β-Ketoenamine-based covalent organic framework for detection and removal of p-phenylenediamine

p-Phenylenediamine (PPD) serves as an important intermediate in materials chemistry and is widely used in the preparation of azo dyes and high polymers. However, the discharge of wastewater from industries containing PPD can pose significant threats to both the environment and human health. Herein, a sensitive and reversible β-ketoenamine-based covalent organic framework (TD-COF) fluorescent probe was fabricated with ketoamine-substituted monomers for detection and facile removal of PPD. Abundant carbonyl groups, the regular pores, and the π-conjugated structure of TD-COF are the key features that help facilitate TD-COF interaction with the analyte. Based on these advantages, TD-COF displayed a low detection limit (0.35 μM), high sensitivity, easy visibility, real-time response, and selective interaction with PPD. Simultaneously, the effective removal of PPD and the circulating utilization of TD-COF provide the potential for practical production applications. Regeneration experimental studies indicated that TD-COF retained satisfactory structural stability after five cycles. Furthermore, based on solid-state NMR, X-ray photoelectron spectroscopy, and density functional theory calculations, these studies verified that hydrogen bonding and π-π interaction mechanisms contribute to fluorescence quenching between PPD and the carbonyl of TD-COF. The research demonstrated the utilization of fluorescent COFs for the sensing and removal of PPD, with the potential for extension to the detection of other pollutants.