New methods for assessing electron storage capacity and redox reversibility of biochar. (January 2019)

• Record Type: Journal Article
• Authors: Xin, Danhui; Xian, Minghan; Chiu, Pei C.
• Is Part Of: Chemosphere. Volume 215(2019)
• Page Start: 827
• Page End: 834
• Publication Date: 2019-01
• Subjects: Biochar -- Electron storage capacity -- Redox reversibility -- Chemical oxidation/reduction -- Rate-limiting step -- Pore diffusion; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2018.10.080
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Black carbon such as biochar has been shown to support microbial redox transformation by accepting and/or donating electrons. Electron storage capacity (ESC) is an important property that determines the capacity of a biochar to mediate redox processes in natural and engineered systems. However, it remained unclear whether a biochar's ESC is constant and reversible and if so to what extent, over what redox potential range ESC is distributed, and what fraction of the ESC is microbially accessible. In this study, we developed chemical methods that employed combinations of reductants and oxidants of different potentials – Ti(III) citrate, ferricyanide, dithionite, and dissolved O2 – to measure the ESC of Soil Reef biochar, a wood-derived biochar that can serve as an electron donor or acceptor for Geobacter metallireducens . For a given oxidant–reductant pair, the ESC obtained over multiple redox cycles was constant and fully reversible, though lower than that of the virgin biochar. Pore diffusion within biochar particles was rate-limiting and controlled the timescale for redox equilibrium. Results suggest that redox-facile functional groups in biochar were distributed over a broad range of potentials. The ESC measured using dithionite indicates approximately 22% of the biochar's reversible ESC was accessible to G. metallireducens . We propose that reversible ESC may be regarded as a constant and quantifiable property of black carbon. Graphical abstract: Highlights: New methods yielded reproducible electron storage capacity (ESC) of biochar. Biochar ESC reversibility and redox potential distribution were evaluated. For a reductant-oxidant pair reversible ESC was constant over repeated redox cycles. Pore diffusion was rate-limiting and controlled biochar oxidation/reduction time. Approximately 22% of biochar's reversible ESC (4 mmol/g) was microbially accessible.