Fluorescent Test Paper via the In Situ Growth of COFs for Rapid and Convenient Detection of Pd(II) Ions

With the extensive use of palladium derivatives in the industry, their environmental pollution has become more and more serious. Herein, allyl functionalized hydrazone 2D COFs (XB-COFs) were found for selective fluorescent detection of Pd2+ (detection concentration of 0.29 μM) in water. The stable structure of the hydrazone bond and the complexation ability of allyl to Pd2+ cause XB-COF to have a good fluorescence sensing effect in both acid and alkaline solutions, and its adsorption capacity for Pd2+ is up to 120 mg g–1. During the interaction between XB-COF and Pd2+, a part of Pd2+ can be reduced to Pd nanoparticles with a diameter of about 10 nm. A fluorescent test paper was prepared by the in situ growth of XB-COF onto a filter paper, which can realize visualization detection of Pd2+ in 10 s with the naked eye or under a 365 nm UV lamp. This is the first time a fluorescent test paper based on in the situ growth of COFs has been applied for the detection of heavy metal ions, which provides a new platform for the application of COF materials in the medical health field, food safety, and environmental protection.