In-situ generation of highly active and four-in-one CoFe2O4/H2PPOP nanozyme: Mechanism and its application for fast colorimetric detection of Cr (VI)

Nanozymes have been widely utilized in colorimetric sensors and developing nanomaterials with multienzyme functions have more application prospects due to their cascaded catalytic efficiency. Here, a unique organic-inorganic nanocomposite CoFe2O4/H2PPOP was synthesized by depositing CoFe2O4 nanocubes on a fully conjugated porphyrin-based porous organic polymer (H2PPOP) in situ. CoFe2O4/H2PPOP revealed outstanding tetra-enzyme-like activities, namely oxidase-like, peroxidase-like, catalase-like and superoxide dismutase-like activities. Compared with pure CoFe2O4 nanocubes, the catalytic activities of CoFe2O4/H2PPOP were significantly boosted because of the large surface area and extended conjugated structure of H2PPOP, abundant active substances (CoFe2O4) on the surface and the effective electronic transfer between CoFe2O4 and H2PPOP. Based on the oxidase-like activity of CoFe2O4/H2PPOP, a colorimetric platform was constructed for Cr (VI) with a wide linear range (0.6-100 μM) and a low detection limit (26 nΜ). Further utilizing the double oxidase-like and peroxidase-like activities, a more sensitive colorimetric platform with a faster detection speed for Cr (VI) was realized with the LOD as low as 2 nΜ. This work opens up a new way to prepare multi-enzyme active nanozyme and excavates its potential for detecting environmental pollutants.