Electromagnetic Shielding by MXene-Graphene

materials Article

Electromagnetic Shielding by MXene-Graphene-PVDF Composite with Hydrophobic, Lightweight and Flexible Graphene Coated Fabric Kanthasamy Raagulan 1 , Ramanaskanda Braveenth 1 , Hee Jung Jang 1 , Yun Seon Lee 2 , Cheol-Min Yang 2, *, Bo Mi Kim 3 , Jai Jung Moon 4 and Kyu Yun Chai 1, * 1 2

3 4

*

Division of Bio-Nanochemistry, College of Natural Sciences, Wonkwang University, Iksan 570-749, Korea; [email protected] (K.R.); [email protected] (R.B.); [email protected] (H.J.J.) Multifunctional Structural Composite Research Center, Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Chudong-ro 92, Bongdong-eup,Wanju-gun, Jeollabukdo 55324, Korea; [email protected] Department of Chemical Engineering, Wonkwang University, Iksan 570-749, Korea; [email protected] Clean & Science Co., Ltd., Jeongeup 3 Industrial Complex 15BL, 67, 3sandan 3-gil, Buk-myeon 56136, Jeongeup-si, Korea; [email protected] Correspondence: [email protected] (C.-M.Y.); [email protected] (K.Y.C.); Tel.: +82-63-219-8143 (C.-M.Y.); +82-63-850-6230 (K.Y.C.); Fax: +82-63-841-4893 (K.Y.C.)

Received: 29 August 2018; Accepted: 20 September 2018; Published: 22 September 2018







Abstract: MXene and graphene based thin, flexible and low-density composite were prepared by cost effective spray coating and solvent casting method. The fabricated composite was characterized using Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray (EDX). The prepared composites showed hydrophobic nature with higher contact angle of 126◦ , −43 mN·m−1 wetting energy, −116 mN·m−1 spreading Coefficient and 30 mN·m−1 lowest work of adhesion. The composites displayed excellent conductivity of 13.68 S·cm−1 with 3.1 Ω·sq−1 lowest sheet resistance. All the composites showed an outstanding thermal stability and constrain highest weight lost until 400 ◦ C. The MXene-graphene foam exhibited excellent EMI shielding of 53.8 dB (99.999%) with reflection of 13.10 dB and absorption of 43.38 dB in 8–12.4 GHz. The single coated carbon fabric displayed outstanding absolute shielding effectiveness of 35,369.82 dB·cm2 ·g−1 . The above results lead perspective applications such as aeronautics, radars, air travels, mobile phones, handy electronics and military applications. Keywords: graphene; MXene; EMI shielding; composite; fabric

1. Introduction The rapid advancement in intricate packing of modern electronic systems causes undesirable radiation; this inevitable radiation is known as electromagnetic interference (EMI), which has negative effects on humans and neighboring electronic systems. EMI pollution causes health hazards such as languidness, insomnia, nervousness, and headaches [1–4]. Electromagnetic compatibility can be achieved by using various materials such as textiles, polymer-based composites, MXene, and fabrics. EMI shielding is expressed in decibels (dB) [5–15]. Conductive and nonconductive polymers such as poly-p-phenylene-benzobisthiazole (PBT) [1,4,5], polythiophene (PTh) [1], Polyvinylidene fluoride (PVDF) [7,8,13], polyacrylic acid (PAA) [1], styrene polymethyl methacrylate (SPMMA) [4,5], and fillers such as metal nanoparticles [14–18], magnetic materials [13,14], carbon black, graphite [11], carbon Materials 2018, 11, 1803; doi:10.3390/ma11101803

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nanotubes [9–12], graphene (GN) [19], and carbon fibers (CF) [17] are used to tune the properties of EMI shielding materials [20]. The polymer Nano composites (PNC) are widely used as advance engineering material in different environment. The functional materials, molecular dynamics, molecular details and micro structure of PNC are important for the application [21]. PNC consist Nano fillers play important role in generating conductive networks and combination of components alter the physicochemical properties of the composites [22–25]. Further, surface properties of the materials can be transformed in to hydrophobic/lyophilic by coating nanoparticle such as TiO2 , ZnO and silica aerogel or polymers like polydimethylsiloxane (PDMS), polytetraflouroethylene (PTFE). The cross link/hydrogen bond between constituents cause by surface functional groups. The cross links improve the thermo mechanical properties [26–28]. Furthermore, in the polymer foams the voids form due to the different nucleation time of constitutional solid and other external factor like temperature pressure [29]. Advanced EMI shielding materials should be lightweight, flexible, cost effective, dielectric, and multifunctional, and should possess a tunable absorption, high thermal resistance, intrinsic conductivity, large aspect ratio, high corrosion resistance, and good magnetic and electronic properties [19,20,30–34]. Recently, flexible, corrosion resistant, high-density, thin carbon-based materials with satisfactory electrical conductance have become attractive candidates for EMI shielding applications such as in the aerospace, aircraft, automobile, and modern electronics fields. Hence, wet-laid synthetic nonwoven fabrics fulfil these criteria with good EMI shielding [34]. In addition, carbon-carbon-based composites possess greater EMI shielding effectiveness than carbon-based polymer matrices. Further, continuous carbon fibers are preferred to discontinuous fibers in carbon-based EMI shielding materials [35]. This is because the properties of carbon fiber that affect EMI shielding those are the length and array [36]. Further, MXene resembles graphene, is an attractive engineering material and used as filler exploited to create flexible electronic devices and other engineering materials [37]. The EMI shielding range of most graphene/PVDF composites of various thicknesses has been reported to be in the range of 20–30 dB. In addition, the graphene can be functionalized by using reduction, oxidation, metal nanoparticles, organic molecules and polymers for various applications like solar cell, antibacterial materials and the EMI shielding of graphene/PVDF has been enhanced by the decoration of nanoparticles [38–42]. Two-dimensional MXenes are explored intensively for various applications including EMI shielding. MXenes are sprouting transition metal (Ti, V, Cr, Nb, and Ta) carbides/nitrides with universal formula Mn+1 Xn Tx (n = 1, 2, and 3), where M is an early transition metal, X is carbon or nitride, and Tx is a surface functional group (−O, =O and F). MXenes are generated from the corresponding layered MAX phase with the general formula Mn+1 AXn by selective engraving of the A-layer (group 13/14 elements) created by a weak M-A bond sandwiched between a strong M-X bond. Minimally intensive layer-delamination (MILD) etching is carried out using the LiF/HCl method, which is advantageous over clay etching in which Hydrogen fluoride (HF) is utilized under various etching conditions [43–47]. Intercalation and exfoliation are conducted using urea, dimethyl sulfoxide (DMSO), tetramethylammonium hydroxide (TMAOH), NH4 OH, tetrabutylammonium hydroxide (TBAOH), and sonication. These exfoliation techniques are inevitable in the clay method. However, LiF/HCl-based in-situ mild etching is highly preferable owing to the number of steps, level of defects and risk, and the fact that exfoliation can be achieved through manual shaking. However, sonication at low temperature and in inert environments (Ar) is preferable [34]. MXene thin-films and foams exhibit the highest EMI shielding in the X-band region. EMI shielding can be achieved by absorption, reflection, and multiple reflection. The MXene film enables internal multiple reflection which facilitates absorption. The reflection on the surface due to the electron and layered structure encourages multiple reflection. When electromagnetic radiation hits the surface, it induces electron mobility (ohmic loss). The lightweight foaming materials are attractive candidate over metal-shielding materials as the latter have higher densities which limit the application range in terms of aerospace [34,35]. In this study, we develop a graphene-flake (GN) coated carbon-fiber reinforced-matrix composite (MC) and solution-casting MXene graphene foam, which exhibit a high EMI shielding effect in the

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S-band region. The required thickness is achievable by adjusting the spraying and drying cycles. Further, we developed MXene graphene foam with internal hollow sphere with surface imbedded balls. Consequently, we analyze the following parameters in detail; EMI shielding, morphology of GN-coated matrix and MXene-graphene foam, electrical conductivity, constitutional chemical species, elemental percentage, and hydrophobic nature. In addition, the pristine carbon-fiber-reinforced matrix composite, graphene, graphene oxide, and reduced graphene oxide are denoted as MC, GN, GNO, and rGNO, respectively. The GN, GNO and rGNO coated fabrics are denoted as GNMC, GNOMC, and rGNOMC, whereas the MXene-graphene coated fabric, MXene-graphene composite, and MXene-graphene oxide composite are symbolized as MGNMC, MGNC, and MGNOC, respectively. 2. Materials and Methods 2.1. Materials Graphene (GN) (M-25, 99.5%, average size and thickness of 25 µm and 7 nm, respectively) was obtained from Ditto Technology Co. Ltd., (Gyeonggi-do, Seoul, Korea). Dimethylformamide (DMF) 99.8 w/w%, lithium fluoride (LiF) (98%, 300 mesh), Polyacrylic acid (PAA), and Polyacrylamide (PAM) were purchased from Sigma Aldrich (Seoul, Korea). Polyvinylidene fluoride (PVDF) (melting point of 155–166 ◦ C) was purchased from Alfa Aesar (Seoul, Korea). Hydrochloric acid (HCl-35%) and nitric acid (HNO3 -70%) were supplied by Samsung Chemical Co., Ltd. (Seoul, Korea), anhydrous lithium chloride (LiCl) was purchased from Tokyo Chemical Industry Co., Ltd (Tokyo, Japan), and Ti3 AlC2 was acquired from Forsman Scientific Co., Ltd. (Beijing, China). Carbon fiber (fiber diameter 7 µm, 6 mm) and polyethylene terephthalate (PET) binder (fiber diameter 2.2 dtex, 5 mm) were purchased from TORAY Product (Osaka, Japan). No purification methods other than those stated were utilized for the chemicals. 2.2. Preparation of Graphene Oxide (GNO) and Reduced Graphene Oxide (rGNO) A total of 1 g of graphene was mixed with 50 mL of HNO3 and stirred at room temperature for 12 h. The reacted graphene was washed with deionized water until it reached a neutral pH. The resulting black flakes were GNO, and these were dried at 80 ◦ C for 24 h. Equal amounts of GNO and NaBH4 were mixed together in deionized water and stirred at room temperature for 12 h. The resultant product was washed several times with deionized (DI) water and dried at 80 ◦ C for 24 h. The obtained product was rGNO. 2.3. Preparation of MXene and MXene Colloidal Solution Equal amounts of Ti3 AlC2 and LiF were immersed in 20 mL of 6M HCl solution and stirred at 35 for 24 h. The resultant mixture was washed with DI water (pH 6) several times by centrifuging at 3500 rpm for 5 min, and the black flakes were dried at 100 ◦ C for 12 h in a vacuum oven. A total of 0.1 g of MXene was dispersed in 10 mL of DI water by sonication for 1 h in an ice bath. The resultant exfoliated solution was centrifuged at 3500 rpm for 30 min. The supernatant was collected and stored at 5 ◦ C for the coating process. ◦C

2.4. Preparation of Carbon Fabric Carbon fiber, PET-binder fiber with a 4:1 weight ratio, and 0.3 wt.% of PAM were dispersed in DI water. Then, the mixture was rotated at 500 rpm for 10 min. A web was produced using a general wet-laid method. During this process, a drum dryer was used with a surface temperature of 140 ◦ C and a speed of 7 m·min−1 . The obtained fabric density was 20 g·m−2 . 2.5. Fabrication of Composite (MC) A series of GN-coated MCs were prepared by a cost-effective spray-coating process. MC was spray-coated using 3 g·L−1 of GN, GNO, and rGNO with a 5 g·L−1 PVDF dispersed solution of DMF.

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After the coating process, the fabrics were subjected to drying at 100 ◦ C for 5 min in a drying oven. This process was repeated up to ten cycles to alter the quantity of GN coated on the MC in each case. MNNC and MGNOC were fabricated using a solvent-casting method; 5 g of PVDF, 3 g of GN, and equal amounts of PAA and LiCl (0.3 g) were stirred in a 50 mL DMF solution at room temperature for 12 h. The resultant mixture was poured into a casting plate and evaporate DMF in vacuum oven at 80 ◦ C (pressure below 0.8 atm). Then, 100 mL of colloidal MXene solution was added and evaporation occurred under the same condition. Finally, the resultant film was separated from the casting plate. 2.6. Characterization The density was measured using a laser flash apparatus, LFA457 (NETZCH, Seoul, Korea). A high-resolution Raman spectrophotometer Jobin Yvon, LabRam HR Evolution (Horiba, Tokyo, Japan) was used to identify the structural features of MC, GN, GNO, rGNO, MXene, and GN-based and MXene composite. The morphologies of the fabrics were investigated using a field-emission scanning electron microscope (SEM, S-4800; Hitachi, Tokyo, Japan). The X-ray diffraction patterns of the materials were recorded using a high-power X-ray diffractometer, D/max-2500V/PC (Ragaku, Tokyo, Japan) with Cu (Kα). The elemental percentages and chemical environments were analyzed using XPS with a spot-size of 30–400 µm at 100 W of Emax (Al anode) K-Alpha, Thermo Fisher (East Grinstead, UK). A contact angle meter, Phonix-300A (S.E.O. Co., Ltd., Suwon, Korea), was used to analyze the wetting ability of the surfaces of the composites. A thermal analyzer, DSC TMA Q400 (TA Instruments Ltd., New Castle, DE, USA), was used to measure the thermogravimetric data. The EMI shielding effectiveness (SE) of the composites were recorded using an EMI shielding tent, ASTM-D4935-10, ASTM International (West Kentucky, PA, USA) at room temperature (For s band). The Savitzky–Golay function (Origin 2017 graphing and analysis, OriginLab; Boston, MA, USA) was used to plot the data. The electrical conductivities were measured using a four-probe method FPP-RS8, DASOL ENG (Seoul, Korea). The thicknesses were measured using a Mitutoyo thickness 2046S dial gage (Mitutoyo, Kanagawa, Japan). The electromagnetic characteristics of the specimens were measured using a vector network analyzer (VNA, Agilent N5230A, Agilent Technologies, Santa Clara, CA, USA) and a rectangular wave guide with the frequency ranging from 8.2 GHz to 12.4 GHz. The samples were prepared by cutting the free-standing film into rectangular shapes (width is 22.16 mm and height is 10.16 mm) (For X band). 3. Results 3.1. Structural Characterization 3.1.1. Scanning Electron Microscopic (SEM) Analysis of Morphology SEM images were used to analyze the surface topological morphology of the Ti3 AlC2 , Ti3 C2 Tx , graphene, MXene composites, and uncoated fabric (MC). Virtually the cracks and annular gaps are entailing with fiber surfaces of MC (Figure 1a,d). The SEM image of MC (Figure 1a) expresses the porous, smooth, and clean nature of the surfaces, which consist of haphazardly packed carbon fibers and GN, GNO, and rGNO. They are oriented randomly and grooves remain owing to the wrinkly nature of graphene (Figure 1b,e) [48]. GNO is disseminated planar in nature (rigid stack) over the MC composite, which exhibits a different pattern to GN and rGNO [49]. This phenomenon is attributed to the presence of carboxylic groups and the flat nature (Figure 1c) of the GNO regulated arrangement of the graphene flakes on MC. In addition, the relevantly sized GN flakes could fill the fissures during fabrication (Figure 1b–e). This could be described in terms of the magnitude of the GN flakes used, and the size of the carbon fibers and gaps present in the fabric. The diameter of the carbon fibers is approximately 7–9 µm, whereas the average size of the GN flakes is 25 µm. Thus, the large size of the GN flakes prevents homogeneous coating of the smaller carbon fiber in the carbon fabric, as shown in Figure 1b–e. As a result, the majority of the pores are covered by carbon flakes owing to infiltration

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in the carbon fabric while smaller GN flakes (2–5 µm) are deposited on the surface of the carbon fiber (Figure 1d). Aggregation Materials 2018, 11, x FOR PEER REVIEWof GN at the carbon-fiber (CF) joints was observed and is shown 5 of in 19 Figure 1b,d,e; this may enhance the hydrophobicity, EMI shielding, and electrical conductivity. Hence, the porosity of MC wasHence, attenuated by the of coating process (Figure and alignment of the GN electrical conductivity. the porosity MC was attenuated by1b–e) the coating process (Figure 1b– flakes can be tuned by oxidation (Figure 1c). This appears to be true based on our study. Ti AlC and e) and alignment of the GN flakes can be tuned by oxidation (Figure 1c). This appears to be true based 3 2 Ti3 C are layered that graphite (Figure 1f,g) gaps (Figure in Ti3 C21f,g) Tx (Figure 1g) on our Ti3AlCmaterials 2 and Ti3C 2Tx are are like layered materials that are[50]. like The graphite [50]. The 2 Txstudy. indicate eradication of Al,that and effective EDX strengthens this statement (Figure The surface gaps in that Ti3Ceffective 2Tx (Figure 1g) indicate eradication of Al, and EDX S3b). strengthens this of MXene-graphene foam arrangement of foam the GN flakes and with small pores statement (Figure S3b). Theillustrates surface ofthe MXene-graphene illustrates theMXene arrangement of the GN (Figureand 1h–k), where graphene flake accommodates several MXene flakes. This couldseveral be an flakes MXene withone small pores (Figure 1h–k), where one graphene flake accommodates effectiveflakes. way toThis enhance multiple and MXene could be an reflection effective and way absorption. to enhanceMoreover, multiple interconnected reflection and MXene absorption. graphene are responsible for electron The of MGNC MGNOC Moreover, interconnected MXene andmobility. graphene arecross-sections responsible for electronand mobility. Theconfirm crossthat the of formation of the foam, which is that a highly attractiveof structural for lightweight sections MGNC and MGNOC confirm the formation the foam,requirement which is a highly attractive EMI shielding (Figure 1j,k) [34,35]. TheEMI cross-sections of MGNC MGNOC visually confirm structural requirement for lightweight shielding (Figure 1j,k)and [34,35]. The cross-sections of the foam structure (Figure 1j–l). It is obvious the pore size of MGNOC is smaller than that of MGNC and MGNOC visually confirm the foamthat structure (Figure 1j–l). It is obvious that the pore size MGNC. Thisiscan be explained thickness of the thicknesses GNOMC, of MGNOC smaller than thatby of the MGNC. This can be material. explainedThe by the thicknessofofGNMC, the material. The rGNOMC, MGNC, andGNOMC, MGNOC rGNOMC, are 0.0191, MGNC, 0.0174, 0.0163, 0.0192, 0.035, and 0.0243 respectively. thicknesses of GNMC, and MGNOC are 0.0191, 0.0174,cm, 0.0163, 0.0192, The thickness of MGNOC is smaller than that ofof MGNC, which meansthan that that the pores in MGNOC 0.035, and 0.0243 cm, respectively. The thickness MGNOC is smaller of MGNC, which are small and is in arranged in a flat stack. Further, cross section of coated revealed the means that theGNO pores MGNOC are small and GNO the is arranged in a flat stack.fabric Further, the cross infiltration of GN,fabric GNO,revealed rGNO and (Figure S2a–f). Most of the GNO flake laid onS2a–f). the surface section of coated the MXene infiltration of GN, GNO, rGNO and MXene (Figure Most fabric while few penetrate (FigureofS2c). MGNC, MGNOC(Figure possessed hollow sphere of the GNO flake laid on the surface fabricThe while few penetrate S2c).internal The MGNC, MGNOC with numerous ballhollow like structure S2g,h). The the hollow sphere was large in MGNC possessed internal sphere (Figure with numerous ballsize likeofstructure (Figure S2g,h). The size of the whereas GNO densely packed with whereas small spheres The EDX confirms the(Figure constitutional hollow sphere was large in MGNC GNO(Figure denselyS2g,h). packed with small spheres S2g,h). elements Ti3 AlC2 the andconstitutional Ti3 C2 Tx (Figure S3a,b) and the2 etching Al and introduced F and The EDXofconfirms elements of that Ti 3AlC and Ti3removed C2Tx (Figure S3a,b) and that the Cl, derived from Al etching solution. The ratio is 6.27 and F/Cl solution. is 100.15, The confirming F isand the etching removed and introduced F and Cl,F/O derived from etching ratio F/Othat is 6.27 majorissurface group. mapping of the MGNC inveterate of the in F/Cl 100.15,functional confirming that FThe is the major surface functional group.distribution The mapping of elements the MGNC the composites are shown in Figure S3c–f. inveterate distribution of the elements in the composites are shown in Figure S3c–f.

Figure 1. 1. Microstructural Microstructuralimages imagesfrom fromscanning scanningelectron electron microscopy surface of MC (×500), Figure microscopy of of (a)(a) surface of MC (×500), (b) (b) surface of GNMC ( × 300), (c) surface of GNOMC ( × 300), (d) fiber surface of GNO-coated GNOMC surface of GNMC (×300), (c) surface of GNOMC (×300), (d) fiber surface of GNO-coated GNOMC (×2000),(e) (e) surface surface of of rGNOMC rGNOMC (×300), (×300),(f) (f)Ti Ti33AlC AlC2 2(×100,000), (×100,000),(g)(g)TiTi surface x (×50,000), 32C (×2000), 3C T2xT(×50,000), (h) (h) surface of of MGNC (×300), (i) MXene on surface of MGNC 3000), (j) cross-section of(×1000), MGNC(k) (×cross1000), MGNC (×300), (i) MXene on surface of MGNC (×3000),(×(j) cross-section of MGNC (k) cross-section MGNC(l)(× 3500) (l) cross-section of (×500). MGNOC (×500). section of MGNCof(×3500) cross-section of MGNOC

3.1.2. Raman Spectroscopic Analysis of the Structure of Carbon-Based Materials Raman spectroscopy is a prominent tool with which to investigate the structural and crystalline nature of Ti3C2Tx, and carbon-based materials including graphite materials [32,33]. In addition, the level of defect and disorder can be predicted by using (ID/IG) [6]. The ID/IG value of GN, GNO, rGNO

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3.1.2. Raman Spectroscopic Analysis of the Structure of Carbon-Based Materials Raman spectroscopy is a prominent tool with which to investigate the structural and crystalline nature of Ti3 C2 Tx , and carbon-based materials including graphite materials [32,33]. In addition, the level of defect and disorder can be predicted by using (ID /IG ) [6]. The ID /IG value of GN, GNO, Materials 2018, 11, x FOR 6 ofdefect 19 rGNO were 0.14, 0.23PEER andREVIEW 0.17, respectively (Figure S4). Hence, oxidation made more in GNO while reduction minimize the defect rGNO. Furthermore, GNMC, GNOMC, rGNOMC, MGNC, were 0.14, 0.23 and 0.17, respectively (Figure S4). Hence, oxidation made more defect in GNO while MGNOC and MC had (ID /IG ) value of 0.4, 0.84, 0.38, 0.17, 0.15 and 0.91 respectively. It was obvious reduction minimize the defect rGNO. Furthermore, GNMC, GNOMC, rGNOMC, MGNC, MGNOC thatand graphene coating diminished defects and films possessed less defects compare with fabric. MGNC MC had (ID/IG) value of 0.4, 0.84, 0.38, 0.17, 0.15 and 0.91 respectively. It was obvious that foam consisted littlediminished high defect thanand MGNOC as MGNC large hollow cavity MGNOC graphene coating defects films possessed lessown defects compare with fabric.than MGNC (Figure Introduction of hydroxyl functional lessen in carbon fabric carboxylic foamS2). consisted little high defect than MGNOC groups as MGNC owndefect large hollow cavity thanwhile MGNOC acid(Figure groupS2). increase the defects [37].functional Even though, carboxylic functional groups Introduction of hydroxyl groups lessen defect in carbon fabric while induced carboxylicplaner acid groupofincrease theflake defects [37]. 1c). Even though,the carboxylic planer arrangement graphene (Figure Further, in-plane functional vibrationalgroups mode induced of surface functional − 1 arrangement of graphene flake (Figure 1c). Further, the in-plane vibrational mode of surface groups Ti and C generate peaks at 624, 263, and 394 cm [51,52]. The weak broad band with similar −1 is attributed functional groups Ti and generate peaks at 624, andand 394 G-bands. cm −1 [51,52].InThe weak broad band intensities at 1350 and 1570Ccm to 263, the Daddition, the presence of −1 with similar intensities at 1350 and 1570 cm is attributed to the D- and G-bands. In addition, the − 1 anatase TiO2 caused peaks at 628, 510, and 396 cm (Figure 2b) [43,53]. The Raman spectra G-bands presence of anatase TiO2 caused peaks at 628, 510, and 396 cm−1 (Figure 2b) [43,53]. The Raman spectra of GN, GNO, and rGNO show bands at 1578, 1580, and 1579 cm−1 , respectively; these have higher G-bands of GN, GNO, and rGNO show bands at 1578, 1580, and 1579 cm−−11, respectively; these have intensities than the corresponding D-bands at 1351, 1352, and 1346 cm , respectively [51]. However, higher intensities than the corresponding D-bands at 1351, 1352, and 1346 cm−1, respectively [51]. − 1 rGNO showsrGNO a weaker at 1346 (Figure 2a). These results agree that However, showspeak a weaker peakcm at 1346 cm−1 (Figure 2a). These results agree thatGNGN-and and GN-based GNmaterials have higher crystallinity. Highly oriented pyrolytic graphite (HOPG) is a form of of ordered based materials have higher crystallinity. Highly oriented pyrolytic graphite (HOPG) is a form graphene sheets(GN) arranged over another; Raman of HOPG manifests as ordered(GN) graphene sheets one arranged one over the another; thespectrum Raman spectrum of also HOPG also −1 at 1 in −1 in manifests band cm−1E2g) (G mode E2g) which corresponds the band at 1578 a single bandasata single 1582 cm (G1582 mode which corresponds to the to band at 1578 cm−cm the GN . The raw material and production methods influence the disparity the GN[32,54,55]. spectrum The [32,54,55] spectrum raw material and production methods influence the disparity properties of properties of carbon fiber, in which the constituents resemble graphite [56]. Thespectrum Raman spectrum carbon fiber, in which the constituents resemble graphite [56]. The Raman of MC of exhibits MC exhibits numerous peaks, in which the D- and 2D-bands are placed at 1348–1374 cm-1 and 2680– − 1 numerous peaks, in which the Dand 2D-bands are placed at 1348–1374 cm and 2680–2740 cm−1 , 2740 cm−1, respectively; these values are from the corresponding boundaries of CF crystalline respectively; these values are from the corresponding boundaries of CF crystalline graphite. In addition, graphite. In addition, the presence of HOPG is confirmed by the G-band at 1503–1634 cm−1 (Figure −1 (Figure 2a) [32,33,56]. The use the presence of HOPG is confirmed by the G-band at 1503–1634 cm 2a) [32,33,56]. The use of PVDF as a binder in the GN coating influences the shape of the spectrum of PVDF binder in theinteractions GN coating the shape of the owing PVDF/GN owingas to athe PVDF/GN thatinfluences cause fluctuation at 2750 cm−1spectrum (2D-band), whichto is the absent in − 1 interactions that cause at 2750 (2D-band), which is absent in MC. The bands MC. The bands in thefluctuation spectrum split into acm few new bands owing to the PVDF molecules [57,58]. In in the spectrum split into aproduces few newweak bands to the PVDF molecules [57,58]. In addition, GNOMC addition, GNOMC 2Dowing band, whereas less oxidized composites exhibit a prominent −1 and new peak at 2750 cm−1 provide 2D band. At 2D the band, same time, the sharp band at 1503–1634 cmexhibit produces weak whereas less oxidized composites a prominent 2D band. At the same 1 and evidence thatband the GN coating occurs MC.new In addition, the MGNC and MGNOC composites time, the sharp at 1503–1634 cm−on peak at 2750 cm−1 provide evidence that the GN −1 while the G- and 2D-band intensities increase generate new peaks at 2452, 2976, and 3243 cm coating occurs on MC. In addition, the MGNC and MGNOC composites generate new peaks at 2452, significantly. This advocates that effective interaction occurred between MXene, GN, and the 2976, and 3243 cm−1 while the G- and 2D-band intensities increase significantly. This advocates that polymers (Figure 2b). effective interaction occurred between MXene, GN, and the polymers (Figure 2b).

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Figure 2. Normalized Raman spectra of (a) MXene, MC, GN, GNO, rGNO, and (b) composites. 2. Normalized Raman spectra of (a) MXene, MC, GN, GNO, rGNO, and (b) composites. 3.1.3. X-rayFigure Diffraction (XRD) Analysis

3.1.3. Diffraction (XRD) Analysis The X-ray crystalline or amorphous nature of the materials can be confirmed using XRD profiles [59,60].

XRD results of the pristine materials and composites are can shown in Figureusing 3a,b. XRD According The crystalline or amorphous nature of the materials be confirmed profiles to the [59,60]. XRD results of the pristine materials and composites are shown in Figure 3a,b. According to the XRD profiles, all of the materials display a crystalline nature. GN, GNO, and rGNO show two type of peaks: one intense peak 2θ located at 24.5°–27.5°, and another small peak 2θ positioned at

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XRDMaterials profiles, allxof the materials 2018, 11, FOR PEER REVIEW display a crystalline nature. GN, GNO, and rGNO show 7 of 19 two type of peaks: one intense peak 2θ located at 24.5◦ –27.5◦ , and another small peak 2θ positioned at ◦ . However, ◦ , 26.5◦ , However,the thelocation location of peak varies slightly such that is 26.56°, 54.854.8°. of 2θ 2θofofthe theintense intense peak varies slightly such2θthat 2θ is 26.5°, 26.56and ◦ represent GN, GNO, andand rGNO, respectively. The XRD pattern of Ti 3Cof 2TTi x confirms the and26.52°, 26.52 which , which represent GN, GNO, rGNO, respectively. The XRD pattern 3 C2 Tx confirms CaoCao et al.etreported that the delamination of MXeneofcan be confirmed by the the formation formationofofMXene. MXene. al. reported that the delamination MXene can be confirmed shifting of the from 9.3° 7.2° [61,62]. Hence, synthesized MXene consisting two peaks of at two ◦ to by the shifting ofpeak the peak fromto9.3 7.2◦ [61,62]. Hence, synthesized MXeneofconsisting 7.15° and ◦9.5° (002)◦ confirm the formation of partially delaminated Ti 3C2Tx. The composites show peaks at 7.15 and 9.5 (002) confirm the formation of partially delaminated Ti3 C2 Tx . The composites three different peaks of 2θ = 19.5°–21.5°, 25.5°–27.2°, and～54.8°. The high intense peaks are located at show three different peaks of 2θ = 19.5◦ –21.5◦ , 25.5◦ –27.2◦ , and ∼54.8◦ . The high intense peaks are 2θ = 25.5°–27.2°, where MGNOC, GNOMC, rGNOMC, MGNMC, GNMC, and MGNC are positioned located at 2θ = 25.5◦ –27.2◦ , where MGNOC, GNOMC, rGNOMC, MGNMC, GNMC, and MGNC at 26.62°, 26.56°, 26.64°, 26.6°, 26.75°, and 26.7°, respectively. The intense peaks are attributed to the ◦ , 26.64◦ , 26.6◦ , 26.75◦ , and 26.7◦ , respectively. The intense peaks are are presence positioned at 26.62◦ ,and 26.56 of graphene PVDF [59,60]. In addition, the intense peak is absent in MC where the attributed the presence andnature PVDFand [59,60]. In addition, the intense structure peak is absent in MC broadertopeak indicates of thegraphene amorphous presence of the graphite-like (Section where the broader peak indicates the amorphous nature and presence of the graphite-like structure 4.1.2) [63]. The peak at 2θ = 54.8 and 25.5°–27.2° confirms the presence of the graphene structure. In (Section 4.1.2,extra [63]).peaks The are peak at 2θ by = 54.8 andat25.5 confirms presence of two the graphene MGNMC, formed MXene 2θ ◦=–27.2 23.8°◦ and 27.9°. the PVDF generates weak ◦ ◦ shoulder peaks at 17.7° 20.6° to alpha PVDF, [60]. MGNC two structure. In 2θ MGNMC, extraand peaks arecorresponding formed by MXene atand 2θ =beta 23.8 andrespectively 27.9 . PVDF generates ◦ and ◦ corresponding and MGNOC2θ display single peaks 20.4°, which supports the peak due to PVDF.respectively This peak is [60]. weak shoulder peaksweak at 17.7 20.6at to alpha and beta PVDF, ◦ absent in the fabric-based composites owing to the low concentration of PVDF. MGNC and MGNOC display weak single peaks at 20.4 , which supports the peak due to PVDF. This peak is absent in the fabric-based composites owing to the low concentration of PVDF. rGNO

GNO

(a) Intensity (CPS)

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Figure 3. XRD of (a) rGNO, GNO, GN, MXene and (b) composites. Figure 3. XRD of (a) rGNO, GNO, GN, MXene and (b) composites.

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3.1.4. X-ray Photoelectron Spectroscopy (XPS) Analysis Materials 2018, 11, x FOR PEER REVIEW 8 of 19 XPS is useful technique that can deliver the structural nature and functional groups of the compound analyzed; a Gaussian–Lorentzian function is used to fit the XPS data. Thus, different binding 3.1.4. X-ray Photoelectron Spectroscopy (XPS) Analysis energy levels were identified by using fitted Ti2p, C1s, F1s, and O1s electron binding energy curves. XPS is useful technique that can deliver the structural nature and functional groups of the In addition, the bonding nature of diverse components is reported based on the chemical shift of compound analyzed; a Gaussian–Lorentzian function is used to fit the XPS data. Thus, different elements (Figure 4a–f) [64,65]. Table 1 expresses the constitutional elements in different proportions. binding energy levels were identified by using fitted Ti2p, C1s, F1s, and O1s electron binding energy In MXene, F isInaaddition, more dominant functional than OH. Theisatomic percentage of the oxygen reveals curves. the bonding nature ofgroup diverse components reported based on the chemical shift slight oxidation GN in GNO (Table 1). The1XPS Ti2p fitting curve confirms the presence of bonds of elementsof(Figure 4a–f) [64,65]. Table expresses the constitutional elements in different In MXene,and F is458.5 a more dominant group percentage such asproportions. TiO2 (464.5(2p1/2) (2p3/2) eV),functional Ti2+ (461.3 and than 456.4OH. eV),The andatomic Ti-C (454.5 eV). of Further, the oxygen reveals slight oxidation of GN in GNO (Table 1). The XPS Ti2p fitting curve confirms the C1s displays bonds such as C–Ti–Tx (281.1 and 283.2 eV), C–C (284.5 eV), and CHx/C=O (286.1 eV) bondsgives such as TiOto 2 (464.5(2p1/2) and 458.5 (2p3/2) eV), Ti 2+ (461.3 and 456.4 eV), and Tiwhere presence the C–Cofbond rise a high intense peak. The functional constitutions, namely TiO2 C (454.5 eV). Further, C1s displays bonds such as C–Ti–Tx (281.1 and 283.2 eV), C–C (284.5 eV), and (529.6 eV), C–Ti–(OH)x (531.1 eV), Al2 O3 (532.3 eV), and H2 Oads (533.8 eV) are inveterate by the O1s CHx/C=O (286.1 eV) where the C–C bond gives rise to a high intense peak. The functional fitting curve. The F1s fitting curve is purely responsible for the C–Ti–Fx bond. Hence, MXene is formed constitutions, namely TiO2 (529.6 eV), C–Ti–(OH)x (531.1 eV), Al2O3 (532.3 eV), and H2Oads (533.8 eV) with the Ti3by C2the T(OH, [52,66–68]. comprise mainly graphene C-C bonds with numbers of F) fitting areformula inveterate O1s curve. GNs The F1s fitting curve is purely responsible for the C–Ti–Fx C–O/C=O comprises 8.8% oxygen (TableTi1); C=OGNs or C–O belonging bond.bonds. Hence, MC MXene is formed with the formula 3Cnevertheless, 2T(OH, F) [52,66–68]. comprise mainlyto the C1s peak are notC-C observed prominently, is confirmed by the C1s fitting of (Table GN. However, graphene bonds with numbers which of C–O/C=O bonds. MC comprises 8.8%curve oxygen 1); nevertheless, C=O or C–O belonging thepeaks C1s peak areand not290.5 observed prominently, whichoriginate is the addition of PVDF introduces two maintonew at 286 eV. These peaks might confirmed by the C1s fitting curve of GN. However, the addition of PVDF introduces two main new from the C–C–F and C–F bonds, respectively, and the 286 eV peak arises owing to the MXene C=O peaks at 286 and 290.5 eV. These peaks might originate from the C–C–F and C–F bonds, respectively, bond (Figure 4f). In addition, the newly generated MGNC and MGNOC peak at 288.1 eV may arise and the 286 eV peak arises owing to the MXene C=O bond (Figure 4f). In addition, the newly owing to the addition of PAA and LiCl [68]. However, the intense peak intensity and corresponding generated MGNC and MGNOC peak at 288.1 eV may arise owing to the addition of PAA and LiCl binding energy causedthe byintense the composites vary asand follows: GNMC (284.17 GNOMC [68]. However, peak intensity corresponding bindingeV), energy causedand byrGNOMC the (284.25composites eV), MGNMC (284.21 eV), and MGNC and MGNOC (284.5 eV) (Figure 4f). The XPS graphs of vary as follows: GNMC (284.17 eV), GNOMC and rGNOMC (284.25 eV), MGNMC GN and othereV), coated carbonand composites showeV) a combination ofXPS GN, PVDF, carbon (284.21 and MGNC MGNOC (284.5 (Figure 4f). The graphs of and GN and otherfabric coatedpeaks. carbon of composites combination of GN, and carbonwhich fabric peaks. The amount of O from The amount O variesshow witha the combination ofPVDF, the composite, is strongly evidenced varies with the combination of the composite, which is strongly evidenced from the XPS data (Table the XPS data (Table 1). After the GN coating, we observed that there is defect at 285.0 eV, which may After the GNofcoating, we observed reduce1). the strength the GNMC fabric.that there is defect at 285.0 eV, which may reduce the strength

of the GNMC fabric.

TiO2 (2p3/2)

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Figure 4. Cont.

682

680

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GNMC GNOMC rGNOMC MGNMC MGNC MGNOC Mxene GNO GN

50,000 40,000 30,000 20,000 287.0 287.5 288.0 288.5 289.0 289.5 290.0 290.5 291.0 291.5

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0

0 292

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-10,000 280 281 282 283 284 285 286 287 288 289 290 291

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(e)

(f)

Figure 4. XPS fitting curves of of TiTi Ti2p(b) (b)C1s, C1s,(c)(c) O1s, (e) fitting of the GN xx (a) 3 C3C 2T Figure 4. XPS fitting curves 2T (a) Ti2p O1s, (d)(d) F1s,F1s, andand (e) fitting curvecurve of the GN C1s; (f) overlapping curves of of GNO, MXene,and and graphene/ MXene-graphene composites. C1s; (f) overlapping curves GNO,rGNO, rGNO, GN, MXene, graphene/ MXene-graphene composites. TableTable 1. Atomic percentages ofof TiTi GN,GNO, GNO,rGNO, rGNO, composites XPS analysis. 3C 2 2TTXX,, GN, 1. Atomic percentages 3C andand composites fromfrom XPS analysis. ElementsC1s (%) C1s (%) O1sO1s F1s (%) Elements (%)(%) F1s (%) MXene 20.54 14.86 58.27 MXene 20.54 14.86 58.27 MC MC 89.5489.54 8.8 8.8 - GNMC 81.38 2.46 15.31 GNMC 81.38 2.46 15.31 GNOMC 73.3473.34 15.02 GNOMC 8.168.16 15.02 rGNOMC 75.4975.49 1.71 rGNOMC 7.667.66 1.71 MGNC 2.41 MGNC 56.5556.55 33.69 33.69 2.41 GN GN 95.4295.42 4.074.07 - GNOGNO 92.4992.49 7.517.51 - rGNO 6.886.88 - rGNO 93.1293.12

Ti (%) (%) Ti 6.32 6.32 ----3.48 3.48 ----

SS(%) Cl (%)Cl (%) (%) N (%) N (%)Si (%) Si (%) -- -1.161.16 0.51 0.51 -0.850.85 -0.630.63 2.85 2.85 -- - 2.34 2.34 -1.551.55 0.52 0.52 - -- -- -

3.2. Surface Property of Composites 3.2. Surface Property of Composites The hydrophilicity associated with wettability plays a vital role in moistening the surfaces. A

The hydrophilicity associated with wettability plays a vital role in moistening the surfaces. contact angle above 90° is considered hydrophobic, and below 90° is hydrophilic. Water-loving A contact angle above 90◦ is considered hydrophobic, and below 90◦ is hydrophilic. Water-loving constitutions reduce the contact angle, whereas water-abhorring compounds increase the contact constitutions reduce the contact angle, compounds increase the contact angle. The contact angle can be tunedwhereas by usingwater-abhorring organic or inorganic materials [69]. The spreading of angle. The contact angle can be tuned by on using organic or inorganic materials The the liquid on the surface depends the surface energy between the solid and[69]. liquid. Thespreading increasing of the and surface causesenergy the hydrophobic [70].and When the roughness liquidsurface on theroughness surface depends on energy the surface between nature the solid liquid. The increasing increases, the airand is trapped in energy nano or micro grooves. This air minimizes the[70]. wetting area and surface roughness surface causes the hydrophobic nature When theleads roughness to hydrophobicity. Hence, the topography of the materials and their other properties, such increases, the air is trapped in nano or micro grooves. This air minimizes the wetting area andasleads to morphology, roughness, and chemical homogeneity, influences the surface wettability [71]. The hydrophobicity. Hence, the topography of the materials and their other properties, such as morphology, wetting ability of the composites are shown in Figure 4. GNMC, GNOMC, and rGNOMC exhibit a roughness, and chemical homogeneity, influences the surface wettability [71]. The wetting ability of hydrophobic nature at 125°, 124°, and 126°, respectively, whereas MGNC and MGNOC show the composites shown at in 78° Figure GNMC, GNOMC, rGNOMC exhibit a hydrophobic hydrophilicare behavior and4.81°, respectively. Theand wetting energies of GNMC, GNOMC, nature ◦ , 124◦ , and 126◦ , respectively, whereas MGNC and MGNOC show hydrophilic ◦ −1 at 125rGNOMC, behavior MGNC, and MGNOC are −41.85, −41, −42.82, 14.89, and 11.48 mN·m , respectively. It is at 78 ◦ , respectively. The wetting energies of GNMC, GNOMC, rGNOMC, MGNC, and MGNOC and 81 obvious that the positive wetting energy increases the hydrophilic nature. The most negative wetting 1 , respectively. m−1) 14.89, causes and the highest angle and the contact is incommensurate are −energy 41.85, (−42.82 −41, −mN· 42.82, 11.48 contact mN·m− It angle is obvious that the positive with the wetting energy. spreadingnature. coefficients of −114.65, −113.8, −115.62, −57.91,(− and −61.31 wetting energy increases the The hydrophilic The most negative wetting energy 42.82 mN·m−1 ) mN·m−1 were generated from GNMC, GNOMC, rGNOMC, MGNC, and MGNOC, respectively. The causes the highest contact angle and the contact angle is incommensurate with the wetting energy. spreading coefficient also expresses a similar behavior to the wetting energy in terms of hydrophobic The spreading coefficients of −114.65, −113.8, −115.62, −57.91, and −61.31 mN·m−1 were generated behavior. The rising work of adhesion increases the water-loving behavior, for instance, GNMC, from GNOMC, GNMC, GNOMC, rGNOMC, MGNC, engender and MGNOC, The spreading coefficient rGNOMC, MGNC, and MGNOC values respectively. of 30.95, 31.8, 29.98, 87.69, and 84.28 also expresses a similar behavior to the wetting energy in terms of hydrophobic behavior. The rising −1 mN·m , respectively; the increasing work of adhesion increases the hydrophilicity of the surface work [69,70]. of adhesion increases the water-loving behavior, for instance, GNMC, GNOMC, rGNOMC, Hence, coating the graphene-based materials increases the hydrophobicity of the surfaces. MGNC, and MGNOC engender values of 30.95, 31.8, 29.98, 87.69, and 84.28 mN·m−1 , respectively; the increasing work of adhesion increases the hydrophilicity of the surface [69,70]. Hence, coating the graphene-based materials increases the hydrophobicity of the surfaces. Tissera et al. reported that GO-coated cotton showed an improvement in hydrophobicity with a maximum contact angle of

Materials 2018, 11, 1803 Materials 2018, 11, x FOR PEER REVIEW 143◦ [72]. Zhang et al. reported that

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poly (vinylidene fluoride—hexafluoropropylene)/graphene Tissera et al. reported that GO-coated showedthis, an the improvement in hydrophobicity a composite is super hydrophobic in naturecotton [73]. Despite MXene-graphene-based foamwith exhibits maximum contact angle is ofdue 143° ZhangMXene et al. flakes. reported that poly (vinylidene a hydrophilic nature which to [72]. the surface The produced composite fluoride— can be used hexafluoropropylene)/graphene composite is super hydrophobic in nature [73]. Despite this, the to protected instruments from harmful water environments. MXene-graphene-based foam exhibits a hydrophilic nature which is due to the surface MXene flakes. produced composite can be used to protected instruments from harmful water environments. 3.3.The Electrical Conductivity

The electrical conductivity of MC is significantly affected by the spray-coating process. 3.3. Electrical Conductivity The incorporation of 2D materials in the polymer alters the electric conductivity owing to the The electrical conductivity of MC is significantly affected by the spray-coating process. The arrangement of the 2D material in the polymer matrix [74]. In graphene, the carbon atoms are incorporation of 2D materials in the polymer alters the electric conductivity owing to the arrangement arranged hexagonally with sp2 hybridization and the free π valance electron aligns at right angles to of the 2D material in the polymer matrix [74]. In graphene, the carbon atoms are arranged thehexagonally hexagonal plane. This electron is responsible for the out-of-plane π bond and electron mobility. with sp2 hybridization and the free π valance electron aligns at right angles to the Thehexagonal conductivity the electron graphene influences by of graphene layers. When the number plane.ofThis is responsible forthe the number out-of-plane π bond and electron mobility. The of layers increases, the electrical conductivity reduces, which is due to the interfacial alignment conductivity of the graphene influences by the number of graphene layers. When the number of of GNlayers which increasethe the resistance [75]. GNOMC electric conductivity increases, electrical conductivity reduces,displays which isthe duehighest to the interfacial alignment of of GNthe composites, whichthe is supported by the SEM image of GNOMC (Figure 1c).conductivity GNO arranges in a which increase resistance [75]. GNOMC displays the highest electric of the flat-stack manner with possible touching of the GNO flakes, which leads to interfacial electron transfer. composites, which is supported by the SEM image of GNOMC (Figure 1c). GNO arranges in a flatHence, best option tuneflakes, the self-assembly flakeselectron on the MC matrix. stacketching mannerwith withHNO possible touching of theto GNO which leadsof toGNO interfacial transfer. 3 is the TheHence, conductivity inversely to the thickness [76], and the conductivity and Ron GNOMC etchingiswith HNO3proportional is the best option to tune the self-assembly of GNO flakes MC s ofthe −1 and 4.2 Ωis·sq −1 , respectively, inversely proportional the thickness [76], and the conductivity and Rs arematrix. 13.68 SThe ·cmconductivity at ato thickness of 0.0174 cm (Figure 5). Nevertheless, −1 and 4.2 Ω·sq−1, respectively, at a thickness of 0.0174 cm (Figure of GNOMC are from 13.68 the S·cm 5). GNOMC deviates MGNC behavior, exhibits a low electric conductivity (9.3 S·cm−1 ) while − 1 Nevertheless, GNOMC deviates from the a low electricexhibits conductivity showing the lowest sheet resistance (3.1 Ω ·sqMGNC ) at a behavior, 0.0350 cmexhibits thickness; MGNOC 8.97 S·(9.3 cm−1 −1 −1 1 sheet resistance S·cm ) while the lowestand sheet resistance (3.1 Ω·sq at the a 0.0350 cm thickness; MGNOC with a 4.6 Ω·sq−showing thickness of 0.0243 cm.) Of fabricated composite, MGNC −1 with a 4.6 Ω·sq−1 sheet resistance and thickness of 0.0243 cm. Of the fabricated exhibits 8.97 S· cm shows a maximum thickness of 0.0350 cm, while the others, such as GNMC (0.0191 cm), GNOMC composite, MGNC shows a maximum thickness of 0.0350 cm, while others, such as GNMC (0.0191 (0.0174 cm), rGNOMC (0.0163 cm), MGNMC (0.0192 cm), and MCthe (0.0127 cm) exhibit values below cm), GNOMC (0.0174 cm), rGNOMC (0.0163 cm), MGNMC (0.0192 cm), and MC (0.0127 cm) exhibit 0.0200 cm. Hence, the highest thickness of MGNC minimizes the electric conductivity. In addition, values below 0.0200 cm. Hence, the highest thickness of MGNC minimizes the electric conductivity. MGNMC shows the highest Rs value owing to the aggregation of the hydrophobic PVDF and In addition, MGNMC shows the highest Rs value owing to the aggregation of the hydrophobic PVDF hydrophilic MXene. The highest electrical mobility increases the EMI SE. Hence, the lowest sheet and hydrophilic MXene. The highest electrical mobility increases the EMI SE. Hence, the lowest sheet resistance of MGNC causes it to possess the highest surface electron mobility, which leads to the surface resistance of MGNC causes it to possess the highest surface electron mobility, which leads to the reflection of EMI SE [47]. Further, the resistivity of GNOMC, rGNOMC, GNMC, MGNMC, MGNC and surface reflection of EMI SE [47]. Further, the resistivity of GNOMC, rGNOMC, GNMC, MGNMC, MGNOC 0.073, 0.083, 0.111 Ω·and cm, respectively. Despite theDespite conductivity MGNCwere and MGNOC were0.087, 0.073,0.101, 0.083,0.108 0.087,and 0.101, 0.108 0.111 Ω·cm, respectively. the depend on thickness of on thethickness materials.ofThe increased the resistivity conductivity depend the functionalized materials. The graphene functionalized graphene increased while the presence of MXene significantly increased the resistivity of the fabric and foam (Figure 6b). Despite this, resistivity while presence of MXene significantly increased resistivity of fabric and foam (Figure other thickness such and as some other and structural features (foams) also influence EMI 6b).parameters Despite this,such otherasparameters thickness some other structural features (foams) also SE influence [46]. Further, the[46]. lowest Rs and resistivity of MGNC is due to the presence of MXene onofthe EMI SE Further, thehigh lowest Rs and high resistivity of MGNC is due to the presence surface of on thethe composite 1i). Further explanation is explanation given in theisEMI-shielding section. MXene surface of(Figure the composite (Figure 1i). Further given in the EMI-shielding section.

Figure Contact anglesofof(a) (a)GNMC, GNMC,(b) (b)GNOMC, GNOMC, (c) (c) rGNOMC, Figure 5. 5. Contact angles rGNOMC,(d) (d)MGNC, MGNC,and and(e)(e)MGNOC. MGNOC.

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Figure 6. (a) Electric conductivity and sheet resistance of the composites and (b) resistivity of the composites (Rs: sheet resistance; σ: electric conductivity). Figure 6. (a) Electric Electric conductivity conductivity and and sheet sheet resistance resistance of of the composites composites and (b) resistivity of the composites (R sheet resistance; σ: electric conductivity). : sheet resistance; σ: electric conductivity). s 3.4. Electromagnetic Shielding Effectiveness of Composites

3.4. Electromagnetic Shielding Effectiveness of this study, solution and spray coating were performed to produce EMI shielding 3.4.In Electromagnetic Shieldingcasting Effectiveness of Composites Composites composites. MC was spray-coated by a dispersed mixture of GN, GNO, and rGNO (3 g·L−1) and PVDF In In this this study, study, solution solution casting casting and and spray spray coating coating were were performed performed to to produce produce EMI EMI shielding shielding −1 − 1 ) and (5composites. g·L ) in in aMC DMF solution. The thickness of MC was adjusted by changing therGNO number of·L coating was spray-coated a dispersed mixture of GN, GNO, composites. MC was spray-coated byby a dispersed mixture of GN, GNO, and and rGNO (3 g·L(3−1)gand PVDF −1 )EMI cycles. All of the SEa calculations were carried out according to the Gamage et al. study.the The EMI PVDF (5 g · L in in DMF solution. The thickness of MC was adjusted by changing number −1 (5 g·L ) in in a DMF solution. The thickness of MC was adjusted by changing the number of coating shielding of all of the composites is illustrated in Figure 7. It is obvious that all of the composites of coating cycles. AllSE ofcalculations the EMI SEwere calculations were carried to outthe according to al. thestudy. Gamage al. cycles. All of the EMI carried out according Gamage et The et EMI show a maximum EMI SE inofthe frequency range ofis1.9–2.6 GHz in in Figure S band 7. region whereasthat GNMC study. The EMI shielding all of the composites illustrated It is obvious all of shielding of all of the composites is illustrated in Figure 7. It is obvious that all of the composites showed increasing trend in X band region other composites exhibited slight downward the composites show maximum EMI SEand in the frequency range GHz in S bandtrend. region show a maximum EMIa SE in the frequency range of 1.9–2.6 GHz inofS1.9–2.6 band region whereas GNMC Ofwhereas the composites, MGNC yields the maximum and minimum EMI shielding of 41 and 31 slight dB, GNMC showed increasing trend in X band region and other composites exhibited showed increasing trend in X band region and other composites exhibited slight downward trend. respectively, whereas MGNOC exhibitsMGNC a 36 dByields maximum and 23.14 dBminimum minimum EMIshielding shielding in41 downward trend. OfMGNC the composites, the maximum Of the composites, yields the maximum and minimum and EMI shieldingEMI of 41 and 31ofdB, S and band31region. The maximum EMI shielding of GNMC, GNOMC, rGNOMC, MGNMC, MC, and dB, respectively, whereas MGNOC a 36 dBand maximum 23.14 dBEMI minimum EMI respectively, whereas MGNOC exhibits a 36exhibits dB maximum 23.14 dBand minimum shielding in GNMC-single are 35.3, 36.2,The 34.6, 35.2, 28.5, and 33.4 dB, respectively, and rGNOMC, the corresponding shielding in S band region. maximum EMI shielding of GNMC, GNOMC, MGNMC, S band region. The maximum EMI shielding of GNMC, GNOMC, rGNOMC, MGNMC, MC, and minimum EMI shieldingare is 35.3, 28.4, 36.2, 29.7,34.6, 28.4,35.2, 28.8, andand 23.2, 28dB, dB,respectively, respectively. EMI MC, and GNMC-single andThe the average corresponding GNMC-single are 35.3, 36.2, 34.6, 35.2, 28.5, 28.5, and 33.433.4 dB, respectively, and the corresponding shielding of GNMC, GNMC-single, GNOMC, rGNOMC, MGNMC, MGNC, and MGNOC is 32, 30, minimum 29.7, 28.4,28.4, 28.8,28.8, and 23.2, dB, 28 respectively. The average shielding minimum EMI EMIshielding shieldingis 28.4, is 28.4, 29.7, and 28 23.2, dB, respectively. The EMI average EMI 32.66, 31.43, GNMC-single, 31.87, 35.7, andGNOMC, 32.86 dB,rGNOMC, respectively in S band region. This trend changed in X band of GNMC, MGNMC, MGNC, and MGNOC is 32, 30, 32.66, 31.43, shielding of GNMC, GNMC-single, GNOMC, rGNOMC, MGNMC, MGNC, and MGNOC is 32, 30, region that can be represented as follow,S band the maximum EMI shielding of in GNMC 53.89 dB with 31.87, 32.86 dB,and respectively region. changed X band region can 32.66, 35.7, 31.43,and 31.87, 35.7, 32.86 dB,inrespectively in SThis bandtrend region. This trend changed in that X band reflection of 13.10 dB and absorption of 43.38 dB (Figure 7 and Table S2). The maximum EMI SE range be represented as follow, the maximum EMI shielding of GNMC 53.89 dB with reflection of 13.10 dB region that can be represented as follow, the maximum EMI shielding of GNMC 53.89 dB with ofand composites was 53.89–31.73 dB while minimum range was 52.4–30.15 dB (Table S2). The maximum absorption ofdB 43.38 (Figure 7 of and Table The7maximum SE range of composites was reflection of 13.10 anddB absorption 43.38 dBS2). (Figure and Table EMI S2). The maximum EMI SE range reflection lossdB(SE R) and absorption loss (SE A) range were 14.75–11.73 dB and 43.38–20.01 dB, 53.89–31.73 while minimum range was 52.4–30.15 dB (Table S2). The maximum reflection loss of composites was 53.89–31.73 dB while minimum range was 52.4–30.15 dB (Table S2). The maximum respectively (Table S2).loss Further, SE R was high in GNMC with 14.75 dB of maximum while exhibited (SE ) and absorption (SE ) range were 14.75–11.73 dB and 43.38–20.01 dB, respectively (Table S2). R A reflection loss (SER) and absorption loss (SEA) range were 14.75–11.73 dB and 43.38–20.01 dB, maximum absorption of 26.97 dB. Among fabricated fabric, absorption played a major role in EMI Further, SER (Table was high GNMC SE with 14.75 dB of maximum while exhibited maximum absorption of respectively S2).inFurther, R was high in GNMC with 14.75 dB of maximum while exhibited shielding. 26.97 dB. Among fabricated fabric, absorption played afabric, majorabsorption role in EMIplayed shielding. maximum absorption of 26.97 dB. Among fabricated a major role in EMI shielding. MC 38 40 36

EMI SE (dB) EMI SE (dB)

38 34 36 32 34 30 32 28 30 26 28

GNMC GNOMC rGNOMC MGNMC MC MGNC GNMC MGNOC GNOMC

55

50 55

EMI SE (dB) EMI SE (dB)

MC GNMC-single GNMC GNOMC rGNOMC MGNMC MC MGNC GNMC-single MGNOC GNMC GNOMC rGNOMC MGNMC MGNC MGNOC

40

rGNOMC MGNMC MGNC MGNOC

45 50

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12 of 19 12 of 19 MC GNMC GNOMC rGNOMC MGNMC MGNC MGNOC

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100 MX/PET Cu bulk

90 80

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70

EMI SE (dB)

stainless steel

CNT/Polym

MX/foam Al foil

60

Ni fiber MGNC- X band

rGO/PbTiO3 CNT/PP

50 MGNC-S band

MWCNT/PC

40

GN/PVDF

GNP/B4C MWCNT/PS

30

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20 10 -0.5

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Figure 7. 7. EMI shielding SE in inS-band, S-band,(b) (b)EMI EMISESEinin X-band, Figure EMI shieldingeffectiveness effectivenessofofcomposites composites (a) (a) EMI SE X-band, (c)(c) SER , SE(d) R, (d) SE A , (e) comparison of EMI SE with thickness and (f) Basic mechanism in MGNC. SEA , (e) comparison of EMI SE with thickness and (f) Basic mechanism in MGNC.

The mechanism GNMC can explained. according structure that MXene film and The mechanism of of GNMC can bebe explained. according to to structure that thethe MXene film and graphene nanoplates reflects incident rays caused moving charges while internal hollow structure, graphene nanoplates reflects incident rays caused byby moving charges while internal hollow structure, free carriers layered structure of MXene caused multiple reflection and scattering the free carriers andand layered structure of MXene caused multiple reflection and scattering within within the core, core, leads finallytoleads to absorption the highest EMI shielding of MGNC arisesto owing finally absorption [77,78]. [77,78]. Further,Further, the highest EMI shielding of MGNC arises owing its to its physical nature, i.e., lowest sheet resistance, highinternal resistivity, internal pores, and thickness physical nature, i.e., lowest sheet resistance, high resistivity, pores, and thickness (Figure 6b). (Figurethe 6b). AmongMC the composites, fabricated MC composites, shows highestinEMI shielding Among fabricated GNOMC showsGNOMC the highest EMI the shielding S band regionin S band region owing to the planer nature causedgroup by thederived functional groupofderived means owing to the planer nature caused by the functional by means etchingby [79]. Evenof etchingin[79]. Even though, in XMGNMC band region, GNMC, MGNMC rGNOMC higher though, X band region, GNMC, and rGNOMC exhibitedand higher EMI SEexhibited compare with EMI SE compare with GNO as they possessed relatively higher reflection and absorption loss GNO as they possessed relatively higher reflection and absorption loss (Figure 7b–d and Table S2). (Figure andcorrelated Table S2).with Thiscross can section be further correlated withcores crossand section of fabric that GN, made This can be7b–d further of fabric that made randomly arrange coresand andMXene randomly GN, rGNO(Figure and MXene flake caused 7b–d and rGNO flakearrange caused absorption 7b–d and Table S2). absorption In addition,(Figure GNO exhibited Table S2). In addition, GNO exhibited EMI shielding in S band region due toitsthe high EMI shielding in S band region whichhigh is due to the high conductivity and inwhich X bandisregion high and in X band region its EMIresponse SE decrease significantly owing to dielectric response EMI SEconductivity decrease significantly owing to dielectric rather than electron mobility [80]. Further, rather than electron mobility [80]. Further, planar structure of GNOMC diminished absorption planar structure of GNOMC diminished absorption (Figure 7b–d and Table S2). Formation of (Figure 7b–d andpromotes Table S2).interfacial Formation of functional promotes interfacial of the functional groups touching of the groups flake-created planner surfacetouching with higher flake-created planner1csurface with higherand conductivity and 7). GNMC and MGNMC conductivity (Figures and 7). GNMC MGNMC (Figures display 1c similar EMI shielding values. display similar EMI shielding values. However, MXene-graphene foam good EMI shielding However, MXene-graphene foam exhibits good EMI shielding which canexhibits be explained by the fact which can be explained by the fact that the coating of and hydrophilic MXene colloidal solution and that the coating of hydrophilic MXene colloidal solution the hydrophobic GN-PVDF polymer the hydrophobic GN-PVDF coatingtoon carbon between fiber are MXene limited and owing to the adhesion coating on the carbon fiber arepolymer limited owing thethe adhesion graphene. Thus, between electron MXene and graphene. Thus, interfacial transfer is minimized owing the improper interfacial transfer is minimized owing to electron the improper arrangement of GN andto MXene flake arrangement of GN and MXene(Figure flake increasing resistance 7). Hence, the (Figure reflection increasing the surface resistance 7). Hence,the thesurface reflection was low(Figure for all the composite wasand lowTable for allS2). the The composite 7b–d andeffectiveness Table S2). The specific EMI shielding effectiveness 7b–d specific(Figure EMI shielding (SSE) of MC, GNMC-single, GNMC, (SSE) of MC, GNMC-single, GNMC, GNOMC, rGNOMC, MGNMC, MGNOC is 381.5, GNOMC, rGNOMC, MGNMC, MGNC, and MGNOC is 381.5, 452.73,MGNC, 394.91, and 189.90, 183.8, 185.3, 46.4, and 56.18 dB·cm3·g−1, respectively; the single GN-coated composite shows the highest SSE. Furthermore, SSE range of all the composite in X band region was 449.95–68.05 dB·cm3·g−1 (Table S2).

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452.73, 394.91, 189.90, 183.8, 185.3, 46.4, and 56.18 dB·cm3 ·g−1 , respectively; the single GN-coated composite shows the highest SSE. Furthermore, SSE range of all the composite in X band region was 449.95–68.05 dB·cm3 ·g−1 (Table S2). Of the fabricated single-coated composites, GNMC shows the highest absolute EMI shielding effectiveness (SSE/t) of 35,369.82 dB·cm3 ·g−1 , whereas MC, GNMC, GNOMC, rGNOMC, MGNMC, MGNC, and MGNOC exhibit values of 30,039, 10,914, 11,275.78, 9649.42, 1324.29, and 2311.83 dB·cm3 ·g−1 , respectively in S band region while SSE/t of composite in X band region was 35428.4–1944.3 dB·cm3 ·g−1 in which MGNC displayed lowest SSE/t (Table S2). Further, the thickness influences the EMI shielding. Reducing the amount of PVDF increases SSE/t (PVDF (1 g·L−1 ) and GN (3 g·L−1 ) in DMF, yielding 31,095.13 dB·cm2 ·g−1 in S band region). According to reported data, PVDF exhibits an EMI shielding effectiveness of approximately 1.1 dB, which is not an effective barrier against electromagnetic radiation compared with carbon-based PVDF composites [48]. Most of the carbon base composite reported showed lower EMI shielding compared to the composite produced and thickness proportional to EMI SE and increasing graphene loading increase the EMI SE. However, in each case, equal amount of dispersed solutions was utilized. Thus, in this case, not only component loading but also structural feature of composite affect EMI SE (Table S1 and Figure 1, Figure 7e and Figure S2) [77,81,82]. Further, the MXene based composite with less thickness generate relatively good EMI SE compare with other composite reported (Figure 7e) and the Al and Cu foil show exceptional EMI shielding of approximately 70 dB (~10 µm). Gonzalez et al. reported that the reflection from CNT and graphene is approximately 10 dB with an absorption of 20 dB. At the same time, ultrathin graphene-based composites have also shown a lower reflection of approximately 10 dB [75,83–85]. According to Zhao et al. the EMI shielding of the PVDF/graphene composite was 22.58 dB at a thickness 0.1 mm and electrical conductivity of 6.56 × 10−3 S·cm−1 [40]. Poly (ether imide) (PEI-rGO nanocomposite films exhibited EMI shielding values of approximately 26 dB at a thickness of 0.086 mm [41]. PVDF/graphene quantum dots showed a 31 dB EMI shielding at an 8 GHz frequency. Further, Ag-nanoparticle reinforced PVDF/graphene quantum dots increase EMI shielding (43 dB at 12 GHz) [42]. Hence, the composition, amount, and status of graphene in the composition alter the EMI shielding. In addition, the incorporation of nanoparticles improves the EMI shielding of the graphene composites [40–42]. Yuan et al. reported that reduced graphene oxide nano-composite films exhibit EMI shielding of 32 dB with 0.27 mm [85]. Based on the literature reviewed, our study shows excellent EMI shielding effectiveness over a frequency range of 1–3 GHz and 8–12.4 GHz. 3.5. Thermal Stability and Thermo Gravimetric Analysis of Composites Thermal stability studies were carried out using well-known thermogravimetric analysis (TGA) and differential thermal analysis (DTG). The temperature range was maintained from room temperature to 1000 ◦ C with a heating rate of 10 ◦ C·min−1 , and during the TGA and DTG analysis, the Al2 O3 crucible and nitrogen environment were maintained. The mass loss and enthalpy changes were investigated using TGA and DTG, respectively. All of the samples exhibit outstanding stability over a higher temperature range (Figure 8a). Swift degradation of all of the composites occurred about 375 ◦ C to 500 ◦ C, which is higher than that of MC, which exhibits a 5% weight loss between 280 ◦ C and 400 ◦ C [7]. Further, MGNOC and MGNC exhibit a 65% and 52% weight loss, respectively, whereas the MC-based composites exhibit a loss of 20% in the aforementioned temperature range. These composites (MGNOC and MGNC) show a higher weight loss than MC (6.5%) [7]. This is due to the introduction of a polymer binder (PVDF and PAA) and GN/GNO to the composite [60,86]. The weight-loss temperature of pristine PVDF and graphene are approximately 400 and 200 ◦ C, respectively [87–91]. We noticed that all of the fabrics exhibit similar behavior below 400 and above 500 ◦ C. All of the fabric shows a minimal weight loss (~20%) which is due to the introduction of graphene species and MXene (Table 2). In addition, the thermal stability of the composites can be altered by amount filler loading, types of polymers used, environment of experience, exposure temperature and duration of exposure of the composites. Presence of oxygen environment burn both polymer, MXene and graphene [92]. The MC had the minimum temperature of the degradation was 40 ◦ C and 174 ◦ C. This trend changed

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after introduction of graphene (Table 2). Though, minimum degradation temperature of the all composite bellow 300 °C that is intermediate temperature of graphene and PVDF. The introduction Materials 2018, 11, x FOR PEER REVIEW 14 of 19 of the oxygen on graphene increase the weight loss considerably (Table 2). On the whole, PVDF, graphene, MXene filmfabric-based possessed low thermal stability compare carbon fabric-based composites. compare with carbon composites. Hence, the carbonwith fabric induces the thermal stability Hence, the carbon fabric induces the thermal stability of the composite [7]. MGNC and MGNOC of the composite [7]. MGNC and MGNOC lost 5% and 20% weight at approximately 100 °C which lost 20%water weight atand approximately 100 ◦ C which was due up to the water and then both was5% dueand to the loss, then both constrained degradations to 400 °C. loss, In addition, above ◦ C. In addition, above 400 ◦ C, MGNC and MGNOC exhibit a 50% constrained degradations up to 400 400 °C, MGNC and MGNOC exhibit a 50% and 65% weight loss, respectively. The DTG curve of the and 65% weight loss, respectively. The curve of the composites shows endothermic peaks at composites shows endothermic peaks at DTG different positions. GNMC, GNOMC, rGNOMC, MGNMC, different GNMC, GNOMC, rGNOMC, MGNC, MGNOC prominent MGNC, positions. and MGNOC show prominent peaks atMGNMC, 476.9, 468.7, 490.5,and 422.4, 453.1, show and 469.33 °C, peaks at 476.9,(Figure 468.7, 8b). 490.5, 422.4, 453.1, where and 469.33 respectively (FigureIn8b). This indicated where respectively This indicated rapid◦ C, weight loss occurred. addition, MC exhibits a rapid loss occurred. addition, MC exhibits a the broad endothermic peak indramatically the range of broadweight endothermic peak in theInrange of 243–390 °C Hence, stability of the composite increases◦ Cwith the coating process. Thecomposite introduction of MXene increases minimizeswith the the degradation of the 243–390 Hence, the stability of the dramatically coating process. composite, which all of the showwhich a lowmeans thermal The introduction of means MXenethat minimizes the MXene-based degradation ofcomposites the composite, thatstability. all of the Further, GNOMC and rGNOMC show another endo-thermic at 350and °C,rGNOMC which is more MXene-based composites show a low thermal stability. Further,peak GNOMC showintense another ◦ C,introduction in rGNO thanpeak in GNO. of intense GNO and rGNO than generates newThe peaks where they endo-thermic at 350The which is more in rGNO in GNO. introduction ofwere GNO absent in GN, and a similar peak is observed at 313 °C, which shifts to a lower temperature owing and rGNO generates new peaks where they were absent in GN, and a similar peak is observedtoat the ◦presence MXene. and MGNOC exhibit endo-thermic at 117 owing 313 C, whichofshifts to a MGNC lower temperature owing to the the same presence of MXene.peaks MGNC and°C MGNOC ◦ C owing to the thermal pores, LiCl, and PAA. The TG oGN/PVDF, curve supports this exhibit the sameconductivity endo-thermicoGN/PVDF, peaks at 117internal to the thermal conductivity internal statement [76]. Finally, the rGO-based composite displays a higher thermal stability than the other pores, LiCl, and PAA. The TG curve supports this statement [76]. Finally, the rGO-based composite composites fabricated. displays a higher thermal stability than the other composites fabricated.

Figure and (b) (b) DTG DTG curves curves of of composites. composites. Figure 8. 8. (a) (a) TGA TGA and Table 2. Comparison of mass changes of composites. Table 2. Comparison of mass changes of composites. No.

Composites

No.

Composites

1 1 2 23 34 45

GNMC GNMC GNOMC GNOMC rGNOMC rGNOMC MGNMC MGNC MGNMC

56

MGNC MGNOC

6

MGNOC

7

MC

7 MC 4. Conclusions

Rapid Change Range (◦ C) Range (°C) 425–505 425–505 435–500 435–500 460–510 460–510 420–510 373–490 420–510 35–75 373–490 375–510 35–75 175–570 375–510

Rapid Change

Rapid Mass Change (%) Change (%) 15.5 15.5 11.6 11.6 16.1 16.1 12.0 38.6 12.0 22.1 38.6 32.6 22.1 6.2 32.6

Rapid Mass

Whole Mass Whole Mass Change (%)

175–570

6.2

6.5

Change (%) 26.0 26.0 19.5 19.5 22.2 22.2 19.1 52.1 19.1 52.1 65.5 65.5

6.5

Degradation Starting Degradation Starting Temperature (◦ C)

Temperature (°C) 245.0 245.0 245.0 245.0 265.0 265.0 275.0 78.5 275.0 35.0 78.5 75.5 35.0 40.0 75.5 174.0 40.0 174.0

Spray-coated composites and solvent casting films were successfully fabricated with high 4. Conclusions flexibility, low apparent density (~0.77 to 0.081 g·cm−3 ) and low thickness (0.0120–0.0350 cm). Spray-coated composites and solvent casting films were successfully fabricated with high The fabricated composites exhibited an uppermost contact angle of 126◦ and the range of wetting flexibility, low apparent density (~0.77 to 0.081 g·cm−3) and−low thickness (0.0120–0.0350 cm). The energy of all of the composites was −42.82 to 14.89 mN·m 1 . Thus, graphene-based constitutions fabricated composites exhibited an uppermost contact angle of 126° and the range of wetting energy of all of the composites was −42.82 to 14.89 mN·m−1. Thus, graphene-based constitutions improve the hydrophobicity. The surface-coated MXene and graphene oxide minimized the sheet resistance and showed a high conductivity of 13.68 S·cm−1 with a sheet resistance of 3.1 Ω·sq−1. The MXene-graphene-

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improve the hydrophobicity. The surface-coated MXene and graphene oxide minimized the sheet resistance and showed a high conductivity of 13.68 S·cm−1 with a sheet resistance of 3.1 Ω·sq−1 . The MXene-graphene-PVDF composition improved the thermal stability and constrained the dramatic weight changes up to 400 ◦ C. The flat stack-like composition displayed an excellent EMI shielding of 41 dB (99.99% efficiency) in S band while exhibited maximum EMI shielding of GNMC 53.8 (99.999%) with reflection of 13.10 dB and absorption of 43.38 dB (Figure 7 and Table S2). and the size of the pore comparatively advanced the property of EMI shielding. The single-coated graphene fabric showed an outstanding absolute shielding effectiveness of 35,369.82 dB·cm2 ·g−1 . Hence, the composites with high EMI SEs and that are hydrophobic in nature can be applied in various applications such as aeronautics, locators, air travel, mobile phones, handy electronics, and military application. Supplementary Materials: The following are available online at http://www.mdpi.com/1996-1944/11/10/1803/ s1, Figure S1: EMI shielding sample loading; Figure S2: Cross section of SEM image; Figure S3: EDX and mapping; Figure S4: Normalized curve of Raman spectrum; Table S1: Comparison of EMI SE with thickness; Table S2: Comparison of maximum (MAX), minimum (MINI), average (AVE) shielding, SSE and SSE/t of composite in each case. Author Contributions: K.Y.C. and R.B. designed the project; K.R., B.M.K. and J.J.M. were performed experiment; H.J.J. and Y.S.L. were analyzed the data; C.M.Y. supervised the analysis; K.R. wrote the manuscript. Funding: This research was supported by the Leading Human Resource Training Program of Regional Neo industry through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and future Planning (NRF-2017H1D5A1043865). C.M.Y. acknowledges the financial support from the Korea Institute of Science and Technology (KIST) Institutional Program and from Nanomaterial Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2016M3A7B4027695). Conflicts of Interest: There are no conflicts to declare.

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