The flexible DADM-based covalent organic frameworks constructed by flexible knots and 4,4′-diaminodiphenylmethane as a linker for fluorescence sensing nitrophenol and adsorping iodine

Abstract

Enrichment of nitro-aromatic compounds (NACs) and radioactive iodine seriously threatens the health of humans, therefore, trace detection of NACs and the efficient capture and storage of radioactive iodine have attracted a great deal of attention in recent years. Herein, we present two highly efficient flexible DADM-based covalent organic frameworks (DADM-based COFs) for the fluorescence sensing of o-nitrophenol (o-NP) and p-nitrophenol (p-NP) and reversible iodine capture, namely TDADM and HDADM. The resulting TDADM and HDADM have excellent thermal and chemical stability, some crystallinity and high BET surface areas of 1035 and 958 m2 g−1, respectively. For fluorescence sensing, TDADM and HDADM show high sensitivity to o-NP and p-NP with quenching constants (Ksv) of 6.77 × 103 and 3.39 × 104 L mol−1, respectively. The fluorescence quenching of TDADM is caused by the action of photo-induced electron transfer (PET) processes. The fluorescence quenching of HDADM is caused by the co-action of PET and resonance energy transfer (RET) processes. For iodine capture, TDADM and HDADM exhibit high iodine capture capacities, which are severally up to 4.08 and 5.32 g g−1. Such high iodine adsorption amounts are caused by the electron transfer of the electron-rich flexible DADM-based COFs to the electron-deficient I2 into the polyiodide anion complexes.