Superhydrophilic and underwater superoleophobic Graphene oxide-Phytic acid membranes for efficient separation of oil-in-water emulsions

The increase in oily wastewater generation from industrial effluents and accidental oil spills has become a severe environmental concern today. Recently, tailored wettability materials have received extensive research interest due to their potential applications in remediation of oily wastewater. Herein, a superhydrophilic and underwater superoleophobic membrane was synthesised by a two-step approach: surface coating of graphene oxide-phytic acid (GO-PA) mixture on a polyvinylidene fluoride (PVDF) support membrane followed by Fe³⁺ deposition via metal-organophosphate coordination interaction. The optimised GO-PA-Fe³⁺/PVDF membrane possessed a water contact angle of 1.4° and an underwater oil contact angle of 163.4°. In the separation of surfactant-stabilised sub-micron sized oil-in-water emulsions (of 0.01 – 1 µm) at 0.4 bar, a permeation flux of up to 43.7 LMH/bar and separation efficiency of > 99.5% were achieved with the synthesised GO-PA-Fe³⁺/PVDF. This permeation flux was also observed to be six times higher than pristine GO/PVDF. The robust membrane exhibited excellent recyclability with a separation efficiency of > 99% and permeation flux of 38.2 – 41.8 LMH/bar for ten cycles. The research establishes a promising avenue towards tuning Graphene-oxide membranes for treatment of sub-micron sized oily wastewater, while maintaining a high permeation flux.