Role of Nitrogenous Functional Group Identity in Accelerating 1,2,3-Trichloropropane Degradation by Pyrogenic Carbonaceous Matter (PCM) and Sulfide Using PCM-like Polymers

Groundwater contamination by 1,2,3-trichloropropane (TCP) poses a unique challenge due to its human toxicity and recalcitrance to degradation. Previous work suggests that nitrogenous functional groups of pyrogenic carbonaceous matter (PCM), such as biochar, are important in accelerating contaminant dechlorination by sulfide. However, the reaction mechanism is unclear due, in part, to PCM’s structural complexity. Herein, PCM-like polymers (PLPs) with controlled placement of nitrogenous functional groups [i.e., quaternary ammonium (QA), pyridine, and pyridinium cations (py+)] were employed as model systems to investigate PCM-enhanced TCP degradation by sulfide. Our results suggest that both PLP-QA and PLP-py+ were highly effective in facilitating TCP dechlorination by sulfide with half-lives of 16.91 ± 1.17 and 0.98 ± 0.15 days, respectively, and the reactivity increased with surface nitrogenous group density. A two-step process was proposed for TCP dechlorination, which is initiated by reductive ß-elimination, followed by nucleophilic substitution by surface-bound sulfur nucleophiles. The TCP degradation kinetics were not significantly affected by cocontaminants (i.e., 1,1,1-trichloroethane or trichloroethylene), but were slowed by natural organic matter. Our results show that PLPs containing certain nitrogen functional groups can facilitate the rapid and complete degradation of TCP by sulfide, suggesting that similarly functionalized PCM might form the basis for a novel process for the remediation of TCP-contaminated groundwater.

Table S1.Peak assignments for NMR Spectra in Figure 1.

Sample
Kf [(mg g -1 ) (L mg -1 )          data are adopted from Sarathy et al. 13 and Salter-Blanc and Tratnyek. 14The abbreviations for the different ZVZ's and ZVI's are given in the original sources.Other data are from this study.The error bars were either directly adopted from the referenced studies, or derived from triplicate samples with 95% confidence level (our study).

Figure S2 .
Figure S2.(A).Point-of-zero charge (pHpzc) of PLP-OH, PLP-QA, PLP-py and PLP-py + used in this study.The PLP samples were prepared by dispersing each PLP in DI water, to which the pH was adjusted by adding HCl or NaOH to the desired values (i.e., pH 2, 3, 5, 7, 8 and 10).(B) Zeta potential of all PLPs measured at pH 7. The error bars were derived from triplicate measurements with 95% confidence level.

Figure S9 .
Figure S9.Mass normalized observed reaction rate constants (kM) of TCP decay by different technologies that involve solid.Zero-valent zinc (ZVZ, cyan) and zero-valent iron (ZVI, purple) data are adopted from Sarathy et al.13 and Salter-Blanc and Tratnyek.14The abbreviations for the different ZVZ's and ZVI's are given in the original sources.Other data are from this study.The error bars were either directly adopted from the referenced studies, or derived from triplicate samples with 95% confidence level (our study).

Figure S11 .
Figure S11.(A) The total mass of allyl chloride in water (dashed line), PBS, 5mM TOTHS, and PLP-py + (0.7g L -1 ) at pH 7 after 5 days.The extraction efficiency of TCP from PLP was above 95%.(B) Allyl chloride degradation by 5mM TOTHS in the absence of PLPs at pH 7 under 25 °C.The calculated kobs was 0.08±0.01h -1 , corresponding to a half-life t1/2 of 8.7±0.6 h for allyl chloride degradation.The error bars were derived from triplicate samples with 95% confidence level.

Figure S12 .
Figure S12.Chromatogram of gas chromatography with an electron capture detector (GC-ECD) for allyl chloride only (blue), and with 5 mM TOTHS after 5 days (cyan).The retention time of allyl chloride and the new peak is 2.24 and 1.73 min, respectively.

Table S3 .
The obtained parameters of adsorption isotherm of SRNOM on PLP-QA and PLP-py + by non-linear fitting to the Freundlich Model.