Core-shell Magnetic Particles Research Articles

Core-shell magnetic particles reinforced magnesium matrix composites with an excellent combination of mechanical and electromagnetic interference shielding properties

Structural and functional integration of metal matrix composites is both a goal pursued by researchers and a challenging issue. In this study, a series of Al3Fe@Fe core-shell structured micro-sized particle reinforced magnesium matrix composites were prepared by using AZ31 alloy and Fe powders. The Al3Fe@Fe core-shell structure induces the “back-stress” strengthening in the composite due to the difference in deformation ability of matrix, Al3Fe “shell” and Fe “core” during the deformation process. This also improves the strain hardening ability of the composite, resulting in synchronous improvement of both strength and ductility. In addition, the reinforcing particles with “core-shell” structure endow the composite with certain magnetism, achieving a synergistic contribution of dielectric and magnetic losses, significantly enhancing the electromagnetic shielding effectiveness of the composite. Compared with the matrix alloy, the addition of 15 wt% Fe in the composite increased the SET by 70 %, and the SEA/SET increased from 0.46 to 0.73.

Enhanced sonophotocatalytic degradation of amoxicillin antibiotics using Fe3O4@SiO2/PAEDTC surrounded by MIL-101(Fe) in aquatic environment under the COVID-19 pandemic

In the conditions of corona disease, the need for antibiotics in the world has quadrupled, so it is required to remove their residues from the environment. A core–shell metal–organic framework (MOF) composed of Fe3O4, SiO2, and MIL-101 was synthesized by hydrothermal method and used as a sonophotocatalyst for the amoxicillin (AMX) degradation from aqueous solution. The features of the new MOF were determined by SEM, TEM, XRD, FTIR, and BET techniques. The specific area of core–shell magnetic particles was 992 m2/g, which was indicative of its usability to adsorb pollutants and photons. Complete degradation of AMX was achieved by sonophotocatalysis process based on prepared nanocomposite at pH of 5, UV intensity of 36 W, AMX concentration of 50 mg/L, US frequency of 36 kHz, and time of 25 min. Kinetic study with pseudo-first order reaction for the decomposition of AMX showed the order of kinetic constant rate as Ksonophotocatalytic > Kphotocatalytic > Ksonocatalytic > Kadsorption. Hydroxyl radicals (•OH) and holes (h+) were respectively determined as the main species in the decomposition of AMX by performing quenching experiments. Less than an 8% reduction in AMX degradation rate was observed by the sonophotocatalytic process in the presence of prepared nanocomposite during six consecutive reaction cycles. Removal rates of TOC > 77% and BOD5/COD ratio > 0.4 showed that AMX was converted to CO2, H2O, and simple degradable compounds during the sonophotocatalysis process. A toxicity study with the microbial culture of Escherichia coli (E. coli) demonstrated a lower inhibition rate in the sonophotocatalytic process compared to photolysis and photocatalytic processes. All the laboratory results proved that the Fe3O4@SiO2@MIL-101(Fe) is an encouraging candidate for AMX degradation to preserve the ecosystem.

Multiplex and Ultrasensitive Detection of Severe Acute Respiratory Syndrome Coronavirus 2 and Influenza A/B Nucleocapsid Proteins Based on Nanometer-Sized Core–Shell Superparamagnetic Antifouling Probes

Infections caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza A (Flu A), and influenza B (Flu B) show similar clinical symptoms, such as cough, fever, and dyspnea, but patients infected by these viruses should be treated differently. The rapid and accurate diagnosis of infections caused by SARS-CoV-2, Flu A or Flu B is critical during the influenza season. Herein, we synthesized core–shell magnetic particles (MNPs) with excellent antifouling properties and applied them in the MNP-based immunochromatographic test (MICT) for simultaneous detection of SARS-CoV-2, Flu A, and Flu B nucleocapsid(N) proteins in 20 min. Two kinds of carboxyl-modified MNPs, MNP@pMBAA and MNP@Si-SA, were prepared and evaluated as probes in the MICT. Among them, the MNP@pMBAA showed lower nonspecific adsorption of proteins and low background noise in the application in MICTs. Particularly, the MNP@pMBAA50 bead-based MICT strip exhibited the highest signal-to-noise ratio for SARS-CoV-2 N protein detection with a limit of detection (LOD) of 0.072 ng/mL. Moreover, the proposed MICT strip demonstrated a minimal cross-reactivity and a broad linear dynamic detection range under a magnetic assay reader in the simultaneous detection of SARS-CoV-2, Flu A, and Flu B N proteins with relative LOD values of 0.0086, 0.012, and 0.018 ng/mL, respectively. The results demonstrated that the synthesized MNPs showed great potential for use as MICT probes for sensitive and multiplex detection of biomarkers in the development of point-of-care testing systems.

Immobilization of boronic acid derivative onto the magnetic Gd-containing composites

Aiming to develop new magnetic materials for neutron shielding applications, B- and Gd-containing magnetic nanoparticles were synthesized. Following bottom-up synthetic approach, core-shell Fe 3 O 4/Gd 2 O 3 nanocomposite particles were synthesized at the first stage. In the next stage, magnetic core-shell particles were modified with amino groups followed by grafting onto their surface of the boronic acid derivative. Such a multifunctional material, containing both boron (B) and gadolinium (Gd) atoms is a promising candidate for developing films and membranes, strongly interacting with neutrons. Due to the presence of boronic acids and bound to the indicator (Alizarin Red S), the material can induce color changes while immersed in sugar-containing solutions. Such a feature enables a possibility to estimate the number of boron atoms left after interaction with neutrons, thus allowing to check composite neutron-capture recourse.

A Magnetically Separable Pd Single-Atom Catalyst for Efficient Selective Hydrogenation of Phenylacetylene.

Selective hydrogenation of alkynes to alkenes plays a crucial role in the synthesis of fine chemicals. However, how to achieve high selectivity and effective separation of the catalyst and substrate while obtaining high activity is the key for this reaction. In this work, a Pd single-atom catalyst is anchored to the shell of magnetic core-shell particles that consist of a Ni-nanoparticles core and a graphene sheets shell (Ni@G) for semi-hydrogenation of phenylacetylene, delivering 93% selectivity to styrene at full conversion with a robust turnover frequency of 7074 h-1 under mild reaction conditions (303 K, 2bar H2 ). Moreover, the catalyst can be recovered promptly from the liquid phase due to its magnetic separability, which makes it present good stability for enduring five cycles. Experimental and theoretical investigations reveal that H2 and substrates are activated by atomically dispersed Pd atoms and Ni@G hybrid support, respectively. The hydrogenation reaction occurs on the surface of Ni@G via hydrogen spillover from the metal to the support. Such a strategy opens an avenue for designing highly active, selective, and magnetically recyclable catalysts for selective hydrogenation in liquid reaction systems.

Magnetic Molecularly Imprinted Polymers: An Update on Their Use in the Separation of Active Compounds from Natural Products.

During the last few years, separation techniques using molecularly imprinted polymers (MIPs) have been developed, making breakthroughs using magnetic properties. Compared to conventional MIPs, magnetic molecularly imprinted polymers (MMIPs) have advantages in sample pretreatment due to their high specificity and selectivity towards analytes as a result of their larger specific surface areas and highly accessible specific binding sites. The techniques of isolation of active compounds from natural products usually require very long process times and low compound yields. When MMIPs are used in sample separation as Solid Phase Extraction (SPE) sorbents, the MMIPs are introduced into the dissolved sample and spread evenly, and they form bonds between the analyte and the MMIPs, which are then separated from the sample matrix using an external magnetic field. This process of separating analytes from the sample matrix makes the separation technique with MMIPs very simple and easy. This review discusses how to synthesize MMIPs, which factors must be considered in their synthesis, and their application in the separation of active compounds from natural products. MMIPs with magnetic core-shells made by co-precipitation can be a good choice for further development due to the high synthesis yield. Further optimization of the factors affecting the size and distribution of magnetic core-shell particles can obtain higher synthesis yields of MMIPs with higher adsorption capacity and selectivity. Thus, they can isolate target compounds from natural plants in high yields and purity.

Magnetic core-shell structure in-situ encapsulated in bamboo-derived carbon skeleton for efficient microwave absorption

A fast renewable bamboo source is first adopted to synthesize carbon-based magnetic composites as efficient and sustainable microwave absorbers through a carbothermal in-situ growth process. The magnetic core-shell particles uniformly encapsulated in porous carbon skeleton can promote magnetic loss and graphitization of carbon shell. The gradient graphitization of graphitic shells and disordered framework is favorable for conductive loss and polarization relaxation. By controlling the magnetic content, the microstructure, magnetic property, graphitization and absorbing performance of the composites can be delicately manipulated. As expected, the strong reflection loss surpassing − 40 dB is achieved at both high frequency of 14.1 GHz (1.9 mm) and low frequency of 5.5 GHz. Meanwhile, a wide effective bandwidth of 4.7 GHz covering from 6.6 GHz to 11.3 GHz is achieved. This work demonstrates that the combination of bamboo carbon with magnetic cores could provide a perspective for refining low frequency and thin thickness characteristics for plant-derived microwave absorption.

Molecularly imprinted electrochemical luminescence sensor based on core–shell magnetic particles with ZIF-8 imprinted material

Abstract A molecularly imprinted electrochemiluminescence (MIP-ECL) sensor with high sensitivity and good structural stability was constructed using the new composite material ZIF-8-NH2 as an imprinted membrane. The ZIF-8-NH2 imprinted composite material was prepared through layer-by-layer self-assembly with carboxyl functionalized magnetic CoFe2O4 nanoparticles as the carrier, ZIF-8-NH2 precursor as the functional monomer, and cinchonine (CCN) as the template molecule. The ZIF-8 MIP@Au@CoFe2O4 core–shell imprinted material was characterized using infrared spectrometry, scanning electron microscopy and X-ray diffraction, and the recognition performance of molecularly imprinted sensor was characterized through electrochemical impedance spectroscopy and electrochemiluminescence (ECL) method. When CCN was re-adsorbed by the imprinted membrane, the ECL intensities of the MIP sensor increased because CCN molecules can promote the ECL intensity of Ru(bpy)32+. As a result, the MIP sensor showed preeminent linear response to CCN in the range of 1.0 × 10−12 – 3.1 × 10−8 mol/L, with a detection limit of 7.0 × 10−13 mol/L, which is much lower than that reported for other detection methods. The sensor shows good practicality and can be used to detect CCN in human serum with recoveries ranging from 96.0%–103.0%.

Fluorescent Fe2O3-CdSe nanocomposite probe for selective detection and removal of picric acid

Here, we present a methodology and promising novel hybrid nano-structure that comprises of magnetic core encapsulated inside a thin silica shell, electrostatically adsorbed with a positively charged spacer arm of fluorescent Cysteamine-capped CdSe quantum dots (QDs). This multimodal nanosensor provides an efficient, sensitive and selective detection of Picric Acid (PA) (LOD ≈ 2.2 μM) (Quenching constant KPA ≈ 4.3 × 104 M−1) in solution via photo-induced electron transfer mechanism. The sensing mechanism is probed via UV–Vis spectroscopy, steady-state and time-resolved fluorescence spectroscopy. The removal of PA, attached to the spherical magnetic core-shell particles, is achieved using an external magnet. This elegant architecture results in an ultra-small magneto-fluorescent nanoparticle (particle size ≈ 12.7 nm), offering a novel platform for the development of a field-based PA sensor. This strategy is having the potential for applications in the field of low-cost and stand-off sensor.

Catalytic Performance of a Magnetic Core-Shell Iron(II) C-Scorpionate under Unconventional Oxidation Conditions.

For the first time, herein is reported the use of a magnetic core-shell support for a C-scorpionate metallic complex. The prepared hybrid material, that consists on the C-scorpionate iron(II) complex [FeCl2{κ3-HC(pz)3}] (pz, pyrazolyl) immobilized at magnetic core-shell particles (Fe3O4/TiO2), was tested as catalyst for the oxidation of secondary alcohols using the model substrate 1-phenylethanol. Moreover, the application of alternative energy sources (e.g., ultrasounds, microwaves, mechanical or thermal) for the peroxidative alcohol oxidation using the magnetic heterogenized iron(II) scorpionate led to different/unusual outcomes that are presented and discussed.

Effect of shell structure of Ti-immobilized metal ion affinity chromatography core-shell magnetic particles for phosphopeptide enrichment

Magnetic materials in sample preparation for shotgun phosphoproteomics offer several advantages over conventional systems, as the enrichment can be achieved directly in solution, but they still suffer from some drawbacks, due to limited stability and selectivity, which is supposed to be affected by the hydrophilicity of the polymeric supports used for cation immobilization. The paper describes the development of an improved magnetic material with increased stability, thanks to a two-step covering of the magnetic core, for the enrichment of phosphopeptides in biological samples. Four materials were prepared featuring a polymeric shell with tunable hydrophilicity, obtained by “grafting from” polymerization of glycidyl methacrylate with 0–8.3% of polyethylene glycol methacrylate (PEGMA), the latter used to modulate the hydrophilicity of the material surface. Finally, the materials were functionalized with iminodiacetic acid for Ti4+ ion immobilization. The materials were analyzed for their composition by a combination of CHN elemental analysis and thermogravimetric analysis, also hyphenated to gas chromatography and mass spectrometric detection. Surface characteristics were evaluated by water contact angle measurements, scanning electron microscopy and energy dispersive X-ray spectrometry. These materials were applied to the enrichment of phosphopeptides from yeast protein digests. Peptides were identified by proteomics techniques using nano-high performance liquid chromatography coupled to mass spectrometry and bioinformatics. Qualitatively the peptides identified by the four systems were comparable, with 1606–1693 phosphopeptide identifications and a selectivity of 47–54% for all materials. The physico-chemical features of the identified peptides were also the same for the four materials. In particular, the grand average of hydropathy index values indicated that the enriched phosphopeptides were hydrophilic (ca. 90%), and only some co-enriched non-phosphorylated peptides were hydrophobic (21–28%), regardless of the material used for enrichment. Peptides had a pI ≤ 7, which indicated a well-known bias for acidic peptides binding, attributed to the interaction with the metal center itself. The results indicated that the enrichment of phosphopeptides and the co-enrichment of non-phosphorylated peptides is mainly driven by interactions with Ti4+ and does not depend on the amount of PEGMA chains in the polymer shell.

Magnetic/Gold Core-Shell Hybrid Particles for Targeting and Imaging-Guided Photothermal Cancer Therapy.

The development of hybrid particles for tumor diagnosis and therapy has received considerable attention because they are capable of combining tumor diagnosis and treatment concurrently. So far hybrid particles for efficient and safe tumor theranostics are still very limited. Herein we have designed a new type of hybrid particles and evaluated its potential to be used in image-guided cancer diagnosis and therapy without the need of any toxic anticancer or contrast agents. The hybrid particles, consist of magnetic nanoparticles which are embedded in the poly(methyl methacrylate) (PMMA) cores and gold shells on chitosan (CTS) (γ-Fe₂O₃ @PMMA/CTS@Au). The hybrid particles were synthesized through initial formation of the core-shell structured γ-Fe₂O₃ @PMMA/CTS particles containing approximately 20% loading of magnetic nanoparticles. A gold layer was then built on top of the core-shell magnetic particles via a reduction of gold salt by amines from the chitosan assisted with the reducing agent NaBH₄, followed by growing to complete gold shells in the presence of ascorbic acid (42.6% Au content). The properties of the composite particles including their chemical composition, morphology, particle size, size distribution, surface charge, magnetic responsiveness and photothermal ability were systematically characterized. The potential application of the γ-Fe₂O₃ @PMMA/CTS@Au hybrid particles in tumor diagnosis and therapy was assessed in vitro and in vivo using 4T1 tumor cells and 4T1 tumor-bearing mice through combining magnetic targeting, photoacoustic (PA)/computed tomography (CT) imaging and photothermal therapy. Results suggest that the γ-Fe₂O₃ @PMMA/CTS@Au particles can serve as a multifunctional tumor theranostic nanoplatform for magnetically targeted photothermal therapy. Breast cancer has been effectively eliminated without the use of any anticancer drugs or contrast agents. Therefore, this type of core-shell hybrid particles represents a new composite particle design for effective and safe tumor theranostics.

Preparation of Core-shell Magnetic Nanoparticles Carrier for Treatment of Emulsified Oil

The Fe3O4 nanoparticles was prepared by chemical co-precipitation method, and modified with polyethylene glycol and lauryl sodium sulfate to obtain amphiphilic magnetic core. Core-shell magnetic particles (CMP) were prepared by modified dispersion polymerization method. After characterization, the contact angle θ of material was 133.4°, and the specific surface area of CMP reached to 1032.43 m2/g. The absorption rate up to 27.1007 g/g, and the oil release rate was up to 96.19%, ensure it fully adsorptive to the emulsified oily wastewater. The saturated magnetization of MPP was 3.95 emu/g, showed strong magnetic response. It is beneficial for recovery and reuse the material. After 12 hour degradation of crude oil, CMP immobilized with petroleum oil degrading strains to treat emulsified oil was 13.86% higher than that of free bacterial cells. The results of this research provide a reference for the rapid adsorption and degradation of emulsified oil wastewater by immobilized microorganisms with novel magnetic materials.

Fabrication of magnetic core shell particles coated with phenylalanine imprinted polymer

In this study, magnetic iron oxide (Fe3O4) nanoparticles with excellent magnetic behavior were synthesized by co-precipitation method followed by their surface modification to obtain Fe3O4@SiO2NH2 and polymerization to fabricate d-phenylalanine (D-Phe) imprinted magnetic core-shell polymer (PIMP) and non-imprinted magnetic core-shell polymer (NIMP), respectively. The as-prepared PIMP and NIMP were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and energy-dispersive X-ray spectroscopy (EDX). PIMP showed maximum adsorption capacity (3.94 mg. g−1) and selectivity factor (1.55) at pH 4 while the adsorption equilibrium was achieved after 1 h. The adsorption of Phe on PIMP followed Langmuir adsorption isotherm with pseudo second order kinetics. PIMP was selective towards template (D-Phe) in the presence of interfering molecules such as L-Phe, tyrosine, and tryptophan. It was concluded that the as-synthesized PIMP is an important material to be used as a recoverable selective adsorbent and sensor for Phe.

Preparation of titanium ion functionalized polydopamine coated ferroferric oxide core-shell magnetic particles for selective extraction of nucleotides from Cordyceps and Lentinus edodes

In this study, a titanium ion (Ti4+) functionalized polydopamine coated ferroferric oxide (Fe3O4@PDA@Ti4+) core-shell magnetic particle was prepared for the selective extraction of nucleotides. Firstly, different metal ions including Ti4+, Zr4+, Fe3+, Al3+, Cu2+, Zn2+, Ni2+ and Mg2+ were respectively immobilized onto Fe3O4@PDA particles and their extraction efficiency for five nucleotides [cytidine-5′-monophosphate (CMP), uridine-5′-monophosphate (UMP), guanosine-5′-monophosphate (GMP), thymidine-5′-monophosphate (TMP) and adenosine-5′-monophosphate (AMP)] were compared. Among these prepared materials, Fe3O4@PDA@Ti4+, which exhibited the highest extraction efficiency for nucleotides, was further characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. After being optimized of the extraction parameters including adsorbent amounts, extraction time, extraction temperature, type and concentration of the eluent, the prepared Fe3O4@PDA@Ti4+ magnetic particles were successfully applied for the selective extraction and determination of CMP, UMP, GMP, TMP and AMP in Cordyceps and Lentinus edodes. Good linearity (varying from 0.063 to 19.000 μg/mL, R2 > 0.999) and low limit of detection (LODs) (ranging between 0.0047 and 0.0141 μg/mL) for target analytes were achieved. These results demonstrated that the synthesized material in this study had potential for selective extraction of phosphorylated small molecular compounds in complicated matrix.

Core-shell magnetic particles obtained by seeded suspension polymerization of acrylic monomers

Abstract Core-shell magnetic polymer particles were synthesized by seeded suspension polymerization. The core was made of poly(methyl methacrylate-co-divinylbenzene) and a mixture of magnetite, maghemite and goethite (P(MMA-co-DVB)-M). The shell was composed of poly(glycidyl methacrylate-co-divinylbenzene) (P(GMA-co-DVB)). These particles were characterized by infrared spectrometry (FTIR), thermal analysis (TG), scanning electron microscopy (SEM), dynamic light scattering (DLS) and vibrating sample magnetometry (VSM). The results showed the formation of core-shells with good magnetic properties (≈7.1 emu/g) and good thermal resistance (≈300 oC). The light scattering experiments showed that the particle size of these materials changed from 5-90 microns (core) to 5-120 microns (core-shell). Scanning electron microscopic images were useful to show the formation of P(GMA-co-DVB) shells on P(MMA- co-DVB)-M cores. The materials synthesized in this work have potential to be modified and employed in magnetic separation processes in the biotech and environmental fields.

Ferromagnetic resonance in core-shell nanoparticles with multitype exchange anisotropy

A phenomenological model for magnetodynamics of core-shell nanoparticles is presented. The term core-shell implies, prima facie, that the spin structures (phases) of the particle components are different, no matter whether or not they are chemically identical. The model takes in two main assumptions. First, the interphase boundary is a thin (in comparison with the core and shell scales) transition layer with strongly inhomogeneous spin arrangement. Second, the shell is a granular structure consisting of spin-ordered crystallites with a wide spread of internal anisotropy, including a fraction of ones with extremely high coercivity. The framework developed on that basis, despite its simplicity, provides a unified explanation for the major specific properties of magnetic core-shell particles. Namely, (i) the growth of observed anisotropy field with reduction of the particle size, (ii) the presence of fixed unidirectional anisotropy, and (iii) the existence of rotatable anisotropy that emerges in a threshold manner under an external field. For a nanoparticle with the above-described core-shell architecture, a theory of ferromagnetic resonance with allowance for the superparamagnetic effect is worked out, and the ferromagnetic resonance absorption lines of noninteracting ensembles of such particles are presented. It is demonstrated that all the qualitatively different contributions to the core-shell-induced anisotropy could be evaluated from the data on a temperature sweep of the resonance field. Moreover, to do that, it suffices to use just the samples with random orientation of the particle axes. Preliminary assessment shows that a set of measurements for complete evaluation of the exchange-mediated anisotropies is feasible with the aid of a standard $X$-band spectrometer.

Facile synthesis of boronic acid-conjugated magnetic particles for an efficient extraction of dopamine neurotransmitter molecules

Boronic acid-functionalized magnetic particles were synthesized in order to detect dopamine (DA) neurotransmitter molecules via fluorescent polydopamine formation. The sol–gel reaction of tetraethy1 orthosilicate with magnetite clusters (Fe3O4) led to the formation of core–shell Fe3O4@SiO2, which then underwent surface functionalization with 3-aminopropyltrimethoxysilane (APTMS). The core–shell magnetic particles exhibited supermagnetic properties with a negligible remanence and coercivity. Finally, amine-terminated Fe3O4@SiO2 was conjugated with 4-formylphenylboronic acid (FPBA) using a sodium cyanoborohydride (NaBH3CN) as the reducing agent, and is called Fe3O4@SiO2@FPBA. The composite particles could capture dopamine molecules via the formation of covalent cyclic ester bonds. The Fe3O4@SiO2@FPBA exhibited a high adsorption capacity (57 µg of DA/g of composite particles), based on the fluorescent intensity of polydopamine converted from the oxidized DA under alkaline conditions.

Immobilization of trypsin onto Fe3O4@SiO2 -NH2 and study of its activity and stability.

The preparation of biocatalysts based on immobilized trypsin is of great importance for proteomic research, industrial applications and organic synthesis. Here in, we have developed a facile method to immobilize trypsin on magnetic nanoparticles. Fe3O4 nanoparticles were synthesized by co-precipitating Fe2+and Fe3+in an ammonia solution and then coated by silicon dioxides were developed by sol-gel method. The silica-coated Fe3O4 nanoparticles were further modified with 3-aminopropyltriethoxysilane, resulting in attaching of primary amine groups on the surface of the particles. Trypsin from porcine pancrease was then immobilized on the magnetic core-shell particles by using glutaraldehyde as a cross-linker. The synthesis steps and characterizations of immobilized trypsin were examined by FT-IR, XRD, TGA, EDX and SEM. The results showed that the enzyme immobilization increased the enzyme activity in different pHs and temperatures, without any changes in the optimum pH and temperature for enzyme activity. The Kinetic results showed that the enzyme immobilization decreased and increased Vmax and Km values, respectively. The stability results showed that the enzyme immobilization improved trypsin thermostability in the absence and presence of 10% (v/v) of the used solvents (DMF, THF, DMSO, ACN and 1, 4-Dioxane). The reusability results indicated that the immobilized enzyme maintained 85% of its activity after 6 periods of activity.

Influence of Shell Thickness on the Colloidal Stability of Magnetic Core-Shell Particle Suspensions.

We present a Discrete Element study of the behavior of magnetic core-shell particles in which the properties of the core and the shell are explicitly defined. Particle cores were considered to be made of pure iron and thus possessed ferromagnetic properties, while particle shells were considered to be made of silica. Core sizes ranged between 0.5 and 4.0 μm with the actual particle size of the core-shell particles in the range between 0.6 and 21 μm. The magnetic cores were considered to have a magnetization of one tenth of the saturation magnetization of iron. This study aimed to understand how the thickness of the shell hinders the formation of particle chains. Chain formation was studied with different shell thicknesses and particle sizes in the presence and absence of an electrical double layer force in order to investigate the effect of surface charge density on the magnetic core-shell particle interactions. For core sizes of 0.5 and 4.0 μm the relative shell thicknesses needed to hinder the aggregation process were approximately 0.4 and 0.6 respectively, indicating that larger core sizes are detrimental to be used in applications in which no flocculation is needed. In addition, the presence of an electrical double layer, for values of surface charge density of less than 20 mC/m2, could stop the contact between particles without hindering their vertical alignment. Only when the shell thickness was considerably larger, was the electrical double layer able to contribute to the full disruption of the magnetic flocculation process.