Control Assembly of Pillar[6]arene-Modified Ag Nanoparticles on Covalent Organic Framework Surface for Enhanced Sensing Performance toward Paraquat

In this study, a class of supramolecular host water-soluble pillar[6]arene (WP6)-modified Ag nanoparticle (WP6@Ag)-functionalized two-dimensional (2D) covalent organic framework (COF) composite is researched for the first time. The obtained 2D heterogeneous hybrid material (WP6@Ag@COF) has excellent electrocatalytic activity and high recognition capability for electrochemical detection of paraquat (PQ). Consequently, a rapid, ultrasensitive, and highly selective electrochemical sensing platform for the determination of PQ is fabricated. The WP6@Ag can be easily prepared by reducing AgNO3 in the presence of WP6. The functionalized WP6@Ag@COF composite can be obtained by the assembly of WP6@Ag onto the surface of COF, where the WP6@Ag serves as a host and electrocatalyst to recognize PQ and enhance the response signal, COF acts as a prominent 2D material for constructing an electrochemical sensing platform, respectively. The electrode, best operated at a working potential of −0.95 to −0.4 V (vs Hg/Hg2Cl2), works in the concentration range of 0.01–50 μM PQ and has a 0.014 μM detection limit. The host–guest interactions are studied by 1H NMR and UV–vis absorption spectroscopies, implying more affinity and high binding constant (Ka) of 1.02 × 108 M–1 by hydrophobic interactions and electrostatic interactions between WP6 and PQ. As a result, this research might offer a prospective strategy for the preparation of the macrocyclic host-modified metal nanoparticle-functionalized 2D heterogeneous hybrid material for sensing, catalysis, and other fields.