2D transition metal carbides or nitrides, known as MXenes, are a new family of 2D materials with close to 30 members experimentally synthesized and dozens more theoretically investigated. Because of the abundant surface terminations, MXenes have been compounded with various materials by multi-interactions. In addition to the prevented aggregation and oxidation of MXene flakes, the MXene/polymer membranes exhibit outstanding mechanical, thermal, and electrical properties due to the synergistic effects. However, relatively little is currently known about the MXene/polymer membranes and a special review on the progress of the synthesis, properties, and applications of MXene/polymer membranes has not been reported to date. Herein, this Review starts with an introduction of the synthesis and properties of MXenes. Then the development of MXene/polymer membranes will be discussed, which aims to summarize various approaches of fabricating MXene/polymer membranes and their fascinating properties. The focus then turns to their exciting potential applications in various fields such as filtration, electromagnetic interference (EMI) shielding, energy storage devices, wearable electronics, etc. Finally, outlooks and perspectives for the future challenges and prospects of MXene/polymer membranes are provided.

Two‐dimensional (2D) Ti3C2Tx (T = F, O, or OH) MXene, a graphene‐like material, is successfully fabricated for an investigation in nonlinear optics. Its nonlinear refractive index (n2 ≈ 10−4 [cm2 W−1]) and third‐order nonlinear susceptibility (χ monolayer false(3false)≈ 10−7 [e.s.u.]) are experimentally confirmed by spatial self‐phase modulation (SSPM) techniques. Applying its strong Kerr effect, a novel all‐optical switcher based on 2D MXene is designed to realize the modulation of pump light to probe light. This indicates that MXene could act as an information converter in an optical light‐control‐light system. Meanwhile, probe light is induced by the pump light to excite diffraction rings, and the ring numbers of the probe light can be controlled to increase by the regulation of the other pump light. Through modulation of the pump light, the “ON” and “OFF” modes in the all‐optical switcher/modulator can be achieved. This work highlights the potential of Ti3C2Tx MXene materials applied in all‐optical switcher/modulators, which can be considered an important step toward MXene‐based advanced photonics devices.

for exploring 2D materials. In the past decade, studies have been extensively reported [2] on diverse optical devices such as absorbers, modulators, detectors, etc. Liu et al. [3] experimentally demonstrated a broadband, high-speed and waveguideintegrated electroabsorption modulator based on monolayer graphene. Vicarelli et al. [4] applied graphene field-effect transistors as room-temperature terahertz detectors. In addition, light/graphene interactions have also been extensively investigated, and graphene shows saturation of the optical absorption, THz emission, SHG under symmetry breakage, and third-order nonlinear refraction. The nonlinear refractive index (n 2 ) and third-order nonlinear susceptibility (χ (3) ) in graphene have been experimentally investigated by four-wave mixing and Z-scan measurements. [5] Furthermore, another measurement technique based on spatial self-phase modulation (SSPM) has been employed to analyze the nonlinear optical responses of different types of nanomaterials. In 2011, Wu et al. investigated the third-order nonlinear susceptibility in chemically exfoliated graphene nanosheets using the SSPM method. [6] Since the discovery of single-layer graphene, much effort has been devoted toward finding new 2D nonlinear optical materials As an analogue compound of black phosphorus, a new 2D semiconducting few-layer SnS is successfully synthesized, and its nonlinear optical response is investigated. It is shown that its nonlinear refractive index and third-order nonlinear susceptibility are measured as n 2 ≈ 10 −5 (cm 2 W −1 ) and monolayer (3) χ χ ≈ 10 −10 (e.s.u.), respectively. By taking advantage of such a large Kerr nonlinearity, an all-optical switching technique based on few-layer SnS is realized through modulating the propagation of the signal beam by another controlling beam. The achievement of all-optical switching indicates that few-layer SnS could be developed as an excellent optical material for alloptical signal processing. More importantly, a conceptually new and reliable information conversion system based on spatial cross-phase modulation in few-layer SnS, that is, the transmission and conversion of a sequence of bit information from one wavelength channel to the other, is presented. The contributions reveal potential applications of few-layer SnS as a new type of optical information material, and it is therefore anticipated that SnS and other IV-VI compound-based 2D nanomaterials could find promising applications in photonic devices such as optical modulators, optical switches, detectors, etc.

2D titanium disulfide (TiS2) is recently found to have strong light absorption properties from visible to infrared (IR) region. This feature is highly attractive for applications in nonlinear photonics; however, the mechanism of broadband light–matter interaction is yet to be determined and nonlinear photonic devices are not developed. Here, for the first time, the experimental evidence supporting the mechanism of the broadband nonlinear photoresponse in ultrathin TiS2 nanosheets ranging from 400 nm to 1390 nm is reported through laser Z‐scan measurements. High‐performance nonlinear photonic devices operating in the telecommunication band are also demonstrated. A novel saturable absorber (SA) device is successfully fabricated based on a 2D TiS2‐decorated fiber, which exhibits outstanding ultrashort pulse generation performance with pulse duration of ≈1.04 ps centered at 1569.5 nm. Furthermore, as a stable all‐optical thresholding component, the device can effectively attenuate noise and boost the signal‐to‐noise ratio of the pulse from 1.90 to 10.68 dB. The findings indicate that TiS2‐based SA devices can be developed into excellent highly nonlinear photonic devices, which may advance the development of TiS2‐based optical communication technologies in the future.

As one of the rising 2D materials, niobium‐carbide (Nb2C, well‐known as a member of MXene family) has attracted considerable attention owing to its unique physical and chemical properties. In this work, few‐layer Nb2C nanosheets (NSs) with large (≈255 nm) and small (≈48 nm) lateral dimensions are obtained via a combination of selective etching and liquid cascade centrifugation. Their relaxation time and photophysics process are systematically investigated by transient absorption spectroscopy, and the size effect is demonstrated by phonon‐bottleneck mechanism. Ultrafast fast relaxation time (37.43 fs) and slow relaxation time (0.5733 ps) are observed due to the symmetric structure and metallicity of Nb2C NSs. The nonlinear optical properties of Nb2C NSs are studied by Z‐scan technique, and both saturable absorption and reverse‐saturable absorption are observed. According to first principle calculations, these phenomena can be attributed to the special band structure of Nb2C near the Fermi level, where two‐photon absorption or multiphoton absorption may occur under the irradiation of long wavelength light. These intriguing results suggest that few‐layer Nb2C NSs can be used as building blocks for broadband ultrafast photonics and optoelectronic devices and also hold the potential for breakthrough developments in these fields.