Carbon quantum dots embedded mesoporous silica for rapid fluorescent detection of acidic gas.

A fluorescent composite consisting of an ordered mesoporous material (MCM-41) and carbon quantum dots (CQDs) was successfully prepared and designated as MCM/CQDs. CQDs with citric acid as a carbon source and diethylenetriamine as a nitrogen doping agent were directly synthesized in MCM-41 via a hydrothermal method and the reaction conditions were optimized. The MCM/CQDs prepared at the optimized condition showed different fluorescent properties (as indicated by the fluorescent emission wavelength and fluorescent response to acid) compared to the CQDs formed in water. It was found that the preparation of MCM/CQDs caused changes in the characteristics (i.e., surface and pore properties) of MCM-41, which in turn could impact the formation of CQDs in MCM-41. The prepared MCM/CQDs combined the porous nature of MCM-41 and the fluorescent properties of CQDs, and can be applied to the rapid detection of acetic acid (HAc) as a model organic volatile compound. The detection was more sensitive for HAc gas (detection limit: 0.2 μmol/L) than for HAc solution (detection limit: 3 μmol/L). The reason was explained by the physical adsorption of HAc gas by MCM-41, which increased the HAc concentration in the MCM/CQDs and therefore enhanced the fluorescent response. This study expanded the potential application of CQDs embedded mesoporous silica in gas sensing, especially in the rapid and sensitive detection of acetic acid as a representative of acidic volatile compounds.