Synthesis of magnetically separable Sn doped magnetite/silica core-shell structure and photocatalytic property

Sn doped Fe₃O₄/SiO₂ core-shell structures with the magnetic and photocatalytic properties have been successfully synthesized using Fe₃O₄ microspheres as the precursor. The morphology, phase and structure of the bifunctional products were investigated by X-ray powder diffraction, transmission electron microscopy, selected-area electron diffraction, high-resolution transmission electron microscopy, energy dispersive spectroscopy, and scanning electron microscopy. The effects of the amount and hydrolysis rate of tetraethyl orthosilicate on the preparation of the Fe₃O₄/SiO₂ core-shell structures were investigated. Low concentration and slow hydrolysis rate of tetraethyl orthosilicate were useful to obtain the uniform silica coated Fe₃O₄. The magnetic measurements indicated that the Sn doped Fe₃O₄/SiO₂ core-shell structures showed ferromagnetic property and the magnetic saturation value slightly decreased after coated the silica layer. The magnetic Sn doped Fe₃O₄/SiO₂ core-shell structures exhibited good photocatalytic activity in the degradation of methyl orange and could be separated by applying an appropriate magnetic field.     

Simple synthesis of functionalized superparamagnetic magnetite/silica core/shell nanoparticles and their application as magnetically separable high-performance biocatalysts

Uniformly sized silica-coated magnetic nanoparticles (magnetite@silica) are synthesized in a simple one-pot process using reverse micelles as nanoreactors. The core diameter of the magnetic nanoparticles is easily controlled by adjusting the w value ([polar solvent]/[surfactant]) in the reverse-micelle solution, and the thickness of the silica shell is easily controlled by varying the amount of tetraethyl orthosilicate added after the synthesis of the magnetite cores. Several grams of monodisperse magnetite@silica nanoparticles can be synthesized without going through any size-selection process. When crosslinked enzyme molecules form clusters on the surfaces of the magnetite@silica nanoparticles, the resulting hybrid composites are magnetically separable, highly active, and stable under harsh shaking conditions for more than 15 days. Conversely, covalently attached enzymes on the surface of the magnetite@silica nanoparticles are deactivated under the same conditions.     

Study of mesoporous silica/magnetite systems in drug controlled release

Ordered mesoporous materials like SBA-15 have a network of channels and pores with well-defined size in the nanoscale range. This particular silica matrix pore architecture makes them suitable for hosting a broad variety of compounds in very promising materials in a range of applications, including drug release magnetic carriers. In this work, magnetic nanoparticles embedded into mesoporous silica were prepared in two steps: first, magnetite was synthesized by oxidation-precipitation method, and next, the magnetic nanoparticles were coated with mesoporous silica by using nonionic block copolymer surfactants as structure-directing agents. The materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), N(2) adsorption, and scanning electron microscopy (SEM). The influence of magnetic nanoparticles on drug release kinetics was studied with cisplatin, carboplatin, and atenolol under in vitro conditions in the absence and in the presence of an external magnetic field (0.25 T) by using NdFeB permanent magnet. The constant external magnetic field did not affect drug release significantly. The low-frequency alternating magnetic field had a large influence on the cisplatin release profile.     

Low-temperature synthesis of magnetically recoverable,superparamagnetic, photocatalytic,nanocomposite particles

A new, simple, low-temperature method for the synthesis of superparamagnetic, photocatalytic, nanocomposite particles for applications in the decomposition of pollutants in water is presented. The method is based on the coating of clusters of superparamagnetic maghemite (γ-Fe₂O₃) nanoparticles with a photocatalytic anatase layer using the hydrolysis of aqueous TiOSO₄. The clusters of an appropriate size between 100 and 200 nm form by the simultaneous agglomeration of the aminopropyl-triethoxy-silane-grafted maghemite nanoparticles with a size of approximately 15 nm in a suspension of diluted TiOSO₄. During a sudden increase of pH with the addition of NaOH the titania is heterogeneously nucleated at the cluster surfaces. If the hydrolysis was conducted at an elevated temperature of 90 °C, the titania layer was nanocrystalline anatase. The composition of the nanocomposite particles, i.e., the thickness of the anatase layer, can be controlled simply by changing the starting TiOSO₄/Fe₂O₃ ratio for low titania contents, and by multiple coatings to get high titania contents. The photocatalytic activity of the nanocomposites was evaluated in the photocatalytic decomposition of formic acid. The activity seems to increase with an increase in the thickness and the crystallinity of the anatase coating, whereas it decreased after the calcination of the as-synthesized nanocomposite. The coating of the maghemite nanoparticles with a thin layer of insulating silica also slightly improves the photocatalytic activity.     

The enhanced coercivity for the magnetite/silica nanocomposite at room temperature

Magnetite/silica nanocomposite was synthesized by a facile solvothermal processing at 150 °C for about 10 h. X-ray diffraction (XRD) analysis revealed the effect of annealing on the crystallinity of silica. Transmission electron microscopy (TEM) images showed the good dispersion of magnetite in the silica matrix. Magnetic properties of the nanocomposite were characterized by vibration sample magnetometer (VSM), and the enhanced coercivity was explained by the intrinsic anisotropy of the particles enhanced by the interparticle dipolar fields.     

Reconfigurable core-satellite nanoassemblies as molecularly-driven plasmonic switches

Molecular control of plasmon coupling is investigated in sub-100 nm assemblies composed of 13 nm gold "satellite" particles tethered by reconfigurable DNA nanostructures to a 50 nm gold "core" particle. Reconfiguration of the DNA nanostructures from a compact to an extended state results in blue shifting of the assembly plasmon resonance, indicating reduced interparticle coupling and lengthening of the core-satellite tether. Scattering spectra of the core-satellite assemblies before and after reconfiguration are compared with spectra calculated using a structural model that incorporates the core/satellite ratio determined by TEM imaging and estimates of tether length based upon prior measurements of interparticle separation in DNA linked nanoparticle networks. A strong correspondence between measured and simulated difference spectra validates the structural models that link the observed plasmon modulation with DNA nanostructure reconfiguration.     

Palladium was supported on superparamagnetic nanoparticles: A magnetically recoverable catalyst for Heck reaction

A novel and high-performance palladium-based catalyst for Heck reaction was prepared easily by the co-precipitation method. The catalyst was characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS) and atomic absorption spectrophotometry (AAS). The catalyst afforded a fast conversion of the 4-bromonitrobenzene to 4-nitrostilbene at a catalyst loading of 5 mol%, and the efficiency of the catalyst remains unaltered even after 6 repeated cycles. The excellent catalytic performance of the Pd/Fe₃O₄ catalyst might be attributed to the enhanced synergistic effect between Pd nanoparticles and magnetite.     

M13 bacteriophage-polymer nanoassemblies as drug delivery vehicles

Poly(caprolactone-b-2-vinylpyridine) (PCL-P2VP) coated with folate-conjugated M13 (FA-M13) provides a nanosized delivery system which is capable of encapsulating hydrophobic antitumor drugs such as doxorubicin (DOX). The DOX-loaded FA-M13-PCL-P2VP assemblies had an average diameter of approximately 200 nm and their structure was characterized using transmission electron microscopy, scanning electron microscopy, and dynamic light scattering. The particles were stable at physiological pH but could be degraded at a lower pH. The release of DOX from the nanoassemblies under acidic conditions was shown to be significantly faster than that observed at physiological pH. In addition, the DOX-loaded FA-M13-PCL-P2VP particles showed a distinctly greater cellular uptake and cytotoxicity against folate-receptor-positive cancer cells than folate-receptor-negative cells, indicating that the receptor facilitates folate uptake via receptor-mediated endocytosis. Furthermore, the DOX-loaded particles also had a significantly higher tumor uptake and selectivity compared to free DOX. This study therefore offers a new way to fabricate nanosized drug delivery vehicles.     

Preparation of magnetically recoverable Fe3O4@SiO2@meso-TiO2 nanocomposites with enhanced photocatalytic ability

A simple and efficient method has been developed to fabricate core–shell structured Fe₃O₄@SiO₂@meso-TiO₂ nanocomposites with enhanced photocatalytic activity in this paper. The as-made core–shell structure is composed of a central magnetite core with a strong response to external fields, an interlayer of SiO₂, and an outer layer of TiO₂ nanocrystals with mesoporous structure. Fe₃O₄@SiO₂ was obtained through a sol–gel process. To avoid magnetic loss caused by magnetite core phase transition and particle reunion, we adopt a mild synthetic method to get anatase shell instead of traditional high-temperature calcination. The structure of resulting composites was characterized and their photocatalytic activities were also tested. Fe₃O₄@SiO₂@meso-TiO₂ composite exhibits higher photocatalytic activities than Fe₃O₄@SiO₂@solid-TiO₂ for the degradation of rhodamine B in aqueous suspension. The excellent photocatalytic activities are ascribed to the high surface area and pore volume created by mesoporous anatase shell.     

Trimetallic PtRhNi alloy nanoassemblies as highly active electrocatalyst for ethanol electrooxidation

Although nanostructures based on noble metal alloys are widely utilized in (electro)catalysis,their low-temperature synthesis remains an enormous challenge due to the different Nernst equilibrium potentials of metal precursors.Herein,we describe the successful synthesis of trimetallic PtRhNi alloy nanoassemblies (PtRhNi-ANAs) with tunable Pt/Rh ratios using a simple mixed cyanogel reduction method and provide a detailed characterization of their chemical composition,morphology,and structure.Additionally,the electrochemical properties of PtRhNi-ANAs are examined by cyclic voltammetry,revealing compositiondependent electrocatalytic activity in the ethanol oxidation reaction (EOR).Compared to a commercial Pt black electrocatalyst,optimized Pt3Rh1Ni2-ANAs display remarkably enhanced EOR electrocatalytic performance in alkaline media.     

High performance magnetically recoverable g-C3N4/Fe3O4/Ag/Ag2SO3 plasmonic photocatalyst for enhanced photocatalytic degradation of water pollutants

The g-C₃N₄/Fe₃O₄/Ag/Ag₂SO₃ nanocomposites have been successfully fabricated by facile refluxing method. The as-obtained products were characterized by XRD, EDX, SEM, TEM, UV–vis DRS, FT–IR, TGA, PL, and VSM techniques. The results suggest that the Ag/Ag₂SO₃ nanoparticles have anchored on the surface of g-C₃N₄/Fe₃O₄ nanocomposite, showing strong absorption in the visible region. The evaluation of photocatalytic activity indicates that for the g-C₃N₄/Fe₃O₄/Ag/Ag₂SO₃ (40%) nanocomposite, the degradation rate constant was 188 × 10^?4 min^?1 for rhodamine B, exceeding those of the g-C₃N₄ (16.0 × 10^?4 min^?1) and g-C₃N₄/Fe₃O₄ (20.2 × 10^?4 min^?1) by factors of 11.7 and 9.3, respectively. The results showed that the nanocomposite prepared by refluxing for 120 min has the superior photocatalytic activity and its activity decreased with rising the calcination temperature. The trapping experiments confirmed that superoxide ion radical was the main active species in the photocatalytic degradation process. Also, it was demonstrated that the magnetic photocatalyst has considerable activity in degradation of one more dye pollutant. Finally, the reusability of the photocatalyst was evaluated by five consecutive catalytic runs. This work may open up new insights into the utilization of magnetically separable nanocomposites and provide new opportunities for facile fabrication of g-C₃N₄-based plasmonic photocatalysts.     

Hierarchical mesoporous silica nanotubes derived from natural cellulose substance

Bioinspired synthesis of hierarchical mesoporous silica nanotubes by using natural cellulose substance (filter paper) and cetyltrimethylammonium bromide (CTAB) micelles as dual templates was achieved. CTAB micelles were adsorbed onto the surfaces of ultrathin titania film precoated cellulose nanofibers, followed by hydrolysis and condensation of tetraethyl orthosilicate around these micelles to form silica. After calcination and sulfuric acid treatment to remove the organic templates and the thin titania film, bulk white sheets composed of natural hierarchical silica nanotubes with mesopores in the walls were obtained, to which silver nanoparticles were further induced to give a silica-nanotube/metal-nanoparticle hybrid.     

Magnetic properties of magnetite nanoparticles coated with mesoporous silica by sonochemical method

In this paper we present the magnetic properties of mesoporous silica-coated Fe₃O₄ nanoparticles. The coating of magnetite nanoparticles with mesoporous silica shell was performed under ultrasonic irradiation. The obtained mesoporous silica-coated magnetite nanoparticles were characterized by powder X-ray diffraction, focused ion beam-scanning electron microscopy, nitrogen adsorption-desorption isotherms and vibrating sample magnetometer. The hysteretic behavior was studied using first-order reversal curves diagrams. The X-ray diffraction result indicates that the extreme chemical and physical conditions created by acoustic cavitations have an insignificant effect on crystallographic structural characteristic of magnetite nanoparticles. Changes in the coercivity distributions of the magnetite nanoparticles were observed on the first-order reversal curves diagrams for the samples with coated particles compared with the samples containing uncoated particles of magnetite. The coated particles show an increased most probable coercivity of about 20% compared with the uncoated particles which can be associated with an increased anisotropy due to coating even if the interaction field distribution measured on the diagrams are virtually identical for coated/uncoated samples.     

Synthesis of magnetite/amphiphilic polymer composite nanoparticles as potential theragnostic agents

This study describes the synthesis of magnetite/amphiphilic polymer composite nanoparticles that can be potentially used simultaneously for cancer diagnosis and therapy. The synthesis method was a one-shot process wherein magnetite nanoparticles were mixed with core-crosslinked amphiphilic polymer (CCAP) nanoparticles, prepared using a copolymer of a urethane acrylate nonionomer (UAN) and a urethane acrylate anionomer (UAA). The CCAP nanoparticles had a hydrophobic core and a hydrophilic exterior with both PEG segments and carboxylic acid groups, wherein the magnetite nanoparticles were coordinated and stabilized. According to DLS data, the ratio of UAN to UAA and the ratio of magnetite to polymer are keys to controlling the size and thus, the stability of the composite nanoparticles. The magnetic measurement indicated that the composite nanoparticles had superparamagnetic properties and high saturation magnetization. The preliminary magnetic resonance imaging showed that the particles produced an enhanced image even when their concentration was as low as 80 microg/ml.     

Hierarchical mesoporous silica prepared from ethyl-cyanoethyl cellulose cholesteric liquid crystalline phase

Porous silica with hierarchical structures was prepared from ethyl-cyanoethyl cellulose/poly(3-(methacryloyloxy)propyl-trimethoxysilane) (E-CE)C/P(MPTOS) composites with fixed cholesteric liquid crystalline (LC) phase. The scanning and transmission electron microscopy (SEM and TEM) and N₂ sorption measurements results indicate that the silica prepared from cholesteric LC composites is of hierarchical macro-, meso- and micro-porous structures, and the average pore size of the silica can be tailored by the content of the cholesteric LC phase in the (E-CE)C/P(MPTOS) composites. The resultant silicas have high specific surface area with the highest value of 837 m²/g at the pore volume of 0.83 cm³/g. This approach provides a new choice for the preparation of porous silica materials, especially from the templates that are not compatible with aqueous system.     

Green synthesis of magnetically recoverable Fe3 O4 /HZSM‐5 and its Ag nanocomposite using Juglans regia L. leaf extract and their evaluation as catalysts for reduction of organic pollutants

In this work, an Fe₃ O₄ /HZSM‐5 nanocomposite was synthesised in the presence of Juglans regia L. leaf extract. Then, silver nanoparticles (Ag NPs) were immobilised on the surface of prepared magnetically recoverable HZSM‐5 using selected extract for reduction of Ag⁺ ions to Ag NPs and their stabilisation on the surface of the nanocomposite. The reduction of Ag⁺ ions occurs at room temperature within a few minutes. Characterisation of the prepared catalysts has been carried out using fourier transform infrared (FT‐IR), X‐ray diffraction, field‐emission scanning electron microscopy (FESEM), energy‐dispersive spectroscopy, Brunauer–Emmett–Teller method, and a vibrating sample magnetometer. According to the FESEM images of the nanocomposites, the average size of the Ag NPs on the Fe₃ O₄ /HZSM‐5 surface was >70 nm. The Ag/Fe₃ O₄ /HZSM‐5 nanocomposite was a highly active catalyst for the reduction of methyl orange and 4‐nitrophenol in aqueous medium. The utilisation of recycled catalyst for three times in the reduction process does not decrease its activity.Inspec keywords: silver, X‐ray chemical analysis, X‐ray diffraction, nanocomposites, reduction (chemical), nanofabrication, nanoparticles, transmission electron microscopy, catalysts, Fourier transform infrared spectra, iron compounds, field emission scanning electron microscopy, zeolites, magnetometry, particle sizeOther keywords: Ag‐Fe₃ O₄ , temperature 293 K to 298 K, green synthesis, catalyst material, 4‐nitrophenol reduction, methyl orange reduction, particle size, vibrating sample magnetometry, Brunauer–Emmett–Teller method, field‐emission scanning electron microscopy, X‐ray diffraction, FT‐IR spectroscopy, silver nanoparticles, Juglans regia L. leaf extract, organic pollutant reduction, magnetically recoverable nanocomposites, energy‐dispersive spectroscopy     

Physicochemical properties and operational stability of Taguchi design-optimized Candida rugosa lipase supported on biogenic silica/magnetite/graphene oxide for ethyl valerate synthesis

Biobased ternary nanocomposites can stabilize enzymes for greater stability, catalytic activity and easy recovery. This study aimed to optimize biogenic silica/magnetite/graphene oxide nanocomposite supported Candida rugosa lipase (CRL/SiO₂/Fe₃O₄/GO) for ethyl valerate (EV) synthesis and characterize the biocatalysts’ physicochemical properties and operational stability. CRL conjugated-oil palm leaves-derived biogenic SiO₂/Fe₃O₄/GO nanocomposite showed a maximum immobilized protein of 44.13 ± 2.1 mg/g with a specific activity (534.87 ± 9.5 U/mg), than free CRL (≥700 U/mg). GL-A-SiO₂/Fe₃O₄/GO exhibited the highest surface area (260.87 m²/g) alongside superior thermal stability in TGA/DTG. XRD revealed an amorphous SiO₂ (crystallinity = 26.7%), while Fe₃O₄ existed as cubic spinel crystal (crystallinity = 90.2%). Taguchi Design-optimization found that CRL/SiO₂/Fe₃O₄/GO best catalyzed the EV synthesis (90.4% in 3 h) at 40 ℃ using 3 mg/mL of biocatalyst, valeric acid/ethanol molar ratio of 1:2, in 10% (m/v) molecular sieves with stirring in heptane at 200 rpm. EV production was confirmed by FTIR- (C=O: 1738 cm^?1 and C–O–C: 1174 cm^?1) and GC–MS ([M]⁺ m/z = 130, C₇H₁₄O₂). CRL/SiO₂/Fe₃O₄/GO’s reusability for 11 successive esterification cycles demonstrated the SiO₂/Fe₃O₄/GO’s exceptional hyperactivation and stabilization properties on immobilized CRL. These findings conveyed the SiO₂/Fe₃O₄/GO’s efficacy to alter CRL's physicochemical properties and operational stability for catalyzing higher yields EV.     

聚苯乙烯/Fe3O4纳米复合材料的制备与表征

采用油酸为表面活性剂表面处理Fe3O4纳米粒子,将其分散在苯乙烯单体中,进行原位聚合,制备PS/Fe3O4纳米复合材料,对该复合材料的分散均匀性和结构进行了表征.实验结果显示,Fe3O4粒子在PS基体中分散均匀;包覆油酸的Fe3O4纳米粒子在基体中起到物理和化学交联点的作用,使得聚合物产生交联,并提高了其耐热性.     

Carboxymethyldextran/magnetite hybrid microspheres designed for hyperthermia

Recently, organic–inorganic hybrids composed of derivatives of dextran, a polysaccharide, and magnetite nanoparticles have attracted much attention as novel thermoseeds. If they can be fabricated into microspheres of size 20–30 μm, they are expected to show not only hyperthermia effects but also embolization effects in human liver and kidney cancers. In this study, we examined the fabrication of carboxymethyldextran/magnetite microspheres using a water/oil emulsion as the reaction medium. Improvement of the chemical stability of the microcapsules by coating with silica using a sol–gel process was also investigated. The obtained hollow microspheres contained particles of size 20–30 μm. Silica coating using an appropriate catalyst for hydrolysis and polycondensation of alkoxysilanes was found to be effective for preventing dissolution and collapse in simulated body environments.