Loose composite nanofiltration membrane with in-situ immobilized β-FeOOH film for effective dyes degradation and separation

Dyes pollution is one of the most serious environmental issues and has drawn increasing public concern. Nano-β-FeOOH can be used to remove dyes in wastewater. However its application is limited due to the problem of easy agglomeration and loss. In this paper, β-FeOOH was in-situ immobilized on a polydopamine (PDA) decorated ceramic ultrafiltration substrate (∼ 5 nm) to prepare a kind of ceramic supported loose composite nanofiltration membrane. The surface morphology and structure of the membranes were analyzed by FESEM, XPS, FTIR, XRD, and TG, which proved the construction of the PDA interlayer on the substrate and the successful in-situ formation of β-FeOOH film. Under the optimized preparation conditions (30 g L−1 FeCl3•6 H2O solution, 0.02 M HCl solution, 18 h mineralization time), the water flux of the obtained membrane is 38 L m−2 h−1 at 0.2 MPa with a dye rejection around 20%. Further, H2O2 was added to activate the Fenton reactions of the immobilized β-FeOOH. Through the combined effects of loose nanofiltration and Fenton oxidation, the dyes removal reaches 98%. In long-term test, the removal of dyes is more than 97% after 6 cycles, and the prepared membrane can treat different kinds of dyes, indicating that the composite membrane has good stability. This research provides a simple way for preparing loose composite membrane with the function of Fenton degradation of dyes. It would have broad applications in industrial wastewater treatment.