Magnetic Carbon Nanotubes Research Articles

Preparation of magnetic molecularly imprinted polymers functionalized carbon nanotubes for highly selective removal of aristolochic acid

In this work, we presented the preparation of magnetic carbon nanotubes (MCNTs) functionalized with molecularly imprinted polymers (MIPs) for effective removal of aristolochic acid I (AAI) in traditional Chinese medicine (TCM). MCNTs@AAI-MIPs was obtained via a facile and environmental friendly sol-gel process. Firstly, MCNTs were synthesized by a solvothermal method. Then, the template molecules were self-assembled with the functional monomer phenyltrimethoxysilane (PTMOS) in the presence of ethanol and water. Finally, AAI-MIPs film was coated on the MCNTs to obtain product MCNTs@AAI-MIPs using tetraethyl-orthosilicate (TEOS) as cross-linker. The morphology and structure of prepared MIPs were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen gas adsorption and vibrating sample magnetometer (VSM). The adsorption properties were demonstrated by kinetic, isothermal and selective adsorption experiments. The results showed that the imprinted nanocomposites exhibited fast separation rate (10 s), high adsorption capacity (18.54 μg∙mg−1), short kinetic equilibrium time (15 min), and good selectivity to template molecule with imprinting factor (IF) of 3.17. A regression equation (y=57294x-4734.1) with good linearity was obtained in the concentration range of 0.1–200 μg∙mg−1 for AAI with a correlation coefficient (R2) of 0.9998. The limit of detection (LOD, S/N=3) was 0.034 μg∙mg-1. Moreover, high recoveries ranged from 80% to 110% (RSD=3.27%-8.16%) were received in spiked TCM samples. The results suggested that the proposed MCNTs@AAI-MIPs could efficiently and specifically capture AAI from an actual complex TCM samples.

Disinfection mechanism of E. coli by CNT-TiO2 composites: Photocatalytic inactivation vs. physical separation

Magnetic carbon nanotube (MCNT) composites with titanium dioxide (TiO2) have an enhanced photocatalytic disinfection efficiency (i.e. higher disinfection rate) and better applicability (i.e. solar light applicability and catalyst separation using its magnetic property) than bare TiO2 and/or MCNT. However, the role and mechanism of MCNT in the disinfection process are still unclear. Therefore, this study aimed at investigating the disinfection mechanism of Escherichia coli using MCNT-TiO2 nanocomposites under various conditions (i.e. the presence and absence of light and reactive oxygen species scavengers, and different MCNT-TiO2 ratio) and photocatalytic disinfection models. The results showed that (i) MCNT and its nanocomposites with TiO2 had much higher disinfection efficiencies than bare TiO2, (ii) the physical bacterial capture was the dominant disinfection mechanism, (iii) the higher disinfection rate was found at an optimum MCNT:TiO2 ratio of 5:1 under the tested experimental conditions, (iv) hydroxyl radical (OH) was the influencing reactive oxygen species on the photocatalytic disinfection using MCNT-TiO2, and (v) good correlation between experimental parameters (i.e. carbon contents, surface area and concentration of MCNT-TiO2) and the contribution rate of physical and photocatalysis reactions. The finding from this study and the methods proposed herein are essential for understanding the photocatalytic disinfection processes using TiO2 and its carbonaceous nanocomposites, which can promote the application of photocatalytic disinfection process.

Polyamidoamine dendrimers functionalized magnetic carbon nanotubes as an efficient adsorbent for the separation of flavonoids from plant extraction

In this study, amine terminated polyamidoamine dendrimer (PAMAM)-functionalized magnetic multi-walled carbon nanotubes (PAMAM@MCNTs) were prepared as an efficient adsorbent for the separation of flavonoids from plant extraction. The obtained PAMAM@MCNT nanoadsorbents were characterized in detail. Rutin was chosen as a model molecule of flavonoids to investigate the adsorption efficiency of PAMAM@MCNTs. The main influences of several parameters, including contact time, initial solution concentration, pH value, and temperature, were optimized to determine the optimum adsorption conditions. Furthermore, the adsorption kinetic and isotherm models were performed to elucidate the adsorption process. The results showed that PAMAM and Fe3O4 were successfully grafted to the surface of carboxylated CNTs (CNTs-COOH) by characterization via several techniques, such as scanning electron microscopy (SEM), X-ray diffraction spectrometry, vibrating sample magnetometry, and Fourier transform infrared spectra. The PAMAM@MCNTs exhibited high efficiency for the rutin at solution pH = 8.0 and room temperature. Adsorption process could be effectively described by Langmuir adsorption isotherm, and the maximum adsorption capacity was calculated as 56.48 mg/g, whereas a pseudo-second-order model was suitable to explain the kinetics of adsorption. The PAMAM@MCNTs can be effectively regenerated by alkaline dimethyl sulfoxide and reused to at least threefold. Moreover, PAMAM@MCNTs demonstrated potential in various applications as an efficient adsorbent for separating flavonoids from plant extraction. The above-mentioned results provided references for further separation of bioactive components from plant extracts using magnetic nanomaterials.

Degradation of diclofenac by heterogeneous electro-Fenton process using magnetic single-walled carbon nanotubes as a catalyst

Degradation of diclofenac (DCF) from aqueous solution was investigated by the heterogeneous electro-Fenton (EF) process using magnetic single-walled carbon nanotubes (MSWCNTs) as a new catalyst. The effect of parameters including initial pH, current density, initial catalyst concentration, the initial concentration of DCF and air flow rate on the efficiency of DCF removal and electrochemical production of H2O2 were studied. A removal efficiency of 97.8% for DCF and 71.12% for COD was obtained at an initial pH of 5, current density of 20 mA/cm2, MSWCNTs concentration of 80 mg/L, DCF concentration of 10 mg/L, air flow rate of 1 mL/min and reaction time of 120 min. Regarding the removal of DCF and COD, and production of H2O2, the heterogeneous EF process with MSWCNTs catalyst showed higher activity and efficiency than other electro-catalytic degradation systems. The stability tests of MSWCNTs after 5 time application confirmed its performance potential for long-term degradation of DCF in aqueous solutions. Intermediate products such as 2,3-dichlorobenzene and 2,4-dichlorophenol were identified by gas chromatography-mass spectrometry (GC–MS). Based on the identification of reactive species and the intermediate products, a possible mechanism of removal and degradation pathways for DCF was suggested.

SYNTHESIS OF MAGNETIC COMPOSITE OF IRON COMPOUNDS/CARBON NANOTUBES IN CHEMICAL VAPOR DEPOSITION

The chemical vapor deposition (CVD) synthesis of magnetic carbon nanotubes (mCNT) using carbon dioxide/carbon catalyst has been successfully carried out in various pressures. The temperatures were set at 800° C for 10 minutes reaction time. Nitrogen (N2) gas in 20 Torr was flown in followed by ethanol vapor until the final pressure reached 80 and 100 Torr without added air, and 180 Torr with added air. The formation of mCNT was confirmed by shifted X-ray diffraction (XRD) peak of graphite from 26.53° to 25.53° which were highly considered to the other carbon allotropes with sp2 hybridized carbon atom hybridization structures. The higher pressure with added atmospheric air led to the excessive oxidation which influenced the growth of mCNT. Transmission electron microscopy (TEM) analysis observed mCNT filled by catalyst particles which suggested as magnetic phase induced the magnetic property of mCNT. The best electrical conductivity performance (lower electrical resistance) was owned by mCNT produced in the lower pressure condition with no air added.

Anchoring of triethanolamine–Cu(II) complex on magnetic carbon nanotube as a promising recyclable catalyst for the synthesis of 5-substituted 1H-tetrazoles from aldehydes

The development of heterogenization of copper nanoparticles on conductive supports is very challenging and has received much attention. Here, we synthesize a practical, efficient, and inexpensive heterogeneous catalyst to grow stable metallic copper(II) nanoparticles on the surface of magnetic carbon nanotube (Fe3O4-CNT) catalyst support physically functionalized with triethanolamine (TEA) that acts as a low-cost and non-toxic ligand to capture the copper nanoparticles [Fe3O4-CNT-TEA-Cu(II)]. The as-prepared heterogeneous catalyst was characterized by different techniques, such as Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, vibrating sample magnetometer, X-ray diffraction patterns, field-emission scanning electron microscopy, and atomic absorption spectroscopy analysis. The catalytic behavior of Fe3O4-CNT-TEA-Cu(II) was investigated in the preparation of 5-substituted 1H-tetrazole derivatives via one-pot, three-component reaction between aromatic aldehydes, hydroxylamine, and sodium azide. The low catalyst loading, wide substrate scope, use of inexpensive materials, simple separation of the catalyst from the reaction mixture by an external magnet, short reaction times, easy workup, affordability, and superb yield are some advantages of this protocol.

Selective and effective adsorption of Hg(II) from aqueous solution over wide pH range by thiol functionalized magnetic carbon nanotubes

In this study, a novel adsorbent thiol functionalized magnetic carbon nanotubes (CNTs-SH@Fe3O4) was synthesized to overcome somewhat existing difficulties during the Hg(II) adsorption process, including low efficiency and selectivity, narrow feasible pH range and difficult to separate and reuse. The Hg(II) adsorption performance of CNTs-SH@Fe3O4 was evaluated using batch experiment and its physiochemical properties were investigated by characterization techniques. The batch experiment results showed that the prepared CNTs-SH@Fe3O4 maintained high Hg(II) adsorption efficiency (>98%) over wide pH range from 3 to 11. The selective adsorption of Hg(II) by CNTs-SH@Fe3O4 was achieved with the coexistence of Cu(II), Mg(II) or Zn(II) ions, in which adsorbate matrix Hg(II) removal efficiency of 81.39%, 89.36% and 95.52% was obtained, respectively. CNTs-SH@Fe3O4 kept high Hg(II) removal efficiency (>80%) and good magnetic property (Ms value > 21 emg g−1) after five cycles of adsorption/regeneration. The Hg(II) adsorption kinetics could be better described by pseudo-second-order kinetic model. Freundlich model showed higher correlation coefficient in adsorption isotherms study, and the calculated maximum adsorption capacity was 172.4 mg g−1. Thermodynamic study suggested that the adsorption process was exothermic in nature. Surface adsorption, complex adsorption and reduction adsorption were all contributed to the removal of Hg(II) using CNTs-SH@Fe3O4.

Synthesis, Characterization, and Evaluation of Disulfide-Containing Polyethylenimine Derivative Functionalized Magnetic Carbon Nanotubes as an Efficient Gene Vector

Magnetic nanoparticles have been widely developed as vectors in targeting drug and gene delivery. Disulfide-containing polyethylenimine derivative- (SSPEI-) functionalized magnetic carbon nanotubes (CNTs/Fe3O4-SSPEI) were synthesized as gene vector. Fourier transform infrared, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis were used to characterize CNTs/Fe3O4-SSPEI nanoparticles. The magnetic nanoparticles displayed typical superparamagnetic behavior and excellent dispersibility in water. Plasmid DNA could be bound by CNTs/Fe3O4-SSPEI to form the complexes. The sizes of complexes are about 400 nm, and the zeta potentials are positive at the w/w ratio over 6. CNTs/Fe3O4-SSPEI nanoparticles displayed higher transfection activity than did PEI (25 kDa), whereas the cytotoxicity was rather lower. Moreover, the transfection efficiency was further increased with the assistance of an external magnetic field. These results indicate that CNTs/Fe3O4-SSPEI nanoparticles would be a promising vector in targeted gene delivery.

Functionalization of amino terminated carbon nanotubes with isocyanates for magnetic solid phase extraction of sulfonamides from milk and their subsequent determination by liquid chromatography-high resolution mass spectrometry

A simple modification method was developed for the functionalization of amino terminated carbon nanotubes (CNT-NH2) by using isocyanates as modifiers via the nucleophilic addition reaction. Two types of functionalized magnetic carbon nanotubes (MCNT) were prepared through deposition of magnetic nanoparticles on CNT-NH2 and modification with different isocyanates. p-Tolyl-functionalized MCNT (Tol-MCNT) with better adsorption performance were selected as adsorbent for magnetic solid phase extraction (MSPE), which could extract sulfonamides (SAs) from various milk samples with a enrichment factor of about 30 after optimization. By combining the MSPE with liquid chromatography–high resolution mass spectrometry (LC–HRMS), a new method was developed. Both skimmed and whole milk samples of three brands were analyzed with this method, and 4 SAs including sulfadiazine, sulfisomidine, sulfamethazine and sulfameter were detected with the concentration from unquantifiable to 72 ng/L, which were all well below the maximum residue limits in milk according to the regulations of China and EU.

Carbon nanotubes as catalysts for wet peroxide oxidation: The effect of surface chemistry

Three magnetic carbon nanotube (CNT) samples, named A30 (N-doped), E30 (undoped) and E10A20 (selectively N-doped), synthesized by catalytic chemical vapor deposition, were modified by introducing oxygenated surface groups (oxidation with HNO3, samples CNT-N), and by heat treatment at 800 °C for the removal of surface functionalities (samples CNT-HT). Both treatments lead to higher specific surface areas. The acid treatment results in more acidic surfaces, with higher amounts of oxygenated species being introduced on N-doped surfaces. Heat-treated samples are less hydrophilic than those treated with nitric acid, heat treatment leading to neutral or basic surfaces, only N-quaternary and N-pyridinic species being found by XPS on N-doped surfaces. These materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4-nitrophenol solutions (4-NP, 5 g L−1) at atmospheric pressure, T = 50 °C and pH = 3, using a catalyst load of 2.5 g L−1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP. The high temperature treatment enhanced significantly the activity of the CNTs towards CWPO, evaluated in terms of 4-NP and total organic carbon conversion, due to the increased hydrophobicity of their surface. In particular, E30HT and E10A20HT were able to remove ca. 100% of 4-NP after 8 h of operation. On the other hand, by treating the CNTs with HNO3, the activity of the less hydrophilic samples decreased upon increasing the concentration of surface oxygen-containing functionalities, whilst the reactivity generated inside the opened nanotubes improved the activity of the highly hydrophilic A30 N.

Facile preparation of magnetic composites based on carbon nanotubes: Utilization for removal of environmental pollutants

The preparation of multifunctional composites that combine magnetic nanoparticles and supported nanomaterials has attracted great attention for various applications. In this work, a facile method was developed for the preparation of carbon nanotube (CNT)-based magnetic composites through a one-pot oxidation method using K2FeO4 as the oxidant, which was subsequently used as the reagent to generate the Fe3O4 nanoparticles and fabricate the magnetic CNT composites. This strategy could be performed at room temperature, so it is very mild and straightforward. The properties and structure of the as-fabricated CNT-Fe3O4 composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and vibrating sample magnetometry. The results suggested that this approach not only generated Fe3O4 magnetic nanoparticles on the surface of the CNTs but also produced a series of functional groups. In addition, the dried CNT-Fe3O4 composites were highly dispersible in water or organic solutions, and they also had a magnetic response that could satisfy the demand for magnetic separation. Finally, we adsorbed copper ions (Cu2+) and methylene blue (MB) using the CNT-Fe3O4 composites as adsorbents. The results indicated that the obtained composites could adsorb both Cu2+ and MB effectively. Taken together, we report a novel strategy for the fabrication of magnetic carbon nanotube composites through a facile oxidation and subsequent deposition procedure. These magnetic composites show great potential for the removal of environmental pollutants.

Adsorption properties of magnetic carbon nanotubes for patulin removal from aqueous solution systems

Patulin (PAT) is a type of mycotoxin produced by the P. expansum, Aspergillus, Penicillium, and Paecilomyces fungal species and constitutes serious food-related and environmental health threats to consumers. In this study, a novel magnetic multi-walled carbon nanotube (MWCNT) adsorbent was successfully synthesized, and its adsorption properties for the efficient removal of PAT from aqueous solution were investigated. The effects of adsorption parameters, such as pH, initial PAT concentration, adsorption time and temperature, were investigated for optimization of the adsorption process. The kinetic and isotherm studies revealed that PAT adsorption was well described by a pseudo-second order model and the Freundlich model, respectively. The maximum adsorption capacity of the as-prepared magnetic MWCNTs reached 640.2 μg/g, which was much higher than that of biological material-based absorbents (p < 0.05), and the adsorption equilibrium time was significantly shortened to 1 h (p < 0.05). Thermodynamic studies revealed that the adsorption process was exothermic. The adsorption activation energy determined from the Arrhenius equation was found to be approximately −27.31 kJ mol−1, suggesting that the adsorption of PAT on magnetic MWCNTs was random and spontaneous in nature within the experimental temperatures. Moreover, the recycling, separation and regeneration of the spent magnetic MWCNTs were evaluated, and the results demonstrated that the spent magnetic MWCNTs could be separated magnetically and regenerated by sodium hydroxide solution for recycling uses up to four cycles without significantly losing adsorption efficiency. Therefore, this novel magnetic MWCNT-based adsorbent could be a potential adsorbent to be applied for PAT removal from many aqueous systems.

Effective and fast adsorptive removal of toxic cationic dye (MB) from aqueous medium using amino-functionalized magnetic multiwall carbon nanotubes

Amino functionalized multi-walled carbon nanotubes (NH2-MWCNTs) were prepared via chemical modification of the surface of multiwall carbon nanotubes. The magnetic nanoparticles (Fe3O4) were embedded with NH2-MWCNTs and the developed magnetic carbon nanotube (NH2-MWCNTs@Fe3O4) were characterized via several analytical techniques including FT-IR, Raman, XRD, TEM, SAED, SEM, BET and VSM. The fabricated NH2-MWCNTs@Fe3O4 was used for the removal of toxic methylene blue dye (MB) from aqueous medium. The results of VSM indicated that the fabricated NH2-MWCNTs@Fe3O4 had magnetic nature and the saturated magnetization was 37.91 emu/g. The effect of initial solution pH, temperature and contact time on MB adsorption was also investigated. The results of adsorption kinetics exhibited that the adsorption followed the linear pseudo-second-kinetic model well. Langmuir and Freundlich isotherm models were applied to understand the adsorption behaviors. The maximum adsorption capacity from the Langmuir isotherm equation reached 178.5 mg g−1 indicated that it was a good adsorbent for MB removal. The thermodynamics parameters such as Gibbs free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0), supported the spontaneous and exothermic nature of adsorption. It was noted that after six repetitive cycles, the adsorption capacity of NH2-MWCNTs@Fe3O4 was 80% of the original value. Hence, it can be concluded that NH2-MWCNTs@Fe3O4 had substantial reusability which made it an economical adsorbent for MB removal from aqueous medium.

Magnetic carbon nanotubes camouflaged with cell membrane as a drug discovery platform for selective extraction of bioactive compounds from natural products

The biomimetic functionalization of carbon nanotubes (CNTs) are promising for its application in solid phase extraction because they can overcome current limitations of covalent functionalization and obtain desired specific recognition ability. The present study aimed to develop a novel dual functionalization CNTs modified with magnetic nanoparticles and high α1A-adrenergic receptor (α1A-AR) expression HEK 293 cell membrane. On the basis of the specific interactions between drugs and receptors on cell membrane, high α1A-AR expression cell membrane camouflaged magnetic CNTs (CMMCNTs) were employed as a drug discovery platform to screen potential α1A-AR antagonists from traditional Chinese medicine (TCM). The resultant CMMCNTs had a right-side-out membrane and desired magnetic property, enabling to rapidly target and separate the bioactive compounds from complex samples. Furthermore, the CMMCNTs possessed high adsorption capacity, fast binding kinetics, and satisfactory selectivity. As a result, two bioactive compounds as lappaconitine and benzoylmesaconine were screened and identified in the actual application. Moreover, the lappaconitine was validated to have favorable antagonism to α1A-AR through preliminary pharmacological assays. Hence, this successful application of CMMCNTs showed significant advantages in drug discovery so as to drive the development of TCM. More importantly, the cell membrane biomimetic modification could be widely used to improve the performance of CNTs in various applications.

Development of magnetic carbon nanotubes for dispersive micro solid phase extraction of the cyanide metabolite, 2-aminothiazoline-4-carboxylic acid, in biological samples

2-aminothiazoline-4-carboxylic acid (ATCA) is a minor metabolite of cyanide and is suggested to be a promising biomarker for cyanide exposure due to its specificity to cyanide metabolism and its excellent short- and long-term stability during storage. In this study, magnetic carbon nanotubes, including magnetic multi-walled carbon nanotubes (Mag-MWCNT) and magnetic single-walled carbon nanotubes (Mag-SWCNT) were synthesized as a novel sorbent for dispersive micro solid phase extraction (d-μSPE) to extract ATCA from biological matrices. ATCA spiked deionized water samples with the addition of the isotopic internal standard (ATCA – 13C, 15N) were subjected to Mag-CNT/d-μSPE to confirm extraction efficiency of this new technique. The extracted ATCA was derivatized and quantitated using gas chromatography/mass spectrometry (GC/MS) analysis. The extraction parameters were optimized and a detection limits of 15 and 25 ng/mL were obtained for synthetic urine and bovine blood respectively with a linear dynamic range of 30–1000 ng/mL. The optimized Mag-CNT/d-μSPE method facilitated efficient extraction of ATCA using 2 mg of Mag-MWCNT with a 10-minute extraction time. The current assay was also found to be effective for the extraction of ATCA with average recoveries of 97.7 ± 4.0% (n = 9) and 96.5 ± 12.1% (n = 9) from synthetic urine and bovine blood respectively. The approach of using Mag-CNT to facilitate d-μSPE offered a novel alternative to extract ATCA from complex biological matrices.

Magnetic multi-walled carbon nanotubes modified with polyaluminium chloride for removal of humic acid from aqueous solution

Magnetic multi-walled carbon nanotubes (MWCNTs) prepared by chemical co-precipitation method were loaded with polyaluminium chloride (PAC) using microwave irradiation to synthesize magnetic PAC multi-walled carbon nanotubes (M-PAC-MWCNTs) for removal of humic acid (HA) from aqueous solution. M-PAC-MWCNTs were characterized by field emission scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, specific surface area (SSA) and vibrating-sample magnetometer (VSM), respectively. The results showed that PAC and magnetic matters Fe3O4 and γ-Fe2O3 were coated on MWCNTs. The effect of M-PAC-MWCNTs dosage, pH value, HA initial concentration and contact time on removing HA from aqueous solution was also investigated. The HA removal rate was high to 98.57% at M-PAC-MWCNTs dosage of 0.5 g·L−1 and pH 7 for reaction time of 30 min at HA concentration 20 mg·L−1. In addition, kinetic, equilibrium and thermodynamic of the adsorption of HA on M-PAC-MWCNTs were studied. The adsorption process was well fitted by the pseudo-second-order kinetic model and Temkin isotherm model, declaring that chemical adsorption was primary and physical adsorption was complementary. Thermodynamics analysis revealed ΔG0 < 0, ΔH0 > 0 and ΔS0 > 0, suggesting that the HA adsorption on M-PAC-MWCNTs was a spontaneous, endothermic in nature and entropy increase process. After MWCNTs were magnetized and modified by PAC, the adsorption performance of MWCNTs was greatly enhanced, mainly attributed to the interaction between PAC and humic acid through hydrogen-bond and electrostatic attraction.

Synergistic effect of a magnetic field and carbon nanotubes on the adsorption performance of metal ions and phenols

Synergistic effect of a magnetic field and carbon nanotubes on the adsorption performance of metal ions and phenols

Simultaneous capture of methyl orange and chromium(vi) from complex wastewater using polyethylenimine cation decorated magnetic carbon nanotubes as a recyclable adsorbent.

Most recently, the continuous deterioration of the aquatic environment triggered by both heavy metals and synthetic organic dyes has imparted serious threats to the ecosphere and drinking water safety. However, it is still extremely challenging to treat complex wastewater containing these two classes of pollutants via a one-step method owing to the significant differences in their physicochemical properties. In the current work, versatile magnetic MWCNTs decorated with PEI (denoted as MWCNTs@Fe3O4/PEI) was fabricated by a facile, rapid and reproducible strategy and applied to as a robust adsorbent for simultaneously removing methyl orange (MO) and Cr(vi) from aqueous solutions. The physicochemical properties of the as-designed nanohybrid were investigated using various analytical techniques, i.e. XRD, FT-IR, SEM, TEM, VSM, zeta potential, etc. It was found that the surface charge properties of the MWCNTs as well as its dispersion in aqueous solution were greatly changed after the introduction of PEI molecules. The resulting nanohybrid exhibited attractive adsorption capabilities toward anionic MO and Cr(vi). In the perspective of a mono-pollutant system, the time-dependent adsorption process matched well with a pseudo-second-order kinetics equation, the adsorption isotherm data at r.t. were well fitted by a Langmuir model with maximum monolayer uptake capacity of 1727.6 mg g−1 for MO and 98.8 mg g−1 for Cr(vi), and the removal process of both pollutants was thermodynamically spontaneous and exothermic. In the MO-Cr(vi) binary system, the uptake of Cr(vi) by the as-prepared adsorbent was evidently enhanced by the presence of MO, while the coexisting Cr(vi) exerted a small negative effect on the sorption of MO; which was attributed to the different adsorption mechanisms of both pollutants on the as-recommend adsorbent. The much better adsorbing performance of the resulting MWCNTs@Fe3O4/PEI for MO and Cr(vi) than that of the pristine MWCNTs or the MWCNTs/Fe3O4 composite was mainly ascribed to the high surface area of the MWCNTs, the high density of protonated N-rich groups of PEI as well as the excellent dispersion and solubility of the resulting nanocomposites. Moreover, the obtained nanohybrids can be easily recovered after being used by a permanent magnet and still retained high stability and excellent reusability after consecutive adsorption–desorption cycles, implying its great potential in practical applications. Therefore, the as-fabricated MWCNTs@Fe3O4/PEI composite could be recommended as a promising candidate adsorbent for the simultaneous capture of MO and Cr(vi) from complex wastewater via multiple uptake mechanisms (e.g. electrostatic attraction, π–π stacking and hydrogen bonding).

Magnetic carbon nanotubes grafted with smart polymer brushes for highly efficient enantioseparation of tryptophan enantiomers

We herein report a novel chiral carbon nanotube nanomaterial (MCNTs–PNG–CD) grafted with smart copolymer brushes for highly efficient chiral recognition and separation of tryptophan enantiomers (dl-Trp).

Highly efficient and acid-corrosion resistant nitrogen doped magnetic carbon nanotubes for the hexavalent chromium removal with subsequent reutilization

Highly efficient and acid-corrosion resistant for carbon adsorbent in hexavalent chromium removal is a significant property in the practical application. In this study, nitrogen doped carbon nanotubes with encapsulated Fe and Fe3C were synthesized through a facile pyrolysis procedure using melamine and ferric chloride as precursors, displaying an excellent efficiency and stability for hexavalent chromium removal. High maximum removal capacities with 35.26 and 970.87 mg g−1 were obtained in neutral and acid solutions, respectively, due to the adsorption process, reduction reaction between Fe0 or Fe2+ nanoparticles and Cr(VI) ions. The unexpected high stability in acid solution (pH at 1) after five recycles was observed for the first time, ascribed to N doping and the tubular structure with encapsulated ferric carbide, which could be resistant to the acid corrosion. After a simple treatment, the used adsorbent could be re-utilized as catalysts for the electrochemical reduction of CO2 with high faradic efficiency (over 90% total efficiency and about 50% for CO production at −0.6 V), demonstrating a promising potential for reutilizing the used carbon adsorbents.