Lawtae Panuwat, Tangsathitkulchai Chaiyot
School of Chemical Engineering, Institute of Engineering, Suranaree University of Technology, Muang District, Nakhon Ratchasima 30000, Thailand.
Molecules. 2021 May 7;26(9):2758. doi: 10.3390/molecules26092758.
A new and simple method, based entirely on a physical approach, was proposed to produce activated carbon from longan fruit seed with controlled mesoporosity. This method, referred to as the OTA, consisted of three consecutive steps of (1) air oxidation of initial microporous activated carbon of about 30% char burn-off to introduce oxygen surface functional groups, (2) the thermal destruction of the functional groups by heating the oxidized carbon in a nitrogen atmosphere at a high temperature to increase the surface reactivity due to increased surface defects by bond disruption, and (3) the final reactivation of the resulting carbon in carbon dioxide. The formation of mesopores was achieved through the enlargement of the original micropores after heat treatment via the CO gasification, and at the same time new micropores were also produced, resulting in a larger increase in the percentage of mesopore volume and the total specific surface area, in comparison with the production of activated carbon by the conventional two-step activation method using the same activation time and temperature. For the activation temperatures of 850 and 900 °C and the activation time of up to 240 min, it was found that the porous properties of activated carbon increased with the increase in activation time and temperature for both preparation methods. A maximum volume of mesopores of 0.474 cm/g, which accounts for 44.1% of the total pore volume, and a maximum BET surface area of 1773 m/g was achieved using three cycles of the OTA method at the activation temperature of 850 °C and 60 min activation time for each preparation cycle. The two-step activation method yielded activated carbon with a maximum mesopore volume of 0.270 cm/g (33.0% of total pore volume) and surface area of 1499 m/g when the activation temperature of 900 °C and a comparable activation time of 240 min were employed. Production of activated carbon by the OTA method is superior to the two-step activation method for better and more precise control of mesopore development.
提出了一种全新且简单的方法，该方法完全基于物理手段，用于从龙眼果核制备具有可控中孔率的活性炭。此方法称为OTA法，由三个连续步骤组成：(1) 对初始微孔活性炭进行空气氧化，烧失约30%的炭以引入氧表面官能团；(2) 在氮气气氛中高温加热氧化后的碳，使官能团发生热破坏，因键断裂导致表面缺陷增加，从而提高表面反应活性；(3) 最终在二氧化碳中对所得碳进行再活化。通过热处理后经由CO气化使原始微孔扩大来实现中孔的形成，同时也产生了新的微孔，与使用相同活化时间和温度的传统两步活化法制备活性炭相比，中孔体积百分比和总比表面积有更大幅度的增加。对于850和900℃的活化温度以及长达240分钟的活化时间，发现两种制备方法下活性炭的孔隙性质均随活化时间和温度的增加而提高。在850℃的活化温度下，每个制备循环的活化时间为60分钟，采用三个循环的OTA法，可实现最大中孔体积为0.474 cm/g，占总孔体积的44.1%，最大BET表面积为1773 m/g。当采用900℃的活化温度和240分钟的可比活化时间时，两步活化法制备的活性炭最大中孔体积为0.270 cm/g（占总孔体积的33.0%），表面积为1499 m/g。OTA法制备活性炭在更好、更精确地控制中孔发展方面优于两步活化法。
