In industrial oily wastewater, surfactant-stabilized oil-water emulsions form a dispersed system with a double-layer structure through interfacial adsorption. Due to the tiny size of oil droplets (micrometer level) and the high stability of the double layer, these emulsions suffer from the difficulty of emulsion breaking and low separation efficiency using the traditional separation technology. Although superwetting materials have achieved progress in emulsion separation by constructing sub-micron pore structures based on the size-sieving mechanism, the separation mechanism relying solely on physical interception, is difficult to satisfy for the processing of complex emulsion systems.

Recently, researchers from the Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, have successfully developed a functionalized stainless steel felt (SiO₂-SSF) with a surface charge, which provides a new strategy for the efficient separation of oil-water emulsions. The researchers used stainless steel felt as a substrate, modified the fiber surface with aminated silica nanoparticles (SiO₂-NH₂) through the sulfur-based three-component coupling reaction, and obtained a separation material with nano- and micrometer multilayer structure by mechanical compression. The functional material exhibited superhydrophilic and underwater superoleophobic properties, and it can effectively separate emulsions stabilized by anionic, cationic, nonionic, and zwitterionic surfactants, with a maximum separation efficiency of 96.2%. Based on above results, the charge-induced aggregation demulsification separation mechanism was proposed. The fiber materials with the charges destabilized the emulsion through electrostatic attraction or repulsion, causing small oil droplets to aggregate into larger ones, thereby achieving the separation of surfactant-stabilized emulsions. Compared to traditional superwetting materials that rely solely on size-sieving mechanisms, the charge-induced aggregation demulsification mechanism precisely controlled the surface charge of the material, effectively destabilizing the emulsion through electrostatic interactions, driving the directional aggregation of dispersed oil droplets, and achieving efficient separation of complex emulsion systems.

Compared with the separation mechanism of traditional superwetting materials that relied solely on size-sieving, the charge-induced aggregation demulsification mechanism precisely controlled the surface charge of the material, effectively destabilized the emulsion through electrostatic interactions, driving the directional aggregation of dispersed oil droplets, and achieved efficient separation of complex emulsion systems.

The research results were published in Separation and Purification Technology, entitled as “Charge-induced aggregation of emulsified oil droplets in water with the presence of functionalized stainless steel felt“ (Separation and Purification Technology, Volume 353, Part B, 2025, 128530). The work was supported by the Youth Innovation Promotion Association of the Chinese Academy of Sciences, the Natural Science Foundation of Xinjiang Uygur Autonomous Region and the Shanghai Cooperation Organization Science and Technology Partnership Program and the International Science and Technology Cooperation Program.

Figure 1: Preparation process of the material and schematic diagram of charge-induced aggregation demulsification separation (Image by Prof MA Peng-Cheng’s group).