Iron oxide nanoparticles coated with green tea extract as a novel magnetite reductant and stabilizer sorbent for silver ions: Synthetic application of Fe3O4@green tea/Ag nanoparticles as magnetically separable and reusable nanocatalyst for reduction of 4‐nitrophenol

Green tea extract having many phenolic hydroxyl and carbonyl functional groups in its molecular framework can be used in the modification of Fe₃O₄ nanoparticles. Moreover, the feasibility of complexation of polyphenols with silver ions in aqueous solution can improve the surface properties and capacity of the Fe₃O₄@green tea extract nanoparticles (Fe₃O₄@GTE NPs) for sorption and reduction of silver ions. Therefore, the novel Fe₃O₄@GTE NPs nano‐sorbent has potential ability as both reducing and stabilizing agent for immobilization of silver nanoparticles to make a novel magnetic silver nanocatalyst (Fe₃O₄@GTE/Ag NPs). Inductively coupled plasma analysis, transmission and scanning electron microscopies, energy‐dispersive X‐ray and Fourier transform infrared spectroscopies, and vibrating sample magnetometry were used to characterize the catalyst. Fe₃O₄@GTE/Ag NPs shows high catalytic activity as a recyclable nanocatalyst for the reduction of 4‐nitrophenol at room temperature.     

Functionalization of superparamagnetic Fe3O4@SiO2 nanoparticles with a Cu(II) binuclear Schiff base complex as an efficient and reusable nanomagnetic catalyst for N‐arylation of α‐amino acids and nitrogen‐containing heterocycles with aryl halides

Fe₃O₄@SiO₂ nanoparticles was functionalized with a binuclear Schiff base Cu(II)‐complex (Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs) and used as an effective magnetic hetereogeneous nanocatalyst for the N‐arylation of α‐amino acids and nitrogen‐containig heterocycles. The catalyst, Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs, was characterized by Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐vis) analyses step by step. Size, morphology, and size distribution of the nanocatalyst were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and dynamic light scatterings (DLS) analyses, respectively. The structure of Fe₃O₄ nanoparticles was checked by X‐ray diffraction (XRD) technique. Furthermore, the magnetic properties of the nanocatalyst were investigated by vibrating sample magnetometer (VSM) analysis. Loading content as well as leaching amounts of copper supported by the catalyst was measured by inductive coupled plasma (ICP) analysis. Also, thermal studies of the nanocatalyst was studied by thermal gravimetric analysis (TGA) instrument. X‐ray photoelectron spectroscopy (XPS) analysis of the catalyst revealed that the copper sites are in +2 oxidation state. The Fe₃O₄@SiO₂/Schiff base‐Cu(II) complex was found to be an effective catalyst for C–N cross‐coupling reactions, which high to excellent yields were achieved for α‐amino acids as well as N‐hetereocyclic compounds. Easy recoverability of the catalyst by an external magnet, reusability up to eight runs without significant loss of activity, and its well stability during the reaction are among the other highlights of this catalyst.     

Magnetically recyclable nano copper/chitosan in O‐arylation of phenols with aryl halides

Interaction of chitosan (CS) with Fe₃O₄, followed by embedding Cu nanoparticles (NPs) on the magnetic surface through adsorption of Cu²⁺, and its reduction to Cu^o via NaBH₄, offers a reusable efficient catalyst (Fe₃O₄/CS‐Cu NPs) that is employed in cross‐coupling reactions of aryl halides with phenols, which affords the corresponding diaryl ethers, with good to excellent yields. The catalyst is completely recoverable from the reaction mixture by using an external magnet. It can be reused four times, without significant loss in its catalytic activity.     

Green synthesis of reduced graphene oxide/Fe3O4/Ag ternary nanohybrid and its application as magnetically recoverable catalyst in the reduction of 4‐nitrophenol

Materials having both magnetic and catalytic properties have shown great potential for practical applications. Here, a reduced graphene oxide/iron oxide/silver nanohybrid (rGO/Fe₃O₄/Ag NH) ternary material was prepared by green synthesis of Ag on pre‐synthesized rGO/Fe₃O₄. The as‐prepared rGO/Fe₃O₄/Ag NH was characterized using Fourier transform infrared spectroscopy, X‐ray diffractometry, Raman spectroscopy, vibrating sample magnetometry, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. rGO sheets were covered with Fe₃O₄ (8–16 nm) and Ag (18–40 nm) nanoparticles at high densities. The mass percentages were 13.47% (rGO), 62.52% (Fe₃O₄) and 24.01% (Ag). rGO/Fe₃O₄/Ag NH exhibited superparamagnetic behavior with high saturated magnetization (29 emu g⁻¹ at 12 kOe), and efficiently catalyzed the reduction of 4‐nitrophenol (4‐NP) with a rate constant of 0.37 min⁻¹, comparable to those of Ag‐based nanocatalysts. The half‐life of 4‐NP in the presence of rGO/Fe₃O₄/Ag NH was ca 1.86 min. rGO/Fe₃O₄/Ag NH could be magnetically collected and reused, and retained a high conversion efficiency of 94.4% after the fourth cycle. rGO/Fe₃O₄/Ag NH could potentially be used as a magnetically recoverable catalyst in the reduction of 4‐NP and environmental remediation.     

α‐Fe2O3 Polyhedral Nanoparticles Enclosed by Different Crystal Facets: Tunable Synthesis,Formation Mechanism Analysis,and Facets‐dependent n‐Butanol Sensing Properties

Three kinds of polyhedral α‐Fe₂O₃ nanoparticles enclosed by different facets including oblique parallel hexahedrons (op‐hexahedral NPs), cracked oblique parallel hexahedrons (cop‐hexahedral NPs), and octadecahedral nanoparticles (octadecahedral NPs), were successfully prepared by simply changing only one reaction parameter in the hydrothermal process. The structural and morphological of the products were systematically studied using various characterizations including X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), revealing that the three kinds of α‐Fe₂O₃ nanoparticles were enclosed by {104}, {110}/{104}, and {102}/{012}/{104} crystal planes, respectively. The exposed facets and shape of the nanocrystals were found to be affected by the adding amount of ethylene glycol in the solvent. The gas‐sensing properties and mechanism of the α‐Fe₂O₃ samples were studied and analyzed, which indicated that the sensitivity of the three samples followed the order of octadecahedral NPs > cop‐hexahedral NPs > op‐hexahedral NPs due to the combined effects of specific surface area and oxygen defects in the nanocrystals.     

Synthesis and characterization of copper(II) Schiff base complex supported on Fe3O4 magnetic nanoparticles: a recyclable catalyst for the one‐pot synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones

Fe₃O₄–Schiff base of Cu(II) is found to be a recyclable and heterogeneous catalyst for the rapid and efficient synthesis of various 2,3‐dihydroquinazolin‐4(1H)‐one derivatives from the two‐component condensation of 2‐aminobenzamide and an aldehyde. This reaction is simple, green and cost‐effective. Separation and recycling can also be easily done by magnetic decantation of the Fe₃O₄ nanoparticles with an external magnet. The prepared catalyst was characterized using thermogravimetry, Fourier transform infrared spectroscopy, vibrating sample magnetometry, inductively coupled plasma analysis, X‐ray diffraction and scanning electron microscopy. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and characterization of bromine source supported on magnetic Fe3O4 nanoparticles: A new,versatile and efficient magnetically separable catalyst for organic synthesis

Tribenzylammonium tribromide supported onto magnetic nanoparticles (Br₃‐TBA‐Fe₃O₄) as a bromine source was successfully synthesized and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and vibrating sample magnetometry. The synthesized catalyst is shown to be a versatile and highly efficient heterogeneous catalyst for the Knoevenagel condensation and synthesis of 2,3‐dihydroquinazolin‐4(1H )‐one and polyhydroquinoline derivatives. To the best of the authors' knowledge, this is the first report of the use of a bromine source immobilized on Fe₃O₄ nanoparticles as a magnetically separable catalyst for these reactions. The nanosolid catalyst can be magnetically recovered and reused readily several times without significant loss in catalytic efficiency.     

Fe3O4‐supported Schiff‐base copper (II) complex: A valuable heterogeneous nanocatalyst for one‐pot synthesis of new pyrano[2,3‐b]pyridine‐3‐carboxamide derivatives

A novel Cu (II) Schiff‐base complex immobilized on core‐shell magnetic Fe₃O₄ nanoparticles (Fe₃O₄@SPNC) was successfully designed and synthesized. The structural features of these nanoparticles were studied and confirmed by using various techniques including FT‐IR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDS), vibrating sample magnetometer (VSM), X‐Ray diffraction (XRD), wavelength dispersive X‐ray spectroscopy (WDX), and inductively coupled plasma (ICP). These newly synthesized nanoparticles have been used as efficient heterogeneous catalytic system for one‐pot multicomponent synthesis of new pyrano[2,3‐b]pyridine‐3‐carboxamide derivatives. Notably, the catalyst could be easily separated from the reaction mixture by using an external magnet and reused for several successive reaction runs with no significant loss of activity or copper leaching. The present protocol benefits from a hitherto unreported MNPs‐immobilized Cu (II) Schiff‐base complex as an efficient nanocatalyst for the synthesis of newly reported derivatives of pyrano[2,3‐b]pyridine‐3‐carboxamide from one‐pot multicomponent reactions.     

Synthesis and characterization of polyvinylpyrrolidone immobilized on magnetic nanoparticles modified by ionic liquid as a novel and recyclable catalyst for the three‐component synthesis of amidoalkyl naphthols

In this study, an efficient and green procedure is explained for the preparation of 1‐amidoalkyl‐2‐naphthols applying one‐pot condensation reaction of 2‐naphthol, amide and aromatic nanoparticles (Fe₃O₄@SiO₂@IL‐PVP) as a novel solid acid catalyst under solvent‐free conditions. The remarkable features of this method are short reaction time, high conversions, and high yield of product, easy workup procedures and solvent‐free conditions. The Fe₃O₄@SiO₂@IL‐PVP catalyst was characterized via Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction patterns (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM), and energy‐dispersive X‐ray spectroscopy (EDS). Also, nanocatalysts could be easily recovered by a simple magnet and reused for the next reactions without significant loss of its catalytic activity.     

Nitro group reduction and Suzuki reaction catalysed by palladium supported on magnetic nanoparticles modified with carbon quantum dots generated from glycerol and urea

Glycerol and urea were used as green and cheap sources of carbon quantum dots (CQD) for modifying Fe₃O₄ nanoparticles (NPs). The obtained CQD@Fe₃O₄ NPs were used for the stabilization of palladium species and the prepared catalyst, Pd@CQD@Fe₃O₄, was characterized using various techniques. This magnetic supported palladium was applied as an efficient catalyst for the reduction of aromatic nitro compounds to primary amines at room temperature using very low palladium loading (0.008 mol%) and also for the Suzuki–Miyaura cross‐coupling reaction of aryl halides as well as challenging heteroaryl bromides and aryl diazonium salts with arylboronic acids and with potassium phenyltrifluoroborate. This magnetically recyclable catalyst was recovered and reused for seven consecutive runs in the reduction of 4‐nitrotoluene to p‐toluidine and for ten consecutive runs in the reaction of 4‐iodoanisole with phenylboronic acid with small decrease of activity. The catalyst reused in the Suzuki reaction was characterized using transmission electron microscopy, vibrating sample magnetometry and X‐ray photoelectron spectroscopy. Using experiments such as hot filtration and poisoning tests, it has been shown that the true catalyst works under homogeneous conditions according to the release–return pathway of active palladium species.     

Environmentally friendly and highly efficient synthesis of benzoxazepine and malonamide derivatives using HPA/TPI‐Fe3O4 nanoparticles as recoverable catalyst in aqueous media

A magnetic inorganic–organic nanohybrid material (HPA/TPI‐Fe₃O₄ NPs) was produced as an efficient, highly recyclable and eco‐friendly catalyst for the one‐pot multi‐component synthesis of malonamide and 2,3,4,5‐tetrahydrobenzo[b ][1,4]oxazepine derivatives with high yields in short reaction times (25–35 min) in aqueous media at room temperature. The nanohybrid catalyst was prepared by the chemical anchoring of H₆P₂W₁₈O₆₂ onto the surface of modified Fe₃O₄ nanoparticles (NPs) with N ‐[3‐(triethoxysilyl)propyl]isonicotinamide (TPI) linker. The magnetic recoverable catalyst was easily recycled at least ten times without any loss of catalytic activity.     

Highly dispersed copper/ppm palladium nanoparticles as novel magnetically recoverable catalyst for Suzuki reaction under aqueous conditions at room temperature

An efficient procedure based on arginine‐modified Fe₃O₄@carbon magnetic nanoparticles (FCA MNPs) with highly dispersed copper nanoparticles (Cu NPs) and 92.8 ppm of Pd is reported for room temperature Suzuki reaction. For enhancing the activity of this Cu‐based heterogeneous catalyst, special arginine amino acid as a ligand with high content of heteroatoms was immobilized onto the Fe₃O₄@carbon MNPs to increase the electron density. Cu(II) ions were then loaded on the surface of the FCA MNPs and reduced to achieve uniformly dispersed Cu NPs. An aqueous mixture of metal hydroxides such as KOH, Ba(OH)₂, Ca(OH)₂, Mg(OH)₂ as a green, non‐toxic and basic medium was used for the Suzuki reaction at room temperature. This catalyst could also be recovered and reused with no loss of activity over six successful runs.     

Recent Developments in the Plant‐Mediated Green Synthesis of Ag‐Based Nanoparticles for Environmental and Catalytic Applications

Among different metallic nanoparticles, sliver nanoparticles (Ag NPs) are one of the most essential and fascinating nanomaterials. Importantly, among the metal based nanoparticles, Ag NPs play a key role in various fields such as biomedicine, biosensors, catalysis, pharmaceuticals, nanoscience and nanotechnology, particularly in nanomedicine. A main concern about the chemical synthesis of Ag NPs is the production of hazardous chemicals and toxic wastes. To overcome this problem, many research studies have been carried out on the green synthesis of Ag NPs using green sources such as plant extracts, microorganisms and some biopolymers without formation of hazardous wastes. Among green sources, plants could be remarkably valuable to exploring the biosynthesis of Ag NPs. In this review, the green synthesis of Ag‐based nanocatalysts such as Ag NPs, AgPd NPs, Au?Ag NPs, Ag/AgPd NPs, Ag/Cu NPs, Ag@AgCl NPs, Au?Ag@AgCl nanocomposite, Ag?Cr‐AC nanocomposite and Ag NPs immobilized on various supports such as Natrolite zeolite, bone, ZnO, seashell, hazelnut shell, almond shell, SnO₂, perlite, ZrO₂, TiO₂, α‐Al₂O₃, CeO₂, reduced graphene oxide (rGO), h‐Fe₂O₃@SiO₂, and Fe₃O₄ using numerous plant extracts as reducing and stabilizing agents in the absence of hazardous surfactant and capping agents has been focused. This work describes the state of the art and future challenges in the biosynthesis of Ag‐based nanocatalysts. The fact about the application of living plants in metal nanoparticle (MNPs) industry is that it is a more economical and efficient biosynthesis biosynthetic procedure. In addition, the catalytic activities of the synthesized, Ag‐based recyclable nanocatalysts using various plant extracts in several chemical reactions such as oxidation, reduction, coupling, cycloaddition, cyanation, epoxidation, hydration, degradation and hydrogenation reactions have bben extensively discussed.     

A highly reactive and magnetic recyclable catalyst based on silver nanoparticles supported on ferrite for N‐monoalkylation of amines with alcohols

Fe₃O₄@SiO₂‐Ag catalyst was found to be highly active and selective in the N ‐alkylation of amines with a variety of aromatic and linear alcohols. The heterogeneous nature of the Fe₃O₄@SiO₂‐Ag catalyst allows easy recovery and regeneration by applying an external magnet for six subsequent reaction cycles. The prepared catalyst was characterized using electron microscopy techniques, X‐ray diffraction, vibrating sample magnetometry and atomic absorption spectroscopy.     

3D Porous Carbon Framework Stabilized Ultra‐Uniform Nano γ‐Fe2O3: A Useful Catalyst System

We present a novel strategy for the scalable fabrication of γ‐Fe₂O₃@3DPCF, a three‐dimensional porous carbon framework (PCF) anchored ultra‐uniform and ultra‐stable γ‐Fe₂O₃ nanocatalyst. The γ‐Fe₂O₃@3DPCF nanocomposites were facilely prepared with the following route: condensation of iron(III) acetylacetonate with acetylacetonate at room temperature to form the polymer precursor (PPr), which was carbonized subsequently at 800 °C. The homogeneous aldol condensation offered an ultra‐uniform distribution of iron, so that the γ‐Fe₂O₃ nanoparticles (NPs) were uniformly distributed in the 3D carbon architecture with the average size of approximate 20 nm. The Fe₂O₃ NPs were capped with carbon, so that the iron oxide maintained its γ‐phase instead of the more stable α‐phase. The nanocomposite was an excellent catalyst for the reduction of nitroarene; it gave >99 % conversion and 100 % selectivity for the reduction of nitroarenes to the corresponding anilines at 100 °C. The fabrication of the γ‐Fe₂O₃@3DPCF nanocatalyst represents a green and scalable method for the synthesis of novel carbon‐based metal oxide nanostructures.     

Water‐Soluble Gold Nanoparticles: From Catalytic Selective Nitroarene Reduction in Water to Refractive Index Sensing

Water‐soluble gold nanoparticles (Au NPs) stabilized by a nitrogen‐rich poly(ethylene glycol) (PEG)‐tagged substrate have been prepared by reduction of HAuCl₄ with NaBH₄ in water at room temperature. The morphology and size of the nanoparticles can be controlled by simply varying the gold/stabilizer ratio. The nanoparticles have been fully characterized by TEM, high‐resolution (HR) TEM, electron diffraction (ED), energy‐dispersive X‐ray spectroscopy (EDS), UV/Vis, powder XRD, and elemental analysis. The material is efficient as a recyclable catalyst for the selective reduction of nitroarenes with NaBH₄ to yield the corresponding anilines in water at room temperature. Furthermore, the potential ability of the Au NPs as a refractive index sensor owing to their localized surface plasmon resonance (LSPR) effect has also been assessed.     

One‐pot multicomponent synthesis of novel 2‐(piperazin‐1‐yl) quinoxaline and benzimidazole derivatives,using a novel sulfamic acid functionalized Fe3O4 MNPs as highly effective nanocatalyst

The immobilization of sulfonic acid on the surface of Fe₃O₄ magnetic nanoparticles (MNPs) as a novel acid nanocatalyst has been successfully reported. The morphological features, thermal stability, magnetic properties, and other physicochemical properties of the prepared superparamagnetic core–shell (Fe₃O₄@PFBA–Metformin@SO₃H) were thoroughly characterized using Fourier transform infrared (FTIR), X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy (EDS), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetric analysis–differential thermal analysis (TGA‐DTA), atomic force microscopy (AFM), dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET), and vibrating sample magnetometer (VSM) techniques. It was applied as an efficient and reusable catalyst for the synthesis of 2‐(piperazin‐1‐yl) quinoxaline and benzimidazole derivatives via a one‐pot multiple‐component cascade reaction under green conditions. The results displayed the excellent catalytic activity of Fe₃O₄@PFBA–metformin@SO₃H as an organic–inorganic hybrid nanocatalyst in condensation and multicomponent Mannich‐type reactions. The easy separation, simple workup, excellent stability, and reusability of the nanocatalyst and quantitative yields of products and short reaction time are some outstanding advantages of this protocol.     

Synthesis of monodispersed Fe3O4@C core/shell nanoparticles

We report a facile method to synthesize dispersed Fe₃O₄@C nanoparticles（NPs）. Fe₃O₄ NPs were firstly prepared via the high temperature diol thermal decomposition method. Fe₃O₄@C NPs were fabricated using glucose as a carbon source by hydrothermal process. The obtained products were characterized by X-ray diffraction（XRD）, transmission electron microscopy（TEM）, vibrating sample magnetometer（VSM） and Raman spectra. The results indicate that the original shapes and magnetic property of Fe₃O₄ NPs can be well preserved. The magnetic particles are well dispersed in the carbon matrix. This strategy would provide an efficient approach for existing applications in Li-ion batteries and drug delivery. Meanwhile, it offers the raw materials to assemble future functional nanometer and micrometer superstructures.     

Magnetically Separable and Versatile Pd/Fe3O4 Catalyst for Efficient Suzuki Cross‐Coupling Reaction and Selective Hydrogenation of Nitroarenes

Magnetic nanoparticle‐supported Pd/Fe₃O₄ was readily prepared and proved to be versatile catalyst for efficient Suzuki cross‐coupling reaction, and the reduction of nitroarenes under mild conditions (balloon H₂ pressure and room temperature). The catalyst could be conveniently recovered and reused several times with sustained catalytic activity.     

Amorphizing of Ag Nanoparticles under Bioinspired One‐step Assembly of Fe3O4‐Ag/rGO Hybrids via Self‐redox Process with Enhanced Activity

Efficient and reusable nanocatalysts fabricated via a facile assembly are highly desirable for the cost‐effective hydrogenation reduction. Inspired by a fishing process with a fishnet, multifunctional nanostructured catalysts are rationally designed to combine interesting features via the self‐redox assembly of Fe₃O₄‐Ag composites on reduced graphene oxide (rGO) (Fe₃O₄‐Ag/rGO). In detail, Fe₃O₄ nanoparticles (NPs) endow the ternary hybrids with superparamagnetism (21.42 emu g^?1), facilitating catalysts to be separated from the reaction system. rGO could provide electron transfer pathways, enhancing catalytic activity. More interestingly, GO and Ag⁺ could behave as oxidants to oxidize Fe²⁺ for the in situ assembly of Fe₃O₄‐Ag/rGO without any addition of reductant/oxidant or organic solvents, and AgNPs endow the ternary hybrids with excellent catalytic behaviour. Meaningfully, the bioinspired process enables the ternary hybrids to possess more abundant micro?/nanopores, larger surface area, and more amorphization. They exhibit exceptional catalytic performance, and could be recycled with excellent activity by means of convenient magnetic separation (at least 7 times). Moreover, the ternary hybrids could degrade methylene blue under UV light due to different valence states of Fe in Fe₃O₄. Therefore, the proposed bioinspired assembly and structure design for hierarchical catalysts would pave a promising way to assemble other catalysts.