Janus sand filter with excellent demulsification ability in separation of surfactant-stabilized oil/water emulsions:...

Developing efficient separation materials for surfactant-stabilized oil/water emulsions is of great importance while significantly challenging. In this work, a sand filter with Janus channels was prepared by simply mixing superhydrophilic and superhydrophobic quartz sand in a mass ratio of 1:1. Due to the imbalanced force of droplets in those Janus channels, better separation performance under gravity was achieved for both surfactant-stabilized oil-in-water and water-in-oil emulsions than the superhydrophilic or superhydrophobic sand filter alone. It also received high flux (1080.13 L m^-2 h^-1 for dichloroethane-in-water emulsion and 1378.07 L m^-2 h^-1 for water-in-dichloroethane emulsion) and high separation efficiency (99.80% for dichloroethane-in-water emulsion and 99.98% for water-in-dichloroethane emulsion). Molecular dynamics based computational work and experimental studies revealed that the Janus channels of mixed sand layer exhibited greater interaction energy with emulsion droplets for more efficient adsorption, resulting in better demulsification capability and separation performance. The as-prepared Janus sand filters retained excellent separation performance after 50 cycles of the stability test. Together with the needs on only cheap and easily accessible raw materials and its environmentally friendly preparation method, this Janus sand filtration process exhibits its great potential for the separation of surfactant-stabilized oil/water emulsions.