High-efficient liquid exfoliation of 2D metal-organic framework using deep-eutectic solvents

The exfoliation of bulk two-dimensional metal-organic framework (MOF) into few-layered nanosheets has attracted much attention recently. In this work, an environmental-friendly route has been developed for layered-MOF (MAMS-1) delamination using deep eutectic solvent (DES), which is more sustainable and efficient alternative than conventional organic solvents for MOF nanosheet preparation. Under sonication condition, DES as solvents, the highest exfoliation rate of MAMS-1 is up to 70% with two host layers via poly(vinylpyrrolidone) (PVP) surfactant-assisted method. The presence of tert-butyl exteriors and the atomically thickness endow the MOF nanosheets stable suspension for at least one month. Due to the 2D structure and excellent stability, MAMS-1 nanosheet (MAMS-1-NS) was chosen as a good candidate to encapsulate Eu³⁺ cations. The obtained Eu³⁺@MAMS-1-NS acts as a multi-responsive luminescent sensor through fluorescence quenching, and can specifically recognize Fe³⁺ (LOD = 0.40 μM, K_SV = 1.05 × 10⁵ M^-l), Hg²⁺ (LOD = 0.038 μM, K_SV = 5.78 × 10⁶ M^-l), Cr₂O₇^2- (LOD = 0.33 μM, K_SV = 1.55 × 10⁵ M^-l) and MnO₄^- (LOD = 0.088 μM, K_SV = 4.49 × 10⁵ M^-l). Compared with bulk Eu³⁺@MAMS-1, the sensitivity of Eu³⁺@MAMS-1-NS is greatly improved owing to its ultrathin nanosheet morphology and highly accessible active sites on the surface.