Adsorption of cationic dye on nanostructured biocarbons: kinetic and thermodynamic study

Abstract

Nanostructured bio-adsorbents were prepared by physical or chemical activation of the residue of supercritical extraction of raspberry seed. Their physicochemical properties were determined by elemental analysis, low-temperature nitrogen adsorption/desorption, Boehm titration and scanning electron microscopy. The biocarbon obtained as a result of physical activation of the precursor showed basic character of the surface and its SBET was 700 m2/g. The chemical activation of the residue of supercritical extraction of raspberry seed with potassium carbonate favored generation of acidic functional groups and SBET of this biocarbon was 1177 m2/g. The nanostructured biocarbons were used for removal of Rhodamine B from its aqueous solutions. The process was best described by the Langmuir isotherm and the maximum capacity of the monolayer was 181.82 mg/g and 277.83 mg/g for the physically and chemically activated samples, respectively. The adsorption energy obtained from the Dubinin–Radushkevich isotherm indicated that the process observed was physisorption, while the kinetics of the process was best described by the pseudo-second-order model. The negative values of Gibbs free energy indicated the spontaneous character of the process. For the chemically activated sample, the highest sorption capacities toward Rhodamine B were obtained in an acidic environment, while for the physically activated sample—in a basic environment. The yield of desorption decreased for the media: distilled water > hydrochloric acid > acetic acid, which means that Rhodamine B molecules were weakly bound to the biocarbon surface.

Methyl Red Adsorption on Biochar Obtained by Physical Activation of Caraway Seeds with Carbon Dioxide

“…This may be explained by the presence of stronger centrifugal forces at 400 rpm/min, leading to repulsive forces between the dye molecules. When the repulsive forces exceed the binding force of the adsorbent, desorption of the dye begins [21,22] . The data presented suggests that optimum results for dye removal are achieved at a mixing speed of 300 rpm/min.…”

“…When the repulsive forces exceed the binding force of the adsorbent, desorption of the dye begins. [21,22] The data presented suggests that optimum results for dye removal are achieved at a mixing speed of 300 rpm/min. To optimise the results, a mixing speed of 300 rpm/min was selected for further investigation.…”

Adsorption of Methyl Red and Methylene Blue on Carbon Bioadsorbents Obtained from Biogas Plant Waste Materials

“…Positive entropy values indicate increased randomness at the interface between the biochar and the solution of methylene blue/methyl red, which increases the effectiveness of removing the studied pollutants. The higher the value of ∆S 0 , the more efficient the process occurs [ 33 ]. Therefore, considering the results presented in Table 6 , it can be concluded that the most efficient adsorption process occurs for methylene blue and the PA7 sample.…”

“…Moreover, there is a possibility of π–π interactions occurring between the dye samples and aromatic rings. Comparable interactions have been documented and discussed in existing literature [ 33 ].…”

“…Moreover, there is a possibility of π-π interactions occurring between the dye samples and aromatic rings. Comparable interactions have been documented and discussed in existing literature [33]. Regeneration is a crucial factor in determining the lifespan of adsorbents, indicating the maximum number of times they can be used in an adsorption process without losing their initial adsorption capacity.…”