The difference between these two configurations is that the H2S has high solubility in the dichloromethane (0.53M) such that the purging process cannot remove H2S from dichloromethane easily [27].
However, H2S has low solubility in the PDMS film and it can absorb by PDMS reversibly depending on the H2S concentration in the surrounding environments [28,29].
Therefore, when the PDMS film is exposed to air again, H2S escapes from the PDMS film, and original ligands recombine with the QDs and fluorescence is regenerated.