Surface characterization of activated carbon cloths developed from a single precursor and various activating agents

M. E. RAMOS; S. BLACHER; J. P. PIRARD; A. L. CUKIERMAN

EDIMBURGO, UK

Congreso; 8th International Symposium on the Characterisation of Porous Solids (COPS VIII); 2008

The University of Edimburgh

Activated carbon cloths (ACCs) have attracted great interest in recent years as they offer several technological advantages over the powder or granular forms of this widely used porous material. As for the traditional forms, methods for preparing ACC can be grouped into physical and chemical activation. The latter leads to activated carbons with developed pore structure in higher yield and at relatively lower temperatures than physical activation. Moreover, the activating agent seems to modify the pyrolysis process leading to a considerable increase in mechanical strength that is especially relevant to ACC. The effect of different chemical reagents used in the impregnation stage on surface and morphological features of activated carbon cloths was investigated. The ACCs were synthesized by chemical activation of regenerated cellulose fabric impregnated separately with solutions (5 wt% concentration) of phosphoric acid, boric acid, ammonium citrate, sodium dihydrogen phosphate, disodium hydrogen phosphate and trisodium phosphate. All the impregnated samples were thermally treated under a N2 flow at 5 ºC/min up to the same final treatment temperature ( 800 ºC). Porosity development of the resulting ACCs was examined by determination of nitrogen adsorption isotherms at 77 K for all the samples. Textural parameters were calculated by applying different models (BET, Dubinin-Radushkevich, alpha ;S). The ACCs were observed by Transmission Electron Microscopy (TEM). The uptake of nitrogen and the shape of the isotherm were strongly dependent on the chemical agent used in the impregnation stage. Phosphoric acid and boric acid led to essentially microporous adsorbents, whereas the ACCs obtained by impregnation with the other phosphorous reagents and ammonium citrate presented development of meso and macroporosity. Micropore volumes calculated by means of the αS model were significantly lower than the values calculated by the DR equation for some ACCs. Results pointed out to a linear relationship between differences in micropore values and external surface areas evaluated by the aplpha ;S method. TEM micrographs revealed variations in ACCs´ surface morphology, in agreement with N2 adsorption data. Present results indicate that the selected activating agent markedly influences physicochemical properties of the ACCs. Hence, porosity could be conveniently tailored depending on the desired application.