Insight into formation of montmorillonite-hydrochar nanocomposite under hydrothermal conditions

Montmorillonite-hydrochar nanocomposite is of great significance in biofuel production, energy storage and conversion, catalysis, environmental protection, and biology and medicine. To understand how montmorillonite facilitates the conversion of cellulose into hydrochar, it is essential to accurately control the properties and structure of hydrochar and its nanocomposites for technological applications. In this work, hydrochar and montmorillonite-hydrochar nanocomposites were produced by hydrothermal carbonization of cellulose at 200°C for 2–24h in the absence and the presence of montmorillonite. The roles of montmorillonite in the formation of hydrochar were explored in detail. Results showed that montmorillonite acted as a catalyst, an adsorbent, and an inorganic template for hydrochar formation. The formation process of montmorillonite-hydrochar nanocomposite can be divided into two stages: first, the hydrolysis of cellulose yielding degraded liquid products (e.g. glucose, fructose, and organic acids); second, the formed liquid products were adsorbed by montmorillonite, which catalyzed condensation and aromatization to form hydrochar particles on the surface of montmorillonite.