Magnetic Multi-walled Carbon Nanotubes Research Articles

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.

Adsorption of phenanthrene onto magnetic multi-walled carbon nanotubes (MMWCNTs) influenced by various fractions of humic acid from a single soil

In the present study, two magnetic multi-walled carbon nanotubes (MMWCNTs) with different ratios of Fe2+/Fe3+ were prepared, and the effects of different fractions of dissolved humic acid (DHA) on the adsorption of phenanthrene by multi-walled carbon nanotubes (MWCNTs) and MMWCNTs from the aqueous solution were investigated. The adsorption kinetics of DHA1 and DHA4 were best fitted with pseudo-second order model. The adsorption of DHAs on MMWCNTs was weaker than that on MWCNTs, and DHA1 was easier to adsorb to MWCNTs and MMWCNTs than DHA4. The phenanthrene adsorption capacities by 1:2:1MMWCNTs and 4:2:1MMWCNTs with higher polar groups and magnetic gradient were less than that of MWCNTs. The pH value had no obvious effect on the adsorption of phenanthrene to MWCNTs loaded with different iron. Additionally, the DHAs could form soluble complexes of DHAs–Fe (II) in solution to reduce the phenanthrene adsorption on MMWCNTs, DHA1 inhibit more obviously phenanthrene adsorbed onto MWCNTs and MMWCNTs than DHA4. As for MMWCNTs, the main mechanisms of phenanthrene adsorbed onto it included new adsorption sites formed by π−π interaction and magnetic gradient. In this study, MMWCNTs after adsorbed DHAs had a weaker inhibitory effect on phenanthrene adsorption than MWCNTs, implying that when phenanthrene is adsorbed by DHAs-coated MMWCNTs, the bioavailability and mobility of phenanthrene will be reduced, and it is easy to be removed by the magnet for further processing.

Simple and efficient method for the determination of Cr(VI) ions in water samples using m-MWCNT@APTMS through dispersive magnetic solid phase extraction

ABSTRACT This work describes the synthesis and characterisation of a promising adsorbent nanocomposite based on magnetic multiwalled carbon nanotubes (m-MWCNTs) functionalised with 3-aminopropyltrimethoxysilane (APTMS). Was developed a method based on dispersive magnetic solid phase extraction (DMSPE). It also details its use in the development of a rapid and simple preconcentration method for Cr(VI) ions in water samples with FAAS detection. The nanocomposite was characterised using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM); the textural data measurements were obtained using the Brunauer-Emmett-Teller (BET) and Barret-Joyner-Halenda (BJH) analyses. The maximum adsorption capacity of the m-MWCNT@APTMS nanocomposite for Cr(VI) ions was 13.37 mg g-1 at an equilibrium time of 20 min. The adsorption process followed the dual-site Langmuir-Freundlich model, while the kinetic data were well fitted by the pseudo-second-order model. The important variables that affect the performance of the MSPE method, such as the pH of the sample, adsorbent mass, preconcentration and elution time, and type of eluent were univariately optimised. Under the optimised condition, an aliquot of 20 mL of sample was preconcentrated using 40 mg of m-MWCNT@APTMS for 4 min under vortex agitation. After this, the nanoparticles were separated from the solution with a magnet, then, the adsorbed Cr(VI) ions in the adsorbent were eluted with 1.0 mL of 2.0 mol L-1 HNO3 for 1.0 min and submitted to FAAS detection. The linear range studied was of 0.02 -0.2 mg L-1. When the enrichment factor was 20, the LOD and LOQ to Cr(VI) ions were 3.18 and 10.7 µg L-1, respectively, presenting RSD of 0.18% and 0.28% for solutions of Cr(VI) at 0.08 mg L-1 and 0.18 mg L-1. Finally, the proposed method was applied for the speciation of Cr(VI) in water samples and the results were compared with reference technique (GF AAS).

Synthesis of magnetic multi walled carbon nanotubes hydrogel nanocomposite based on poly (acrylic acid) grafted onto salep and its application in the drug delivery of tetracyceline hydrochloride

Current discovery of different modifications of multi walled carbon nanotubes has motivated research for their potential applications in various field such as adsorbent materials, and drug delivery. Many different modified carbon nanotubes have been achieved, including combinations with iron oxide nanoparticles (NPs) for their unique properties including magnetic properties, nontoxicity, biocompatibility and capability which have considerable impact on the delivery of the drug at the targeted area. However, one of the disadvantages of this nanocomposite in biological fluids is that iron oxide NPs might be quickly cleared by the bloodstream before realization of their targets. In order to overcome this obstacle, polymers could be used as stabilizer to achieve a highly stable NPs@MWCNT composite. As a result, a magnetic multi walled carbon nanotube hydrogel nanocomposite based on poly (acrylic acid) grafted onto salep was synthesized and then fully characterized by using FTIR spectroscopy, thermogravimetric analysis, EDAX spectrum, SEM, TEM, AFM images, and vibrating sample magnetometer (VSM) and synthesis mechanism was suggested. Besides, swelling kinetics and loading and releasing of tetracycline hydrochloride as a model drug in various conditions were also investigated.

Vortex-assisted magnetic solid phase extraction of Pb and Cu in some herb samples on magnetic multiwalled carbon nanotubes.

This study is the development of a new solid phase extraction method based on using magnetic multiwalled carbon nanotubes impregnated with 1-(2-pyridylazo)2-naphthol (PAN) for separation, preconcentration, and flame atomic absorption spectrometric determination of Pb(II) and Cu(II). Optimization of the method was done by investigating pH effect, amount of magnetic multiwalled carbon nanotubes impregnated with PAN, eluent type and volume, matrix effects, and volume of the sample. The optimum adsorbent amount was found to be 75 mg and the optimum pH value was found as 5.5. The detection limits were 16.6 μg L-1 for Pb(II) and 18.9 μg L-1 for Cu(II). The relative standard deviations (RSD%) were less than 4%. Two certified reference materials: SPS-WW2 wastewater and NCS-DC73349 (bush branches and leaves) were used to test the validation of the method. The method was successfully applied to the analysis of Pb(II) and Cu(II) ions in daisy, mint, paprika, sage, rosemary, daphne leaves, heather, green tea, andViburnum opulussamples.

Magnetic MWCNTs-dendrimer: A potential modifier for electrochemical evaluation of As (III) ions in real water samples

Abstract Herein, the novel synthesis, characterisation and further application of magnetic multi-walled carbon nanotubes modified with polyamidoamine (PAMAM) dendrimers (MMWCNTs-D-NH2) as highly sensitive and selective recognition element in sensor development for the electrochemical determination of As(III) in water matrices is presented. The synthetized nanomaterials were characterised by Fourier transform- infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. Thus, the glassy carbon electrode (GCE) was subjected to functionalisation with the MMWCNTs-D-NH2 to produce the sensor. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetric (CV) measurements were performed to characterise the surface of modified electrode. The electrochemical performances of the developed sensor towards different concentration of As(III) were studied by square wave anodic stripping voltammetric (SWASV) measurements. The sensor shown its high sensitivity and selectivity against possible interferents, such as Hg(II), Pb(II), Cd(II), Cu(II). The limit of detection (LOD) was found to be 0.46 µgL−1. The suitability of the proposed sensor in spiked water samples (drinking, tap and mineral water) is also discussed.

Progress in the application of deep eutectic solvents to extraction and separation technology

随着绿色化学的发展,开发和应用符合绿色化学要求的溶剂和方法备受关注。作为离子液体类似物,低共熔溶剂(deep eutectic solvent, DES)是通过氢键受体(hydrogen bond acceptor, HBA)和氢键供体(hydrogen bond donator, HBD)的氢键作用而形成的一种混合物,具有环境友好、制备简单、成本低、可生物降解等优点,在很多领域均有越来越广泛的应用。DES可以从不同样品中萃取和分离不同的目标化合物,其作为萃取溶剂具有独特的优势,可以获得较高的萃取效率且样品基质对分析过程的影响较小。在分散液液微萃取(dispersive liquid-liquid micro-extraction, DLLME)程序中,DES可以萃取复杂基质中的残留药物、金属离子和生物活性成分;与传统的萃取方法相比,该方法具有对有机试剂需求少,萃取效率更高等明显优势。而且,在DLLME中加入DES作为分散剂,能够加速萃取剂在样品溶液中的扩散,具有小型化、成本低等优点。相比于传统分散剂甲醇、乙腈的高挥发性、易燃性,DES的高稳定性、低毒性使其在绿色化学领域中更具有优势,应用更广。因此,DES与DLLME的结合近年来发展迅速。不仅如此,DES与固相萃取联合应用也具有广泛的应用前景,在与固相萃取小柱和搅拌棒联合应用时,DES可以作为洗脱剂,氢键供体及氢键给体的用量之比是洗脱效率的重要考察因素之一。在与磁性材料联用时,DES能与磁性多壁碳纳米管、磁性氧化石墨烯等纳米复合材料结合,通过氢键、π-π作用力和静电作用力等特异性吸附目标分析物。并且能够参与磁性凝胶和分子印迹聚合物的合成,推动磁性材料向绿色化学的方向发展,进一步拓展DES的应用。作为一类新兴的绿色溶剂,DES在化合物的萃取分离技术方面受到广泛关注,在不同的萃取技术中扮演了不同的角色,并表现出良好的性能,因此逐渐成为绿色化学领域的研究重点。该文整合了DES在萃取分离技术中的研究进展,介绍了DES的制备、性质和分类,对DES在DLLME和固相萃取中的应用进行了总结和归类,并展望了DES在萃取分离技术中的应用前景,为DES未来的应用提供参考。

Ionic liquid and magnetic multiwalled carbon nanotubes for extraction of N-methylcarbamate pesticides from water samples prior their determination by capillary electrophoresis

A simple and rapid microextraction procedure is reported on the use of ionic liquid (IL) in combination with magnetic multiwalled carbon nanotubes (MMWCNTs). The procedure is based on temperature-controlled IL dispersive liquid phase microextraction (DLPME) and MMWCNTs, for selective preconcentration of N-methylcarbamate pesticides in water samples, followed by their hydrolysis in alkaline buffer, prior to being analyzed by capillary electrophoresis. The extraction procedure uses small volume of organic solvents, and there is no need for centrifugation. In the experimental approach the IL was quickly disrupted by an ultrasonic probe, heated with the temperature controlled at 90 °C and dispersed in water samples in a homogenous form. At this stage, N-methylcarbamate pesticides migrate into the IL. Then the solution was cooled and small amounts of MMWCNTs were dispersed into the sample solutions to adsorb the ionic liquid containing the analytes and phase separation was completed. The ionic liquid allowed the microextraction of the analytes and a small volume of dichloromethane (DCM) was used for elution. MMWCNTs favored the adsorption of the ionic liquid with the analytes and improved the final recovery with respect to the use of simple magnetic nanoparticles as a sorbent material. Under the optimum conditions, limit of quantifications (LOQ) were achieved in the 5.6–9.3 ng mL−1 range, with recoveries between 85.0% and 102.4%.

Improvement of Laccase Activity Via Covalent Immobilization over Mesoporous Silica Coated Magnetic Multiwalled Carbon Nanotubes for the Discoloration of Synthetic Dyes.

Due to its environmental friendliness and biodegradable ability, the enzymatic decolorization of azo dyes is the best option. However, the free enzyme suffers from various limitations, including poor stability, no repeatable use, and a high expense, which is the key drawback for its practical use. In this analysis, the laccase enzyme was immobilized in mesoporous silica coated magnetic multiwalled carbon nanotubes (Fe3O4-MWCNTs@SiO2) by a glutaraldehyde cross-linker to create an easily separable and stable enzyme. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the as-synthesized Fe3O4-MWCNTs@SiO2. Laccase immobilized in Fe3O4-MWCNTs@SiO2 showed a good improvement in temperature, pH, and storage stability. Moreover, the operational stability of the biocatalyst was improved, retaining 87% of its original activity even after 10 cycles of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) oxidation. The biocatalysts were applied for the decolorization of selected azo dyes without a mediator, and up to 99% of Eriochrome Black T (EBT), 98% of Acid Red 88 (AR 88), and 66% of Reactive Black 5 (RB5) were decolorized. Based on these properties, the biocatalysts can be potentially utilized in various environmental and industrial applications.

Determination of cesium ions in environmental water samples with a magnetic multi-walled carbon nanotube imprinted potentiometric sensor.

A potentiometric sensor, based on the glassy carbon electrode (GCE) modified with a magnetic multi-walled carbon nanotubes/cesium ion-imprinted polymer composite (MMWCNTs@Cs-IIP), is introduced for the detection of cesium(i). The IIP was synthesized using cesium ions as the template ions, chitosan as the functional monomer and glutaraldehyde as the cross-linking agent. The membrane, which was coated on the surface of the GCE, was prepared using MMWCNTs@Cs(i)-IIP as the modifier, PVC as the neutral carrier, 2-nitrophenyloctyl ether as the plasticizer and sodium tetraphenylborate as the lipophilic salt. The proposed sensor exhibited a Nernstian slope of 0.05954 V dec−1 in a working concentration range of 1 × 10−7 to 1 × 10−4 M (mol L−1) with a detection limit of 4 × 10−8 M. The sensor exhibited high selectivity for cesium ions and was successfully applied for the determination of Cs(i) in real samples.

Recovery of lanthanum cations by functionalized magnetic multi-walled carbon nanotube bundles.

Rare-earth elements (REE), including La, are critical raw materials in many technological advancements. Collection of physically adsorbed REEs on clay minerals can be realized first by ion-exchange leaching, followed by adsorption enrichment. Ever increasing demand and limited resources of REEs have fueled the development of nanostructured adsorbents. In this paper, multi-walled carbon nanotubes (MWCNTs) were purified using concentrated H2SO4 and HNO3, then coupled with magnetic Fe3O4 nanoparticles to make low concentration La ion extraction from water possible. The MWCNT@Fe3O4 composites were further crosslinked with 0.1 wt% epichlorohydrin and functionalized with 0.5 wt% carbon disulfide to achieve a La3+ adsorption capacity of 23.23 mg g−1. We fully probed the morphology, crystallinity, chemical composition, and magnetic properties of the as-prepared adsorbent by scanning/transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, vibrating-sample magnetometry, and thermal gravimetry. These results indicated that the MWCNT@Fe3O4 nanohybrid may be a promising candidate for recovering La ions from aqueous solutions.

Magnetic solid-phase extraction using polydopamine-coated magnetic multiwalled carbon nanotube composites coupled with high performance liquid chromatography for the determination of chlorophenols.

Polydopamine (PDA)-coated magnetic multiwalled carbon nanotube (M-MWCNT) composites were synthesized in two facile preparation steps, and were used as adsorbents for magnetic solid-phase extraction (MSPE) coupled with high-performance liquid chromatography (HPLC) for simultaneous extraction, enrichment and determination of five kinds of typical chlorophenols (CPs) in water samples. The as-prepared magnetic composites showed excellent magnetic properties and high thermal stability. Various main parameters influencing the extraction efficiency of MSPE were systematically investigated. Under the optimized MSPE-HPLC conditions, a high enrichment factor (EF) was obtained in the range of 85-112 for 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,6-dichlorophenol (2,6-DCP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP). Good linearity was obtained in the range of 2.0-200 μg L-1 for 2-CP and 4-CP and 1.0-200 μg L-1 for 2,6-DCP, 2,4-DCP and 2,4,6-TCP, with a correlation coefficient (R2) higher than 0.9964. The limits of detection (LODs) and the limits of quantification (LOQs) were in the range of 0.10-0.31 μg L-1 and 0.35-1.03 μg L-1, respectively. The intraday and interday precisions evaluated using relative standard deviation (RSD) values were in the range of 1.05-2.25% and 1.88-2.83%, respectively. The validated MSPE-HPLC method was also successfully applied to analyze five kinds of CPs in tap water, lake water, river water and seawater samples, and satisfactory recoveries were obtained in the range of 76.87-106.5% with RSDs of 1.64-6.78%.

Synergic photocatalytic degradation of 2,4,6-trichlorophenol using magnetic multi-walled carbon nanotubes/cobalt monoxide/ionic crystal quaternary system

Magnetic and photoactive carbon based materials with the use of polyoxometalate-based ionic crystal [Fe(phen)3]2[SiW12O40]·3DMF (IC–Fe) on cobalt(II) monoxide decorated magnetic multi-walled carbon nanotubes(MWCNTs/Fe3O4/CoO) were synthesized and characterized. The prepared nanocomposites were characterized by FT-IR, XRD, Raman, TEM, VSM, XPS and UV–Vis. We have shown that synthesized MWCNTs/Fe3O4/CoO/IC-Fe nanocomposite can be used as a stable photocatalyst for the photodegradation of 2,4,6-Trichlorophenol (2,4,6-TCP) pollutant, under visible-light irradiation. The examination of the photocatalytic activity of the synthesized nanocomposite was compared with the one of the pristine IC-Fe nanoparticles. The main effect of the introduction of MWCNTs in such nanocomposites is the decrease of the band gap, with a consequence on the absorbance. The results show that the synthesized photocatalyst demonstrated better photocatalytic activity than the starting materials. In addition, the magnetic properties of the composite's materials can be used for the collection and reuse of the nanocomposite at the end of the photocatalytic reactions.

Polyethyleneimine-modified magnetic carbon nanotubes as solid-phase extraction adsorbent for the analysis of multi-class mycotoxins in milk via liquid chromatography-tandem mass spectrometry.

Polyethyleneimine-modified magnetic multi-walled carbon nanotubes were developed to extract 10 mycotoxins. Simple modification of polyethyleneimine was achieved on the magnetic substrate by using an epoxy-containing silane agent as a linker. The resultant magnetic adsorbent was integrated with reverse phase and anion exchange interaction sites. Under optimal extraction conditions, only 20.0mg adsorbent was used to extract the mycotoxins from 50.0mL loading solution. The maximum adsorption capacities of the adsorbent toward the mycotoxins ranged from 4.9 to 10.2mg/g. Adsorption and desorption were completed within 3.0 and 2.0min, respectively. The adsorbent could be used for six repeated runs without evident change in extraction performance. The adsorbent combined with liquid chromatography-tandem mass spectrometry was applied further to analyze the mycotoxins in milk. The absolute recoveries of the 10 mycotoxins ranged from 88.3 to 103.5% with relative standard deviations that ranged from 2.4 to 6.5%, and their limits of detection were 0.003 to 0.442μg/kg. The proposed adsorbent has great potential in the routine analysis of mycotoxins in ordinary analytical chemistry laboratory.

Multi-Walled Carbon Nanotubes for Magnetic Solid-Phase Extraction of Six Heterocyclic Pesticides in Environmental Water Samples Followed by HPLC-DAD Determination.

Magnetic multi-walled carbon nanotubes were prepared as magnetic solid-phase extraction (MSPE) adsorbent for the enrichment of six heterocyclic pesticides in environmental water samples, including imidacloprid, triadimefon, fipronil, flusilazole, chlorfenapyr and fenpyroximate. Then six heterocyclic pesticides were separated and determined by high-performance liquid chromatography-diode-array detector (HPLC-DAD). Major factors influencing MSPE efficiency, including the dose of mag-multi-walled carbon nanotubes (mag-MWCNTs), extraction time, solution pH, salt concentration, type and volume of eluent and desorption time were investigated. Under the optimized conditions, the enrichment factor of the method reached to 250. The linearity was achieved within 0.05–10.0 μg/L for imidacloprid and chlorfenapyr, 0.10–10.0 μg/L for fipronil, flusilazole, triadimefon and fenpyroximate. Limits of detection were in the range of 0.01–0.03 μg/L. Good precision at three spiked levels were 1.1–11.2% (intra-day) and 1.7–11.0% (inter-day) with relative standard deviation of peak area, respectively. The developed method was utilized to analyze tap water, river water and reservoir water samples and recoveries at three spiked concentration levels ranged from 72.2% to 107.5%. The method was proved to be a convenient, rapid and practical method for sensitive determination of heterocyclic pesticides.

Amphiphilic block copolymer-grafted magnetic multi-walled carbon nanotubes as QuEChERS adsorbent for simultaneous determination of mycotoxins and pesticides in grains via liquid chromatography tandem mass spectrometry.

An amphiphilic block copolymer consisting of poly(N-acryloyl-glucosamine) (PAGA) and poly(tert-butyl methacrylate) (PtBMA) was designed and grafted on magnetic multi-walled carbon nanotubes (Fe3O4MWCNTs). The resultant Fe3O4MWCNTs@copolymer was proposed as QuEChERS adsorbent for determinationof 15 mycotoxins and 25 pesticides in grains via liquid chromatography tandem mass spectrometry. The adsorbent was characterized by a transmission electron microscope, scanning electron microscope, elemental analysis, and other techniques. The common matrix interferences were efficiently removed by the proposed adsorbent, such as pigment, fatty acids, and the saccharide. PAGA segment played animportant role in removing the hydrophilic interferences through hydrogen bonding due tothehigh density of hydroxyl groups. PtBMA segment removed the fatty residues through its strong hydrophobic carbon moiety. In comparison with the commercially available QuEChERS adsorbents, the proposed adsorbent had higher adsorption capacities towards the typical matrix interferences. To achieve satisfactory recoveries of analytes, various parameters in theQuEChERS procedure werecomprehensively investigated. Under the optimal conditions, 95.0% of the analytes showedsatisfactory recoveries in the range 70.0-120% as well as negligible matrix effects. The limits of detection (LOD) were in the range 0.00015-1.3μgkg-1. Compared with previously reported QuEChERS methods, the proposed method had improved sensitivity andbenefited from low matrix effects. The recoveries of analytes in various grains were in the range 60.8-108% with relative standard deviations (RSD) less than 13%. Moreover, the Fe3O4MWCNTs@copolymer exhibited good synthetic reproducibility and rapid magnetic separation (less than 10s). The research provides a versatile platform to develop multi-functional QuEChERS adsorbents based on the amphiphilic block copolymer.

Magnetic bentonite nanocomposite for removal of amoxicillin from wastewater samples using response surface methodology before determination by high performance liquid chromatography

Antibiotics and pharmaceutical products cannot remove by conventional sewage treatment. In this work, an effective adsorbent Magnetic Multiwalled Carbon nanotube (MMWCNTs) was synthesized by co-precipitation of MWCNTs with Fe3O4 and used for removal of Amoxicillin from aqueous solutions. Response surface methodology on Central Composition Design (CCD) was applied for designing of experiments and building of models. Four factors including pH, adsorbent dose, time, and temperature were studied and used for the quadratic equation model to the prediction of optimal points. By solvent the equation and considering the regression coefficient (R2 =0.99) the optimal points obtained as follows: pH =2.98; adsorbent dosage =2.16 g; time =22 min and temperature = 37.88 o C. Isotherm study of adsorption showed that the adsorption of amoxicillin onto MMWCNTs follows the Langmuir model. The maximum adsorption capacity is 215 mg g-1 obtained from Langmuir isotherm.