PDA and ZIF-8 double-modified melamine foam for efficient adsorption co-removal of multiple organic phosphorus flame retardants in environmental water.

ZIF-8 and polydopamine (PDA) double-modified melamine foam (MF), namely ZIF-8@PDA MF was fabricated using a new in-situ growth method for the co-removal of multiple organophosphorus flame retardants (OPFRs) from environmental water. The resulting ZIF-8@PDA MF exhibited a porous, three-dimensional (3D) cross-linked network in which ZIF-8 evenly distributed on MF via the PDA's adhesive properties, leading to a 17-fold increase in surface area (from 1.357 to 22.964 m/g) to facilitate mass transfer and target binding. Through experimental confirmation, the mechanisms of hydrogen bonding, π-π, electrostatic and hydrophobic adsorption enable the effective removal of 11 types of OPFRs including aryl-, alkyl- and Cl-OPFRs. Compared to the adsorbents reported previously, ZIF-8@PDA MF achieved higher removal efficiencies (53.8%-99.7%), particularly a 30% improvement for highly polar TEP and TCEP. The adsorption behavior of OPFRs by ZIF-8@PDA MF followed a spontaneous, endothermic process, conforming to the pseudo-second-order model and Langmuir model. The adsorption equilibrium could be reached within 1 h, 2-48 times faster than most reported studies (2-48 h). In addition, ZIF-8@PDA MF was demonstrated to efficiently remove multiple OPFRs from raw environmental water and the reusability reached up to four cycles without requiring secondary separation, highlighting its practical applicability.