Membrane cleaning strategy via in situ oscillation driven by piezoelectricity

Despite of the advanced progress made in membrane techniques, cleaning of membrane fouling remains challenging in membrane filtration process, especially during water purification, chemical and food production, etc. Existing techniques for alleviating membrane fouling such as ultrasound treatment can achieve limited improvement. Thus, developing more environmental-friendly, low-cost, and convenient cleaning strategies is highly desired. Here, we propose a self-cleaning concept of self-vibrating membrane with piezoelectric characteristics and demonstrate its feasibility in membrane anti-fouling. A well-designed piezoelectric membrane (ZnO-CNT/PVDF) has been constructed, where the in situ synthesized zinc oxide (ZnO) nanoparticles are served as a nucleation seed promoting the β-phase formation of poly (vinylidene fluoride) (PVDF) and the percolation network structure is formed by carbon nanotubes (CNTs) to achieve piezoelectric vibration. Encouragingly, the piezoelectric membrane resonated to external AC stimulus at 8 kHz and showed the highest vibration amplitude. The resultant ZnO-CNT/PVDF membrane demonstrated strong antifouling properties and excellent permeation recovery efficiency of 98.0% (AC, 12.5 V, 8 kHz), compared to 58.5% of the control ZnO-CNT/PVDF (0 V) and 53.0% of bare PVDF membrane (AC, 12.5 V, 8 kHz). The improved antifouling capacity benefited from that piezoelectric vibration could reduce the filtration resistances caused by concentration polarization (CP) layer and membrane fouling. Moreover, this antifouling mode of piezoelectric vibration is effective toward different charged foulants. This work demonstrates a novel and effective self-cleaning strategy for employing piezoelectric membrane in high-efficiency anti-fouling.