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The membrane fouling is the obstruction that limits the efficiency and durability of the nanofibrous membrane in oil-water emulsion separation. Herein, a polyvinyl alcohol (PVA) hydrogel nanofibrous membrane could continuously separate emulsion by using squeezing coalescence demulsification (SCD). During this SCD process, the small oil droplets can coalesce into bigger ones under the mandatory compression of the pore wall. And then the coalesced oil droplets will pass through the nanofibrous membrane and form an oil layer, and the oil layer can be easily removed. Furthermore, a two-phase numerical model is proposed to demonstrate this coalescence process of oil droplets in the pore. The numerical results also indicate that the pore size, wettability of membrane, and the interface tension coefficient between oil and water can control the efficiency of SCD. This SCD method endows PVA hydrogel nanofibrous membrane with a sustained separation capability, which implys that this method has great potential in practical application.

Efficiently purifying metal ions contained emulsified oily wastewater has become a great challenge. Herein, a novel charged hydrogel nanofibrous membrane (CHNM) with negative surface charges, favorable mechanical ability and anti-fouling capacity was prepared via electrospinning and twice crosslinking process. The obtained CHNM with a surface potential of -32.9 mV at pH = 7.2 possesses outstanding oil-in-water emulsion separation performance with high permeation flux of around 10800 L h-1 m-2 bar-1 for surfactant free emulsion and high permeation flux of around 7100 L h-1 m-2 bar-1 for surfactant stabilized emulsion. The excellent oil/water emulsion separation performance can be attributed to the surface charge demulsification (SCD), which is theoretically demonstrated by a finite element analysis simulation. In addition, CHNM can absorb many kinds of metal ions (Fe3+, Ni2+ and Al3+) due to the chelation effect between high-density phosphate groups and metal ions. With outstanding separation performance for oil/water emulsion and good adsorption capacity for metal ions, the multifunctional CHNM may offer a promising approach to develop a new-generation membrane for treating metal ions contained oily wastewater.