The Construction of n‐n Heterojunction in Polyoxometalate Based Nanozyme to Enhance Peroxidase‐Like Activity for Nitrite Detection

Nitrite (NO 2 − ) is a notorious pollutant that has attracted increasing concern. This study synthesizes a novel polyoxometalate (POM) nanozyme Fe 2 V 4 O 13 /V 2 O 5 and leverages its excellent catalytic performance to develop asmartphone‐based platform for the highly sensitive detection of NO 2 − . An n–n heterojunction formed between Fe 2 V 4 O 13 and V 2 O 5 induces electron redistribution, generating a built‐in electric field that improves the interaction between Fe 2 V 4 O 13 and substrates in peroxidase‐like (POD‐like) catalysis. Given the excellent POD‐like activity of Fe 2 V 4 O 13 /V 2 O 5, NO 2 − can undergo diazotization reaction with the blue oxidized product ox‐TMB generated by the nanozyme catalyzing 3,3,5,5‐tetramethylbenzidine (TMB), resulting in the solution color changing from blue to yellow. Consequently, a visible colorimetry is developed for NO 2 − detection with a low limit of detection (LOD). The method has demonstrated excellent performance in the actual detection of NO 2 − in water samples. This work not only offers a new construction strategy to enhance the catalytic activity of POM‐based nanozymes, but also provides an efficient and practical platform for the highly sensitive NO 2 − detection.