Water-sensitive phase-transition of a carbon dot–calcium carbonate composite for moisture detection in organic solvents

We report herein a nanocomposite that has a continuous phase of amorphous calcium carbonate (ACC) filled with fluorescent carbon quantum dots (CDs) and undergoes phase transitions triggered by changes in moisture content in organic solvents. The phase transitions involve aggregation of the nanocomposite particles (in the order of 20 nm) and crystallization of the ACC phase, expelling the CDs from the composite and generating fluorescent signals at the same time. This can be triggered with a moisture content as low as 15 ppm, and the intensity of the fluorescent signal can be correlated quantitatively with a moisture content of up to 100%.