Graphene oxide enhances the Fenton-like photocatalytic activity of nickel ferrite for degradation of dyes under visible light irradiation

Graphene oxide (GO) was added to nickel ferrite (NiFe₂O₄) to yield GO-doped NiFe₂O₄ (GO–NiFe₂O₄). The as-prepared GO–NiFe₂O₄ samples were characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy, scanning electronic microscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry at room temperature. GO–NiFe₂O₄ was utilized as a photo-Fenton catalyst and found to be capable of catalyzing the degradation of organic dyes in the presence of oxalic acid under visible light irradiation. Further studies showed that GO–NiFe₂O₄ has a catalytic function in the presence of hydrogen peroxide (H₂O₂). Although the absorbance of the diffuse reflectance spectrum of NiFe₂O₄ extended to 788 nm, NiFe₂O₄ failed to degrade organic dyes in the presence of H₂O₂ despite white light irradiation containing ultraviolet light. The results of this study indicate that GO has a vital function in catalyzing the photo-Fenton process. The photo-catalytic reaction mechanism was investigated by analyzing the data obtained.     

Synthesis of magnetic citric‐acid‐functionalized graphene oxide and its application in the removal of methylene blue from contaminated water

A magnetic nanocomposite of citric‐acid‐functionalized graphene oxide was prepared by an easy method. First, citric acid (CA) was covalently attached to acyl‐chloride‐functionalized graphene oxide (GO). Then, Fe₃O₄ magnetic nanoparticles (MNPs) were chemically deposited onto the resulting adsorbent. CA, as a good stabilizer for MNPs, was covalently attached to the GO; thus MNPs were adsorbed much more strongly to this framework and subsequent leaching decreased and less agglomeration occurred. The attachment of CA onto GO and the formation of the hybrid were confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction spectrometry and transmission electron microscopy. The specific saturation magnetization of the magnetic CA‐grafted GO (GO‐CA‐Fe₃O₄) was 57.8 emu g^?1 and the average size of the nanoparticles was found to be 25 nm by transmission electron microscopy. The magnetic nanocomposite was employed as an adsorbent of methylene blue from contaminated water. The adsorption tests demonstrated that it took only 30 min to attain equilibrium. The adsorption capacity in the concentration range studied was 112 mg g^?1. The GO‐CA‐Fe₃O₄ nanocomposite was easily manipulated in an external magnetic field which eases the separation and leads to the removal of dyes. Thus the prepared nanocomposite has great potential in removing organic dyes. © 2014 Society of Chemical Industry     

Development of an S-doped titania nanotube (TNT) site-selectively loaded with iron(III) oxide and its photocatalytic activities

We investigated an S-doped titania nanotube (TNT) loaded with Fe₂O₃ nanoparticles in order to improve photocatalytic activity of S-doped TNT under visible light irradiation. S-doped TNT was successfully prepared using the solid-phase method at 350 °C under aerated conditions. S-doped TNT showed photoabsorption in the 400–500 nm visible light region and showed photocatalytic activity for oxidation of acetaldehyde under visible light irradiation. Loading of Fe₂O₃ on S-doped TNT remarkably improved the photocatalytic activity of S-doped TNT. PA spectra measurement, which was performed in order to elucidate the mechanism of activity improvement, showed that the efficiency of charge separation between photoexcited electrons and holes was improved because the electrons were trapped by Fe₂O₃. Enhancement of photocatalytic activity was strongly dependent on the site of Fe₂O₃ nanoparticles loaded on TNT. PA spectra measurement showed that the photoexcited electrons transferred to Fe₂O₃ from S-doped TNT under UV light irradiation or to S-doped TNT from Fe₂O₃ under visible light irradiation.     

Magnetic resonance of the NiFe2O4 nanoparticles in the gigahertz range

We report an adjustable magnetic resonance frequency from 1.45 to 2.54 GHz for NiFe₂O₄ nanoparticles which were prepared by a sol–gel process. X-ray diffraction and scanning electron microscopy results indicate that the samples are polycrystalline nanoparticles, and the size of the particles increases obviously with the thermal treatment temperature. The consequence of the surface composition suggests that the oxygen defects are present in the nanoparticle surface, and this surface magnetic state can show a strong surface anisotropy. With decreasing size of the particle, the surface magnetic effect is predominant, resulting in an increase of resonance frequency for NiFe₂O₄ nanoparticles. This finding provides a new route for NiFe₂O₄ materials that can be used in the gigahertz range.     

Development of internal electric field induced NiFe2O4/CdO p-n nano-heterojunctions for solar light activated photodegradation of methylene blue dye

NiFe₂O₄/CdO nanocomposites were prepared using a facile co-precipitation method. A series of characterization techniques such as X-rays diffraction, Fourier transform infrared spectroscopy, and UV–Visible absorbance spectroscopy were performed to validate that weight percentage of CdO can efficiently manage the textural characterization, crystal size, and other parameters meant for photocatalysis. Experimental findings have shown that the weight percentage of CdO has an influential effect on the photocatalytic degradation of methylene blue (MB) under solar irradiation. Compared with bare NiFe₂O_4, all NiFe₂O₄/CdO composites have shown better photocatalytic activity. Among all composites, NiFe₂O₄/CdO composite with 15% CdO has displayed the best photocatalytic efficiency (72%) for MB degradation. The enhanced photocatalytic activity may be ascribed to the delayed electron-hole recombination and availability of active sites for degradation. Furthermore, NiFe₂O₄/CdO composite could quickly be recovered from the solution using a magnet. Intermediate species trapping experiments have shown that photocatalysis by NiFe₂O₄/CdO is highly dependent on superoxide radicals.     

Structural,spectral, dielectric and photocatalytic studies of Zr-Ni doped MnFe2O4 co-precipitated nanoparticles

In this study the Mn_1–2xZr_xFe_2−yNi_yO₄ nanoparticles fabricated by co-precipitation technique were investigated. Thermo-gravimetric analysis (TGA) exhibited the annealing temperature of the nanoparticles ~990 °C. Cubic spinel structure of Mn_1–2xZr_xFe_2−yNi_yO₄ nanoparticles was confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. Crystallite size was calculated by XRD data and found in the range of 32–58 nm. Photocatalytic activity of Mn_0.92Zr_0.04Fe_1.88Ni_0.12O₄/graphene nanocomposites was tested by degrading methylene blue (MB) under visible light irradiation. The MB was almost completely degraded in the presence of Mn_0.92Zr_0.04Fe_1.88Ni_0.12O₄-graphene nanocomposites under visible light irradiation. Dielectric parameters were also investigated in the frequency range 1×10⁶–3×10⁹ Hz. An overall decrease in the values of dielectric constant, dielectric loss and tangent loss was observed on account of the substitution of Zr and Ni with Mn and Fe cations.     

Ag/αFe2O3-rGO novel ternary nanocomposites: Synthesis,characterization, and photocatalytic activity

In this research, novel ternary Ag/αFe₂O₃-rGO nanocomposites with various contents of GO were synthesized via a facile one-pot hydrothermal method. Ag/αFe₂O₃-rGO nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometer (EDX), photoluminescence (PL) spectroscopy, and Fourier transform infrared (FTIR). The results showed that hematite nanoparticles and Ag nanoparticles were well decorated on the graphene surface. Photocatalytic activity of Ag/αFe₂O₃-rGO ternary nanocomposites and pure Ag/αFe₂O₃ was investigated for photodegradation of Congo red dye solution as a model pollutant under UV light irradiation. The ternary nanocomposite with 1.8?mg/ml GO aqueous solution concentration shows higher degradation efficiency under UV light irradiation than the pure Ag/αFe₂O₃ and the nanocomposites with other GO aqueous solution concentrations. It was observed that the adsorption of the dyes on the nanocomposites surface is dependent on the graphene content due to a decrease in the recombination rate, particles size, and increase charge carrier transfer. The results show that the Ag/αFe₂O₃-rGO nanocomposite can be used as an excellent photocatalytic material for degradation of Congo red dye in wastewater. A possible photocatalytic mechanism was proposed for degradation of Congo red dye.     

One-step hydrothermal synthesis and microwave electromagnetic properties of RGO/NiFe2O4 composite

The reduced graphene oxide (RGO)/NiFe₂O₄ composite was synthesized by a facile one-pot hydrothermal route, which avoided the usage of chemical reducing agent. The reduction of graphene oxide (GO) and the crystallization of NiFe₂O₄ crystals happened in a one-step hydrothermal process. The morphology, microstructure and magnetic properties of the composite were detected by means of XRD, XPS, TEM, EDX, TG-DSC and VSM. The maximum R_L of the RGO/NiFe₂O₄ composite is −39.7 dB at 9.2 GHz with the thickness of 3.0 mm, and the absorption bandwidth with the R_L below −10 dB is up to 5.0 GHz (from 12.7 to 17.7 GHz) with a thickness of 1.9 mm. The introduction of RGO signally enhanced microwave absorption performance of the NiFe₂O₄ NPs. It is believed that such composite will be applied widely in microwave absorbing area.     

Room temperature in situ chemical synthesis of Fe3O4/graphene

A simple, cost-effective, efficient, and green approach to synthesize iron oxide/graphene (Fe₃O₄/rGO) nanocomposite using in situ deposition of Fe₃O₄ nanoparticles on reduced graphene oxide (rGO) sheets is reported. In the redox reaction, the oxidation state of iron(II) is increased to iron(III) while the graphene oxide (GO) is reduced to rGO. The GO peak is not observed in the X-ray diffraction (XRD) pattern of the nanocomposite, thus providing evidence for the reduction of the GO. The XRD spectra do have peaks that can be attributed to cubic Fe₃O_4. The field emission scanning electron microscopy (FESEM) images show Fe₃O₄ nanoparticles uniformly decorating rGO sheets. At a low concentration of Fe²⁺, there is a significant increase in the intensity of the FESEM images of the resulting rGO sheets. Elemental mapping using energy dispersive X-ray (EDX) analysis shows that these areas have a significant Fe concentration, but no morphological structure could be identified in the image. When the concentration of Fe²⁺ is increased, the Fe₃O₄ nanoparticles are formed on the rGO sheets. Separation of the Fe₃O₄/rGO nanocomposite from the solution could be achieved by applying an external magnetic field, thus demonstrating the magnetic properties of the nanocomposite. The Fe₃O₄ particle size, magnetic properties, and dispersibility of the nanocomposite could be altered by adjusting the weight ratio of GO to Fe²⁺ in the starting material.     

Solvothermal synthesis and characterizations of graphene-ZnBi12O20 nanocomposites for visible-light driven photocatalytic applications

The Bismuth based Zinc metal oxide (ZnBi₁₂O₂₀) nanorods were synthesized via single step solvothermal approach. The characterization of synthesized hybridized structure was done by several analysis such as X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (UVvis–DRS), Fourier transform-infrared spectroscopy (FT–IR), Thermogravimetric analysis (TGA), Raman spectroscopy, Field-Emission scanning electron microscopy (FESEM), Energy dispersive analysis of X-rays (EDX), High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy. The photocatalytic activity of ZnBi₁₂O₂₀ and an incorporation of varying weight percentages of GO (1–4 wt %) into ZnBi₁₂O₂₀ catalyst (GZBC) were analyzed under visible light irradiation by the degradation of an aqueous solution of Methylene blue (MB) and Methyl orange (MO) dye. Among various developed nanocomposites, 3 wt% GZBC reduced graphene oxide exfoliated nanocomposites has revealed the degradation efficiency as 96.04, 94.52% at 100 and 120 min for MB and MO respectively with enriched visible light absorption range. The photocatalytic property of 3 wt % reduced graphene oxide exhibits higher degradation behavior than that of other synthesized nano-composites.     

Synthesis and Characterization of NiFe2O4 Nanoparticles via Solid‐State Reaction

NiFe₂O₄ nanoparticles were synthesized via solid‐state reaction. The effects of the reaction parameters, namely dispersant content, calcination temperature and annealing time on particle size and morphology were investigated. Magnetic properties of NiFe₂O₄ nanoparticles were tested. The formation mechanism of nanoparticles by solid‐state reaction was also discussed. The results indicated that the synthesized nickel ferrite particles were of nanometer size with different morphologies by slight variation of the reaction conditions. The solid‐state reaction technique is a simple, convenient, inexpensive and effective preparation method of NiFe₂O₄ in high yield.     

Preparation,characterization and electromagnetic properties of polyaniline/carbon nanotubes/nickel ferrite nanocomposites

New electromagnetic nanocomposites were prepared from polyaniline (PANI)/oxidized single‐walled carbon nanotubes (OxSWCNTs)/NiFe₂O₄ by in situ polymerization of aniline using hexanoic acid as a soft template. OxSWCNT and NiFe₂O₄ were prepared first so as to be used in the formulation of PANI composites. Transmission electron microscope (TEM) results revealed the formation of PANI nanoparticles of 60 nm diameter, OxSWCNT of 24 nm, and NiFe₂O₄ of 54 nm. Also, TEM image of the ternary composite indicated agglomerative coating of PANI appearing as a gray shells and black core of NiFe₂O₄ with widening the diameter of OxSWCNT to be around 66 nm. Dc conductivity was measured as a function of temperature. Magnetic susceptibility was measured as a function of temperature and magnetic field intensity. All samples revealed NiFe₂O₄‐dependent ferromagnetism. The activation energies for dc conductivity suggest that the conductivity is owing to hopping conduction mechanism. A synergistic effect between NiFe₂O₄ and PANI/OxSWCNT is observed. POLYM. COMPOS.,, 2012. © 2012 Society of Plastics Engineers     

A novel SnS2–MgFe2O4/reduced graphene oxide flower-like photocatalyst: Solvothermal synthesis,characterization and improved visible-light photocatalytic activity

Flower-like SnS₂ decorated with MgFe₂O₄ nanoparticles and reduced graphene oxide (rGO) nanosheets were successfully synthesized by a facile solvothermal method. The morphological and crystal structure results confirmed that MgFe₂O₄ nanospheres were uniformly anchored on the surface of SnS₂ flower-like structure with the decoration of rGO nanosheets. The UV–vis diffuse reflectance spectra indicated that the SnS₂–MgFe₂O₄/rGO photocatalyst had a strong visible light absorption. The sample exhibited the highest photocatalytic activity for the degradation of methylene blue under visible light irradiation. The mechanism of improved photocatalytic activity was finally proposed.     

Synthesis of magnetically separable core–shell structured Ni<Subscript>x</Subscript>Fe<Subscript>1−x</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>@TiO<Subscript>2</Subscript> nanoparticles photocatalysts for the degradation of organic dyes

In this paper, the core–shell structured NiFe₂O₄@TiO₂ nanoparticles and nanochains as photocatalysts were successfully prepared through hydrothermal and hydrolysis method. The as-prepared core–shell structure was composed of a magnetic NiFe₂O₄ core and photocatalytic titanium oxide coating shell. SEM and TEM images characterized the morphology of NiFe₂O₄@TiO₂ nanoparticles. Moreover, the results of XRD patterns proved that the TiO₂ coating shell consisted of anatase. The VSM measurements showed that the saturation magnetization values of NiFe₂O₄ and NiFe₂O₄@TiO₂ nanoparticles was 65 and 53 emu/g, respectively. The photocatalyst of NiFe₂O₄@TiO₂ nanoparticles exhibited the outstanding recyclable performance for RhB. And, the photo_degradation ration of maintained 69 % after the photocatalyst experienced ten photocatalysis experiments, which is better than that of Fe₃O₄@TiO₂ photocatalysts.     

Hydrothermal synthesis of Ag2CO3-TiO2 loaded reduced graphene oxide nanocomposites with highly efficient photocatalytic activity

Abstract

In this work, a growth of Ag₂CO₃-TiO₂ NPs over GO sheets and reduction of GO were simultaneously achieved by the hydrothermal process at 130 °C for 4?h. The photocatalytic activity of the as-prepared Ag₂CO₃-TiO₂ NPs decorated reduced graphene oxide (Ag₂CO₃-TiO₂/rGO) composite was studied by the degradation of methylene blue (MB) solution under visible light irradiation. A remarkable enhancement in the photocatalytic activity of the TiO₂ was achieved after sensitizing with Ag₂CO₃ and loading in rGO sheets which is attributed to the reduced charge recombination, enhanced dye adsorption, and the improvement in the light harvesting capacity of the composite.     

Magnetically recyclable Ni1-xCdxCeyFe2-yO4-rGO nanocomposite photocatalyst for visible light driven photocatalysis

In this study, a magnetically recyclable Ni_1-xCd_xCe_yFe_2-yO₄-rGO (x, y = 0.05) (NCCF-rGO) nanocomposite photocatalyst has been prepared by following a facile in-situ co-precipitation method combined with ultra-sonication means. The as-synthesized magnetically separable NCCF-rGO nanocomposite photocatalyst efficiently degrades methylene blue (MB) dye in comparison to bare Ni_1-xCd_xCe_yFe_2-yO₄ (x, y = 0.05) (NCCF) nanoparticles (NPs) under visible light irradiation. The photo-degradation rate of MB with NCCF-rGO was ~9 times higher than NCCF nanoparticles (NPs). This enhanced photocatalytic performance of NCCF-rGO photocatalyst was due to the presence of reduced graphene oxide, which greatly help in production of photoactive species by reducing the rate of electro-hole pair recombination. The role of photoactive species that were responsible for the photocatalytic degradation of methylene blue has also been investigated. The as-synthesized NCCF-rGO photocatalyst expressed superb chemical stability and photocatalytic activity even after seven cycle runs. Moreover, the NCCF-rGO nanocomposite worked at all pH values and showed good acid resistance. In particular, the as-synthesized NCCF-rGO photocatalyst could be collected for the next cycle run by simply applying an external magnetic field. Hence, the NCCF-rGO nanocomposite could have potential use in organic dyes contained wastewater treatment.     

Graphene non-covalently tethered with magnetic nanoparticles

We describe a novel approach for coupling pristine graphene with superparamagnetic iron oxide nanoparticles to create dispersed, magnetically responsive hybrids. The magnetic iron oxide (Fe₃O₄) nanoparticles are synthesized by a co-precipitation method using ferric (Fe³⁺) and ferrous (Fe²⁺) salts and then grafted with polyvinylpyrrolidone (PVP). These PVP-grafted Fe₃O₄ nanoparticles are then used to stabilize colloidal graphene in water. The PVP branches non-covalently attach to the surface of the pristine graphene sheets without functionalization or defect creation. These Fe₃O₄–graphene hybrids are stable against aggregation and are highly responsive to external magnetic fields. These hybrids can be freeze-dried to a powder or magnetically separated from solution and still easily redisperse while retaining magnetic functionality. At all stages of synthesis, the Fe₃O₄–graphene hybrids display no coercivity after being brought to magnetic saturation, confirming superparamagnetic properties. Microscopy and light scattering data confirm the presence of pristine graphene sheets decorated with Fe₃O₄ nanoparticles. These materials show promise for multifunctional polymer composites as well as biomedical applications and environmental remediation.     

Effect of surfactants (PVB/EDTA/CTAB) assisted sol-gel synthesis on structural,magnetic and dielectric properties of NiFe2O4 nanoparticles

Nanocrystalline NiFe₂O₄ was synthesized by sol-gel route using various surfactants such as PVP, EDTA and CTAB. The effect of different surfactants on structure, magnetic and dielectric properties of the NiFe₂O₄ nanoparticles (NPs) were investigated. The prepared samples were inspected by XRD, HRSEM, and TEM. Powder XRD studies confirmed the realization of single crystalline cubic structure of the NiFe₂O₄ nanoferrites. The addition of surfactants significantly modified the crystallite size of the final products. Dielectric features of NiFe₂O₄ NPs were slightly modified with different surfactants. The magnetic results revealed an enormous decrease in coercivity and a moderate reduction in the saturation magnetization when EDTA and CTAB were used as compared to PVP. The present results declare that the adding of various surfactants in the sample preparation controls the size of NiFe₂O₄ NPs and thus noticeably influences the magnetic parameters.     

Synthesis of hierarchical core-shell NiFe2O4@MnO2 composite microspheres decorated graphene nanosheet for enhanced microwave absorption performance

A ternary functional composite NiFe₂O₄@MnO₂@graphene was synthesized successfully via a facile method. The phase constitution, microstructures, morphologies and chemical compositions of the samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) and X-ray photoelectron spectroscopy (XPS). It was observed that the NiFe₂O₄ nanoparticles were coated by hierarchically MnO₂ shells and distributed on the surface of graphene. Investigations of EM wave absorption indicated that NiFe₂O₄@MnO₂@ graphene composite has the strongest reflection loss of −47.4 dB at 7.4 GHz at the matching thickness of 3 mm, compared to NiFe₂O₄ and NiFe₂O₄@MnO₂, and its maximum absorption bandwidth (<−10 dB) is 4.3 GHz (from 5.1 to 9.4 GHz). The enhanced microwave absorption performance can be attributed to the hierarchical structure of MnO₂, void space between MnO₂ and graphene, and better impedance matching of ternary composite. The above results indicate that the novel hierarchical NiFe₂O₄@MnO₂@graphene composite, with intense absorption and wide absorption bandwidth, would be a promising absorber with less EM wave interference.     

Envisioning the composition effect on structural,magnetic, thermal and optical properties of mesoporous MgFe2O4-GO nanocomposites

The effect of variation in composition on the structural, magnetic, optical and photo catalytic activity of magnesium ferrite (MgFe₂O₄) -graphene oxide (GO) nanocomposites was studied. Magnetic nanocomposites of GO and MgFe₂O₄ nanoparticles (NPs) with varying w/w ratio were synthesized by facile sonication method. X-Ray diffraction patterns confirmed the presence of spinel ferrite phase in the nanocomposites with the crystalline size 8–32 nm. Fourier transformation infrared (FT-IR) spectra of the nanocomposites displayed absorption bands corresponding to GO and MgFe₂O₄ NPs along with red shift of bands corresponding to C=O, C=C and O-H stretching. Thermo gravimetric analysis confirmed higher stability of nanocomposites over pristine GO. Saturation magnetization increased from 3.63 to 11.10 emu/g with the increase in content of MgFe₂O₄ NPs in the nanocomposites. Scanning electron microscopy analysis along with energy dispersive spectroscopy (SEM-EDX) confirmed the presence of MgFe₂O₄ NPs along with GO sheets. Immobilization of clusters of MgFe₂O₄ NPs onto GO sheets was evident from transmission electron micrographs (TEM) of all the nanocomposites. BET surface area of the nanocomposites ranged from 63.04 to 165.29 m²/g and was maximum when GO:MgFe₂O₄ w/w ratio was 1:0.5. It was markedly higher than pristine GO and MgFe₂O₄ NPs. Optical studies revealed lowering of the band gap in the nanocomposites upto 2.21 eV as compared to pristine MgFe₂O₄ NPs. Photoluminescence (PL) spectra of nanocomposites displayed quenching of PL intensity with increase of GO content. Band gap also displayed similar trend. The synthesized nanocomposites were used as photocatalysts for methylene blue dye degradation under visible light irradiation. The nanocomposite with GO to MgFe₂O₄ ratio 1:0.5 displayed best activity with complete degradation of dye in 30 min. The results confirmed that the composition of GO based magnetic nanocomposites can be tailored for efficient removal of contaminants.