A microgel-structured cellulose nanofibril coating with robust antifouling performance for highly efficient oil/water and immiscible organic solvent separation

Recently, superhydrophilic-underwater superoleophobic hydrogel coatings with excellent antifouling performance have attracted increased attention for oily wastewater purification. However, the antifouling performance of hydrogel coatings is destroyed when they are exposed to air or oily conditions without prewetting. In addition, their application in industry is limited by toxic crosslinking agents, poor adhesion to substrates, and complex synthesis processes, among other factors. Herein, a versatile cellulose nanofiber microgel coating is developed via a strategy of catechol-amine chemistry that can be simply applied on various substrates through a layer-by-layer method without any additional toxicant crosslinking agents or nanoparticles. Consequently, the resultant coating, which has underwater superoleophobic and underoil superhydrophilic properties, exhibits long-term stable antifouling performance without prehydration. In addition, it displays ultrahigh physical durability and chemical stability, even with exposure to various harsh conditions, e.g., acidic, alkaline, salt and UV light environments, as well as mechanical attrition. Moreover, under gravity, coated stainless steel mesh can rapidly separate various oil/water and immiscible organic solvents (with a water flux of 139556 ± 3733 L m−2 h−1). Even coated melamine sponges can efficiently separate surfactant-stabilized oil-in-water and water-in-oil emulsions. Thus, this study provides a general method for preparing a robust microgel coating and discusses prospective applications in on-demand multitype liquid separation in practical hazardous water purification applications.