Blue hydrochars formed on hydrothermal carbonization of glucose using an iron catalyst

We hypothesized that the morphology of the hydrochar from hydrothermal carbonization of glucose would be affected by Fe2+; and indeed, with such ions, large pieces of hydrochar formed that comprised aggregated spherical particles and blue and thin films. Thin carbonized films formed at the bottom of the autoclave liners or on TeflonTM tape used as a template. Free-standing films could be prepared by stretching the TeflonTM tape after the synthesis. The carbonized films that formed at the bottom of the autoclave adhered to spherical hydrochar particles. The blueness was ascribed to thin-film interference under white-light irradiation and related to the film thickness, which was about 200 nm. Analysis of transmission electron microscopy (TEM) images showed that the films consisted of a layered amorphous carbon. The amorphous and thin films were more carbonized than the amorphous carbon of the TEM grid, as derived via electron energy loss spectroscopy (EELS). Additional analysis of one of the thin films by X-ray photoelectron spectral analysis showed a higher carbon fraction than for bulk hydrochar, supporting the EELS analysis. We believe that the synthesis of thin films of hydrochar can open up new colloidal processing pathways, which could be useful in the preparation of carbon-based materials and alike. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Automated summary

We investigated the effect of Fe2+ on the morphology of hydrochar produced from the hydrothermal carbonization of glucose. The presence of Fe2+ resulted in the formation of large pieces of hydrochar composed of aggregated spherical particles and blue thin films. The films were found to be composed of layered amorphous carbon and exhibited blueness due to thin-film interference under white-light irradiation.