Toward an Enhanced Hydrophilic TiO₂ Nanoparticles Adsorption at Air–Liquid Interface Through Ion Regulation

This study investigates the dynamic properties of air–liquid interfacial tension for hydrophilic TiO 2 P25 utilizing the pendant drop method. Additionally, it examines the interfacial adsorption mechanism of hydrophilic TiO 2 particles, considering the characteristics of particle surface charge distribution in relation to ion regulation to enhance particle interface adsorption. Experimental results reveal that in the absence of ion addition, the TiO 2 P25 suspension system exhibits limited interfacial adsorption due to its superhydrophilicity, regardless of particle concentration. The addition of NaCl increases the surface charge density of the particles, strengthens the electrostatic attraction between particles and the interface, and enhances particle adsorption. Specifically, at a low NaCl concentration (0.01 wt %), the increased surface charge density and contact angle of the particles elevate particle activity and high interfacial packing density. At a higher NaCl concentration (0.1 wt %), while NaCl further increases the particle contact angle, the increased effective cross-sectional area of the air–liquid interface occupied by individual particles leads to a reduction in surface free energy. Despite the enhanced electrostatic attraction, this results in a lower packing density.