## 1 Introduction  
Graphene was discovered in 2004, breaking the classical theory that thermodynamic fluctuations do not happen in any two-dimensional (2D) crystal at a finite temperature [1,2]. Graphene had shown many excellent physical and chemical properties into wide material applications, such as big specific surface area is (2630 m\({}^{2}\)/g) [3], high electron mobility (\(1.5\times 10^{5}\) cm\({}^{2}\)/v-s) [4], good thermal conductivity (5000 W/m-K) [5], high Young's modulus (1.0 TPa) [6] and visible light transmittance (approximately 97.7%) [7]. However, the zero-band gap of graphene limits its application in the field of electronic devices, leading to a series of studies on graphene-like 2D materials [8], such as hexagonal boron nitride, transition metal sulfur compounds, transition metal oxides, black phosphorus and various MXenes. Many graphene-like materials making up for the inadequacy of graphene materials showed better physical and chemical properties, and then were applied in optoelectronics, spintronics, catalysis, biological and chemical sensors, lithium/sodium ion batteries, supercapacitors, fuel cells, polymer composite materials and other fields [9]. MXene is a new kind of graphene-like nanosheet, which is composed of transition metals and carbon/carbonitride/nitride compounds. In 2011, the [PERSON] used HF acid to selectively etch the Al atomic layer of ternary-layered carbide material Ti\({}_{3}\)AlC\({}_{2}\) to obtain Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) (T\({}_{x}\) stands for the surface terminations, for example, hydroxyl, oxygen or fluorine) [10]. Ti\({}_{3}\)AlC\({}_{2}\) is a MAX phase material, namely a typical ternary-layered ceramic. Generally, they may be shown as M\({}_{n+1}\)AX\({}_{n}\), M meaning the early transition metal, such as Sc, Ti, V, Zr, Hf, Nb, Ta, Cr and Mo, A meaning the main group 13-14 elements in the periodic table, such as Al, Si, P, S, Ga, As, In and Sn and X meaning C or N. n is generally 1, 2 or 3 [11]. Ti\({}_{3}\)C\({}_{2}\)T\({}_{x}\) has the precursor MAX structure and its properties are similar to the graphene. Thus, it was named MXene. The graphene-like MXene nanosheet may be shown as M\({}_{n+1}\)X\({}_{n}\)T\({}_{x}\), where T\({}_{x}\) is the functional group attached to the surface of MXene, such as -O, -OH and -F. M\({}_{2}\)XT\({}_{x}\), M\({}_{3}\)X\({}_{2}\)T\({}_{x}\) and M\({}_{4}\)X\({}_{3}\)T\({}_{x}\) structures for \(n\) = 1, 2 and 3, respectively, had been created [12]. Recently, the (M\({}^{\prime}\)M\({}^{\prime}\))\({}_{n+1}\)X\({}_{n}\)T\({}_{x}\) structure was found, meaning that M may also be composed of two transition metal elements [13]. Currently, more than 70 precursors of MAX phase have been reported, and an increasing number of graphene-like MXene nanosheets have been experimentally fabricated, including Ti\({}_{3}\)C\({}_{2}\), Ti\({}_{2}\)C, Nb\({}_{2}\)C, V\({}_{2}\)C, (Ti\({}_{0.5}\),Nb\({}_{0.5}\))\({}_{2}\)C, (V\({}_{0.5}\), Cr\({}_{0.5}\))\({}_{3}\)C\({}_{2}\), Ti\({}_{3}\)CN, Ta\({}_{4}\)C\({}_{3}\), Ti\({}_{4}\)N\({}_{3}\), etc. [14]. Ti\({}_{4}\)N\({}_{3}\) nanosheet is one of the first nitrogen series of MXene obtained experimentally [15]. The graphene-like MXene nanosheet family with the unique hexagonal lattice and symmetry group P63/mmc structure have metallicity, but they have many advantages of a ceramic material. A covalent bond exists between M-X ion atoms-mixed valence metallic bonding in MXene, whereas only a C-C bond exists in graphene. The graphene-like MXene nanosheet had been predicted to have more adjustable performances than the graphene [16]. Therefore, the graphene-like MXene nanosheet has a broad application prospect in transparent conductive film, supercapacitors, polymer reinforcement phase, purifying agent, field effect tube, hybrid nanocomposite and electromagnetic shielding [17]. They may be also used widely in many areas such as electronic devices [18], optical devices [19], magnetic materials [20; 21; 22; 23; 24], thermoelectric materials [25; 26; 27; 28] and biosensors [29].