Atomic Layer Tailoring Titanium Carbide MXene To Tune Transport

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Atomic Layer Tailoring Titanium Carbide MXene to Tune Transport and Polarization for Utilization of Electromagnetic Energy beyond Solar and Chemical Energy Peng He, Maosheng Cao, Jin-cheng Shu, Yong-Zhu Cai, Xixi Wang, Quanliang Zhao, and Jie Yuan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b00593 • Publication Date (Web): 14 Mar 2019 Downloaded from http://pubs.acs.org on March 17, 2019

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ACS Applied Materials & Interfaces

Atomic Layer Tailoring Titanium Carbide MXene to Tune Transport and Polarization for Utilization of Electromagnetic Energy beyond Solar and Chemical Energy Peng He,† Mao-Sheng Cao†,* Jin-Cheng Shu,† Yong-Zhu Cai,† Xi-Xi Wang,† Quan-Liang Zhao,‡ Jie Yuan,┴ †School

of Materials Science and Engineering, Beijing Institute of Technology, Beijing,

100081, China. ‡School

of Mechanical and Material Engineering, North China University of Technology,

Beijing, 100144, China. ┴School

of Information Engineering, Minzu University of China, Beijing, 100081, China.

* Corresponding Authors: Email: [email protected] (Mao-Sheng Cao).

Key words: MXene, electromagnetic property, electromagnetic energy absorption, power generation, energy conversion

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Abstract Neither is the utilization of electromagnetic (EM) energy affected by the weather nor does it produce harmful substances. How to utilize and convert EM energy is of practical concern. Herein, delaminated titanium carbide (D-Ti3C2Tx) MXene nanosheet (NS) was successfully fabricated by the modified Gogotsi’s method. The choice of atomic layer processing allows tailoring of layer distance of Ti3C2Tx so as to improve the polarization. High-performance EM wave absorption of D-Ti3C2Tx MXene NS composites were obtained, and their comprehensive performance is the best of Ti3C2Tx-based composites. Due to the competition between conduction loss and polarization loss, the higher the concentration of D-Ti3C2Tx in composites is, the more the conversion of EM energy to thermal energy will be. Based on the mechanism, a prototype of thermoelectric generator is designed, which can convert EM energy into power energy effectively. This thermoelectric generator will be energy source for low power electric devices. Our finding will provide new ideas for the utilization of EM energy.


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1. Introduction The research and utilization of new energy has become the focus due to the aggravation of greenhouse effect. Chemical energy, and its utilization is always accompanied by harmful substances.1 Solar energy, on the other hand, is widely recognized as a green energy source but is heavily weather-dependent.2,3 Electromagnetic (EM) energy as a widespread energy can not be affected by the weather. Utilization and conversion of EM energy have always been a topic of concern due to the increasing serious EM pollution.4-14 Most of current works focus on how to prepare materials that can effectively absorb and shield electromagnetic waves.15-24 For example, Che et al. reported that CNT/crystalline Fe nanocomposites have excellent microwave-absorption characteristics.25 Numerous researches indicate that two-dimensional (2D) materials with high specific surface area and light weight show high-performance EM wave absorption and shielding.26-35 However, the utilization and conversion of EM energy and the corresponding mechanism have always been in the exploratory stage. MXene as a novel 2D material has attracted much attention since it was discovered by Gogotsi, Barsoum and co-workers in 2011.36 Typically, MXene can be written as Mn+1XnTx. M denotes transition metal, X represents C or/and N, Tx is used to represent functional group (=O, -OH and –F).37 Till now, various types of MXenes (Ti3C2Tx, Ti2CTx, Nb2CTx, Ti3CNTx, Mo2CTx, etc.) are obtained.38-40 MXene have demonstrated promise for a variety of applications and in particular for sewage purification,41 energy storage,42 photoelectron43 and electrocatalyst.44 Compared with graphene and other 2D materials, MXene has the native defects, the chemically active surfaces and high conductivity.45 These characteristics render MXene a promising candidate for utilization of EM energy. Noteworthily, Ti3C2Tx MXene is the most widely studied among various MXenes due to its excellent volumetric capacitance and extreme high conductivity. Due to its high conductivity, some of the initial researches focused on the electromagnetic interference (EMI)



shielding performance of Ti3C2Tx MXene. For example, Gogotsi et al. prepared a micron-scale Ti3C2Tx film showing EMI shielding effectiveness (SE) of 92 dB.46 Yu and co-workers fabricated Ti3C2Tx foam exhibiting excellent EMI shielding performance.47 Recently, the EM wave absorbing properties of Ti3C2Tx MXene have gradually attracted the interest of researchers. Initially, Yin and co-workers reported the EM wave absorbing property of multilayered Ti3C2Tx (M-Ti3C2Tx) and modified M-Ti3C2Tx MXene.48-51 Then, more researches about EM wave absorption performance of M-Ti3C2Tx MXene and hybrid M-Ti3C2Tx have been reported.52-61 All of these studies show that Ti3C2Tx MXene presents excellent EM wave attenuation potential. Ti3C2Tx MXene obtained by high-concentration acid etching has an accordion-like structure, which is often called as multilayered Ti3C2Tx (M-Ti3C2Tx) MXene. Only after the further processes of centrifugation and separation, M-Ti3C2Tx can be separated into delaminated Ti3C2Tx (D-Ti3C2Tx) MXene nanosheet (NS) effectively. It is very difficult to achieve the above process. Compared with M-Ti3C2Tx, D-Ti3C2Tx NS has higher specific surface area. Particularly, as an absorber, the increasing specific surface area will lead more polarization. This will help to improve the EM wave absorbing properties significantly. In this work, D-Ti3C2Tx NS was successfully fabricated by the modified Gogotsi’s method and the corresponding preparation process is described in detail. As expected, D-Ti3C2Tx MXene NS composite shows excellent EM wave absorption performance. The conversion of EM energy is systematically discussed in D-Ti3C2Tx composites. The role of conduction loss and polarization loss in the attenuation of EM energy are revealed in detail. More importantly, a prototype device is designed based on the mechanism of the EM energy conversion. Our work will provide new ideas for the utilization of EM energy.


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2. Experimental section 2.1 Experimental materials Ti3AlC2 powders (300 mesh) were supplied from Lianlixin Technology Ltd (Beijing, China). LiF was purchased from Macklin Technology Ltd (Shanghai, China). HCl (35 wt.%) was provided by Beijing Chemical Factory (Beijing, China). All the chemicals are grade of analytical purity. 2.2 Preparation of delaminated Ti3C2Tx nanosheets Delaminated Ti3C2Tx (D-Ti3C2Tx) nanosheet (NS) was fabricated by the modified Gogotsi’s method. 1 g LiF was dispersed in 20 mL 6 M HCl and the solution was allowed to mix completely for 5 minutes. And, 1 g of Ti3AlC2 powders were added into the mixture and stirred at 40 °C for 16 h. After reaction, the resultant was repeatedly washed by deionized water until pH was neutral (≥ 6). Then, the sediment was centrifuged at 3500 rpm for 1 min, 3 min and 5 min, respectively. The supernatant was gathered, which is the colloidal solution of D-Ti3C2Tx NSs. Finally, the colloidal solutions were filtered through a membrane and dried in a desiccator under vacuum at room temperature. 2.3 Characterization Scanning electron microscopy (SEM) images were obtained by a scanning electronmicro scope system (SEM Hitachi S-4800). Transmission electron microscopy (TEM) images were collected by a TEM-2100F microscope. Atomic force microscopy (AFM) images were collected on a Veeco Dimension Fast Scan system. X-ray diffraction (XRD) were performed on an X'Pert PRO system (Cu Kα). Raman spectra were measured on a HORIBA Jobin Yvon HR800

Raman

spectrometer

equipped.

X-ray

photoelectron

spectroscopy

(XPS)

measurements were performed by a PHI Quantera system. Electromagnetic parameters were measured by coaxial method with a vector network analyzer (VNA, Anritsu 37269D) in the range of 2-18 GHz. Typically, The D-Ti3C2Tx NSs



(20, 40, 60, 80 wt.% loading) were mixed with wax, respectively. The mixtures were pressed into a toroidal shape (Φouter = 7.03 mm; Φin = 3.00 mm) with thicknesses of ~1.5 mm. Meanwhile, their direct-current (DC) conductivity (σ) were measured by a Keithley 4200-SCS semiconductor characterization system. 3. Results and discussion Figure 1A-E shows the products of the process for preparing D-Ti3C2Tx NSs. Granular Ti3AlC2 transforms into sheet D-Ti3C2Tx MXene after LiF/HCl etching and centrifugation. At first, Ti3AlC2 particles is etched by LiF/HCl for 16 h to form multilayered Ti3C2Tx (M-Ti3C2Tx), which has accordion-like structure. After a brief centrifugation (Figure 1C), the layer distance of M-Ti3C2Tx gets larger. Then, the layer distance is rising further with the increasing centrifugal time (Figure 1D). Finally, M-Ti3C2Tx totally transforms into D-Ti3C2Tx NS after 5 min centrifugation, and the mean lateral dimension of D-Ti3C2Tx NS is 1-4 μm (Figure 1E), which is in accordance with the result reported by Zhang and co-workers.62 TEM was performed to further characterize the morphology of Ti3C2Tx MXene NS. As shown in Figure 1F, D-Ti3C2Tx MXene with sheet form is ~3 μm in lateral dimension, which is in accordance with the results of SEM (Figure 1E). High-resolution (HR) TEM image shows a hexagonal arrangement of atoms in the plane (Figure 1G), which is further confirmed by the selected area electron diffraction (SAED) pattern (Figure 1H). The AFM height profile measured along the yellow dashed line shows that D-Ti3C2Tx NS has the height of 2.6 nm (Figure 1I), which is in accordance with the previous work.63 Figure 2 shows the atomic phase of D-Ti3C2Tx. It’s clearly to see that there are many defects in the surface of D-Ti3C2Tx NS (Figure 2A-E). According to the previous theoretical research of Sang and co-workers, there are four types of defects existed on the surface of D-Ti3C2Tx NS (Figure 2F),64 which is in accordance with the results of the experiment. These defects are caused by the process of LiF/HCl etching.64,65


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The XRD patterns of Ti3AlC2 particle and D-Ti3C2Tx NS are shown in Figure 3A. There is a shift of the (002) peak of Ti3AlC2 at ~9.5° to ~6.0° for D-Ti3C2Tx, which is ascribed to the elimination of the Al of Ti3AlC2. Raman spectra of Ti3AlC2 and D-Ti3C2Tx are present in Figure 3B. Peaks I, II and III vanished after LiF/HCl etching, which is due to the removal of Al layers from the Ti3AlC2.32 The D and G peak of D-Ti3C2Tx gets weak and broad after LiF/HCl etching. XPS is performed to further investigate the surface environment of D-Ti3C2Tx. As shown in Figure 3C-F, there are three function groups (-F, -OH, =O) attached in the surface of D-Ti3C2Tx, which is in accordance with the result reported by Cook and co-workers.66 Besides, the Ti (IV) peak seems too strong (Figure 3D), indicating oxidation exists in the preparation of MXene.67,68 Figure 4 shows the dielectric parameters of D-Ti3C2Tx/wax composites. As shown in Figure 4A and 4B, both εʹ and εʺ raise with the increase of D-Ti3C2Tx mass fraction. Meanwhile, both εʹ and εʺ of each composite reduce with the increase in frequency, especially in high-concentration composites. This phenomenon is mainly due to the decrease in polarization capability of absorber with the increasing frequency. There are obvious relaxation peaks observed in the loss tangent (tanδ) (Figure 4C), which is due to the polarization. Besides, the behavior of tanδ is similar to that of εʺ, which indicates that conductivity and polarization have a synergistic effect on the εʺ and tanδ.69 To investigate the EM wave absorption of D-Ti3C2Tx/wax composites, the reflection loss (RL) can be calculated from relative complex permittivity and permeability70-72

Zin  1 Zin  1

(1)

  2 fd  r tanh  j    r r r   c 

(2)

RL(dB)  20log

Zin 

where Zin represents the normalized input impedance. εr and µr are the relative complex permittivity and permeability of the composite medium, respectively. c is the velocity of light.



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d is the thickness of the absorber. f is the frequency of EM wave. Figure 5A-D shows the EM wave absorption of D-Ti3C2Tx/wax composites. All the samples exhibit excellent EM wave absorbing properties. Particularly, the minimum RL of 40 wt.% composite is –47.9 dB at 12.48 GHz with a thickness of 2.5 mm, and the corresponding absorption bandwidth (˂-10 dB) is 3.6 GHz. Moreover, 80 wt.% composite realizes a large bandwidth at the thickness of only 1 mm. Furthermore, the EM wave absorbing properties of D-Ti3C2Tx/wax composites are evaluated in Figure S1 (Supporting Information). The minimum RL and the bandwidth generally drive from 80 wt.% to 20 wt.% with the increase of thickness, which means that the EM wave absorption performance of composites can be tuned by changing the filling amount of D-Ti3C2Tx. Figure S2 shows the EM wave absorbing properties of Ti2C3Tx-based composites. It’s clearly to see that the comprehensive performance (bandwidth (

Atomic Layer Tailoring Titanium Carbide MXene To Tune Transport

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