Core shell‐structured NiFe2O4@TiO2 nanoparticle‐anchored reduced graphene oxide for rapid degradation of rhodamine B

In this work, the NiFe₂O₄@TiO₂/reduced graphene oxide (RGO) ternary nanocomposites with high saturation magnetization and catalytic efficiency have been synthesized through the following steps. First, graphene oxide was prepared using the modified Hummer's method. Second, the NiFe₂O₄ nanoparticles were successfully prepared using the hydrothermal method. Third, the core shell‐structured NiFe₂O₄@TiO₂/RGO nanocomposite precursors were easily obtained through hydrolysis reaction. The morphology of NiFe₂O₄@TiO₂/RGO nanocomposites was characterized from scanning electron microscope (SEM) and transmission electron microscope (TEM) images. Moreover, the results of X‐ray diffraction (XRD) patterns proved that the TiO₂ coating shell consisted of anatase. The vibrating sample magnetometer (VSM) measurements showed that the saturation magnetization value of NiFe₂O₄@TiO₂/RGO ternary nanocomposites was 25 emu/g. The X‐ray photoelectron spectroscopy (XPS) analysis confirmed that only part of the graphite oxide (GO) was reduced to RGO in the ternary nanocomposite. The degradation experiments proved that NiFe₂O₄@TiO₂/RGO nanocomposite exhibited the high catalytic efficiency and outstanding recyclable performance for rhodamine B (RhB).     

磁性TiO2/CoFe2O4纳米复合光催化材料的制备

以磁性CoFe2O4为核,采用改进的溶胶-凝胶法,制备了磁性TiO2/CoFe2O4纳米复合光催化材料.利用VSM(振动样品磁强计)技术对其磁性能进行了研究,结果表明:由该法所得的TiO2/CoFe2O4纳米复合光催化材料的饱和磁化强度虽稍弱于纯CoFe2O4纳米材料,但其矫顽力则优于CoFe2O4.TEM、XRD、UV-Vis等的结果表明,该纳米复合材料中的TiO2为锐钛矿结构;与TiO2相比,纳米复合材料对光的吸收拓展到了整个紫外-可见区,且吸收强度大大增强.对染料废水光催化降解的模拟研究表明,该复合材料在紫外光下,6 h可以使亚甲基蓝染料溶液的脱色率达95%,且重复使用3次时染料溶液的脱色率仍能保持在90%,明显优于纯TiO2.     

Comparative study of the synthesis of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> in silica through the polymerized complex route of the sol–gel method

In this work the synthesis of CoFe₂O₄-SiO₂ and NiFe₂O₄-SiO₂ nanocomposites was studied via the sol–gel method, using the polymerized complex route. The polymerized precursors obtained by the reaction of citric acid, ethylene glycol, tetraethylorthosilicate, ferric nitrate, and cobalt nitrate or nickel chloride were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. NMR and IR spectra of the precursors, without and with metallic ions, show the formation of polymeric chains with ester and ether groups and complexes of metal-polymeric precursor. The nanocomposites were obtained by the thermal decomposition of the organic fraction and characterized by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). XRD patterns show the formation of CoFe₂O₄ and NiFe₂O₄ in an amorphous silica matrix above 400 °C in both cases. When the calcination temperature was 800 °C the particle size of the crystalline phases, calculated using the Scherrer equation, reached ∼35 nm for the two oxides. VSM plots show the ferrimagnetic behavior that is expected for this type of magnetic material; the magnetization at 12.5 KOe of the CoFe₂O₄-SiO₂ and NiFe₂O₄-SiO₂ compounds was 29.5 and 17.4 emu/g, respectively, for samples treated at 800 °C.     

Inactivation of Escherichia coli on Immobilized CuO/CoFe2O4‐TiO2 Thin‐Film under Simulated Sunlight Irradiation

Composite photocatalysts of CuO/CoFe₂O₄‐TiO₂ were successfully synthesized by a sol‐gel method and fixed on ordinary tiles. The photosterilization of Escherichia coli was examined on CuO/CoFe₂O₄‐TiO₂ thin films under a xenon lamp irradiation. The film was characterized by XRD, and the morphology was observed by SEM. Disinfection data indicated that CuO/CoFe₂O₄‐TiO₂ composite photocatalysts have the much better photocatalytic activity than CuO/CoFe₂O₄ and TiO₂. The optimized composition of the nanocomposites has been found to be m_CuO/CoFe2O4:m_TiO2=3:7, with loadings ranging from 790 to 1400 mg/m². The photocatalytic inactivated rate of E. coli (10⁵ CFU/mL) reached 98.4% under the xenon lamp of 150 W within 30 min.     

Hydrothermal Synthesis of g‐C3N4/NiFe2O4 Nanocomposite and Its Enhanced Photocatalytic Activity

Herein, for the first time, a direct Z‐scheme g‐C₃N₄/NiFe₂O₄ nanocomposite photocatalyst was prepared using facile one‐pot hydrothermal method and characterized using XRD, FT‐IR, DRS, PL, SEM, EDS, TEM, HRTEM, XPS, BET and VSM characterized techniques. The result reveals that the NiFe₂O₄ nanoparticles are loaded on the g‐C₃N₄ sheets successfully. The photocatalytic activities of the as‐prepared photocatalysts were evaluated for the degradation of methyl orange (MO) under visible light irradiation. It was shown that the photocatalytic activity of the g‐C₃N₄/NiFe₂O₄ nanocomposite is about 4.4 and 3 times higher than those of the pristine NiFe₂O₄ and g‐C₃N₄ respectively. The enhanced photocatalytic activity could be ascribed to the formation of g‐C₃N₄/NiFe₂O₄ direct Z‐scheme photocatalyst, which results in efficient space separation of photogenerated charge carriers. More importantly, the as‐prepared Z‐scheme photocatalyst can be recoverable easily from the solution by an external magnetic field and it shows almost the same activity for three consecutive cycles. Considering the simplicity of preparation method, this work will provide new insights into the design of high‐performance magnetic Z‐scheme photocatalysts for organic contaminate removal.     

Olefins oxidation with molecular O2 in the presence of chiral Mn (III) salen complex supported on magnetic CoFe2O4@SiO2@CPTMS

In the present study, CoFe₂O₄@SiO₂@CPTMS nanocomposite was synthesized and the homogeneous chiral Mn‐salen complex was anchored covalently onto the surface of CoFe₂O₄@SiO₂@CPTMS nanocomposite. The heterogeneous Mn‐salen magnetic nanocatalyst (CoFe₂O₄@SiO₂@CPTMS@ chiral Mn (III) Complex) was characterized by different techniques including transmission electron microscopy (TEM), Fourier transform infrared (FT‐IR), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), powder X‐ray diffraction (XRD) and thermogravimetric analysis (TGA). Then, the aerobic enantioselective oxidation of olefins to the corresponding epoxide was investigated in the presence of magnetic chiral CoFe₂O₄@SiO₂@Mn (III) complex at ambient conditions within 90 min. The results showed the corresponding products were synthesized with excellent yields and selectivity. In addition, the heterogeneous CoFe₂O₄@SiO₂@ CPTMS@ chiral Mn (III) complex has benefits such as high selectivity and comparable catalytic reactivity with its homogeneous analog as well as mild reaction condition, facile recovery, and recycling of the heterogeneous catalyst.     

Nanostructured ternary composites of PPy/CNT/NiFe2O4 and PPy/CNT/CoFe2O4: Delineating and improving microwave absorption

Two different ternary nanocomposites, PPy/CNT/CoFe₂O₄ and PPy/CNT/NiFe₂O₄, were synthesized by in situ polymerization method. The resulting composites were characterized using Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. They were evaluated with the aim of investigating microwave absorption properties. The results showed that the value of microwave reflection decreases as that of prepared nanocomposites increases. This happens with increase in the PPy content and polymerization on the surface.     

Nanocomposite based on epoxy and MWCNTs modified with NiFe2O4 nanoparticles as efficient microwave absorbing material

In order to make a microwave absorbent material with good dielectric and magnetic properties, well dispersed microwave absorbing hybrid epoxy polymer composites containing nickel doped Fe₃O₄ nanocrystals coated on carbon nanotubes (NiFe₂O₄‐MWCNTs/epoxy) were synthesized by the combined precipitation‐hydrothermal method in 1‐30 wt.% of nanoparticles. Nickel possess well interaction with microwave radiation and represents fine electromagnetic interference (EMI) shielding and by dopping it into ferrite spinel structures, does not show any tendency to oxidation. Well‐dispersed NiFe₂O₄–MWCNTs/epoxy nanocomposite prepared by new in‐situ polymerization method. First, NiFe₂O₄–MWCNT nanoparticles ultrasonicated in acetone and after mixing with epoxy resin ultrasonicated again. Finally, hardner added to the composite and tuned temperature for evaporating solvent. X‐ray diffraction (XRD) and energy dispersive spectroscopy (EDS) confirmed the synthesizing NiFe₂O₄ nanoparticles. Saturation magnetization value of NiFe₂O₄‐MWCNTs is about 29 emu/g with very low remanence and coercivity content, which revealed that the NiFe₂O₄‐MWCNTs is ferromagnetic nanocrystal. Transmission electron microscopy (TEM) used to characterize the distribution of NiFe₂O₄ nanocrystals on the surface of MWCNTs. The TEM images show that NiFe₂O₄ nanocrystals have a mean size of 12 nm, and completely coated on the exterior surface of MWCNTs. The obtained results of reflection loss revealed that the maximum values of reflection loss of the NiFe₂O₄‐MWCNTs/epoxy increase by enhancing the content of nanoparticles until 10 wt.% and decreases in 30 wt.%.     

Cu(II)‐supported graphene quantum dots modified NiFe2O4: A green and efficient catalyst for the synthesis of 4H‐pyrimido[2,1‐b]benzothiazoles in water

NiFe₂O₄ nanoparticles are modified by graphene quantum dots (GQDs) and utilized to stabilize the Cu(II) nanoparticles as a novel magnetically retrievable catalytic system (Cu(II)/GQDs/NiFe₂O₄) for green formation of 4H‐pyrimido[2,1‐b]benzothiazoles. The prepared catalyst can be isolated assisted by an outer magnet and recovered for five courses without significant reduction in its efficiency. The as‐prepared magnetic heterogeneous nanocomposite was characterized by UV–Vis, FT‐IR, XRD, EDS, VSM, TEM, and ICP. Performing the reactions in environmentally friendly and affordable conditions (water), the low catalyst percentage, high yield of products, short reaction times, and easy workup are the merits of this protocol.     

CoFe2O4/SiO2 nanocomposites by thermal decomposition of some complex combinations embedded in hybrid silica gels

The study reports the preparation of CoFe₂O₄/SiO₂ nanocomposites by a new modified sol–gel method starting from cobalt nitrate, iron nitrate, and diols: 1,2-ethanediol (EG), 1,3-propanediol (1,3PG), and tetraethylorthosilicate (TEOS), for final compositions of 30 %CoFe₂O₄/70 %SiO₂ and 50 %CoFe₂O₄/50 %SiO₂. The method is based on the formation of a Co(II), Fe(III)—carboxylate precursors mixture, during the redox reaction between the NO ₃ ^? ion and the diol (~140 °C) within the silica gels. The thermal decomposition of these complex combinations takes place at ~300 °C leading to the corresponding amorphous metal oxides within the pores of the hybrid gels. Depending on the subsequent thermal treatment, CoFe₂O₄ can be obtained as single phase or in a mixture with Co₂SiO₄. The CoFe₂O₄ crystallites sizes are in the nanometer range (3–10 nm). The obtained nanocomposites have a hard magnet behavior, as a result of the high anisotropy of CoFe₂O₄ having large hysteresis cycles.     

Magnetically separable ZnO/ZnFe2O4 and ZnO/CoFe2O4 photocatalysts supported onto nitrogen doped graphene for photocatalytic degradation of toxic dyes

Advanced oxidation processes (AOPs) counting heterogeneous photocatalysis has confirmed as one of the preeminent method for waste water remediation. In the present work, we have successfully fabricated novel visible-light-driven nitrogen-doped graphene (NG) supported magnetic ZnO/ZnFe₂O₄ (ZnO/ZF/NG) and ZnO/CoFe₂O₄ (ZnO/CF/NG) nanocomposites. ZnO synthesized via direct precipitation method. Hydrothermal method was used for the preparation of nitrogen-doped graphene supported magnetic ZnO/ZF (ZnO/ZnFe₂O₄) and ZnO/CF (ZnO/CoFe₂O₄) nanocomposites. The procured materials were scrutinized by assorted characterizations to acquire information on their chemical composition, crystalline structure and photosensitive properties. The absorption and photocatalytic performance of photocatalysts were studied via UV–Visible spectra. Photodegradation performance of the synthesized nanocomposites was estimated toward mineralization of methyl orange (MO) and malachite green (MG) dyes in aqueous solution. The high surface area of ZnO/ZF/NG and ZnO/CF/NG was suitable for adsorptive removal of MO and MG dyes. The photodegradation performance of heterojunction photocatalysts was superior to bare photocatalyst in 140 min under visible-light irradiation. Spectrophotometer, GC–MS (Gas chromatography–mass spectrometry) elucidation was carried out to expose the possible intermediates formed. Both ZnO/ZF/NG and ZnO/CF/NG were rapidly isolated from the aqueous phase by applying an external magnetic field in 20 sec and 2 min, respectively. The photocatalytic performance and stability of ZnO/ZF/NG and ZnO/CF/NG nanocomposites were confirmed by conducting 10 consecutive regeneration cycles. Owing to recyclability of ZnO/ZF/NG and ZnO/CF/NG, these heterogeneous nanocomposites might be used as cost-effective for treatment of discarded water. The observations endorse that the synthesized ternary heterogeneous nanocomposites facilitates wastewater decontamination using photocatalytic technology.     

New Synthesis and Magnetic Properties of NiFe2O4/SiO2 and Co0.5Zn0.5Fe2O4/SiO2 Nanocomposites Using Tetraglycolatosilane as Precursor

In this work the new synthesis and magnetic properties of NiFe₂O₄/SiO₂ and Co_0.5Zn_0.5Fe₂O₄/SiO₂ nanocomposites using a water‐soluble silica precursor, tetraglycolatosilane (THEOS), by the sol‐gel method were reported. Nanocomposite were obtained by the thermal decomposition of the organic part at different annealing temperatures varying from 400 to 900 °C. Studies carried out using XRD, FT‐IR, TEM, STA (TG‐DTG‐DTA) and VSM techniques. XRD patterns show that NiFe₂O₄ and Co_0.5Zn_0.5Fe₂O₄ have been formed in an amorphous silica matrix at annealing temperatures above 600 and 400 °C, respectively. It is found that when the annealing temperature is up to 900 °C NiFe₂O₄/SiO₂ and Co_0.5Zn_0.5Fe₂O₄/SiO₂ samples show almost superparamagnetic behavior with a magnetization 4.66 emu/g and ferromagnetic behavior with a magnetization 10.11 emu/g, respectively. The magnetization and coercivity values of nanocomposites using THEOS were considerably less than previous reports using TEOS. THEOS as a silica matrix network provides an ideal nucleation environment to disperse ferrite nanoparticles and thus to confine them to aggregate and coarsen. By using THEOS over the currently used TEOS and TMOS, organic solvents are not needed due to the entire solubility of THEOS in water. Synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of ferrites even more versatile.     

Ultrasound-assisted synthesis of CoFe2O4/Ce-UiO-66 nanocomposite for photocatalytic aerobic oxidation of aliphatic alcohols

During the past years, light-driven selective oxidation of various alcohols has attracted increasing attention as a green and eco-friendly manner to convert visible light energy into valuable compounds. In this work, magnetic CoFe₂O₄/Ce-UiO-66 embedded structure composites are elaborately designed for the photocatalytic oxidation of aliphatic alcohols under visible-light irradiation and aerobic condition at room temperature. The CoFe₂O₄/Ce-UiO-66 structure was prepared using a simple and fast ultrasound-assisted technique in 60 min at room temperature. As compared with the unmodified CoFe₂O₄, the embedded composite exhibited better visible-light sensitization performance. The catalyst showed high chemical stability in the reaction conditions and can be recovered quickly and reused for at least five reaction runs in the aerobic oxidation reaction condition.     

Magnetic NiFe2O4 nanoparticles: efficient,heterogeneous and reusable catalyst for synthesis of acetylferrocene chalcones and their anti‐tumour activity

A robust synthesis of magnetic NiFe₂O₄ nanoparticles via a hydrothermal technique was investigated. The prepared magnetic NiFe₂O₄ nanoparticles were characterized using powder X‐ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), high‐resolution TEM, energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis, infrared spectroscopy and vibrating sample magnetometry. XRD and TEM analyses confirmed the formation of single‐phase ultrafine nickel ferrite nanoparticles with highly homogeneous cubic shape and elemental composition. Moreover, the prepared magnetic NiFe₂O₄ nanoparticles were used as an efficient, cheap and eco‐friendly catalyst for the Claisen–Schmidt condensation reaction between acetylferrocene and various aldehydes (aromatic and/or heterocyclic) yielding acetylferrocene chalcones in excellent yields, with easy work‐up and reduced reaction time. The products were purified via crystallization. The structures of the produced compounds were elucidated using various spectroscopic analyses (¹H NMR, ¹³C NMR, GC–MS). The catalyst is readily recovered by simple magnetic decantation and can be recycled several times with no discernible loss of catalytic activity. Furthermore, the prepared chalcone derivatives were evaluated for their anti‐tumour activity against three human tumour cell lines, namely HCT116 (colon cancer), MCF7 (breast cancer) and HEPG2 (liver cancer), and showed a good activity against colon cancer. Copyright © 2016 John Wiley & Sons, Ltd.     

Detection of acetaminophen using cyclic voltammetry on MnFe2O4/polyaniline

A novel sensing material, MnFe₂O₄/polyaniline (PANI), was fabricated by doping PANI to MnFe₂O₄ on a modified glassy carbon electrode (GCE). This sensing material was characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and high‐resolution transmission electron microscopy (HR‐TEM). Using a cyclic voltammetry electrochemical‐sensing method, we tested MnFe₂O₄/PANI, and an acetaminophen concentration of 0.0625–5 mM was recorded. Furthermore, the sensor responses were 2.05–22.44. The detection limit was 2.23 × 10^?7 M. Strong selectivity was observed for MnFe₂O₄/PANI, which is a possible sensing mechanism.     

CoFe2O4@TiO2@Au Core-Shell Structured Microspheres: Synthesis and Photocatalyltic Properties

A facile and efficient method for fabrication of magnetic composite microspheres CoFe₂O₄@TiO₂@Au is demonstrated. The shells of anatase TiO₂ were coated onto a magnetic CoFe₂O₄ core via liquid-phase deposition procedure, and then Au nanoparticles were deposited onto CoFe₂O₄@TiO₂ microspheres through seed-mediated growth. XRD, TEM, and VSM were used to investigate the structure, morphology and magnetic properties of the samples, their photocatalytic activity were also tested. Heterostructure of CoFe₂O₄@TiO₂@Au was confirmed by different measurements. Compared to unmodified CoFe₂O₄@TiO₂ microspheres, CoFe₂O₄@TiO₂@Au microspheres showed higher photocatalytic activity for Rhodamine B (RhB) degradation in water.

     

CoFe2O4@SiO2-NH2-CoII NPs catalyzed Hantzsch reaction as an efficient,reusable catalyst for the facile,green, one-pot synthesis of novel functionalized 1,4-dihydropyridine derivatives

A magnetically heterogeneous CoFe₂O₄@SiO₂-NH₂-Co^II nanoparticle was synthesized by the immobilization of Co (II) complex onto CoFe₂O₄@SiO₂ nanoparticles, and the heterogeneous magnetic nanocatalyst was characterized by XRD, TEM, TGA, EDX, and FT-IR techniques. Then, the green and reusable method was introduced for a multicomponent synthesis of 1,4-dihydropyridine derivatives via Hantszch reaction. The synthesis of 1,4-dihydropyridine derivatives was proceeded by the reaction of aldehyde, ethyl acetoacetate, and ammonium acetate in the presence of this magnetic nanocatalyst in EtOH/Water (1:1). Simple work-up, short reaction times, excellent yields (60–96%) as well as green solvent are some advantages of this novel approach, and the corresponding products were purified with no need for chromatographic separation.     

One‐pot synthesis of magnetic palladium–NiFe2O4–graphene oxide composite: an efficient and recyclable catalyst for Heck reaction

A magnetically separable NiFe₂O₄@GO–Pd composite (GO = graphene oxide) was successfully prepared by a facile one‐pot hydrothermal strategy. This new kind of hybrid material was fully characterized using powder X‐ray diffraction, Raman spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy and vibrating sample magnetometry. Structural characterizations confirmed the formation of NiFe₂O₄ and Pd nanocrystals, and the close anchoring between nanoparticles and GO sheets. Additionally, the as‐prepared NiFe₂O₄@GO–Pd nanocomposite was effectively employed in the palladium‐catalyzed Heck reaction in an ethanol–water system as a green solvent. The catalyst was completely recoverable with the simple application of an external magnetic field and with no obvious loss of catalytic activity even after six repeated cycles. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation of magnetic CoFe2O4-functionalized graphene sheets via a facile hydrothermal method and their adsorption properties

Magnetic CoFe₂O₄-functionalized graphene sheets (CoFe₂O₄-FGS) nanocomposites have been synthesized by hydrothermal treatment of inorganic salts and thermal exfoliated graphene sheets. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that cobalt ferrite nanoparticles with sizes of 10-40 nm are well dispersed on graphene sheets. OH⁻ was recognized as a tie to integrate the inorganic salts with the graphene sheets, which made reaction started and developed on the surface of graphene sheets and formed cobalt ferrite nanoparticles on graphene sheets. The adsorption kinetics investigation revealed that the adsorption of methyl orange from aqueous solution over the as-prepared CoFe₂O₄-FGS nanocomposites followed pseudo-second-order kinetic model and the adsorption capacity was examined as high as 71.54 mg g⁻¹. The combination of the superior adsorption of FGS and the magnetic properties of CoFe₂O₄ nanoparticles can be used as a powerful separation tool to deal with water pollution.     

Green and rapid synthesis of dihydropyrimido [4,5‐b]quinolinetrione derivatives using CoFe2O4@PPA as high efficient solid acidic catalyst under ultrasonic irradiation

A new high efficient and green protocol for the preparation of dihydropyrimido[4,5‐b]quinolinetrione derivatives using magnetically solid acid catalyst was presented. High performance solid acid catalyst was prepared through a three‐step reaction. Firstly, CoFe₂O₄ nano particles were synthesized using co‐precipitation method. In second step, CoFe₂O₄ nano particles were coated with SiO₂ shell through treatment with tetraethyl orthosilicate (CoFe₂O₄@SiO₂). Finaly, CoFe₂O₄@SiO₂ was modified with polyphosphoric acid (CoFe₂O₄@SiO₂/PPA) in a simple manner. Green reusable catalyst was characterized in details using FTIR, VSM, TEM, FESEM, EDX and used as catalyst for the synthesis of dihydropyrimido[4,5‐b]quinolinetrione derivatives. Reaction was performed under ultrasonic irradiation as green, effective and mild conditions and products were achieved in high to excellent yields. Green and eco‐friendly conditions, short reaction times with high yield of products in addition to easy workup are some merits of presented method.