Defluorination
of Per- and Polyfluoroalkyl Substances
(PFASs) with Hydrated Electrons: Structural Dependence and Implications
to PFAS Remediation and Management
Version 3 2019-03-17, 19:29
Version 2 2019-03-15, 13:48
Version 1 2019-03-15, 13:44
Posted on 2019-03-17 - 19:29
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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Bentel, Michael
J.; Yu, Yaochun; Xu, Lihua; Li, Zhong; Wong, Bryan M.; Men, Yujie; et al. (2019). Defluorination
of Per- and Polyfluoroalkyl Substances
(PFASs) with Hydrated Electrons: Structural Dependence and Implications
to PFAS Remediation and Management. ACS Publications. Collection. https://doi.org/10.1021/acs.est.8b06648
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AUTHORS (7)
MB
Michael
J. Bentel
YY
Yaochun Yu
LX
Lihua Xu
ZL
Zhong Li
BW
Bryan M. Wong
YM
Yujie Men
JL
Jinyong Liu