RCDs@ZIF-8 fluorescent nanocomposites: A dual-functional platform for Cr(VI) visualization detection and latent fingerprint development

Developing solid-state red light–emitting carbon quantum dots (CQDs) with high photothermal stability remains a key challenge in this field. This study successfully constructed a new dual–function fluorescent nanocomposite material (RCDs@ZIF-8) by encapsulating 4,4-dihydroxybenzophenone and o-phenylenediamine-derived red fluorescent carbon quantum dots in ZIF-8 metal–organic frameworks. The porous structure of ZIF-8 effectively confines RCDs, significantly improving their photostability and fluorescence specificity, and successfully imparting them with intense red solid–state fluorescence. The RCDs@ZIF-8 composite material exhibits extremely high red fluorescence intensity in a solid state and can be used as an efficient, ratio–type fluorescent probe. In solution, it exhibits a highly selective fluorescence quenching response to Cr 6+ ions with a detection limit of 0.49 μM, making it suitable for the rapid, visual detection of trace amounts of Cr 6+ in environmental water samples. More importantly, the strong solid-state fluorescence of this material enables the high-contrast visualization of latent fingerprints, with clear and distinct fingerprint lines. RCDs@ZIF-8 integrates efficient solution sensing (Cr 6+ detection) and high–performance solid-state light emission/imaging (fingerprint identification, optical applications) in a dual-function manner. It has a wide range of applications in environmental monitoring, forensic identification, and optical anti–counterfeiting.