Importance of iron oxides on the carbons surface vs the specific surface for VOC's adsorption

The VOC's adsorption in dynamic systems using three different sorbents (carbonaceous materials) prepared from biomass residue as precursor, was studied. The sorbents were prepared from pecan nut shell (Carya illinoinensis), peach stone shell (Prunus persica) and sawdust (Pinus cembroides), using a L9 orthogonal array of Taguchi method to identify the most important factors in the VOC's sorbent preparation. To determine the most important characteristic from VOC's sorbent (i.e. the textural parameters of carbons have more effect in the adsorption of VOC's than the surface chemistry of the carbon), some specific activating agents were studied (H3PO4, CaCl2 and FeCl3). The obtained samples were characterized using FT-IR spectroscopy, nitrogen adsorption isotherms at 77 K, SEM/EDX analysis and X-ray diffraction. The obtained results indicated that the specific surface and the iron oxides formation (Fe2O3 and Fe3O4) plays the most important role in the adsorption of VOC's (toluene and 1-butanol considered as model compounds). According with the Taguchi analysis, the precursor and the concentration of the impregnating agent were the most important factors in the synthesis and activation of carbons for the removal of toluene and 1-butanol, respectively. Specifically, the adsorption of toluene was favored by the Fe2O3 formation on the carbon surface of the sample denominated E5, which was obtained by activation of peach stone with FeCl3 (0.1 M) and carbonized at 1000 °C. Additionally, the adsorption capacity of the carbon with high specific surface (654 m2/g) was 102 and 237 mg/g for toluene and 1-butanol, respectively. An adsorption mechanism was proposed so it can be seen that iron species would interact with the VOC's molecules.