Effects of Acidic and Alkaline Metal Triflates on the Hydrothermal Carbonization of Glucose and Cellulose

The transformation of glucose and cellulose into carbon-rich solid materials was carried out in hydrothermal media at 200 degrees C for 48 h with and without the use of acidic (Al(OTf)(3)) and alkaline (NaOTf) catalysts. The effects of the catalyst type on the yield of hydrothermal carbons (HTCs) and their properties were investigated. The use of Al(OTf)(3) led to a decrease in the yields of HTCs for both feedstocks. This result was reversed for the runs with NaOTf. Glucose-derived solid product without the use of a catalyst produced carbon spheres of a diameter between 500 and 600 nm. The use of a catalyst (regardless of whether Al(OTf)(3) or NaOTf) produced larger particles. Scanning electron microscopy images of HTC from cellulose exhibited irregular morphology. Carbon spheres produced from cellulose without the use of a catalyst ranged between 200 nm and 2 mu m. HTC products from cellulose with Al(OTf)(3) yielded aggregated carbon spheres with a diameter ranging between 300 and 600 nm. The use of NaOTf inhibited the secondary char formation. Although a small number of carbon spheres were observed on the surface, the surface was mostly smooth, like raw cellulose. The final chemical structures of HTC products were further investigated using advanced C-13 solid-state nuclear magnetic resonance (NMR). NMR spectra demonstrated that glucose was completely transformed into HTCs with and without a catalyst, because there were no peaks identified with carbon atoms of glucose. However, the peaks identified with carbon atoms of cellulose were observed in the non catalytic and catalytic runs with NaOTf. Cellulose was completely transformed into HTCs with only Al(OTf)(3).