C. Valenzuela-Calahorro

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.

Adsorption of mercury, cadmium and lead from aqueous solution on heat-treated and sulphurized activated carbon

The adsorption of mercury, cadmium and lead from aqueous solutions on heat-treated and sulphurized activated carbon has been studied comparatively. The adsorption isotherms for the various metals were measured at 298 K, using adsorptive solutions at two pH values. The adsorption was much higher for mercury than for cadmium and lead for all adsorbents. The adsorption of mercury greatly increased for the samples of sulphurized carbon and also, though less, for the sample prepared in N2. The decrease of pH in the adsorptive solution to pH 2.0 drastically reduced the adsorption of mercury. The effect of pH change on the adsorption of Cd2+ and Pb2+ occurred with less adsorbents than for mercury.

Oxidation of activated carbon by hydrogen peroxide. Study of surface functional groups by FT-i.r.

Abstract Outgassed activated carbon was oxidized using H2O2 aqueous solutions and the surface oxygen groups were identified by FT-i.r. spectroscopy. The influence of solution concentration and pH, outgassing and oxidation conditions of the carbon, and the addition of catalytic or stabilizer agents to the oxidizing solution was investigated. The stability of the surface groups was also studied for a series of samples. The surface groups initially present in the carbon were largely OH and COC. Oxidation of material with H2O2 solution, at unchanged pH, increased the OH groups present in the oxidized products. With solutions of pH 2.5 and 11.5, the OH groups decreased and various oxygen groups such as CO and C O, or CO2−, were formed. At the lowest pH value, formation of COC structures with an increased number of CO bonds occurred. Ether structures were lost when outgassing under more drastic conditions and when contact with the oxidizing solution was established at very different temperatures. The addition of Fe2+ to the oxidizing solution favoured the oxidation of carbon. However, Fe3+, ethanol and ether were not effective agents. Significant changes in the surface chemistry of samples were observed after a long period of time.

Adsorption of Pb2+ by heat-treated and sulfurized activated carbon

Abstract Using activated carbon (AC) and samples obtained by heat and sulfurizing treatments of the material, the adsorption of Pb2+ from aqueous solution was studied at two pH values and at three temperatures in the range 25–45°C. Adsorbents were prepared either by heat treatment of AC from 30 to 900°C in N2 or H2S, or by treatment of the material first at 30°C successively in SO2 and H2S and then at 200°C in N2. Their characterization was in terms of textural properties and surface chemistry. Techniques used were gas adsorption (N2, −196°C), mercury porosimetry, density measurements (He, 30°C) and FT-IR spectroscopy. The treatments effected on AC originated a great increase in the adsorption of Pb2+, but only when it occurred from solutions of metallic ion at unchanged pH and at 25°C. Adsorption decreased strongly by pH and temperature variations, except for AC. The adsorption rate depended on the adsorbent, pH and temperature.

Characterization study of char and activated carbon prepared from raw and extracted rockrose

Abstract Using raw rockrose ( Cistus Ladaniferus, L. ) and rockrose extracted into petroleum ether, the effect of extraction on the thermal behaviour and chemical-physical properties of chars and activated products was studied. Chars were prepared by heat treatment of the starting materials under dynamic and isothermal conditions over the temperature range 200–1000°C. Activations of two carbonized products, which were obtained at 600°C, was accomplished in air, CO 2 , or steam at 850°C until burnoff 40%. Techniques used were thermogravimetry, gas adsorption, mercury porosimetry, density measurements and FT-IR spectroscopy. Extraction delayed the rockrose pyrolysis, as inferred from the thermal behaviour of the starting materials and by the composition and texture of the chars prepared between 200–600°C. At higher temperatures, extraction reduced the ash content of chars and mitigated the loss produced in the surface area and the microporosity. Differences in textural properties of activated carbon depended on the starting material and the activating agent, being especially significant between air and CO 2 or steam. The FT-IR spectra of the carbonized and activated products displayed absorption bands compatible with the presence in the materials of surface olefinic CC double bonds, aromatic rings, and oxygen functional groups.

Adsorption of cadmium by sulphur dioxide treated activated carbon

Merck carbon (1.5 mm) was treated in three ways: heating from ambient temperature to 900 degrees C in SO(2); treatment at ambient temperature in SO(2); or successive treatments in SO(2) and H(2)S at ambient temperature. All samples were then characterised and tested as adsorbents of Cd(2+) from aqueous solution. The characterisation was in terms of composition by effecting ultimate and proximate analyses and also of textural properties by N(2) adsorption at -196 degrees C. Kinetics and extent of the adsorption process of Cd(2+) were studied at 25 and 45 degrees C at pH of the Cd(2+) solution (i.e., 6.2) and at 25 degrees C also at pH 2.0. The various treatments of the starting carbon had no significant effect on the kinetics of the adsorption of Cd(2+), but increased its adsorption capacity. The most effective treatment was heating to 900 degrees C, the adsorption in this case being 70.3% more than that of the starting carbon. The adsorption increased at 45 degrees C but decreased at pH 2.0 when compared to adsorption at 25 degrees C and pH 6.2, respectively.

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.

Characterization of rockrose wood, char and activated carbon

Abstract The starting rockrose ( Cistus ladaniferus L.), as well as charred and activated products prepared by heat treatment conducted under different conditions, were characterized in terms of composition, calorific value, texture and surface chemistry. Techniques used were thermogravimetric analysis, gas adsorption, mercury porosimetry, density measurements, scanning electron microscopy and FT-IR. The rockrose composition and calorific value were similar to other woods. Rockrose chars were prepared by heat treatment of the material over the temperature range 200–1000°C. The production of charcoal occurred at 400°C. Above 600dgC the microporous structure of the chars became partially closed. Activated carbons were prepared by gasification (burnoff = 40%) of a carbonized product (carbonization temperature = 600°C) in air at 600°C and in CO 2 and steam at 750°C. Significant differences in properties of the activated carbons were noted depending on the activating agent. Activated carbon produced in steam possessed better textural characteristics, in particular the development of mesoporosity was observed. The presence of surface oxygen groups containing CO bonds, which may be formed from C=C bonds, was greater with air and steam than with CO 2 .

Oxidation of activated carbon in liquid phase. Study by FT-IR

Abstract Surface chemistry of a commercial activated carbon (AC) and of products oxidized in liquid phase using aqueous solutions of a series of oxidizing agents (H2SO4, HNO3, HClO4, H2O2, O3, ClO2, KlO4 and KMnO4) has been studied by FT-IR. Oxidation led to surface groups and structures which, and also the extend of formation, depended on the oxidizing agent and the pH and concentration of the solution used. Most oxidizing agents proved to be effective for the formation of surface C[dbnd]O groups. Variations in pH of solutions of H2O2, KlO4 and KMnO4 unequally affected the oxidation of AC. This was unfavourable with the increase in concentration of the solutions of HNO3 and KMnO4. The reverse was noted with KlO4.