Nanoparticle-Induced Charge Redistribution of the Air–Water Interface

*S Supporting Information ABSTRACT: The air−water interface is believed to carry a negative electrostatic potential that is nontrivial to invert through pH, electrolyte, or electrolyte strength. Here, through a combined experimental and theoretical study, we show that the close approach of a negatively charged nanoparticle induces a charge redistribution of the air−water interface. Using different electrolytes to control the interfacial potential of the nanoparticles, X-ray photoelectron spectroscopy (XPS) results establish that nanoparticles with a more negative zeta potential adsorb closer to the air−water interface than do the same particles with a less negative zeta potential. The short-ranged attractive force between two (nominally) negative surfaces is caused by charge redistribution under the strong electric field of the nanoparticle that locally inverts the charge density of the air−water interface from negative to positive. The nature of the nanoparticle’s counterions modulates the attractive interaction, which thus could be used to control reactivity, stability, and nanoparticle self-assembly at air−water interfaces.