Activated carbons were prepared from olive stones either by the addition of zinc chloride (25-50 wt%) or by gasifying non-activated carbon with steam to burn-offs between 25% and 49%. The adsorption of nitrogen at 77 K was investigated and the adsorption data interpreted by the application of the Langmuir equation, the BET equation and the a S -method. The adsorption of carbon dioxide at 273 K was also followed and the data analyzed using the DR and DA equations. The adsorption of iodine from aqueous potassium iodide solution, and of Methylene Blue and p-nitrophenol from aqueous solutions at 298 K was also determined.Activation with zinc chloride produced physical and chemical changes which modified the thermal degradation process. Carbonization with zinc chloride restricted the formation of tars with the subsequent formation of solid carbon, the amount of zinc chloride incorporated in the precursor governing the porosity of the resulting carbon. The atmosphere under which activation of samples containing zinc chloride was undertaken was another factor in determining the texture of the carbon. Activation with steam to low burn-offs created new micropores by burning off the more reactive carbon atoms, but at high burn-offs erosion of the pore walls occurred leading to pore widening.Adsorption from solution was determined by the solubility of the solute in the solvent and by competition for this solute between the solvent and the adsorbent. The pore size of the carbon adsorbent and the molecular size of the adsorbate molecule were prominent factors in determining the extent of adsorption from solution.
Activated carbons were prepared by carbonizing ground apricot stones impregnated with 20–60 wt% phosphoric acid at 300–600°C, in a limited air supply. Highly activated carbons with surface areas amounting to 1200 m2/g and pore radii of 8–10 Å were obtained when a mixture of apricot stones and 50 wt% phosphoric acid was carbonized at 450°C. Activation with phosphoric acid proceeds via the creation of pores of radii between 8 Å and 10 Å. The adsorption data for nitrogen at 77 K obey models based on surface coverage satisfactorily and also models based on pore volume filling. Although a slight upward deviation was shown in the Dubinin–Radushkevich (DR) plots, this model was still verified and allowed the determination of useful sorption parameters.
A series of activated carbons ‘Z’ was prepared from Aleppo Pistacia Vera shells using different percentages of zinc chloride at 873 K in the absence of air. Another series ‘ZN’ was prepared using the same conditions as for the ‘Z’ series but employing a nitrogen atmosphere to effect carbonization. The textural properties of the two series of samples were determined from the adsorption of carbon dioxide and methylene blue at 298 K. Activated carbons with a high adsorptive capacity for methylene blue were obtained. Activation with zinc chloride proceeded with increasing microporosity via the creation of new micropores. At high percentages of zinc chloride, slight partial pore widening may take place. Carbon dioxide was accessible to the entire pore system and was therefore suitable as a probe for the investigation of the textural properties of the activated carbons studied. A fraction of the porosity was inaccessible to methylene blue molecules and consequently lower surface areas were calculated from the adsorption of this dye molecule.
Activated carbons were prepared by activation of cherry and wild cherry stones with phosphoric acid and zinc chloride. The adsorption of nitrogen at −196°C and of carbon dioxide at 0°C was followed and the data obtained analyzed through the use of models based on theories of surface coverage and micropore filling.
Chemically-activated carbons obtained from cherry and wild cherry stones exhibited high surface areas and large total pore volumes. Most of the pores lay in the micropore region while a small fraction of the total surface area was located in non-micropores.
Fair agreement was established on comparing the textural parameters derived from models based on the theory of surface coverage with those derived from the micropore filling theory. Micropores should be classified into ultrafine pores, micropores and super-micropores, such sub-division helping in the prediction of the adsorption behaviour and in the interpretation of the data derived therefrom.
Chemically activated carbons were obtained from olive stones either by carbonization with H 3 PO 4 at 300-600ºC or by carbonization with ZnCl 2 at 600ºC. Nitrogen adsorption at 77 K was determined for all the activated carbons. The adsorption data were interpreted by considering some conventional adsorption models.Maximum activation with H 3 PO 4 occurred at 450ºC. However, the adsorption capacities of the ZnCl 2 -activated carbons were far higher than those of carbons activated with H 3 PO 4 . Carbons activated with H 3 PO 4 or ZnCl 2 are mainly microporous with the non-micropores representing a small fraction of the total porosity. Although, the nitrogen isotherms are Langmuirian in shape, application of the Langmuir equation led to large monolayer capacities of uncertain confidence. The surface areas and micropore volumes determined by the application of the t-method of de Boer and the a S -method of Sing were comparable and were slightly higher than those determined by the application of the DR model based on micropore filling. The t-method and the a S -method are complementary to each other and would seem to give confident values because they are based on standard reference non-porous materials. The micropore region may be sub-divided into two sub-regions distinguished by the different filling mechanisms involved.
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