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Hydrovoltaic energy technology that generates electricity directly from the interaction of materials with water has been regarded as a promising renewable energy harvesting method. With the advantages of high specific surface area, good conductivity, and easily tunable porous nanochannels, two‐dimensional (2D) nanomaterials have promising potential in high‐performance hydrovoltaic electricity generation applications. Herein, this review summarizes the most recent advances of 2D materials for hydrovoltaic electricity generation, including carbon nanosheets, layered double hydroxide (LDH), and layered transition metal oxides and sulfides. Some strategies were introduced to improve the energy conversion efficiency and the output power of hydrovoltaic electricity generation devices based on 2D materials. The applications of these devices in self‐powered electronics, sensors, and low‐consumption devices are also discussed. Finally, the challenges and perspectives on this emerging technology are outlined. Hydrovoltaic energy technology that generates electricity directly from the interaction of materials with water has been regarded as a promising renewable energy harvesting method. This review summarizes the most recent advances of 2D materials for hydrovoltaic electricity generation, including carbon nanosheets, layered double hydroxide, and layered transition metal oxides and sulfides. Perspectives toward the future applications of 2D materials in hydrovoltaic electricity generation are also outlined.

MXenes, a new family of two-dimensional materials, are also known as transition metal carbides and nitride, with a general formula of M (  = 1–3). Their inherent metallic conductivity and hydrophilic nature endow MXenes with fascinating physicochemical properties (optical, electronic, magnetic, light-to-heat conversion. etc.). The ultrathin layer structure and photothermal property attract many interests in biomedical applications, especially as phototherapeutic agents for cancer treatment. In this review, we summarize the recent progress of MXenes in the field of photothermal therapy and highlight the crucial biotic index for their preparation and evaluation. First, we introduce the main strategies for the preparation and surface modifications of biologically applied MXenes. Then, representative cases in the field of MXene-based photothermal application, such as photothermal therapy, synergistic therapy, and targeting treatments, are reviewed. Finally, the cytotoxicity and long-term biosafety are introduced. We also propose the underlying challenges and perspectives for MXene applications in terms of photothermal therapy.

Chemical vapor deposition (CVD) approach offers a controllable strategy for preparing large‐area and high‐quality few‐layer (mainly bilayer or trilayer) twisted or untwisted two‐dimensional (2D) materials, and is predicted to boost the development of 2D materials from laboratory research to industrial applications. Chemical vapor deposition approach offers a controllable strategy for preparing large‐area and high‐quality few‐layer (mainly bilayer or trilayer) twisted or untwisted two‐dimensional (2D) materials, and is predicted to boost the development of 2D materials from laboratory research to industrial applications.

Two‐dimensional (2D) materials with free of dangling bonds have the potential to serve as ideal channel materials for the next generation of field‐effect transistors (FETs) due to their atomic‐thin and excellent electronic properties. However, the performance of 2D materials‐based FETs is still dictated by the interface between electrodes/dielectrics and 2D materials. Several technical challenges such as improving device stability, reducing contact resistance, and advancing mobility need to be overcome. Herein, we focus on the effects of atomic‐scale interface engineering on the contact resistance and dielectric layer for 2D FETs. Universal strategies we consider to achieve ohmic contact and develop high‐quality, defect‐free dielectric layers are provided. Furthermore, advancing the performance of 2D materials‐based FETs and binding to silicon substrates are briefly analyzed. Atomic‐scale interface engineering in 2D materials‐based field‐effect transistors (FETs) for ohmic contacts and high‐κ dielectric layer are reviewed. Treatments and electrode fabrication methods are introduced for ohmic contact. Methods including inserting buffer layer, utilizing native oxides, and van der Walls transfer are introduced to form high quality and defect‐free dielectric layer.

Retaining the ultrathin structure of two‐dimensional materials is very important for stabilizing their catalytic performances. However, aggregation and restacking are unavoidable, to some extent, due to the van der Waals interlayer interaction of two‐dimensional materials. Here, we address this challenge by preparing an origami accordion structure of ultrathin two‐dimensional graphitized carbon nitride (oa‐C3N4) with rich vacancies. This novel structured oa‐C3N4 shows exceptional photocatalytic activity for the CO2 reduction reaction, which is 8.1 times that of the pristine C3N4. The unique structure not only prevents restacking but also increases light harvesting and the density of vacancy defects, which leads to modification of the electronic structure, regulation of the CO2 adsorption energy, and a decrease in the energy barrier of the carbon dioxide to carboxylic acid intermediate reaction. This study provides a new avenue for the development of stable high‐performance two‐dimensional catalytic materials. We develop a three‐dimensional origami accordion‐like structure of graphitized carbon nitride (oa‐C3N4) that completely prevents restacking, where the existence of N vacancies promotes efficient surface adsorption of CO2 molecules and lowers the energy barrier of the CO2 → *COOH reaction. The as‐required origami accordion‐like oa‐C3N4 achieves remarkable photocatalytic activity and selectivity for the CO2 reduction to CO reaction.

Two-dimensional (2D) materials have been extensively studied in recent years due to their unique properties and great potential for applications. Different types of structural defects could present in 2D materials and have strong influence on their properties. Optical spectroscopic techniques, e.g. Raman and photoluminescence (PL) spectroscopy, have been widely used for defect characterization in 2D materials. In this review, we briefly introduce different types of defects and discuss their effects on the mechanical, electrical, optical, thermal, and magnetic properties of 2D materials. Then, we review the recent progress on Raman and PL spectroscopic investigation of defects in 2D materials, i.e. identifying of the nature of defects and also quantifying the numbers of defects. Finally, we highlight perspectives on defect characterization and engineering in 2D materials.

We propose a deterministic method to measure the optical permittivity of two-dimensional (2D) materials without knowledge of the electronic transitions over the spectral window of interest. Using the thin-film approximation, we show that the ratio of reflection coefficients for s and p polarization can give a unique solution to the permittivity of 2D materials within the measured spectral window. The uniqueness and completeness of our permittivity measurement method do not require knowledge of the electronic transitions of a given material. We experimentally demonstrate that the permittivity of monolayers of MoS , WS , and WSe in the visible frequency range can be accurately obtained by our method. We believe that our method can provide fast and reliable measurement of the optical permittivity of newly discovered 2D materials.

Two‐dimensional (2D) transition metal carbides, carbonitrides, and nitrides, known as MXenes, have been widely studied at the frontier of 2D materials. The excellent mechanical properties, electrical conductivity, excellent photoelectrical performance, and good thermal stability of MXenes enable wide applications in many fields, including but not limited to energy storage, supercapacitors, EMI shielding, catalysis, optoelectronics, and sensors. In particular, MXene‐based materials exhibit exceptional sensing performance due to their unique tunable surface chemistry, 2D architecture, and exotic electrical/mechanical/electromechanical properties, which are rarely found in other materials. This paper discusses the MXene sensing properties and their mechanisms in different types of sensors, including piezoresistive sensors, flexible sensors, gas sensors, and biosensors. The unique roles of these MXene‐based sensors toward the future of smart living are also outlined. This article may shed light on the rational design of MXene‐based sensors and provide valuable references for corresponding scenario applications. Two‐dimensional (2D) transition metal carbides, carbon‐nitrides, and nitrides (i.e., MXene) exhibit excellent mechanical properties, electrical conductivity, unique tunable surface chemistry, and two‐dimensional structure. MXene‐based material sensors demonstrate excellent sensing performance. This paper discusses the MXene sensing properties and their mechanisms of action in different types of sensors, outlining the unique role of these MXene‐based sensors in the future of smart living.

Single-element two-dimensional (2D) tellurium (Te) which possesses an unusual quasi-one-dimensional atomic chain structure is a new member in 2D materials family. 2D Te possesses high carrier mobility, wide tunable bandgap, strong light-matter interaction, better environmental stability, and strong anisotropy, making Te exhibit tremendous application potential in next-generation electronic and optoelectronic devices. However, as an emerging 2D material, the research on fundamental property and device application of Te is still in its infancy. Hence, this review summarizes the most recent research progresses about the new star 2D Te and discusses its future development direction. Firstly, the structural features, basic physical properties, and various preparation methods of 2D Te are systemically introduced. Then, we emphatically summarize the booming development of 2D Te-based electronic and optoelectronic devices including field effect transistors, photodetectors and van der Waals heterostructure photodiodes. Finally, the future challenges, opportunities, and development directions of 2D Te-based electronic and optoelectronic devices are prospected.

Photodetectors (PDs) are optoelectronic devices that convert optical signals into electrical responses. Recently, there has been a tremendous increase in research interest in PDs based on colloidal quantum dots (QDs) and two‐dimensional (2D) material heterostructures owing to the strong light‐absorption capacity and the well‐adjustable band gap of QDs and the superior charge carriers transfer ability of 2D materials. In particular, the heterojunction formed between QDs and 2D materials can effectively enhance the separation and transport of photogenerated charge carriers, which is expected to establish PDs with ultrahigh photoconductive gain, high responsivity, and detectivity. This review aimed to summarize the state‐of‐the‐art advances in the research of QDs/2D material nanohybrid PDs, including the device parameters, architectures, working mechanisms, and fabrication technologies. The progress of hybrid PDs based on the heterojunction of QDs with different 2D materials, along with their innovative applications, are comprehensively described. In the end, the challenges and feasible strategies in future research and development are briefly proposed. Heterostructures with tailored optoelectronic properties hold great potential in achieving high‐performance photodetector (PD) devices. This review summarizes recent advances in PDs based on heterostructures combining zero‐dimensional colloidal quantum dots with two‐dimensional materials, including basic device parameters, working mechanism, advanced fabrication techniques and various emerging optoelectronic applications, offering a promising strategy to promote the development of future optoelectronics.