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@CeO2 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 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 CeO2 improved the ratio of Ce3+/Ce4+, which promoted the decomposition of dissolved oxygen and H2O2 by CeO2 to produce superoxide radicals (·O2–) and hydroxyl radicals (·OH), respectively. The facile and sensitive sensor system constructed by TpPa@CeO2 with promising applications provides a new platform for the detection of AA in real sample analysis.

中文翻译：

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具有催化活性的共价有机框架复合材料TpPa@CeO2用于抗坏血酸的灵敏比色检测


二氧化铈 （CeO2） 通常用作比色测定的催化剂。然而，低催化效率限制了它们的进一步应用。共价有机框架 （COF） 引发了人们对大表面积、高孔隙率和良好热化学稳定性等独特特性的日益兴趣。在此，通过简单的水热法成功合成了一种具有双重模拟酶活性 （氧化酶和过氧化物酶） 的新型共价有机框架复合物 （TpPa@CeO2）。TpPa@CeO2显示出比 CeO2 更高的催化活性。TpPa@CeO2 优异的催化性能可归因于复合材料中比 CeO2 更高的表面积、更多的表面活性物质和更高的 Ce3+/Ce4+ 比率。基于此，构建了一种视觉灵敏的比色传感器，可在 0.2–35 μM 的线性范围内检测抗坏血酸 （AA），检测限 （LOD） 为 0.061 μM。此外，出色的比色传感器成功用于检测饮料和片剂样品中的 AA，回收率从 95.78 % 到 100.84 % 不等。催化机理可能是 TpPa 和 CeO2 的组成提高了 Ce3+/Ce4+ 的比例，从而促进了 CeO2 分解溶解氧和 H2O2 生成超氧自由基（·O2–） 和羟基自由基 （·OH） 的 Alpha T� S STpPa@CeO2构建的简单灵敏的传感器系统具有广阔的应用前景，为实际样品分析中 AA 的检测提供了一个新的平台。