Structure And Properties Of Activated Carbon Prepared From Walnut Shell By Phosphoric Acid Activation

Activated carbon is absorbent which has been widely used because of its large surface area and abundant pore volume, however these absorbing properties can be greatly affected by the preparation process. Therefore, the researches of activated carbon usually focus on improving its properties by adjusting the preparation parameters.In this paper, the activated carbon was prepared from walnut shell by phosphoric acid activation.The effect of different impregnating methods and adding different additives in activator on the ability of absorbing methylene blue solution, iodine solution and crash strength were investigated. Two kinds of impregnating methods were developed, which were the combination of the vacuum impregnation and normal impregnation and the the combination of the stirring impregnation and normal impregnation. The specific surface area and pore size distribution of activated carbon was analyzed via calculating the nitrogen adsorption-desorption curve. The pyrolysis process of walnut shell was analyzed and the pore morphology of activated carbon was observed.It is found that in the processing time of 2 hours, the iodine adsorption values of the activated carbon increases first then declines with increasing the time of both vacuum and stir. However, the methylene blue adsorption values of them are changing in different rules, and the crash strength of those all decreases. The increase of vacuuming time leads to the rise of the total volume and the mesopore volume, but leads to the decrease of its micropore volume. The maximum values of them are 0.7282ml/g,0.148ml/g,0.5786ml/g respectively when the vacuuming time was 2 hours. With the increase of stirring time, all of the total volume, micropore volume and mesopore volume rise first then drop, which reached 1210.0m2/g、 0.8178ml/g,0.6192 ml/g、0.170 ml/g respectively after stirring 1 hour.The absorbing ability and crash strength were decreased in different degrees when impregnated with tetraethoxysilane, tetrabutyl titanate, citric acid, sodium citrate, boric acid and saccharin in the activator respectively. The results show that sodium citrate can improves the special specific surface area, the boric acid can promote the quantity of mesopore and saccharin decreases both the micropore volume and the mesopore volume of activated carbons.The pyrolysis process of walnut shell was little impacted by different impregnating way. However, when adding additive in the activator, the change of the thermal decomposition curve is mainly manifested in the water-losing stage. The pore structure of activated carbons consists of cellular carbon bodies and pores which were distributed on them. Different impregnating methods and adding different additive in the activator have no influence on the morphology of the activated carbons.