Superhydrophilic Silica Coatings via a Sequential Dipping Process

A superhydrophilic silica coating was prepared using a sequential dipping process involving acid-catalyzed silica, base-catalyzed silica, and 3-(trihydroxysilyl)propanesulfonic acid. Acid-catalyzed and base-catalyzed silica particles with varying diameters were synthesized by hydrolyzing tetraethyl orthosilicate using HCl and NH₃·H₂O as catalysts, respectively. 3-(Trihydroxysilyl)propanesulfonic acid was obtained by oxidizing mercaptopropyl trimethoxysilane with hydrogen peroxide under acidic conditions. The resulting silica coating exhibited exceptional superhydrophilicity, with a water static contact angle of 5.0°, and demonstrated underwater superoleophobicity, with a hexadecane underwater contact angle exceeding 140°. Surfaces coated with the superhydrophilic silica coatings showed excellent performances in oil-water separation, anti-protein adsorption, and anti-fogging applications.