Enhanced Electromagnetic Microwave Absorption Performance of

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Enhanced electromagnetic microwave absorption performance of lightweight bowl-like carbon nanoparticles Jingyi Fu, Wang Yang, Liqiang Hou, Zhuo Chen, Tian Qiu, Haitao Yang, and Yongfeng Li Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b02860 • Publication Date (Web): 19 Sep 2017 Downloaded from http://pubs.acs.org on September 24, 2017

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Industrial & Engineering Chemistry Research

Enhanced electromagnetic microwave absorption performance of lightweight bowl-like carbon nanoparticles

Jingyi Fu1, Wang Yang1, Liqiang Hou1, Zhuo Chen1, Tian Qiu1, Haitao Yang2, and Yongfeng Li1, *

1

State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Changping, 102249, Beijing, China

2

Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing, 100190, China

* Corresponding Author: Prof. Yongfeng Li College of Chemical Engineering, China University of Petroleum, 18# Fuxue Road, Changping, Beijing 102249, China E-mail: [email protected]; Tel: +86-10-8973-9028

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ACS Paragon Plus Environment


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Abstract: Rational structure design of the microwave absorption material (MAM) is of fundamental significance in terms of enhancing the electromagnetic microwave absorption performance and deeply understanding of the specific correlation between the material structure and its electromagnetic microwave absorption (EMA) performance. Here, bowl-like carbon nanoparticles (BLCNs) as a novel MAM have been successfully fabricated via calcination of bowl-like polydopamine. Interestingly, BLCNs have exhibited dramatically enhanced EMA performance with minimum reflection loss of -45.3 dB and effective bandwidth of below -10 dB in the wide range of 4.2 GHz, implying the unique critical role of the microstructure in adjusting the EMA performance. Our work not only paves an attractive way for design of advanced and lightweight MAM, but also provides valuable insights into the relationships between the material structure and its EMA performance.

Keywords: Bowl-like, carbon-based, electromagnetic wave, absorption.

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1. INTRODUCTION With the popularized application of electronic

instruments, expanded

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electromagnetic (EM) problems, such as EM inference, leakage, radiation and

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pollution, have promoted the demand of robust microwave absorption materials

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(MAMs).1-3 As is known, in addition to excellent electromagnetic properties - strong

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absorption with wide frequencies towards microwave, desirable MAMs should

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simultaneously have the features of light weight, durability, stability, and etc.4-6

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Carefully choosing the elements or controlling the element contents of the

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absorber is an effective and practical way to eliminate the limitation of heavy weight

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for MAMs. Carbon-based composites have been gradually coming into highlight due

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to the advantages of low density, oxidation resistance, thermal stability, as well as

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potential applications.7-10 Great attentions have been drawn and several efforts have

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been taken on the relationship between the morphology and EMA performance.11-14

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Previous work has demonstrated that hollow carbon nanospheres display dramatically

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enhanced EMA performance (RLmin = -50.8 dB) in comparison with the counterpart

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carbon nanospheres because of the intensified interface polarization as well as the

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multiplied reflections induced both inner and outer the hollow structure.15 Further

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researches have already been carried out that hollow nanospheres with designable

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mesoporous shell and interior voids exhibit RLmin reaching to -84 dB, due to the

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enhanced carbon-air interface polarization.16 What can be learnt from them is that the

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EMA performance can be dramatically enhanced by rationally designing the

22

microstructure and carefully tuning the morphology of MAMs. However, up to now, 3



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the understanding of the relationships between geometric morphology and EMA

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performance is still under its early stage.

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Aiming at revealing the influence of different microstructures on the

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electromagnetic properties, we have conducted sequence of studies to compare the

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EMA performances between bowl-like nanoparticles and spherical counterparts.

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Actually, the unique bowl-like structure not only covers all the advantages of hollow

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structure, including plenteous interfaces, augmented reflections and so on, but also

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multiplies the contacting interfaces neighboring originated from the diverse packing

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states,17-19 substantially strengthening the interface polarizations which is of great

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importance to the EMA performance. Therefore, it is urgently desired to investigate

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the feasibility of BCLNs for the application of MAMs.

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Herein, a kind of novel bowl-like carbon nanoparticles (BLCN) with designed

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pores has been fabricated by calcination of polydopamine which is obtained via

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emulsion-induced interface anisotropic self-assembly strategy. The morphologies of

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BLCNs can be converted from symmetry to asymmetry by simply adjusting the

16

amount of the reagent 1,3,5-trimethyl benzene. As expected, both lightweight feature

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and the enhanced strong microwave absorption ability are obtained from BLCNs. The

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minimal RL is -45.3 dB when the thickness is only 1.5 mm, while the maximum

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effective EMA bandwidth (RL < -10 dB) can cover 4.2 GHz. Our results indicate that

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BLCNs have great potential in application for MAMs, and simultaneously confirm

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that the morphologies of MAMs exhibit a critical role on EMA performance.

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2. EXPERIMENTAL 4


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2.1 Chemical reagents

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All materials in the research are of analytical grade and are used directly without

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any further purification. 1,3,5-trimethyl benzene (TMB), dopamine hydrochloride,

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block copolymer F127, and ammonia are purchases from Alfa Aesar.

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2.2 Preparation for BLCN

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BLCN were fabricated by the calcination of the bowl-like polydopamine which

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was

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polymerization.20 Typically, different certain volumes (1.6 ml, 1.8 ml, 2.0 ml, 2.2ml)

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of TMB were added into the homogenous mixture of 1 g block copolymer F127 and

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1.5 g dopamine hydrochloride. The solution system was the mixture of 50ml

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deionized water and 50 ml ethanol. Then, 3.75 ml of ammonia was dropped into the

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mixed solution with stirring at the room temperature. As-prepared polydopamine

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particles were collected via centrifugation after reacting for 2 h and then washed by

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the deionized water and ethanol for several times. To stabilize the nanostructure, the

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obtained polydopamine particles were redispersed in the water/ethanol solution and

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set in a sealed Teflon-lined autoclave at 100 oC for 24 h. The final carbon

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nanoparticles were collected after a sequence of calcination process under N2

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atmosphere: pre-heating at 300 oC for 3 h and further raising to 800 oC for another 2 h.

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To be brief, final products are called as BLCN1, BLCN2, BLCN3 and BLCN4

20

corresponding to TMB’s volumes (1.6 ml, 1.8 ml, 2.0 ml, 2.2 ml).

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2.3 Characterization

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produced

by

emulsion-induced

interface

anisotropic

self-assembly

The morphologies and structures of the yielded carbon nanoparticles were 5



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characterized by transmission electron microscopy (TEM, FEI F20) and scanning

2

electron microscopy (SEM, Hitachi, SU8010). Raman spectroscopy was measured on

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a Renishaw InVia Reflex with laser wavelength 532nm. X-ray photoelectron

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spectroscopy (XPS) measurements were performed with a Thermo Fisher KAlpha

5

spectrometer. The surface specific area and pore size distribution were characterized

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by nitrogen adsorption at 77 K using Micromeritics ASAP 2020 instrument. The

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Fourier transform infrared (FT-IR) spectra of the samples were recorded on a Nicolet

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NEXUS 470 FT-IR spectrometer using a pressed disc of powder combined with KBr

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(1.0 mg powder per 200 mg KBr) over a range of 800-4000 cm-1.

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2.4 EM absorption measurements

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The relative complex permittivity and permeability were measured by a vector

12

network analyzer (Agilent N5224A, USA) in the frequency range 2-18 GHz. The

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absorbers were made by mixing the as-prepared BLCNs with wax at the mass loading

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ratio of 2:8 and pressed into a coaxial cylinder with an outer diameter of 7.0 mm and

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inner diameter of 3.04 mm.

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3.

RESULTS AND DISCUSSIONS

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As illustration in Fig. 1, the BLCNs are successfully synthesized by a facile

18

self-assembly of dopamine on the surface of TMB droplet. With continuous reaction,

19

the pores are induced at the spherical surface. Additionally, different volumes of TMB

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induce different interactions on the surfactant F127 between the dopamine and TMB,

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which gives rise to different morphologies for carbon nanoparticles under the same

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reaction time. 6


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Figs. 2a-d and Fig. S1 show the TEM and SEM images of BLCN1-4, respectively.

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The morphologies of BLCN1-3 (Figs. 2a-c) range from the sphere, to the mixture of

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sphere and bowl-like sphere, and finally to the bowl-like sphere with identical

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diameter (~230 nm), confirming the structural adjustable function of TMB in the

5

polymerization reaction. Nevertheless, BLCN4 (Fig. 2d) returns to spherical structural

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nanoparticle with shrinking diameter for ~ 140 nm when the volume of TMB further

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increases. There is no doubt that the surplus TMB accelerates the polymerization

8

reaction rate, leading to the spherical polydopamine at the same reaction time.

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Meanwhile, the average amount of dopamine gathering around the TMB/water

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interfaces can be inevitably reduced under the same concentration of dopamine in the

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reaction system, ending up with the smaller polydopamine nanoparticle. As shown in

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Figs. 2e-f, there are pores, existing as uneven contours, on spherical surface of

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BLCN3. The tested surface areas for BLCN3 is 174 m2/g (Fig. 3a), and the pore size

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distribution calculated using the Brunauere Emmette Teller (BET) model (the inset of

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Fig. 3a) further confirms the existence of pores and indicates that the size of the

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majority of the pores is 3-5 nm. The nitrogen sorption isotherms images of BLCN1,

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BLCN2 and BLCN4 are shown in the supporting information (Fig. S2).

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Fig. 3b shows the Raman spectrum for BLCNs, in which the D band and G band

19

are observed at 1341 cm-1 and 1566 cm-1, respectively. Generally speaking, D band is

20

associated with the defects or lattice distortion, while G band is related to monocrystal

21

structure and attributed to the in-plane bond stretching of sp2-C pairs. The intensity

22

ratio of D band and G band (ID/IG) directly indicates the average level of defects and 7



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degree of graphitization crystallinity.21-22 The high ID/IG in BLCNs suggests that

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BLCNs have low crystallinity, possibly due to the pores and voids generated in the

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synthesis process. And the identical ratios (ID/IG~1) for BLCNs mean that the BLCNs

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have the same graphitization degrees and the same levels of defects. In addition, the

5

image obtained from selected area electron diffraction (SAED) pattern (Fig. S3) is

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well consistent with the results from Raman spectra, and a weak light ring mean the

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low level of crystalline, which is strongly favor of electromagnetic properties.23

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X-ray photoelectron spectroscopy (XPS) is employed for element analysis. Fig.

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S4 shows the XPS survey spectrum, and the relative atomic ratios of each element are

10

summarized in Table S1. The spectrum demonstrates the existence of C, N and O

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element, which becomes the prerequisite for the feature of lightweight. And according

12

to Table S1, there is no great difference among the constitution for each element. The

13

high-resolution N1s XPS spectrum of BLCN3 (Fig. S5), demonstrates that the binding

14

energies around 398.3 eV, 400.5 eV, 401.3 eV and 403.3 eV are assigned to pyridinic

15

N, pyrroilic N, graphitic N and pyridinic N-oxide, respectively.24 The high resolution

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C1s XPS spectrum of BLCN3 (Fig. 3c), demonstrates that the binding energies

17

around 284.6 eV, 285.0 eV, 286.2 eV and 289.1 eV are attributed to C-O, C-C, C=O,

18

C-N, respectively.25-27 The existence of sp3 C bonded with H, C-O, C-N(-C)-C or

19

C-NH-C, -OH, C=O from the FT-IR is also observed in Fig. 3d.28-31 The abundant

20

heteroatoms functional groups in the BLCNs are the part of the reason for the low

21

graphitization degree, which also leads to more defects.32

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Typically, the performance of EM absorber significantly depends on their 8


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complex permittivity ( εr =εᇱ -jεᇱᇱ ), permeability (μr =μᇱ -jμᇱᇱ ) and impedance

2

matching. In our work, μᇱ ≈1, and μᇱᇱ ≈0, mean that BLCNs have no magnetic loss.33

3

Both of the real part εᇱ and the imaginary part εᇱᇱ (Figs. 4a-b) decrease with the

4

frequency rising, attributed to the relaxation effect of the composites.9 εᇱ from

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BLCN1 is the lowest, while BLCN4’s εᇱ is at the top. Interestingly, εᇱ for BLCN3

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decreases from 16.7 to 11.1 at the frequency from 2 GHz to 12 GHz and then slightly

7

rises to 8.7 within the following measuring frequency, which can be seen in some

8

other previous reviews.34 BLCN1’s εᇱᇱ is still at the bottom, and BLCN3’s εᇱᇱ is on

9

the top. As is known that εᇱ represents the storage of electric energy, while εᇱᇱ

10

symbolizes the loss of electric energy, respectively.8 Generally, when perfectly

11

balancing each other, the higher εᇱᇱ implies higher chances for microwave to

12

transform from electromagnetic energy into heat energy.35 Therefore, BLCN3 is

13

dominant for dissipating electric energy on condition of the good storage capability of

14

electric energy, boding well for its improved EMA performance. There is no doubt

15

that εr of carbon materials relies strongly on these two factors: the degree of

16

graphitization and microstructure.16, 36 Therefore, its special geometrical morphology

17

should take responsibility for the enhanced complex permittivity, since the degrees of

18

graphitization make no difference among the BLCNs which have been proven in the

19

aforementioned Raman tests. Thus, it is easy to come up with an assumption that the

20

bowl-like microstructures may have some positive effects in capability for storing and

21

dissipating the electric energy, further facilitating the consumption the microwave

22

energy and do well for EMA performance. 9



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1 2

The EM absorption performance can be represented by RL based on the transmit line theory.37 The calculation is based on the following formula: RL=20log|

Zin -Z0 | Zin +Z0

Zin =(µr /εr )1/2 tanh൛j(2πfd/c)(µr εr )1/2 ൟ 3

Where f, d, c are the frequency, the thickness of the testing absorber, the speed of

4

light in vacuum, respectively, and Zin represents the input impedance of a

5

metal-banked EM wave absorbing layer, µr and εr are the relative complex

6

permeability and permittivity, respectively.38

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The calculated RL for each kind of BLCNs with various thicknesses is shown in

8

Figs. 5a-d. All BLCNs can reach effective absorption (-10 dB, 90% absorption). The

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RLmin for BLCN1 as thick as 5.0 mm is -21.48 dB with the effective band width of 2.0

10

GHz, while its average RL is only -10 dB. BLCN4 has relative greater absorption

11

performance, its average RL is -20 dB covering all the testing thicknesses from 1.3

12

mm to 5.0 mm. Although both of them have the same spherical morphology, BLCN4

13

takes the advantage of the shrinking diameters which give rise to the relatively larger

14

surface areas (553 m2/g) than that of the surface areas for BLCN1 (463 m2/g).

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Therefore, BLCN4 can provide access for microwave to multiple reflections, resulting

16

to the advanced EM absorption performance.39 BLCN2 also has relative enhanced

17

results in comparison with BLCN1 and BLCN4. Obviously, as expected, BLCN3

18

shows the optimum enhanced EM absorption with the RLmin for -45.35 dB at 14.5

19

GHz with only 1.5 mm thickness, and the corresponding effective band width can

20

reach as wide as 4.2 GHz. BLCN3 has championed the others under the same 10


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thickness of 1.5 mm (Fig. 5e). For further comparing the EMA performances of

2

BLCNs, RLs of some typical carbon materials are listed in Table 1. It is obvious that

3

microwave absorption performance of BLCN3 is on the top level.

4

To deeply comprehend the microwave absorption mechanism, the dielectric loss

5

tangent (tan δe =ε'' /ε' ) is occupied to indicate the dielectric loss capability of the

6

microwave absorbers via giving the clue about the existence of the dipoles and

7

interfacial polarization. BLCN1 owns the lowest value among the other samples (Fig.

8

5f) which means that there is least polarization because of the lowest ε''. However,

9

compared to BLCN1, BLCN4 has higher dielectric loss tangent due to its shrinking

10

size, which is also seen in pre-works.39 Once the bowl-like structural nanoparticle are

11

formed, the dielectric loss tangent can increase a lot, suggesting the electromagnetic

12

energy is inclined to be consumed considerably. Usually, the dielectric loss capability

13

mainly generates from polarization loss and conductive loss40. While the polarization

14

mainly originates from electronic polarization, dipole polarization, and interfacial

15

polarization. The interfacial polarization appears at the phase interfaces41. Definitely,

16

the interfaces between the paraffin and BLCN, between the air and BLCN, etc. do

17

have the phenomenon of interface polarization in this work. Besides, the bowl-like

18

structural nanoparticles facilitate to generate more cavities and channels due to its

19

complex and various states of stacking and gathering. According to the previous

20

research, cavities and channels are going to cause defects, which further intensify the

21

interfacial polarization14, 42-44.

22

BLCN2 with higher dielectric loss tangent has lower ability of EMA performance 11



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in comparison with BLCN3, which is possibly due to the proper impedance matching

2

where complex permittivity and complex permeability are perfectly complementary

3

each other in the microwave absorbers.45 It is necessary to point out that too high

4

permittivity might do harmful to the impedance matching and hinder the absorption,46

5

just in coincidence with this situation. On the other hand, the whole bowl-like

6

morphology of BLCN3 inevitably increases the volumetric packing density, so that

7

realize the maximum of the contacts each other.19 Previous works have already proved

8

that the attenuation intensity is highly related to the contact area.47 Thus the bowl-like

9

structural BLCN3 may have the powerful attenuation ability towards microwave,

10

further improving the EMA performance. Therefore, the excellent microwave

11

absorption properties can be explained by the following reasons, as schematically

12

shown in Fig. 6. Firstly, the incident microwave can be scattered and reflected through

13

the multiple interfaces with the assistance of proper impedance matching, which

14

provides the opportunities for microwave to be taken in and further transferred to heat.

15

Secondly, plenteous defects originated from the heteroatoms functional groups and

16

pores generated in the spherical surfaces, and voids produced in the synthesis process,

17

contribute a lot to strengthening the interfacial polarization, which is in favor of

18

consuming the entered microwave. Thirdly, the unique bowl-like structure induces

19

more reflections, and then further attenuates the microwave as much as possible.

20

4. Conclusion

21

In summary, BLCNs are successfully prepared via soft-template self-assembly

22

method, and different morphologies ranging from spherical structure to bowl-like 12


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structure are synthesized by carefully controlling the slight amount of TMB.

2

Remarkably, BLCN3, which has bowl-like structure with designed pores on the

3

spherical surface, exhibits the high level EMA performance among the spherical

4

counterparts and the other typical carbon-based MAMs, owing to its perfect

5

impedance matching and intensified interface polarizations. Its RLmin can reach to

6

-45.3 dB with the thickness of only 1.5 mm, and the effective band width can cover

7

4.2 GHz. Substantially, not only does our work verify the beneficial function of the

8

unique bowl-like structure towards the EMA performance, but also is of guiding

9

significance and gives the insight for the method of design and fabrication the practice

10

nanoparticles as absorbers in the future.

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Acknowledgement

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This work was financially supported by the National Natural Science Foundation of

13

China (Nos. 21576289), Science Foundation of China University of Petroleum,

14

Beijing (No. C201603), Science Foundation Research Funds Provided to New

15

Recruitments of China University of Petroleum, Beijing (2462014QZDX01) and

16

Thousand Talents Program.

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21



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Page 22 of 36

1

Table 1. Comparisons of EM absorption performance for typical carbon materials in

2

previous reports and our work. d

RLmin

Effective Ref.

Sample (mm)

(dB)

bandwidth(GHz)

2.3

-31.0

~3

46

3

-25.9

4.2

30

CuS nanoflasks/G

2.5

-54.5

4.5

48

rGO & BN

1.6

-40.5

5

9

Graphene & CNT

3.0

-44.6

3.3

49

Carbon fibers/Fe/epoxy resin

3.5

-48.6

3.2

50

2.5

-33.85

3.2

51

--

-44.7

4.7

2

2

-28.5

6.5

39

Co/C nanocomposites

4.5

-35.3

5.8

52

Hollow carbon sphere

1.9

-50.8

4.8

15

Hollow Co@Fe spheres

1.5

-47.3

4.8

53

Yolk-shell C@C

1.85

-34.8

5.4

14

BLCN3

1.5

-45.3

4.2

Porous carbon fibers Fe3O4/polypyrrole/CNT

Flaky graphite/cobalt zinc ferrite CNT film-Fe3O4-0.04 M-1L LSG CoNi microflowers

This work 3 22


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1

Figure captions

2

Figure 1. Schematic illustration for the synthesis process of BLCNs.

3

Figure 2. TEM images of (a) BLCN1. (b) BLCN2. (c) BLCN3. (d) BLCN4. (e) two

4

nanoparticles of BLCN3 contacting each other, (f) a magnified TEM image

5

for an individual BLCN3.

6

Figure 3. (a) Nitrogen sorption isotherms and pore size distribution (inset) of BLCN3.

7

(b) Raman spectra of BLCNs. (c) High resolution XPS spectra of C1s in

8

BLCN3 (d) FT-IR spectra of BLCNs.

9

Figure 4. Real part and (b) imaginary part of complex permittivity of BLCNs.

10

Figure 5. Reflection loss of (a) BLCN1. (b) BLCN2. (c) BLCN3 and (d) BLCN4. (e)

11

Reflection loss for BLCN3 with thickness of 1.5 mm. (f) Dielectric loss

12

tangent of BLCNs.

13

Figure 6. The mechanism of the EM microwave absorption in BLCNs: (a)

14

consumption via multiplied reflections among BLCNs. (b) consumption in

15

the pores or voids.

16

23



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1

Figure 1

2 3

24


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1

Figure 2

2 3

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

1

Figure 3

2 3

26


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1

Figure 4

2 3

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

1

Figure 5

2 3

28


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1

Figure 6

2 3

29



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1

A graphic abstract

2 3

30


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Figure 1. Schematic illustration for the synthesis process of BLCNs. 234x61mm (150 x 150 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

Figure 2. TEM images of (a) BLCN1. (b) BLCN2. (c) BLCN3. (d) BLCN4. (e) two nanoparticles of BLCN3 contacting each other, (f) a magnified TEM image for an individual BLCN3. 304x202mm (150 x 150 DPI)


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Figure 3. (a) Nitrogen sorption isotherms and pore size distribution (inset) of BLCN3. (b) Raman spectra of BLCNs. (c) High resolution XPS spectra of C1s in BLCN3 (d) FT-IR spectra of BLCNs. 266x197mm (150 x 150 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

Figure 4. (a) Real part and (b) imaginary part of complex permittivity of BLCNs. 237x87mm (150 x 150 DPI)


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Figure 5. Reflection loss of (a) BLCN1, (b) BLCN2, (c) BLCN3 and (d) BLCN4. (e) Reflection loss for BLCN3 with thickness of 1.5 mm. (f) Dielectric loss tangent of BLCNs. 144x159mm (150 x 150 DPI)



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Figure 6. The mechanism of the EM microwave absorption in BLCNs: (a) consumption via multiplied reflections among BLCNs. (b) consumption in the pores or voids. 237x101mm (150 x 150 DPI)


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Enhanced Electromagnetic Microwave Absorption Performance of

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