Hydrostable ZIF-8 layer on polyacrylonitrile membrane for efficient treatment of oilfield produced water

The treatment and reclamation of oilfield produced water by membrane technology is severely limited by fouling. Zeolitic imidazole framework-8 (ZIF-8) nanoparticles are promising functional materials for antifouling membrane modifications. However, their limited stability as a separating layer during filtration is a major challenge. Here, we describe a facile route for chemical stabilization of the ZIF-8 layer on a polyacrylonitrile membrane using a redox-grafted zwitterionic methacrylate hydrogel. Microscopic and spectroscopic techniques confirmed the structure and stability of the ZIF-8/methacrylate hydrogel layer. Furthermore, no detectable ZIF-8 particles leached out from the modified membrane during filtration experiments. The hydrostability is achieved via coordination interactions between the negatively charged sulfonate groups of the hydrogel and the positively charged ZIF-8 nanoparticles. Compared to the pristine membrane, the modified membrane showed higher hydrophilicity, lower surface roughness, and its pure water permeance was ∼13% higher. Treatment of simulated oilfield produced water by the membranes for three 4-h filtration cycles showed that the modified membrane exhibited exceptionally high antifouling properties compared to the pristine membrane (flux recovery ratio of 98.5 ± 0.6% vs. 8.1 ± 0.7%) and showed 99.7 ± 0.3% oil rejection efficiency. In a longer treatment duration, after 10 filtration cycles for 42 h, the modified membrane showed a flux recovery ratio of 90.3% and oil rejection efficiency >99%, indicating its outstanding performance for oilfield produced water treatment. Thus, our membrane with a hydrostable ZIF-8 layer holds excellent promise for produced water treatment applications.