Adsorption Kinetics of 2,2′,4,4′-Tetrabromodiphenyl Ether (BDE-47) on Maize Straw-Derived Biochars

Abstract The chars in the natural environment can affect the migration of polybrominated diphenyl ethers (PBDEs). However, there is insufficient research relating to the adsorption behavior and mechanisms of PBDEs on biochars. This study examined the adsorption kinetics of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) on maize straw-derived biochars (MSBCs) pyrolyzed at four different temperatures via batch experiments. The biochar samples were characterized using Fourier transform infrared (FTIR) spectroscopy, Raman spectra, and elemental analysis. A two-compartment first-order model and pseudo-second-order model exhibited a better fit compared to a pseudo-first-order model in describing the BDE-47 adsorption on biochars, which was dominated by a slow adsorption compartment and chemisorption. The MSBC pyrolyzed at 600 °C had the highest BDE-47 adsorption capacity owing to its relatively large specific surface area and relatively high aromaticity compared with the other three MSBCs pyrolyzed at 300, 400, and 500 °C. However, there was no significant difference in adsorption capacity among the other three biochars. The organic functional groups coupled with the graphene structures of biochars and the hydrophobic effect of the functional groups promoted the adsorption of BDE-47. Pore diffusion was not the sole rate-limiting step; film diffusion was also involved in the adsorption process of BDE-47 on biochars. The overall results demonstrate the transport and potential treatment of PBDEs using biochars.