Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: Liliana Giraldo x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

The adsorption process of 3-chloro phenol from aqueous solution on a activated carbon prepared from African palm stone and which presents a specific surface area of 685 m2 g−1, a greater quantity of total acid groups and a pHPZC of 6.8 is studied. The adsorption isotherms are determined at pH values of 3, 5, 7, 9 and 11. The adsorption isotherms are fitted to the Langmuir model and the values of the maximum quantity adsorbed that are between 96.2 and 46.4 mg g−1 are obtained along with the constant KL with values between 0.422 and 0.965 L mg−1. The maximum quantity adsorbed diminishes with the pH and the maximum value for this is a pH of 5. The immersion enthalpies of the activated carbon in a 3-chloro phenol solution of constant concentration, of 100 mg L−1, are determined for the different pH levels, with results between 37.6 and 21.2 J g−1. Immersion enthalpies of the activated carbon in function of 3-chloro phenol solution concentration are determined to pH 5, of maximum adsorption, with values between 28.3 and 38.4 J g−1, and by means of linearization, the maximum immersion enthalpy is calculated, with a value of 41.67 J g−1. With the results of the immersion enthalpy, maximum quantity adsorbed and the constant KL, establish relations that describe the adsorption process of 3-chloro phenol from aqueous solution on activated carbon.

Restricted access

Abstract  

The specific and non-specific interactions of twelve activated carbon cloth samples prepared from commercial cotton fabric, and that present different activation degrees are studied through the determination of immersion enthalpies in CCl4 and H2O, and in aqueous solutions of NaOH and HCl. The immersion enthalpies found for the solvents CCl4 and H2O are in a range of 5.49–45.84 and 1.77–7.76 J g−1, respectively. The enthalpic values for the materials in aqueous solutions of NaOH and HCl, allow characterizing the chemical surface of these materials, which are in a range of 6.63 and 21.49 J g−1, finding through them important relations in company with other characterizing techniques used in the study of these materials.

Restricted access

Abstract  

The interactions among five samples of activated carbons, obtained from different lignocellulosic materials with different degrees of activation of approximately 20% and aqueous solutions of phenol and 4-nitro phenol are studied by means of the determination of immersion enthalpies. It is established that the obtained activated carbons are of a basic character and show values for the pH at the point of zero charge, pHPZC, that range from 7.4 to 9.7 and, in all cases, higher total basicity contents than the values obtained for total acidity. The immersion heat of the activated carbons in CCl4 and water is determined obtaining values which are higher for CCl4 immersion and vary from 31.4 to 48.6 J g−1. The hydrophobic factor, hf, it is calculated from the relation between of the immersion heat of the activated carbons in CCl4 and the immersion heat in water, the obtained values were 2.98 and 6.75, which are greater than 1 due to the greater values obtained in CCl4 when compared to the values obtained in water. Immersion enthalpies in phenol solution range from 7.6 to 13.9 J g−1 and for the case of 4-nitro phenol such enthalpies range from 12.7 to 20.5 J g−1; all the 5 samples studied showed a higher value for the heat of immersion in aqueous solutions of 4-nitro phenol.

Restricted access

Abstract  

The immersion enthalpies of modified activated carbons were determined, with commercial CarbochemTM–PS230 (CAG) as the initial activated carbon, which was modified by: chemical treatment with HNO3 7 mol L−1 (CAO) and thermal treatment under flow of H2 (CAR) in function of the adsorbed quantity of monohydroxilated phenols, catechol, resorcinol and hydroquinone at a pH of 7 in aqueous dissolutions in order to characterize the solid–solution interaction and evaluate the influence of the chemical characteristics of the activated carbon in the phenol adsorption. The results show a variation in the immersion enthalpy in function of the adsorbed quantity of phenol and the initial dissolution concentration; which shows that the intensity of the interaction changes in function of the composition of the liquid phase. The immersion enthalpies present the following arrangement: catechol > resorcinol > hydroquinone, with a −ΔHinm of 35.7; 30.8 and 24.6 Jg−1, respectively, at a pH of 7 for a 100 mg L−1 phenol monohydroxilated solution.

Restricted access

Abstract  

Total acidity for a series of modified clays obtained from a natural vermiculite is determined through temperature programmed desorption (TPD) using ammonia as probe molecule. Results obtained for the acidity range from 15.1 to 68.5 meq/100 g. Immersion enthalpies of the clays in benzene, water and aqueous solutions of NH3 0.058 M and NaHCO3 0.053 M are determined. The results obtained show that immersion enthalpies in benzene and water are between −6.26 and −25.6 J g−1 and −2.10 and 5.55 J g−1, respectively and are smaller than the values obtained for the immersion enthalpies in the solutions. Immersion enthalpy values in NH3 solution are greater than the obtained using NaHCO3. Linear relations between the total acidity of the clays and the immersion enthalpies in the basic solutions are determined. An interaction factor using ammonia is calculated since the relation between the immersion enthalpy in ammonia solution and in water and it may be deduced that the relation with the total acidity is of second order tendency between them.

Restricted access