Abstract
As a multifunctional material, biochar is widely used in environmental remediation, agricultural enhancement, energy storage, and more recently, has shown great potential in the medical field. Biochar's unique physical and chemical characteristics make it an attractive candidate for medical applications due to its large specific surface area, high porosity, and surface activity. However, current research on biochar's adsorption capacity in medical applications remains limited, particularly regarding how to optimise specific surface area and adsorption properties through controlled pyrolysis and activation processes. Thus, further research and optimisation are necessary.Five representative biomass materials – poplar wood, bamboo slice, coconut shell, peanut shell, and rice straw – were selected as research subjects due to their distinct structural characteristics and economic viability. Significant variations in lignocellulosic composition were observed: cellulose and lignin predominated in poplar wood, cellulose constituted the primary component in bamboo slice, while rice straw was distinguished by its elevated ash content. Coconut shell was characterised by high carbon concentration and intrinsic porosity, whereas peanut shell and rice straw fragments demonstrated advantages in resource availability, cost-effectiveness, and collection feasibility. This diversified material selection facilitates a mechanistic understanding of how biomass compositional variations affect pyrolysis kinetics and biochar pore architecture. Five types of biomass were subjected to pyrolysis, and the KOH activation process further improved the pore structure and specific surface area of the biochar. The effects of temperature, raw material type, and activator on pore structure were investigated. The chemical composition, surface morphology, functional groups, and specific surface area of the biochar were characterised using thermogravimetric analysis (TGA), lignocellulose content determination, elemental analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area analysis. Additionally, the relationship between the specific surface area of biochar, pyrolysis parameters, and raw material type was systematically analysed.
The lignocellulose content analysis revealed that the cellulose content of poplar wood and coconut shell reached 51.36% and 51%, respectively, while the cellulose content of rice straw was significantly lower. These differences contribute to variations in volatile release and the specific surface area of different biomass types during pyrolysis. Elemental analysis showed that the H/C ratio of biochar decreased significantly with increasing pyrolysis temperature, indicating a transition from hydrocarbon structures to more stable aromatic carbon structures. Simultaneously, the decrease in the O/C ratio reflects reduced polarity in the biochar, which enhances its antioxidant properties. Ash content increased with temperature, potentially clogging pores and negatively affecting surface area. FTIR analysis demonstrated a significant reduction in hydroxyl (-OH) and carbonyl (C=O) groups in the biochar, forming more stable aromatic compounds. Additionally, the surface functional groups of AKP800 biochar, produced by KOH activation, were further enhanced. BET analysis revealed that poplar wood biochar prepared at 800℃ exhibited a higher specific surface area of 451.06 m²/g. Under different activation conditions, the specific surface area of biochar (AKP800 and BKP800) was 2028.96 m²/g and 1042.86 m²/g, respectively, which is much larger than the values reported by other researchers. SEM observations showed that, under the combined effects of high-temperature pyrolysis and KOH activation, the porous structure of the biochar became more pronounced, offering favourable conditions for its application in medical adsorption.
This study revealed the effects of biomass chemical composition, pyrolysis conditions, and activation processes on the specific surface area and adsorption properties of biochar. Biomass with high cellulose and lignin content demonstrated a higher specific surface area during pyrolysis, and KOH activation further enhanced the porosity and specific surface area of the biochar, resulting in stronger adsorption properties. The biochar produced exhibited a significantly higher specific surface area compared to those available on the market, indicating substantial potential for medical applications.
| Date of Award | 15 Jul 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Cheng Heng Pang (Supervisor), Sze Shin Low (Supervisor) & Siew Shee Lim (Supervisor) |