Two-dimensional(2D) cadmium chalcogenides have triggered worldwide interests due to their unique merits in both structure and physical properties, including thickness-dependent bandgaps, narrow emission line widths, high intrinsic absorption coefficient and large absorption cross sections, etc., rendering their great potential for next-generation electronics and optoelectronics devices. In this article, the progress of 2D cadmium chalcogenides in the past few years is comprehensively reviewed. We first discussed several synthetic strategies for various 2D cadmium chalcogenides. Then, their optoelectronic applications in photodetectors, lasers, LEDs, and piezoelectric devices are summarized and commented in detail. Finally, a brief conclusion of the article and the future prospects of the 2D cadmium chalcogenides are provided.

Oxygen evolution reaction(OER) plays an important role in many electrochemical systems. However, its sluggish kinetics severely limits the development of next-generation energy technologies. Recently, two-dimensional(2D) metal-organic frameworks(MOFs) have attracted much attention as a class of promising electrocatalysts. Their diverse components and tunable structures provide a new platform to design and explore ideal electrocatalysts. The ultrathin characteristics including high specific surface area, abundant exposed metal sites and fast electronic transfer further promote the electrocatalytic performance of 2D MOFs. Therefore, many attempts have been made in synthesizing 2D MOF-based electrocatalysts in recent years. This review focuses on the strategies to fabricate 2D MOFs with high electrocatalytic performances for OER. The discussion on challenge and development of their electrocatalytic application is also presented.

Two-dimensional(2D) transition metal dichalcogenides(TMDCs) semiconductors, such as monolayers of molybdenum disulfide(MoS₂) and tungsten disulfide(WS₂) can potentially serve as ultrathin channel materials for building short channel field-effect transistors(FETs) to further extend Moore’s Law. It is essential to develop control-lable approaches for the synthesis of large single crystals of these 2D semiconductors to promote their practical applications in future electronics. In this short review, we summarized the recent advances on the chemical vapor deposition(CVD) of single crystalline semiconducting 2D TMDCs with a large size. We first discussed the driving force and urgent demands on developing controllable approaches for the growth of large 2D TMDCs single crystals and then summarized the current strategies and representative studies on the CVD growth of large 2D single crystals. Finally, we discussed the challenges and future directions in this topic.

Controlled large-quantity synthesis of two-dimensional materials is vital for the research on their physical and chemical characters and potential applications. Utilizing structural features of layered compounds, intercalation of molecules or ions can be applied to the acceleration of liquid-phase exfoliation. In this review, we aim at recent progress on synthesis of two-dimensional materials via intercalation-assisted exfoliation strategy. Works on wet chemical intercalation and electrochemical intercalation, together with product exfoliation afterwards, are summarized. Furthermore, the features and advantages of intercalation-assisted exfoliation strategy for two-dimensional materials synthesis are discussed.

Among 108423 unique, experimentally known 3D compounds, there exist 1825 ones that are either easily or potentially exfoliable. This increasingly broad library of 2D layered materials(2DLMs) with variable physical properties as well as the unique ability to vertical stacking or lateral stitching 2DLMs into complex heterostructures enables a new dimension for materials engineering and device design, offering novel functional electronics and optoelectronics for flexible industry. In this review, we present a comprehensive summary of the state-of-the-art scalable fabrication technologies, the unique properties as well as the potential device applications of the emerging 2D hetero-structures. Firstly, we depict an overall picture of the 2D vertical van der Waals heterostructures. Secondly, we focus on the 2D lateral heterostructures by CVD technique. For a quick access and full coverage, both the vertical and lateral 2D heterostructures are classified into several types according to their chemical compounds with different dimensions. In the end, both the challenges and potential applications of these 2D heterostructures are discussed.

Tellurium(Te) nanomaterials have aroused a wide interest in semiconductor, thermoelectric, piezoelectric, as well as biomedical applications. The last decades of reports indicated a major nanostructure of one-dimensional (1D) Te on account of its inherent structural anisotropy. Two-dimenional(2D) Te has been newly developed and drawn a lot of interests recently. This review presents the intrinsic biological potential of Te-based nanomaterials and summarizes their up-to-date advance in phototherapy and reactive oxygen species(ROS)-related applications in the biomedical field.

Developing new types of rechargeable batteries with high energy densities and low cost have received increasing attentions, aiming to reduce the dependence on high-priced lithium. Beyond Li-ion batteries, the potential alternatives including Na-ion batteries, Li-S batteries and Li-air batteries have been investigated recently, which are required to be viable for commercial applications. From this point of view, to understand the electrochemical reaction mechanisms and kinetics of these batteries has become the key challenge to make breakthroughs in the field of new energy storage. In this review, we present a critical overview of the two dimensional nanomaterials-based batteries (except Li-ion-based batteries) that could meet such demonds. To develop new energy storage devices with more promising performances, the microstructure evolution and atomic scale storage mechanism of these batteries are comprehensively summarized. In addition, the major challenges and opportunities of advanced characterization techniques are finally discussed. We do hope that this review will give the readers a clear and profound understanding of the electrochemical reaction mechanisms and kinetics of the as-discussed batteries, thus effectively contributing to the smart design of future-generation energy storage devices.

Two-dimensional(2D) layered materials have attracted great attention due to their unique electrical, optical, thermal and mechanical properties. 2D layered materials have unique van der Waals gaps, thus the foreign substance, such as atoms, molecules and ions, can be inserted into the gaps to change the physical and chemical properties of 2D layered materials, which is conducive to realize their multi-functional application. Herein, we present a critical review of recent research progress of 2D intercalated materials, including the synthesizing methods, theoretical calculation, characterization and multifunctional application. Finally, we will summarize the current challenges and future opportunities in the development of 2D intercalated materials.

Two-dimensional noble metal nanomaterials(2D NMNs) are widely used as electrocatalyst. In recent years, the researchers have focused on the synthesis of 2D NMNs at the atomic scale, and realize the improvement of electrocatalytic performance through further structural modification to reduce the usage of noble metals. Herein, we systematically introduce the synthesis methods of 2D NMNs categorized by element type. Subsequently, the catalytic applications toward a variety of electrocatalytic reactions are described in detail including the hydrogen evolution reaction(HER), oxygen reduction reaction(ORR), oxygen evolution reaction(OER) and CO₂ reduction reaction (CO₂RR). Finally, the potential opportunities and remaining challenges in this emerging research area are proposed.

Due to their unique electronic and structural properties triggered by high atomic utilization and easy surface modification, two-dimensional(2D) materials have prodigious potential in electrocatalysis for energy conversion technology in recent years. In this review, we discuss the recent progress on two-dimensional nanomaterials for electrocatalysis. Five categories including metals, transition metal compounds, non-metal, metal-organic framework and other emerging 2D nanomaterials are successively introduced. Finally, the challenges and future development directions of 2D materials for electrocatalysis are also prospected. We hope this review may be helpful for guiding the design and application of 2D nanomaterials in energy conversion technologies.

The modern internet-of-things era has witnessed an increasing growth in the demand for advanced sensors to collect precise information. To meet this demand, extensive efforts have been devoted to exploring competent materials and designing rational architectures for the fabrication of sensing devices. Graphdiyne represents a promising material due to the attractive electronic, optical and electrochemical properties deriving from its unique molecular structure. In this review, we firstly provide the points of view on the architectures and work principles of the graphdiyne-based sensing devices with respect to resistive, electrochemical, photoelectrochemical and fluorescent categories. Secondly, we present the promising applications on biochemical sensing, such as the detection of DNA, micro-RNA, and glucose. Finally, the challenges and prospects of graphdiyne-based biochemical sensing platforms are also discussed, in order to provide a cornerstone for understanding this rapidly developing area.

Effectively trapping lithium polysulfide species and accelerating the reaction conversion kinetics are the main strategies to improve the performance of lithium-sulfur(Li-S) batteries. Since the researchers found in 2014 that two-dimensional(2D) phosphorene nanosheets could be exfoliated from the bulk black phosphorus, numerous researches have been devoted to exploring the phosphorene with unique properties for the application in Li-S batteries. In this review, we summarize the recent theoretical and experimental progress of phosphorene for Li-S batteries. Besides, we also introduce the relationship between the interfacial interaction on phosphorene and the performance enhancement of Li-S batteries. Furthermore, future challenges and remaining opportunities for phosphorene in Li-S batteries are finally discussed.

Two-dimensional crystalline covalent triazine frameworks(CTFs) have received much attention because of their unique triazine structure, which endows CTFs with high thermal and chemical stability, high proportion of nitrogen and permanent porosity. Based on this unique structure characteristic, CTFs have shown great potential in energy storage and conversion due to the intrinsically strong conjugated structure, delocalized electron and rich active sites. However, charge carrier(electron, hole or ion) transport can’t reach the deep active sites and charge diffusion was impeded by defects in bulk CTFs. Hence, to break through this barrier, increasing attention has been paid to get few layered CTFs or CTFs nanosheets in order to shorten the pathways of charge diffusion and expose more active sites. This review summarizes the synthetic methodologies of CTFs nanosheets and the potential application in photocatalytic and electrochemical energy storage and conversion.

Ammonia is a commodity chemical with high added value. Electrochemical reduction of nitrogen has great promise for the sustainable synthesis of ammonia in recent years. Because of its rich resources and unique electronic structure and characteristics, 2D transition metal compounds have been used as electrocatalysts for electrochemical reduction of nitrogen for clean and sustainable production of ammonia. This review outlines the latest development in the use of 2D transition metal compounds as high-efficiency electrocatalysts for nitrogen reduction reaction(NRR). First, we introduce the N₂ reduction mechanism, and briefly summarize the performance indicators of the catalyst. Then, we focused on the functionalization of unique 2D materials to design high-performance 2D electrocatalysts in respect of simulation calculation and experimental development. Finally, the current challenges and future opportunities for NRR electrocatalysts are introduced.

The most important topics in the world today are environmental and resource issues. The development of green and clean energy is still one of the great challenges of social sustainable development. Two-dimensional(2D) metal-organic frameworks(MOFs) and derivatives have exceptional potential as high-efficiency electrocatalysts for clean energy technologies. This review summarizes various synthesis strategies and applications of 2D MOFs and derivatives in electrocatalysis. Firstly, we will outline the advantages and uniqueness of 2D MOFs and derivatives, as well as their applicable areas. Secondly, the synthetic strategies of 2D MOFs and derivatives are briefly classified. Each category is summarized and we list classic representative fabrication methods, including specific fabrication methods and mechanisms, corresponding structural characteristics, and insights into the advantages and limitations of the synthesis method. Thirdly, we separately classify and summarize the application of 2D MOFs and derivatives in electrocatalysis, including electrocatalytic water splitting, oxygen reduction reaction(ORR), CO₂ reduction reaction(CO₂RR), and other electrocatalytic applications. Finally, the development prospects and existing challenges to 2D MOFs and derivatives are discussed.

The derivatives of aromatic cores bearing alkyl chains with different lengths are of potential interest in on-surface chemistry, and thus have been widely investigated both at liquid-solid interfaces and in vacuum. Here, we report on the structural evaluation of self-assembled 1,3,5-tri(4-dodecylphenyl)benzene(TDPB) molecules with increased molecular coverages on both Au(111) and Cu(111) surfaces. As observed on Au(111), rhombic and herringbone structures emerge successively depending on surface coverage. In the case of Cu(111), the same process of phase conversion is also observed, but with two distinct structures. In comparison, the self-assembled structures on Au(111) surface are packed more densely than that on Cu(111) surface under the same preparation conditions. This may fundamentally result from the higher adsorption energy of TDPB molecules on Cu(111), restricting their adjustment to optimize a thermodynamically favorable molecular packing.

Li[Ni_0.6Co_0.2Mn_0.2]O₂(NCM622) is one of the best commercialized cathodes in the battery field. However, poor cyclability at relatively high temperature hinders its multiple usages. Here, operando tests were performed to investigate the phase transitions and electron/ion transfer process of layered NCM622 at 25 and 55 °C. The identified spinel structure resulting in the poor cyclability at 55 °C guides the commercialization of batteries at high temperature.

Flexible on-chip microsupercapacitors(MSCs) are highly desired for integrated wearable or portable electronics due to their advantages of small size, high power density, easy integration, long lifespan, high security, and flexibility. The output voltage of MSCs can be improved by designing MSC arrays, which could further expand their application fields. In this work, we proposed a facile laser direct cutting method to prepare an on-chip flexible MSC array using Ti₃C₂T _xMXene as both current collector and electrode materials. The designed MSC in PVA/H₂SO₄ all-solid-state gel electrolyte exhibits a large volume/areal capacitance of 770.72 F/cm³(46.24 mF/cm²) at a scan rate of 20 mV/s, a high energy density of 68.51 mW·h/cm³ at a power density of 6.16 W/cm³, excellent cycling stability with capacitance retention of 98.50% after 10000 charge/discharge cycles. The MSC also shows superior flexibility and stability even after repetition of charge/discharge cycles under the convex and concave bending states. In addition, the assembled MSC array(4 in series) provides a high voltage of 3.2 V, which could easily power a purple light-emitting diode more than 10 min, demonstrating its potential application in integrated portable/wearable devices.

Solar-thermal water evaporation has attracted increasing attention owing to the promising potential to solve the global clean water and energy crisis. But, the development of this strategy is limited by the lack of materials with high solar-thermal conversion efficiency, local heating of superficial water, easy preparation and low cost. Herein, we proposed a facile strategy to prepare a reduced graphene oxide/carbon fiber composite membrane, denoted as RGO/CF membrane. The surface of the RGO/CF membrane was highly hydrophobic, endowing the composite membrane with the self-floating ability on the water without any assistance. The light absorbance ability achieved as high as ca. 98% in the wavelength range of 300–1200 nm. The steam evaporation efficiency under the illumination of 3-sun was 97%, generating water steam at a rate of 4.54 kg·m⁻²·h⁻¹. Moreover, the solar-thermal steam production rate showed high stability during successive 30 cycle tests.

In recent decades, dual-band photodetectors have received widespread attention due to better target identification, which are considered as the development trend of next generation photodetectors. However, the traditional dual-band photodetectors based on heteroepitaxial growth, superlattice and multiple quantum well structures are limited by complex fabrication process and low integration. Herein, we report a UV/IR dual-band photodetector by integrating ultra-wide gap β-Ga₂O₃ and narrow-gap black phosphorous(BP) nanoflakes. A vertical van der Waals (vdW) heterostructure is formed between BP and β-Ga₂O₃ by mechanically exfoliated method integrated without the requirement of lattice match. The heterostructure devices show excellent rectification characteristics with high rectifying ratio of ca. 10⁶ and low reverse current around pA. Moreover, the device displays obvious photoresponse under UV and IR irradiations with responsivities of 0.87 and 2.15 mA/W, respectively. We also explore the band alignment transit within the heterostructure photodetector at different bias voltages. This work paves the way for fabricating novel dual-band photodetectors by utilizing 2D materials.

Rational construction of low-cost, efficient, and durable electrocatalysts for the hydrogen evolution reaction(HER) is essential to further develop water electrolysis industry. Inspired by the natural enzyme catalysis with coordination environments of catalytic sites and three-dimensional structures, we construct an efficient Ru-based catalyst anchored on the nitrogen dopant on graphene aerogel(Ru-NGA). The Ru-NGA catalyst exhibits dramatically improved electroactivity and stability towards HER with a near-zero onset overpotential, a low Tafel slope of 32 mV/dec, and a high turnover frequency of 5.5 s⁻¹ at −100 mV. The results show that the electronic modulation of metallic Ru nanoparticles by nitrogen coordination weakens the affinity of Ru towards H and hence facilitates the desorption of hydrogen. This research provides in-depth insights into the fundamental relationship between metallic nanostructure and HER activity, and also guides the rational design of high-performance electrocatalysts in energy conversion.

In this work, NiCo₂O₄(NCO) was synthesized via microwave hydrothermal method and a further annealing treatment. Research results have shown that the surface defects(Co²⁺ site) and pore size of the materials can be adjusted by simply changing the calcination temperatures, and porous nanowire arrays structure can be obtained. The porous structure is conducive to the penetration of the electrolyte and enables the NCO to fully participate in the electrochemical reaction. What’s more, the NCO material has ample space to buffer the volume change in the cycle test, improving the cycling stability. The NCO obtained at 350 °C has better performance. It exhibits a specific capacitance of 648.69 F/g at 1 A/g and good rate capability. Especially, at 10 A/g, the specific capacitance can still be maintained at 80.00% after 10000 galvanostatic charge/discharge(GCD) cycles, showing excellent cycling stability.

Ultrathin antimony oxide single crystals with high dielectric constant and large breakdown electric field were synthesized via an expressly substrate-buffer-controlled chemical vapor deposition strategy. This strategy is also versatile for the synthesis of other ultrathin oxides.

Given the fact that aldehydes are among the most fundamental and versatile building blocks in organic synthesis, the development of highly efficient and selective methods for their preparation, especially for those delicately functionalized ones remains significant challenging. To address such an issue, Xu and co-workers have recently reported an elegant electrochemical approach realizing the highly regioselective oxidation of functionalized methyl aromatic hydrocarbons towards the desired aromatic acetals without the use of any chemical oxidants or transition metal catalysts. These acetals can be then conveniently converted into corresponding structurally diverse aldehydes via hydrolysis. In addition, the synthetic practicability of current method was further highlighted as the key step in the preparation of the antihypertensive drug telmisartan. This work has been published in the Nature Communications and can be reached at https://doi.org/10.1038/s41467-020-16519-8.

To improve the water splitting performance of photoelectrode, Wang’s group borrowed the lithiation mechanism of Li-ion battery to create ordered lattice strain in the electrode. The stressed lattice induced by Li-ion insertion generates a polarized electric field in the bulk, which greatly improves the bulky charge separation and transfer capability and remarkably promotes the photoelectrocatalytic water splitting. This work paves a new avenue for photoelectrochemical water splitting towards efficient solar hydrogen production. The related work was published in Nature Communications on May 1, 2020.

Remote C-H bond functionalization of arenes with precise control is a recognized extraordinary challenge in organic synthesis. Recently, Yu and Houk et al. developed an elegant strategy to distinguish and functionalize remote C_sp ²-H bonds of (hetero)arenes within one-bond distance by the interplay of a remote directing template and a transient norbornene-type mediator. A wide range of medicinally important benzoazines are well compatible with this method. The chemistry significantly expands the toolbox for site-selective functionalization of remote C_sp ²-H bond of (hetero)arenes. This work has been published in Nature Chemistry in March, 2020.

In the latest issue of Nature Nanotechnology, Ling and coworkers reported the first potassium nanosensor applicable in a freely moving animal. It was developed by embedding the mesoporous silica nanoparticle framework with optical potassium indicators and then shielding the framework with an ultrathin layer of a potassium-permeable membrane. This nanosensor achieved highly sensitive monitoring of the dynamic changes of the extracellular potassium in the brain of freely moving mice with epilepsy.

The building and engineering of an artificial molecular signaling system in encapsulated vesicles is a key step towards artificial cells. Recently, Tan et al. reached a new milestone by integrating an intelligent DNA nanogatekeeper with an artificial vesicle system. The DNA nanogatekeeper driven by adenosine triphosphate(ATP) is able to receive outside stimulus, which in turn switches the diffusion of environmental ions into the integrated vesicle. Most importantly, this system enables triggering downstream signaling cascaded reactions confined in the artificial vesicle, as well as returning feedback to the DNA nanogatekeeper, mimicking real cellular behaviors of reception, transduction and response. This work has been published online in Nature Communications on February 20, 2020.