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

Abstract

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°, and the underwater oil contact angle increased from 132 to 162°. 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.

Covalent organic framework-based lamellar membranes for water desalination applications

“…Among them, COF-based membranes (Table 1) have been proven to be one of the best platforms for producing size-selective ionic and molecular separation membranes because of their adjustable pore size, ultrathin thickness, high porosity, exceptional mechanical strength, well-organized pore structures, and chemical inertness. 104–116 In this section, the ionic and molecular separation properties of COF laminates are discussed in detail.…”

Recent Developments in Two-Dimensional Materials-Based Membranes for Oil–Water Separation

“…In another work, the carboxylated COF (COF-COOH) integrated with polydopamine (PDA) was assembled on the surface of the PVDF microfiltration membrane by employing a dip-coating method [ 160 ]. The high interfacial compatibility between COF-COOH and PDA resulted in a uniform and stable coating with high bond strength.…”

“…The high interfacial compatibility between COF-COOH and PDA resulted in a uniform and stable coating with high bond strength. The hierarchical structure along with the hydrophilic carboxyl groups enabled the membrane to demonstrate superhydrophilic and underwater superoleophobic wettability [ 160 ]. The membrane showed an oil rejection ratio of >98% and the permeate flux of up to 1843.48 L m −2 h −1 bar −1 [ 160 ].…”

Highly Permeable Sulfonated Polydopamine Integrated MXene Membranes for Efficient Surfactant-Stabilized Oil-in-Water Separation

“…Similarly, the pyromellitic acid-grafted Ti 3 C 2 T x membranes were applied to separate the oil-in-water emulsions and remove heavy metal ions . Polydopamine (PDA) has emerged as a unique polymer with a great capacity to adhere to the surface. , The functionalization of MXene with PDA can improve the structural stability and assembly of MXene sheets on the membrane support. , PDA-functionalized MXene can improve MXene sheet stacking on membrane support yet struggles to prevent fouling during surfactant-stabilized oil-in-water emulsion separation. We envisaged that improving hydrophilicity by anchoring hydrophilic groups may improve the antifouling properties of the PDA-functionalized MXene membranes.…”

“…27 Polydopamine (PDA) has emerged as a unique polymer with a great capacity to adhere to the surface. 33,34 The functionalization of MXene with PDA can improve the structural stability and assembly of MXene sheets on the membrane support. 35,36 PDA-functionalized MXene can improve MXene sheet stacking on membrane support yet struggles to prevent fouling during surfactant-stabilized oil-in-water emulsion separation.…”