Pyrolysis Creates Electron Storage Capacity of Black Carbon (Biochar) from Lignocellulosic Biomass

Abstract

Black carbon such as biochar has been shown to possess electron storage capacity (ESC), which enables black carbon to store and reversibly exchange electrons with its surroundings. However, the origin of black carbon ESC remains unknown to date. To answer this question, we measured the ESC of cellulose, lignin, hemicellulose, and biochars prepared from these biopolymers, their mixture, and a pinewood, through pyrolysis at 350−650 °C. Mediated electrochemical analysis (MEA) with ABTS and diquat as mediators and chemical redox titration (CRT) with O 2 and titanium(III) citrate were used to quantify ESC. MEA could measure lignin ESC but significantly underestimated biochar ESC; CRT could measure the total reversible ESC of biochars but not that of lignin. Lignin was the only biopolymer that possessed ESC, which was largely destroyed during pyrolysis at 350 °C. After pyrolysis at ≥450 °C, the three biopolymers, their mixture, and pinewood all yielded biochars that possessed a highly reversible ESC of 1−2 mmol e − /g. This indicates that pyrolysis created reversible ESC of biochar from lignocellulosic biomass, presumably by converting oxygen-containing moieties of the biopolymers into (hydro)quinones in biochar. The implications of our findings for biogeochemistry, climate, contaminant fate, and engineering applications are discussed.

Abiotic reduction of 3-nitro-1,2,4-triazol-5-one (NTO) and other munitions constituents by wood-derived biochar through its rechargeable electron storage capacity

“…31,34,40,44 Rogue was included because its BET surface area (407 ± 9 m 2 g −1 ) and ESC (7.07 ± 0.15 mmol g −1 ) measured with titanium( iii ) citrate and dissolved O 2 (DO) were the highest of all commercial biochars we have tested. 35 These values are roughly two times those of SRB (158 ± 3 m 2 g −1 and 3.54 ± 0.13 mmol g −1 , respectively).…”

“…The ESC of biochar has been shown to be reversible over multiple oxidation–reduction cycles. 34,35 This suggests that, as a rechargeable electron storage medium, biochar should be able to reduce contaminants repeatedly through recharging. This is demonstrated in Fig.…”

“…Based on our previous work, SRB and Rogue needed to be oxidized in aerated deionized water for at least 3 d to ensure thorough oxidation of reduced functional groups. 34,35 Oxidized biochar samples were collected on a glass microfiber filter, dried at 65 °C for 24 h, and stored in a desiccator until use.…”

“…30,31,34 While EDC and EAC vary with the redox state of a biochar, the ESC is constant for a given pair of reductant and oxidant used to measure ESC. 34,35 Studies have shown that ESC is a common property of biochar prepared via pyrolysis of lignocellulosic biomass. 35 Biochar ESC can range from 0.2 to 7 mmol e − g −1 , is distributed over a broad range of reduction potential ( E H ), and is highly reversible over multiple redox cycles.…”

“…34,35 Studies have shown that ESC is a common property of biochar prepared via pyrolysis of lignocellulosic biomass. 35 Biochar ESC can range from 0.2 to 7 mmol e − g −1 , is distributed over a broad range of reduction potential ( E H ), and is highly reversible over multiple redox cycles. 30,34,36–39…”