Study on immobilization of lipase onto magnetic microspheres with epoxy groups

Magnetic microspheres were synthesized by the suspension polymerization of glycidyl methacrylate (GMA), methacrylic acid (MAA) and divinyl benzene (DVB) in the presence of oleic acid-coated Fe₃O₄ nanoparticles. Triacylglycerol lipase from porcine pancreas was covalently immobilized on the magnetic microspheres via the active epoxy groups with the activity yield up to 63% (±2.3%) and enzyme loading of 39 (±0.5) mg/g supports. The resulting immobilized lipase had higher optimum temperature compared with those of free lipase and exhibited better thermal, broader pH stability and excellent reusability. Furthermore, the catalyzed capability of immobilized lipase was also investigated by catalyzing synthesis of hexyl acetate and the esterification conversion rate reached to 83% (±2.5%) after 12 h in nonaqueous solvent.     

Fabrication of urchin-like NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> microspheres assembled by using SDS as soft template for anode materials of Lithium-ion batteries

In this paper, the urchin-like NiCo₂O₄ microspheres assembled by using sodium dodecyl sulfate (SDS) as soft template are successfully fabricated by a facile procedure including microemulsion-solvothermal reaction and subsequent calcination at 400 °C for 4 h. The structure and morphology of synthesized NiCo₂O₄ particles are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It has been clearly revealed that the prepared three-dimensional urchin-like NiCo₂O₄ microspheres are constituted by one-dimension nanowires. As it is applied to anode for lithium-ion batteries (LIBs), the initial coulombic efficiency is up to 75.7%, and the specific reversible capacity retains up to 1034.2 mAh/g even after 40 cycles at a current density of 100 mA/g. Furthermore, as the current density gradually increases to 800 mA/g, it still delivers the reversible capacity of 895.4 mAh/g. The high reversible specific capacity, perfect cyclability, and rate performance are attributed to the unique urchin-like NiCo₂O₄ microspheres, which can alleviate the volume expansion and shorten the diffusion path of ions and electrons during lithiation/delithiation process. The self-standing urchin-like NiCo₂O₄ microspheres may be a very promising candidate in place of the commercial graphite-based anode materials for high-performance LIBs.     

Preparation and mechanism of magnetic carbonaceous polysaccharide microspheres by low-temperature hydrothermal method

In this study, the preparation method for magnetic carbonaceous polysaccharide (Fe₃O₄@CP) microspheres was developed to increase the yield and encapsulation efficiency using a suitable quantity of NaOH as the catalysis. The optimum fabrication condition was identified through a series of experiment, under which the resulting Fe₃O₄@CP microspheres show good magnetic properties. The saturation magnetization was 60.629 emu/g and the magnetite content increased up to 81.7%. The shell of the microspheres was carbonaceous polysaccharide with rich hydroxyl and carbonyl groups located on the surface, and the mean size was less than 300 nm. The formation mechanism of Fe₃O₄@CP was also discussed in this paper.     

Synthesis and studies of trisubstituted biphthalonitrile/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic hybrid microspheres

New trisubstituted biphthalonitrile/magnetite (TSB/Fe₃O₄) magnetic hybrid microspheres were synthesized from TSB and FeCl₃ · 6H₂O using the method of one-stage thermal temperature crystallization of solvents. The morphology and structure of magnetic hybrid microspheres were inspected using a scanning electron microscope, IR Fourier spectroscopy, and X-ray diffraction. It was found that the grown TSB/Fe₃O₄ magnetic hybrid microspheres represent spherical particles with an average size of ~137 nm and a small size spread. The size and size distribution of magnetic hybrid microspheres can be controlled by a small change in the ratio of TSB and Fe³⁺ ion contents in the microsphere. TSB/Fe₃O₄ hybrid microspheres exhibit a rather high saturation magnetization (58.16 emu g^–1) and new microwave electromagnetic properties, i.e., lower (in comparison with published) dielectric losses at low frequencies; magnetic losses are increased obviously due to an increase in the TSB content. Furthermore, it is detected that magnetic hybrid microspheres absorb microwaves, and strong reflection losses in a wide frequency range are established. The effective reflection loss of–31 dB is obtained in the microwave range from 2 to 16 GHz due to TSB content variations. Wide absorption properties of microwaves along with regular spherical shape and excellent magnetic properties offer wide opportunities for various applications of TSB/Fe₃O₄ magnetic hybrid microspheres as functional materials.     

Urea-assisted solvothermal synthesis of monodisperse multiporous hierarchical micro/nanostructured ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> microspheres and their lithium storage properties

High-quality monodisperse multiporous hierarchical micro/nanostructured ZnCo₂O₄ microspheres have been fabricated by calcinating the Zn_1/3Co_2/3CO₃ precursor prepared by urea-assisted solvothermal method. The as-prepared products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller (BET) measurement to study the crystal phase and morphology. When tested as anode material for lithium ion batteries, the multiporous ZnCo₂O₄ microspheres exhibit an initial discharge capacity of 1,369 mAh g^?1 (3,244.5 F cm^?3) and retain stable capacity of 800 mAh g^?1 (1,896 F cm^?3) after 30 cycles. It should be noted that the good electrochemical performances can be attributed to the porous structure composed of interconnected nanoscale particles, which can promote electrolyte diffusion and reduce volume change during discharge/charge processes. More importantly, this ZnCo₂O₄ 3D hierarchical structures provide a large number of active surface position for Li⁺ diffusion, which may contribute to the improved electrochemical performance towards lithium storage.     

A novel approach to preparing magnetic protein microspheres with core-shell structure

Magnetic protein microspheres with core-shell structure were prepared through a novel approach based on the sonochemical method and the emulsion solvent evaporation method. The microspheres are composed of the oleic acid and undecylenic acid modified Fe₃O₄ cores and coated with globular bovine serum albumin (BSA). Under an optimized condition, up to 57.8 wt% of approximately 10 nm superparamagnetic Fe₃O₄ nanoparticles could be uniformly encapsulated into the BSA microspheres with the diameter of approximately 160 nm and the high saturation magnetization of 38.5 emu/g, besides of the abundant functional groups. The possible formation mechanism of magnetic microspheres was discussed in detail.     

Preparation of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> hollow microsphere/graphene/carbon nanotube flexible film as a binder-free anode material for lithium-ion batteries

A flexible Co₃O₄ hollow microsphere/graphene/carbon nanotube hybrid film is successfully prepared through a facile filtration strategy and a subsequent thermally treated process. The composition, morphology, and structure of the as-prepared film are characterized by X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscopy, and transmission electron microscopy. Based on the morphology characterizations on the hybrid film, the Co₃O₄ hollow microspheres are uniformly and closely attached on three-dimensional (3D) graphene/carbon nanotubes (GR/CNTs) network, which decreases the agglomeration of Co₃O₄ microspheres effectively. In this hybrid film, the 3D GR/CNT network which enhances conductance as well as prevents aggregation is a benefit to help Co₃O₄ to exert its lithium storage capabilities sufficiently. When used as a binder-free anode material for lithium-ion batteries, the hybrid film delivers excellent electrochemical properties involving reversible capacity (863 mAh g^?1 at a current density of 100 mA g^?1) and rate performance (185 mAh g^?1 at a current density of 1600 mA g^?1).     

Magnetism and phase transformation of Cu-Fe composite oxides prepared by the sol-gel route

The Cu-Fe composite oxides were prepared by an epoxide assisted sol-gel route. The structural and magnetic properties of Cu-Fe composite oxides calcinated at different temperatures were determined by X-ray diffraction (XRD), Mössbauer spectroscopy measurements, and magnetic measurements. These results indicated that CuFe₂O₄ was only formed as calcination temperature increased to 500 °C, and a crystalline phase transformation from c-CuFe₂O₄ to t-CuFe₂O₄ occurred in elevating calcination temperature above it. All Cu-Fe oxides had ferromagnetic nature, and the significant superparamagnetic behavior was observed in the results of magnetic and Mössbauer spectroscopy measurements.     

Mo-doped V<Subscript>2</Subscript>O<Subscript>5</Subscript> hierarchical nanorod/nanoparticle core/shell porous microspheres with improved performance for cathode of lithium-ion battery

Mo-doped V₂O₅ hierarchical nanorod/nanoparticle core/shell porous microspheres (MVHPMs) were prepared via a simple hydrothermal approach using ammonium metavanadate and ammonium molybdate as precursors followed by a thermal annealing process. The samples were characterized by XRD, SEM, TEM, EDS, and XPS carefully; it confirmed that porous microspheres with uniform Mo doping in the V₂O₅ matrix were obtained, and it contains an inner core self-assembled with 1D nanorods and outer shell consisting of nanoparticles. A plausible growth mechanism of Mo-doped V₂O₅ (Mo-V₂O₅) porous microspheres is suggested. The unique microstructure made the Mo-V₂O₅ hierarchical microspheres a good cathode material for Li-ion battery. The results indicate the synthesized Mo-V₂O₅ hierarchical microspheres exhibit well-improved electrochemical performance compared to the undoped samples. It delivers a high initial reversible capacity of 282 mAh g^?1 at 0.2 C, 208 mAh g^?1 at 2 C, and 111 mAh g^?1 at 10 C, and it also exhibits good cycling stabilities; a capacity of 144 mAh g^?1 is obtained after 200 cycles at 6 C with a capacity retention of >?82%, which is much high than that of pure V₂O₅ (95 mAh g^?1 with a capacity retention of 72%).

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Graphical Abstract Mo-doped V₂O₅ hierarchical porous microspheres with improved LIB performance

     

Synthesis of an Organic-Inorganic Hybrid Polymeric Material and its Adsorption Performance Characterization Toward Acrylamide

An organic-inorganic hybrid functionalized material was successfully synthesized by a surface molecular imprinting technique combined with a nonhydrolytic sol-gel (NHSG) process using acrylamide (AA) as the template, methacrylic acid as the functional monomer, methacryloxypropyltrimethoxysilane as the cross-linker and magnetic chitosan (CTS) microspheres as the support material. The adsorption ability and selectivity of this material toward AA was characterized. Experimental results showed that the imprinted polymer exhibited better recognition and selective performance toward AA than the nonimprinted polymer (NIP). The saturated binding capacity (Q _max) was 104.68 mg/g, and the equilibrium dissociation constant was 263.16 mg/mL. This prepared material also offered fast kinetics for the adsorption and desorption of AA. After shaking for 5 min, an adsorption capacity of 4.71 mg/g was obtained, and it almost reached the adsorption equilibrium within 90 min.     

Synthesis,characterization, and cytotoxicity of glutathione-PEG-iron oxide magnetic nanoparticles

Recently, increasing interest is spent on the synthesis of superparamagnetic iron oxide nanoparticles, followed by their characterization and evaluation of cytotoxicity towards tumorigenic cell lines. In this work, magnetite (Fe₃O₄) nanoparticles were synthesized by the polyol method and coated with polyethylene glycol (PEG) and glutathione (GSH), leading to the formation of PEG-Fe₃O₄ and GSH-PEG-Fe₃O₄ nanoparticles. The nanoparticles were characterized by state-of-the-art techniques: dynamic light scattering (DLS), atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and superconducting quantum interference device (SQUID) magnetic measurements. PEG-Fe₃O₄ and GSH-PEG-Fe₃O₄ nanoparticles have crystallite sizes of 10 and 5 nm, respectively, indicating compression in crystalline lattice upon addition of GSH on the nanoparticle surface. Both nanoparticles presented superparamagnetic behavior at room temperature, and AFM images revealed the regular spherical shape of the nanomaterials and the absence of particle aggregation. The average hydrodynamic sizes of PEG-Fe₃O₄ and GSH-PEG-Fe₃O₄ nanoparticles were 69 ± 37 and 124 nm ± 75 nm, respectively. The cytotoxicity of both nanoparticles was screened towards human prostatic carcinoma cells (PC-3). The results demonstrated a decrease in PC-3 viability upon treatment with PEG-Fe₃O₄ or GSH-PEG-Fe₃O₄ nanoparticles in a concentration-dependent manner. However, the cytotoxicity was not time-dependent. Due to the superparamagnetic behavior of PEG-Fe₃O₄ or GSH-PEG-Fe₃O₄ nanoparticles, upon the application of an external magnetic field, those nanoparticles can be guided to the target site yielding local toxic effects to tumor cells with minimal side effects to normal tissues, highlighting the promising uses of iron oxide nanoparticles in biomedical applications.     

LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> hollow nano-micro hierarchical microspheres as advanced cathode for lithium ion batteries

The high-voltage spinel-type LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode material for next-generation lithium ion batteries. In this study, hollow LNMO microspheres have been synthesized via co-precipitation method accompanied with high-temperature calcinations. The physical and electrochemical properties of the materials are characterized by x-ray diffraction (XRD), TGA, RAMAN, CV, scanning electron microscope (SEM), transmission electon microscopy (TEM), electrochemical impendence spectroscopy (EIS), and charge-discharge tests. The results prove that the microspheres combine hollow structures inward and own a cubic spinel structure with space group of Fd-3m, high crystallinity, and excellent electrochemical performances. With the short Li⁺ diffusion length and hollow structure, the hierarchical LNMO microspheres exhibit 138.2 and 108.5 mAh g^?1 at 0.5 and 10 C, respectively. Excellent cycle stability is also demonstrated with more than 98.8 and 88.2 % capacity retention after 100 cycles at 1 and 10 C, respectively.     

Preparation and characterization of Y-Fe alloy nanowires by template-assisted electrodeposition from aqueous solution

In this study, a method was proposed for the preparation of Y-Fe alloy nanowires by PC membrane template-assisted electrodeposition from aqueous solution. Citric acid  acted as complexing agent was used into the solution to fabricate Y-Fe alloy nanowires. The electrolyte solution consisted of 5 g L^?1 YCl₃, 12.5 g L^?1 FeSO·6H₂O, different concentrations of citric acid , 25 g L^?1 boric acid in deionized water. The energy dispersive spectroscopy (EDS) found that the content of Y in the nanowires can be controlled by citric acid concentration and the current intensity, and the content of Y could reach up to 33.16 wt%. Scanning electron microscopy (SEM), BET specific surface area (BET), and X-ray diffraction (XRD) showed that there was a shift in the structure of nanowires from semicrystalline to amorphous due to the change of Y content, and their shapes were approximately 100 nm in diameter and 6 μm in length; the surface areas of nanowires were about 3.97 m²/g. Fourier transform infrared (FTIR) spectroscopy, UV–Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS) indicated the formation of Y-Fe alloy, Y₂O₃ and Fe₂O₃   existed  in the outer layer of nanowires. The magnetic field applied both parallel and perpendicular to the nanowires by alternating gradient magnetometer (AGM) showed small magnetic anisotropy and low coercivity with easy axis of magnetization perpendicular to the nanowires. In addition, the magneto-optic Kerr effect (MOKE) was investigated, and a Kerr rotation angle of 29 mdeg was obtained.     

Superparamagnetic silica nanoparticles with immobilized metal affinity ligands for protein adsorption

Superparamagnetic silica-coated magnetite (Fe₃O₄) nanoparticles with immobilized metal affinity ligands were prepared for protein adsorption. First, magnetite nanoparticles were synthesized by co-precipitating Fe²⁺ and Fe³⁺ in an ammonia solution. Then silica was coated on the Fe₃O₄ nanoparticles using a sol–gel method to obtain magnetic silica nanoparticles. The condensation product of 3-Glycidoxypropyltrimethoxysilane (GLYMO) and iminodiacetic acid (IDA) was immobilized on them and after charged with Cu²⁺, the magnetic silica nanoparticles with immobilized Cu²⁺ were applied for the adsorption of bovine serum albumin (BSA). Scanning electron micrograph showed that the magnetic silica nanoparticles with an average size of 190 nm were well dispersed without aggregation. X-ray diffraction showed the spinel structure for the magnetite particles coated with silica. Magnetic measurement revealed the magnetic silica nanoparticles were superparamagnetic and the saturation magnetization was about 15.0 emu/g. Protein adsorption results showed that the nanoparticles had high adsorption capacity for BSA (73 mg/g) and low nonspecific adsorption. The regeneration of these nanoparticles was also studied.     

Fabrication of Au nanorod‐coated Fe3O4 microspheres as SERS substrate for pesticide analysis by near‐infrared excitation

Au nanorods coated Fe3O4 (Fe₃O₄@NRs) microspheres were designed as functional surface‐enhanced Raman scattering substrate with a feature of magnetic property and used for detection of pesticide residues that are annually used in agriculture by near‐infrared (NIR) excitation. With this strategy, the Fe₃O₄ microspheres were synthesized by hydrothermal method and surface functionalized with polyethylenimine, and then coated with Au nanorods densely. The Raman spectra were carried out by NIR excitation and 4‐ATP was chosen as the probe molecule. The results showed a good SERS activity of the Fe₃O₄@NRs microspheres. Moreover, this substrate could be used for pesticide analysis by portable Raman spectrometer with NIR excitation. Especially, the microspheres could be transferred from pesticides contaminated fruits peel to specially cleaned glass slide with the aid of the external magnetic field, by which the strong fluorescence of the apple components can be avoided while performing the pesticide analysis of fruits peel. Copyright © 2015 John Wiley & Sons, Ltd.     

The optimized preparation and electrochemical properties of LiMn1.95Co0.05O4 and Al2O3-coated LiMn1.95Co0.05O4

Cathode material LiMn_1.95Co_0.05O₄ for lithium ion battery was synthesized via solid state reaction, and calcination temperature and time were investigated, respectively. Thermogravimetry (TG) and differential thermal analysis (DTA) measurements were utilized to determine the calcination temperature of precursor sample. The optimized calcination temperature and time are 850 °C and 15 h. The surface of LiMn_1.95Co_0.05O₄ cathode is coated using Al₂O₃ coating materials. The phase structures, surface morphologies, and element types of the prepared LiMn_1.95Co_0.05O₄ and Al₂O₃-coated LiMn_1.95 Co_0.05O₄ were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy spectrum analysis (EDS). The 0.5 wt% Al₂O₃-coated compound exhibited better specific capacity and capacity retention than bare sample. The initial discharge capacity was 140.9 mAh/g and capacity retention was 96.7 % after 10 cycles at 0.1 C. Such enhancements are attributed to the presence of a stable Al₂O₃ layer which acts as the interfacial stabilizer on the surface of LiMn_1.95Co_0.05O₄.     

Preparation and characterization of magnetic P(St-co-MAA-co-AM) microspheres

In this study, magnetic polymer-coated microspheres were prepared by the microemulsion polymerization of styrene (St), methacrylic acid (MAA), acryamide (AM) in the presence of emulsifiers with the size of 1–5 μm. The magnetic material (i.e. Fe₃O₄) coated with oleic acid used in the preparation of the microspheres was synthesized in a classical co-precipitation procedure. The morphological and magnetic properties of the microspheres were investigated by different techniques (i.e. TEM, TGA, optical microscopy, vibrating sample magnetometer). The results indicated that the magnetic microspheres were superparamagnetic, well shaped spheres, mono-dispersed with abundant functional groups on the surfaces of the magnetic microspheres and good thermal stability. The microspheres could be linked well with the avidin and FITC antibody.     

Clean and reproducible SERS substrates for high sensitive detection by solid phase synthesis and fabrication of Ag‐coated Fe3O4 microspheres

The solid‐phase synthesis of Ag‐coated Fe₃O₄ microsphere was elaborated under argon atmosphere. This straightforward process utilized neither reducing agents nor electric current and involved the dry mixing of a precursor of CH₃COOAg with Fe₃O₄ microspheres followed by heating in an inert atmosphere. Ag nanoparticles with diameters of 30–50 nm were well‐decorated on the surfaces of Fe₃O₄ microspheres. The as‐synthesized Ag‐coated Fe₃O₄ microspheres were assembled into a surface‐enhanced Raman scattering (SERS) substrate holding clean and reproducible properties under an externally exerted magnetic force. Using these nanoprobes, analyte molecules can be easily captured, magnetically concentrated, and analyzed by SERS. This clean SERS substrate was used to detect 4‐aminothiophenol, even at a concentration as low as1.0 × 10^–12 M. In particular, the Ag‐coated Fe₃O₄ microspheres, acting as reproducible SERS substrates, were applied to detect methyl‐parathion and 4‐mercaptopyridine. Strong SERS signals were obtained with the analytes at a concentration of 1.0 × 10^–6 M. The unique, clean, and reproducible properties indicate a new route in eliminating the single‐use problem of traditional SERS substrates and show promising applications for detecting other organic pollutants. Similarly, this work may provide a new model system to a series of metal–Fe₃O₄ decorating reactions for a reproducible utilization. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of an Organic–Inorganic Hybrid Polymeric Material and Its Adsorption Performance Characterization Toward Acrylamide

An organic–inorganic hybrid functionalized material was successfully synthesized by a surface molecular imprinting technique combined with a nonhydrolytic sol–gel process using acrylamide as the template, methacrylic acid as the functional monomer, methacryloxypropyltrimethoxysilane as the cross-linker, and magnetic chitosan microspheres as the support material. The adsorption ability and selectivity of this material toward acrylamide was characterized. Experimental results showed that the imprinted polymer exhibited better recognition and selective performance toward acrylamide than the nonimprinted polymer. The saturated binding capacity (Q _max) was 104.68 mg/g, and the equilibrium dissociation constant was 263.16 mg/mL. This prepared material also offered fast kinetics for the adsorption and desorption of acrylamide. After shaking for 5 min, an adsorption capacity of 4.71 mg/g was obtained, and it almost reached the adsorption equilibrium within 90 min.     

One‐Dimensional Magnetic Composite of Polypyrrole‐Containing Carbon Nanotubes/Ni0.75Zn0.25Fe2O4

A novel one‐dimensional electromagnetic nanocomposite of polypyrrole (PPY) containing carbon nanotubes (CNTs)/Ni_0.75Zn_0.25Fe₂O₄ was synthesized by an in‐situ polymerization method. The composite was characterized by x‐ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and Fourier transform infrared. The XRD results confirmed that PPY, CNTs, and Ni_0.75Zn_0.25Fe₂O₄ coexisted in the composite. The TEM and HRTEM results indicated that PPY coated the surface of the CNTs/Ni_0.75Zn_0.25Fe₂O₄ with a thickness of 15–30 nm. The lattice spacings, according to the first main peak of the CNTs, Ni_0.75Zn_0.25Fe₂O₄, and PPY, was about 0.34 nm, 0.25 nm, and 0.42 nm, respectively. The FTIR result also indicated that the PPY formed in the composite. A test of magnetic properties indicated that the composite was ferromagnetic with the saturated magnetization of 12.86 electromagnetic units (emu)/g, and the coercive of 127.18 Oersted (Oe).