研究了在椰子壳活性炭上浸渍金属盐(硝酸铁和硫酸铁)后,在二氧化碳气氛中催化活化对中孔结构的影响.发现硝酸铁对活性炭比表面积(-1 930 m2/g)的增加和中孔结构(-10 nm)的发展更有效.改性活性炭具有发达的中孔结构,显示了更大的维生素B12吸附容量(是改性前的5倍～8倍)和更快的吸附速度.中孔结构的发展基于三个方面的原因:(1)在活化过程中,浸渍在活性炭微孔内的金属盐分解所释放的氧化性气体与微孔碳壁反应,扩大了孔径;(2)在高温下,来自于金属盐的金属氧化物被碳还原,扩大了孔径;(3)在金属铁存在下,碳壁被催化活化,大大提高了活性炭的中孔率.由此提供了一种廉价的从商业活性炭制备中孔活性炭的有效途径.
Commercial coconut shell based activated carbon (AC) was used to investigate the production of increased mesoporosity by impregnating with catalytic metal salts such as Fe(NO3)3 and Fe2(SO4)3 followed by CO2 gasification. The salts are found be effective in enlarging the pore size of AC and Fe(NO3)3 is the more effective one to increase pore size and a much larger adsorption capacity (5 -8 times as large as that of as-received AC) and a more rapid adsorption rate for vitamin B12. Three mechanisms are proposed to modify the surface properties and pore size of AC: (1) NOx and SOx liberated from the impregnated salts burn the carbon wall to enlarge pore size; (2) Metal oxide reacts with the carbon wall to enlarge pore size, accompanied by reduction to the corresponding metal; and (3) Metal has a catalytic effect during CO2 gasification of the carbon wall of the AC. Graphitization of the carbon wall caused by metal is also observed. The present modification method is a promising, convenient and cheap way to modify AC to obtain mesopores.
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