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 °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 °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 °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.The authors thank the Bulgarian Academy of Sciences and the Division of International Affaires of CSIC for financial support (grant 2007BG0015). COA thanks the Spanish MICINN for a Ramon y Cajal research contract and the financial support (project CTM2008-01956). BC thanks CSIC for a Marina Bueno fellowship (EST001047)Peer reviewe

Synthesis of nanoporous carbons from mixtures of coal tar pitch and furfural and their application as electrode materials

Synthetic nanoporous carbons are prepared by polymerization of mixtures containing coal tar pitch and furfural in different proportions, followed by carbonization of obtained solid product and steam activation of the carbonizate. The chemical composition of the initial mixture significantly affects the physicochemical properties (surface area, pore structure, electro resistance and amount of oxygen-containing groups on the surface) of the obtained materials. The incorporation of oxygen in the precursor mixture by means of furfural, has a strong influence in the synthetic step; increasing the furfural content facilitates the formation of a solid product characterized by a large oxygen content. Moreover, the solid product is more reactive towards activation as the furfural content increases, giving rise to nanoporous carbons with large surface areas and unique chemical features (high density of oxygen functionalities of basic nature). These nanoporous carbons have been investigated as electrodes in electrochemical applications.The authors acknowledge financial support for this work from MEJS-NFSI, Bulgaria (Award 02-222/17.12.2008)Peer reviewe

Carbon foams as catalyst supports for phenol photodegradation

A carbon foam using coal tar pitch as precursor was prepared and investigated as support for titanium oxide for the photocatalytic degradation of phenol. The performance of the carbon foam/titania composite was compared to those of unsupported titania and other activated carbon composites from the literature. The photodegradation rate of phenol over the catalysts under UV illumination was fitted to the Langmuir–Hinshelwood model; data showed that the apparent rate constant of the carbon foam supported titania was almost three times larger than that of bare titania, and comparable to that of other carbon supported composites. Considering the low porous features of the carbon foam, this suggests that large surface area supports are not essential to achieve high degradation rates and efficiencies. Moreover, when titania is supported on the carbon foam large amounts of catechol are detected in solution after UV irradiation, indicating a better degradation efficiency.This work was supported by the Spanish MICINN (CTM2008-01956). LFV thanks CSIC for a predoctoral fellowship. The authors acknowledge the support of Bulgarian MEYS -contracts MU01-149-.Peer reviewe

Synthesis and electrochemical properties of the electrode materials for supercapacitors

New electrode materials for supercapacitors -activated carbons, produced by carbonization of mixtures of coal tar pitch and furfural, with a subsequent hydrothermal treatment, were characterized and tested electrochemically. The microstructure, surface morphology and porous structure of the carbon materials were studied, and the main textural parameters and micropore size distribution were determined. Symmetric sandwich-type supercapacitor cells, with identical carbon electrodes and organic electrolyte, were assembled and subjected to charge-discharge cycling study at different current rates. Four types of carbons as electrodes with different specific surface area (1000 -1600 m 2 g -1 ) and texture parameters, as well as tree types of organic electrolytes (Et 4 NBF 4 -PC, LiBF 4 -PC, LiPF 6 -DMC/EC), were tested and compared with an asymmetric supercapacitor, composed by graphitized-activated carbon (carbon foam) as a negative electrode, and activated carbon/Li 4 Ti 5 O 12 oxide composite as a positive electrode. The capacitance values of up to 75 F.g -1 were obtained for the symmetric supercapacitors, depending on the microstructure and the conductivity of the carbon material, and about two times higher capacitance was obtained for the asymmetric supercapacitor, with good cycleability of both supercapacitor systems

Synthesis of nanoporous carbon from plant wastes and coal treatment products

Synthetic nanoporous carbons are produced from mixtures containing coal tar pitch and furfural in different proportions. It was determined that the surface area and amount of oxygen containing groups on the surface significantly depend on the composition of the initial mixture. Best quality carbon with developed pore structure with prevailing content of micropores was obtained from the precursor containing 50% furfural. Various oxygen containing structures are established on the synthetic nanoporous carbon surface

Synthesis of nanoporous carbon from plant wastes and coal treatment products

Synthetic nanoporous carbons are produced from mixtures containing coal tar pitch and furfural in different proportions. It was determined that the surface area and amount of oxygen containing groups on the surface significantly depend on the composition of the initial mixture. Best quality carbon with developed pore structure with prevailing content of micropores was obtained from the precursor containing 50% furfural. Various oxygen containing structures are established on the synthetic nanoporous carbon surface

Dynamic studies on carbon dioxide capture using lignocellulosic based activated carbons

In this work, CO2 adsorption tests are carried out in a lab-scale fixed-bed reactor from a simulated flue-gas,at four temperature levels (30, 45, 60 and 80 °C) and different CO2 concentrations (3–30 %). Three different activated carbons (AC) derived by agricultural raw materials, namely peach stones, olive stones and apricot stones, were synthesized by a combination of pyrolysis and activation by water vapour. The textural characterization of the AC samples by N2 adsorption at -196 °C shows that the AC derived from apricot stones has the highest micropore volume, almost shifted toward ultramicropores, while the AC derived from olive stones shows the highest contribution of meso and macropores. Adsorption tests show that the AC derived from apricot stones has the highest CO2 adsorption capacity at 30 °C, due to its microstructural properties. Differently, at higher temperatures, the AC derived from apricot and peach show similar performances, due to their similar content of basic functional groups and pHPZC values. In all the cases, the Freundlich model provides very good data interpretation. The kinetic patterns reveal that the adsorption rate is mainly related to the mean Sauter particle diameter of the AC samples and, at less extent, to their meso and macropore content. Finally, a modelling analysis allowed individuating the intraparticle diffusion as the adsorption rate-limiting step

CO2 adsorption onto synthetic activated carbon: Kinetic, thermodynamic and regeneration studies

An activated carbon for CO2 adsorption from flue gas was synthesized using an industrial by-product (coal tar pitch) and furfural. The produced activated carbon possesses a well-developed pore structure and an alkaline character, as testified by the presence of different oxygen containing functional groups on the carbon surface. Adsorption tests have been carried out in lab-scale fixed-bed column, at different temperatures and CO2 concentrations, in order to investigate both kinetic and thermodynamic aspects. Moreover, regeneration studies have been conducted in order to verify the possibility of activated carbon reutilization, to determine its CO2 adsorption capacity within consecutive cycles of adsorption-desorption and to assess the optimal operating conditions for CO2 recovery by desorption. It was established that the synthesized activated carbon has a good CO2 adsorption capacity, likely related to its surface area and composition, as well as to the intrinsic nature of the solid. Adsorption rate increases with CO2 concentration and temperature, even if an increase in temperature significantly reduces the adsorption capacity. Experimental results confirmed that CO2 adsorption is a reversible process and that desorption temperature is the main controlling parameter. It was demonstrated that the regenerated carbon can be used in consecutive adsorption-desorption cycles without any significant loss in its CO2 adsorption capacity. Finally, the most suitable operating set parameters for CO2 recovery has been defined

Activated carbons from waste biomass and low rank coals as catalyst supports for hydrogen production by methanol decomposition

Activated carbons with different textural and chemical surface characteristics were synthesized from waste biomass and low rank coals, and furthermore used as a host matrix for cobalt species, varying the preparation and modification methods. The obtained activated carbons and modified samples were characterized by complex of various physicochemical methods, such as: low temperature physisorption of nitrogen, XRD, EPR, XPS, UV–Vis and TPR with hydrogen. Boehm method was applied for qualitative and quantitative determination of oxygen-containing groups on the carbon surface before and after cobalt deposition. The catalytic properties of cobalt modifications were tested in methanol decomposition. The dominant effect of activated carbon texture over the surface chemistry on the state and catalytic behavior of cobalt species was discussed.Financial support from Bulgarian Academy of Sciences and Bulgarian Ministry of Education (Projects DFNI-Е01/7/2012 and DFNI-E02/2/2014) is gratefully acknowledged.Peer reviewe