The thermal gravimetric (TG) analysis of the coconut shell raw material reveals that it undergoes rapid decomposition between 240°C and 400°C. During this stage, a significant amount of organic volatiles and tar is released, leaving behind solid carbon. However, no pores are formed in the activated carbon at this temperature range. As the temperature increases further to 400–900°C, the pyrolysis rate 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, and micropores within the crystallites begin to develop, which are essential for activated carbon.
To investigate the impact of high-temperature reforming on the pore structure of coconut shell, experiments were conducted by pyrolyzing the raw material at both 400°C and 900°C. Prior to the experiment, the system was sealed to prevent air from entering, avoiding unwanted oxidation or combustion of the char. This ensured that the carbonization process remained controlled and accurate.
The preparation conditions for coconut shell-based activated carbon involved pyrolysis under a closed system. The samples were labeled as AC-400 (pyrolyzed at 400°C for 4 hours) and AC-900 (pyrolyzed at 900°C for 4 hours). The adsorption performance of these samples was evaluated, and the results showed that AC-900 exhibited significantly higher adsorption capacity compared to AC-400. Specifically, the iodine adsorption value of AC-900 reached 1194 mg/g, and the methylene blue adsorption value was 105 mg/g—substantially higher than that of the low-temperature sample.
This indicates that high-temperature pyrolysis under a sealed system plays a crucial role in promoting the formation and development of micropores during carbonization. In a closed environment, the high-temperature treatment reduces the content of heteroatoms such as oxygen and hydrogen, breaks bonds between oxygen atoms and aromatic layers, and allows for the rearrangement of the crystallite structure. This leads to an increase in the degree of graphitization and the formation of a material with well-developed, uniform pores, resembling a carbon molecular sieve.
Such characteristics make the resulting activated carbon highly suitable for various applications, including gas purification, water treatment, and industrial filtration. The study highlights the importance of controlling pyrolysis conditions to optimize the pore structure and enhance the functional properties of activated carbon derived from coconut shells.
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