Drosera-inspired zirconium-based coagulant for simultaneous removal of F⁻, PFAS and heavy metals from wastewater

Semiconductor wastewater containing pollutants such as fluoride ions (F⁻), per- and polyfluoroalkyl substances (PFAS) and heavy metals has become an increasingly severe issue. Coagulation is a conventional technique for treating semiconductor wastewater. However, existing coagulants face challenges in efficiently removing PFAS, along with issues such as high metal residues, poor settleability and low floc strength. Inspired by the insect-trapping mechanism of Drosera, we synthesized two silane-modified metal-based coagulants, with significantly enhanced performance. Among them, the Drosera-inspired zirconium-based coagulant (DZHC) outperformed the Drosera-inspired aluminum-based coagulant (DAHC) in terms of F⁻ and PFAS removal efficiency, metal residue, settleability, floc size, Zeta potential and floc strength. Mechanistic analyses revealed that F⁻ removal by DZHC occurs via ligand exchange between Zr-OH and F⁻, whereas DAHC requires initial Al–F complexation followed by hydrolysis-polymerization to form coprecipitates. Additional mechanisms including electrostatic interactions, hydrogen bonding and polycondensation also contribute to defluoridation. The removal of copper citrate primarily relies on ligand exchange between metal hydroxyl groups and [Cu-citrate]⁻, assisted by electrostatic attraction from quaternary ammonium groups. Molecular dynamics simulations and density functional theory (DFT) calculations demonstrated that hydrophobic interactions from C18 chains on the coagulants dominate PFAS removal. In summary, this study provides a novel strategy for simplifying semiconductor wastewater treatment.