Formation and evolution of pectin-derived hydrothermal carbon from pectin

Abstract

• Chemical reaction of hydrothermal conversion of pectin starts from 100 °C. • The hydrothermal conversion pathway of pectin was revealed. • Carbon spheres with a diameter of 10 nm–3 μm were formed from the pectin surface. • Pectin-derived nanospheres had an internal and external uniform structure. Hydrothermal conversion can convert biomass into carbon materials in catalysis, energy storage, and water purification. Pectin, a polysaccharide widely presented in plant cell walls, is an important component of biomass. However, the formation and evolution of pectin-derived hydrothermal carbon are not clear. In this study, we conducted the hydrothermal treatment of pectin at 100–300 °C to investigate the properties at different hydrothermal stages. With the characterization of the solid products with scanning electron microscopy (SEM), elemental analysis, N 2 adsorption/desorption, Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and pyrolysis behavior in thermogravimetric analyzer (TGA), we proposed the formation and evolution pathway of pectin-derived hydrothermal carbon from original pectin. Pectin first underwent a physical change of gelation during the hydrothermal process, and then was hydrolyzed to liquid monomers. Pectin-derived hydrothermal carbon was formed by the polymerization of liquid monomers resulting from the hydrolysis of pectin. Moreover, the hydrothermal carbon was further carbonized, accompanied by dehydration and aromatization. Meanwhile, the originally irregular pectin bulk structure was completely transformed into carbon spheres above 200 °C. This work can provide some fundamental guidance for the sustainable synthesis of carbon materials from the hydrothermal process of pectin.