Fabrication of Photothermal Membranes with High-Efficiency Oil–Water Separation Capabilities: Applicable for Oil-in-Water Emulsions, Dyes, and Metal Salt Ions

Water pollution has become increasingly prominent due to the rapid advancement of modern industrialization. Consequently, there is a need for oil-water separation membranes capable of removing various water pollutants, including oil/water mixtures, dye wastewater, and wastewater containing heavy metals and metal salt ions. This study introduces an underwater superhydrophilic and underwater superoleophobic oil-water separation photothermal membrane (PDA/Sr-MOF@RGO) synthesized by in situ growth of a metal-organic framework (Sr-MOF) on two-dimensional reduced graphene oxide (RGO). This approach synergistically regulates the surface roughness and hydrophilicity of the composite membrane and is assisted by polydopamine (PDA) synthesis. The resulting membrane demonstrates high efficiency in separating various oil-in-water emulsions, achieving a separation efficiency of up to 99.4%. Furthermore, the composite membrane exhibits photothermal properties under simulated sunlight irradiation. It maintains a high oil-water separation efficiency under harsh conditions, including high salinity and extreme pH levels. The separation efficiency remains above 99% even after 10 cycles of oil-in-water emulsion separation experiments using <i>n</i>-hexane, indicating the membrane's potential for operation under adverse conditions. Importantly, the composite membrane also demonstrates the capability to separate dye wastewater, heavy metal ions, and metal salts, offering a versatile solution for wastewater treatment applications.