Silica-coated Fe3O4 Magnetic Nanoparticles Research Articles

Magnetic silica particles functionalized with guanidine derivatives for microwave-assisted transesterification of waste oil

This study aimed to develop a facile synthesis procedure for heterogeneous catalysts based on organic guanidine derivatives superbases chemically grafted on silica-coated Fe3O4 magnetic nanoparticles. Thus, the three organosilanes that were obtained by reacting the selected carbodiimides (N,N′-dicyclohexylcarbodiimide (DCC), N,N′-diisopropylcarbodiimide (DIC), respectively 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) with 3-aminopropyltriethoxysilane (APTES) were used in a one-pot synthesis stage for the generation of a catalytic active protective shell through the simultaneous hydrolysis/condensation reaction with tetraethyl orthosilicate (TEOS). The catalysts were characterized by FTIR, TGA, SEM, BET and XRD analysis confirming the successful covalent attachment of the organic derivatives in the silica shell. The second aim was to highlight the capacity of microwaves (MW) to intensify the transesterification process and to evaluate the activity, stability, and reusability characteristics of the catalysts. Thus, in MW-assisted transesterification reactions, all catalysts displayed FAME yields of over 80% even after 5 reactions/activation cycles. Additionally, the influence of FFA content on the catalytic activity was investigated. As a result, in the case of Fe3O4@SiO2-EDG, a higher tolerance towards the FFA content can be noticed with a FAME yield of over 90% (for a 5% (weight) vs oil catalyst content) and 5% weight FFA content.

Synthesis of various 2-benzylbenzoxazole derivatives catalyzed by deep eutectic solvent-supported onto magnetic nanoparticles

Magnetic nanoparticle supported deep eutectic solvents have been synthesized by preparing and grafting [Urea]4[ZnCl2] deep eutectic solvent onto the surface of silica-coated Fe3O4 magnetic nanoparticles using 3‐ chloropropyltrimethoxysilane as a linker. DES@MNP was fully characterized using scanning and transmission electron microscopies, Fourier transforms infrared, energy-dispersive X-ray spectroscopies, vibrating sample magnetometer X-ray diffraction, and thermogravimetric analysis. In this study, we have developed the synthesis of 2-benzylbenzoxazole via condensation reaction of 2-nitrophenols and acetophenones using a magnetic nanoparticle supported [Urea]4[ZnCl2] deep eutectic solvent as a novel, green and efficient catalyst. In the presence of 1,4-diazabicyclo[2.2.2]-octane, elemental sulfur acted as an excellent reductant in promoting oxidative rearranging coupling in this reaction. The reaction has been conducted via the stirring method and the reaction conditions were surveyed (16 h, 130 °C, acetophenone, 2-nitrophenol, DABCO and sulfur molar ratio of 2:1:1:3, 10 mol% DES@MNP catalyst). Six 2-benzylbenzoxazole derivatives have been synthesized via this method with good yield (86-91%). The structure of the pure product has been confirmed through FT-IR, 1H NMR, 13C NMR, and GC-MS methods. More importantly, DES@MNP has been separated from the reaction mixture by a magnet and reused over five consecutive runs without significant loss of catalytic activity.

Fluorescent nanoparticles light up rocks’ pores

A team of researchers has developed a simple, robust method for imaging the pores in rocks using magnetic, fluorescent nanoparticles (ACS Earth Space Chem. 2019, DOI: 10.1021/acsearthspacechem.9b00071). Measuring the porosity of rocks is important in petroleum engineering and for understanding geological carbon dioxide sequestration, groundwater flow, and the use of rocks as building materials. Na Li of the Chengdu University of Technology and colleagues used silane molecules to covalently attach a dye, rhodamine B, to silica-coated Fe3O4 magnetic nanoparticles. The team then used a strong magnetic field to pull the nanoparticles through rock samples about 30 µm thick. The samples showed stronger fluorescence than others that were loaded with nanoparticles that were physically coated with dye, without the silane linker. To measure the sizes of the pores and pore junctions, the team made nanoparticles ranging from 65 to 120 nm in size, each of which had different peak fluorescence wavelengths,

Chiral amine and macrocycle fabricated magnetic nanoparticle asymmetrically catalyzed direct aldol reaction

Chiral amine and their derivatives have been proved to be powerful organocatalysts for asymmetric transformations. There is a trend to combine organocatalyst with sustainable matrix, such as, magnetic nanoparticles (MNPs) to form a selective and recyclable catalyst. Therefore, silica-coated Fe3O4 MNP was fabricated to establish a large macrocycle with glutamate (MNP-17 and 18), Pro-Glu (MNP-21), or cyclohexyl-1,2-diamine (MNP-28, 29, and 30). Their bifunctional enamine activities were evaluated with direct aldol reaction. Among them, MNP-30 having the largest macrocyclic ring and the longest lipophilic chain achieved better yield and ee value (up to 96%). It seems the affinity toward substrate was enhanced by the macrocyclic effect. The rigidity of cyclohexyl-1,2-diamine contributed the enantioselectivity. Moreover, MNP-30 is recyclable and stayed on high activity and enantioselectivity after 3 recycles.

S-Triazinium-based ionic liquid immobilized on silica-coated Fe3O4 magnetic nanoparticles: an efficient and magnetically separable heterogeneous catalyst for synthesis of 2-amino-4,8-dihydropyrano[3,2-b]pyran-3-carbonitrile derivatives for antioxidant and antifungal evaluation studies

We have described a new method to heterogenize s-triazine catalyst by easy preparation of ionic liquid-based s-triazine-immobilized silica-coated Fe3O4 magnetic nanoparticles [Fe3O4@SiO2-s-triazinium chloride]. The structure of the newly prepared nanoparticles was characterized by Fourier transform infrared, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray method, vibrating sample magnetometery and thermo-gravimetric analysis. These nanoparticles were identified as an efficient catalyst for one-pot three-component synthesis of 4,8-dihydropyrano[3,2-b]pyran derivatives in excellent yields. The catalyst was easily separated by magnetic decantation, and the recovered nanoparticles were reused for four fresh runs without any significant loss of catalytic activity. The synthesized dihydropyrano[3,2-b]pyrans were evaluated for their antioxidant and antifungal activities and found they are relatively active.

A non-enzymatic electrochemical immunoassay for quantitative detection of Escherichia coli O157:H7 using Au@Pt and graphene

Herein, a non-enzymatic sandwich-type electrochemical immunoassay was fabricated for quantitative monitoring of Escherichia coli O157:H7 (E. coli O157:H7). Silica coated Fe3O4 magnetic nanoparticles (Fe3O4@SiO2) were modified with mouse anti-E. coli O157:H7 monoclonal antibody (Ab1) to act as capture probes to reduce detection time and increase the sensitivity of the immunoassay. The Au@Pt nanoparticles were loaded on neutral red (NR) functionalized graphene to form composite complex rGO-NR-Au@Pt. rGO-NR-Au@Pt has high specific surface area and good biocompatibility. rGO-NR-Au@Pt was used as the carriers of detection antibodies (Ab2). Au@Pt catalyzed the reduction of hydrogen peroxide (H2O2) to detection of E. coli O157:H7 with the thionine (TH) as electron mediator to effectually amply the current signal. Under the optimized conditions, a linear relationship between the reduction peak current change (ΔIpc) and the logarithm of the E. coli O157:H7 concentration is obtained in the range from 4.0 × 103 to 4.0 × 108 CFU mL−1 and the limit of detection (LOD) is 4.5 × 102 CFU mL-1 at a signal-to-noise ratio of 3. The immunoassay exhibits acceptable specificity, reproducibility and stability on the detection of E. coli O157:H7. Furthermore, the immunoassay showed good performance in pork and milk samples. The results suggest that this immunoassay will be promising in the food safety area.

Photodegradation of 2,4-dichlorophenol by supported Pd(X2) catalyst (X = Cl, Br, N3): a HOMO manipulating point of view.

Three different palladium(II) complexes with ligands containing nitrogenized aromatic rings were investigated theoretically as model to obtain the computational band gap energies. The results demonstrated promising possibility for designing palladium(II) complexes with photocatalytic properties at visible light irradiation. Deliberated products were synthesized via grafting on the silica-coated Fe3O4 magnetic nanoparticles (Fe3O4@SiO2). Formation of complexes on the surface of Fe3O4@SiO2, as insoluble and reusable photocatalysts, was proved by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric (TGA), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), transmission electron microscope (TEM), and scanning electron microscopy (SEM) analyses. The trend of the band gap energies of prepared structures was calculated via experimental and theoretical methods. The photocatalytic capability of these nanoparticles was investigated in degradation of 2,4-dichlorophenol by means of HPLC analysis. A tentative reaction mechanism for the formation of intermediates was proposed. Graphical abstract ᅟ.

Efficient synthesis of new pyrano[3,2-b]pyran derivatives via Fe3O4@SiO2-IL-Fc catalyzed three-component reaction

Abstract Ferrocene-containing ionic liquid supported on silica-coated Fe3O4 magnetic nanoparticles (nano Fe3O4@SiO2-IL-Fc), a novel heterogeneous nanocatalyst, was synthesized. The structure of the catalyst was characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction patterns (XRD), energy-dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FE-SEM). The novel nanomagnetic catalyst was used in the one-pot synthesis of pyrano[3,2-b]pyran derivatives by the three-component reaction of various aldehydes, malononitrile and kojic acid or chlorokojic acid at room temperature under ultrasonic irradiation. This new method has many advantages such as simplicity, short reaction times, high yields, easy workup and easy purification. Also, the nanocatalyst can be separated on an external magnet and reused for at least six consecutive runs without any significant loss of its catalytic activity.

Synthesis of the first magnetic nanoparticles with a thiourea dioxide-based sulfonic acid tag: application in the one-pot synthesis of 1,1,3-tri(1H-indol-3-yl) alkanes under mild and green conditions

Synthesis of the first thiourea dioxide-based silica-coated Fe3O4magnetic nanoparticles as an exquisite, extraordinary and effective catalyst for the synthesis of 1,1,3-tri(1H-indol-3-yl) alkane derivatives.

N-Propylcarbamothioyl benzamide complex of Bi(III) supported on superparamagnetic Fe3O4/SiO2 nanoparticles as a highly efficient and magnetically recoverable heterogeneous nanocatalyst for the one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones (DHPMs) via the Biginelli reaction

The N-propylcarbamothioyl benzamide complex of Bi(III) immobilized on silica coated Fe3O4 magnetic nanoparticles has been prepared as a highly efficient and recyclable heterogeneous nanocatalyst using simple processes for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones via a one-pot multicomponent condensation reaction of urea, aldehydes and β-dicarbonyl compounds under solvent-free conditions at 100 °C. The structural and magnetic properties of the nanocatalyst were characterized using various techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, vibrating sample magnetometery and elemental analyses. Also, this nanocatalyst can be easily recovered by a magnetic field and reused for subsequent reactions for at least five times without deterioration in catalytic activity.

Highly efficient degradation of hazardous dyes in aqueous phase by supported palladium nanocatalyst—A green approach

In this report, supported palladium nanocatalyst on silica coated Fe3O4 magnetic nanoparticles was employed as a novel catalyst towards the degradation of methyl red, methyl orange and methylene blue. The reaction between palladium nanoparticles and dissolved oxygen in acidic media produced palladium hydroperoxide, which has strong ability to oxidize the proposed dyes. The results showed that, the concentration of dyes changes exponentially with time and Langmuir–Hinshelwood model was used to describe the catalytic decolorization of these dyes in the presence of palladium nanoparticles. The efficiency of the catalyst and the effects of different variables such as initial pH, catalyst loading and temperature have been discussed in detail. Degradation sequence of dyes was further investigated by liquid chromatography–mass spectroscopy technique, which confirmed the degradation of dyes to non-toxic end products.

Preparation of Fe3O4 encapsulated-silica sulfonic acid nanoparticles and study of their in vitro antimicrobial activity

A simple and efficient method for the functionalization of silica-coated Fe3O4 magnetic nanoparticles (Fe3O4@SiO2) using chlorosulfonic acid is described. The prepared compounds were screened for antibacterial activity against Escherichia coli (E. coli ATCC 25922) and Staphylococcus aureus (S. aureus ATCC 25923) under UV-light and dark conditions. It was found that the Fe3O4@SiO2–SO3H was significantly indicated the higher photocatalytic inactivation than both Fe3O4 and Fe3O4@SiO2 against E. coli in compared with S. aureus. Furthermore, the inactivation efficiency against both organisms under light conditions has been higher than this efficiency under dark conditions.

Sugar and pH dual-responsive snap-top nanocarriers based on mesoporous silica-coated Fe3O4 magnetic nanoparticles for cargo delivery.

A facile strategy to prepare snap-top magnetic nanocarriers has been developed where ultrasmall superparamagnetic Fe3O4 nanoparticles were used as the core with mesoporous silica as the shell followed by the covalent installation of a layer of β-cyclodextrins on the outer surfaces. The smart hybrid nanomaterials showed remarkable pH- and sugar-responsive cargo release property and low cytotoxicity as proved by an MTT assay with HEK293T cell lines.

Preparation and Characterization of Ag-Deposited Silica-Coated Fe<sub>3</sub>O<sub>4</sub> Magnetic Nanoparticles with Recycling Antibacterial Properties

In this paper, a novel anti-bacterial agent of Ag-deposited silica-coated Fe3O4 magnetic nanoparticles was prepared by a template-activated strategy, which possess a silica coated magnetic core and silver nanoparticles on the outer shell. The as-synthesized nanoparticles have been characterized by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX). The obtained products exhibited dispersibility and high magnetization, which also show a good recycling antibacterial activity, and the antibacterial rates against Escherichia coli was all 100 % for 3 cycles.

In situ synthesis and characterization of fluorinated polybenzobisoxazole/silica-coated magnetic Fe3 O4 nanocomposites exhibiting enhanced electromagnetic wave absorption property

A series of magnetic fluorinated polybenzobisoxazole (6FPBO)/silica-coated Fe3O4 magnetic nanoparticles composites were synthesized through in-situ polymerization. The structure and morphology of the obtained nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, and scanning electronic microscope (SEM). The SEM images indicated that the crosslinking structure is formed in magnetic 6FPBO nanocomposites. The magnetic and electromagnetic properties of magnetic 6FPBO nanocomposites in the 2–18 GHz frequency range were characterized by vibration sample magnetometer and vector network analyzer, respectively. The calculated reflection loss of the as-prepared magnetic 6FPBO nanocomposites showed that the best microwave absorption reached to −20 dB at 17 GHz with a matching thickness of 3.00 mm. POLYM. COMPOS., 36:884–891, 2015. © 2014 Society of Plastics Engineers

Rapid screening and analysis of alcohol dehydrogenase binders from Glycyrrhiza uralensis root extract using functionalized magnetic nanoparticles coupled with HPLC−MS/MS

Alcohol dehydrogenase (ADH) is a key enzyme that converts ethanol into acetaldehyde. Its binders could be used to efficiently treat human toxic alcohol poisoning and suppress the acetaldehyde accumulation in alcohol hypersensitive alcoholics. In the present study, a new assay based on ADH-functionalized magnetic nanoparticles coupled with high-performance liquid chromatography − tandem mass spectrometry (HPLC−MS/MS) was developed for the rapid screening and identification of ADH binders. ADH was immobilized on silica-coated Fe3O4 magnetic nanoparticles via covalent bonds and the synthesized nanoparticles were characterized by TEM, XRD, FT-IR, and VSM. The amount of bound ADH onto magnetic nanoparticles was 80.6 μg/mg. The optimum temperature and pH for the enzymatic activity of immobilized ADH were 25 °C and 7.0, respectively. The relative activity of immobilized ADH remained 68.14% after 10 times of recycle, which exhibited good durability. Nine compounds with ADH-binding activity were screened and identified in Glycyrrhiza uralensis root extracts, among which seven compounds were first screened and identified. Experimental results proved that the proposed method could rapidly screen ADH binders from complex mixtures.

A highly efficient nano-Fe3O4 encapsulated-silica particles bearing sulfonic acid groups as a solid acid catalyst for synthesis of 1,8-dioxo-octahydroxanthene derivatives

The functionalization of silica-coated Fe3O4 magnetic nanoparticles (Fe3O4@SiO2) using chlorosulfonic acid were afforded sulfonic acid-functionalized magnetic Fe3O4 nanoparticles (Fe3O4@SiO2–SO3H) that can be applied as an organic–inorganic hybrid heterogeneous catalyst. The used Fe3O4 magnetic nanoparticles are 18–30 nm sized that was rapidly functionalized and can be used as catalyst in organic synthesis. The prepared nanoparticles were characterized by X-ray diffraction analysis, magnetization curve, scanning electron microscope, dynamic laser scattering, and FT-IR measurements. The resulting immobilized catalysts have been successfully used in the synthesis of 1,8‐dioxo-octahydroxanthene derivatives under solvent free condition. This procedure has many advantages such as; a much milder method, a shorter reaction time, a wide range of functional group tolerance, and absence of any tedious workup or purification. Other remarkable features include the catalyst can be reused at least five times without any obvious change in its catalytic activity. This procedure also avoids hazardous reagents/solvents, and thus can be an eco-friendly alternative to the existing methods.Graphical A highly efficient nano-Fe3O4 encapsulated-silica particles bearing sulfonic acid groups as a solid acid catalyst for synthesis of 1,8-dioxo-octahydroxanthene derivatives Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-013-2026-2) contains supplementary material, which is available to authorized users.

Magnetic field intensified bi-enzyme system with in situ cofactor regeneration supported by magnetic nanoparticles

Efficient dynamic interactions among cofactor, enzymes and substrate molecules are of primary importance for multi-step enzymatic reactions with in situ cofactor regeneration. Here we showed for the first time that the above dynamic interactions could be significantly intensified by exerting an external alternating magnetic field on magnetic nanoparticles-supported multi-enzymatic system so that the inter-particle collisions due to Brownian motion of nanoparticles could be improved. To that end, a multienzyme system including glutamate dehydrogenase (GluDH), glucose dehydrogenase (GDH) and cofactor NAD(H) were separately immobilized on silica coated Fe3O4 magnetic nanoparticles with an average diameter of 105nm, and the effect of magnetic field strength and frequency on the kinetics of the coupled bi-enzyme reaction was investigated. It was found that at low magnetic field frequency (25Hz and 100Hz), increasing magnetic field strength from 9.8 to 161.1Gs led to only very slight increase in reaction rate of the coupled bi-enzyme reaction expressed by glucose consumption rate. At higher magnetic field of 200Hz and 500Hz, reaction rate increased significantly with increase of magnetic field strength. When the magnetic field frequency was kept at 500Hz, the reaction rate increased from 3.89μM/min to 8.11μM/min by increasing magnetic field strength from 1.3 to 14.2Gs. The immobilized bi-enzyme system also showed good reusability and stability in the magnetic field (500Hz, 14.2Gs), that about 46% of original activity could be retained after 33 repeated uses, accounting for totally 34 days continuous operation. These results demonstrated the feasibility in intensifying molecular interactions among magnetic nanoparticle-supported multienzymes by using nano-magnetic stirrer for efficient multi-step transformations.

Synthesis of Carboxyl-functionalized Silica Coated Fe3O4 Magnetic Nanoparticles and Their Adsorption Ability of Cu2+

在以共沉淀法制备的磁性纳米Fe 3 O 4 粒子(Magnetic nanoparticles, MNP)表面进行了化学修饰, 制备了一种新型富含羧基功能团的核壳磁性纳米吸附剂(Carboxylic functionalized Fe 3 O 4 magnetic nanoparticles, CMNP). 利用透射电子显微镜(TEM)、 X射线衍射仪(XRD)、 X射线能量色散谱(EDS)、 振动样品磁强计(VSM)、 傅里叶变换红外光谱(FIIR)和热重分析仪(TGA)对CMNP的形貌、 结构、 化学组成和磁性能进行了表征, 并考察了吸附剂对Cu 2+ 的吸附性能, 研究了溶液pH值、 吸附时间和Cu 2+ 初始浓度对吸附性能的影响. 结果表明, 羧基化核壳磁性纳米Fe 3 O 4 颗粒的平均粒径为15 nm, 具有良好的超顺磁性, 饱和磁化强度为41.84 A·m 2 /kg, 在10 min中内可达到吸附平衡, 在pH=7.0时吸附量最高, 吸附等温数据符合Langmuir模型, 饱和吸附量 q m = 43.48 mg/g.

Ag-deposited silica-coated Fe3O4 magnetic nanoparticles catalyzed reduction of p-nitrophenol

In this paper, a novel approach was successfully developed for advanced catalyst Ag-deposited silica-coated Fe3O4 magnetic nanoparticles, which possess a silica coated magnetic core and growth active silver nanoparticles on the outer shell using n-butylamine as the reductant of AgNO3 in ethanol. The as-synthesized nanoparticles have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectra (FT-IR), vibration sample magnetometer (VSM), and have been exploited as a solid phase catalyst for the reduction of p-nitrophenol in the presence of NaBH4 by UV–vis spectrophotometry. The obtained products exhibited monodisperse and bifunctional with high magnetization and excellent catalytic activity towards p-nitrophenol reduction. As a result, the as-obtained nanoparticles showed high performance in catalytic reduction of p-nitrophenol to p-aminophenol with conversion of 95% within 14min in the presence of an excess amount of NaBH4, convenient magnetic separability, as well as remained activity after recycled more than 6 times. The Fe3O4@SiO2–Ag functional nanostructure could hold great promise for various catalytic reactions.