Stimuli-responsive wettability quartz sand filter material for efficient separation of oil/water mixture and controllable demulsification of oil/ water emulsion

Stimuli-responsive separation materials with reversible wettability transition have been attracting increasing attention because they have excellent oil/water separation performance. In this study, a facile and environmentally friendly approach was used to produce a quartz sand filter material with pH-controllable wettability between superhydrophobicity/superoleophilicity and superhydrophilicity/underwater superoleophobicity. PEI/ ZnO-SA/CS-coated quartz sand filter material (PEI/ZnO-SA/CS@QS) was fabricated by introducing ZnO nano particles, hydrophobic alkyl long chain, and amino group-rich hydrophilic groups into the surface of quartz sand filter material. Rich amino groups on the surface of the PEI/ZnO-SA/CS@QS has high adsorption capacity and separation efficiency of industrial Congo red dye and methylene blue. Before and after wettability conversion, the pH-controllable PEI/ZnO-SA/CS@QS was applied to separate oil/water mixtures and separate various water in-oil emulsions and oil-in-water emulsions. In addition, PEI/ZnO-SA/CS@QS is recyclable, and 10 cycles of oil/ water mixture separation of specific experiments in this study were performed, remaining unchangeable separation efficiency (>98.89%). PEI/ZnO-SA/CS@QS provides a new research direction for on-demand oil/water separation and modification of hard filter media. The resulted PEI/ZnO-SA/CS@QS has promising application prospects in on-demand oil/water separation and demulsification.

Automated summary

This study developed a pH-controllable quartz sand filter material that can switch between different wettability states. The material showed high adsorption capacity and separation efficiency, making it effective for separating oil/water mixtures and emulsions.