Adsorption of a reactive dye on chemically modified activated carbons - Influence of pH

J. J. M. Órfão, Andreia I. M. Silva, João C. V. Pereira, S. A. Barata, I. M. Fonseca, Patrícia C. C. Faria, Manuel Fernando R. Pereira

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239 Citations (Scopus)


The surface chemistry of a commercial activated carbon with a slightly basic nature was modified by appropriate treatments in order to obtain two additional samples, respectively with acidic and basic properties, without changing its textural parameters significantly. Different techniques (N 2 adsorption at 77 K, temperature programmed desorption, and determination of acidity, basicity, and pH at the point of zero charge) were used to characterize the adsorbents. Kinetic and equilibrium adsorption data of a selected textile reactive dye (Rifafix Red 3BN, C.I. reactive red 241) on the mentioned materials were obtained at the pH values of 2, 7, and 12. The kinetic curves are fitted using the second-order model. The respective rate constants seem to diminish progressively with the initial concentration for the more diluted solutions tested, reaching a constant value at higher concentrations, which depends on the experimental system under consideration (adsorbent and pH). In general, the Langmuir model provides the best fit for the equilibrium data. The different uptakes obtained are discussed in relation to the surface chemical properties of the adsorbents. It is shown that the adsorption of the reactive (anionic) dye on the basic sample (prepared by thermal treatment under H 2 flow at 700 °C) is favored. This conclusion is explained on the basis of the dispersive and electrostatic interactions involved. Moreover, it is also shown that the optimal adsorption condition for all the activated carbons tested corresponds to solution pH values not higher than the pH pzc of the adsorbents, which may be interpreted by taking into account the electrostatic forces present.

Original languageEnglish
Pages (from-to)480-489
Number of pages10
JournalJournal of Colloid and Interface Science
Issue number2
Publication statusPublished - 15 Apr 2006


  • Activated carbon
  • Adsorption
  • pH
  • Reactive dyes
  • Surface chemistry

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