Concentrated Solar Combined With Hydrothermal Treatment to Unlock Lignin Graphitization Mechanisms

ABSTRACT Biocarbons are carbon‐rich materials produced from biomass and are increasingly used as sustainable alternatives to fossil‐based materials for energy and environmental applications. Their production for commercial usages requires high temperature (above 2000°C), which calls for particular attention on energy consumption and environmental impact. Hydrothermal carbonization, selected as prestructuration step, produces small graphitic units with 6 stacked layers of 2.34 nm diameter. Further pyrolysis at 800°C increases layer length and the number of small graphitic units, giving an ideal graphitization precursor. Conventional and concentrated solar carbonization are compared in the graphitization step. At 1800°C, conventional carbonization leads to a turbostratic structure with a quality of graphitic domains characterized by low interlayer spacing ( d 002 = 0.357 nm) and long defective graphene layers ( L a(XRD) = 5.81 nm, L a(Raman) = 3.17 ± 0.46 nm). Solar carbonization at 1800°C also yields long defective graphene layers, but the structure is heterogeneous with both a turbostratic ( L c = 2.41 nm, d 002 = 0.368 nm) and a graphitic ( L c = 5.58 nm, d 002 = 0.345 nm) phase. Even though solar carbonization relies on an intermittent energy source, it enables higher graphene layer stacking biocarbon as compared to conventional carbonization route.