Magnetic Multi-walled Carbon Research Articles

S and N co-doped graphene quantum dots as an effective fluorescence probe for sensing of furazolidone after magnetic solid-phase microextraction using magnetic multiwalled carbon nanotubes

Sulfur and nitrogen-doped graphene quantum dots (S, N-GQDs) was synthesized and a selective measurement method was designed for the quantification of furazolidone based on fluorescence quenching of synthesized quantum dots. Furazolidone was first separated and preconcentrated from samples with complex matrices by magnetic solid-phase microextraction using magnetic multiwalled carbon nanotubes (MMWCNTs) as the sorbent. The effective parameters on the extraction of furazolidone were investigated and optimized by one variable at a time and central composite design methods. Under the optimized conditions, the fluorescence quenched linearly with the furazolidone concentration in the range of 8.0–250.0 µg L−1 with a limit of detection (LOD) 2.1 µg L−1. The relative standard deviation (RSD) for intra-day and inter-day analysis (at 40.0 μg L−1 of furazolidone, n = 6) was 3.6 and 5.6%, respectively. The developed method was successfully applied to the quantification of trace amounts of furazolidone in chicken liver, biological fluids, and poultry effluent.

Preconcentration of Nickel by Magnetic Solid-Phase Extraction (MSPE) as the 2-(5-Bromo-2-Pyridylazo)-5-Diethylamino-Phenol (PADAP) Chelate upon Multiwalled Carbon Nanotubes (MWCNTs) with Determination by Flame Atomic Absorption Spectrometry (FAAS)

A magnetic solid phase extraction (MSPE) method for nickel as the 2-(5-bromo-2-pyridylazo)-5-diethylamino-phenol (PADAP) chelate was established prior to flame atomic absorption spectrometric (FAAS) determination. Magnetic multiwalled carbon nanotubes were used as the adsorbent. Analytical parameters affecting the extraction efficiency of nickel such as pH of the medium (8.0), mass of adsorbent (8.0 mg), eluent concentration and volume (4.0 mL of 1 M HNO3), extraction time (6.0 min), and model solution volume (20 mL) were optimized. In addition, matrix effects were investigated. The preconcentration factor was 5. The relative standard deviation was less than 5%. A standard addition recovery study was performed on water samples to evaluate the accuracy of the method and certified reference materials were used for validation. The limits of detection (LOD) and quantitation (LOQ) were 7.1 µg L−1 and 24.4 µg L−1, respectively. The proposed method was applied to determine nickel in tobacco samples.

Effective sorptive removal of five cationic dyes from aqueous solutions by using magnetic multi-walled carbon nanotubes

Abstract The excellent properties of micro-nano materials and structures have attracted extensive attention especially in wastewater treatment. Based on this, magnetic multi-walled carbon nanotubes (MMWCNTs) have been prepared and used for the sorptive removal of five typical cationic dyes from aqueous solutions in the present study. Effects of several operational and environmental factors were investigated carefully, including initial pH values, common ions, contact time and temperature. The kinetics processes were well fitted by the pseudo-second-order kinetic model. The maximum adsorption capacities on MMWCNTs at 298.15 K for malachite green oxalate, auramine O, neutral red, crystal violet and rhodamine B were 442.2, 295.2, 183.4, 165.3 and 143.0 mg g−1, respectively. Differences in the size, structure and properties of these dyes led to the difference of adsorption amounts. ΔG0 were all negative within the temperature range tested, which meant the adsorption processes were spontaneous in nature. Moreover, the adsorption processes of targeted dyes, except auramine O, were exothermic and entropy decreasing. The regeneration studies indicated that the MMWCNTs showed high reusability and removal efficiencies above 75% can be achieved after four consecutive cycles. For the adsorption mechanism, electrostatic interaction, hydrogen bonds, π-π interaction together with hydrophobic interaction could coexist during the adsorption process.

Preparation of magnetic molecularly imprinted polymer based on multiwalled carbon nanotubes for selective dispersive micro-solid phase extraction of fenitrothion followed by ion mobility spectrometry analysis.

A novel molecularly imprinted polymer based on magnetic multiwalled carbon nanotubes was fabricated and applied for selective dispersive micro-solid phase extraction of fenitrothion prior its determination by ion mobility spectrometry. The composite was synthesized using magnetic multiwalled carbon nanotubes as the support. Methacrylic acid was used as the functional monomer, fenitrothion as the template, ethylene glycol dimethacrylate as the cross-linker, and 2,2-azoisobutyronitrile as the initiator. The resultant polymer was characterized by FTIR spectroscopy, X-ray diffraction, field emission scanning electron microscopy, Brunauer-Emmet-Teller analysis, thermogravimetric analysis, and vibrating sample magnetometer techniques. Experimental factors affecting the extraction efficiency such as pH and amount of sorbent were evaluated. Under optimum experimental conditions, the developed method displayed the linear range of 5-220 μg/L with a detection limit of 1.3 μg/L. The intra- and interday relative standard deviations for determination of fenitrothion were 3.6 and 4.7% (n=6), respectively. Ultimately, the proposed method was used to monitor trace amounts of fenitrothion in fruits, vegetables, and water samples.

Dispersive Solid-Phase Extraction Using 3-Mercaptopropyltrimethoxysilane Functionalized Magnetic MWCNT-Based Nanocomposite for Selective and Efficient Preconcentration of Pb2+ with FAAS Determination

A novel nanocomposite based on magnetic multiwalled carbon nanotubes coated with SiO2 and functionalized with 3-mercaptopropyltrimethoxysilane (3-MPTMS) was prepared for the efficient extraction and quantification of lead ions from water samples. The adsorption capacity of this adsorbent could reach 1.995 mg g-1 Pb2+ in an equilibrium time of 30 min. Under optimized conditions derived using the 25-1 fractional factorial design, a 45 mL aliquot of the sample was preconcentrated onto 90 mg of nanocomposite during 4 min. The lead ions adsorbed on the nanocomposite were eluted using 2 mol L-1 HNO3. The proposed method provided a preconcentration factor of 15.25 times, yielding limits of detection (LOD) and quantification (LOQ) of 0.56 and 1.86 µg L-1, respectively, and a linear range between 1.86 and 100.00 µg L-1. The relative standard deviations (RSD, n = 10), determined using solutions of Pb2+ at 10 and 120 µg L-1, were 2.3 and 2.1%, respectively. A high tolerance toward potentially foreign ions was observed. The proposed method was successfully applied to the rapid extraction of Pb2+ ions from different water samples, confirming good recovery values (90.33-109.53%); the accuracy of the method was evaluated through graphite furnace atomic absorption spectrometry (GF AAS) as a reference technique.

Nanocomposites of boronic acid-functionalized magnetic multi-walled carbon nanotubes with flexible branched polymers as a novel desorption/ionization matrix for the capture and direct detection of cis-diol-flavonoid compounds coupled with MALDI-TOF-MS

Novel boronic acid-functionalized magnetic multi-walled carbon nanotubes with flexible branched polymer (Fe3O4@MWCNTs@ε-PL@BA) nanocomposites were fabricated and applied as the desorption/ionization matrix for the MALDI-TOF-MS determination of low molecular weight flavonoids. The prepared nanocomposite was systematically characterized by various techniques. Compared to the traditional organic matrix, the proposed Fe3O4@MWCNTs@ε-PL@BA matrix has excellent ionization efficiency and low-background noise interference due to the MWCNTs unique electron-phonon interaction and the high introduction density of boronic acid functional groups. Good sensitivity and ultra-high salt tolerance of the Fe3O4@MWCNTs@ε-PL@BA-assisted MALDI-TOF-MS were permitted for the determination and quantification of flavonoids in actual samples. Noticeably, the limits of detection (LODs) for the target flavonoids were in the range 17–33 nM. The relative standard deviations (RSDs) of spot-to-spot and sample-to-sample (n = 10) were ≤ 9.8% and ≤ 10.1%, respectively. Furthermore, the wide linear ranges (0.1 – 500 µg/mL) and satisfactory calibration plot coefficients (R2 > 0.99) of flavonoids were achieved by MALDI-TOF-MS with the Fe3O4@MWCNTs@ε-PL@BA matrix. Good recoveries (92–105.5%) were achieved for the target flavonoids in practical food samples. Hence, the prepared Fe3O4@MWCNTs@ε-PL@BA nanocomposites have applications in the selective and efficient capture of target flavonoids active biomolecules coupled with MALDI-TOF-MS determination in actual samples.

Magnetic Amino-Modified Multiwalled Carbon Nanotube (MWCNT) Based Magnetic Dispersive Solid-Phase Extraction (m-dSPE) for the Determination of Paralytic Shellfish Toxins in Bivalve Mollusks with Hydrophilic Interaction Liquid Chromatography–Tandem Mass Spectrometry (HILIC-MS/MS)

A sensitive and efficient magnetic amino modified multi-walled carbon nanotubes (m-MWCNT-NH2)-based magnetic dispersive solid-phase extraction (m-dSPE) coupled with hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC-MS/MS) strategy is reported for the simultaneous determination of 13 paralytic shellfish toxins (PSTs) in bivalve mollusks. The samples were extracted twice with 1% acetic acid and purified using optimized m-dSPE procedures with Fe3O4 coated MWCNT-NH2 composites as magnetic adsorbents. The adsorbed PSTs on the m-MWCNT-NH2 adsorbents were separated using a Ni-coated neodymium magnet and subsequently eluted with 2 mL water–acetonitrile–acetic acid (80:20:1, v/v/v) and analyzed by HILIC-MS/MS. The correlation coefficients (r) of the targeted toxins obtained in matrix-matched external standard curves were from 0.997 to 0.999. The PSTs were acquired and quantified in the multiple reaction-monitoring mode and the limits of detection and quantitation in bivalve mollusks were 1.10 to 4.51 μg/kg and 3.67 to 13.5 μg/kg, respectively. Spiked recoveries at three concentrations in negative samples were from 73.4% to 92.5% with precision less than 10.6%. The method validation was in accordance with 2002/657/EC guidelines and method application in commercial bivalve mollusk samples. The developed method was rapid, convenient and economical for the determination of the targeted toxins.

Synthesis of magnetic multi-walled carbon nanotubes via facile and solvent-free direct doping method for water remediation

BackgroundOwing to the requirement of additional processing steps to separate the spent adsorbents from treated water, magnetic multi-walled carbon nanotubes (MMWCNTs) have recently been hailed as novel adsorbent. MethodsIn this study, MWCNTs doped with iron oxide (Fe3O4) nanoparticles (n-MMWCNTs) and MWCNTs doped with polydiallyldimethylammonium chloride (PDDA) coated Fe3O4 nanoparticles (PDDA-MMWCNTs) were synthesized via solvent-free direct doping method. Prior to the doping process, the pristine MWCNTs were pre-treated with nitric acid. Significant findingsCharacterization results such as FTIR, EDX, XRD and zeta potential analysis confirmed the deposition of Fe3O4 onto the MWCNTs. The stability of the synthesized MMWCNTs under different pH was examined. Detachments of Fe3O4 from n-MMWCNTs and PDDA-MMWCNTs was found at pH 9 and 3, respectively. Both types of MMWCNTs were applied to the removal of methylene blue (MB). It was found that the MB adsorption capacity of n-MMWCNTs was 11% higher than PDDA-MMWCNTs, due to significantly higher specific surface area of n-MMWCNTs. n-MMWCNTs was found to perform better in alkaline condition in which the adsorption capacity increased about 87% from pH 3 to pH 11. The adsorption of MB on n-MMWCNTs was found to obey the Langmuir isotherm (indicating monolayer MB molecules adsorption on the n-MMWCNTs) with the calculated maximum adsorption capacity of 20.37 mg/g. Moreover, the adsorption of MB followed the pseudo-second order kinetic model.

Removal of Cu(Ⅱ) ions from aqueous solution by a magnetic multi-wall carbon nanotube adsorbent

Copper (Cu(Ⅱ)) pollution has a hazardous effect on human health. However, designing new adsorbents with prominent properties is a tremendous challenge in effectively removing Cu(Ⅱ) ions from the environment. In this study, new adsorbent—MnFe2O4/multi-wall carbon nanotubes (MMWCNTs), with excellent magnetic properties were synthesized and then systematically characterized. Introducing MnFe2O4 addressed the challenge of separating the nano-adsorbent from the liquid medium. Batch adsorption experiment results indicated that effective adsorption occurred in a relatively neutral range (pH=6–8). The adsorption behaviors were consistent with the pseudo-second-order model and the Freundlich model. The maximum adsorption capacity reached 46.41 mg/g at 308 K. The adsorption thermodynamics revealed the endothermic character of adsorption by MMWCNTs, and increasing the temperature benefitted the adsorption process. Furthermore, many surface functional groups of MMWCNTs facilitated adsorption performance. Compared with the MWCNTs before modified, the adsorbent had a nearly tenfold improvement from 3.4% to 34.8% in the removal efficiency of Cu(Ⅱ) ions. These results demonstrated that MMWCNTs are a suitable, efficient adsorbent that can be used in natural water bodies for adsorbing Cu(Ⅱ) ions.

Determination of gaseous formaldehyde by derivatization using magnetic multiwalled carbon nanotubes (MWCNTs) modified with 2,4-dinitrophenylhydrazine (DNPH) and high-performance liquid chromatography – ultraviolet detection (HPLC-UV)

Formaldehyde, a common indoor air pollutant, may have adverse effects on human health. The detection of formaldehyde is vital for assessing personal exposure risks. In this study, a method for indoor gaseous formaldehyde detection was developed based on the derivatization of formaldehyde by magnetic multi-walled carbon nanotube (MWCNT)-supported 2,4-dinitrophenyl hydrazine (DNPH) and analysis by high-performance liquid chromatography with ultraviolet detection. The method exhibited high derivatization efficiency due to the immobilized DNPH and rapid separation of derivatives and impurities due to the magnetic solid material. The optimal analysis conditions were 30 min for the derivatization reaction time and 35 °C for the derivatization reaction temperature in an acidic reaction medium. Under these conditions, the linear range for the proposed formaldehyde detection method was from 0.01 to 5.00 mg/L, and the detection limit was 0.005 mg/L. This formaldehyde detection method is advantageous due to its simplicity, sensitivity, linearity, and stability.

Magnetic solid-phase extraction based on multi-walled carbon nanotubes combined ferroferric oxide nanoparticles for the determination of five heavy metal ions in water samples by inductively coupled plasma mass spectrometry

Abstract An excellent magnetic multi-walled carbon nanotubes (MMWCNT) containing carboxyl material modified with ferroferric oxide (Fe3O4) nanoparticles was synthesized as the adsorbent for magnetic solid-phase extraction (MSPE) of five heavy metal ions (Pb2+, Cu2+, Co2+, Cd2+, Cr4+) in water samples followed by on-line inductively coupled plasma mass spectrometry (ICP-MS) detection. The characteristics of the adsorbent were analyzed using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and vibrating sample magnetometer (VSM). Some factors affecting extraction efficiency including pH of sample solution, the amount of adsorbent, extraction method and time, concentration and volume of desorption solvent, desorption time and evaluation of coexisting ions were optimized. Under the optimum conditions, good linearity (r ≥ 0.9951) was obtained within the range of 0.1–50.0 ng·mL−1. The limits of detection (LODs) and limits of quantification (LOQs) were 4.0–25.0 ng·L−1 and 15.0–80.0 ng·L−1, respectively. And satisfactory recoveries of five heavy metal ions ranged from 81.11% to 105.53% were acquired, and the relative standard deviations (RSDs) were no more than 6.05%. The MMWCNT synthesized had strong adsorption force for the five investigated heavy metal ions, respectively. Hence, the proposed method was so suitable and sensitive that it can be applied to the determination of trace analysis of heavy metals in water samples.

Vortex-assisted magnetic solid-phase extraction of cadmium in food, medicinal herb, and water samples using silica-coated thiol-functionalized magnetic multiwalled carbon nanotubes as adsorbent

The current work focuses on the facile and effective synthesis of a new nanocomposite based on multiwalled carbon nanotubes (MWCNT) decorated with magnetic core–shell Fe3O4@SiO2 and functionalized with 3-mercaptopropyltrimethoxysilane (3-MPTS) used in the vortex-assisted dispersive magnetic solid-phase extraction (VA–DMSPE) of Cd(II) ions in environmental and food samples. The nanocomposite was characterized and the parameters that influenced the VA–DMSPE were optimized through a fractional factorial design 25–1. The proposed method provided a preconcentration factor of 33.14 times, detection and quantification limits of 0.090 μg L−1 and 0.302 μg L−1, respectively, and a linearity range of 0.001–40.0 μg L−1. The developed method was effectively applied to preconcentrate and determine Cd(II) in water, tobacco, green tea leaves, ginkgo biloba, carrots, and rice samples, and its accuracy was evaluated using GF AAS.

Fabrication of dual responsive imprinted materials of magnetic and solvent and their solvent-regulated binding performance for bisphenol A

Facile and versatile adsorbents with fast separation and tunable adsorption performance based on molecularly imprinting polymers hold significant potential to improve the efficiency of sample pretreatment. In this work, a type of magnetic imprinted materials (SMMIPs) was prepared, using magnetic multi-walled carbon nanotubes (MWNTs@Fe3O4) as carrier, triethylene glycol dimethacrylate as cross-linker, and acryloyl-modified beta-cyclodextrin (β-CD-MA) as functional monomer, which can interact with bisphenol A (BPA) by host–guest interaction. MWNTs@Fe3O4 not only was served as substrates, but also contributed to the immobilization of β-CD-MA/BPA complex on their surface due to hydrogen bonding interaction between pre-assembly complex and carboxyl groups on its surface. Taking advantages of excellent solvent-responsiveness, SMMIPs can easily adsorb templates BPA in water with the adsorption capacity of 13.84 mg/g while desorb the adsorbed BPA in organic solvents (i.e. methanol, acetonitrile, ethanol and isopropanol) without the aid of acid. Significantly, even after reuse in successive four cycles, SMMIPs maintained high adsorption. Under the optimal extraction conditions, the proposed SMMIPs were successfully employed for the determination and separation of trace BPA in environmental waters and orange juice, exhibiting great potential in the determination of BPA in environmental and food samples.

Removal of nitrate from radioactive wastewater using magnetic multi-walled carbon nanotubes

In the solidification process using asphalt as a medium, nitrate oxidizes the medium and makes it unstable. Therefore, in order to efficiently remove nitrate from wastewater, a magnetic adsorbent was synthesized (m-MWCNTs), and physicochemical properties of m-MWCNTs were confirmed by SEM, TEM, XRD, FT-IR, BET, and VSM analyses. In the process of synthesizing m-MWCNTs, the amount of magnetite introduced on the surface of MWCNTs could be controlled by increasing the concentration of the chemical agent that becomes the Fe precursor. In addition, the amount of nitrate adsorption increased with higher magnetite content on the surface of MWCNTs. The adsorption process followed the Langmuir model and pseudo-second-order kinetics. In nitrate adsorption using m-MWCNTs, pH was the main condition to determine the adsorption amount, and as the pH increased, the amount of nitrate adsorption decreased. Thermodynamic experiments revealed that the adsorption of nitrate by m-MWCNTs is an endothermic and spontaneous process.

Magnetic Carbon Nanotubes‐Silica Binary Composite for Effective Pb(II) Sequestration from Industrial Effluents: Multivariate Process Optimization

AbstractIn this work, magnetic multiwalled carbon nanotubes‐silica binary composite (mCNT@APS) is synthesized via amide bond and utilized for the Pb(II) adsorption from aqueous solutions in batch mode. The composite is characterized using Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM), X‐ray diffraction (XRD), and point of zero charge (pHpzc) studies. Three levels and three factorial Box–Behnken design in response surface methodology is employed to assess and optimize the effects of influential parameters: pH, initial concentration, and contact time. Using the desirability function, the obtained optimum conditions are pH 5.4, feed concentration 757 µg mL−1 and contact time 4 min. The electrostatic attraction between the active binding sites of adsorbent and Pb(II) at pHpzc < pH results in higher saturation capacity (79.69 mg g−1) in accordance with the best fitted non‐linearized Langmuir isotherm model. The pseudo‐second‐order model fits well to the kinetic data implying chemisorption of Pb(II) onto mCNT@APS. The material can be regenerated up to 15 sorption–desorption cycles using 5 mL of 1.5 M HNO3. The adsorbent exhibits excellent Pb(II) removal efficiency (>98%) from industrial effluents and tap water samples.

Adsorption of aflatoxins and ochratoxins in edible vegetable oils with dopamine-coated magnetic multi-walled carbon nanotubes

A new, green, and cost-effective magnetic solid-phase extraction of aflatoxins and ochratoxins from edible vegetable oils samples was developed using polydopamine-coated magnetic multi-walled carbon nanotubes (PDA@Fe3O4-MWCNTs) as the absorbent. PDA@Fe3O4-MWCNTs nanomaterials were prepared by chemical co-precipitation and in situ oxidation and self-polymerization of dopamine and was characterized. Factors affecting MSPE and the adsorption behavior of the adsorbent to mycotoxins were studied, and the optimal extraction conditions of MSPE and the complexity of the adsorption process were determined. Based on this, the magnetic solid-phase extraction-high-performance liquid chromatography-fluorescence detection method (MSPE-HPLC-FLD) was established for determining six mycotoxins [aflatoxin B1 (AFB1), AFB2, AFG1, and AFG2, and ochratoxin A (OTA) and OTB)] in vegetable oils. The recovery was 70.15%~89.25%, and RSD was ≤6.4%. PDA@Fe3O4-MWCNTs showed a high affinity toward aflatoxins and ochratoxins, allowing selective extraction and quantification of aflatoxins and ochratoxins from complex sample matrices.

OILY WASTEWATER TREATMENT BY MAGNETIC CARBON NANOTUBES NANOCOMPOSITE

A magnetic multi-wall carbon nanotube (MCNTs) nanocomposite was synthesized and was used as an adsorbent for removal of oil from aqueous solutions. The MCNTs nanocomposite was composed of commercial multi-wall carbon nanotubes and iron oxide nanoparticles. The property of this magnetic adsorbent was characterized by scanning electron microscopy, X-ray diffraction and VSM. Adsorption characteristics of the MCNT nanocomposite was examined using diesel oil (DO) as adsorbate. The sorption capacity was affected significantly by the initial concentration of DO, sorbent amount and contact time. Batch experiments were conducted to investigate the affect of different DO initial concentration (ranging from 0.2 to 1.0%) and contact time (10 to 90 min) to the removal efficiency. This MCNTs nanocomposite can be recycled conveniently from water with the assist of an external magnet because of their exceptional properties.

Residue analysis and removal of procymidone in cucumber after field application

Residue behavior monitoring and removal of pesticide residues are always a topic of concern. In this study, a modified QuEChERS method for the determination of procymidone in cucumbers was established using the prepared magnetic multi-walled carbon nanotubes (m-MWCNTs). The recovery ranged from 96 to 114% with RSDs of 1%–4%, and the limit of quantification (LOQ) was 0.02 mg/kg. The dissipation dynamic results showed that procymidone on cucumbers dissipated rapidly, of which the half-life was about two days. The effect of the ultrasonic washing on the removal of procymidone in cucumbers was evaluated and the removal rate ranged from 54.7% to 70.6%. The content of antioxidant phenols in cucumbers was measured under different washing conditions. The results showed that the total phenol content in cucumbers decreased by 3.2%–16.3% during the ultrasonic washing process. This work intended to evaluate the dissipation behavior of procymidone and explore practical ways to remove procymidone residue from cucumbers.

The effective removal of nickel ions from aqueous solution onto magnetic multi-walled carbon nanotubes modified by β-cyclodextrin

β-cyclodextrin was covalently grafted onto the surface of magnetic multi-walled carbon nanotubes to synthesize a novel composite material (denoted as β-CD@Fe3O4/MWCNT). The structure of the magnetic material was characterized by using Fourier transform infrared (FT-IR spectroscopy), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and specific surface area (BET). The results from SEM showed that the dispersion of carbon nanotubes was better after β-cyclodextrin was compounded. TGA indicated that about 7.1% of the β-cyclodextrin was grafted onto the surface of the magnetic carbon nanotubes. In addition, β-CD@Fe3O4/MWCNT had larger specific surface area and pore volume. The adsorption of nickel ions on β-CD@Fe3O4/MWCNT was affected by pH, temperature and adsorption time. The pseudo-second-order kinetic model and Langmuir model describe the adsorption process well. Thermodynamic data showed that the adsorption process was spontaneous and exothermic, and the maximum adsorption amount of nickel ions (Ni2+) on the β-CD@Fe3O4/MWCNT was 103 mg g−1 at room temperature. Moreover, regeneration experiments showed that the adsorbent still maintained a high adsorption capacity after 5 cycles. On this basis, the interaction mechanism between magnetic nanoparticles and Ni2+ was discussed. In summary, as an environmentally friendly adsorbent, β-CD@Fe3O4/MWCNT has the potential to remove nickel ions from wastewater.

Sorptive removal of methylene blue from water by magnetic multi-walled carbon nanotube composites.

In the present study, five magnetic multi-walled carbon nanotubes (MMWCNTs) with different diameters were prepared and their performance on the sorptive removal of methylene blue (MB) from water was investigated. Transmission electron microscope, scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction, and vibrating sample magnetometer confirm that the surface of these MMWCNTs has been decorated by Fe3O4 nanoparticles, which renders the MMWCNTs superparamagnetic. Thus, these MMWCNTs can be easily separated from water after the adsorption. During the adsorption process, pH slightly affected the removal efficiency of MB and the adsorption performed better under weak alkaline conditions. Adsorption kinetics followed the pseudo-second-order kinetic model well, and the Dubinin-Radushkevich model fitted the isotherms best. The maximum adsorption capacity for MB reached 204.2 mg/g, and the values decreased with increasing diameters of MMWCNTs due to decreasing specific surface areas. The thermodynamics parameters indicated the spontaneous and exothermic nature of the adsorption. The reusability test showed that MMWCNTs could be used for 6 cycles without significant loss of the adsorption capacity. And common ions (K+, Na+, Ca2+ and Al3+) and SDS in water did not show greatly effects on the removal efficiency of MB. Hence, MMWCNTs prepared in this study could be promising adsorbents for dyes removal from wastewater.