Tiantian Li

Robust superhydrophilic polylactide (PLA) membranes with a TiO2 nano-particle inlaid surface for oil/water separation

To overcome the surface instability of traditional polymeric membranes especially with superwetting behaviour, a robust superhydrophilic surface was fabricated with nano-TiO2 inlaid on a hierarchical polylactide (PLA) ultrafiltration membrane via a spin coating process. Distinctly different from most previously reported nano-particle involved polymeric membranes, both the micro-/nano-architecture of the PLA membrane and the size matched nano-particle assembly constructed the robust superhydrophilic interface mimicking coral tentacle predatory behavior. The rigid surface based on the flexible polymeric membrane with the hierarchical architecture showed robust superhydrophilicity and underwater superoleophobicity even after long-term water washing treatment, which was also verified by the morphology, contact angle, XPS and adhesive force in contrast to smooth membranes. The as-prepared PLA membrane showed excellent separation performance for varieties of oil/water mixtures with a robustly high permeate flux (above 950 L m−2 h−1 under 0.1 MPa) and oil rejection (above 99%) even after 10 cycles of operation. Besides, the superhydrophilic PLA membrane exhibited outstanding anti-protein fouling properties. The PLA membrane showed relatively high BSA and ink rejection as well as water flux recovery and continuous separation stability due to rigid interface strengthening effects. The unique interface combination strategy between functional nanoparticles and polymeric membranes provided a window of opportunity for constructing robust polymeric membranes for advanced applications e.g. oil/water separation, ion exchange, in membrane catalytic reactors etc.

Facile fabrication of nanofiber- and micro/nanosphere-coordinated PVDF membrane with ultrahigh permeability of viscous water-in-oil emulsions

To achieve highly efficient purification of emulsified oil, a superhydrophobic, superoleophilic and under-oil superhydrophobic poly(vinylidene fluoride) (PVDF) nanofibrous membrane was developed through a facile electrospinning strategy. The PVDF nanofibrous membrane exhibited a synchronous combination of nanofibers and micro/nanospheres, which was produced by solely controlling the PVDF concentration of the electrospun solutions. The fabricated PVDF nanofibrous membrane exhibited a water contact angle of 152° ± 2°, oil contact angle of 0° in air and under-oil–water contact angle of 152° ± 1° due to the inherently low surface energy and unique structures composed of nanofibers and micro/nanospheres. Thanks to the under-oil superhydrophobicity, hierarchical structure and high porosity (∼95%), the composite membrane showed extremely high permeability of 88 166 ± 652 L m−2 h−1 bar−1 with separation efficiency higher than 99%, which was few orders of magnitude higher than the previous findings. Moreover, the nanofibrous membrane exhibited robust continuous separation, indicating its scalable application for purifying emulsified oil.

Flexible PVDF membranes with exceptional robust superwetting surface for continuous separation of oil/water emulsions

Instability of superwetting surface is the stumbling block of flexible polymeric membranes for continuous separation of water-in-oil or oil-in-water emulsions. Manipulation of rigid superwetting nano-TiO2 on hierarchical poly(vinylidene fluoride) (PVDF) membrane by mimicking the plant roots holding soil behaviour enabled the generation of robust superwetting surface withstanding the harshly physical and chemical torture. The unique interface combination, which fabricated by a compacted nano-layer with the thickness of ~20 μm, was disclosed by systematic structure characterization. As demonstrated by SEM, LSCM and nano-CT, the pristine PVDF membrane with large quantities of cilia-like micro/nano-fibrils can function as the plant roots to capture, cage and confine the nanoparticles to form a robustly rigid nano-coating. The as-prepared membranes showed excellent durable separation performance both in varieties of stabilized water-in-oil and oil-in-water emulsion separation for a long term with few nanoparticles loss in a continuous crossflow mode. The strategy of assembling rigid inorganic nano-particles on flexible surface offers a window of opportunity for preparation of robust organic-inorganic hybrid membranes not only for continuous oil/water emulsion separation, but also for other functional application, such as electric conduction, heat conduction, ion exchange, and in membrane catalytic reactors etc.

Janus Polyvinylidene Fluoride Membrane with Extremely Opposite Wetting Surfaces via One Single-Step Unidirectional Segregation Strategy

Janus membranes with asymmetric wettability have attracted intense attention in oil/water separation, membrane distillation, liquid/fog collection, liquid diode, etc. Facile manipulation of the paradoxical wetting/antiwetting property on opposite surfaces of a 2D membrane is challenging. Different from most postmodification methods, herein, we propose one single-step unidirectional segregation strategy to fabricate a polymeric Janus membrane with extremely opposite wetting surfaces showing almost a 150° contact angle difference for the first time. We achieved the unidirectional segregation of the hydrophilic copolymer poly(vinylpyrrolidone-vinyltriethoxysilane) in a polyvinylidene fluoride (PVDF) membrane during phase separation. A glycerol coating on the nonwoven fabric support locally limited the phase separation on the bottom surface, blocked the segregation of hydrophilic copolymer, and promoted the segregation to the top surface. Working collaboratively with the asymmetric micro-/nanostructure on both surfaces, the resulting Janus membrane exhibited a superhydrophilic top surface and a superhydrophobic bottom surface. The Janus PVDF membrane showed switchable separation performance and high separation efficiency for both oil-in-water emulsions and water-in-oil emulsions because of its anisotropic wettability compared with solely hydrophobic or hydrophilic PVDF membranes.