π-Conjugation-Regulated Vesicular Carbon Nitride Z-Type Homojunctions: Toward Integration of Pollutant Degradation and Detection

Food safety requires both efficient removal of organic dyes and on-site visualization, yet most methods are single-function, focusing only on degradation or detection. We propose a π-conjugated porous vesicular carbon nitride (CPCN), where pyrimidine rings are introduced via hydrogen-bonding self-assembly, forming an in-plane Z-type homojunction within the g-C3N4 skeleton and enabling electron density redistribution. The vesicular hierarchical porous structure enhances light absorption and interfacial reactivity. Multiscale characterization and theoretical analysis show that the built-in electric field significantly promotes exciton dissociation and carrier migration, achieving rapid degradation of malachite green (MG) under visible light with ∼99.3% efficiency within 30 min. A ratiometric fluorescent probe using rhodamine B and CPCN nanosheets (CPCN NS) enables highly sensitive MG detection with a limit of 0.013 μg mL–1. CPCN loaded in sodium alginate gel microspheres easily removes malachite green from fish tissues, enabling portable on-site detection in conjunction with fluorescent test strips with cell phone RGB recognition. This provides a scalable solution for environmental remediation and food safety.