Superhydrophilic Modification of Polyvinylidene Fluoride Membrane via a Highly Compatible Covalent Organic Framework-COOH/Dopamine-Integrated Hierarchical Assembly Strategy for Oil-Water Separation

The integration of membranes with additives such as functionalized nanomaterials can be recognized as an effective method to enhance membrane performance. However, to obtain an efficient nanoparticle-decorated membrane, the compatibility of nanomaterials remains a challenge. Hydrophilic carboxylated covalent organic frameworks (COF-COOH) might be expected to avoid the drawbacks of aggregation and easy shedding of inorganic materials caused by the poor interfacial compatibility. Herein, a highly compatible dip-coating strategy was proposed for the superhydrophilic modification of polyvinylidene fluoride membrane via COF-COOH integrated with dopamine. COF-COOH together with polydopamine nanoparticles were uniformly and stably attached to the membrane due to the high interfacial compatibility, constructing a coating with rough hierarchical nanostructures and abundant carboxyl groups. The synergistic effects of multiscale structures and chemical groups endow the membrane with superhydrophilicity and underwater superoleophobicity, the water contact angle decreased from 123 to 15 degrees, and the underwater oil contact angle increased from 132 to 162 degrees. Accordingly, the modified membrane exhibits an ultrahigh oil rejection ratio (>98%), a high flux (the maximum reaches 1843.48 L m-2 h-1 bar-1), attractive antifouling ability, and impregnable stability. This work would provide a momentous reference for the application of COF-COOH in practical oily wastewater treatment.

Automated summary

The integration of hydrophilic carboxylated covalent organic frameworks (COF-COOH) with dopamine was used to modify polyvinylidene fluoride membranes, resulting in a highly compatible and superhydrophilic membrane with rough hierarchical nanostructures and abundant carboxyl groups. The modified membrane exhibited superhydrophilicity and underwater superoleophobicity, with high oil rejection ratio, high flux, and excellent antifouling ability.