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Metal-organic framework (MOF) nanosheets and covalent organic framework (COF) nanosheets as emerging porous materials nanosheets have captured increasing attention owing to their attractive properties originating from the advantages of large lateral size, ultrathin thickness, tailorable physiochemical environment, flexibility and highly accessible active sites on surface, and the applications of them have been explored in a wide range of fields. Although MOF and COF nanosheets own many similar properties, their applications in various fields show significant differences, probably due to their different compositions and bonding modes. Hence, we summarize the recent progress of MOF and COF nanosheets by comparative analysis on their advantages and limitations in synthesis and applications, providing a more profound and full-scale perspective for researchers or beginners to understand this field. Herein, the categories of preparation methods of MOF and COF nanosheets are firstly discussed, including top-down and bottom-up methods. Secondly, the applications of MOF and COF nanosheets for separation, catalysis, sensing and energy storage are summarized. Finally, based on current achievements, we put forward our personal insights into the challenges and outlooks on the synthesis, characterizations, and promising applications for future research of MOF and COF nanosheets.

Lithium–sulfur batteries (LSBs) have shown great potential as a rival for next generation batteries, for its relatively high theoretical capacity and eco‐friendly properties. Nevertheless, blocked by the shuttle effect of lithium polysulfides (LPSs, Li2S4‐Li2S8) and insulation of sulfur, LSBs show rapid capacity loss and cannot achieve the practical application. Herein, a composite of carbon nanofibers coated by Co3S4 nanosheets (denoted as CNF@Co3S4) is successfully synthesized as freestanding sulfur host to optimize the interaction with sulfur species. The combination of the two materials can lead extraordinary cycling and rate performance by alleviating the shuttle of LPSs effectively. N‐doped carbon nanofibers serve as long‐range conductive networks and Co3S4 nanosheets can accelerate the conversion of LPSs through its electrocatalytic and chemical adsorption ability. Benefiting from the unique structure, the transporting rate of Li+ can be enhanced. Distribution of Li+ is uniform for enough exposed negative active sites. As a result, the cell with CNF@Co3S4 as sulfur host is able to stabilize at 710 mA h g−1 at 1 C after 200 cycles with average coulombic efficiency of 97.8% in a sulfur loading of 1.7 mg cm−2 and deliver 4.1 mA h cm−2 at 0.1 C even in 6.8 mg cm−2 for 100 cycles. CNF@Co3S4 as a freestanding sulfur host optimizes the interaction between sulfur species and the host material by the polarity and catalytical effect of Co3S4 nanosheets. The electronegative property of Co3S4 can further alleviate the growth of Li‐dendrites through realizing the uniform Li+ flux and deposition. These advantages guarantee extraordinary cycling and rate performance of corresponding Li–S batteries.

The key to solve increasingly severe electromagnetic (EM) pollution is to explore sustainable, easily prepared, and cost-effective EM wave absorption materials with exceptional absorption capability. Herein, instead of anchoring on carbon materials in single layer, MoS 2 flower-like microspheres were stacked on the surface of pomelo peels-derived porous carbon nanosheets (C) to fabricate MoS 2 @C nanocomposites by a facile solvothermal process. EM wave absorption performances of MoS 2 @C nanocomposites in X-band were systematically investigated, indicating the minimum reflection loss (RL min ) of −62.3 dB (thickness of 2.88 mm) and effective absorption bandwidth (EAB) almost covering the whole X-band (thickness of 2.63 mm) with the filler loading of only 20 wt.%. Superior EM wave absorption performances of MoS 2 @C nanocomposites could be attributed to the excellent impedance matching characteristic and dielectric loss capacity (conduction loss and polarization loss). This study revealed that the as-prepared MoS 2 @C nanocomposites would be a novel prospective candidate for the sustainable EM absorbents with superior EM wave absorption performances.

Two-dimensional (2D) nanomaterials are categorized as a new class of microwave absorption (MA) materials owing to their high specific surface area and peculiar electronic properties. In this study, 2D WS -reduced graphene oxide (WS -rGO) heterostructure nanosheets were synthesized via a facile hydrothermal process; moreover, their dielectric and MA properties were reported for the first time. Remarkably, the maximum reflection loss (RL) of the sample-wax composites containing 40 wt% WS -rGO was - 41.5 dB at a thickness of 2.7 mm; furthermore, the bandwidth where RL < - 10 dB can reach up to 13.62 GHz (4.38-18 GHz). Synergistic mechanisms derived from the interfacial dielectric coupling and multiple-interface scattering after hybridization of WS with rGO were discussed to explain the drastically enhanced microwave absorption performance. The results indicate these lightweight WS -rGO nanosheets to be potential materials for practical electromagnetic wave-absorbing applications.

HighlightsThe microwave absorbing performance of alloy@C composites can be controlled through regulating ratio of metal ions.Carbon-based alloy@C composites exhibit the potential stability of microwave absorption with almost the whole Ku band for the practical application.Magnetic/dielectric@porous carbon composites, derived from metal–organic frameworks (MOFs) with adjustable composition ratio, have attracted wide attention due to their unique magnetoelectric properties. In addition, MOFs-derived porous carbon-based materials can meet the needs of lightweight feature. This paper reports a simple process for synthesizing stacked CoxNiy@C nanosheets derived from CoxNiy-MOFs nanosheets with multiple interfaces, which is good to the microwave response. The CoxNiy@C with controllable composition can be obtained by adjusting the ratio of Co2+ and Ni2+. It is supposed that the increased Co content is benefit to the dielectric and magnetic loss. Additionally, the bandwidth of CoNi@C nanosheets can take up almost the whole Ku band. Moreover, this composite has better environmental stability in air, which characteristic provides a sustainable potential for the practical application.

HighlightsA MgH2/TiO2 heterostructure with nano MgH2 assembled on oxygen vacancy-rich 2D TiO2 nanosheets was successfully fabricated via a simple solvothermal strategy.The MgH2/TiO2 heterostructure shows rapid desorption kinetics, low dehydrogenation temperature, and excellent cycling stability.In situ HRTEM observations and ex situ XPS analyses reveal that multi-valance of Ti species, presence of abundant oxygen vacancies, formation of catalytic Mg-Ti oxides, and confinement of TiO2 nanosheets, contribute to the high stability and kinetically accelerated hydrogen sorption performances of Mg.MgH2 has attracted intensive interests as one of the most promising hydrogen storage materials. Nevertheless, the high desorption temperature, sluggish kinetics, and rapid capacity decay hamper its commercial application. Herein, 2D TiO2 nanosheets with abundant oxygen vacancies are used to fabricate a flower-like MgH2/TiO2 heterostructure with enhanced hydrogen storage performances. Particularly, the onset hydrogen desorption temperature of the MgH2/TiO2 heterostructure is lowered down to 180 °C (295 °C for blank MgH2). The initial desorption rate of MgH2/TiO2 reaches 2.116 wt% min−1 at 300 °C, 35 times of the blank MgH2 under the same conditions. Moreover, the capacity retention is as high as 98.5% after 100 cycles at 300 °C, remarkably higher than those of the previously reported MgH2-TiO2 composites. Both in situ HRTEM observations and ex situ XPS analyses confirm that the synergistic effects from multi-valance of Ti species, accelerated electron transportation caused by oxygen vacancies, formation of catalytic Mg-Ti oxides, and stabilized MgH2 NPs confined by TiO2 nanosheets contribute to the high stability and kinetically accelerated hydrogen storage performances of the composite. The strategy of using 2D substrates with abundant defects to support nano-sized energy storage materials to build heterostructure is therefore promising for the design of high-performance energy materials.

HighlightsGraphene-like 2D V2O5 nanosheets rich in oxygen vacancies are designed as multi-functional catalysts to fabricate MgH2-H-V2O5 composites.Hydrogen release starts from 185 °C and capacity retention is as high as 99% after 100 cycles at 275 °C.The composites present rapid kinetics and impressive hydrogen absorption capability at near room temperature.The oxygen vacancies could directly enhance kinetics of MgH2 while indirectly exciting “hydrogen pump” effect of VH2/V.MgH2 is a promising high-capacity solid-state hydrogen storage material, while its application is greatly hindered by the high desorption temperature and sluggish kinetics. Herein, intertwined 2D oxygen vacancy-rich V2O5 nanosheets (H-V2O5) are specifically designed and used as catalysts to improve the hydrogen storage properties of MgH2. The as-prepared MgH2-H-V2O5 composites exhibit low desorption temperatures (Tonset = 185 °C) with a hydrogen capacity of 6.54 wt%, fast kinetics (Ea = 84.55 ± 1.37 kJ mol−1 H2 for desorption), and long cycling stability. Impressively, hydrogen absorption can be achieved at a temperature as low as 30 °C with a capacity of 2.38 wt% within 60 min. Moreover, the composites maintain a capacity retention rate of ~ 99% after 100 cycles at 275 °C. Experimental studies and theoretical calculations demonstrate that the in-situ formed VH2/V catalysts, unique 2D structure of H-V2O5 nanosheets, and abundant oxygen vacancies positively contribute to the improved hydrogen sorption properties. Notably, the existence of oxygen vacancies plays a double role, which could not only directly accelerate the hydrogen ab/de-sorption rate of MgH2, but also indirectly affect the activity of the catalytic phase VH2/V, thereby further boosting the hydrogen storage performance of MgH2. This work highlights an oxygen vacancy excited “hydrogen pump” effect of VH2/V on the hydrogen sorption of Mg/MgH2. The strategy developed here may pave a new way toward the development of oxygen vacancy-rich transition metal oxides catalyzed hydride systems.

HighlightsThe 1T-WS2@TiO2@Ti3C2 photocatalyst is highly active for water splitting to produce hydrogen at 3409.8 μmol g−1 h−1.The Ti3C2 MXene and octahedral (1T) phase WS2 act pathways transferring photogenerated electrons.

Metal phosphorous trichalcogenides (MPX3) are novel 2D nanomaterials that have recently been exploited as efficient photothermal–chemodynamic agents for cancer therapy. As a representative MPX3, FePSe3 has the potential to be developed as magnetic resonance imaging (MRI) and photoacoustic imaging (PAI) agents due to the composition of Fe and the previously revealed PA signal. Here, a FePSe3‐based theranostic agent, FePSe3@APP@CCM, loaded with anti‐PD‐1 peptide (APP) as the inner component and CT26 cancer cell membrane (CCM) as the outer shell is reported, which acts as a multifunctional agent for MR and PA imaging and photothermal and immunotherapy against cancer. FePSe3@APP@CCM induces highly efficient tumor ablation and suppresses tumor growth by photothermal therapy under near‐infrared laser excitation, which further activates immune responses. Moreover, APP blocks the PD‐1/PD‐L1 pathway to activate cytotoxic T cells, causing strong anticancer immunity. The combined therapy significantly prolongs the lifespan of experimental mice. The multimodal imaging and synergistic therapeutic effects of PTT and its triggered immune responses and APP‐related immunotherapy are clearly demonstrated by in vitro and in vivo experiments. This work demonstrates the potential of MPX3‐based biomaterials as novel theranostic agents. In this work, it is shown that the novel biomimetic nanosystem FePSe3@APP@CCM can be used for magnetic resonance/photoacoustic imaging‐guided synergistic anticancer photothermal therapy (PTT) and immunotherapy. The nanosheets (NSs) are decorated with cancer cell membranes and show immune escape and homologous targeting abilities. Under near‐infrared laser irradiation, these NSs provide direct PTT and multiple immunotherapies.

Exploring bifunctional catalysts for the hydrogen and oxygen evolution reactions （HER and OER） with high efficiency, low cost, and easy integration is extremely crucial for future renewable energy systems. Herein, ternary NiCoP nanosheet arrays （NSAs） were fabricated on 3D Ni foam by a facile hydrothermal method followed by phosphorization. These arrays serve as bifunctional alkaline catalysts, exhibiting excellent electrocatalytic performance and good working stability for both the HER and OER. The overpotentials of the NiCoP NSA electrode required to drive a current density of 50 mA/cm2 for the HER and OER are as low as 133 and 308 mV, respectively, which is ascribed to excellent intrinsic electrocatalytic activity, fast electron transport, and a unique superaerophobic structure. When NiCoP was integrated as both anodic and cathodic material, the electrolyzer required a potential as low as -1.77 V to drive a current density of 50 mA/cm2 for overall water splitting, which is much smaller than a reported electrolyzer using the same kind of phosphide-based material and is even better than the combination of Pt/C and Ir/C, the best known noble metal-based electrodes. Combining satisfactory working stability and high activity, this NiCoP electrode paves the way for exploring overall water splitting catalysts.