Carbon 41 (2003) 2873–2884 Letters to the Editor Preparation of activated carbons from cork waste by chemical activation with KOH * A.P. Carvalho , B. Cardoso, J. Pires, M. Brotas de Carvalho ´ ´ ˆ Departamento de Quımica e Bioquımica, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande Ed. C8, 1749-016 Lisbon, Portugal Received 12 March 2003; accepted 23 June 2003 Keywords: A. Activated carbon; B. Chemical treatment; C. Adsorption; D. Surface areas; Texture In the western Mediterranean region, and specially in the final temperature attained values in the range 500–900 8C south of Portugal, cultivation of cork oak, Quercus suber, and was maintained for a time, t (h), from 0 to 16 h. After is an important economic activity, with Portugal being the carbonisation the samples were cooled to room tempera- world’s major producer. Besides the production of stop- ture under nitrogen flow, washed up to pH 7 and dried at pers, an economically important product, the industry 100 8C. The samples will be designated according to the creates enormous volumes of waste formed by particles expression: ratio KOH:cork / T ( 8C)/ t (h). Adsorption iso- with very small dimensions, generally designated cork therms of N at 2196 8C were determined in a convention- 2 powder. This industrial waste was the raw material used in al volumetric apparatus. Hydrocarbon ( n-hexane and this work since it has the essential features of an activated cyclohexane) vapour adsorption was studied at 25 8C by carbon precursor and, according to the results of previous the gravimetric method. The samples were studied in the studies [1,2], allows one to obtain materials with textural form of small wafers made by pressing (without binder) characteristics, e.g. apparent surface areas, comparable the as-obtained form, i.e. finely divided powders. From N 2 with those of commercially available carbons. This work adsorption data, the apparent surface area, A , was BET 0 reports the first systematic evaluation of the influence of determined through BET equation (0.05,p / p ,0.15). several experimental parameters (activating agent content Using the Dubinin-Radushkevich (DR) equation, the mi- and temperature and duration of calcination) on the textural cropore volume, V , the characteristic adsorption energy, DR characteristics of the activated carbons prepared from E , and the mean micropore half width, L , were esti- 0 0 industrial cork waste using KOH as activating agent. mated. To calculate L , the empirical equation: L 5 0 0 25 3.5 The raw material was a sample of industrial waste, (13.028–1.53310 E )/ E [3] was used. The micropor- 0 0 previously treated with H SO (10%) at room temperature, osity was also assessed by applying the a method, taking 2 4 S washed up to pH 7, dried at 80 8C and finally sieved to as reference the isotherm reported in Ref. [4]. Hydrocarbon obtain the fraction of cork particles smaller than 0.297 adsorption data were analysed by the DR equation. mm. Cork powder was physically mixed with different The N adsorption isotherms displayed in Fig. 1 are 2 volumes of KOH solution (25%), to obtain mixtures with representative of the curves obtained in this study and weight ratios of KOH:cork between 0:1 and 4:1. After reveal the essential microporous nature of the materials. drying at 80 8C, the mixtures were heated in a horizontal The values of apparent A (Table 1) show that the BET 3 21 furnace under a nitrogen flow (2 cm s ). The tempera- experimental parameters have different effects on the ture was increase in two steps: from room temperature up development of the microporous structure of the samples. 21 to 300 8C (5 8C min ), maintained for 3 h, and afterwards In fact, the increase in the calcination time and in the 21 raised (10 8C min ) up to a higher value, T ( 8C). The calcination temperature promote a continuous increase in the A values, which is considerably more accentuated BET in the case of the temperature. The increase of the KOH:cork weight ratio, although initially (until * KOH:cork51:1), also has a positive effect on the apparent Corresponding author. Fax: 1351-217-500-088. E-mail address: ana.carvalho@fc.ul.pt (A.P. Carvalho). surface area of the samples, for high contents of KOH, the 0008-6223 / 03 / $ – see front matter  2003 Published by Elsevier Ltd. doi:10.1016 / S0008-6223(03)00323-3