Atmospheric plasma-sprayed Al₂O₃–TiO₂ composite ceramic membranes for oil-in-water emulsion separation with UV-assisted cleaning

To address membrane fouling and flux decline during oil-in-water (O/W) emulsion separation, Al₂O₃–TiO₂ composite ceramic membranes were directly fabricated on porous ceramic supports by atmospheric plasma spraying (APS). The effects of feedstock-powder uniformity, TiO₂ content, and membrane-layer thickness on surface pore-opening characteristics, wettability, cyclic filtration behavior, and ultraviolet (UV)-assisted cleaning were systematically investigated. Compared with mechanically mixed powders, spray-granulated composite powders produced a more uniform TiO₂ distribution in the separation layer, leading to a more refined and concentrated surface pore-opening distribution, faster dynamic wetting, and improved underwater oleophobicity. Among the 150 μm-thick membranes with different compositions, AT13Z-150 exhibited the best overall performance, with a stable flux of 847.27 L m⁻² h⁻¹ and an oil rejection of 98.03% at 0.1 MPa under the non-UV-assisted cleaning condition. When UV-assisted cleaning was applied, its stable flux reached 991.76 L m⁻² h⁻¹ at 0.1 MPa, corresponding to a stable-flux gain ratio of 117.05%. Further thickness optimization showed that a membrane-layer thickness of 150 μm provided the best balance between water-transport resistance and fouling resistance. Although UV-assisted cleaning improved stable-flux retention, no direct evidence for photocatalytic degradation of organic or oily foulants was obtained in this work; therefore, the UV-assisted effect is mainly discussed in terms of UV-induced surface-state modification and interfacial wetting recovery. These results indicate that feedstock-powder uniformity, TiO₂ content and distribution, and membrane-layer thickness are important factors for stable cyclic O/W emulsion filtration and UV-assisted stable-flux retention in APS-fabricated Al₂O₃–TiO₂ composite ceramic membranes under the defined model-emulsion and cleaning conditions.