C.J. Durán-Valle

FT-IR STUDY OF ROCKROSE AND OF CHAR AND ACTIVATED CARBON

Fourier transform-infrared spectroscopy was used in the study of rockrose (Cistus ladaniferus, L.) and of rockrose chars and activated carbons. Chars were prepared by heating the starting material between 200 and 1000 °C in nitrogen. Also, a sample was obtained at 600 °C in the atmosphere of the products of the thermal decomposition of rockrose. This charred product was used in the preparation of activated carbons. It was heated at 800 °C in air, CO2 or steam to 40% burn-off. The presence of oxygen groups and of olefinic and aromatic structures was detected in rockrose. The heat treatment of rockrose in the range 300–500 °C produced the most significant changes in the chemical structure of the material. Olefinic CC bonds and ether structures increased first in the chars and then the aromatic structure developed. Above 500 °C, the oxygen groups decreased with the temperature increase. The charring method of rockrose also influenced markedly the chemical structure of the chars. The use of a greater mass of sample slowed down the pyrolysis of rockrose. The activated carbons possessed aromatic CC bonds and oxygen groups.

Formation of oxygen structures by air activation. A study by FT-IR spectroscopy

Abstract Using cherry stones (CS) as starting material and commonly air as activating agent, formation of oxygen structures in activated carbon is investigated. In the preparation of samples, CS was first heated at temperatures between 450 and 900°C in N2 atmosphere. Then, in a successive activation stage, the product carbonized at 600°C was maintained in contact with an air stream at 25–325°C for 24 h, 300–600°C for 1 h, and 250°C for 1–96 h. The rest of the carbonization products of CS were also heated at 250°C in air for 24 h. Moreover, the product carbonized at 900°C was activated at 750 or 900°C in CO2 for 1 h. Furthermore, in a second activation stage, the products activated at such temperatures in CO2 and those at 300–600°C in air were heated at 250°C in air for 24 h. The starting material, carbonized products, and activated carbons were examined by FT-IR spectroscopy. A number of carbon–hydrogen atomic groupings and of oxygen groups and structures, i.e., OH, CO, and C–O–C) have been identified in CS. The yield of the activation and carbonization processes and also the chemical structure of the resultant products are strongly dependent on the carbonization temperature. In the products carbonized at 600–900°C, only ether type structures are detected. The activation at 250°C in air results in activated carbons that contain different oxygen structures when CS is carbonized at 450 or 600°C. At 750 or 900, by contrast, oxygen structures are not formed as a result of the activation treatment. This also applies when the carbonization product of CS at 900°C is activated solely in CO2 or first in CO2 and then in air. The heating conditions in air greatly influence the formation of oxygen structures (specifically, of lactonic and ion-radical types) to a large extent. It only occurs when activating at relatively low temperatures for a long time; at 300–600°C for 1 h, however, the oxygen structures are not formed.

Synergic adsorption in the simultaneous removal of acid blue 25 and heavy metals from water using a Ca(PO3)2-modified carbon

We report the simultaneous adsorption of acid blue 25 dye (AB25) and heavy metals (Zn(2+), Ni(2+) and Cd(2+)) on a low-cost activated carbon, whose adsorption properties have been improved via a surface chemistry modification using a calcium solution extracted from egg shell wastes. Specifically, we have studied the removal performance of this adsorbent using the binary aqueous systems: AB25-Cd(2+), AB25-Ni(2+) and AB25-Zn(2+). Multi-component kinetic and equilibrium experiments have been performed and used to identify and characterize the synergic adsorption in the simultaneous removal of these pollutants. Our results show that the presence of AB25 significantly favors the removal of heavy metals and may increase the adsorption capacities up to six times with respect to the results obtained using the mono-cationic metallic systems, while the adsorption capacities of AB25 are not affected by the presence of metallic ions. It appears that this anionic dye favors the electrostatic interactions with heavy metals or may create new specific sites for adsorption process. In particular, heavy metals may interact with the -SO(3)(-) group of AB25 and to the hydroxyl and phosphoric groups of this adsorbent. A response surface methodology model has been successfully used for fitting multi-component adsorption data.

Pore structure of activated carbons prepared by carbon dioxide and steam activation at different temperatures from extracted rockrose

The influence of the activation temperature on the pore structure of granular activated carbons prepared from rockrose (Cistus ladaniferus L.), extracted previously into petroleum ether, is comparatively studied. The preparation was carried out by pyrolysis of a char in nitrogen and its subsequent activation by carbon dioxide and steam (flow of water controlled to generate the same mol number per minute of water as well as carbon dioxide/nitrogen) at 700–950°C to 40% burn-off. The techniques applied to study the pore structure were: pycnometry (mercury, helium), adsorption (carbon dioxide, 298 K; nitrogen, 77 K), mercury porosimetry and scanning electron microscopy. The preparation by steam activation, especially at 700°C, yields activated carbons showing a total pore volume larger than those prepared by carbon dioxide activation. The pore structures present the greatest differences when the activations are carried out between 700 and 850°C and closer at higher temperatures. At high temperatures, the decrease of differences in pore development caused by carbon dioxide or steam is attributed to an external burn-off. The micropore structure of each activated carbon is mainly formed by wide micropores. At the lowest activation temperatures, especially at 700°C, steam develops the mesoporosity much more than carbon dioxide. At 950°C, a similar reduction of pore volume in the macropore range occurs.

Heat treatment of rockrose char in air. Effect on surface chemistry and porous texture

The surface chemistry and the porous texture of activated carbons prepared from a charred product (Cjex-600), which was obtained from rockrose (Cistus ladaniferus, L.) extracted previously into petroleum ether, were studied. Activated carbons were prepared by heating Cjex-600 between 350 and 850 °C in air to 40% burnoff. Methods of chemical analysis and FTIR spectroscopy as well as techniques of gas adsorption (N2, 77 K; CO2, 298 K), mercury porosimetry, and density measurements were applied. In the FTIR study of the samples, the presence of surface olefinic CC double bonds, aromatic rings, and oxygen functional groups was detected. Carbonyl groups were only found to a significant extent in Cjex-600 and in the activated carbon prepared at 350 °C. The microporosity developed with increasing temperature between 350 and 750 °C. At higher temperatures, pore narrowings occurred. The gasifying action of air was strongly dependent on the removal of nonorganized matter from Cjex-600 and on the pore size. The reaction time needed at 850 °C in air to reach burnoff 40% was less than a half of that at 350 °C, and was comparable to the times required in CO2 and steam under the same experimental conditions.

Organic chemical structure and structural shrinkage of chars prepared from rockrose

Abstract Chars were prepared by heating rockrose ( Cistus ladaniferus L) under dynamic and isothermal conditions between 200 and 1000°C in nitrogen. Several techniques including chemical analysis, Fourier transform infrared (FTIR) spectroscopy, molecular simulation, density measurements, mercury porosimetry and adsorption were used to study the chemical structure and pore structure. The chars prepared at high temperatures in particular contain oxygen in ether type structures, which may cross-link aromatic sheets. The degree of development of porosity in the chars and the porosity distribution seem to depend on the amount of volatile matter removed at each temperature during pyrolysis and on the structural shrinkage of the residual carbon. Both factors act contrarily on the pore structure of the chars, the latter effect being stronger at high temperatures. The shrinkage of the carbon structure may be caused by break down of interlayer carbon–oxygen bonds.

Chemical study of extracted rockrose and of chars and activated carbons prepared at different temperatures

Abstract This paper discusses the chemical composition and chemical structure of rockrose ( Cistus ladaniferus L.) extracted into petroleum ether and resulting chars as well as activated carbons. The isothermal temperature of carbonization of extracted rockrose (Jex) in N 2 ranged between 600 and 1000°C. The char (C Jex -600) employed in the preparation of activated carbons was prepared by treatment of Jex at 30–600°C. This char was heated in N 2 before activation, which was carried out in CO 2 or steam at 700–950°C to 40% burn-off. Chemical analyses, Fourier transform infrared spectroscopy, thermogravimetry and X-ray diffraction techniques have been applied. The extraction does not exert a significant influence on the organic chemical structure of raw material. In ash prepared at 600°C from Jex (ash content 1.29%), the major elements are Ca, K, Mg and P; calcite is the main component. When this ash is heated at 950°C, lime is the main component. The chars and activated carbons contain carbon–carbon double bonds and ether structures; C Jex -600 also contains carbonyl groups. The ether groups decrease with the temperature increase. The analyses of chars and activated carbons show an ash content close to 6–8%, and calcite as the main component. The presence of whewellite, CaC 2 O 4 ·H 2 O, indicates that the pyrolysis is delayed in the preparation of C Jex -600, that a partial calcium-carboxylate association occurs, and that hydration takes place during storage period. The mineral matter of the activated carbons prepared at 700°C depends on the activating agent: calcite is the only component identified using CO 2 , whereas lime, portlandite and vaterite are also identified using steam. At higher temperatures, the mineral matter is practically independent of the activating agent. Probably, CaO transforms into Ca(OH) 2 and CaCO 3 during the char and activated carbon storage periods.

Pore structure of chars and activated carbons prepared using carbon dioxide at different temperatures from extracted rockrose

Abstract This paper discusses the pore structure of chars and activated carbons prepared at different temperatures from rockrose ( Cistus ladaniferus L.), extracted previously into petroleum ether. The isothermal temperature of carbonization in nitrogen ranged from 600 to 1000°C. The starting char for activated carbons was prepared by treating a larger amount of precursor in the atmosphere formed as temperature increased from 30–600°C, at 10°C min −1 , being the total heating time 120 min. This char was heated in nitrogen before activation, which was carried out using carbon dioxide at 700–950°C to 40% burn-off. Pycnometry (Hg, He), adsorption (N 2 , 77 K), mercury porosimetry and scanning electron microscopy techniques have been applied to the characterization. In the chars prepared in nitrogen, a shrinkage of the carbon structure is responsible for the pore narrowing in all the pore ranges, including a micropore closing above 800°C, which is attributed to the disappearance of ether groups. This shrinkage is less important in comparison with that occuring in chars prepared from rockrose without extraction. The starting char of the activated carbons presents a rudimentary pore structure due to the different conditions of its preparation. In the activated carbons, the pore volumes (micro, meso and macro) increase up to 750°C. At higher temperatures, the mesopore volume increases, whereas the micro- and macropore volumes decrease. These structural changes are discussed considering the starting char as a Ca-supported catalyst. A shrinkage of the carbon structure also occurs at high temperatures, without causing micropore closing.

Adsorption of Aqueous Mercury(II) Species by Commercial Activated Carbon Fibres with and without Surface Modification

The adsorption of HgCl2, [HgCl4]2– and Hg2+ onto a series of activated carbon fibres was studied. These included the as-received commercial activated carbon fibre (K), that obtained after modification via by sulphuric acid oxidation (KAC) and that obtained after modification by reaction with pentaethylenehexamine (KBAS). The effects of concentration (10–1500 mg/l), solution pH (1–10) and temperature (25°C, 35°C and 45°C) were studied. The mercury(II) adsorption isotherms followed the Langmuir model with maximum adsorption capacities of 361.0, 142.2 and 300.3 mg/g for HgCl2, [HgCl4]2– and Hg2+, respectively. Fibre K proved to have the highest adsorption capacity towards HgCl2 but the best results for the adsorption of [HgCl4]2– and Hg2+ were obtained with the fibre KAC. The performance of fibre KBAS was always worse than those of the other two fibres tested. The negative values obtained for ΔH0 and ΔG0 indicate that the adsorption was an exothermic and spontaneous process and also demonstrated that the adsorption of Hg(II) is a feasible process.

Enhanced catalytic properties of carbons supported zirconia (Zr) and sulfated zirconia (SZr) in the green synthesis of benzodiazepines

This work reports for the first time a new series of promising porous catalytic carbon materials, functionalized with Lewis and Brønsted acid sites useful in the green synthesis of 2,3‐dihydro‐1H‐1,5‐benzodiazepine – nitrogen heterocyclic compounds. Benzodiazepines and derivatives are fine chemicals exhibiting interesting therapeutic properties. Carbon materials have been barely investigated in the synthesis of this type of compounds. Two commercial carbon materials were selected exhibiting different textural properties: i) Norit RX3 (N) as microporous sample and ii) mesoporous xerogel (X), both used as supports of ZrO2 (Zr) and ZrO2/SO42− (SZr). The supported SZr led to higher conversion values and selectivities to the target benzodiazepine. Both chemical and textural properties influenced significantly the catalytic performance. Particularly relevant are the results concerning the non‐sulfated samples, NZr and XZr, that were able to catalyze the reaction leading to the target benzodiazepine with high selectivity (up to 80 %; 2 h). These results indicated an important role of the carbon own surface functional groups, avoiding the use of H2SO4. Even very low amounts of SZr supported on carbon reveal high activity and selectivity. Therefore, the carbon materials herein reported can be considered an efficient and sustainable alternative bifunctional catalysts for the benzodiazepine synthesis.