Probing laser-induced structural transformation of lignin into few-layer graphene

Abstract

Laser-induced graphene (LIG) is a versatile form of graphene materials synthesized through direct laser writing (DLW) onto a carbon-rich precursor. Lignin is a promising natural precursor for LIG. However, the lack of understanding of the relationship between lignin chemistry and LIG properties limits the effective utilization of lignin. Herein, we aimed to understand the structural evolution of lignin into few-layer graphene during direct laser writing via the combined experimental investigation and reactive force field molecular dynamics (MD) simulation. Strong correlations were found between structural features of lignin and LIG characteristics, especially the sheet resistance (electrical conductivity) and defects in graphene domains. Specifically, higher molecular weight lignin demonstrated a superior propensity for generating the graphitic structure in the turbostratic matrix of LIG. This phenomenon led to better graphene quality in terms of morphological continuity, conductivity, and graphene domains. The glass transition temperature (T_g) of fractionated lignin was identified to have the strongest linear correlation with both sheet resistance and defect density in LIG. Additionally, the MD simulations shed light on the role of closely positioned carbon atoms in the initial substrate, highlighting their facilitative effect on the formation of large graphene domains. The proposed LIG formation pathway offers a new avenue for lignin biorefinery, facilitating efficient production of graphene materials from renewable resources.