RESUMO
Mercury and its compounds are toxic substances, whose uncontrolled presence in the environment represents a danger to ecosystems and the organisms that inhabit in it. For this reason, in this work, we carried out a study of mercury [Hg(II)] adsorption from aqueous solution on functionalized activated carbon. The activated carbons were prepared by chemical activation of a mango seed with solutions of CaCl2 and H2SO4 at different concentrations, later, the carbonaceous materials were functionalized with Na2S, with the aim of increasing the sulfur content in the carbonaceous matrix and its affinity to mercury. The materials were characterized using: proximal analysis, scanning electron microscopy, Boehm titrations, point zero charge (pHPZC), and infrared spectroscopy. Additionally, immersion calorimetries were performed in the mercury solution. The results of textural and chemical characterization show materials with low Brunauer-Emmett-Teller (BET) surface areas between 2 and 33 m2·g-1 and low pore volumes. However, they had a rich surface chemistry of oxygenated groups. The enthalpies of immersion in the mercury solutions are between -31.71 and -77.31 J·g-1, showing a correlation between the magnitude of the enthalpic data and the adsorption capacity of the materials. It was evidenced that the functionalization process produces a decrease in the surface area and pore volume of the activated carbons, and an increase in the sulfur content of the carbonaceous matrix. It was evidenced that the functionalization process generated an increase in the mercury [Hg(II)] adsorption capacity between 21 and 49% compared to those of the nonfunctionalized materials, reaching a maximum adsorption capacity of 85.6 mgHg2+g-1.
RESUMO
The aim of this research is to prepare various carbonaceous materials with different textural, structural and chemical characteristics, using mango seed a rarely used residue for the preparation of activated carbons, as the precursor material. The mango seed was analyzed by TGA and SEM also methodological data about the preparation of activated carbons are provided. Four activated carbons were prepared using sulfuric acid (H2SO4) and calcium chloride (CaCl2) as activating agents and were characterized by means of TGA, SEM/EDX, Boehm Titration, isotherm determination of N2 adsorption-desorption at -196 °C and immersion calorimetry. Four carbons were obtained with superficial areas BET between 6 and 33 m2 g-1 and different chemical characteristics associated with the changes in the concentration of the activating agents. The activated carbons that were prepared with the highest activating agent concentrations, obtained better results in the amount of oxygenated surface groups, the total acidity and the amount of fixed carbon. The enthalpy of immersion in water was between 7 and 16 J g-1.