Oxygen vacancies rich Co-Mo metal oxide microspheres as efficient oxidase mimetic for colorimetric detection of sulfite

Modulation of surface oxygen vacancies (O-v) by defect engineering is an attractive strategy for designing high performance transition metal oxide nanozymes. In this work, we reported the fabrication of the CoMoO4 oxidaselike nanozyme, i.e. CoMo-300r, by first pyrolyzing the CoMo layered double hydroxide precursor in an air atmosphere at 300 degrees C and subsequent NaBH4 reduction strategy. Various characterization outcomes confirm the mesoporous structures of both CoMo-300r and no NaBH4 treated CoMo-300, while the specific surface area of CoMo-300 is significantly increased from 103.54 m(2)center dot g(-1) to 165.24 m(2)center dot g(-1) after NaBH4 reduction. Also, NaBH4 reduction treatment leads to the formation of O-v rich CoMoO4 and reduced metal ion species on the surface, promoting the redox reaction kinetics. The CoMo-300r prepared at a molar ratio of Co to Mo of 1:2, pyrolysis temperature of 300 degrees C and 10 mM NaBH4 exhibited the best oxidase-like activity. The oxidase-like activity of CoMo-300r is 2.6-fold times that of no NaBH4 treated optimal CoMo-300. The CoMo-300r can effectively promote TMB oxidation to produce blue color and has the Michaelis-Menten constant of 0.0428 mM, which was lower than most cobalt-based oxide nanozymes and indicated a higher affinity for TMB. In terms of inhibition of SO32- on the CoMo-300r/TMB system, a sensitive SO32- colorimetric sensing platform was established. The linear range and limit of detection for sulfite determination were 0.2-40 mu M and 0.09 mu M, respectively. The relative standard deviation for the determination of 10 mu M sulfite was 1.41% (n = 11). The method was successfully applied to the detection of sulfite in white wine. This work provides a new strategy to fabricate high activity oxidase mimetic for food analysis.