Activation of Waste Materials with Carbon(IV) Oxide as an Effective Method of Obtaining Biochars of Attractive Sorption Properties towards Liquid and Gas Pollutants

Microwave Heating for Synthesis of Carbonaceous Adsorbents for Removal of Toxic Organic and Inorganic Contaminants

The residues obtained from the extraction of Inonotus obliquus fungus were used to produce carbonaceous adsorbents. The initial material was subjected to pyrolysis in a microwave oven. The adsorbents were characterized through elemental analysis, low-temperature nitrogen adsorption/desorption isotherms, and Boehm titration. The carbonaceous adsorbents were tested for the removal of NO2, methylene blue, and malachite green. The results indicated that the obtained carbonaceous adsorbents exhibited basic characteristics and possessed specific surface areas of 372 and 502 m2/g. The adsorption process of liquid contaminants was modeled using the single-layer Langmuir model. The maximum adsorption capacities were found to be 101 and 109 mg/g for methylene blue, and 75 and 77 mg/g for malachite green. The kinetic study demonstrated that the adsorption of methylene blue and malachite green was better described by a pseudo-second order model. The study affirmed that the adsorption of organic dyes onto the resultant carbonaceous adsorbents was both spontaneous and endothermic. The study also demonstrated that the presence of an air stream during the NO2 adsorption process and prehumidization of the adsorbent with humid air had a beneficial effect on the obtained sorption capacities. In conclusion, the study demonstrated that pyrolysis of the extraction residues from the fungus Inonotus obliquus yields highly effective, environmentally friendly, and cost-efficient carbonaceous adsorbents for the removal of both gaseous and liquid pollutants.

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

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.