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  • Valorization of coffee husk into carbonaceous materials for adsorption of nitrophenols
    Publication . Guides, George Leme; Gomes, Helder; Marin, Pricila; Díaz de Tuesta, Jose Luis
    With the exponential increase of the world population over the years, the organic waste generated from coffee also increased, since it is one of the most consumed commodities of world. Nowadays, many research studies aim to reduce or avoid environmental impacts. One way is the valorization of solid waste into high-added value products, as is the case of the preparation of activated carbons from raw biomass. Due to their well-developed porosity, activated carbons can be used to remove pollutants contained in wastewater effluents through adsorption processes. The main objective of this work is the development of activated carbons from coffee husks, considering HNO3 and KOH as activation agents, and their assessment in the removal of 2-nitrophenol and 4-nitrophenol, selected as target pollutants. The activating agents were used at different concentrations (1 and 5 mol L-1) and the precursor was activated for 3 hours at 60 °C. Then, the resultant materials were carbonized by pyrolysis at 800 °C under continuous flow of N2. The activated carbons were used to adsorb 2-nitrophenol and 4-nitrophenol at 25 °C and pH 6.0. Upon analysis of the adsorption isotherms obtained, it was possible to conclude that the activated carbon that leads to a high percentage of pollutant removal was the one activated with KOH 5 mol L-1, considering an initial concentration of 25 mg L-1 of 2-nitrophenol and 50 mg L-1 of 4-nitrophenol with a concentration of adsorbent of 2.5 gads L-1. This activated carbon, prepared with a low burn-off, had 92.9% (9.7 mg2-NP gads-1) of removal of 2-nitrophenol and 97.7% (22.5 mg4-NP gads-1) of removal of 4-nitrophenol. It had 84.1% of burn-off in its development process. Due to the superior results of this material, the kinetic analysis was done using only the activated carbon activated with KOH 5 mol L-1. The kinetic results show that the material reached its maximum adsorption after 4 h adsorbing around 85% of both pollutants. The modelling of the kinetic results was also done. The best model to predict in a representative way the adsorption isotherm was the Freundlich model for both pollutants. For the adsorption kinetic model, the best fittings were obtained with the Bangham model for 2-nitrophenol adsorption and with the pseudo-second-order model for 4-nitrophenol adsorption.
    2021Dissertação de mestrado Acesso restrito Ver mais