Renewable hydrothermal chars have potential applications in catalysis, water purification, and energy storage. To be effective for these applications, functionalization of the carbon surface will be required. Mechanochemical processes have the potential to reduce the environmental burden of hydrochar functionalization. Here, we produced hydrothermal char from a renewable glucose feedstock at 180°C and autothermal pressure. The synthesized hydrothermal chars were then subjected to ball milling at times ranging from 30 to 180 min and the structural changes were followed using IR (both DRIFTS and ATR), Raman, and ESR spectroscopy. IR spectroscopy reveals that ball milling converts furanic structures (prominent at 1520 cm-1 wavenumbers) into aromatic structures with prominent features at 1590 and 1180 cm-1. A new peak, present at 1710 cm-1 wavenumbers and assigned as a carbonyl, appears during ball milling. Raman microscopy was used to probe the changes in longer range structural organization that occur during ball milling. Using assignments based on brown coal, Raman microscopy indicates a loss of bridge-head carbons during ball milling and a parallel increase in large (&gt;6 rings) condensed aromatic structures. ESR indicates the formation of carbon radicals with ball-milling &lt;90 min, followed by recombination causing a decrease in the radical population. These three data sets suggest a chemical mechanism consisting of surface oxidation in parallel with radical formation due to breaking of weak aliphatic bonds followed by recondensation into stable aromatic structures.

Mechanochemical modification of hydrothermal chars

250th National Meeting (2015)

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