Surface modification of PVDF membrane via deposition-grafting of UiO-66-NH2 and their application in oily water separations

UiO-66-NH2 is a well-known metal organic framework with high porosity and surface area, and there are modifiable reactive amino groups in its structure, it has been applied in membrane modifications. A novel composite membrane (U1gFx) is successfully prepared by depositing UiO-66-NH2 onto polyvinylidene fluoride (PVDF) membrane, and subsequently grafting with perfluoroalkyl polyethoxy acetic acid (FPEOAA). The water contact angle of the modified membrane declines from 124.27° to 71.05°, and the under-water oil contact angle increases from 86.03° to 149.45°, indicating a good hydrophilic and oleophobic change. The modified membranes show enlarged porosity and water flux due to the introduction of UiO-66-NH2. The optimum membrane (U1gF10) shows excellent separation performance for various oil/water emulsions, including n-hexadecane, petroleum ether, dichloromethane and soybean oil. > 95 % oil rejection and up to 8081.9 L·m−2·h−1 of permeation flux are achieved under the vacuum filtration mode (0.085 MPa). While treating the n-hexadecane/water emulsion, all membranes show > 99 % oil rejection in six filtration cycles. Under a dead-end filtration mode, membrane U1gF10 gives a high relative flux recovery rate at 93 % under 0.1 MPa, its pure water flux still keeps as highly as 982.5 L·m−2·h−1, even after three filtration cycles, indicating a good antifouling property and great engineering application potential.