Ultra-efficient electromagnetic wave absorption with ethanol-thermally treated two-dimensional Nb₂CT_x nanosheets

Nb₂CT_x, an emerging type of MXene, should be a promising electromagnetic wave (EMW) absorbing material to overcome the EMW pollution nowadays due to its unique layered structure and extremely thin monolayer thickness, but was lack of systematic study till now. Meanwhile, Nb₂CT_x nanosheets obtained upon HF etching of Nb₂AlC MAX was unfortunately found with limited absorption performance due to its mainly dielectric loss mechanism herein. Therefore, the Nb₂CT_x nanosheets were further treated with solvothermal strategy in various solvents. As a result, the absorption performance of the as-treated Nb₂CT_x nanosheets could be significantly improved, while the ones in ethanol showed much more superior absorption capability, especially in the low-frequency band (2.0-4.0 GHz). The minimum reflection loss value could reach -52.2 dB at 3.93 GHz with the thickness of only 2.90 mm, indicating more than 99.999% EMW was absorbed. These should be due to the multi-loss mechanism including dielectric, interfacial, and multiple reflection ones resulting from the enlarged interlayer spacing, and increased surface functional groups on the Nb₂CT_x nanosheets upon the ethanol-based solvothermal treatment.