Improving Pullulanase Catalysis via Reversible Immobilization on Modified Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@Polydopamine Nanoparticles

To improve the catalysis of pullulanase from Anoxybacillus sp.WB42, Fe₃O₄@polydopamine nanoparticles (Fe₃O₄@PDA) were prepared and modified with functional groups for immobilization of pullulanases via covalent binding or ionic adsorption. Immobilized pullulanases had lower thermal stability than that of free pullulanase, whereas their catalysis depended on the surface characteristics of nanoparticles. As for covalent immobilization of pullulanases onto Fe₃O₄@PDA derivatives, the spacer grafted onto Fe₃O₄@PDA made the catalytic efficiency of pullulanase increase up to the equivalence of free enzyme but dramatically reduced the pullulanase thermostability. In contrast, pullulanases bounded ionically to Fe₃O₄@PDA derivatives had higher activity recovery and catalytic efficiency, and their catalytic behaviors varied with the modifier grafted onto Fe₃O₄@PDA. Among these immobilized pullulanases, ionic adsorption of pullulanase on Fe₃O₄@PDA-polyethyleneimine-glycidyltrimethylammonium gave a high-performance and durable catalyst, which displayed not only 1.5-fold increase in catalytic efficiency compared to free enzyme but also a significant improvement in operation stability with a half of initial activity after 27 consecutive cycles with a total reaction time of 13.5 h, and was reversible, making this nanoparticle reusable for immobilization.     

Hydrophilic Fe3O4 nanoparticles prepared by ferrocene as high‐efficiency heterogeneous Fenton catalyst for the degradation of methyl orange

Hydrophilic Fe₃O₄ nanoparticles were prepared with ferrocene as an iron source via the thermal decomposition method and their catalytic response towards methyl orange was investigated. The effects of the pH, temperature, H₂O₂ dosage, catalyst dosage and initial dye concentration on the degradation of methyl orange were researched in detail. Furthermore, the stability of the catalyst was evaluated by measuring the degradation rate in eight successive cycles. The study demonstrates that methyl orange can be completely degraded i.e., a 99% degratation rate was obtained within 3 min. This excellent catalytic activity is attributed to the small size and good dispersibility of the nanoparticles, which stimulate the rapid and massive generation of reactive oxygen species in the heterogeneous Fenton reaction. In addition, the magnetic separation of the catalyst offers great prospects for fast and economical decontamination of dye polluted water.     

Magnetically recoverable AlFe/Te nanocomposite as a new catalyst for the facile esterification reaction under neat conditions

In this work, a new Fe₃O₄/AlFe/Te nanocomposite was synthesized by a one‐step sol–gel method. The Fe₃O₄ magnetic nanoparticles (MNPs) were prepared and then mixed with aluminum telluride (Al₂Te₃) in an alkali medium to produce the desired catalyst. After characterization of the Fe₃O₄/AlFe/Te nanocomposite by SEM, TEM, EDS, XRD, and ICP analyses, it was used in the esterification reaction. This heterogeneous catalyst showed high catalytic activity in the esterification of commercially available carboxylic acids with various alcohols to produce the desired esters at high conversions under neat conditions. The Fe₃O₄/AlFe/Te nanocomposites were separated from the reaction mixture via an external magnet and re‐used 8 times without significant loss of catalytic activity.     

One Step Preparation of Reduced Graphene Oxide/Pd–Fe3O4@Polypyrrole Composites and Their Application in Catalysis

The simple preparation of catalysts with superior catalytic activity and good reusability is highly desirable. Herein, we report a novel strategy to construct reduced graphene oxide (rGO)/Pd–Fe₃O₄@polypyrrole (PPy) catalysts with Pd and Fe₃O₄ nanoparticles anchored on a rGO nanosheet surface and wrapped in a PPy shell. The synthesis and assembly of both the Pd and Fe₃O₄ nanoparticles, the preparation of the PPy layer, and the reduction of graphene oxide nanosheets were finished in one step. In the system, the PPy layer not only prevented aggregation of Pd and Fe₃O₄ nanoparticles, but also generated a synergistic effect with precursor Pd²⁺ ions, which led to a high dispersity of as‐prepared Pd nanoparticles. Although the procedure was simplified to one step, the catalytic activity and reusability were not sacrificed. In the reduction of 4‐nitrophenol, their catalytic performance was better than that in recent reports. Moreover, the catalysts showed good reusability owing to their magnetic properties.     

Preparation of Polyvinyl Acetate (PVAc) and PVAc–Ag–Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Composite Nanofibers by Electro-spinning Method

Magnetite (Fe₃O₄) and silver nanoparticles were synthesized via simple chemical reactions at room temperature. Poly vinyl acetate (PVAc) nano-fibers and their nanocomposites with Ag and Fe₃O₄ were prepared by electro-spinning method. Effect of various electric potentials and distance on the morphology and diameter of fibers were investigated. Photocatalytic properties of silver in degradation five different dyes as organic pollutants in water were investigated. Fe₃O₄ nanoparticles exhibit a super-paramagnetic behavior at room temperature. Nontoxic nanoparticles appropriately enhanced both thermal stability and flame retardant property of the PVAc matrix. In the presence of flame, Fe₃O₄ nanoparticles remain together (show resistance to drip falling because of magnetic interaction) and build a barrier against flame.     

Preparation of a novel Fe3O4/graphene oxide hybrid for adsorptive removal of methylene blue from water

In this work, a novel Fe₃O₄/graphene oxide (GO) hybrid was prepared and its removal ability of cationic methylene blue dye from water was investigated. To improve the dispersability of Fe₃O₄/GO hybrid in water, GO was first modified by polyethylene glycol (PEG) via a click approach before deposition of Fe₃O₄ nanoparticles onto its surface. The successful modification of GO surface and the deposition of Fe₃O₄ nanoparticles were confirmed by transmission electron microscopy directly. The saturation magnetization of the resultant Fe₃O₄/GO hybrid is 7.8 eum/g. The adsorption capacities of Fe₃O₄/GO hybrid for methylene blue at 35 and 60°C were as high as 96.05 and 120.05 mg/g, respectively. Moreover, the Langmuir, Freundlich, and Temkin models are used to investigate the isothermal adsorption behavior of Fe₃O₄/GO hybrid.     

Fe3O4@L‐arginine magnetic nanoparticles: A novel and magnetically retrievable catalyst for the synthesis of 1′3‐diaryl‐2N‐azaphenalene

The catalytic activity of l ‐arginine‐coated nano‐Fe₃O₄ particles (Fe₃O₄@l ‐arginine) proves they are a novel magnetic catalyst without the use of heat and reflux for the synthesis of 1,3‐diaryl‐2‐N‐azaphenalene derivatives and n‐acyl‐1,3‐diaryl‐2‐N‐azaphenylene derivatives in a one‐pot pseudo‐five‐component condensation reaction of compounds of 2,7‐naphthalene diol, aldehydes, and ammonia derivatives (ammonium acetate or ammonium hydrogen phosphate) and solvent (water and alcohol) with high yield and short reaction times, economical, and simple workup. The structure and magnetic properties of the obtained nanoparticles were characterized via Fourier transform infrared spectroscopy (IR) and field emission scanning electron microscopy (FE‐SEM). The results demonstrated that the average size of the synthesized magnetite nanoparticles is about 21 nm. In addition, the heterogeneous catalyst can be easily recovered magnetically and can be reused for further runs without significant loss of its catalytic activity.     

Synthesis of Fe3O4, Fe2O3, Ag/Fe3O4 and Ag/Fe2O3 nanoparticles and their electrocatalytic properties

Two important iron oxides:Fe3O4 and Fe2O3,as well as Fe3O4 and Fe2O3 nanoparticles mingling with Ag were successfully synthesized via a hydrothermal procedure.The samples were confirmed and characterized by X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).The morphology of the samples was observed by transmission electron microscopy(TEM).The results indicated Fe3O4,Fe2O3,Ag/Fe3O4 and Ag/Fe2O3 samples all were nanoparticles with smaller sizes.The samples were modified on a glassy carbon electrode and their elctrocatalytic properties for p-nitrophenol in a basic solution were investigated.The results revealed all the samples showed enhanced catalytic performances by comparison with a bare glassy carbon electrode.Furthermore,p-nitrophenol could be reduced at a lower peak potential or a higher peak current on a glassy carbon electrode modified with Ag/Fe3O4 or Ag/Fe2O3 composite nanoparticles.     

Thermally responsive complex polymer networks containing Fe3O4 nanoparticles: Composition/morphology/property relationship

In this research, the synthesis and properties of thermally responsive complex polymer networks containing Fe₃O₄ nanoparticles were studied. First, a stable ferrofluid containing Fe₃O₄ nanoparticles was synthesized via a coprecipitation method in the presence of a poly(acrylic acid) oligomer. This stable ferrofluid could mix well with water‐soluble monomers by the adjustment of its pH value. Second, a thermally responsive copolymer was synthesized in the presence of the ferrofluid containing Fe₃O₄ nanoparticles to obtain the complex polymer networks. By the adjustment of the pH value, the ferrofluid could remain stable in the polymerization system, in which N‐isopropylacrylamide (NIPAAm) and methacrylic acid (MAA) were used as comonomers to provide thermoresponsive properties and acid groups and ammonium persulfate and sodium metabisulfite were used as the redox initiator system. Several variables, such as the molar ratio of MAA to NIPAAm, the concentrations of the monomers and crosslinking agent, the addition of an ammonium solution, and the content of the ferrofluid, were studied in this polymerization. Their effects on the morphology, structure, polymerization rate, and thermal properties of the complex polymer networks were discussed. The swelling and thermoresponsive behaviors of the complex polymer networks containing Fe₃O₄ nanoparticles were also studied, and the composition–morphology–property relationship was established. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5923–5934, 2005     

Green synthesis of Fe3O4/ZnO magnetic core-shell nanoparticles by Petasites hybridus rhizome water extract and their application for the synthesis of pyran derivatives: Investigation of antioxidant and antimicrobial activity

In this research, Fe₃O₄/ZnO magnetic core-shell nanoparticles (Fe₃O₄/ZnO MCNPs) were synthesized through a green method using Petasites hybridus rhizome water extract as a reducing and stabilizing agent. The morphology and size of the Fe₃O₄/ZnO MCNPs was identified by X-ray diffraction, scanning electron microscopy, and Energy-dispersive X-ray spectroscopy (EDX) analysis. The catalytic activity of the Fe₃O₄/ZnO MCNPs was evaluated in the efficient and green preparation of pyran derivatives in excellent yield using three-component reactions of dimedone, aldehydes, and malononitrile in ethanol at room temperature. The ability of some synthesized compounds to scavenge the 2,2-diphenyl-1-picrylhydrazyl radical was measured and the results proved this observation. Moreover, the antimicrobial activity of some synthesized compounds was proved by employing the disk diffusion test on Gram-positive and Gram-negative bacteria. The results for the disk diffusion test showed that compounds ( 4c, 4d, 4f and 4g ) prevented bacterial growth.     

High catalytic performance of the first electrospun nano-biohybrid,Mn3O4/copper complex/polyvinyl alcohol,from Amaranthus spinosus plant for biomimetic oxidation reactions

In this study, a novel nano-biocomposite, polyvinylalcohol/Mn₃O₄/water-soluble copper complex (PVA/Mn₃O₄/CuWSC), was produced from Amaranthus spinosus. By combining water-soluble copper nanocomplex and Mn₃O₄ nanoparticles along with polyvinyl alcohols and extracts of this plant, this bio nanomaterial was prepared via electrospinning process. This nanohybrid was characterized using transmission electron microscopy, scanning electron microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and elemental analysis. Based on its catalytic activities, it is considered a heterogeneous catalyst and is used for the oxidation of alcohols in industrial reactions. It can oxidize the primary and secondary alcohols to corresponding aldehyde and ketone products with high yield and excellent selectivity using H₂O₂ under solvent-free conditions. The recyclability and reusability of PVA/Mn₃O₄/CuWSC show that it can be a promising catalyst for clean industrial catalytic applications.     

Thermogravimetric studies on catalytic effect of metal oxide nanoparticles on asphaltene pyrolysis under inert conditions

This study investigated the catalytic effect of NiO, Co₃O₄ and Fe₃O₄ nanoparticles toward asphaltene thermal decomposition (pyrolysis) under inert conditions. Asphaltene adsorbed onto the selected nanoparticles were subjected to thermal decomposition up to 800?°C in a thermogravimetric analyzer. The presence of nanoparticles caused a significant decrease in the asphaltene decomposition temperature and activation energy. Activation energies for the process were calculated using the Ozawa?CFlynn?CWall method. All the selected metal oxide nanoparticles showed high catalytic activity toward asphaltene decomposition in the following order NiO?>?Co₃O₄?>?Fe₃O₄. This study confirms that metal oxide nanoparticles can significantly enhance the thermal decomposition of heavy hydrocarbons, like asphaltenes.     

Preparation of ultrafine Cu1.5Mn1.5O4 spinel nanoparticles and its application in p-nitrophenol reduction

In this work, ultrafine Cu_1.5Mn_1.5O₄ spinel nanoparticles were successfully synthesized by a sol–gel method combined with two complexing agents, which was firstly employed in the reductive transformation from p-nitrophenol into p-aminophenol. The effect of calcination temperature on the crystal phase and microstructure of Cu_1.5Mn_1.5O₄ nanoparticles was investigated in this article. It was found that Cu_1.5Mn_1.5O₄ nanoparticles with pure spinel phase can be obtained at 500 °C with the help of EDTA acid–citric acid complexing agents. Below 500 °C, there exists some Mn₂O₃ impure phase. SEM characterization indicated that the particle size of the spinel Cu_1.5Mn_1.5O₄ rapidly increases above 600 °C. The catalytic experimental results show that the Cu_1.5Mn_1.5O₄ nanoparticles prepared at 500 °C exhibit the highest catalytic activity which is even superior to some precious metal catalysts. With the calcination temperature increasing, the catalytic activity of Cu_1.5Mn_1.5O₄ spinel nanoparticles gradually degrades which can be ascribed to the particle size growth of Cu_1.5Mn_1.5O₄. It can also be observed that all the oxide samples, namely CuO, Mn₂O₃ and Cu_1.5Mn_1.5O₄, possess certain catalytic ability for the transformation from p-nitrophenol into p-aminophenol. However, the catalytic activity of Cu_1.5Mn_1.5O₄ spinel nanoparticles is obviously higher than CuO and Mn₂O₃. Especially, Mn₂O₃ alone has very poor catalytic activity in the reduction of p-nitrophenol.

     

Preparation of choline chloride–urea deep eutectic solvent‐modified magnetic nanoparticles for synthesis of various 2‐amino‐4H‐pyran derivatives in water solution

A novel hybrid magnetic nanocatalyst was synthesized by covalent coating of Fe₃O₄ magnetic nanoparticles with choline chloride–urea deep eutectic solvent using 3‐iodopropyltrimethoxysilane as a linker. The structure of this new catalyst was fully characterized via elemental analysis, transmission and scanning electron microscopies, X‐ray diffraction and Fourier transform infrared spectroscopy. It was employed in the synthesis of various 2‐amino‐4H ‐pyran derivatives in water solution via an easy and green procedure. The desired products were obtained in high yields via a three‐component reaction between aromatic aldehyde, enolizable carbonyl and malononitrile at room temperature. The employed nanocatalyst was easily recovered using a magnetic field and reused four times (in subsequent runs) with less than 8% decrease in its catalytic activity.     

Nano-Co3O4-catalyzed microwave-assisted one-pot synthesis of some seleno [2 , 3-b ] pyridine/quinoline derivatives

For the efficient synthesis of transition-metal cobalt oxide nanoparticles (Co₃O₄ NPs) without using any costly and toxic solvent or complicated equipment, the co-precipitation method was used in this work. Using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), UV–Vis spectrophotometry, Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), the prepared Co₃O₄ NPs were characterized and identified. The influence of prepared Co₃O₄ NPs on the developmental synthesis of some selenopyridine/quinoline derivatives under different microwave irradiation powers and irradiation times was investigated via click (reaction) chemistry. The reusable Co₃O₄ nanoparticles have high catalytic activity under microwave irradiation for the synthesis of organoselenium compounds with higher yields (>?90%), milder reaction conditions and shorter time without significantly decreasing the reaction rates and yields.

     

Synthesis of Co3O4 nanoparticles with controllable size and their catalytic properity

Co₃O₄ nanoparticles of controllable size were synthesized via a variant microemulsion method combined with hydrothermal treatment. With this improved method, Co₃O₄ nanoparticles with uniform shape and narrow size distribution were controllably synthesized. By varying the surfactant and water ratio, particles of around 27.97 nm, 42.88 nm and 48.99 nm were synthesized. These nanoparticle catalysts behaved differently at low and high temperature. These samples showed high activity for CO oxidation and 100% CO conversion was achieved at 30 °C. However, the catalysts gradually lost their activity after about 100 min. Our research found that CO₂ had a huge influence on the stability of catalysts at low temperature. The relationship between stability at 30 °C and ratio of Co³⁺/Co²⁺, as well as particle size and desorption rate of CO₂, was also thoroughly investigated in this work.     

Synthesis of pH‐responsive magnetic yolk–shell nanoparticles: A comparison between conventional etching and new deswelling approaches

Iron oxide (Fe₃O₄) magnetic nanoparticles as movable cores were used to synthesize yolk–shell nanoparticles with pH‐responsive shell composed of ethylene glycol dimethacrylate (EGDMA)‐crosslinked poly(acrylic acid) (PAA) via two different routes. In the first more common route, Fe₃O₄ nanoparticles were coated with silica layer via the Stöber process to yield Fe₃O₄@SiO₂ core–shell nanoparticles, subsequently used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe₃O₄@SiO₂@P(AA‐EGDMA). The silica layer was selectively removed through alkali etching to yield Fe₃O₄@air@P(AA‐EGDMA). In the second route, Fe₃O₄ nanoparticles without any stabilization were used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe₃O₄@P(AA‐EGDMA) core–shell nanoparticles. The nanoparticles were subsequently dispersed in acidic medium of pH = 2. Yolk–shell Fe₃O₄@air@P(AA‐EGDMA) nanoparticles were formed through deswelling of crosslinked PAA because of protonation of carboxyl groups at low pH values. Various techniques were utilized to investigate the characteristics of the synthesized core–shell nanoparticles. Formation of yolk–shell nanostructure was observed for both synthesis routes, namely etching of silica layer and deswelling approaches, from vibrating sample magnetometry and transmission electron microscopy results. Both types of nanoparticles showed pH‐responsive behaviour, i.e. decrease in absorption with increase in pH, as examined using UV–visible spectroscopy.     

Fe3O4/SiO2 nanoparticles: an efficient and magnetically recoverable nanocatalyst for the one-pot multicomponent synthesis of diazepines

In this research, a new protocol for the one-pot multicomponent synthesis of diazepine derivatives using a 1,2-diamine, a linear or cyclic ketone, and an isocyanide in the presence of a catalytic amount of silica-supported iron oxide (Fe₃O₄/SiO₂) nanoparticles at ambient temperature in excellent yields is described.     

Fe3O4 MNPs-DETA/Benzyl-Br3: A new magnetically reusable catalyst for the oxidative coupling of thiols

We report a new strategy to immobilize a bromine source on the surface of magnetic Fe₃O₄ nanoparticles (Fe₃O₄ MNPs-DETA/Benzyl-Br₃) leading to a magnetically recoverable catalyst, which exhibits high catalytic efficiency in oxidative coupling of thiols to the disulfides (89–98%). The Fe₃O₄ MNPs-DETA/Benzyl-Br₃ catalyst was fabricated by anchoring 3-chloropropyltrimethoxysilane (CPTMS) on magnetic Fe₃O₄ nanoparticles, followed with N-benzylation and reaction with bromine in tetrachloridecarbon. The resulting nanocomposite was analyzed by a series of characterization techniques such as FT-IR, SEM, TGA, VSM and XRD. The catalyst could be recovered via magnetic attraction and could be recycled at least 5 times without appreciable decrease in activity.     

Synthesis of Chromene Derivatives via Three‐Component Reaction of 4‐hydroxycumarin Catalyzed by Magnetic Fe3O4 Nanoparticles in Water

An easy and effective procedure for one‐pot three components coupling of 4‐hydroxycumarin, isothiocyanates, and isocyanides in water by employing magnetically recoverable Fe₃O₄ nanoparticles is described. Variety of chromene were produced a derivatives in high yields by using of this procedure. The catalyst can be recovered and recycled without a considerable decrease in the catalytic activity.