Synthesis of activated carbons by chemical activation of the endocarp of babassu coconut.E. Barcellos, G. R. Gonalves, D. F. Cipriano, H. D. A. Honorato, M. A. Schettino Jr., A. G. Cunha, F. G. Emmerich, J. C. C. Freitas.Laboratory of Carbon and Ceramic Materials, Department of Physics, Federal University of Esprito Santo, Av. Fernando Ferrari, 514, 29075-910, Vitria, ES, Brazile-mail: ewerton.junior@hotmail.comCNPq, CAPES, FINEP, FAPES, LabPetro and UFES.Activated carbon is a material composed primarily of carbon, hydrogen and oxygen, presenting large porosity and high adsorption capacity. These materials are vastly used in applications including water cleaning, medical treatments, odor removal, gas separation and catalysis [1,2]. This work describes an investigation on the chemical activation of the endocarp of babassu coconut (EB), which is an important agro-industrial byproduct in Brazil. Two different routes were followed for the synthesis of the activated carbons: In the first, EB was carbonized at 700 c (EBC) and the resulting char was impregnated with an aqueous solution of H3PO4, using two different H3PO4 : char weight ratios (1:1 or 1:2). After impregnation and drying, the materials were heat-treated in a horizontal tube furnace under N2 flow, with residence time of 1 h at temperatures ranging from 400 to 700 C. In the second route, the impregnation with H3PO4 was carried out directly with the raw EB, again using H3PO4 :EB weight ratios of 1:1 or 1:2. The activation heat treatments were conducted in a similar way to the described for the samples of the first route. The produced materials were characterized by X-ray diffraction, textural analysis and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy. The results showed the formation of the compound SiP2O7 in large amount in the samples prepared from the EBC, which is a consequence of the natural occurrence of silicon-containing species in EB [3]. The activated carbon prepared from the EB char at 400 C exhibited a SSA (2 m2/g) much smaller than the one obtained for the nonactivated char (347 m2/g). In contrast, the samples prepared by the second route (i.e., directly from the raw EB) exhibited much higher SSA (1909 m2/g). The solid-state 31P NMR spectra showed also that phosphorus-containing groups remained in the structure of the activated carbons, mainly as phosphate groups. These results illustrate how the details of the procedures employed in the synthesis of activated carbons can strongly affect their chemical and textural properties.Samples preparation: Chemical treatment with H3PO4, using different weight ratios and various heat-treatment temperatures (HTTs); details in the diagram.

Characterization:31P Solid State NMR: spectra recorded at room temperature on a Varian / Agilent VNMR 400 spectrometer at 161.8MHz (9.4T), with single pulse excitation (SPE), MAS (13 kHz), 5s recycle delay, chemical shifts externally referred to na aqueous solution of 85% H3PO4, using ammonium dihydrogen phosphate as a secondary reference. X-Ray diffraction: XRD patterns recorded at room temperature using a Shimadzu XRD-6000 powder diffractometer, with Cu-Ka radiation ( = 1.5418 ) and the diffraction angle (2) varying from 10 to 90 in steps of 0.05. Textural analysis : The porous structure of the samples was investigated by recording N2 adsorption/desorption isotherms at 77K, using a Quantachrome Autosorb-1 instrument. The specific surface area values were determined by the Brunauer, Emmett and Teller (BET) method and the pore size distributions were computed using the non-linear density functional theory (NLDFT) approach.

[1] S. M. Manocha, Porous carbons, Sadhana. 28 (2003) 335348.[2] T. J. Bandosz, Activated Carbon Surfaces in Environmental Remediation, Elsevier, Amsterdam, 2006.[3] J. C. C. Freitas, F. G. Emmerich, T. J. Bonagamba, High-resolution solid-state NMR study of the occurrence and thermal transformations of silicon-containing species in biomassmaterials, Chem. Mater. 12 (2000) 711-718.The results of this work showed that the sample EBC_P for weight ratios 1:1 and 1:2 have relatively low specific surface area (between 2 and 5 m2 / g) compared with the surface area of the EBC (347 m2 / g). One of the possible reasons for the low surface area is the presence of the compound SiP2O7.In the case of EB_P for weight ratios 1:1 and 1:2 have there was a considerable increase in surface area (between 1300 and 1900 m2 / g).Figure 1. X-ray diffractograms recorded for EB_P and EBC_P for the same ratio and the same temperatures.Figure 2. Surface areas due to the activation temperature of the EB_P in the ratios by weight of 1:1 to 1:2.