Sorption behavior and mechanism of organophosphate flame retardants on activated carbons

- Reactivated activated carbon exhibits high removal for OPFRs.
- Powdered activated carbon has fast and high OPFRs adsorption.
- OPFRs and activated carbon properties have significant impact on the sorption.
- Hydrophobic, electrostatic, hydrogen bonding, and π-π interactions are involved.
- Spent adsorbent is fully regenerated by methanol and can be reused.

Organophosphate flame retardants (OPFRs) are widely distributed in aquatic environment, but their adsorptive removal is not clear. For the first time, the removal of OPFRs from water using activated carbons (ACs) was investigated in this study. Adsorption kinetics, effects of activated carbon characteristics, OPFR property, and solution pH, as well as adsorption mechanism and reuse were studied. Adsorbent size significantly affected the adsorption kinetics and capacity, and powdered activated carbon (PAC) exhibited much faster sorption and higher sorption capacity than granular activated carbon (GAC) due to the easier intraparticle diffusion of OPFRs. The sorption kinetics of OPFRs at the initial stage followed the intraparticle diffusion-controlled adsorption, and the molecular size and hydrophobicity influenced greatly the sorption rate. The reactivated GAC exhibited higher OPFR removal than GAC because more enlarged pores were produced and available for OPFR sorption. Based on the sorption behavior of OPFRs, hydrophobic, electrostatic, hydrogen bonding, and π-π interactions were proposed to be involved in the sorption process. Additionally, the spent ACs could be successfully regenerated and reused at least four times with stable sorption capacity. This work indicated that the appropriate ACs have a promising application in the water or wastewater treatment for OPFRs removal.

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