Ultrathin two-dimensional metal-organic framework nanosheets decorated with tetra-pyridyl calix[4]arene: design, synthesis and application in pesticide detection

Abstract Chemical pesticides are highly toxic and widely spread as environmental pollutants. New strategies are being developed to selectively and sensitively detect pesticides. Herein, we prepared ultrathin two-dimensional (2D) metal-organic framework (MOF) nanosheets, decorated with tetra-pyridyl calix[4]arene, for determination of pesticide based on host-guest chemistry. The 3D layered MOF {[Cd2(5-NO2-BDC)2L(MeOH)]∙2MeOH}n (MOF-Calix; 5-NO2-H2BDC = 5-nitro-1,3-benzenedicarboxylic acid; L = 25,26,27,28-tetra-[(4-pyridylmethyl)oxy]calix[4]arene) was elaborately constructed, with features of 2D layered structure that are held together by weak π…π interactions. Due to the cup-shaped characteristic of calix[4]arene ligand and easy-to-departure MeOH molecules in the interspaces of the 2D layers in MOF-Calix, the 3D bulk MOF-Calix can be readily exfoliated into ultrathin single (2.20 nm) or double-layer (3.73 nm) of 2D nanosheets by ultrasound method with high efficiency. We take the intrinsic advantages of calix[4]arene and the highly accessible active site of calix[4]arene on the surface of the 2D MOF-Calix nanosheets for selective and sensitive sensing of glyphosate via fluorescence enhancement effect with a detection limit of 2.25 μM. This work demonstrates the simple preparation of a 2D MOF nanosheet as fluorescent sensor for glyphosate detection.