Biochar as porous material: bridging nature and technology

Biochar, carbon-based materials derived from the thermochemical decomposition of biomass or bio-wastes in elevated temperature and inert atmosphere (pyrolysis), offers outstanding performance in various applications while minimizing environmental impact and economic concerns. During pyrolysis, the aliphatic carbon chains in biomass are transformed into aromatic carbon structures in biochar. As a natural resource, biochar serves as a viable alternative to the previous porous carbon-based materials because of its distinctive physical, chemical, and environmental characteristics. Examples are soil Amendment, catalyst and catalyst support, the electrode of supercapacitors, anode in the lithium-ion battery, and absorbent. Biochar is classified as non-graphitic and non-graphitizable carbon, and its effectiveness in many applications is largely influenced by its pore structure. Based on the structure of initial biomass, most biochars possess a non-ordered structure with low surface area and limited porosity, which restricts their use in many applications. To enhance their specific properties, various modification strategies can be employed, including selecting suitable biomass, optimizing pyrolysis conditions, heteroatom doping, surface functionalization, activation, and compositing with other materials. Several methods have been developed to activate biochar and engineer hierarchical porous structures, including physical and chemical activation as well as templating techniques. Biochar materials generally exhibit a disordered arrangement of interconnected carbon sheets with cross-links. During thermochemical decomposition, these cross-links break, generating free carbon layers. This characteristic facilitates the incorporation of heteroatoms such as O, N, and S, particularly on the outer surfaces of the carbon sheets. Meanwhile, the internal region undergoes a structural transformation known as localized crystallization, which enhances porosity, a key factor in many applications. Additionally, physical activation with steam, CO₂, or air can expand biochar pore volume, promoting the formation of micro-, meso-, and macro-structured hierarchical porosity.

کلیدواژه ها:

Biochar ، Carbon ، Porosity ، localized order ، self-doped ، functionalized