Quinones (QNs) are ubiquitous and play a significant role in mediating electron transport in natural and biological systems. The redox reactivity of natural organic matter (NOM) and biochars (BCs) have been attributed to their quinone components, although there is a lack of direct evidence. In this study, we examined the recyclability of aqueous phase biochar (a-BC) during the dehalogenation process of Triclosan (TCS) to test the presence of quinoidic moieties, which are active redox capable, functional groups. We found that over three six-day reaction cycles between TCS and reduced a-BC, TCS was degraded by 60%, 47%, and 50%, respectively. Within the three reduction cycles, chlorine recovery based on residual TCS and generated Cl<sup>−</sup>ranged from 59% to 74%, indicating that a significant fraction of TCS was fully dechlorinated. Electron acceptance measurements for the three cycles ranged from 0.077 to 0.58 mol e<sup>−</sup>/mol C. Along with the recyclability of TCS, solid-phase extraction was done to separate the a-BC into three fractions based on the pKa to test the reactive components of reduced a-BC. The three pKa ranges chosen for this study were 4-7, 7-11, and greater than 11 to represent the carboxylic, phenolic, and ketonic functional group-containing compounds. Subsequent reactions with TCS showed that the fraction representing the pKa range 7-11 reduced 65% of TCS during the 12 day reaction period while the pKa ranges 4-7 and greater than 12 reduced TCS by 38.5% and 4.6%, respectively. These results indicate that the most reactive components of a-BC are the molecules containing the phenolic functional groups. Further studies will study the influence of particle size, ozonation, and sonication on the mobilization of a-BC to increase the reactive components of a-BC.

Recyclability and reactivity of aqueous biochar in the dehalogenation of triclosan

ACS Spring 2022

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