Synergistic CO2-K2C2O4 activation of furfural residue toward high-adsorption activated carbon for phenol removal

The activation approach plays a critical role in determining the structural properties of activated carbon (AC). In this study, porous activated carbon was prepared from furfural residue through a combined physical-chemical activation using CO₂ and potassium oxalate as co-activators. The results revealed that CO₂ and K₂C₂O₄ had a synergistic effect that enhanced the activation efficiency. Compared to single activation, the co-activation markedly increased the specific surface area (1380 m²/g) of the resulting AC, although this came at the cost of a reduced solid yield. In addition, the co-activation process boosted the elimination of hydrogen and oxygen from the carbon material, thus impacting the surface functionality. The co-activated sample K₂C₂O₄-CO₂-800 exhibited superior adsorption performance for phenol, achieving a maximum removal rate of 95 %, owing to its well-developed porous structure. Furthermore, it demonstrated good reusability, maintain a 74 % removal rate after five cycles. These findings proposed that physical-chemical co-activation is an effective strategy for tuning the porous structure and improving the adsorption performance of activated carbon.