Carbon Composite Microspheres

Subscriber access provided by RMIT University Library

Article

Facile Synthesis of Porous Nickel/Carbon Composite Microspheres with Enhanced Electromagnetic Wave Absorption by Magnetic and Dielectric Losses Song Qiu, Hailong Lyu, Jiurong Liu, Yuzhen Liu, Nannan Wu, and Wei Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b03159 • Publication Date (Web): 21 Jul 2016 Downloaded from http://pubs.acs.org on July 22, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Facile Synthesis of Porous Nickel/Carbon Composite Microspheres with Enhanced Electromagnetic Wave Absorption by Magnetic and Dielectric Losses

Song Qiu,a Hailong Lyu,a Jiurong Liu,a,* Yuzhen Liu,a Nannan Wu,a and Wei Liub

a

Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials,

Ministry of Education and School of Materials Science and Engineering, Shandong University, Jinan, Shandong 250061, People’s Republic of China b

State Key Laboratory of Crystal Materials, Shandong University, Shandong 250100,

China *Corresponding author. E-mail addresses: [email protected] (J. Liu) Tel: +86-531-88390236; Fax: +86-531-88392315

1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 44

ABSTRACT: Porous nickel/carbon (Ni/C) composite microspheres with diameters of ca. 1.2-1.5 µm were fabricated by a solvothermal method combining with carbon reduction. The pore size of the synthesized Ni/C composite microspheres is ranged from several to 50 nm. The porous Ni/C composite microspheres exhibited saturation magnetization (MS) of 53.5 emu g-1 and coercivity (HC) of 51.4 Oe. When tested as electromagnetic wave (EM) absorption material, the epoxy resin composites containing 60% and 75% porous Ni/C microspheres provided high-performance EM absorption at the thicknesses of 3.0-11.0 mm and 1.6-7.0 mm in the corresponding frequency range of 2.0-12 GHz and 2.0-18 GHz, respectively. The superior EM absorption performances of porous Ni/C composite microspheres derived from the synergy effects generated by the magnetic loss of nickel, the dielectric loss of carbon, as well as the porous structure. KEYWORDS:

electromagnetic

wave

absorption,

nickel,

porous

composite

microspheres, magnetic loss, dielectric loss

2


Page 3 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. INTRODUCTION With the development of wireless communications, electromagnetic (EM) wave absorption materials have attracted much research attention.1-11 They are usually applied in mobile phones, intelligent transport systems, electronic toll collection, local area network systems and other electronics to prevent EM wave interference among electronic equipment or integrated devices. To achieve high-speed data transmission, the applied frequency of EM waves has being expanded from MHz to the higher GHz range. Great efforts have been made to explore efficient EM absorbing materials that possess high absorption capacity, broad absorption bandwidth, low density, as well as thinness. Recently, metallic magnets including Fe, Co, Ni, and related alloys have drawn growing attention as effective EM absorption materials because of their large saturation magnetization and their Snoek’s limit at a high frequency level,12-15 thereby keeping their high relative permeability (µr) in high frequency range and making it possible to prepare thin absorbers. Among the aforementioned metallic magnets, nickel, regarded as one promising absorption material in the 1-18 GHz range, has drawn much research devoted to investigating its EM absorption performance.16,17 However, similar to other metallic magnets, the electric conductivity of nickel is high, and its permeability reduces drastically with increasing frequency due to large EM wave-induced eddy current loss, which results in weak EM wave absorption.18 A variety of approaches have been employed to improve the EM absorption strength of metallic magnets. One efficient way is to design various nano/micro-structures (e.g., hollow spheres, porous particles, nanowires, nanoflakes, and flower-like particles) 3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 44

with large surface area or aspect ratio, which can efficiently suppress eddy current and maintain high permeability, and hence achieve strong EM wave absorption and lightweight absorption materials.19-23 The design of nanocomposites with two or multiple components in synergy is another effective way. The nanocomposites of metallic magnets with non-conductive materials (including SiO2, Y2O3, ZnO, carbon materials, etc.) improved EM absorption performance since the addition of non-conductive materials efficiently reduced eddy current loss.24-27 Among the additives, carbon materials have attracted wide attention for constructing hybrid nanocomposites due to their lightweight, high surface-to-volume ratio, low cost, natural abundance and environmental benignity.28-32 Benefiting from the incorporation of carbon materials with low conductivity (compared to metallic magnets) and metallic magnets with high permeability, as well as dielectric loss from carbon materials, carbon-based nanocomposites exhibited strong EM wave absorption and thin absorption thickness. For example, Ni/C nanocapsules with carbon shells prepared by a modified arc-discharge using ethanol as a carbon source showed the reflection loss (RL) of less than -20 dB in the 2.6-8.2 GHz range and a minimum RL value of -40 dB at 3.2 GHz with an absorber thickness of 7.8 mm.33 The island-like nickel/carbon nanocomposites were prepared via the calcination of nickel nitrate-polyacrylamide mixture under flowing ammonia.34 The nickel/carbon-paraffin composites exhibited efficient microwave absorption performance (RL< -20 dB) in a broad frequency range (4.5-18.0 GHz) with absorber thicknesses of 2.3-7.0 mm. Our previous research also confirmed that the α-Fe/amorphous carbon nanocomposite 4


Page 5 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


displayed EM wave absorption performances superior to pure α-Fe, mainly attributable to the carbon addition acting as separator to reduce α-Fe eddy current loss.35 In this research, the porous nickel/carbon (Ni/C) composite microspheres with diameters of ca. 1.2-1.5 µm have been fabricated by a solvothermal method combining with carbon reduction. The electromagnetic absorbing performances of the porous Ni/C composite microspheres were surveyed. Utilizing the magnetic loss of Ni and the dielectric loss of carbon, the as-prepared porous Ni/C composite microspheres exhibited superior EM wave absorption performances. Meanwhile, the porous structure not only facilitates the suppression of eddy current loss, but also reduces the density of absorption materials. 2. EXPERIMENTAL SECTION 2.1. Materials. Nickel acetate (Ni(CH3COO)2·4H2O), methanol, and pyrrole were supplied by Sinopharm Chemical Reagent Co., Ltd. All chemicals are of analytical grade and used as received. 2.2. Synthesis of porous Ni/C composite microspheres. In a typical precursor synthesis procedure, a green solution was received by dissolving nickel acetate (2 mmol) into methanol (50 mL) under magnetic stirring, and then treated at 180 ºC for 4 h in a sealed Teflon-lined stainless steel autoclave. After the solvothermal process, the precursor was obtained by centrifuging and washing with deionized water several times, and subsequently drying at 50 ºC overnight. Before the carbon reduction process, the precursor was sintered at 300 ºC for 2 h in a muffle furnace to remove the 5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 44

precursor’s hydroxyl groups. The porous Ni/C composite microspheres were fabricated by adding 0.5 mL pyrrole (as carbon resource) into 1.4 g of the annealed precursor in a stainless steel autoclave, which was sealed and heated in a furnace at 550 ºC for 5 h. 2.3. Characterizations. The synthesized Ni/C composite microspheres was characterized by X-ray diffraction (Rigaku Dmax-rc X-ray diffractometer: I = 50 mA, V = 40 kV, Cu Kα radiation) to determine the crystal structure of products. Fourier transform infrared spectroscopy (FT-IR) was recorded on a VERTEX-70FT-IR spectrometer. Field emission scanning electron microscope (FE-SEM, JSM-6700F: V = 20 kV, I = 1.0 × 10-10 A) and high-resolution transmission electron microscopy (HR-TEM, JEOL JEM-2100: V = 200 kV) were used to inspect the microstructure and morphology of samples. To evaluate carbon content in the resultant product, thermogravimetric

analysis/differential

scanning

calorimetry

(TGA/DSC,

TA

Instruments SDT Q600) were operated on a SDT thermal-microbalance apparatus from room temperature to 800 °C with a heating rate of 5 °C min-1 in air. N2 adsorption-desorption isotherms were recorded using a Quadrasorb-SI instrument at 77 K. The specific surface area and pore size distribution were calculated by the Brunauer–Emmett–Teller (BET) model and Barrett–Joyner–Halenda (BJH) method, respectively. Magnetic measurement was conducted with a vibration sample magnetometer (Tamakawa, TM-VSM2014-MHR-Type). For the characterization of EM absorption performances, the toroidal samples of the epoxy resin composites containing 60% and 75% porous Ni/C composite 6


Page 7 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


microspheres were prepared referring to our previous report.15 The network analyzer (Agilent Technologies E8363A) was used to measure the scattering parameters of the samples. The relative permeability (µr) and permittivity (εr) values were determined from the scattering parameters as measured in the frequency range of 2.0-18.0 GHz. The reflection loss (RL) curves were calculated from µr and εr at the given frequency and absorber thickness with the following equations:24,35 12

Ζin = Z 0 (µ r ε r ) tanh{ j (2πfd c)( µ r ε r )1 2 }

(1)

RL = 20 log (Zin − Z0 ) (Zin + Z0 )

(2)

where ƒ, d, c, Z0 and Zin represent EM wave frequency, absorber thickness, light velocity, free-space impedance, and input impedance, respectively.24,35 When RL value equals to -10 dB, the EM wave absorption rate will reach to 90% from equations (1) and (2), and therefore in this work, the RL values smaller than -10 dB denote efficient EM wave absorption. 3. RESULTS AND DISCUSSION The phases of the as-prepared precursor and porous Ni/C composite microspheres are investigated by XRD (Fig. 1). As shown in Fig. 1a, the diffraction peaks of precursor can be mainly indexed to α-Ni(OH)2 (JCPDS: 22-0444).36 During the solvothermal process, the Ni2+ ions in methanol react with OH- anions generated by the hydrolysis of crystallization water from nickel acetate (Ni(CH3COO)2·4H2O) to form Ni(OH)2 precipitate. After being sintered at 300 ºC for 2 h, the as-prepared Ni(OH)2 precursor was converted to cubic NiO (JCPDS: 65-2901) by the removal of hydroxyl groups. However, the diffraction peaks of nickel (JCPDS: 65-0380) were also observed, 7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 44

attributable to the partial reduction of NiO by the precursor’s methanol residue after calcination (Fig. 1b), which was confirmed by the following FT-IR measurement. The XRD pattern of product reduced by carbon (Fig. 1c) matched well with the fcc Ni (JCPDS: 65-0380) and without other peaks were found, indicating that NiO has been reduced completely to Ni and the formed carbon component was mainly amorphous, which is in accord with the later HR-TEM measurement. FT-IR was employed to survey Ni(OH)2 precursor and the porous Ni/C composite microspheres in 400-4000 cm-1 range. There are two broad peaks at 3450 and 1630 cm−1 for Ni(OH)2 precursor (Fig. 2a), corresponding to the stretching vibration and the bending mode of hydroxyl (O-H) groups, respectively.37 The bands around 2906 and 2800 cm-1 could be attributed to the asymmetric and symmetric stretching vibrations of C-H, respectively.38 The absorption peak at 1085 cm-1 is associated with the stretching vibration of C-O in methoxyl species.39 The band at ca. 611 cm-1 corresponds to Ni-O-H. The FT-IR result indicates that the precursor is Ni(OH)2 and methanol residue exists in the precursor. After being sintered at 300 ºC for 2 h, the FT-IR measurement confirmed the formation of NiO based on the appearance of Ni-O (676 cm-1) and the disappearance of the C-H (2906 and 2800 cm-1) and C-O (1085 cm-1) groups. Two weakened absorption peaks at 3450 and 1630 cm-1 assigned to O-H groups still exist due to the water molecules’ absorption on the surface of the annealed sample after exposure to air. From the FT-IR spectrum of the Ni/C product, there is no obvious absorption peak corresponding to C-H groups to indicate the complete carbonization of pyrrole, and two small absorption peaks assigned to Ni-O and O-H 8


Page 9 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


were observed mainly attributable to the slight oxidation of Ni and some water molecules absorbed on the product’s surface after exposure to air. The carbon form in the porous Ni/C composite microspheres was determined by Raman spectroscopy. As shown in Fig. 2b, two broad peaks located at 1330 and 1604 cm-1 corresponding to the D and G band represent amorphous carbon and graphitic carbon, respectively.40,41 The ratio of peak intensity (ID/IG) can be utilized to assess the disorder degree of carbon materials. The value of ID/IG is about 1.2 for the porous Ni/C composite microspheres, demonstrating the low graphitization degree of carbon, which agrees with the XRD result. In addition, the D and G bands show large full width at half maximum (FWHM). The broadening of the G band is dependent on an increase in bond angle disorder, and the width of the D-peak is correlated to a distribution of sp2 bonded clusters of different sizes.42 Therefore, the broadening of the D and G peaks also suggests that carbon in the porous Ni/C microspheres has a low degree of graphitization.

Figure 1. XRD patterns of the as-prepared precursor (a), annealed sample (b), and porous Ni/C composite microspheres (c). 9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 44

Figure 2. (a) Infrared spectra of the as-prepared precursor, annealed sample, and porous Ni/C microspheres, and (b) Raman spectrum of porous Ni/C microspheres. The morphology and structure of the samples were further investigated by FE-SEM (Fig. 3). From the low-magniﬁcation SEM image (Fig. 3a), the synthesized Ni(OH)2 is microspheres with sizes of 1.0-1.5 µm. A close inspection reveals that the precursor microspheres are composed of curled nanosheets with a thickness of ca. 30 nm (Fig. 3b). In order to reduce the surface free energy, these nanosheets are agglomerated to generate a loose spherical structure. When Ni(OH)2 microspheres were sintered in air at 300 ºC for 2 h, the size and morphology of the microspheres showed no obvious variation (Figs. 3c, d). After NiO microspheres reduced by carbon, there was no apparent change in size, but a lot of tiny particles were observed on the surface (Fig. 3e). From the higher magnification image (Fig. 3f), the Ni/C microspheres are constructed with two-dimensional nanosheets and particles with sizes of ca. 50-200 10


Page 11 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


nm. Fig. 4 shows the HR-TEM images of the Ni/C microspheres. The apparent contrast between the gray and black parts confirms the porous characteristic of the Ni/C composite microspheres (Fig. 4a). It is interesting to note that, from the enlarged image, the porous microspheres are composed of Ni particles with sizes of ca. 50-200 nm and hollow carbon nanospheres with a size of ca. 50 nm (Fig. 4b). In the high resolution TEM (HR-TEM) image (Figs. 4c, d), it can be clearly observed that the Ni nanoparticle is coated by a carbon layer (ca. 5 nm), which is beneficial to the anti-oxidation of Ni nanoparticles, and the shell thickness of the hollow carbon nanospheres is ca. 5 nm. Summarizing the above analysis, the NiO nanosheets (Fig. 3d) were reduced to Ni nanoparticles by carbon coating, and the hollow carbon nanospheres generated during the carbonization of pyrrole were connected together to form carbon sheets (Fig. 3f). The possible formation process of the porous Ni/C microspheres can be proposed on the basis of experimental results. During the carbonization process, liquid pyrrole initially evaporated, and then absorbed onto the surface of the NiO sample. With the temperature increasing to 550 ºC, the absorbed pyrrole was pyrolyzed to form carbon, while NiO was reduced to Ni nanoparticles by carbon. In this process, most of nanosized Ni coated with carbon escaped from the shell, resulting in the formation of hollow carbon nanospheres, and Ni nanoparticles were agglomerated to form large clusters. Therefore, the pores are mainly derived from the voids between hollow carbon nanospheres and Ni nanoparticles, as well as the hollow structure of carbon nanospheres.

11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 44

Figure 3. FE-SEM images of the as-prepared precursor (a, b), annealed sample (c, d), and porous Ni/C microspheres (e, f).

Figure 4. HR-TEM images of porous Ni/C microspheres with various magnifications (a-d). To evaluate carbon content in the porous Ni/C microspheres, TGA measurement was performed and the result was shown in Fig. 5a. From room temperature to 200 °C, the weight loss of about 1.0 % corresponds to the evaporation of water absorbed on the surface of porous microspheres due to exposure to air. The weight loss associated with the oxidation of carbon and the weight gain corresponding to the oxidation of nickel to nickel oxide occurred simultaneously between 200-600 °C. Carbon was oxidized in air to generate CO and CO2 gases. A broad exothermic peak observed in the DSC curve at 200-500 °C is attributed to the exothermic process of carbon and Ni 12


Page 13 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


oxidation reactions. After 600 °C, the TG curve becomes horizontal with a total 4.7% weight gain, indicating the complete oxidation of Ni to NiO and the complete removel of carbon. Therefore, the total 105.7% (1.0 % weight loss from the evaporation of water) weight corresponds to the left NiO. The calculated weight gain associated with the oxidation process of nickel to nickel oxide is 27.3 wt% ( M NiO /M Ni = 1.273 ). Based on the above analysis, the calculated content of nickel in porous Ni/C microspheres is 83.03 wt% (105.7/1.273), and the calculated carbon content is 15.97 wt% (1-1.0%-83.03%). The porosity feature and surface area were determined from the N2 absorption-desorption isotherms of porous Ni/C composite microspheres. The isotherms exhibit a type V with a distinct hysteresis loop (Fig. 5b), demonstrating the existence of mesopores.43 It is evident that, from the inset in Fig. 5b, the porous Ni/C microspheres contain non-uniform pores in sizes of several to 50 nm, with pores about 10 nm in size dominant. The calculated surface area is 14.0 m2 g-1.

13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 44

Figure 5. (a) TGA-DSC curves and (b) isotherms of N2 adsorption (solid squares) and desorption (solid triangles) for porous Ni/C microspheres. The pore size distribution is shown in inset. The magnetic hysteresis loop at room temperature for the porous Ni/C composite microspheres is displayed in Fig. 6. The measured saturation magnetization (MS), coercivity (HC), and remnant magnetization (MR) are 53.5 emu g-1, 51.4 Oe, and 3.8 emu g-1, respectively. The slightly smaller MS value of porous Ni/C microspheres compared to bulk Ni (ca. 55 emu g-1)44,45 is mainly attributable to the existence of non-magnetic carbon. In addition, the porous Ni/C microspheres showed slightly lower coercivity (51.4 Oe) than bulk nickel (ca. 100 Oe).44,45 A similar coercicity reduction was also observed in the graphitically encapsulated Ni nanocrystals, mainly due to the demagnetization of thermal energy over spontaneous magnetization, which is associated with the smaller nickel particle size with respect to the bulk nickel.44

Figure 6. Magnetization loop of porous Ni/C microspheres measured at 300 K. Figure 7 shows the frequency dependencies of the relative permittivity (εr) and relative permeability (µr) for the epoxy resin composites containing 60 wt% and 75 wt% porous Ni/C microspheres in the 2-18 GHz range. The real part (εr′ and µr′) and imaginary part (εr″ and µr″) represent the energy storage and dissipation capabilities, respectively. For the epoxy resin composite with 60 wt% porous Ni/C microspheres, 14


Page 15 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the real part of permittivity εr′ shows less fluctuation (from 8.3 to 6.3) in the 2-14 GHz range, and then declines to ca. 4.8 as frequency increases to 18 GHz. The imaginary part εr″ exhibits two resonance peaks around 10 GHz and 16 GHz , which may be attributed to the interfacial polarization resonance due to the electronegativity difference between the Ni core and carbon shell,46,47 and the permanent electric dipoles resulting from defects in the carbon shell and hollow carbon nanospheres.48,49 When the loading amount of porous Ni/C microspheres increases to 75 wt%, the real part (εr′) and imaginary part (εr″) of permittivity display an increscent trend compared with the 60 wt% loaded sample. The εr′ value declines gradually with frequency in the range of 2-11.0 GHz (from 14.6 to 11.1), followed by a drastic decline to ca. 7.0 at 18 GHz, while the imaginary part (εr″) shows a wide peak in the frequency range of 12-18 GHz and the peak value is ca. 7.0 appeared at 14.5 GHz. Comparing with the epoxy resin composite with 75 wt% Ni/C microspheres, the sample with 60 wt% loading exhibits a lower permittivity level, which can be attributed to the decrease of space-charge polarization among Ni/C microspheres separated more efficiently by epoxy resin.19 Figure 8 displays the plots of εr′ versus εr″ for the epoxy resin composites with 60 wt% and 75 wt% porous Ni/C microspheres. According to the Debye dipolar relaxation formulas,49,50 the curve of εr′ versus εr″ is a single semicircle defined as the Cole-Cole semicircle. The epoxy resin composites containing 60 wt% and 75 wt% porous Ni/C microspheres all exhibit a segment of two overlapped Cole-Cole semicircles suggesting the existence of dual dielectric relaxation processes, which are related to the Debye dipolar relaxation and the interfacial relaxation on the 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 44

Ni/C core-shell interfaces (Fig. 4c). In other previous researches, similar multiple dielectric

relaxation

processes

have

also

been

found

on

the

core-shell

composites.49,51-53

Figure 7. εr (a) and µr (b) spectra of the epoxy resin composites containing 60 wt% and 75 wt% porous Ni/C microspheres in the 2-18 GHz range. As shown in Fig. 7b, the real part of relative permeability (µr′) for the epoxy resin composite loaded with 60 wt% porous Ni/C microspheres declines from 1.29 to 0.84 slowly in the 2.0-14.7 GHz range, and then increases to 1.15 with the frequency increased to 18 GHz. The imaginary part of relative permeability (µr″) exhibits a broad magnetic loss peak in the frequency range of 2.0-16.2 GHz because of the natural resonance of Ni nanoparticles,54 and a peak value of 0.24 appears at 2.4 GHz. The natural resonance is located at GHz frequency range, which is higher than dozens of MHz for fcc bulk Ni.47 A linear dependence of natural resonance frequency on anisotropy field can be shown by the equation in accordance with ferromagnetic resonance theory:55 2πf r = γH eff , where ƒr is the resonance frequency, γ is the gyromagnetic ratio, and Heff is the effective anisotropy field. For nano-structured 16


Page 17 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


magnetic materials, Heff can be influenced by size, morphology, magnetocrystalline anisotropy, as well as the magnetic interactions among particles. The Heff increase of nano-structured magnetic materials leads to the rise of natural resonance frequency, which have also been found on the flower-like nickel particles and the branched nickel nanowires.21,22 For the epoxy resin composite containing 75 wt% porous Ni/C microspheres, the µr′ value decreased from 1.42 to 0.74 in the 2-14 GHz range, and then increased to 1.23 at 18 GHz. The µr″ displayed a wide peak in the frequency range of 2.0-15.7 GHz, and its maximal value is 0.41 located at 2.4 GHz. The maximum value of µr″ is larger than that (0.24) of the epoxy resin composite containing 60 wt% porous Ni/C microspheres due to the magnetic content increase to 75 wt%. It is noteworthy that the partial values of µr″ are negative in the frequency range from ca. 13 to 18 GHz, suggesting that the porous Ni/C microspheres might be used as left-handed materials with negative reflection, which usually have negative permittivity and permeability.56-58 Negative permittivity and permeability values have also been found in the Ni/C and Ni/Ag core-shell structures.33,53

17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 44

Figure 8. Typical Cole-Cole semicircles of the epoxy resin composites containing (a) 60 wt% and (b) 75 wt% porous Ni/C microspheres. Figure 9a exhibits the RL spectra of the composite containing 60 wt% Ni/C microspheres versus frequency with various thicknesses. When the absorber thickness varied from 3.0 to 11.0 mm, the RL values below -20 dB were achieved in the frequency range of 2.0-10.4 GHz, suggesting 99% EM wave absorption. The minimal RL value reached to -44.5 dB at 2.6 GHz corresponding to an absorber thickness of 9.5 mm. For the resin composite containing 75 wt% Ni/C microspheres, the RL values below -10 dB appeared in the frequency range of 2-18 GHz corresponding to the matching thicknesses of 1.6-7.0 mm, and when the absorber thickness is 1.8 mm, the minimal value reached to -28.4 dB at 15.4 GHz (Fig. 9b). The reflection loss was also measured from the reflection scattering parameter S11-Short (the back-face of sample was terminated by a short circuit with a metallic plug installed in coaxial line) by 18


Page 19 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


using a coaxial transmission line, into which the toroidal-shaped test sample was put.59 As shown in Fig. 9, the calculated RL values at the thicknesses of 3 mm for the sample containing 60 wt% porous Ni/C microspheres and 2.5 mm for the 75 wt% loaded sample are in good agreement with the measured results ( 20log S11-Short ), confirming that the impedance matching solution is suitable for the calculation of RL at matching frequency and thickness.

Figure 9. RL curves versus frequency for the epoxy resin composites containing (a) 60 wt% and (b) 75 wt% porous Ni/C microspheres with various thicknesses in the frequency range of 2-18 GHz. (thickness: mm). The above results indicate that the porous Ni/C microspheres exhibit higher absorbing strength and broader absorption bandwidth (RL < -20 dB) than other reported Ni materials such as Ni urchinlike chains, Ni nanowires, and Ni hollow spheres.20,60,61 Moreover, comparing with some other Ni/C composite EM wave absorbers, the synthesized porous Ni/C microspheres also display more efficient EM wave 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 44

absorption performance. For example, minimum RL values for the reported Ni/graphene nanocomposites62 and Ni nanocrystals/graphene29 are -13 and -17.8 dB, while the composites including 60 wt% and 75 wt% porous Ni/C microspheres show a minimum RL of -44.5 dB at 2.6 GHz and -28.4 dB at 15.4 GHz, respectively, confirming stronger EM wave absorption. In contrast with the Ni/C nanocapsules (e.g., thickness of 3.8 mm at ca. 8 GHz)33 and Ni-C nanocomposites (e.g., thickness of 2.5 mm at ca. 14 GHz) ,28 when efficient EM absorption (RL < -10 dB) appeared at the same frequencies, the sample with 75 wt% porous Ni/C microspheres also showed thinner absorption thicknesses at 8 GHz (ca. 3 mm) and 14 GHz (< 2 mm), respectively (Fig. 9b). The relevant comparison is summarized in table 1. In order to examine the dielectric loss and magnetic loss contribution to the EM wave absorption of the porous Ni/C microspheres, the frequency dependencies of dielectric tangent loss ( tan δE = ε′′/ε′ ) and magnetic tangent loss ( tan δM = µ ′′/µ ′ ) are calculated. As shown in Fig. 10a, the tanδE values are close to tanδM within the 2-8 GHz range, suggesting the presence of both dielectric loss and magnetic loss for the sample with 60 wt% loading. In the 8-18 GHz range, it is observed that the values of dielectric tangent loss are much higher than those of magnetic tangent loss, indicating that EM wave attenuation is mainly caused by dielectric loss at high frequencies. Fig. 10b shows the frequency dependences of tanδE and tanδM of the epoxy resin composite with 75 wt% porous Ni/C microspheres. Compared with the sample with 60 wt% loading, the tanδE and tanδM have similar variation tendencies, and tanδE shows higher values within the frequency range of 2-18 GHz. The tanδM values also increase in the 20


Page 21 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2-8 GHz range with increasing the content of porous Ni/C microspheres to 75 wt%. The increase of magnetic loss and dielectric loss is favorable for the enhancement of EM wave absorption. By comparison, these two epoxy resin composites all achieved a absorption peak (RL < -10 dB) at ca. 4.5 GHz, while the absorbing thickness of the 75 wt% loaded sample reduced from 6 mm (60 wt% loading) to 4 mm (Fig. 9). In Fig. 10b, we can also observe that tanδE and tanδM show the complementary variation tendency with frequency in high frequency region. In accordance with the Maxwell formulas, permeability and permittivity are coupling parameters since a magnetic field can be induced by an ac electric field caused by eddy current in EM wave absorbing materials and be radiated out, with µr″ and εr″ representing the loss of magnetic and electric energy, respectively. The radiated magnetic energy converted to electric energy, resulting in the increase of εr″ and the decrease of µr″, which gave rise to the inverse variation tendency of tanδE and tanδM with frequency.63,64 As shown in Fig. 7b, the magnetic energy loss (µr″) decreased gradually with frequency even to negative value in the 13-18 GHz range. The negative µr″ means that magnetic energy is radiated out from the EM wave absorbing material, and could be ascribed to the eddy current loss. When EM wave is irradiated into the Ni/C microspheres, electrons will come into being rotation caused by the Lorentz force to form eddy current. The eddy current induced a magnetic field opposite to the applied field and radiated EM energy, leading to negative µr″.65 The transfer of magnetic energy to electric energy suggests that the EM attenuation is mainly caused by dielectric loss at high frequency.66,67 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 44

Table 1. Electromagnetic wave absorption properties of Ni and Ni/C composites Sample

Mass ratio (wt%)

Minimum RL value (dB)

dm (mm) (minimum RL)

ƒm (GHz) (minimum RL)

dm (mm) (RL ≤ -20 dB)

Frequency range (GHz) (RL ≤ -20 dB)

Ref.

Ni urchinlike chains

60

-25.3

2.0

9.6

----

----

20

Ni nanowires

65

-8.5

3.0

10.0

----

----

60

Ni hollow spheres

25

-27.2

1.4

13.4

1.4-1.5

12.5-13.4

61

Ni/graphene

20

-13

2.0

11.0

----

----

62

Ni nanocrystals/graphene

60

-17.8

5.0

3.5

----

----

29

Ni/C nanocapsules

40

-40

7.8

3.0

3.8-8.8

2.6-8.2

33

Ni-C nanocomposites

50

-35

4.0

7.8

2.0-5.0

5.9-18

28

Ni/C microspheres

60

-44.5

9.5

2.6

3.0-11.0

2.0-10.4

this work

Ni/C microspheres

75

-28.4

1.8

15.4

1.7-2.0

12.9-16.6

this work

Figure 10. Frequency dependences of dielectric tangent loss and magnetic tangent loss for epoxy resin composites containing (a) 60 wt% and (b) 75 wt% porous Ni/C microspheres in the 2-18 GHz range. For the EM wave absorber derived from the porous Ni/C composite microspheres, the carbon coating and carbon sheet served as the dielectric loss component, and the Ni nanoparticles provided high magnetic loss. The core/shell structure of Ni nanoparticles with carbon coating induces dual dielectric relaxations including the Debye dipolar relaxation and the interfacial relaxation on the Ni/C core-shell 22


Page 23 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


interfaces, which further enhances the dielectric loss. The combination of dielectric and magnetic losses is beneficial to the enhancement of EM wave absorption. The porous structure is liable to the import and absorption of EM waves. In addition, the presence of carbon components among Ni nanoparticles can efficiently reduce the eddy current of Ni and maintain high permeability. As expected, porous Ni/C composite microspheres exhibit superior EM wave absorption performance.

4. CONCLUSIONS In summary, the porous Ni/C composite microspheres were fabricated by a feasible solvothermal route and subsequently a novel carbon reduction method. As EM absorption material, the as-prepared porous Ni/C composite microspheres showed strong EM wave absorption, wide absorption frequency range, and thin thickness. Compared to some other nickel nanomaterials or nickel/carbon composites, the porous Ni/C composite microspheres showed high-performance EM absorption, mainly attributed to the synergistic effects of magnetic loss and dielectric loss, and the porous structure.

ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (No. 51572157) and the Fundamental Research Funds of Shandong University (2015JC016, 2015JC036). J. Liu and W. Liu also acknowledge financial support from the Science and Technology Development Plan (2014GGX102004) and Natural Science Fund for Distinguished Young Scholars of Shandong (JQ201312).

REFERENCES 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 44

(1) Sun, G.; Dong, B.; Cao, M.; Wei, B.; Hu, C. Hierarchical Dendrite-Like Magnetic Materials of Fe3O4, γ-Fe2O3, and Fe with High Performance of Microwave Absorption. Chem. Mater. 2011, 23, 1587-1593. (2) Wang, F.; Wu, L.; Zhou, J.; Jiang, Z.; Shen, B. Chemoselectivity-Induced Multiple Interfaces in MWCNT/Fe3O4@ZnO Heterotrimers for Whole X-Band Microwave Absorption. Nanoscale 2014, 6, 12298-12302. (3) Wang, F.; Liu, J.; Kong, J.; Zhang, Z.; Wang, X.; Itoh, M.; Machida, K. Template Free

Synthesis

and

Electromagnetic

Wave

Absorption

Properties

of

Monodispersed Hollow Magnetite Nano-Spheres. J. Mater. Chem. 2011, 21, 4314-4320. (4) Wei, S.; Wang, Q.; Zhu, J.; Sun, L.; Lin, H.; Guo, Z. Multifunctional Composite Core-Shell Nanoparticles. Nanoscale 2011, 3, 4474-4502. (5) Wu, H.; Wu, G.; Wang, L. Peculiar Porous α-Fe2O3, γ-Fe2O3 and Fe3O4 Nanospheres: Facile Synthesis and Electromagnetic Properties. Powder Technol.

2015, 269, 443-451. (6) Wu, H.; Wang, L.; Wang, Y.; Guo, S.; Shen, Z. Enhanced Microwave Performance of Highly Ordered Mesoporous Carbon Coated by Ni2O3 Nanoparticles. J. Alloys Compd. 2012, 525, 82-86. (7) Wu, G.; Cheng, Y.; Ren, Y.; Wang, Y.; Wang, Z.; Wu, H. Synthesis and Characterization of γ-Fe2O3@C Nanorod-Carbon Sphere Composite and its Application as Microwave Absorbing Material. J. Alloys Compd. 2015, 652, 346-350. 24


Page 25 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(8) Wu, H.; Wu, G.; Ren, Y.; Yang, L.; Wang, L.; Li, X. Co2+/Co3+ Ratio Dependence of Electromagnetic Wave Absorption in Hierarchical NiCo2O4-CoNiO2 Hybrids. J. Mater. Chem. C 2015, 3, 7677-7690. (9) Kong, L.; Yin, X.; Yuan, X.; Zhang, Y.; Liu, X.; Cheng, L.; Zhang, L. Electromagnetic Wave Absorption Properties of Graphene Modified with Carbon Nanotube/Poly(Dimethyl Siloxane) Composites. Carbon 2014, 73, 185-193. (10) Han, M.; Yin, X.; Kong, L.; Li, M.; Duan, W.; Zhang, L.; Cheng, L. Graphene-Wrapped ZnO Hollow Spheres with Enhanced Electromagnetic Wave Absorption Properties. J. Mater. Chem. A 2014, 2, 16403-16409. (11) Kong, L.; Yin, X.; Zhang, Y.; Yuan, X.; Li, Q.; Ye, F.; Cheng, L.; Zhang, L. Electromagnetic Wave Absorption Properties of Reduced Graphene Oxide Modified by Maghemite Colloidal Nanoparticle Clusters. J. Phys. Chem. C 2013, 117, 19701-19711. (12) Snoek, J. L. Dispersion and Absorption in Magnetic Ferrites at Frequencies above One Mc/s. Physica 1948, 14, 207-217. (13) Toneguzzo, P.; Viau, G.; Acher, O.; Fiévet-Vincent, F.; Fiévet, F. Monodisperse Ferromagnetic Particles for Microwave Applications. Adv. Mater.1998, 10, 1032-1035. (14) Bregar, V. B. Advantages of Ferromagnetic Nanoparticle Composites in Microwave Absorbers. IEEE Trans. Magn. 2004, 40, 1679-1684. (15) He, C.; Qiu, S.; Wang, X.; Liu, J.; Luan, L.; Liu, W.; Itoh, M.; Machida, K. Facile Synthesis of Hollow Porous Cobalt Spheres and their Enhanced 25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 44

Electromagnetic Properties. J. Mater. Chem. 2012, 22, 22160-22166. (16) Gong, C.; Zhang, J.; Zhang, X.; Yu, L.; Zhang, P.; Wu, Z.; Zhang, Z. Strategy for Ultrafine Ni Fibers and Investigation of the Electromagnetic Characteristics. J. Phys. Chem. C 2010, 114, 10101-10107. (17) Zhao, B.; Shao, G.; Fan, B.; Sun, B.; Guan, K.; Zhang, R. Facile Synthesis and Novel Microwave Electromagnetic Properties of Flower-Like Ni Structures by a Solvothermal Method. J. Mater. Sci.: Mater. Electron. 2014, 25, 3614-3621. (18) Rousselle, D.; Berthault, A.; Acher, O.; Bouchaud, J. P.; Zérah, P. G. Effective Medium at Finite Frequency: Theory and Experiment. J. Appl. Phys. 1993, 74, 475-479. (19) Liu, J.; Itoh, M.; Terada, M.; Horikawa, T.; Machida, K. Enhanced Electromagnetic Wave Absorption Properties of Fe Nanowires in Gigaherz Range. Appl. Phys. Lett. 2007, 91, 093101. (20) Wang, C.; Han, X.; Xu, P.; Wang, J.; Du, Y.; Wang, X.; Qin, W.; Zhang, T. Controlled Synthesis of Hierarchical Nickel and Morphology-Dependent Electromagnetic Properties. J. Phys. Chem. C 2010, 114, 3196-3203. (21) Kong, J.; Liu, W.; Wang, F.; Wang, X.; Luan, L.; Liu, J.; Wang, Y.; Zhang, Z.; Itoh, M.; Machida, K. Fabrication of Monodispersed Nickel Flower-Like Architectures Via a Solvent-Thermal Process and Analysis of their Magnetic and Electromagnetic Properties. J. Solid State Chem. 2011, 184, 2994-3001. (22) Qiao, L.; Han, X.; Gao, B.; Wang, J.; Wen, F.; Li, F. Microwave Absorption Properties of the Hierarchically Branched Ni Nanowire Composites. J. Appl. Phys. 26


Page 27 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2009, 105, 053911. (23) Deng, Y.; Liu, X.; Shen, B.; Liu, L.; Hu, W. Preparation and Microwave Characterization of Submicrometer-Sized Hollow Nickel Spheres. J. Magn. Magn. Mater. 2006, 303, 181-184. (24) Liu, J. R.; Itoh, M.; Machida, K. Electromagnetic Wave Absorption Properties of α-Fe/Fe3B/Y2O3 Nanocomposites in Gigahertz Range. Appl. Phys. Lett. 2003, 83, 4017-4019. (25) Zhang, X. F.; Huang, H.; Dong, X. L. Core/Shell Metal/Heterogeneous Oxide Nanocapsules: The Empirical Formation Law and Tunable Electromagnetic Losses. J. Phys. Chem. C 2013, 117, 8563-8569. (26) Wang, G.; Peng, X.; Yu, L.; Wan, G.; Lin, S.; Qin, Y. Enhanced Microwave Absorption of ZnO Coated with Ni Nanoparticles Produced by Atomic Layer Deposition. J. Mater. Chem. A 2015, 3, 2734-2740. (27) Xiang, J.; Li, J.; Zhang, X.; Ye, Q.; Xu, J.; Shen, X. Magnetic Carbon Nanofibers Containing Uniformly Dispersed Fe/Co/Ni Nanoparticles as Stable and High-Performance Electromagnetic Wave Absorbers. J. Mater. Chem. A 2014, 2, 16905-16914. (28) Li, N.; Cao, M.; Hu, C. A Simple Approach to Spherical Nickel-Carbon Monoliths as Light-Weight Microwave Absorbers. J. Mater. Chem. 2012, 22, 18426-18432. (29) Chen, T.; Deng, F.; Zhu, J.; Chen, C.; Sun, G.; Ma, S.; Yang, X. Hexagonal and Cubic Ni Nanocrystals Grown On Graphene: Phase-Controlled Synthesis, 27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 44

Characterization and their Enhanced Microwave Absorption Properties. J. Mater. Chem. 2012, 22, 15190-15197. (30) Pan, G.; Zhu, J.; Ma, S.; Sun, G.; Yang, X. Enhancing the Electromagnetic Performance of Co through the Phase-Controlled Synthesis of Hexagonal and Cubic Co Nanocrystals Grown on Graphene. ACS Appl. Mater. Interfaces 2013, 5, 12716-12724. (31) Lü, Y.; Wang, Y.; Li, H.; Lin, Y.; Jiang, Z.; Xie, Z.; Kuang, Q.; Zheng, L. MOF-Derived Porous Co/C Nanocomposites with Excellent Electromagnetic Wave Absorption Properties. ACS Appl. Mater. Interfaces 2015, 7, 13604-13611. (32) Che, R. C.; Peng, L. M.; Duan, X. F.; Chen, Q.; Liang, X. L. Microwave Absorption Enhancement and Complex Permittivity and Permeability of Fe Encapsulated within Carbon Nanotubes. Adv. Mater. 2004, 16, 401-405. (33) Wang, H.; Guo, H.; Dai, Y.; Geng, D.; Han, Z.; Li, D.; Yang, T.; Ma, S.; Liu, W.; Zhang, Z. Optimal Electromagnetic-Wave Absorption by Enhanced Dipole Polarization in Ni/C Nanocapsules. Appl. Phys. Lett. 2012, 101, 083116. (34) Meng, H.; Zhao, X.; Yu, L.; Jia, Y.; Liu, H.; Lv, X.; Gong, C.; Zhou, J. Island-Like

Nickel/Carbon

Nanocomposites

as

Potential

Microwave

Absorbers-Synthesis Via in Situ Solid Phase Route and Investigation of Electromagnetic Properties. J. Alloys Compd. 2015, 644, 236-241. (35) Liu, J. R.; Itoh, M.; Horikawa, T.; Machida, K.; Sugimoto, S.; Maeda, T. Gigahertz

Range

Electromagnetic

Wave

Absorbers

Made

of

Amorphous-Carbon-Based Magnetic Nanocomposites. J. Appl. Phys. 2005, 98, 28


Page 29 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


054305. (36) Zhao, Y. L.; Wang, J. M.; Chen, H.; Pan, T.; Zhang, J. Q.; Cao, C. N. Al-Substituted α-Nickel Hydroxide Prepared by Homogeneous Precipitation Method with Urea. Int. J. Hydrogen Energy 2004, 29, 889-896. (37) Wang, X.; Qiu, S.; Liu, J.; He, C.; Lu, G.; Liu, W. Synthesis of Mesoporous SnO2 Spheres and Application in Gas Sensors. Eur. J. Inorg. Chem. 2014, 2014, 863-869. (38) Zhang, R.; Sun, Y.; Peng, S. In Situ FTIR Studies of Methanol Adsorption and Dehydrogenation Over Cu/SiO2 Catalyst. Fuel 2002, 81, 1619-1624. (39) Manzoli, M.; Chiorino, A.; Boccuzzi, F. Decomposition and Combined Reforming of Methanol to Hydrogen: A FTIR and QMS Study On Cu and Au Catalysts Supported On ZnO and TiO2. Appl. Catal., B 2004, 57, 201-209. (40) Lu, M. M.; Cao, M. S.; Chen, Y. H.; Cao, W. Q.; Liu, J.; Shi, H. L.; Zhang, D. Q.; Wang, W. Z.; Yuan, J. Multiscale Assembly of Grape-Like Ferroferric Oxide and Carbon Nanotubes: A Smart Absorber Prototype Varying Temperature to Tune Intensities. ACS Appl. Mater. Interfaces 2015, 7, 19408-19415. (41) Chen, Y. J.; Xiao, G.; Wang, T. S.; Ouyang, Q. Y.; Qi, L. H.; Ma, Y.; Gao, P.; Zhu, C. L.; Cao, M. S.; Jin, H. B. Porous Fe3O4/Carbon Core/Shell Nanorods: Synthesis and Electromagnetic Properties. J. Phys. Chem. C 2011, 115, 13603-13608. (42) Urbonaite, S.; Hälldahl, L.; Svensson, G. Raman Spectroscopy Studies of Carbide Derived Carbons. Carbon 2008, 46, 1942-1947. 29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 44

(43) Tshavhungwe, A. M.; Layh, M.; Coville, N. J. Cobalt Ion Incorporation Into Periodic Mesoporous Organosilica Materials Synthesized by Co-condensation of 1,2-Bistrimethoxysilylethane with 3-Glycidoxypropyltriethoxysilane. J. Sol-Gel Sci. Technol. 2004, 29, 167-177. (44) Hwang, J.-H.; Dravid, V. P.; Teng, M. H.; Host, J. J.; Elliott, B. R.; Johnson, D. L.; Mason, T. O. Magnetic Properties of Graphitically Encapsulated Nickel Nanocrystals. J. Mater. Res. 1997, 12, 1076-1082. (45) Ning, M.; Zhu, H.; Jia, Y.; Niu, H.; Wu, M.; Chen, Q. Synthesis of Hollow Microspheres of Nickel Using Spheres of Metallic Zinc as Templates Under Mild Conditions. J. Mater. Sci. 2005, 40, 4411-4413. (46) Liu, X. G.; Jiang, J. J.; Geng, D. Y.; Li, B. Q.; Han, Z.; Liu, W.; Zhang Z. D. Dual Nonlinear Dielectric Resonance and Strong Natural Resonance in Ni/ZnO Nanocapsules. Appl. Phys. Lett. 2009, 94, 053119. (47) Zhang, X. F.; Dong, X. L.; Huang, H.; Liu, Y. Y.; Wang, W. N.; Zhu, X. G.; Lv, B.; Lei, J. P.; Lee C. G. Microwave Absorption Properties of the Carbon-Coated Nickel Nanocapsules. Appl. Phys. Lett. 2006, 89, 053115. (48) Watts, P. C. P.; Hsu, W. K.; Barnes, A.; Chambers, B. High Permittivity from Defective Multiwalled Carbon Nanotubes in the X-Band. Adv. Mater. 2003, 15, 600-603. (49) Dong, X. L.; Zhang, X. F.; Huang, H.; Zuo, F. Enhanced Microwave Absorption in Ni/polyaniline Nanocomposites by Dual Dielectric Relaxations. Appl. Phys. Lett. 2008, 92, 013127. 30


Page 31 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(50) Frenkel, J.; Dorfman, J. Spontaneous and Induced Magnetisation in Ferromagnetic Bodies. Nature 1930, 126, 274-275. (51) Chen, D.; Quan, H.; Huang, Z.; Luo, S.; Luo, X.; Deng, F.; Jiang, H.; Zeng, G. Electromagnetic and Microwave Absorbing Properties of RGO@Hematite Core-Shell nanostructure/PVDF Composites. Compos. Sci. Technol. 2014, 102, 126-131. (52) Gupta, T. K.; Singh, B. P.; Mathur, R. B.; Dhakate, S. R. Multi-Walled Carbon Nanotube-Graphene-Polyaniline

Multiphase

Nanocomposite

with

Superior

Electromagnetic Shielding Effectiveness. Nanoscale 2014, 6, 842-851. (53) Lee, C. C.; Chen, D. H. Ag Nanoshell-Induced Dual-Frequency Electromagnetic Wave Absorption of Ni Nanoparticles. Appl. Phys. Lett. 2007, 90, 193102. (54) Lu, B.; Dong, X. L.; Huang, H.; Zhang, X. F.; Zhu, X. G.; Lei, J. P.; Sun, J. P. Microwave Absorption Properties of the Core/Shell-Type Iron and Nickel Nanoparticles. J. Magn. Magn. Mater. 2008, 320, 1106-1111. (55) Kittel, C. On the Theory of Ferromagnetic Resonance Absorption. Phys. Rev.,

1948, 73, 155-161. (56) Smith, D. R.; Padilla, W. J.; Vier, D. C.; Nemat-Nasser, S. C.; Schultz S. Composite Medium with Simultaneously Negative Permeability and Permittivity. Phys. Rev. Lett. 2000, 84, 4184-4187. (57) Chui, S. T.; Hu L. Theoretical Investigation on the Possibility of Preparing Left-Handed Materials in Metallic Magnetic Granular Composites. Phys. Rev. B 2002, 65, 144407. 31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 44

(58) Kasagi, T.; Tsutaoka, T.; Hatakeyama, K. Negative Permeability Spectra in Permalloy Granular Composite Materials. Appl. Phys. Lett. 2006, 88, 172502. (59) Qiao, L.; Li, X.; Wang, T.; Tang, L.; Li, F. Matching Conditions of Single Layer Absorber with Sendust Flaky-Filler Composite. J. Magn. Magn. Mater. 2015, 393, 347-351. (60) Gao, B.; Qiao, L.; Wang, J.; Liu, Q.; Li, F.; Feng, J.; Xue, D. Microwave Absorption Properties of the Ni Nanowires Composite. J. Phys. D: Appl. Phys.

2008, 41, 235005. (61) Wang, G.; Wang, L.; Gan, Y.; Lu, W. Fabrication and Microwave Properties of Hollow Nickel Spheres Prepared by Electroless Plating and Template Corrosion Method. Appl. Surf. Sci. 2013, 276, 744-749. (62) Cao, Y.; Su, Q.; Che, R.; Du, G.; Xu, B. One-Step Chemical Vapor Synthesis of Ni/graphene Nanocomposites with Excellent Electromagnetic and Electrocatalytic Properties. Synth. Met. 2012, 162, 968-973. (63) Shi, X.; Cao, M.; Yuan, J.; Fang, X. Dual Nonlinear Dielectric Resonance and Nesting Microwave Absorption Peaks of Hollow Cobalt Nanochains Composites with Negative Permeability. Appl. Phys. Lett. 2009, 95, 163108. (64) Zhou, J.; He, J.; Li, G.; Wang, T.; Sun, D.; Ding, X.; Zhao, J.; Wu, S. Direct Incorporation

of

Magnetic

Constituents

within

Ordered

Mesoporous

Carbon-Silica Nanocomposites for Highly Efficient Electromagnetic Wave Absorbers. J. Phys. Chem. C 2010, 114, 7611-7617. (65) Wu, H.; Wang, L.; Wang, Y.; Guo, S.; Shen, Z. Enhanced Microwave Absorbing 32


Page 33 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Properties

of

Carbonyl

Iron-Doped

Ag/Ordered

Mesoporous

Carbon

Nanocomposites. Mater. Sci. Eng., B 2012, 177, 476-482. (66) Zhang, X. F.; Guan, P. F.; Dong, X. L. Transform between the Permeability and Permittivity in the Close-Packed Ni Nanoparticles. Appl. Phys. Lett. 2010, 97, 033107. (67) Zhang, J.; Yan, C.; Liu, S.; Pan, H.; Gong C.; Yu, L.; Zhang, Z. Preparation of Fe2Ni2N and Investigation of its Magnetic and Electromagnetic Properties. Appl. Phys. Lett. 2012, 100, 233104.

33



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 44

TOC

Porous nickel/carbon composite microspheres synthesized via a facile solvothermal route followed by a novel carbon reduction process exhibit superior electromagnetic wave absorption performances.

34


Page 35 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


XRD patterns of the as-prepared precursor (a), annealed sample (b), and porous Ni/C composite microspheres (c). 80x95mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) Infrared spectra of the as-prepared precursor, annealed sample, and porous Ni/C microspheres, and (b) Raman spectrum of porous Ni/C microspheres. 80x128mm (300 x 300 DPI)


Page 36 of 44

Page 37 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


FE-SEM images of the as-prepared precursor (a, b), annealed sample (c, d), and porous Ni/C microspheres (e, f). 85x89mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

HR-TEM images of porous Ni/C microspheres with various magnifications (a-d). 85x63mm (300 x 300 DPI)


Page 38 of 44

Page 39 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a) TGA-DSC curves and (b) isotherms of N2 adsorption (solid squares) and desorption (solid triangles) for porous Ni/C microspheres. The pore size distribution is shown in inset. 80x113mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Magnetic hysteresis loop of porous Ni/C microspheres. 80x59mm (300 x 300 DPI)


Page 40 of 44

Page 41 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


εr (a) and µr (b) spectra of the epoxy resin composites containing 60 wt% and 75 wt% porous Ni/C microspheres in the 2-18 GHz range. 80x121mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Typical Cole-Cole semicircles of the epoxy resin composites containing (a) 60 wt% and (b) 75 wt% porous Ni/C microspheres. 80x124mm (300 x 300 DPI)


Page 42 of 44

Page 43 of 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


RL curves as a function of frequency for the epoxy resin composites containing (a) 60 wt% and (b) 75 wt% porous Ni/C microspheres with various thicknesses in the frequency range of 2-18 GHz. (thickness: mm). 82x125mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Frequency dependences of dielectric tangent loss and magnetic tangent loss for epoxy resin composites containing (a) 60 wt% and (b) 75 wt% porous Ni/C microspheres in the 2-18 GHz range. 80x123mm (300 x 300 DPI)


Page 44 of 44

Carbon Composite Microspheres

Recommend Documents