Importance of the interaction adsorbent –adsorbate in the dyes adsorption process and DFT modeling

Abstract

Abstract The objective of this work is to highlight the importance of the textural and functional groups present in the carbon surface for the adsorption process of basic, acid and reactive dyes through experimental and theoretical adsorption studies. The adsorption of dyes on activated carbon prepared from peach endocarp shell by simple carbonization (CP) and chemical activation of the precursor by impregnation with CaCl2 (CPCa) were compared with theoretical calculations under the DFT framework. The carbonaceous materials were characterized with TGA, FTIR, XRD, SEM/EDX and the textural parameters by N2 isotherms. The adsorbents used in this study presented a higher adsorption capacity for the basic dye when compared with the reactive and acid dyes evaluated. The CPCa carbon had a higher adsorption capacity and surface area (943 m2 g−1) than the CP carbon. The adsorptive properties of the material obtained are a result of the combination of the high specific surface area of the carbon and the presence of CaCO3, Ca(OH)2 and the abundance of oxygenated moieties on the material’s surface. The theoretical calculation showed that the adsorption stability of anionic dyes on adsorbent is due to the interplay of dispersion, charge transfer and electrostatic intermolecular effects; this behavior is not sustained for the cationic dyes, where the adsorption stability is entirely reached by dispersion forces. These results support the relevance of the functionalization of the carbon surface.