Nanostructural Manipulation of Polyphenol Coatings for Superwetting Membrane Surfaces

Abstract

Functional coatings have gained significant attention in multiple environmental and energy-related research fields. One of the coatings with superwetting surfaces has received significant interest, owing to the favorable properties like self-cleaning and antifouling as well as the roles it plays in processes of water harvesting and oil–water separation. Hydrophilic polyphenol molecules show good adhesion to different substrates and provide multiple interactive sites, which serve as building blocks for the preparation of superwetting coatings. In this study, to realize the controlled formation of a polyphenol-based coating and to demonstrate the nanostructural dependence of its superwetting performance, tannic acid (TA) complexed with cations was employed to construct coating networks with either nanorough or nanosmooth surface morphology through a layer-by-layer (LbL) self-assembly method. Both nanostructures could be precisely controlled by adjusting the TA concentration and number of LbL cycles to observe the evolution of the wetting state of the coating. More importantly, while the nanosmooth and nanorough coatings exhibited similar surface chemistry, pore sizes, and superwetting properties, the separation efficiency for oil-in-water emulsions using the membrane with the nanorough coating is 2–5 and 2–10 times that of the one with a nanosmooth coating and the pristine one without a coating, respectively. The experimental results confirmed that the nanorough coating structure contributed to the superwetting state of the membrane surface and, therefore, possessed a stronger ability to repel oil than the nanosmooth coating during the separation process. This work demonstrates a novel strategy for the molecular self-assembly of polyphenols and may provide guidance for designing superwetting coatings.

Regulating interfacial polymerization via a multi-functional calcium carbonate based interlayer for a highly permselective nanofiltration membrane

“…The layer-by-layer (LbL) mineralization method was used to form a CaCO 3 interlayer atop the PK substrate, as reported in our previous work. 30 Briefly, the PK membrane was pretreated by immersion in TA aqueous solution (0.1 wt%) for 12 h to warrant sufficient adsorption of TA molecules on the PK substrate. Afterwards, the membrane was sequentially immersed in CaCl 2 aqueous solution (0.05 M), DI water, Na 2 CO 3 aqueous solution (0.02 M), and DI water for 5 min, 30 s, 5 min, and 30 s, respectively.…”

One-Step Phase Separation and Mineralization Fabrication of Membranes for Oily Wastewater Treatment

“…24,25 Therefore, there is a strong interaction between the PK polymer chains, TA, and Ca 2+ ions. 22,26 When the casting solution is immersed in the coagulation bath and undergoes phase inversion, part of the Ca 2+ ions is firmly fixed on the polymer matrix through TA instead of diffusing into the coagulation bath. The Ca 2+ ions fixed on the polymer matrix will react with the Na 2 CO 3 in the coagulation bath during the phase separation process, eventually forming CaCO 3 nanoparticles on the surface of the membrane (Figure 2b).…”

“…Although this technique enhances membrane surface hydrophilicity, deposited mineral particles also reduce pore size, resulting in greater resistance to oil–water emulsion transportation . Moreover, the mineralization process usually requires a cumbersome and time-consuming layer-by-layer self-assembly/multistep method to complete …”

“…21 Moreover, the mineralization process usually requires a cumbersome and time-consuming layer-by-layer self-assembly/multistep method to complete. 22 In this study, we developed a one-step nonsolvent induced phase separation (NIPS)-mineralization process (Figure 1) to prepare oil/water separation membranes with excellent performance. Herein, polyketone (PK) was utilized as a membrane material.…”

Tannic acid-based functional coating: surface engineering of membranes for oil-in-water emulsion separation

“…23,[25][26][27] Among them, the surface engineering strategy based on tannic acid (TA) has received extensive attention. 28,29 As a promising substitute for dopamine, TA has similar adhesion ability to dopamine [30][31][32][33] and possesses some distinct advantages such as better hydrophilicity, more functional groups, and lower cost. Generally speaking, tannic acid is not a single pure compound but a mixture, which was called tannin in the past.…”