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

Abstract

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.

Keywords

• Hydrothermal carbonization
• Glucose
• Iron sulfate
• Carbon spheres
• Thin films
• Thin film interference