Smart pH-regulated foams with tunable wettability and photothermal enhancement for controllable recovery of oil-contaminated water

Oil contamination in water poses persistent environmental risks, making the efficient removal and recovery of oil pollutants a pressing challenge. Materials capable of adapting their interfacial properties in response to environmental stimuli are highly desirable for oil pollution control. Herein, we develop a pH-responsive smart composite foam (SCF) that integrates reversible wettability switching, controllable oil absorption-desorption, and photothermal-assisted oil recovery within a single porous architecture. The SCF exhibits pronounced pH-dependent wettability switching (0°∼155°), enabling controllable separation of various immiscible oil-water mixtures. In acidic media, the SCF surface displays superhydrophilicity and underwater superoleophobicity, while it transitioned to hydrophobic/oleophilic state under neutral or alkaline conditions, with oil-water separation efficiency exceeding 99%. The SCF demonstrates reversible pH-regulated oil uptake and release, with high uptake capacity under alkaline conditions and desorption efficiency above 80% upon acidification. Integrated with a dissolved oxygen probe, the SCF enables real-time oil spill monitoring, and its photothermal conversion effectively reduce oil viscosity and accelerate absorption. Unlike traditional responsive materials relying mainly on wettability transitions, this study establishes a strategy for efficient oil recovery by exploiting pH-dependent interfacial energy changes to regulate the capillary driving force, thereby providing new mechanistic understanding of controllable oil transport and recovery in porous materials.