Catalytic growth of a colloidal carbon sphere by hydrothermal reaction with iron oxide (Fe3O4) catalyst

•Hydrothermal growth of carbon spheres is time-consuming process with low yield.•Fe3O4, TiO2, and Ni2O3 enhance the glucose conversion in hydrothermal reaction.•With metal oxides, the production of fructose and 5-HMF was promoted.•Enhanced isomerization reaction resulted in catalytic growth of the carbon spheres.

Carbon spheres with uniform shape and narrow size distribution have been fabricated through various methods. Hydrothermal reaction is one of the synthesis methods that operate at relatively low reaction temperature and pressure. However, the application of hydrothermal synthesis is limited due to the long reaction time and low production yield. Metal oxides, Fe3O4, TiO2, and Ni2O3, were applied to enhance the hydrothermal reaction. Catalytic glucose conversion with these metal oxides was observed. When Fe3O4 was added, the fastest conversion of glucose with a considerable amount of intermediates was demonstrated with spherical shape of the carbon product. Additionally, from the intermediates concentration, it was confirmed that the growth of the carbon spheres is catalyzed by the enhancement of isomerization reaction from glucose to fructose with the addition of Fe3O4.