In-situ generation of highly active and four-in-one CoFeO/HPPOP 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 CoFeO/HPPOP was synthesized by depositing CoFeO nanocubes on a fully conjugated porphyrin-based porous organic polymer (HPPOP) in situ. CoFeO/HPPOP revealed outstanding tetra-enzyme-like activities, namely oxidase-like, peroxidase-like, catalase-like and superoxide dismutase-like activities. Compared with pure CoFeO nanocubes, the catalytic activities of CoFeO/HPPOP were significantly boosted because of the large surface area and extended conjugated structure of HPPOP, abundant active substances (CoFeO) on the surface and the effective electronic transfer between CoFeO and HPPOP. Based on the oxidase-like activity of CoFeO/HPPOP, 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.