Boyko Tsyntsarski

Adsorption of naphthalene from aqueous solution on activated carbons obtained from bean pods

The preparation of activated carbons from bean pods waste by chemical (K(2)CO(3)) and physical (water vapor) activation was investigated. The carbon prepared by chemical activation presented a more developed porous structure (surface area 1580 m(2) g(-1) and pore volume 0.809 cm(3) g(-1)) than the one obtained by water vapor activation (258 m(2) g(-1) and 0.206 cm(3) g(-1)). These carbons were explored as adsorbents for the adsorption of naphthalene from water solutions at low concentration and room temperature and their properties are compared with those of commercial activated carbons. Naphthalene adsorption on the carbons obtained from agricultural waste was stronger than that of carbon adsorbents reported in the literature. This seems to be due to the presence of large amounts of basic groups on the bean-pod-based carbons. The adsorption capacity evaluated from Freundlich equation was found to depend on both the textural and chemical properties of the carbons. Naphthalene uptake on biomass-derived carbons was 300 and 85 mg g(-1) for the carbon prepared by chemical and physical activation, respectively. Moreover, when the uptake is normalized per unit area of adsorbent, the least porous carbon displays enhanced naphthalene removal. The results suggest an important role of the carbon composition including mineral matter in naphthalene retention. This issue remains under investigation.

Improved phenol adsorption on carbons after mild temperature steam reactivation

The purpose of this work is to explore steam reactivation at moderate temperatures of activated carbon exhausted with phenol, a highly toxic compound frequently present in industrial wastewater. The spent carbon was treated with steam at various temperatures (450, 600 and 850 degrees C) and times (from 5 to 60 min). Promising results were obtained by applying moderate temperatures and times. Whereas at low temperatures the complete regeneration of the carbon is not accomplished, an almost quantitative desorption of the pollutant was achieved at 600 degrees C after exposure times below 30 min, with minimal damages in the porous network of the carbon. Further reutilization of the regenerated carbon resulted in a superior performance towards phenol uptake. The regeneration efficiency at 850 degrees C strongly depends on the time of reactivation, with an enhanced phenol uptake when short treatment times are applied. Prolonged duration of the regeneration treatment reduced phenol adsorption capacities, due to overreactivation of the carbon in the steam atmosphere, and to the blockage of the porous carbon network.

Activated carbon from waste biomass as catalyst support: formation of active phase in copper and cobalt catalysts for methanol decomposition

Activated carbons (AC) from various waste agriculture precursors with different texture and surface characteristics were obtained by different preparation procedures. These AC were used as a host matrix of mono- and bi-component copper and cobalt nanoparticles. The effect of carbon properties on the formation of copper/cobalt phases was studied by Boehm method, XRD, nitrogen physisorption, UV–Vis, FTIR, TPR–TG analysis and methanol decomposition as a catalytic test. The elucidation of activated carbons from waste biomass as catalyst support was based on the comparative study with similar materials supported on mesoporous silica KIT-6. It was demonstrated that contrary to KIT-6, the reduction properties of AC support hinders the formation of spinel CuCo2O4 phase in the bi-component materials, but provides formation of mixture of finely dispersed and highly active and selective in methanol decomposition Cu2O and CoO nanoparticles.

Cobalt and iron modified activated carbon from coal tar pitch: preparation and application as catalysts for methanol decomposition

Activated carbons were prepared from waste coal treatment by-products by different preparation and activation procedures and applied as a host matrix of nanodispersed cobalt and iron species. Thus obtained composites were characterized by nitrogen physisorption, XRD, UV–Vis, FTIR, TPR and tested as catalysts in methanol decomposition to hydrogen and CO. It was established that the activated carbon, prepared from waste coal treatment by-products could be successfully used for the preparation of highly active catalysts for methanol decomposition. The facilitated effect of surface functionality decrease on the dispersion and catalytic activity of loaded metal species was demonstrated.

Removal of detergents from water by adsorption on activated carbons obtained from various precursors

AbstractThe adsorption of detergents—sulfonic and phenolic compounds—from aqueous solutions by activated carbons (AC), obtained on the base of different precursors, was studied. The carbon adsorbents used were prepared by water vapor pyrolysis of different raw materials: peach stones, olive stones, natural asphaltite, mixtures from coal tar pitch, and furfural. It was established that all the samples of ACs have close values of high adsorption capacities toward the studied detergents. Some factors affecting the adsorption process—the time of treatment and the amount of the adsorbent—were investigated. It was established that the amount of adsorbent has no significant influence on the adsorption process.

Microstructural investigations of carbon foams derived from modified coal-tar pitch

This work reports the microstructural evaluation of carbon foams derived from coal-tar pitch precursors treated with H2SO4 and HNO3 and finally annealed at 1000°C and 2000°C. Our experimental investigations combine scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and micro-spot near-edge X-ray absorption fine structure (μ-NEXAFS) spectroscopy. This set of complementary techniques provides detailed structural and chemical information of the surface and the bulk of the carbon foams. The high-resolution microscopy data indicate the formation of carbonaceous amorphous microspheres (average diameters of 0.28±0.01μm) embedded in the partially graphitized carbon foam matrix at 1000°C. The microspheres are enriched with sp-bonded species and their microstructural characteristics depend on the reagent (nitric vs. sulfuric acid) used for pitch treatment. A complete chemical transformation of the microspheres at temperatures >1000°C occurs and at 2000°C they are spectroscopically identical with the bulk material (sp(2)- and sp(3)-hybridised forms of carbon). The microstructure-property relationship is exemplified by the compressive strength measurements. These results allow a better description of coal-tar pitch-derived carbon foams at the atomic level, and may account for a better understanding of the processes during graphitization step.

Thermochemical Conversion of Bean Pods to Carbon Materials and Gas

The preparation of activated carbons from bean pods by chemical (K 2 C0 3 ) and physical (water vapor) activation was investigated. The carbon prepared by chemical activation presented more developed porous structure than one obtained by water vapor activation. Carbon adsorbent with very low ash content and developed micropore structure is obtained by thermochemical treatment with conc .H 2 S0 4 of liquid products from carbonization of bean pods and activation with water vapour. K e y w o r d s : bean pods, K 2 C 0 3 activation, water vapor activation