Activation of different parts of a ginkgo tree form activated carbon of distinct pore characteristics and mass yields

Abstract

Components of a tree typically include fruits, leaves, bark, and wood, which might be processed together through thermochemical routes such as activation. Different parts of a tree with varied structures might have distinct contributions towards pore development of activated carbon (AC). This was investigated herein by conducting activation of different parts of a ginkgo tree with K₂C₂O₄ at 800 °C. The results indicated that the organics in ginkgo leaves were rather aliphatic and thermally unstable. Their high propensity towards cracking formed a lower yield of AC-leaves (18.0 %) than that from activation of shell, bark, and wood (ca. 22 %). The significant removal of carbonaceous species in the activation of leaves led to much lower carbon yield than that from shell and wood (12.3 % versus ca. 19 %). However, intensive cracking of leaves generated more developed pores (mesopores for AC-leaves: 17.1 % versus ca. 7 % for others). The S_BET followed the order: AC-leaves (1082.9 m²g⁻¹) > AC-wood (974.6 m²g⁻¹) > AC-shell (880.7 m²g⁻¹) > AC-bark (850.7 m²g⁻¹). Substantial deoxygenation of cellulose/lignin in activation of the shell and wood formed oxygen-deficient AC (oxygen content: ca. 7 %), while AC-leaves and AC-bark were oxygen-rich (ca. 27 %, oxygen in C-O-C form). In-situ IR analysis of activation of leaves confirmed highly unstable aliphatic structures like alcoholic/phenolic -OH, -C-H, and CO species, forming AC-leaves of fragmented morphology. Carbon skeleton of the shell and wood was thermally more stable, retaining fibrous biological structures in the resulting ACs. Additionally, AC-leaves showed the highest efficiency for removal of Cr VI via monolayer sorption through complexation or chemisorption mechanisms.