Demulsification of oil-in-water emulsions with long cleaning interval by superhydrophilic copper foams with enhanced hydration capacity

Abstract

Three-dimensional superhydrophilic materials, with large pores and extensive permeation channels, can achieve high-flux separation of oil-in-water emulsions. However, complex internal structure and high specific surface area also lead to severe oil contamination during the separation process, resulting in rapid declines in separation efficiency and permeation flux, necessitating frequent cleaning and significantly limiting their practical applications. The oleophobicity of superhydrophilic materials mainly relies on the hydration layer on the surface. Enhancing the combination strength of superhydrophilic surfaces to water can effectively reduce the hydration layer damage caused by oil, thereby extending the demulsification lifespan of the material. In this study, we enhance the hydration strength of the copper foam surface by constructing a special pocket-like nano structure and endowing it with a substantial number of hydrated groups. During continuous separation of oil-in-water emulsions, the copper foam filter can achieve a separation efficiency exceeding 99.1 % and a permeation flux greater than 20,000 L·m⁻²·h⁻¹. In cyclic separation tests, under conditions where the cleaning interval up to 150 mL of emulsion, the declined efficiency remains at 98.4 %, while the declined flux exceeds 18,000 L·m⁻²·h⁻¹. The cleaning interval is as high as 85 mL·cm⁻². Furthermore, after cleaning, both the separation efficiency and permeation flux of the copper foam can be completely restored, significantly outperforming the copper foam without hydration strengthen modification and various other three-dimensional materials.