Highly luminescent S-doped carbon dots for the selective detection of ammonia

Carbon dots (S-CDs) were obtained from two different S-containing polymer precursors using a hydrothermal treatment. They were used as highly sensitive and selective ammonia sensors based on a change in the fluorescence intensity. The gas detection test was carried out through the direct insertion of gaseous ammonia into the CD solutions. The results showed a time-dependent (concentration dependent) fluorescence quenching in the presence of ammonia. The detection time was as low as 30 s. The fluorescence quenching was linked to the involvement of sulfur and oxygen containing surface functional groups in a chemical reaction with NH3. In particular, sulfonic and carboxylic acids participated in acid-base reactions with ammonia to form ammonium salts. In the reaction of the target gas with carboxylic acids/acid anhydrites or phenols, cyclic ethers and ketone groups (diketones), amides and amines were formed, respectively. Strongly acidic sulfones and sulfonic acids played the most crucial role. The sample with the highest contribution of those groups showed the highest affinity for the reaction with ammonia, and thus the highest sensitivity among two samples tested.

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