The Role of the Surface Energy of Tannin‐Based Adsorbent Materials on the Lead Removal Capacity in Contaminated Water

Sample with low concentration of surface groups presents low surface energy and in consequence low adsorption capacity independently of the specific surface area and micro and mesoporosity.

In this work, inverse gas chromatography at infinite dilution was used to associate the surface properties (London component, acid and basic constants, and enthalpy) of two tannic based adsorbent materials with the removal capacity against lead pollutant in contaminated water. Such materials have been prepared with same molar ratio TEOS/tannic (5/1) using p-toluene sulfonic (p-TSA) and nitric acids (NA) as catalyst. The dispersive component of the surface (London component, γ _S ^D) is higher for the p-TSA material (64.7 mJ.m⁻²) than NA material (35.3 mJ.m⁻²). Identical behavior is found for enthalpy (81.2 mJ.m⁻² for p-TSA and 39.2 mJ.m⁻² for NA) and acid constant of the surface (0.25 and 0.15 for p-TSA and NA, respectively). The porous structure is not very important in the removal capacity for these materials due to the very low specific surface area and pore volume being very close for both samples. Kinetically, the adsorption of Pb(II) on p-TSA material follows a Freundlich isotherm model indicating that the surface is heterogeneous. The maximum adsorption capacity of the best TEOS/tannic sample for Pb (II) was 62 mg.g⁻¹. The results obtained in this work establishes that the surface energy also would play a very important role on the removal capacity of contaminants independent of the textural characteristics of the adsorbent.

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