Layered Rare‐Earth Hydroxide/Polyacrylamide Nanocomposite Hydrogels with Highly Tunable Photoluminescence

Polymer nanocomposite (NC) hydrogels, with 3D networks composed of delaminated inorganic nanoparticles and a polymer matrix, usually display super mechanical toughness. However, the few types of inorganic materials and relatively scarce research for NC hydrogel functions seriously limit their applications. For the first time layered rare‐earth hydroxide (LRH)/polyacrylamide NC hydrogels with highly tunable photoluminescence (PL) function are reported, prepared via a convenient and green in situ polymerization process. Interestingly, the NC hydrogels reveal exciting multicolored PL phenomenon (green, yellow, orange, reddish‐orange to bluish violet), long luminescence lifetime, and relatively high quantum efficiency. Furthermore, the fascinating PL function is highly tunable by adjusting LRH constituent or its concentration, and excitation wavelength. The results highlight the fabrication and applications of functional polymer NC hydrogels with highly tunable PL function.     

Two‐Photon Up‐Conversion Photoluminescence Realized through Spatially Extended Gap States in Quasi‐2D Perovskite Films

A new approach to generate a two‐photon up‐conversion photoluminescence (PL) by directly exciting the gap states with continuous‐wave (CW) infrared photoexcitation in solution‐processing quasi‐2D perovskite films [(PEA)₂(MA)₄Pb₅Br₁₆ with n = 5] is reported. Specifically, a visible PL peaked at 520 nm is observed with the quadratic power dependence by exciting the gap states with CW 980 nm laser excitation, indicating a two‐photon up‐conversion PL occurring in quasi‐2D perovskite films. Decreasing the gap states by reducing the n value leads to a dramatic decrease in the two‐photon up‐conversion PL signal. This confirms that the gap states are indeed responsible for generating the two‐photon up‐conversion PL in quasi‐2D perovskites. Furthermore, mechanical scratching indicates that the different‐n‐value nanoplates are essentially uniformly formed in the quasi‐2D perovskite films toward generating multi‐photon up‐conversion light emission. More importantly, the two‐photon up‐conversion PL is found to be sensitive to an external magnetic field, indicating that the gap states are essentially formed as spatially extended states ready for multi‐photon excitation. Polarization‐dependent up‐conversion PL studies reveal that the gap states experience the orbit–orbit interaction through Coulomb polarization to form spatially extended states toward developing multi‐photon up‐conversion light emission in quasi‐2D perovskites.     

Confinement Catalysis with 2D Materials for Energy Conversion

The unique electronic and structural properties of 2D materials have triggered wide research interest in catalysis. The lattice of 2D materials and the interface between 2D covers and other substrates provide intriguing confinement environments for active sites, which has stimulated a rising area of “confinement catalysis with 2D materials.” Fundamental understanding of confinement catalysis with 2D materials will favor the rational design of high‐performance 2D nanocatalysts. Confinement catalysis with 2D materials has found extensive applications in energy‐related reaction processes, especially in the conversion of small energy‐related molecules such as O₂, CH₄, CO, CO₂, H₂O, and CH₃OH. Two representative strategies, i.e., 2D lattice‐confined single atoms and 2D cover‐confined metals, have been applied to construct 2D confinement catalytic systems with superior catalytic activity and stability. Herein, the recent advances in the design, applications, and structure–performance analysis of two 2D confinement catalytic systems are summarized. The different routes for tuning the electronic states of 2D confinement catalysts are highlighted and perspectives on confinement catalysis with 2D materials toward energy conversion and utilization in the future are provided.     

Triboelectric Series of 2D Layered Materials

Recently, as applications based on triboelectricity have expanded, understanding the triboelectric charging behavior of various materials has become essential. This study investigates the triboelectric charging behaviors of various 2D layered materials, including MoS₂, MoSe₂, WS₂, WSe₂, graphene, and graphene oxide in a triboelectric series using the concept of a triboelectric nanogenerator, and confirms the position of 2D materials in the triboelectric series. It is also demonstrated that the results are obviously related to the effective work functions. The charging polarity indicates the similar behavior regardless of the synthetic method and film thickness ranging from a few hundred nanometers (for chemically exfoliated and restacked films) to a few nanometers (for chemical vapor deposited films). Further, the triboelectric charging characteristics could be successfully modified via chemical doping. This study provides new insights to utilize 2D materials in triboelectric devices, allowing thin and flexible device fabrication.     

Emitting/Sensitizing Ions Spatially Separated Lanthanide Nanocrystals for Visualizing Tumors Simultaneously through Up‐ and Down‐Conversion Near‐Infrared II Luminescence In Vivo

Near‐infrared lights have received increasing attention regarding imaging applications owing to their large tissue penetration depth, high spatial resolution, and outstanding signal‐to‐noise ratio, particularly those falling in the second near‐infrared window (NIR II) of biological tissues. Rare earth nanoparticles containing Er³⁺ ions are promising candidates to show up‐conversion luminescence in the first near‐infrared window (NIR I) and down‐conversion luminescence in NIR II as well. However, synthesizing particles with small size and high NIR II luminescence quantum yield (QY) remains challenging. Er³⁺ ions are herein innovatively combined with Yb³⁺ ions in a NaErF₄@NaYbF₄ core/shell manner instead of being codoped into NaLnF₄ matrices, to maximize the concentration of Er³⁺ in the emitting core. After further surface coating, NaErF₄@NaYbF₄@NaYF₄ core/shell/shell particles are obtained. Spectroscopy studies are carried out to show the synergistic impacts of the intermediate NaYbF₄ layer and the outer NaYF₄ shell. Finally, NaErF₄@NaYbF₄@NaYF₄ nanoparticles of 30 nm with NIR II luminescence QY up to 18.7% at room temperature are obtained. After covalently attaching folic acid on the particle surface, tumor‐specific nanoprobes are obtained for simultaneously visualizing both subcutaneous and intraperitoneal tumor xenografts in vivo. The ultrahigh QY of down‐conversion emission also allows for visualization of the biodistribution of folate receptors.     

2D V‐V Binary Materials: Status and Challenges

2D phosphorene, arsenene, antimonene, and bismuthene, as a fast‐growing family of 2D monoelemental materials, have attracted enormous interest in the scientific community owing to their intriguing structures and extraordinary electronic properties. Tuning the monoelemental crystals into bielemental ones between group‐VA elements is able to preserve their advantages of unique structures, modulate their properties, and further expand their multifunctional applications. Herein, a review of the historical work is provided for both theoretical predictions and experimental advances of 2D V‐V binary materials. Their various intriguing electronic properties are discussed, including band structure, carrier mobility, Rashba effect, and topological state. An emphasis is also given to their progress in fabricated approaches and potential applications. Finally, a detailed presentation on the opportunities and challenges in the future development of 2D V‐V binary materials is given.     

Strong Coupling of MoS2 Nanosheets and Nitrogen‐Doped Graphene for High‐Performance Pseudocapacitance Lithium Storage

Layered material MoS₂ is widely applied as a promising anode for lithium‐ion batteries (LIBs). Herein, a scalable and facile dopamine‐assisted hydrothermal technique for the preparation of strongly coupled MoS₂ nanosheets and nitrogen‐doped graphene (MoS₂/N‐G) composite is developed. In this composite, the interconnected MoS₂ nanosheets are well wrapped onto the surface of graphene, forming a unique veil‐like architecture. Experimental results indicate that dopamine plays multiple roles in the synthesis: a binding agent to anchor and uniformly disperse MoS₂ nanosheets, a morphology promoter, and the precursor for in situ nitrogen doping during the self‐polymerization process. Density functional theory calculations further reveal that a strong interaction exists at the interface of MoS₂ nanosheets and nitrogen‐doped graphene, which facilitates the charge transfer in the hybrid system. When used as the anode for LIBs, the resulting MoS₂/N‐G composite electrode exhibits much higher and more stable Li‐ion storage capacity (e.g., 1102 mAh g^?1 at 100 mA g^?1) than that of MoS₂/G electrode without employing the dopamine linker. Significantly, it is also identified that the thin MoS₂ nanosheets display outstanding high‐rate capability due to surface‐dominated pseudocapacitance contribution.     

Rational Design of Carbon‐Rich Materials for Energy Storage and Conversion

Carbon‐rich materials have drawn tremendous attention toward a wide spectrum of energy applications due to their superior electronic mobility, good mechanical strength, ultrahigh surface area, and more importantly, abundant diversity in structure and components. Herein, rationally designed and bottom‐up constructed carbon‐rich materials for energy storage and conversion are discussed. The fundamental design principles are itemized for the targeted preparation of carbon‐rich materials and the latest remarkable advances are summarized in terms of emerging dimensions including sp² carbon fragment manipulation, pore structure modulation, topological defect engineering, heteroatom incorporation, and edge chemical regulation. In this respect, the corresponding structure–property relationships of the resultant carbon‐rich materials are comprehensively discussed. Finally, critical perspectives on future challenges of carbon‐rich materials are presented. The progress highlighted here will provide meaningful guidance on the precise design and targeted synthesis of carbon‐rich materials, which are of critical importance for the achievement of performance characteristics highly desirable for urgent energy deployment.     

High‐Throughput Continuous Production of Shear‐Exfoliated 2D Layered Materials using Compressible Flows

2D nanomaterials are finding numerous applications in next‐generation electronics, consumer goods, energy generation and storage, and healthcare. The rapid rise of utility and applications for 2D nanomaterials necessitates developing means for their mass production. This study details a new compressible flow exfoliation method for producing 2D nanomaterials using a multiphase flow of 2D layered materials suspended in a high‐pressure gas undergoing expansion. The expanded gas–solid mixture is sprayed in a suitable solvent, where a significant portion (up to 10% yield) of the initial hexagonal boron nitride material is found to be exfoliated with a mean thickness of 4.2 nm. The exfoliation is attributed to the high shear rates ( > 10⁵ s^?1) generated by supersonic flow of compressible gases inside narrow orifices and converging‐diverging channels. This method has significant advantages over current 2D material exfoliation methods, such as chemical intercalation and exfoliation, as well as liquid phase shear exfoliation, with the most obvious benefit being the fast, continuous nature of the process. Other advantages include environmentally friendly processing, reduced occurrence of defects, and the versatility to be applied to any 2D layered material using any gaseous medium. Scaling this process to industrial production has a strong possibility of reducing the cost of creating 2D nanomaterials.     

Dual‐Additive Assisted Chemical Vapor Deposition for the Growth of Mn‐Doped 2D MoS2 with Tunable Electronic Properties

Doping of bulk silicon and III–V materials has paved the foundation of the current semiconductor industry. Controlled doping of 2D semiconductors, which can also be used to tune their bandgap and type of carrier thus changing their electronic, optical, and catalytic properties, remains challenging. Here the substitutional doping of nonlike element dopant (Mn) at the Mo sites of 2D MoS₂ is reported to tune its electronic and catalytic properties. The key for the successful incorporation of Mn into the MoS₂ lattice stems from the development of a new growth technology called dual‐additive chemical vapor deposition. First, the addition of a MnO₂ additive to the MoS₂ growth process reshapes the morphology and increases lateral size of Mn‐doped MoS₂. Second, a NaCl additive helps in promoting the substitutional doping and increases the concentration of Mn dopant to 1.7 at%. Because Mn has more valance electrons than Mo, its doping into MoS₂ shifts the Fermi level toward the conduction band, resulting in improved electrical contact in field effect transistors. Mn doping also increases the hydrogen evolution activity of MoS₂ electrocatalysts. This work provides a growth method for doping nonlike elements into 2D MoS₂ and potentially many other 2D materials to modify their properties.     

A High‐Performance Lithium‐Ion Capacitor Based on 2D Nanosheet Materials

Lithium‐ion capacitors (LICs) are promising electrical energy storage systems for mid‐to‐large‐scale applications due to the high energy and large power output without sacrificing long cycle stability. However, due to the different energy storage mechanisms between anode and cathode, the energy densities of LICs often degrade noticeably at high power density, because of the sluggish kinetics limitation at the battery‐type anode side. Herein, a high‐performance LIC by well‐defined ZnMn₂O₄‐graphene hybrid nanosheets anode and N‐doped carbon nanosheets cathode is presented. The 2D nanomaterials offer high specific surface areas in favor of a fast ion transport and storage with shortened ion diffusion length, enabling fast charge and discharge. The fabricated LIC delivers a high specific energy of 202.8 Wh kg^?1 at specific power of 180 W kg^?1, and the specific energy remains 98 Wh kg^?1 even when the specific power achieves as high as 21 kW kg^?1.