In the present work, we reported on the efficiency of the removal of organic dyes by adsorption on activated carbons prepared from the residue of supercritical extraction of marigold. The performance of adsorbents prepared was tested towards methyl red, methylene blue, malachite green, and crystal violet at room temperature. The effects of carbonization (500 and 700 °C) and activation (700 and 800 °C) temperatures, textural parameters, and acid-base character of the adsorbent surface on the sorption properties of the activated carbons were established. Activated carbons are characterized by low developed specific surface area, from 2 to 206 m2/g, and have a basic character of the surface (pH of carbons water extracts ranging from 10.4 to 11.2). Equilibrium adsorption isotherms were investigated. The equilibrium data were analyzed in the Langmuir, Freundlich, and Temkin models. The adsorption capacities of activated carbons studied varied from 47.62 to 102.43 mg/g towards methyl red, 53.14 to 139.72 mg/g towards methyl red, 425.46 to 622.80 towards malachite green and 155.91 to 293.75 mg/g towards crystal violet, from their water solutions. Kinetics of the adsorption of the organic dyes studied were found to be described by the pseudo-second-order model. It was proven that through the physical activation of the residue of supercritical extraction of marigold, it is possible to obtain carbonaceous materials of very high adsorption capacity towards organic pollutants.

The aim of this study was to prepare biocarbons by biomass activation with carbon(IV) oxide. Fennel and caraway fruits were used as the precursors of bioadsorbents. The impact of the precursor type and temperature of activation on the physicochemical properties of the obtained biocarbons and their interaction with methyl red sodium salt upon adsorption process have been checked. The obtained bioadsorbents were characterized by determination of-low temperature nitrogen adsorption/desorption, elemental analysis, ash content, Boehm titration, and pH of water extracts. The biocarbons have surface area varying from 233–371 m2/g and basic in nature with acidic/basic oxygen-containing functional groups (3.23–5.08 mmol/g). The adsorption capacity varied from 63 to 141 mg/g. The influence of different parameters, such as the effectiveness of methyl red sodium salt adsorption, was evaluated. The adsorption kinetics was well fitted using a pseudo-second-order model. The Freundlich model best represented the equilibrium data. The amount of adsorbed dye was also found to increase with the increasing temperature of the process.

In this study, fennel (Foeniculum vulgare) seeds were used as a precursor for obtaining nanostructured activated carbons by chemical activation with various reagents. The obtained activated carbons were characterized using nitrogen adsorption–desorption isotherms, ash content, Boehm titration and pH of water extracts. It was shown that the choice of activator had an important effect on the physicochemical and sorption properties of the obtained activated carbons. The specific surface area of the obtained adsorbents ranged from 345 to 1052 m2/g. Chemical activation of the starting material with potassium carbonate made it possible to obtain activated carbons with the strongest developed specific surface area and the best sorption capacity against the tested pollutants. 1 g of this carbon is able to adsorb 1215 mg of iodine and 454 mg of methylene blue. The least effective adsorbent turned out to be the carbon obtained by chemical activation of fennel seeds with sodium carbonate, whose sorption capacity toward the pollutants from aqueous solutions was 77 mg/g and 317 mg/g for methylene blue for iodine, respectively. The alkaline pH of the solution promotes effective adsorption of methylene blue on the surface of the obtained adsorbents. The reaction of the dye molecules adsorption on the activated carbons occurs according to the pseudo-second-order model. The Langmuir isotherm best described the process under study. In addition, it was shown that chemical activation of fennel seeds leads to carbon adsorbents with acidic surface character. The negative values of Gibbs free energy indicate the spontaneous character of the process. The study has shown that fennel seeds can be successfully used to obtain low-cost and effective nanostructured carbon adsorbents with good sorption capacity toward organic and inorganic contaminants, from the aqueous phase.

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