Co-hydrolyzed bio-inspired antifouling coatings for functional membranes in oily wastewater treatment

The fast and unregulated bio-inspired Schiff base and Michael addition reactions between phenol- and amino-based materials often lead to the formation of uneven coatings with large aggregates, affecting the coating efficiency and various designed functionalities. Therefore, a co-hydrolysis strategy was proposed to modulate the phenol/amino reaction and the self-assembly coating process, achieving uniform and compact phenol/amino-based antifouling coating.

A uniform bio-inspired antifouling coating was fabricated by modulating the Schiff base and Michael addition reactions between tannic acid with amino groups within the co-hydrolyzed amino, zwitterionic, and fluorine-containing silane system. The surface morphology and underlying molecular interaction mechanism was probed by atomic force microscopy (AFM). The wettability of the coating was tuned through optimization of the coating composition and its interfacial antifouling performance was evaluated using quartz crystal microbalance (QCM) and optical photothermal infrared (O-PTIR) spectroscopy. The separation efficiency of the coated polyvinylidene difluoride (PVDF) membrane for treating oil-in-water emulsions was assessed using dead-end filtration tests.

Molecular force measurements and antifouling test results showed that incorporating zwitterionic and fluorine-containing silane not only regulated the Schiff base and Michael addition reaction rates, enabling the formation of a uniform surface coating, but also provided a stable hydration layer and low-surface-energy sites to enhance the fouling resistance and fouling release properties of the prepared antifouling surfaces. The proposed coating can be extended for membrane surface functionalization, showing enhanced water flux (over 5700 L m^-2 h^-1 bar^-1) and excellent separation performance of oil-in-water emulsions even in the presence of additional bio-foulants, with a flux recovery ratio over 90 %. This study proposes and validates a co-hydrolysis strategy that enables precise control over the structure and morphology of phenol/amino-based coating systems by modulating steric and hydration effects as well as electrostatic repulsion between reactive colloids. This strategy can be extended to other phenol/amino-based coating systems to modulate surface functionality and morphology through interfacial design.