Pyrogenic carbonaceous materials (PCMs), such as activated carbon (AC) and biochar, can exchange electrons with aqueous contaminants and microorganisms. This reactive behavior may provide new strategies to quickly and thoroughly degrade organic contaminants. To realize these benefits, a better understanding of how we can tune the chemical and physical properties that influence electron exchange is needed. While studies have examined how PCM synthesis conditions (e.g., feedstock, pyrolysis temp.) impact resulting electron exchange behavior, there is a lack of information on how post-pyrolysis treatment methods influence electron exchange. Towards filling this knowledge gap and to provide the basis for tailoring PCMs for specific contaminant transformations, we subjected AC cloth to hydrogen peroxide and nitric acid treatments. These oxidative treatments have previously been shown to increase the oxygen content of PCMs. After the treatments, we used mediated electrochemical reduction (MER) tests to quantify the electron accepting capacity (EAC) and mediated electrochemical oxidation (MEO) tests to quantify the electron donating capacity (EDC) of the AC. Our preliminary results indicate that both chemical treatments resulted in the appearance of several chemical functional groups containing C=O and C-H bonds, as revealed by fourier-transform infrared spectroscopy. The MER tests showed that both treatments increased the EAC; however, the magnitude was dependent on the chemical type and concentration, and treatment incubation time. In all cases, nitric acid treatment resulted in a higher EAC than hydrogen peroxide-treated AC, reaching as high as 409% larger EAC (9.2 mmol e-/g) than the pristine AC (1.8 mmol e-/g). Density functional theory analysis revealed that for both treatments, pore volume and sample surface area decreased. Nitric acid treatment resulted in the largest decline in both pore volume and surface area with decreases of 25.9% (0.47 cc/g) and 16.6% (1271.89 m3/g) respectively, in comparison to pristine AC (0.64 cc/g and 1525.96 m3/g). We are currently conducting MEO tests to quantify the EDC of the treated materials and to evaluate the resiliency of repeated electron exchange cycles. Additionally, we will determine if larger EAC and EDC values correlate with transformation rates and completeness of a model organic contaminant. These results provide a foundation for customizing the redox activity of PCMs for organic contaminant transformations.

Chemical treatment of activated carbon to improve electron exchange capacities and transformation of organic compounds

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