Covalent organic framework composites TpPa@CeO2 with catalytic activities for sensitive colorimetric detection of ascorbic acid

Schematic diagram of the dual enzyme activities of TpPa@CeO 2 and the colorimetric detection of AA in beverage and vitamin C tablet samples. • The novel covalent organic framework composite (TpPa@CeO 2 ) was successfully synthesized. • TpPa@CeO 2 has dual mimic enzyme activity of oxidase and peroxidase. • The colorimetric sensor constructed by TpPa@CeO 2 has good sensitivity to AA. • The mechanism of catalytic reaction was discussed. • This sensor has been useful for evaluating the level of AA in beverage and tablet samples. Cerium dioxide (CeO 2 ) 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@CeO 2 ) with dual mimic enzyme activities (oxidase and peroxidase) was successfully synthesized via a facile hydrothermal method. TpPa@CeO 2 showed higher catalytic activity than CeO 2 . The excellent catalytic performance of TpPa@CeO 2 could be attributed to the higher surface area, more surface active species and higher Ce 3+ /Ce 4+ ratio in the composite than CeO 2 . Based on this, a visual and sensitive colorimetric sensor was constructed to detect ascorbic acid (AA) in the linear range of 0.2–35 μM with a low detection limit (LOD) of 0.061 μM. 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 CeO 2 improved the ratio of Ce 3+ /Ce 4+ , which promoted the decomposition of dissolved oxygen and H 2 O 2 by CeO 2 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.