Photothermal-pancaking synergy in interfacial absorption enables rapid purification of viscous oil-in-water emulsions

Recovery of water resources from oily wastewater is essential, but the purification of current separation materials to high-viscosity oil-containing emulsions (e.g., those with viscosity over hundreds of mPa·s) constitutes a particularly formidable challenge. This limitation encompasses three critical challenges: (i) oil droplets stabilized as surfactant-encapsulated microspheres, (ii) severe interfacial fouling, and (iii) irreversible efficiency degradation due to oil's conglutination and accumulation. Herein, we demonstrated photothermal-pancaking synergy in interfacial absorption as an efficient separation strategy for challenging high-viscosity oil-water emulsions where conventional methods fail. Emulsified oils were harvested by polypyrrole-wrapped biomass superhydrophobic aerogel (M-PPy@KF/SA) through an in-situ oscillation process, whereby oil droplets evolved into pancake shapes, triggering a sequential capillary absorption from water with separation efficiency of over 98.3 %. The purification dynamics were found to be primarily governed by oil viscosity, light intensity, and oscillation speed. Surfactant-coated more viscous oil droplet reflected sluggish oil diffusion kinetics. Consequently, purifying viscous emulsions (0.3–400.0 mPa·s) required repeated striking-pancaking-absorption with demulsification time increasing by 7.7–80.0 %. Notably, photothermal stimulation led to a significant acceleration of oil-diffusion kinetics by 105.9–183.5 % (e.g., motor oil #3 , ~ 400.0 mPa·s). This effect suppressed repeated emulsified oil absorption-detachment behavior at the interface, which reduced the purification time of viscous motor oil #3 -in-water emulsion by up to 80.0 % compared to non-irradiated controls. Additionally, increasing oscillation speed (100–300 rpm) boosted initial kinetic energy, leading to a 55–90 % reduction in purification time. This acceleration was primarily driven by enhanced interfacial dynamics at higher oscillation frequencies.