Unlocking the mechanism of nanocatalytic Fenton oxidation and membrane distillation for efficient produced water treatment.

Membrane distillation (MD) is a promising technology for desalinating saline wastewater, but its efficiency is constrained by membrane fouling and wetting. To elucidate the role of nanocatalytic Fenton oxidation in enhancing MD performance for hydraulic fracturing produced water (HFPW) treatment, this study employs hydrolyzed aluminum and iron nanoparticles as active catalysts, with commercial Cu2O included as a benchmark. The three oxidative pretreatment methods increased the normalized flux from 0.46 to over 0.85. Under optimal conditions, Fe-based Fenton achieved removal rates of 67.86 % (UV254), 41.96 % (fluorescent organics), and 83.19 % (hydrophobic organics), outperforming the other two systems. The extended Derjaguin-Landau-Verwey-Overbeek theory showed that the energy barrier was nearly doubled compared to the HFPW, and both exceed 40 kT. Density functional theory calculations show Fe-based catalysts strongly adsorb and activate H2O2, enabling energetically favorable •OH formation, whereas Al-based catalysts exhibit non-spontaneous H2O2 adsorption and instead act primarily through pollutant adsorption and flocculation. The superiority of Fe-based Fenton MD systems was further confirmed during long-term operation. Overall, this study has efficiently improved MD performance through the use of simply prepared nanocatalyst and provided the corresponding mechanism, offering a promising solution to the membrane fouling and wetting problems during long-term MD operation.