Mechanistic understanding of perfluorooctane sulfonate (PFOS) sorption by biochars

Effects of Environmental Factors on the Sorption of Per- and Polyfluoroalkyl Substances by Biochars

“…Recent studies indicated that the Freundlich model typically fits PFAS sorption data better, although the Langmuir model fitting performs better for other cases. ,, In this study, both Langmuir ( R 2 = 0.98 and 0.95 for commercial and Douglas Fir 900 biochars, respectively) and Freundlich ( R 2 = 0.95 and 0.96 for commercial and Douglas Fir biochars, respectively) models fitted the experimental data well (Figure ). These partially suggest that PFOS was sorbed onto biochar heterogeneous surface sites via different sorption mechanisms and subsequently percolating into biochar pores when the surface was fully occupied, ,, which is depicted in our recent study. Values of n ( n = 1.59 and 2.18 for commercial and Douglas Fir 900 biochars, respectively) in the Freundlich model indicate favorable sorption to heterogeneous surface sites, confirming nonlinear sorption. ,, This observation coincides with our previous findings that biochars sorb PFAS from a variety of sorption mechanisms such as hydrophobic and electrostatic interactions with positively charged N-containing functional groups and pore size trapping mechanisms. , The Langmuir model estimated a maximum monolayer sorption capacity ( Q m ) of 42.3 and 4.97 mg/g, respectively, for commercial and Douglas Fir 900 biochars (Table ).…”

“…Nevertheless, high R 2 values obtained from the pseudo-first-order kinetic model suggest that physical interactions, such as pore filling, hydrogen bonding, and hydrophobic interactions, also likely contribute to PFAS removal by biochars. The measured contact angles of the commercial biochar and Douglas Fir 900 biochar were 135.3 and 145.5°, respectively, indicating that both PFAS and biochar had a great hydrophobicity and hydrophobic interaction, which was one of the factors facilitating PFAS sorption by biochars …”

“…The Douglas Fir (Pseudotsuga menziesii) feedstock was used to obtain the biochar at a targeted pyrolysis temperature of 900 °C through a slow pyrolysis method documented in our recent study. 11 A commercially available biochar was donated by Oregon Biochar Solutions. The detailed physicochemical properties of the two biochars were documented previously, 11 which are also given in the SI (Table S3).…”

“…11 A commercially available biochar was donated by Oregon Biochar Solutions. The detailed physicochemical properties of the two biochars were documented previously, 11 which are also given in the SI (Table S3). Our recent study 11 showed that the Douglas Fir 900 biochar and the commercial biochar exhibited the greatest potential efficiency for removing PFOS from water.…”

“…Additionally, our recent study deepened the mechanistic understandings of PFOS sorption by biochars, suggesting that biochar pore diameter, pore diameter/pore volume ratio, and specific surface area, among others, played a significant role in sorbing PFOS in water. 11 However, it is largely unclear how biochars perform for PFAS sorptive removal under environmentally relevant conditions. Environmental factors (e.g., water matrices) like different salts (e.g., Na + and Ca 2+ ) and organic matters (e.g., humic acid (HA) and fluvic acid) are reported to impact PFAS sorptive removal by biochars, likely due to the competition for biochar sorption sites and other physicochemical mechanisms.…”