Hydrogen Bonding Promoting Charge Recombination over Carbon Nitride Nanodots for Fluorescent Chemosensing of Carbon Dioxide

Developing a sample fluorescent sensor without modification of fluorophores with specific CO₂-responsive groups for high efficient CO₂ detection presents considerable technical challenges, particularly for room-temperature detection. Herein, an innovative fluorescent turn-on chemosensor based on amino- and hydroxyl-comodified carbon nitride nanodots (CNNDs) was developed, which exhibited remarkable room-temperature CO₂ detection performance without introducing any other organic compounds. This impressive performance was attributed to the dissolution of CO₂ in water to form H₂CO₃ and the ionized H⁺ protonated the secondary amino groups of CNNDs, while the primary amino groups interacted with the HCO₃^- to form a carbamate (-NH-COO^-)-like structure. The protonation of CNNDs and formation of carbamate-like units together promoted the formation of hydrogen bonding between the negatively charged CNNDs. These hydrogen bonding sites were proved to serve as charge recombination centers to enhance fluorescent yield, making the fluorescence of CNNDs sensitive to CO₂. In addition, the introduced CO₂ was easy to remove via simple bubbling of Ar into the system, making the chemosensor highly repeatable. Thanks to these merits, the as-constructed CNNDs-based chemosensors exhibited high applicability potential in monitoring grain preservation status via the CO₂ concentration.