Long-acting removal of high-toxic p-nitrophenol in wastewater via peroxymonosulfate activation by cyclic membrane catalysis

In this work, the commonly-used peroxymonosulfate (PMS) activator (copper oxide nanoparticles, CuO NPs) was steadily loaded on a polydopamine (PDA)/polyethyleneimine (PEI)-modified non-woven fabric (NWF) membrane via the typical in-situ deposition method. Distinguished from the simple membrane catalysis separation, the as-prepared hybrid membrane (CuO@PDA/PEI-NWF) showed the better ability in oxidizing the high-toxic p-nitrophenol (4-NP) in feed while its permeate liquid backflowing constantly with the aid of a cross flow device. Within 60 min, even a small area of CuO@PDA/PEI-NWF (9.0 cm2) with only ∼0.2 g weight could generate vast of reactive species (1O2, SO4•‾, and •OH) with trace PMS (1 mM) activation, and then reduced ∼40% of COD in a large volume (1 L) of 5 ppm 4-NP polluted water. The removal of 4-NP was further increased with more PMS added in the cyclic membrane catalysis system. The highest degradation rate could be achieved at pH close to the neutral state due to the better redox circle of Cu2+/Cu+ in the system. Electrospray ionization mass spectrometry (ESI-MS) revealed that the 4-NP structure was primarily destroyed by the addition reaction of radicals (SO4•‾, and •OH), while its oxidation mineralization was caused by the formed 1O2, during the cyclic membrane catalysis system. Most importantly, this CuO@PEI/PDA-NWF/PMS cyclic system displayed excellent robustness and sustainability without tedious catalyst separation/regeneration processes in treating the 4-NP polluted real water. During 360 min of cyclic membrane catalysis, CuO@PEI/PDA-NWF caused the decrease of COD in Pearl River water with high concentration of 4-NP (20 ppm) up to ∼80%, indicating its high-efficiency and long-effectiveness. This study offers significant insights into developing novel cyclic membrane reactors with PMS activation for practically tricky wastewater treatment.