Magnetic Properties of Cellulose-Grafted Reduced Graphite Oxide Decorated with Ni Nanoparticles.
In recent years, graphene and its derivatives have attracted considerable attention owing to their amazing unique physical and chemical properties significantly improving electrical, mechanical and gas barrier properties of graphene-based nanocomposites [1-6]. The most suitable method for large scale production of graphene is based on the oxidation of graphite leading to graphite oxide sheets (GO) that can be functionalized and then reduced to restore electrical conductivity . In addition, metal nanoparticles can improve the physical properties of GO and, in particular, Benayad et al.  controlled the sheet resistance of reduced GO (rGO) films by using a Au-ion treatment. However, one limitation to the synthesis of metal nanoparticles is their reactivity toward air environment, which may degrade their ferromagnetic character by forming an antiferromagnetic oxide layer. Recently, rGO decorated with metallic nanoparticles such as Au, Ag, Pt, Pd, and Ni have been used in new catalytic, magnetic, and optoelectronic materials [9-11]. Indeed, the presence of oxygen functional groups in GO can act as nucleation centers or anchoring sites for the nanoparticles, which improves both their stability and their dispersion onto the GO surface . Magnetic particles are a great interest for a wide range of scientific fields including magnetic fluids , data storage , biotechnology/ biomedicine , and catalysis  and their magnetic properties depend on the chemical composition, the size, and the aspect ratio. As discussed by Lu , magnetic nanoparticles are superparamagnetic below a critical diameter with their magnetic moment having a fast response to a magnetic field. Therefore, the dispersion of magnetic nanoparticles such as nickel nanoparticles (Ni NPs) onto the GO surface provides great interests because of their low cost and remarkable performances in various scientific fields [18-23]. As exemples, Yang et al.  reported the homogeneous growing of Ni[(OH).sub.2] nanoparticles on rGO for applications in the field of supercapacitors while Zhu et al.  prepared a graphene supported Ni[(OH).sub.2] with graphene sheets inhibiting the stacking of Ni[(OH).sub.2] sheets and enhancing the electrochemical performance of the corresponding electrode. Moreover, a few works described the synthesis NiNPs/rGO nanocomposite having different architectures by varying the concentration of the starting nickel ions and displaying a ferromagnetic behavior and catalytic activities for the reduction 4-nitrophenol by NaB[H.sub.4] [26, 27], In addition, cellulose is a polysaccharide exhibiting hydrophilicity, biocompatibility, and biodegradability and containing hydroxyl and carboxyl groups that can be used for the functionalization of graphene in presence of Nickel nanoparticles with potential applications in the areas of biocomposites, and biosensors [28, 29]. Several works reported the synthesis of cellulose/GO nanocomposite materials and the most common methods to synthesize polymer/graphene (oxide) hybrid materials are based on the use of melt and solvent blending techniques [30-34]. Wu et al.  and Sitko et al.  reported the adsorption of nickel ions on graphene oxide/cellulose membranes prepared by a filtration assembly and a freeze drying method, respectively. Recently, we reported the immobilization of gold nanoparticles on the surface of cellulose-grafted to increase the number of anchor groups for AuNPs in comparison with neat GO.graphene oxide sheets and he grafting of cellulose onto rGO was conducted in three steps followed by the deposition of the gold particles via a chemical reduction of Au3+ . In this work, cellulose-grafted GO and nickel ions were reduced simultaneously in presence of hydrazine to form NiNPs/cellulose-grafted rGO nanocomposite, which was thoroughly characterized with the help of DRX, TGA, SEM, and TEM images. Moreover, its magnetic properties were investigated and it was demonstrated that the NiNPs/cellulose-grafted rGO nanocomposite exhibits a ferromagnetic behavior.
Graphite powder was kindly provided by TIMCAL Graphite & Carbon, France (4 pm in size). GO was synthesized from graphite powder using the Hummers' method . A C/O atomic ratio of 2.22 was determined by elemental analysis. Potassium permanganate, sodium nitrate (NaN03), concentrated sulfuric acid ([H.sub.2]S04), Ni[Cl.sub.2].6[H.sub.2]O, l-ethyl-3-methylpyridinium bis (trifluoromethylsulfonyl) imide, polyvinylacetate, Ethylenediamine (ED), Hydrazine hydrate 60%, lithium chloride, 2-(7-aza-1 H-benzotriazole-1 yl)-1,1,3,3-tetramethyluronium hexafluorophosphate, cellulose fibrous, and thionyl chloride were all purchased from Aldrich. Solvents such as dimethylformamide, dimethylacetamide, and acetone were purchased from Sigma-Aldrich-France: 99% pure.
Preparation of NiNPs/Cellulose-Grafted rGO Nanocomposite
Cellulose-grafted-GO sheets were prepared according to our previous work . Then, typically, 35 mg of cellulose-grafted GO was dispersed in 70 mL of desionized water with ultrasonication for 30 min and then mixed with 20 mL of Ni[Cl.sub.2] aqueous solution (76 mM). The pH of the corresponding brown solution was then adjusted to 10.5 by dropping an appropriate amount of a NaOH aqueous solution (0,3 M). Subsequently, 5 mL of hydrazine hydrate solution (60 wt%) were added under stirring and the reaction was conducted at 100[degrees]C for 3 h under argon atmosphere, according to the procedure of Ji et al. , The resulting homogeneous black solution was centrifugated and the isolated solid product was washed thoroughly with water and absolute ethanol and then dried in an oven at 50[degrees]C under vacuum for 24 h.
The powder X-ray diffraction (XRD) measurements were performed on a Siemens D500 diffractometer (Ni-filtered Cu KR radiation, 1.54 A). The d(0 0 2) basal spacings were calculated from the 20 values using the Bragg's law.
TGA analyses were carried out with a TA SDT Q600. Samples were heated at 5[degrees]C [min.sup.-1] under helium flow (25 mL [min.sup.-1]).
Sonication was accomplished using an Elma S40 Ultrasonic apparatus (Sheller, 37 kHz, 140 W).
The powder conductivity measurements were carried out with a high voltage source-measure unit Keithley 237. The sieved powder (0.5 mm diameter) was introduced into a 1 cm internal diameter Teflon ring capped with aluminum electrodes. The aluminum caps were compressed at 100 N (~2 MPa) between a two point electrode system.
Scanning electron microscopy (SEM) images were taken by a commercial FEI Quanta 250.
Magnetic measurements were performed at 300 K on powdered samples packed in polycarbonate capsules using a Quantum Design MPMS-XL SQUID magnetometer.
Transmission electronic microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) analysis were performed on a high resolution field emission transmission electron microscopy (Philips CM 120 electron microscope operating at 200 kV). In a typical experiment, one drop of the colloidal dispersion was deposited on a carbon film supported by a copper grid and allowed to air-dry before observation.
RESULTS AND DISCUSSION
As described in a previous article , we synthesize cellulose-grafted GO by using ED-grafted GO sheets followed by amidation with chlorocellulose and thermal gravimetric analysis (TGA) allowed us to determine a cellulose weight content of 45%. After hydrazine addition to the Ni[(OH).sub.2]/ccllu!ose-grafted GO aqueous suspension, Ni[(OH).sub.2] is expected to decomposes to yield NiO particles, as discussed by several authors [37-39], and simultaneously GO-based sheets are reduced yielding rGO-based sheets (Fig. 1).
Chacracterization of the NiNPs/Cellulose-Grafted rGO Composite
The deposition of Ni nanoparticles (NiNPs) on the surface of cellulose-grafted rGO was first confirmed by studying the aqueous suspensions of cellulose-grafted GO and NiNPs/cellulose_grafted rGO without and with a magnet on the outer wall of the vessel (Fig. 2). As expected, after 10 min of sonication, we can observe that cellulose-grafted GO in aqueous solution gives a homogeneous black suspension (Fig. 2A) while the NiNPs/cellulose-grafted rGO one sediments quickly (Fig. 2B).
Moreover, it can be observed that the NiNPs/Cellulose-grafted rGOs nanocomposite is completely held on the inner wall of the vessel by using a magnet. The latter behavior provides a proof that the NiNPs deposited on the surface of cellulose-grafted-rGO sheets made the nanocomposite magnetically recoverable. The immobilization of NiNPs onto the cellulose-grafted rGO surface was also evidenced by using both EDX analysis (Fig. 3) and XRD (Fig. 4). Indeed, as the energies of the X-rays are characteristic of the difference in energy between the two shells and of the atomic structure of the emitting element, EDX allows the elemental composition of the specimen to be confirmed. As expected, Fig. 3 displays the EDX spectrum of cellulose-grafted rGO, which mainly shows the presence of carbon, oxygen, and Nickel.
The XRD patterns of GO, and cellulose-grafted GO and NiNPs/cellulose-grafted rGO are plotted in Fig. 4.
A peak centered around 20 = 11.5[degrees] (d (0 0 1) = 7.6 [Angstrom]) attributable to a degree of ordering is observed for GO (Fig. 4a). By introducing cellulose chains onto the GO sheets, a new diffraction peak appears at 20 = 22.7[degrees], which may be attributed to the crystalline nature of the grafted cellulose instead of restacking of the GO sheets (Fig. 4b) , For the NiNPs/cellulose- grafted rGO sample, three main characteristic peaks are observed at 20 = 44.5[degrees], 51.6[degrees], and 76.4[degrees] corresponding to the (111), (200), and (220) planes, respectively, of the face-centered cubic structure of Ni crystal confirming the reduction of [Ni.sup.2+] ions in presence of hydrazine (Fig. 4c).  Moreover, there is no detection of GO peak suggesting that GO is well reduced to rGO in presence of hydrazine. Then, thermogravimetric (TG) measurements were carried out to determine the mass ratio of NiNPs/ cellulose-grafted rGO in the composite (Fig. 5).
On the TG curves, two main steps of weight loss are observed whatever the sample. The first step occurs at temperatures below 200[degrees]C, which is due to the removal of the physisorbed water. The larger weight loss in the temperature range 200[degrees]C-500[degrees]C is attributed to the removal of cellulose and the content of NiNPs was calculated to be around 20 wt% (Fig. 5b) considering a remaining weight content of 35% for Cellulose-grafted rGO at 800[degrees]C (Fig. 5a).
The morphology of the NiNPs/cellulose-grafted rGO composite was studied by both SEM and transmission electron microscopy, as shown in Fig. 6.
SEM image of cellulose-grafted rGO show some randomly aggregated thin large flakes with wavy wrinkles (Fig. 6a) while the immobilization of NiNPs on the cellulose-grafted rGO surface leads to the presence of lots of sphere-like structures that are homogeneously distributed (Fig. 6b). A few large agglomerates NiNPs can be observed and the NiNPs average diameter is ~20 nm while the particle size distribution is broad, ranging from 10 to 60 nm (Fig. 6b). The TEM image (Fig. 6c) confirmed the in situ formation of NiNPs (black spots) onto the rGO-based surface.
Magnetic Properties of NiNPslCellulose-Grafted rGO
The magnetic properties were studied at 300 K with a SQUID magnetometer for NiNPs, NiNPs/rGO, and NiNPs/cellulose-grafted rGO. The plots of magnetization versus magnetic field at are examplified in Fig. 7 for NiNPs and NiNPs/cellulose-grafted rGO nanocomposite.
The NiNPs/cellulose-grafted rGO nanocomposite exhibits a typical ferromagnetic behavior (Fig. 7A). The saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) could be determined to be 30.87 emu/g, 2.53 emu/g, and 130.55 Oe, respectively (Fig. 7B, Table 1).
These values compare well with those obtained by, Tian et al.  as 37.8 emu/g, 6.7 emu/g, and 78.1 Oe, respectively, for the direct grafting of NiNPs onto the GO surface and 55.9 emu/g, 7.4 emu/g, and 46.2 Oe, respectively, for NiNPs. The decrease in Ms for NiNPs/cellulose-grafted rGO and NiNPs/rGO samples in comparison with the pure NiNPs one may be attributed to the presence of non-magnetic rGO sheets. Herein, the use of cellulose-grafted rGO sheets may favor the efficiency by increasing the number of anchor groups for Ni NPs in comparison with neat GO. In addition, the electron exchange between rGO grafting cellulose and supported NiNPs in NiNPs/cellulose-grafted rGO hybrids could also quench the magnetic moment and lower the Ms, as discussed by Tian et al.  and Veiga et al. ,
In situ generation of nickel nanoparticles has been done successfully onto the surface of cellulose-grafted. Qualitative evidence of NiNPs immobilization was done by EDX analysis and X-ray EDX analysis while SEM and TEM observations showed that NiNPs with an average diameter of 20 nm are homogeneously decorated onto the cellulose-grafted rGO surface. A NiNPs content of 20 wt% was determined by TGA. The magnetic properties of the corresponding nanocomposite was investigated and we showed that it exhibits a typical ferromagnetic behavior with a Ms, a Mr, and a Hc of 30.87 emu/g, 2.53 emu/ g, and 130.54 Oe, respectively. This NiNPs/cellulose-grafted rGO nanocomposite have potential applications in the field of biosensor and biocatalyst.
The authors would like to acknowledge Pierre Alcouffe and all the staff of the Technological Centre of Microstructures of the University of Lyon 1 for their technical help as well as the financial support from Region Rhone-Alpes (France) through a CMIRA exchange program.
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Abdelwaheb Dhahri, (1,2) Hend Jaoua-Bahloul, (1) Mohammed Hassen V. Baouab, (2) Dominique Luneau, (3) Emmanuel Beyou [iD] (1)
(1) Ingenierie des Materiaux Polymeres, UMR CNRS 5223, Universite de Lyon Universite Lyonl, Villeurbanne F-69622, France
(2) Laboratoire de Microelectroniques et Instrumentations, Universite de Monastir, Faculte des Sciences de Monastir, Boulevard de l'environnement, Monastir 5019, Tunisie
(3) Laboratoire des Multimateriaux et Interfaces, UMR CNRS 5615, Universite de Lyonl, Universite Lyonl, Villeurbanne F-69622, France
Correspondence to: E. Beyou; e-mail: firstname.lastname@example.org
Contract grant sponsor: Region Rhone-Alpes (France).
Published online in Wiley Online Library (wileyonlinelibrary.com).
Caption: FIG. 1. Immobilization of NiNPs onto cellulose-grafted rGO.
Caption: FIG. 2. Digital images of aqueous suspensions (c = 0.35 mg/mL) of (A) Cellulose-grafted GO, (B) NiNPs/Cellulose-grafted rGO, and (C) NiNPs/Cellulose-grafted rGO with a magnet on the outer wall of the vessel.
Caption: FIG. 3. EDX spectrum of NiNPs/cellulose-grafted rGO.
Caption: FIG. 4. XRD patterns of (a) GO, (b) cellulose-grafted iGO, and (c) NiNPs/cellulose-grafted rGO.
Caption: FIG. 5. TGA curves of (a) cellulose-grafted rGO and (b) NiNPs/cellulose-grafted rGO.
Caption: FIG. 6. SEM images of (a) cellulose-grafted rGO, (b) NiNPs/cellulose-grafted rGO, and TEM image of (c)NiNPs/ cellulose-grafted rGO.
Caption: FIG. 7. Magnetization versus magnetic field recorded at 300 K for (A) NiNPs, NiNPs/rGO and NiNPs/cellulose-grafted rGO, (B) NiNPs/cellulose-grafted rGO, (C) NiNPs/rGO, and (D) NiNPs.
TABLE 1. Ms, Mr, Mr/Ms ratio, and coercviity (He) for the NiNPs-based samples. Ms Mr He Sample (emu/g) (emu/g) Mr/Ms (Oe) NiNPs/cellulose-g-rGO 30.87 2.53 0.08 130.54 NiNPs/rGO 37.42 6.98 0.18 38.39 NiNPs 44.52 9.66 0.21 38.40
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|Author:||Dhahri, Abdelwaheb; Jaoua-Bahloul, Hend; Baouab, Mohammed Hassen V.; Luneau, Dominique; Beyou, Emman|
|Publication:||Polymer Engineering and Science|
|Date:||Sep 1, 2018|
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