Cross-Interaction of Fish Scales and Poplar-Derived Bio-oil Enhance Pore Development via Carbonization and Activation

Fish scales (FS) are not only a kitchen waste but can also serve as a resource when used as a precursor for the production of activated carbon. However, pore development in activated carbon derived from the FS could be hindered by the excessive cracking of the thermally unstable collagens and fats in FS. Herein, an approach of impregnating FS with bio-oil, before being activated with K₂C₂O₄ at 800 °C, was executed, aiming to increase the activated carbon yield, tailor the porous structures of activated carbon, and find another outlet for application of bio-oil. The results confirmed that the formation of activated carbon was diminished due to the extreme conversion of proteins/fats to gaseous products during FS activation. Cross-interactions between organics in the bio-oil for impregnation with proteins in FS led to a doubling of the yield of activated carbon and also increased the carbon content in activated carbon (from 46.2% in the control sample to 62.0%) due to the formation of organics with higher resistance to conversion to gaseous products. Besides, more developed pore structures (more mesopores: 22.3% versus 12.0%) were generated through bio-oil impregnation (1349.3 m²/g versus 1206.3 m²/g in the control sample). In-situ IR characterization indicated the formation of pores via cracking of aliphatic structures in FS. Bio-oil impregnation formed more aliphatic structures and destroyed strong hydrogen bonds in FS, generating more developed pore structures. Additionally, hydrothermal carbonization (HTC) of FS led to substantial leaching of organics to the extent of generation of almost no pores from activation of the resulting hydrochar. The co-HTC of FS with bio-oil can induce the transfer of organics present in bio-oil to FS, facilitating pore development.