Fig. 1: Identification of water adsorption on partially hydroxylated CQD surfaces.

a Schematic representation of surface conditions on octahedral PbS CQDs. The ideal model of PbS CQDs with atomic halide passivation is shown on the left. The proposed surface conditions on the Pb-terminated {111} facet are zoomed on the right. Top: the OA-capped facet with partial surface hydroxylation introduced in the synthetic process¹⁵; Medium: Atomic iodine-passivated facet after ligand exchange; Below: the aggravation of surface hydroxylation followed by water adsorption under humid air. b The geometric structures of iodine-passivated (left), partially hydroxylated (middle) and water adsorbed PbS {111} facets (right) used in DFT calculation. The E_ad and E_vac stand for the adsorption energy of H₂O and the vacancy formation energy, respectively. The purple spheres stand for iodine atoms, black ones for Pb atoms, yellow ones for S atoms, red ones for O atoms, and white ones for H atoms. c The temperature-dependent O1s XPS spectra of PbS-I film. d Atomic ratio of surface species relative to Pb 4f core recorded at a temperature from 290 K to 450 K. e XAS spectra of PbS CQD films at the oxygen K-edge prepared under different ambient conditions. The “Spin-humid” and “Spin-dry” represent the sample deposited and ligand exchanged under ambient air with a high RH (50–60%) or low RH (<10%), respectively. The XAS spectra of liquid water and different surface chemical species observed in XPS O1s core are also shown. The XAS spectra of liquid water are extracted from Wernet et al. (2004)². Reprinted with permission from AAAS. The spectra difference between “Spin-humid” and “Spin-dry” is calculated for a clearer comparison.