Adsorption behavior and mechanism of organophosphate flame retardants on montmorillonite modified with hexadecyltrimethylammonium bromide

Abstract

The widespread presence of organophosphate flame retardants (OPFRs) in aquatic environments has raised significant concerns regarding environmental and human health risks. In this study, the adsorption behavior of two representative aromatic OPFRs, triphenylphosphine oxide (TPPO) and triphenyl phosphate (TPhP), was systematically investigated using organically modified montmorillonite (MMT). The effects of various environmental and operational parameters, including cationic surfactant dosage, temperature, pH, ionic strength, and humic acid (HA) concentration, on OPFR adsorption were thoroughly examined. Results revealed that modification with hexadecyltrimethylammonium bromide enhanced the TPPO and TPhP adsorption capacities of MMT. The adsorption process was largely independent of pH and HA concentration, and the presence of inorganic cations significantly improved the adsorption efficiency. Adsorption equilibrium was achieved within 30 min, with kinetics best described by a pseudo-second-order model. The adsorption isotherms exhibited a linear relationship, and the distribution coefficients for TPPO and TPhP were 0.16 and 0.51 L/g, respectively. Thermodynamic analysis indicated that the considered adsorption was more favorable at lower temperatures. The primary adsorption mechanism was attributed to the partitioning behavior facilitated by the organophilic nature of the modified MMT. Moreover, the adsorbent demonstrated excellent regeneration performance, with its adsorption capacity remaining stable over five consecutive cycles. Overall, these findings show that cationic surfactant-modified MMT has a promising potential for application in wastewater treatment to effectively remove OPFRs from aqueous systems.

Keywords

montmorillonite / hexadecyltrimethylammonium bromide / organophosphate flame retardants (OPFRs) / adsorption / modification

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Funding

National Natural Science Foundation of China(42377020)

Innovation Project of Nanjing Water Group Co., Ltd.(YF2025-009)