The thermal gravimetric (TG) analysis of the raw coconut shell reveals that it undergoes rapid decomposition between 240°C and 400°C. During this stage, a significant amount of organic volatiles and tar are released, leaving behind solid carbon. However, no pores are formed in this phase, as the structure remains largely intact. As the temperature increases further to the range of 400°C to 900°C, the pyrolysis process slows down. At this point, the solid carbon undergoes polycondensation reactions, leading to the aromatization of thermal decomposition products and the formation of microcrystalline carbon. Around 900°C, structural reorganization occurs, allowing micropores to develop within the activated carbon structure.
To investigate the impact of high-temperature reforming on the pore structure of coconut shell, experiments were conducted at two different temperatures: 400°C and 900°C. Before the experiments, the reaction system was sealed to prevent air from entering, which could cause unwanted oxidation or shelling reactions and potentially burn out the solid carbon. The preparation conditions for the coconut shell-based activated carbon were set as follows: 4 hours of pyrolysis at 400°C, labeled as AC-400, and 4 hours at 900°C, labeled as AC-900.
The adsorption performance of these samples showed remarkable differences. The iodine adsorption value of AC-900 reached 1194 mg/g, while its methylene blue adsorption value was 105 mg/g—substantially higher than that of AC-400. This demonstrates that high-temperature pyrolysis under a closed system significantly enhances the development of micropores during carbonization. The reason for this improvement lies in the reduction of heteroatoms (such as oxygen and hydrogen) at high temperatures, the breaking of bonds between heteroatoms and aromatic layers, and the subsequent rearrangement of the crystallite structure. These changes increase the degree of graphitization, resulting in a material with well-developed, uniform pores, similar to a carbon molecular sieve.
This study highlights the importance of controlled pyrolysis conditions in producing high-quality activated carbon with superior adsorption properties. The results suggest that optimizing temperature and atmosphere can greatly influence the final structure and functionality of the material. Such findings have important implications for the production of activated carbon for environmental and industrial applications, where high surface area and pore uniformity are critical factors.
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