Mixed valence state cerium metal organic framework with prominent oxidase-mimicking activity for ascorbic acid detection: Mechanism and performance

It is indispensable to establish a simple, effective and accurate method for ascorbic acid (AA) detection since it plays a crucial role in human health. Herein, a novel oxidase mimic of mixed valence state cerium metal organic framework (MVCM) was successfully synthesized by in-situ partial oxidation of cerium metal organic framework (Ce-MOF). On account of the Ce (Ⅲ)/Ce (Ⅳ) redox couple inside, MVCM could directly catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate a blue color product (ox TMB) without adding H2O2, exhibiting a prominent intrinsic oxidase mimetic activity compared to Ce-MOF. Moreover, this catalytic mechanism of MVCM was further clarified by means of cyclic voltammetry (CV) test, UV–vis absorption spectra with O2 or N2 saturated condition and electron paramagnetic resonance (EPR) measurements. In the presence of AA, a redox reaction occurred between AA and ox TMB, and then resulting in a conspicuous blue color fading. By optimizing the testing conditions, a linear absorbance response was well correlated with the AA concentration ranging from 20 to 500 μM with a detection limit of 3.57 μM. MVCM also displayed the excellent selectivity and anti-interference performance for AA detection. Benefitting from the above, this AA detection method was applied in real Vitamin C effervescent tablets, showing a favorable reproducibility and feasibility. These results strongly indicated that the proposed method based on MVCM as an oxidase mimic might be a promising candidate for AA detection in food field.