Comparison of Cadmium Cd2+ and Lead Pb2+ Binding by Fe2O3@SiO2‐EDTA Nanoparticles – Binding Stability and Kinetic Studies

This study describes the synthesis and characterization of ethylenediaminetetraacetic acid (EDTA) functionalized magnetic nanoparticles of 20 nm in size – Fe₃O₄@SiO₂‐EDTA – which were used as a novel magnetic adsorbent for Cd(II) and Pb(II) binding in aqueous medium. These nanoparticles were obtained in two‐stage synthesis: covering by tetraethyl orthosilicate and functionalization with EDTA derivatives. Nanoparticles were characterized using TEM, FT‐IR, and XPS methods. Metal ions were detected under optimized experimental conditions using Differential Pulse Anodic Stripping Voltammetry (DPASV) and Hanging Mercury Drop Electrode (HDME) techniques. We compared the ability of Fe₃O₄@SiO₂‐EDTA to bind cadmium and lead in concentration of 553.9 μg L^?1 and 647.5 μg L^?1, respectively. Obtained results show that the adsorption rate of cadmium binding was very high. The equilibrium for Fe₃O₄@SiO₂‐EDTA‐Cd(II) was reached within 19 min while for the Fe₃O₄@SiO₂‐EDTA‐Pb(II) was reached within 25 minutes. About 2 mg of nanoparticles was enough to bind 87.5 % Cd(II) and 54.1 % Pb(II) content. In the next step the binding capacity of Fe₃O₄@SiO₂‐EDTA nanoparticles was determined. Only 1.265 mg of Fe₃O₄@SiO₂‐EDTA was enough to bind 96.14 % cadmium ions while 5.080 mg of nanoparticles bound 40.83 % lead ions. This phenomenon proves that the studied nanoparticles bind Cd(II) much better than Pb(II). The cadmium ions binding capacity of Fe₃O₄@SiO₂‐EDTA nanoparticles decreased during storage in 0.5 M KCl solution. Two days of Fe₃O₄@SiO₂‐EDTA storage in KCl solution caused the 32 % increase in the amount of nanoparticles required to bind 60 % of cadmium while eight‐days storage caused further increase to 328 %. The performed experiment confirmed that the storage of nanoparticles in solution without any surfactants reduced their binding capacity. The best binding capacity was observed for the nanoparticles prepared directly before the electrochemical measurements.     

Preparation of carbon coated Fe3O4 nanoparticles for magnetic separation of uranium

Uranium(VI) was removed from aqueous solutions using carbon coated Fe₃O₄ nanoparticles (Fe₃O₄@C). Batch experiments were conducted to study the effects of initial pH, shaking time and temperature on uranium sorption efficiency. It was found that the maximum adsorption capacity of the Fe₃O₄@C toward uranium(VI) was ∼120.20 mg g⁻¹ when the initial uranium(VI) concentration was 100 mg L⁻¹, displaying a high efficiency for the removal of uranium(VI) ions. Kinetics of the uranium(VI) removal is found to follow pseudo-second-order rate equation. In addition, the uranium(VI)-loaded Fe₃O₄@C nanoparticles can be recovered easily from aqueous solution by magnetic separation and regenerated by acid treatment. Present study suggested that magnetic Fe₃O₄@C composite particles can be used as an effective and recyclable adsorbent for the removal of uranium(VI) from aqueous solutions.     

Characterization and analytical application of surface modified magnetic nanoparticles

Fe₃O₄ superparamagnetic nanoparticles with various functionalities were synthesized using a chemical co-precipitation method and used to demonstrate their analytical applications for protein separation of protein and metal ion extraction. The chemically inert silica layer coated with tetraethoxysilane (TEOS) protected the Fe₃O₄ core from a chemical attack and allowed the nanoparticles to be well dispersed in an aqueous solution. Particularly, the beads were resistant to an acidic solution with a pH ≥ 3. The amino (− NH₂) groups were covalently bonded to the silica coated Fe₃O₄, and then the carboxyl (− COOH) groups were functionalized to the nanoparticle surface through the reaction of − NH₂ and glutaric anhydride. The synthesized magnetic nanoparticles (MNP) were characterized using FT-IR, FE-TEM, XRD, and SQUID. The presence of functional groups on the nano beads was confirmed using molecular fluorescence spectrometry. For the presence of the amino (− NH₂) groups, FITC was tagged and monitored using an excitation laser with a wavelength of 473 nm and a fluorescence emission of 518 nm. Biotin was immobilized on the MNP and the fluorescent of FITC tagged on avidin was monitored to identify the carboxyl (− COOH) group.The proteins of Cytochrome C (12,000 Da), Rnase B (15,000 Da), and Myoglobin (17,000 Da) were separated using the MNP functionalized with the carboxyl (− COOH) group and identified using MALDI-TOF-MS. Amino benzyl EDTA (ethylenediaminetetraacetic acid) was immobilized on the MNP for metal–EDTA complexation to use the synthesized magnetic particles to extract metal ions for environmental and clinical application. Cu, Cd, Co, and Pb ions were extracted from ∼ 10 ng/mL solutions in the batch-type procedure and the extraction efficiency was > 90% at a pH of 4.     

Enrichment and Identification of Metallothionein by Functionalized Nano-Magnetic Particles and Matrix Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry

As a low molecular weight protein with the ability of binding metal ions and high inducibility, metallothionein (MT) is often regarded as an important biomarker for assessment of heavy metal pollution in water environment. In the light of that the traditional process of enrichment and identification is time-consuming and complicated, we prepared a core-shell nanoparticle, gold-coated iron oxide nanoparticles (Fe₃O₄@Au NPs) herein. It possessed the advantages of fast response to magnetic fields and optical properties attributing to Fe₃O₄ and Au nanoparticles, respectively. The Fe₃O₄@Au nanoparticles could be used to enrich MT simply through Au–S interaction, and the purified proteins were determined by matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS). The results showed that the Fe₃O₄@Au nanoparticles could directly enrich MT from complex solutions and the detection limit could be as low as 10 fg mL^?1.     

Magnetic Nitrogen-Doped Porous Carbon Nanocomposite for Pb(II) Adsorption from Aqueous Solution

We report in the present study the in situ formation of magnetic nanoparticles (Fe₃O₄ or Fe) within porous N-doped carbon (Fe₃O₄/N@C) via simple impregnation, polymerization, and calcination sequentially. The synthesized nanocomposite structural properties were investigated using different techniques showing its good construction. The formed nanocomposite showed a saturation magnetization (M_s) of 23.0 emu g⁻¹ due to the implanted magnetic nanoparticles and high surface area from the porous N-doped carbon. The nanocomposite was formed as graphite-type layers. The well-synthesized nanocomposite showed a high adsorption affinity toward Pb²⁺ toxic ions. The nanosorbent showed a maximum adsorption capacity of 250.0 mg/g toward the Pb²⁺ metallic ions at pH of 5.5, initial Pb²⁺ concentration of 180.0 mg/L, and room temperature. Due to its superparamagnetic characteristics, an external magnet was used for the fast separation of the nanocomposite. This enabled the study of the nanocomposite reusability toward Pb²⁺ ions, showing good chemical stability even after six cycles. Subsequently, Fe₃O₄/N@C nanocomposite was shown to have excellent efficiency for the removal of toxic Pb²⁺ ions from water.     

用于检测重金属离子的磁性荧光复合微球

采用静电逐层自组装的方法,首先将PSS和PAH聚电解质交替沉积在CaCO3中空微球表面,然后将Fe3O4磁性纳米粒子与CdSe量子点负载在中空微球表面不同的聚电解质层中,制备出具有磁性和荧光双重功能的复合微球,并将其作为荧光离子探针,研究了其对Cu2+和Pb2+离子检测的灵敏度、选择性及可行性。结果表明,复合微球显示出良好的磁性和荧光性能,对Cu2+和Pb2+离子的检测具有较高的灵敏度和选择性。尤为重要的是,可通过磁分离的方法将微球快速地从待测液中回收,从而能够避免量子点对环境造成的二次污染。     

Soap-free synthesis of highly monodisperse magnetic polymer particles with amphoteric initiator

A method applying soap-free emulsion polymerization with an amphoteric initiator, 2,2′-azobis[N-(2-carboxyethyl)-2-2-methyl-propionamidine], is proposed for synthesis of highly monodisperse particles composed of magnetic nanoparticles (Fe₃O₄/γ–Fe₂O₃) and polystyrene. The magnetic nanoparticles were pretreated by surface modification for introducing double bonds onto the particles. In the polymerization, magnetic nanoparticles were continuously supplied to the system for a certain period after the initiation of polymerization at various pH. Dissociation degrees of ionizable groups in the initiator molecules were controlled through pH by changing NH₃ concentrations at a constant NH₄Cl concentration. Selection of suitable pH in the polymerization could produce polymer particles that perfectly incorporated the supplied magnetic nanoparticles. The magnetic polymer particles had a coefficient of variation of size distribution as low as 4.3% with an average diameter of 515 nm and a saturation magnetization of 7.3 emu/g-sample. Electrophoresis measurements indicated that the magnetic polymer particles had an isoelectric point of pH 4.1.     

Synthesis,characterization and catalytic performance of core‐shell structure magnetic Fe3O4/P(GMA‐EGDMA)‐NH2/HPG‐COOH‐Pd catalyst

A strategy has been developed for the synthesis, characterization and catalysis of magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd core‐shell structure supported catalyst. The P(GMA‐EGDMA) polymer layer was coated on the surface of hollow magnetic Fe₃O₄ microspheres through the effect of KH570. The core‐shell magnetic Fe₃O₄/P(GMA‐EGDMA) modified by ‐NH₂ could be grafted with HPG. Then, the hyperbranched glycidyl (HPG) with terminal ‐OH were modified by ‐COOH and adsorbed Pd nanoparticles. The hyperbranched polymer layer not only protected the Fe₃O₄ magnetic core from acid–base substrate corrosion, but also provided a number of functional groups as binding sites for Pd nanoparticles. The prepared catalyst was characterized by UV–vis, TEM, SEM, FTIR, TGA, ICP‐OES, BET, XRD, DLS and VSM. The catalytic tests showed that the magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd catalyst had excellent catalytic performance and retained 86% catalytic efficiency after 8 consecutive cycles.     

Iron oxide modified with pyridyl‐triazole ligand for stabilization of gold nanoparticles: An efficient heterogeneous catalyst for A3 coupling reaction in water

Fe₃O₄ nanoparticles were modified with pyridyl‐triazole ligand and the new magnetic solid was applied for the stabilization of very small and uniform gold nanoparticles. The resulting magnetic material, Fe₃O₄@PT@Au, was characterized using various methods. These gold nanoparticles on a magnetic support were applied as an efficient heterogeneous catalyst for the three‐component reaction of amines, aldehydes and alkynes (A³ coupling) in neat water with 0.01 mol% Au loading. Using magnetic separation, this catalyst could be recycled for seven consecutive runs with very small decrease in activity. Characterization of the reused catalyst did not show appreciable structural modification.     

Magnetic fluids’ stability improved by oleic acid bilayer-coated structure via one-pot synthesis

To improve the magnetic fluids’ stability and demonstrate the relationships between the bilayercoated structure and the stability, a simple method was proposed for preparingoleic acid bilayercoated Fe₃O₄ magnetic fluids. The hydrophilic Fe₃O₄ nanoparticles coated with the bilayer-oleic acid were synthesised by a one-pot process through the chemical co-precipitation under alkaline conditions. Next, the hydrophilic Fe₃O₄ particles were transformed to hydrophobic particles via carboxyl-protonated modification. Carboxyl-protonated modification was found to be a reversible process, i.e. the lipophilicity of the coated Fe₃O₄ nanoparticles could be controlled by protonating/ deprotonating the terminal carboxyl group. In addition, the space steric effect could be significantly enhanced by maximising the oleic acid adsorption and increasing the thickness of the coated layer, resulting in the oleic acid bilayer-coated Fe₃O₄ nanoparticles exhibiting better performance in the stability of the hexanemagnetic fluids than oleic acid monolayer-coated Fe₃O₄ nanoparticles.     

用于检测重金属离子的磁性荧光复合微球

采用静电逐层自组装的方法,首先将PSS和PAH聚电解质交替沉积在CaCO₃中空微球表面,然后将Fe₃O₄磁性纳米粒子与CdSe量子点负载在中空微球表面不同的聚电解质层中,制备出具有磁性和荧光双重功能的复合微球,并将其作为荧光离子探针,研究了其对Cu²⁺和Pb²⁺离子检测的灵敏度、选择性及可行性。结果表明,复合微球显示出良好的磁性和荧光性能,对Cu²⁺和Pb²⁺离子的检测具有较高的灵敏度和选择性。尤为重要的是,可通过磁分离的方法将微球快速地从待测液中回收,从而能够避免量子点对环境造成的二次污染。     

Facile Solvothermal Synthesis of Mesostructured Fe3O4/Chitosan Nanoparticles as Delivery Vehicles for pH‐Responsive Drug Delivery and Magnetic Resonance Imaging Contrast Agents

We report a facile fabrication of a host–metal–guest coordination‐bonding system in a mesostructured Fe₃O₄/chitosan nanoparticle that can act as a pH‐responsive drug‐delivery system. The mesostructured Fe₃O₄/chitosan was synthesized by a solvothermal approach with iron(III) chloride hexahydrate as a precursor, ethylene glycol as a reducing agent, ammonium acetate as a porogen, and chitosan as a surface‐modification agent. Subsequently, doxorubicin (DOX), acting as a model drug (guest), was loaded onto the mesostructured Fe₃O₄/chitosan nanoparticles, with chitosan acting as a host molecule to form the NH₂? Zn^II? DOX coordination architecture. The release of DOX can be achieved through the cleavage of coordination bonds that are sensitive to variations in external pH under weakly acidic conditions. The pH‐responsive nature of the nanoparticles was confirmed by in vitro releases and cell assay tests. Furthermore, the relaxation efficiency of the nanoparticles as high‐performance magnetic resonance imaging contrast agents was also investigated. Experimental results confirm that the synthesized mesostructured Fe₃O₄/chitosan is a smart nanovehicle for drug delivery owing to both its pH‐responsive nature and relaxation efficiency.     

Heavy Metal Removal from Synthetic Solutions with Magnetic Beads Under Magnetic Field

The aim of this study is to prepare magnetic beads which can be used for the removal of heavy metal ions from synthetic solutions. Magnetic poly(ethylene glycol dimethacrylate‐vinyl imidazole) [m‐poly(EGDMA‐VIM)] beads were produced by suspension polymerization in the presence of magnetite Fe₃O₄ nano‐powder. The specific surface area of the m‐poly(EGDMA‐VIM) beads was found to be 63.1 m²/g with a size range of 150–200 µm in diameter and the swelling ratio was 85%. The average Fe₃O₄ content of the resulting m‐poly(EGDMA‐VIM) beads was 12.4%. The maximum binding capacities of the m‐poly(EGDMA‐VIM) beads were 32.4 mg/g for Cu²⁺, 45.8 mg/g for Zn²⁺, 84.2 mg/g for Cd²⁺and 134.5 mg/g for Pb²⁺. The affinity order on mass basis is Pb²⁺>Cd²⁺>Zn²⁺>Cu²⁺. Equilibrium data agreed well with the Langmuir model. pH significantly affected the binding capacity of the magnetic beads. Binding of heavy metal ions from synthetic wastewater was also studied. The binding capacities were 26.2 mg/g for Cu²⁺, 33.7 mg/g for Zn²⁺, 54.7 mg/g for Cd²⁺ and 108.4 mg/g for Pb²⁺. The magnetic beads could be regenerated up to about 97% by treating with 0.1 M HNO₃. These features make m‐poly(EGDMA‐VIM) beads a potential candidate for support of heavy metal removal under magnetic field.     

Adsorption of uranium ions from aqueous solution by amine-group functionalized magnetic Fe3O4 nanoparticle

The magnetic Fe₃O₄ nanoparticle was functionalized by covalently grafting amine group with (3-aminopropyl) trimethoxy silane, and the Fe₃O₄–NH₂ nanoparticle and the Fe₃O₄ nanoparticle were characterized by Fourier transform infrared, and X-ray diffraction. And the results indicated the amine-group was immobilized successfully on the surface of Fe₃O₄. The adsorption behavior of uranium from aqueous solution by the Fe₃O₄ nanoparticle and the Fe₃O₄–NH₂ nanoparticle was investigated using batch experiments. The pH of initial aqueous solution at 5.0 and 6.0 were in favour of adsorption of uranium, and the adsorption percentage of uranium by the Fe₃O₄ nanoparticle and the Fe₃O₄–NH₂ nanoparticle were 81.2 and 95.6 %, respectively. In addition, the adsorption of uranium ions could be well-described by the Langmuir, Freundlich isotherms and pseudo-second kinetic models. The monolayer adsorption maximum capacity of the Fe₃O₄ nanoparticle and the Fe₃O₄–NH₂ nanoparticle were 85.35 and 268.49 mg/g at 298.15 K, respectively, which indicate the adsorption capacity the Fe₃O₄ nanoparticle was improved by amine functionalization.     

Preparation and characterization of flexible polyurethane foam nanocomposites reinforced by magnetic core-shell Fe3O4@APTS nanoparticles

Novel magnetic polyurethane flexible foam nanocomposites were synthesized by incorporation of aminopropyltriethoxysilane (APTS) functionalized magnetite nanoparticles (MNPs) via one-shot method. The functionalized MNPs (Fe₃O₄@APTS) were synthesized by co-precipitation of the Fe²⁺ and Fe³⁺ with NH₄OH and further functionalization with APTS onto the surface of MNPs by sol–gel method. The magnetic core-shell NPs were used up to 3.0 % in the foam formulation and the magnetic nanocomposites prepared successfully. The results of thermogravimetric analysis (TGA) showed an increasing in thermal stability of polyurethane nanocomposite foam at initial, 5 and 10 %, and maximum thermal decomposition temperatures by incorporation of Fe₃O₄@APTS. In addition SEM images revealed the uniformity of the foam structures and decreasing in pore sizes. Furthermore, VSM result showed super paramagnetic behavior for Fe₃O₄@APTS-PU nanocomposites.     

纳米Fe_3O_4及钴离子掺杂Fe_3O_4:有机碱共沉淀制备和磁性质

以有机碱四甲基氢氧化铵(TMAH)为沉淀剂合成了纳米Fe3O4和Co2+掺杂的纳米Fe3O4粒子。分别讨论了碱用量,铁盐溶液浓度,反应温度,有机碱及PEG-4000的分散性等因素对纳米Fe3O4的形貌影响。结果表明,所合成的纳米Fe3O4为30nm左右的反尖晶石型面心立方结构,有机碱除了起沉淀剂作用,还能够提高纳米Fe3O4的分散性。本文还讨论了不同Co2+掺入量的纳米Fe3O4粒子的磁性质,结果表明Co2+掺杂的纳米Fe3O4粒子的矫顽力在不同掺入量的下有较大的改变。当Co2+掺入量为10.0%时,纳米Fe3O4的矫顽力达到最大值,为1628Oe。     

Preparation,characterization and heterogeneous catalytic applications of GO/Fe3O4/HPW nanocomposite in chemoselective and green oxidation of alcohols with aqueous H2O2

Graphene oxide ‐ Fe₃O₄ ‐ NH₃⁺H₂PW₁₂O₄₀ ^‐ magnetic nanocomposite (GO/Fe₃O₄/HPW) was prepared by linking amino ‐ functionalized Fe₃O₄ nanoparticles (Fe₃O₄ ‐ NH₂) on the graphene oxide (GO), and then grafting 12 ‐ tungstophosphoric acid (H₃PW₁₂O₄₀) on the graphene oxide ‐ magnetite hybrid (GO ‐ Fe₃O₄ ‐ NH₂). The obtained GO/Fe₃O₄/HPW nanocomposite was well characterized with different techniques such as FT ‐ IR, TEM, SEM, XRD, EDX, TGA ‐ DTA, AGFM, ICP and BET measurements. The used techniques showed that the graphene oxide layers were well prepared and the various stages of preparation of the GO/Fe₃O₄/HPW nanocomposites successfully completed. This new nanocomposite displayed excellent performance as a heterogeneous catalyst in the oxidation of alcohols with H₂O₂. The as ‐ prepared GO/Fe₃O₄/HPW catalyst was more stable and recyclable at least five times without significantly reducing its catalytic activity.     

Synthesis and characterization of amino-functionalized single magnetic core–silica shell composites

The thermal decomposition approach, reverse micro-emulsion system and surface modification technique had been successfully used to synthesis single magnetic core Fe₃O₄@Organic Layer@SiO₂–NH₂ complex microspheres. The magnetization of the magnetic microspheres core could be easily tuned between 28 and 56 emu/g by adjusting the amount of 2-mercaptobarbituric acid. It was found that the Organic Layer to some extent had a protective effect on avoiding Fe₃O₄ being oxidized into Fe₂O₃. Each Fe₃O₄@Organic Layer microsphere could be coated uniformly by about 30 nm of silica shell. The average diameter of the Fe₃O₄@Organic Layer@SiO₂ composites was about 538 nm. The saturation magnetization of the Fe₃O₄@Organic Layer@SiO₂ complex microspheres was 12.5% less than magnetic microspheres cores. The Fe₃O₄@Organic Layer@SiO₂–NH₂ composites possessed a huge application potentiality in specificity enriching and separating biological samples.     

Highly Sensitive and Selective Fluorescence “Turn-On” Detection of Pb (II) Based on Fe3O4@Au–FITC Nanocomposite

New nanocomposites, Fe₃O₄@Au–FITC, were prepared and explored to develop a fluorescent detection of Pb²⁺. The Fe₃O₄@AuNPs–FITC nanocomposites could be etched by Pb²⁺ in the presence of Na₂S₂O₃, leading to fluorescence recovery of FITC quenched by Fe₃O₄@Au nanocomposites. With the increase of Pb²⁺ concentration, the fluorescence recovery of Fe₃O₄@AuNPs–FITC increased gradually. Under optimized conditions, a detection limit of 5.2 nmol/L of Pb²⁺ with a linear range of 0.02–2.0 µmol/L were obtained. The assay demonstrated negligible response to common metal ions. Recoveries of 98.2–106.4% were obtained when this fluorescent method was applied in detecting Pb²⁺ spiked in a lake-water sample. The above results demonstrated the high potential of ion-induced nanomaterial etching in developing robust fluorescent assays.     

Individual and Simultaneous Voltammetric Determination of Cd(II), Cu(II) and Pb(II) Applying Amino Functionalized Fe3O4@Carbon Microspheres Modified Electrode

Amino‐functionalized Fe₃O₄@carbon microspheres (NH₂?Fe₃O₄@C) were prepared and the electrochemical sensor was constructed using NH₂?Fe₃O₄@C modified glassy carbon electrodes (GCE) to determine toxic heavy metals in aqueous solution. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the structure and phase of NH₂?Fe₃O₄@C. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results indicate that NH₂?Fe₃O₄@C modified GCE possesses large active area and excellent electron transfer. Under optimized electrochemical condition, Cd(II), Pb(II) and Cu(II) were determined using NH₂?Fe₃O₄@C modified GCE. The electrode through amino functionalization exhibits higher sensitivity and lower detection limit toward Cd(II) and Cu(II) due to the acid‐base pairing interaction between the electron‐rich ?NH₂ ligand and the electron‐deficient heavy metal ions. Compared with other similar results reported in the literature, the NH₂?Fe₃O₄@C modified electrode exhibits wider linear response range while with comparable lower detection limit. It also exhibits excellent stability, reproducibility and anti‐interference ability.