Morphological and structural differences between glucose, cellulose and lignocellulosic biomass derived hydrothermal carbons

TLDR

Hydrothermal carbonization (HTC) efficiently converts simple carbohydrates into functionalized carbon materials, with their chemical structure elucidated by solid‑state MAS 13C NMR. This study aims to determine how processing temperature and time influence the chemical structure and morphology of HTC carbon, thereby enabling a mechanistic model. Using SEM, elemental and yield analyses, and MAS 13C NMR, the authors examined the temperature‑time effects, revealing that mild HTC (180–280 °C) drives biopolymers directly toward an aromatic carbon network analogous to pyrolysis. By selecting processing parameters, the HTC carbon’s structure can be tuned from polyfuran‑rich, oxygen‑functionalized material to a highly aromatic network, and lignocellulosic precursors exhibit distinct HTC mechanisms for glucose versus cellulose.

Abstract

Hydrothermal carbonization (HTC) has demonstrated that it is an effective technique for the production of functionalized carbon materials from simple carbohydrates, such as monosaccharides and disaccharides. The chemical structure of the HTC carbon has been identified in detail by means of solid-state MAS 13C NMR investigations. However, it has not yet been clearly shown what the effects are of the processing temperature and time on the chemical structure and morphology of the generated HTC carbon. This study shows, with the help of SEM, elemental and yield analysis and solid-state MAS 13C NMR, the effects of these two key variables on the final nature of the produced material, allowing the development of a mechanistic model. According to the chosen set of processing parameters, the chemical structure of the HTC carbon can be tuned from polyfuran rich in oxygen containing functional groups to a carbon network of extensive aromatic domains. The same kind of investigation using lignocellulosic biomass as a carbon precursor shows a striking difference between the HTC mechanism of glucose and cellulose. The biopolymer, when it is treated under mild hydrothermal conditions (180–280 °C), tends to react according to a reaction scheme which leads to its direct transformation into an aromatic carbon network and which has strong similarities with classical pyrolysis.