Superoleophobic Hierarchical Honeycomb Hydrogels for Effective Heavy Metal Removal in Crude Oil Emulsion

Here, we designed a bioinspired hydrogel surface with underwater superoleophobicity for heavy metal adsorption, effectively addressing the challenge of adsorption site clogging caused by crude oil emulsions. Mimicking the reentrant structures of lotus leaf undersides, silica dioxide (SiO₂) nanoparticles were self-assembled on the hydrogel surface, forming a stable hydration layer that imparts unique superoleophobic properties in an aqueous environment. The poly(vinyl alcohol)-sodium alginate-SiO₂ capsule (PSSC) exhibited a hierarchical honeycomb pore structure with a nano screen mesh, achieving excellent adsorption capacities for typical cationic heavy metals (Pb²⁺, Cu²⁺, Cd²⁺, and Cr³⁺) in both aqueous solutions and crude oil emulsions. The optimal pH for heavy metal adsorption was determined to be between 4 and 5, while increasing temperature significantly inhibited the adsorption process. Maximum adsorption capacities of Pb²⁺, Cd²⁺, Cu²⁺, and Cr³⁺ reached 291.5 mg/g, 278.7 mg/g, 259.4 mg/g, and 171.4 mg/g in crude oil emulsions. Competitive adsorption was observed in multicomponent systems, with Cr³⁺ being adsorbed preferentially. The adsorption mechanisms were primarily governed by chemical adsorption, physical adsorption, and electrostatic attraction, with functional groups such as -COOH and -OH on the hydrogel surface playing a key role in metal ion binding. This study demonstrates the potential of PSSC as an efficient, cost-effective adsorbent for removing heavy metals from complex matrices, such as wastewater and crude oil emulsions, and highlights its applicability in various environmental remediation scenarios.