Covalent Organic Framework Composites TpPa@CeO2 with Catalytic Activities for Sensitive Colorimetric Detection of Ascorbic Acid

Cerium dioxide (CeO2) has usually been used as a catalyst for colorimetric assays. However, the low catalytic efficiency has limited their further application. Covalent organic frameworks (COFs) have sparked increasing interest in the unique properties of large surface area, high porosity, and good thermochemical stability. Herein, a novel covalent organic framework composite (TpPa@CeO2) with dual mimic enzyme activities (oxidase and peroxidase) was successfully synthesized via a facile hydrothermal method. TpPa@CeO2 showed higher catalytic activity than CeO2. The excellent catalytic performance of TpPa@CeO(2 )could be attributed to the higher surface area, more surface active species and higher Ce3+/Ce4+ ratio in the composite than CeO2. Based on this, a visual and sensitive colorimetric sensor was constructed to detect ascorbic acid (AA) in the linear range of 0.2-35 mu M with a low detection limit (LOD) of 0.061 mu M. Moreover, the excellent colorimetric sensor was successfully applied to detect AA in beverage and tablet samples with satisfactory recoveries ranging from 95.78 % to 100.84 %. The catalytic mechanism could be that the composition of TpPa and CeO2 improved the ratio of Ce3+/Ce4+, which promoted the decomposition of dissolved oxygen and H2O2 by CeO2 to produce superoxide radicals (.O-2(-)) and hydroxyl radicals (.OH), respectively. The facile and sensitive sensor system constructed by TpPa@CeO(2 )with promising applications provides a new platform for the detection of AA in real sample analysis.