Tannic Acid-Mediated Layered Double Hydroxide Hybridizing PVDF Superwetting Catalytic Membranes Constructed via Ion Diffusion-Induced Interfacial Self-Assembly for Boosting Water Purification

Abstract

It is a great challenge to fabricate superwetting catalytic membranes with intrinsic self-cleaning capacity for highly stable and effective water purification by simple, mild and energy-efficient manufacturing technologies. Herein, diffusion-induced interfacial self-assembly and polyphenol-mediated strengthening strategies were employed to fabricate tannic acid -mediated layered double hydroxide hybridizing PVDF superwetting catalytic membranes (named as TA@CoFe-LDH@PVDF). The simultaneous phase transformation/in-situ synthesis of CoFe-LDH nanosheets and subsequent coordination assembly with tannic acid (TA) was implemented. Superhydrophilic and underwater-superoleophobic properties were achieved through the cooperation effect of the rough microstructures of CoFe-LDH nanosheets and the strong hydration ability of TA molecules. This enabled efficient separation of various oil-in-water emulsions with more than 99 % separation efficiency and permeation flux up to 593.9 L m-2h−1 bar−1 in cross-flow filtration. Furthermore, due to the reducibility of TA molecules that promoted the Mn+1/Mn+ cycle, TA@CoFe-LDH@PVDF membrane exhibited high static degradation efficiency and kinetics (nearly 100 % in 5.0 min) toward methylene blue by PMS activation. The degradation rate constant (1.04 min−1) was 2.67 times compared to that of CoFe-LDH@PVDF. Surprisingly, it was found that the dynamic mass transfer process in the membrane significantly accelerated the catalytic kinetics, resulting in a degradation rate in dead-end filtration was 23.89 times higher than that under static conditions. Additionally, it was proved that assembled TA could inhibit and reduce metal ion leaching during the catalytic and separation process. This simple manufacturing process of multifunctional membranes with superior performances offers a high application potential in wastewater treatment.