MXene composite thin film

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ScienceDirect Materials Today: Proceedings 7 (2019) 738–743

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Nanotech Malaysia 2018

Highly flexible and stretchable 3D graphene/MXene composite thin film Nik Nurul Nazipah Ab Alima, Mohamed Salleh Mohamed Saheeda, Norani Muti Mohameda,b, Mohamed Shuaib Mohamed Saheeda,b* b

a Fundamental & Applied Science Department, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysi Centre of Innovation Nanostructures & Nanodevices (COINN), Universiti Teknologi PETRONAS, 32610 Bandar Seri Iskandar, Perak, Malaysia

Abstract Flexible and stretchable hybrid 3D graphene/Ti3C2Tx MXene composite thin film was fabricated using chemical vapor deposition (CVD) and selective etching method. The 3D graphene was grown via CVD approach at low pressure and methane as carbon source. While, the synthesis of Ti3C2Tx MXene was done using selective etching of Ti3AlC2 MAX phase. The 3D graphene and Ti3C2Tx MXene was sonicated and centrifuge with an organic solvent to form hybrid 3D graphene/ Ti3C2Tx MXene. As-product obtain in the form of clay-like then, it was encapsulated with the poly (dimethyl-siloxane) (PDMS) solution. The sample was baked to form composite thin film. The encapsulation of 3D graphene/Ti3C2Tx MXene with polymer matrix enables it to be used as flexible composite thin film. © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Nanotech Malaysia 2018. Keywords: 3D graphene; Ti3C2Tx MXene; Ti3AlC2 MAX Phase; selective etching; CVD

1. Introduction Graphene has been widely used in flexible electronics devices due to its superior electrical and mechanical properties. Graphene is two dimensional monolayer of carbon atoms forming the shape of honeycomb lattice which influence the electron mobility in the lattice itself. Through each of the hexagonally bonded carbon, it allows fast transmission of electron. Furthermore, graphene has a strong thermodynamic stability with high mechanical strength

* Corresponding author. Tel.: +6019-7326422; fax: +605-3685905. E-mail address: [email protected] 2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Nanotech Malaysia 2018.

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thus, giving it high flexibility properties. Moreover, the synthesis method using chemical deposition vapour (CVD) showing that the 3D graphene will exhibit more superior performance rather than chemically derived graphene sheets. The introduced method allows the synthesis of a large area of highly quality graphene films. 3D graphene growth from nickel template via CVD method has monolith of a graphene 3D network. The continuous CVD-grown graphene building blocks allows fast charge carrier mobility with slightest resistance implying high quality graphene 3D network [1][2][3]. MXenes discovered by Yury Gogotsi from Drexel University scientists’ et.al in 2011 as a new niche of 2D materials. MXenes coming from a group of transition metal carbides, carbonitrides and nitrides which is known as Mn+1Xn, where M is define as transition metals and X is carbon and/or nitrogen. MXene is used to show the comparability between graphene with 2D material group at the same time to emphasize the parent ternary carbide and nitrides, MAX phase, which is MXene precursor. MAX phases are consist of stratified ternary carbides and nitrides with general formula Mn+1AXn, where A describe group 13 and 14 elements in the table of periodic. These 2D materials exhibit excellent mechanical properties, metallic conductivity with hydrophilic surface and have great performance in electrochemical energy field [4 -11]. In this work, Ti3C2Tx MXene was hybridized with 3D graphene and encapsulated with PDMS polymer matrix to produce flexible and stretchable composite thin films. The sandwich-like 3D graphene/ Ti3C2Tx MXene/PDMS were fabricated using drop coating of 3D graphene/Ti3C2Tx MXene clay composite on a thin film of PDMS matrix. The composite was then fully encapsulated with PDMS polymer solution to give sandwich structure and making it flexible thin films. 2. Materials and experimental The nickel foam and Ti3AlC2, MAX phase were shopped from Shanghai Winfay Industry Ltd. Then, for nickel cleaning acetone and ethanol were bought from Merck KGaA. Poly (methyl methacrylate) and surfactant anisole were purchased from Sigma Aldrich to act as a support layer for 3D graphene grown from CVD. Hydrochloric acid, iron (III) chloride (FeCl3) that was used for nickel etched and hydrofluoric acid, HF with dimethyl sulfoxide (DMSO) for selective etching process and delamination of Ti3C2Tx MXene were purchased from Merck KGaA. Poly (dimethyl-siloxane) (PDMS) and base were purchased from Sigma Aldrich for 3D graphene/MXene encapsulation to form a flexible and stretchable film. For the CVD process, methane gas (99.9%) was used as a carbon source, then argon gas (99.9%) will act as a carrier gas and hydrogen gas (99.9%) as an activation gas. All the chemicals were stored in a safe condition based on material safety data sheets (MSDS). In this experiment, microporous nickel foam template was used to grow 3D graphene. Firstly, the nickel foam was sonicated in acetone and ethanol solution subsequently for 30 minutes each to purify the nickel foam before undergoes CVD process. Next, the nickel foam template was loaded into a low pressure CVD (LPCVD) furnace, with hydrogen (H2) and argon (Ar) gaseous were flowed into the tube furnace. Tube furnace was heated until it reaches 1000 ℃ then, methane (CH4) gas was allowed to flow into it. The decomposition of CH4 gas at 1000 ℃ will allow the precipitation of carbon atoms to form graphene films on the surface of nickel foam. The growth process took 30 minutes to complete and rapid cooling process was done. Next, 1.4 wt. % polymethyl methacrylate (PMMA) was drop coated onto the 3D graphene-Ni foam. In order to prevent the graphene network from collapsing during the nickel etching process, PMMA coating will be used as a support layer. The 3D graphene-Ni/PMMA sample was dissolved into 0.1 M hydrochloric acid and iron (III) chloride solution for 24 hours to etch the nickel out from the 3D graphene foam. The free-standing 3D graphene was obtained after PMMA was fully etched in the tube furnace at 550 ℃ under H2 and Ar gas flow. The Ti3C2Tx MXene was synthesis via selective etching of MAX phase, Ti3AlC2 with 50 wt. % HF. The reaction took place at room temperature for 100h. Then, the Ti3C2Tx sediment was collected using polyvinyl difluoride (PVDF) filter membrane via vacuum-assisted filtration. After vacuum assist filtration was done the clay-like Ti3C2Tx MXene was obtained. Then, the clay-like Ti3C2Tx MXene was dried using vacuum oven at 80 ℃ for 24h. The resulting powder was collected and sonicated with the DMSO solution for the delamination process of the MXene into single sheets. The solution was mixed with 3D graphene foam and centrifuge at 300 rpm for 1h. The collected slurry was then paste onto a thin film of PDMS polymer solution in the ratio of 10:1 (base: curing agent) then baked at 80 ℃ for 1h to form composite thin film. The synthesis process as shown in the Figure 1 below;

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HF treatment

Sonication

Ti3C2Tx MXene

Ti3AlC2

Centrifugation

Delaminated Ti3C2Tx MXene

Polymer encapsulation

3D graphene/Ti3C2Tx MXene

3D graphene/Ti3C2Tx MXene/PDMS

Fig. 1: Synthesis of 3D graphene/Ti3C2Tx MXene/PDMS thin film.

The morphology and material composition of free-standing 3D graphene and Ti3C2Tx MXene grown sample were analysed using Variable Pressure Field Emission Scanning Electron Microscope (VPFESEM, Zeiss Supra55 VP). While, energy dispersive x-ray spectroscopy (EDX) was done on multiple points of the sample to prove the percentage of nickel present in the graphene foam after etched. The same process was done to prove that the aluminium, Al was etched from the MAX phase to produce Ti3C2Tx MXene. X-ray photoelectron spectroscopy (XPS) was characterized using Thermo Scientific, K-alpha machine. The result was further supported with x-ray diffraction (XRD) analysis to prove the Ti3C2Tx was synthesized via selective etching of Ti3AlC2 MAX phase using HF 50 wt. %. 3. Results and Discussion The synthesis of 3D graphene from nickel foam template giving the 3D graphene structure with morphology of a foam-like network which allows transportation of charge carriers. During CVD process, on the outer surface of nickel foam the graphene films will precipitate resulting from the changes in thermal expansion coefficients between nickel and graphene. Thus, it forms ripples and wrinkles that will provide better adhesion for the 3D graphene when integrated with polymer matrix resulting in the improvement of mechanical interlocking to form composite materials. The formation of 3D graphene from nickel foam template was proven via electron scanning microscopy (SEM) and energy dispersive x-ray analysis (EDX). (b)

(a)

500 µm

Fig. 2: (a) Free-standing 3D graphene and the SEM image of 3D graphene after CVD process at using LPCVD machine (b) EDX analysis shows element composition in the 3D graphene foam.

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SEM images for 3D graphene in Figure 2 above shows that the 3D graphene films stick well to the nickel foam surface. Through EDX, it shows the element composition present in the 3D graphene foam hence, proves that the nickel was fully etched from the template. However to obtain free-standing 3D graphene, nickel must be etched by 0.1 wt. % HCl solution with addition of FeCl3 that will act as catalyst. Then, a layer of PMMA was coated on top of the 3D graphene to prevent the graphene network from defect. The PMMA support layer was removed by annealing method to preserve the graphene skeleton from shrinkage.

(a)

(b)

2 µm

1 µm

(d)

(c)

20 µm

2 µm

Fig. 3: SEM image of (a) low-magnification of Ti3AlC2 precursor (b) Accordion-like morphology of Ti3C2Tx MXene observed after etched with 50 wt. % HF (c) low-magnification of the hybrid 3D graphene/Ti3C2Tx del-MXene (d) highmagnification image of hybrid composite 3D graphene/Ti3C2Tx del-MXene.

The Ti3C2Tx MXene powder was prepared using the method discuss in experimental work. The Ti3AlC2 precursor was exfoliated by 50 wt. % HF etchant. Then, the multilayered Ti3C2Tx as-product was collected after vacuum-assist filtration. The clay-like Ti3C2Tx MXene was rinsed a few times with distilled water followed by ethanol then the powder was dried in the vacuum oven. The SEM images of Ti3AlC2 powder was compared with the collected Ti3C2Tx powder in Figure 3 (a) above, it shows the structures of the Ti3AlC2 precursor before being etched with 50 wt. % HF for 100h and Figure 3 (b) shows the accordion-like structures of Ti3C2Tx MXene after treated with the acid. MAX powder which is Ti3AlC2 shows solid layered structure then after acid treatment, the opening of MXene lamellas was observed. The formation of expanded accordion-like structure was due to the large amount of H2 gas escaped from the exothermic reaction of HF with aluminium, Al nanoparticles. Then, from Figure 3 (c) and (d) it shows the distribution of Ti3C2Tx MXene with 3D graphene foam which is bigger than the MXene particles. This proves the formation of hybrid 3D graphene/Ti3C2Tx MXene as a composite material.

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Apart from this, XRD analysis for Ti3AlC2 precursor and Ti3C2Tx was done. Figure 4 below proves that the aluminium presence in the MAX phase was selectively etched using hydrofluoric acid. Peak shift of the (002) for Ti3C2Tx at 9.00 prove the formation Ti3C2Tx due to the elimination of Al particles in the Ti3AlC2 and presence of surface terminations group in Ti3C2Tx. It was further confirmed by the existence of satellite peaks for the elements at (002), (004), (006), and (008) after MAX phase was selectively etched for 100 h. Furthermore, the XPS was done to analyze the element composition on the surface of the powder thus, the oxidation state of titanium can be determined. Survey spectrum shows that Ti, O, C and F elements are present. The C1s region represented from six components positioned at 281.2, 282.1, 284.8, 286.4, 287.9 and 288.9 eV which is equivalent with C-Ti, C-Ti-O, CC/C-H, C-O, C=O and (O-C=O and C-F) bonds. Next, the Ti2p3/2 components were exist at 454.5, 455.9, 457.4 and 485.8 eV respectively. While, the Ti-C bond present at peak 454.5 eV. The first peak at 531.3 eV and 531.7 eV refer to the O1s region, that confirm the present of C-Ti-Ox and C-Ti-(OH) x species. Then, the second peak at 685.2 eV confirmed the present of C-Ti-Fx group in F1s region. The Figure 4 below shows the prominent peaks changes after the MAX phase was selectively etched with HF etchant through both XRD and XPS analysis.

(a)

Fig. 4: XRD analysis for MAX phase-Ti3AlC2 and Ti3C2Tx MXene after etched with 50 wt. % HF. (b) XPS analysis showing that changes in the element composition after selective etching had been done.

Fig. 5: Sample of 3D graphene/Ti3C2Tx MXene/PDMS composite thin film.

The 3D graphene was combined with Ti3C2Tx MXene and encapsulated with PDMS polymer matrix to produce a flexible and stretchable composite thin film. Figure 5 below shows the sample of 3D graphene/ Ti3C2Tx MXene/PDMS composite thin film. Further analyses on the electromechanical characteristics of the composite thin film are in progress.

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4. Conclusions The hybrid 3D graphene/Ti3C2Tx MXene/PDMS were fabricated via CVD method and selective etching of Ti3AlC2. Through CVD-assist template method the 3D graphene had been successfully synthesized and the Ti3C2Tx MXene was synthesized via selective etching method. The hybridization of this newly discovered 2D metal carbides with 3D graphene foam will enhanced the electrical properties of the thin film. Then, the combination of both hybrid material with PDMS substrate will make it excellent flexible and stretchable composite materials to be applied in strain sensing field. Furthermore, combination of 3D graphene and Ti3C2Tx MXene will improve the structural network of the composite material thus, allowing fast transport channel of charge carriers for high electrical conductivity. Acknowledgements This work is supported by Universitas Pertamina-Universiti Teknologi PETRONAS grant scheme (Grant No: 015ME0-005). The authors would also like to express their gratitude to Mr Rosli Mohd, Nanotechnology Laboratory, Universiti Technology PETRONAS for their technical support. References [1] C. C. and K. S. N. Nazmul Karim, Shaila Afroj, Sirui Tan, Pei He, Anura Fernando, ACS Nano, 11 (2017) 12266–12275. [2] Z. Chen, W. Ren, L. Gao, B. Liu, S. Pei, and H. M. Cheng, Nat. Mater., 10 (2011) 424–428. [3] M. S. M. Saheed, N. M. Mohamed, B. S. M. Singh, and M. S. M. Saheed, Diam. Relat. Mater., 79 (2017) 93–101. [4] L. Ding et al., Nat. Commun., 9 (2018) 1–7. [5] M. Ghidiu, J. Halim, S. Kota, D. Bish, Y. Gogotsi, and M. W. Barsoum, Chem. Mater., 28 (2016) 3507–3514.. [6] Z. Ma, X. Zhou, W. Deng, D. Lei, and Z. Liu, ACS Appl. Mater. Interfaces, 10 (2018) 3634–3643. [7] Y. Wu, P. Nie, J. Wang, H. Dou, and X. Zhang, ACS Appl. Mater. Interfaces, 9 (2017) 39610–39617. [8] M. Alhabeb et al., Chem. Mater., 29 (2017) 7633–7644. [9] B. Anasori et al., ACS Nano, 9 (2015) 9507–9516. [10] Y. Ma et al., Nat. Commun., 8 (2017) 1–7. [11] J. Yan et al., Adv. Funct. Mater. 27 (2017).