Pickering emulsion-embedded hierarchical solid-liquid hydrogel spheres for static and flow photocatalysis.

Pickering emulsion and TiO 2 are subtle assembled by one-step gelation to form the gel sphere with strong adsorption and high catalytic activity. The gel sphere solve the difficulty recovery of powder catalysts, enhance the stability of the Pickering emulsion, and can be used as column filler to build flow photocatalytic systems. • A hierarchical (IL/W) Pickering emulsion gel spheres was designed and fabricated. • The static and flow catalysis systems based on gel spheres were built. • The flow catalysis system exhibited ~100% removal efficiency of 2-naphthol. • Synergistic effect between adsorption and charge transfer was revealed and proved. Pickering emulsion-based photocatalysis is considered to be a promising system due to its large active surface area and water/oil spatial separation capability for enrichment of substrates and products. In this work, a novel hierarchical structure composed of calcium alginate gel sphere wrapped ionic liquid-in-water Pickering emulsion with TiO 2 in the water phase, which are stabilized by graphene oxide, is prepared via a facile one-step emulsion gelation method. Such subtle combination of Pickering emulsion, hydrogel and TiO 2 with a multi-stage solid-liquid assemblage structure shows enhanced degradation activity of 2-naphthol into small molecular alkanes under simulated solar irradiation. The photodegradation activity is attributed to the ionic liquid as adsorption medium for 2-naphthol, and the high-efficient charge separation at graphene oxide/TiO 2 interface superior to that of pure TiO 2. More importantly, the as-prepared millimeter-sized assembled gel spheres can be directly used as the column filler to construct continuous flow photocatalytic system, maintaining the promising performance in removing pollutants from water with ~100% remove ability of 2-naphthol on stream. A charge transfer mechanism of the photocatalyst is proposed, i.e. photogenerated charges are separated in TiO 2 /graphene oxide p-n heterostructure at the interface of Pickering emulsion droplets. [ABSTRACT FROM AUTHOR]