From Electrochemically Depolymerized Lignin Residues to Functional Carbon Materials for Phenol Adsorption and Redox...

Lignin, a waste component of lignocellulosic biomass, can be valorized as a feedstock for chemical production. One promising approach is its electrochemical degradation under controlled conditions using a suitable electrocatalyst. However, achieving complete utilization of lignin remains challenging. In this work, residues remaining after partial electrochemical depolymerization of Kraft lignin were investigated as precursors for the preparation of activated carbon intended for adsorption and catalytic applications. The degradation process was performed for up to 360 min at -1.5 V vs. Ag/AgCl using Cu, Ag, Al, or Ni electrocatalysts in the presence of potassium carbonate, which remained in the material after the process and could subsequently act as a chemical activating agent during carbonization at 850°C for 4 h. As a result, the obtained carbons exhibited a highly developed specific surface area and micro/mesoporosity. Longer electrochemical exposure produced materials with more ordered stacked-layer structures, an increased mesopore volume, and a reduced content of surface oxygen functional groups. Nevertheless, these changes did not diminish their effectiveness in the adsorption of phenol from aqueous solutions or the catalytic oxidation of sulfurous acid to sulfuric acid. The catalytic activity could be further enhanced by nitrogen doping introduced by gas-phase NH₃ treatment.