Effect of compressed liquid CO₂antisolvent treatment on the synthesis of hierarchically porous nanocarbon from kraft lignin

Carbon nanoparticles with hierarchical micro/mesoporous structure were developed from a commercial kraft lignin using a facile, one-pot green technology of a compressed liquid CO₂antisolvent treatment, followed by thermostablization and carbonization processes. The as-synthesized carbon nanoparticles were systematically characterized by investigating the surface properties of morphology, particle size, and chemical states with FESEM, HRTEM and XPS, respectively; surface areas and porous structures with BET analyzer; crystalline state with XRD and Raman spectroscopy; chemical features with FTIR; and elemental compositions with an elemental analyzer. The results indicated that the carbon nanoparticles fabricated from the smallest quasi-spherical lignin nanoparticles contained high nanocrystalline and amorphous carbons levels. The enhanced phenolic, carbonyl, and carboxylic functional groups on the particle surface promoted the dispersibility of the particles in deionized water. The size and morphology of the lignin precursor particles significantly affected the fabrication of the carbon nanoparticles by carbonization. The experiment suggested that such dispersible and porous carbon nanoparticles could be applicable in the fields of energy, biotechnology, and environmental pollution control.