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.