The effect of surface chemistry (nature and amount of oxygen groups) in the removal of ammonia was studied using a modified resin-based activated carbon. NH 3 breakthrough column experiments show that the modification of the original activated carbon with nitric acid, i.e. the incorporation of oxygen surface groups, highly improves the adsorption behaviour at room temperature. Apparently, there is a linear relationship between the total adsorption capacity and the amount of the more acidic and less stable oxygen surface groups. Similar experiments using moist air clearly show that the effect of humidity highly depends on the surface chemistry of the carbon used. Moisture highly improves the adsorption behaviour for samples with a low concentration of oxygen functionalities, probably due to the preferential adsorption of ammonia via dissolution into water. On the contrary, moisture exhibits a small effect on samples with a rich surface chemistry due to the preferential adsorption pathway via Brønsted and Lewis acid centers from the carbon surface. FTIR analyses of the exhausted oxidized samples confirm both the formation of NH 4 + species interacting with the Brønsted acid sites, together with the presence of NH 3 species coordinated, through the lone pair electron, to Lewis acid sites on the graphene layers.

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Sulfonated carbons were prepared from carbonized rice husk and further treatment with sulfuric acid (TC-6M, sulfuric acid 6 mol L–1 under reflux, TC-L, concentrated 96% sulfuric acid under reflux, TC-V, vapor of concentrated 96% sulfuric acid). The catalytic activity of carbons was evaluated in esterification of glycerol with acetic acid (AA) and etherification of glycerol with tert-butyl alcohol (TBA). Only the TC-L carbon showed a significant amount of sulfur in its composition (2.2 mmol g–1). This catalyst also had the highest total acidity (5.8 mmol g–1) and improved the best catalytic performance in glycerol esterification and etherification. In the esterification reaction of glycerol, 90% conversion was observed after 5 h of reaction, with selectivities of 11%, 52%, and 37% to mono-, di-, and tri-glycerides, respectively. In the etherification of glycerol, after 4 h of reaction a conversion of 53% was achieved, with 25% selectivity to di- and tri-tert-butylglycerol. Thus, the use of sulfonated carbons in glycerol conversion proved to be an interesting alternative to add value to the production chains of rice and biodiesel by using their byproducts: rice husk and glycerol.

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Sulfonated carbon-based catalysts were prepared from agroindustrial wastes (sugar cane bagasse, coconut husk, and coffee grounds). These catalysts showed high activity for glycerol etherification with tert-butyl alcohol. Yields of mono-tertbutyl glycerol (MTBG), di-tert-butyl glycerol (DTBG), and tri-tert-butyl-glycerol (TTBG) were higher than that obtained using Amberlyst-15 commercial resin. At 393 K and 5 wt % catalyst loading, glycerol conversion and selectivity to DTBG+TTBG after 4 h reaction time were 80.9% and 21.3%, respectively, with the sugar cane bagasse-based catalyst. Both catalytic activity and selectivity were affected by the presence of water in the reaction medium. However, the flexible and hydrophilic structure of the oxidized carbon allows the adsorption of water without compromising the activity of acid sites.

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The piassava fiber, residue of the broom industry, was used as precursor for the preparation of activated carbons (AC). AC were prepared by chemical activation with zinc chloride (AC ZnCl(2)) or phosphoric acid (AC H(3)PO(4)) and by physical activation with carbon dioxide (AC CO(2)) or water vapor (AC H(2)O). These materials were characterized by adsorption/desorption of N(2) to determine the BET areas, elemental analysis (CHN), thermogravimetric analysis (TG, DTA) and scanning electron microscopy (SEM). The carbons were tested with respect to their adsorption capacity of methylene blue, reactive red, phenol and metallic ions (Cr(+6), Cu(+2) and Zn(+2)). AC ZnCl(2) presented the highest surface area (1190 m(2)g(-1)) and AC H(3)PO(4), the largest pore volume (0.543 cm(3)g(-1)). AC ZnCl(2) was more efficient in the adsorption of methylene blue, Cr(+6) and Cu(+2) ions. AC H(2)O was the better adsorbent for phenol, while AC CO(2) was better for Zn(+2) ions.