Pickering emulsion catalysis in a continuous flow system for methyl orange degradation

Pickering emulsions stabilized by solid particles provide a well-defined interfacial environment for catalytic reactions. In this study, a continuous-flow Fenton oxidation system was developed using an oil-in-water Pickering emulsion stabilized by a nickel–aluminum layered double hydroxide/graphene composite. The material functions both as a solid emulsifier and a heterogeneous Fenton catalyst, forming a stable emulsion column under continuous operation. The system degraded over 97% of methyl orange within 8 h and maintained about 90% removal efficiency over 50 h of uninterrupted operation. In contrast, a conventional batch Fenton process achieved only ∼44% degradation under similar conditions. The enhanced performance is attributed to the coupled adsorption and catalytic oxidation at the oil–water interface. The emulsifier enriches methyl orange and activates H2O2 to generate reactive radicals. Even in the absence of externally added Fe2+, Ni2+ in the composite can activate H2O2, while the coexistence of Ni2+ and Fe2+ further promotes sustained radical generation. These results demonstrate that Pickering emulsion-based continuous reactors provide a robust and scalable strategy for the efficient removal of refractory organic pollutants.