麻炭的制备及其微观结构

Preparation and microstructure of hemp stem-based activated carbons

以汉麻秆为原料,通过直接炭化、磷酸/氯化锌活化法制备了麻炭.采用扫描电镜（SEM）、液N2吸附、亚甲基蓝吸附和碘吸附分别对麻炭的微观骨架结构、表面织构、孔分布及吸附性能进行了表征.结果表明,麻炭微观形貌呈现多孔性的骨架结构,由彼此平行且直通的两种管道构成,管与管之间由管壁隔断,管壁本身分布着丰富的微孔,而且三种麻炭样品中均以微孔为主且微孔分布呈多分散性.未经活化处理的麻炭,其孔径主要分布在小于1.3nm的范围内,但其比表面积和孔容较小.磷酸和氯化锌活化的麻炭的比表面积分别达1388m2/g和1691m2/g,两者的孔分布较为相似,除了在小于2nm的范围内均有微孔分布外,还存在2～4nm范围内的中孔分布.麻炭对亚甲基蓝及碘的吸附值随比表面积的增大而增加,氯化锌活化的麻炭对亚甲基蓝和碘的吸附值最大,其次依次为磷酸活化的麻炭和未经活化处理的麻炭.

Hemp stem-based activated carbon samples have been prepared by conventional pyrolysis and and by means of activation processes with H3PO4 or ZnCl2. The skeletal microstructure, textural properties, pore size distribution and adsorption properties of the samples were characterized by SEM, N2 adsorption-desorption isotherms at 77 K, and by adsorption of methylene blue and iodine. The results showed that the resultant carbon samples have a porous skeleton, containing two types of parallel end-to-end pore channels. These pores are partitioned by walls in which a large number of smaller micropores are present. Micropores were found to predominate in all of the hemp stem carbons prepared. The sample obtained by the simple carbonization process was microporous with pore sizes mostly less than 1.3 nm, with relatively low surface area and pore volume. Samples obtained using the H3PO4 and ZnCl2 activation processes had a well developed porous texture, with surface areas of 1388 and 1691m^2/g, respectively. The pore size distributions of these two activated carbons were very similar; containing a large quantity of micropores and some mesopores with diameter 2 - 4 nm. All carbon samples exhibited a multimodal pore size distribution within the micropore range. The adsorption ability of the materials increased with increasing surface area. The sample obtained by ZnCl2 activation had the highest surface area and was relatively regular in shape, resulting in the highest amounts of methylene blue and iodine being adsorbed, followed by the activated carbon obtained by activation by H3PO4, whilst the conventional carbonized carbon prepared without activation had the lowest surface area and affinity for methylene blue and iodine.