analysis methods. The effects of various parameters affecting the adsorption process were examined. The adsorption systems were compatible with the Langmuir isotherm model and the pseudo‐second‐order kinetic model. The maximum monolayer adsorption capacities of the MAC adsorbent (298 K) and the MMWCNT (308 K) were 109.20 and 71.59 mg g−1, respectively. According to desorption studies, adsorbents could be regenerated by around 70 % in 6 hours.

Magnetic multi-walled carbon nanotubes as an efficient sorbent for pirimicarb removal from aqueous solutions in continuous (FBAC) and batch formats: thermodynamic, kinetic, isotherm study, optimization and modeling by RSM-ANN

In this study magnetic carbon nanotubes (CNT) were synthesized and used for the removal of pirimicarb insecticide. For characterization of CNT/Fe3O4 nanocomposite, various analyses such as FT-IR, XRD, VSM, SEM, EDX, Map, and TEM were used. The results of this analysis showed that the CNT/Fe3O4 nanocomposite was well-synthesized and had great paramagnetic properties (with Ms = 38.12 emu/g) and effective functional groups. The removal of pirimicarb process by this nanocomposite was performed in fixed bed adsorption column (FBAC) and batch format. In batch format, the effects of pH, contact time, composite dosage, and concentration of pirimicarb were studied using surface response method-central composite design (RSM-CCD) and artificial neural network (ANN). The results of response surface methodology demonstrated that the maximum efficiency of adsorption is 94.62 % while pH, contact time, composite dosage, and concentration of pirimicarb are 6.72, 47.56 min, 1.07 g/L and 43.91 ppm, respectively. Also, RSM-CCD modeling was more capable of expressing the adsorption process than artificial neural network modeling due to higher correlation coefficient and lower error. The equilibrium and kinetic studies showed that the process follows the sips model and pseudo-second-order model respectively and is physically desirable. Also, the mechanism of adsorption was best fitted in double-exponential model and is consisted of both inter and intra-particle diffusion. Thermodynamic studies suggested that pirimicarb adsorption onto CNT/Fe3O4 was a spontaneous and exothermic process. In addition, the results of FBAC showed that the breakthrough time was reduced from 365 min to 9 min by increasing temperature (25 °C, 35 °C and 45 °C) and exhaustion time was diminished by increasing in temperature.

Facile Fabrication of Amino Functionalized Magnetic Multi-walled Carbon Nanotubes for Removal of Congo Red from Aqueous Solutions

Facile Fabrication of Amino Functionalized Magnetic Multi-walled Carbon Nanotubes for Removal of Congo Red from Aqueous Solutions

Ice thermal energy storage enhancement using aligned carbon nanotubes under external magnetic field

In this work, the magnetic Multi-walled Carbon Nanotubes (MWCNTs) with the magnetization range of 27.6–55.6 emu/g were prepared. It is indicated the aligned MWCNTs are distributed along with the magnetic field direction, and their ultra-high thermal conductivity at the axial direction could be fully utilized. Furthermore, the effect of magnetic field on ice thermal energy storage using aligned MWCNTs was studied. Specifically, the solidification characteristics including nucleation and solidification phase change process under various magnetic field intensities were investigated experimentally and theoretically. The results showed the optimal magnetic field intensity exists for aligned MWCNTs Phase Change Material (PCM), at which PCM has the lowest supercooling degree, the shortest solidification phase change time, and phagocytosed MWCNTs by growing solid-liquid interface. The optimal magnetic field intensities are 150 mT, 100 mT, 75 mT, 75 mT with increased mass ratios of Fe3O4 on the wall of MWCNTs from 1:1 to 4:1, and their supercooling degree are decreased by 36.0 %, 46.5 %, 70.0 %, 65.1 % compared with pure water. For solidification phase change process, the results showed that nearly 50 % of the aligned MWCNTs PCM is solidified in 25 % of the total solidification time. It is concluded aligned MWCNTs fully exhibited nucleating agent and the heat transfer enhancement as they uniformly distributed in the PCM under optimal magnetic field intensity.

A facile approach for grafting ion imprinted polymer onto magnetic multi-walled carbon nanotubes for selective removal and preconcentration of cadmium in food and wastewater samples prior to atomic spectrometric determination

A 3D Fe3O4@MWCNT-CdIIP was synthesized by the oxidizing surface of multi-walled carbon nanotubes with carboxylic acid end groups and its subsequent termination with an ion imprinted polymer. An artificial neural network manifests better predictability than the central composite design methodology for optimising the adsorption procedure. The adsorption capacity was 109 mg g−1 (2.5 times more than non-imprinted polymer) under optimized conditions (pH; 5.6, time; 15 min, concentration; 800 μg mL−1 temperature; 25 °C), which was in accord with Toth isotherm. Fractal-like pseudo-second-order kinetics was found reasonably fast, with 66 % adsorption in 5 min. Solid phase extraction coupled Flame atomic absorption spectrometry method provides selective recognition towards Cd(II), with limit of detection; 1.13 µg/L, limit of quantification; 3.21 µg/L after preconcentration (preconcentration factor; 50) and good robustness. The developed method was applied for Cd(II) determination in food (tea, coffee, bread, tobacco, radish, spinach), water and wastewater (>99 % removal as well). Cd(II) loaded IIP was further utilized to remove anionic dyes with >95 % removal.

Amino functionalization of magnetic multiwalled carbon nanotubes with flexible hydrophobic spacer for immobilization of Candida rugosa lipase and application in biocatalytic production of fruit flavour esters ethyl butyrate and butyl butyrate

Amino functionalization of magnetic multiwalled carbon nanotubes with flexible hydrophobic spacer for immobilization of Candida rugosa lipase and application in biocatalytic production of fruit flavour esters ethyl butyrate and butyl butyrate

Variable activity and selectivity for electrochemical oxidation wastewater treatment using a magnetically assembled electrode based on Ti/PbO2 and carbon nanotubes

Magnetic multi-walled carbon nanotubes (CNTs) were loaded on Ti/PbO2 electrode by a magnet in this study to improve the efficiency of electrochemical oxidation wastewater treatment (EOWT). These physically attached carbonaceous small granules worked as additional modules, giving the newly created electrode unique characteristics. Series of electrodes’ electrochemical properties, as well as their electrochemical oxidation performances against the azo dye acid red G, phenol, and real petrochemical wastewater, were studied. These carbonaceous granules improved the electrode's electroactivity as well as the affinity between the organics and the electrode. More importantly, the amount of CNTs loaded had a strong influence on the degrading efficiency and selectivity towards various target contaminants as well as their intermediate products in treating synthetic or real wastewaters. Lower CNTs loading resulted in heterogeneous electrode properties, whereas higher CNTs loading resulted in the new electrode acting as a porous carbonaceous electrode. The deeper operating mechanism of the new magnetically assembled electrode were discussed based on both the experiment results and multiphysics simulation.

Preconcentration of heavy metal ions on magnetic multi-walled carbon nanotubes using magnetic solid-phase extraction and determination in vegetable samples by electrothermal atomic absorption spectrometry: Box–Behnken design

Preconcentration of heavy metal ions on magnetic multi-walled carbon nanotubes using magnetic solid-phase extraction and determination in vegetable samples by electrothermal atomic absorption spectrometry: Box–Behnken design

Ternary metal-organic framework/multi-walled carbon nanotube/iron oxide nanocomposite for removal of butachlor pesticide

BackgroundButachlor (BUT) as an organochlorine pesticide (OCP) that prevents weeds from growing has been used in the agriculture field. It remains in the environment for a long time and causes mutagenicity and cancer.ResultsIn the current study, magnetic multi-walled carbon nanotube with zeolitic imidazolate frameworks-67 (Fe3O4–MWCNT–ZIF67) was used as adsorbent to remove BUT from the aqueous solution. The characteristics and the chemical composition of the adsorbent were evaluated using FE-SEM, TEM, MAP, EDX, FTIR, BET, TGA and VSM. The response surface methodology (RSM) as a method for the design of experiment was applied to optimize variables such as the initial concentration of BUT, adsorbent dosage, contact time and temperature in the batch experiment by central composite design (CCD). The optimum adsorption condition predicted by RSM was pH = 4.5, initial concentration = 5.75 ppm, dosage = 0.07 g and contact time = 95 min. The results showed that maximum removal efficiency for the butachlor is 86%.ConclusionsDifferent adsorption isotherms were evaluated using adsorption equilibrium data and results showed that Temkin model has the best compatibility with the experimental data. In addition, the adsorption kinetics data were closer with pseudo-second-order model. Thermodynamic study showed that the adsorption process was spontaneous, endothermic and physical. This composite can be effectively used for the remediation/clean-up of groundwater and agricultural run-off water which are contaminated with harmful pesticides.Graphical