TY - JOUR
T1 - Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons
T2 - Structural Dependence and Implications to PFAS Remediation and Management
AU - Bentel, Michael J.
AU - Yu, Yaochun
AU - Xu, Lihua
AU - Li, Zhong
AU - Wong, Bryan M.
AU - Men, Yujie
AU - Liu, Jinyong
N1 - Financial support was provided by the UCR Initial Complement for J.L., UCR Collaborative Seed Grant for J.L., B.M.W., and L.X; the National Science Foundation (CHE-1709719 for J.L. and CHE-1709286 for Y.M. and Y.Y.), and the Strategic Environmental Research and Development Program (ER-1289 for J.L. and B.M.W, and ER-1497 for J.L.). M.J.B. received a scholarship from the UCR Water SENSE Integrative Graduate Education and Research Traineeship (IGERT) supported by NSF. UCR undergraduate researchers, Taylor Brantner, Robert Chavarria-Vivar, Vanessa Coria, Duy Dao, Maggy Harake, and Vivian Ngo provided technical assistance on photochemical reactions.
PY - 2019/4/2
Y1 - 2019/4/2
N2 - This study investigates critical structure-reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While CnF2n+1-COO- with variable fluoroalkyl chain lengths (n = 2 to 10) exhibited a similar rate and extent of parent compound decay and defluorination, the reactions of telomeric CnF2n+1-CH2CH2-COO- and CnF2n+1-SO3- showed an apparent dependence on the length of the fluoroalkyl chain. Cross comparison of experimental results, including different rates of decay and defluorination of specific PFAS categories, the incomplete defluorination from most PFAS structures, and the surprising 100% defluorination from CF3COO-, leads to the elucidation of new mechanistic insights into PFAS degradation. Theoretical calculations on the C-F bond dissociation energies (BDEs) of all PFAS structures reveal strong relationships among (i) the rate and extent of decay and defluorination, (ii) head functional groups, (iii) fluoroalkyl chain length, and (iv) the position and number of C-F bonds with low BDEs. These relationships are further supported by the spontaneous cleavage of specific bonds during calculated geometry optimization of PFAS structures bearing one extra electron, and by the product analyses with high-resolution mass spectrometry. Multiple reaction pathways, including H/F exchange, dissociation of terminal functional groups, and decarboxylation-triggered HF elimination and hydrolysis, result in the formation of variable defluorination products. The selectivity and ease of C-F bond cleavage highly depends on molecular structures. These findings provide critical information for developing PFAS treatment processes and technologies to destruct a wide scope of PFAS pollutants and for designing fluorochemical formulations to avoid releasing recalcitrant PFASs into the environment.
AB - This study investigates critical structure-reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While CnF2n+1-COO- with variable fluoroalkyl chain lengths (n = 2 to 10) exhibited a similar rate and extent of parent compound decay and defluorination, the reactions of telomeric CnF2n+1-CH2CH2-COO- and CnF2n+1-SO3- showed an apparent dependence on the length of the fluoroalkyl chain. Cross comparison of experimental results, including different rates of decay and defluorination of specific PFAS categories, the incomplete defluorination from most PFAS structures, and the surprising 100% defluorination from CF3COO-, leads to the elucidation of new mechanistic insights into PFAS degradation. Theoretical calculations on the C-F bond dissociation energies (BDEs) of all PFAS structures reveal strong relationships among (i) the rate and extent of decay and defluorination, (ii) head functional groups, (iii) fluoroalkyl chain length, and (iv) the position and number of C-F bonds with low BDEs. These relationships are further supported by the spontaneous cleavage of specific bonds during calculated geometry optimization of PFAS structures bearing one extra electron, and by the product analyses with high-resolution mass spectrometry. Multiple reaction pathways, including H/F exchange, dissociation of terminal functional groups, and decarboxylation-triggered HF elimination and hydrolysis, result in the formation of variable defluorination products. The selectivity and ease of C-F bond cleavage highly depends on molecular structures. These findings provide critical information for developing PFAS treatment processes and technologies to destruct a wide scope of PFAS pollutants and for designing fluorochemical formulations to avoid releasing recalcitrant PFASs into the environment.
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U2 - 10.1021/acs.est.8b06648
DO - 10.1021/acs.est.8b06648
M3 - Article
C2 - 30874441
AN - SCOPUS:85063397566
SN - 0013-936X
VL - 53
SP - 3718
EP - 3728
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 7
ER -