Porous Fe-doped graphitized biochar: An innovative approach for co-removing per-/polyfluoroalkyl substances with different chain lengths from natural waters and wastewater
Zhaoyang Liu, Peng Zhang, Zixuan Wei, Feng Xiao, Shun Liu, Hao Guo, Chenchen Qu, Juan Xiong, Hongwen Sun, Wenfeng Tan
Abstract
Legacy long-chain per-/polyfluoroalkyl substances (PFAS) are being replaced by short-chain homologs, which have been widely detected in the environment. To achieve the co-removal of different chain length PFAS, this study systematically explored the single and synergistic effects of FeCl 3 -impregnation, wet ball-milling and different carbonization temperatures on the surface chemistry and pore structures of different biochars as well as sorption performances and mechanisms towards long-chain perfluorooctanoic acid (PFOA) and short-chain perfluorobutyric acid (PFBA). As a consequence, we presented a new method to synthesize magnetic sorbents by wet ball-milling with FeCl 3 solution and high-temperature carbonization. Through this process, we tailored a magnetic porous Fe-doped graphitized biochar (named Fe-M−BC 900 ) that contains abundant dispersed positive iron sites with stable Fe 0 /Fe 3 C, multi-stage pore structure, highly hydrophobic graphite-like carbon, and O-containing functional groups. Fe-M−BC 900 exhibited a high sorption capacity of 10.1 mg PFBA/g and 39.1 mg PFOA/g. PFAS sorption on Fe-M−BC 900 was mainly governed by pore-filling, electrostatic interaction, and hydrophobic partitioning. The sorption of PFBA on Fe-doped biochars depends more on electrostatic interaction and is less affected by hydrophobic partitioning compared to PFOA. Finally, we demonstrated that Fe-M−BC 900 performed high co-removal rates (>96 %) for a wide range of legacy and emerging PFAS with different chain lengths and functional groups in natural waters (∑PFAS: 142 ∼ 265 μg/L) and simulated wastewater (∑PFAS: 600 μg/L), with a high relative sorption capacity of > 91 %, even after four consecutive recycling processes. This new adsorbent could help water facilities comply with upcoming PFAS regulations if tested on a larger scale.