PDA-Assisted Fabrication of Calcium Alginate Hydrogel-Coated Stainless Steel Meshes for High-Efficiency Oil/Water Separation

Abstract This study introduces an environmentally friendly and straightforward dip-coating technique for preparing stainless steel meshes (SSM) coated with calcium alginate (CA) hydrogel. The prepared mesh possesses high hydrophilicity and underwater superoleophobicity, enabling highly efficient separation of diverse oil/water mixtures. Initially, dopamine undergoes in situ self-polymerization to form a polydopamine (PDA) interlayer anchored on the SSM substrate. This PDA layer was then firmly coated with sodium alginate (SA) through hydrogen bonding and electrostatic interactions. The introduction of Ca2+ facilitates the formation of a stable CA composite hydrogel coating on the substrate surface via metal-ion coordination and chelation. Characterization results demonstrated that the CA hydrogel introduced abundant hydrophilic functional groups and micro/nanoscale hierarchical roughness on the mesh surface, significantly enhancing its wettability. The treated mesh exhibited underwater–oil contact angles (UOCA) greater than 153° for various oils, accompanied by an in-air water contact angle (WCA) of 18.3°. It also demonstrates superior antifouling properties and recyclability. Utilizing only gravitational force, the coated mesh demonstrated effective separation of multiple oil/water mixtures. The separation efficiency consistently exceeds 99%, achieving a maximum water flux of 31254 L·m–2·h–1. Remarkably, the mesh’s separation ability was not impaired by exposure to harsh stimuli, including UV exposure, various corrosive solutions, mechanical damage, and extreme thermal cycling, demonstrating its high environmental adaptability. Given its environmentally friendly preparation method and superior properties, this coated mesh shows great promise for practical applications in treating oily wastewater and addressing challenges associated with aquatic environment remediation.