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Carbonaceous materials have been extensively studied as highly efficient adsorbents for the removal of dyes from wastewater. However, investigations of thermodynamic aspects of the interactions between these materials and dyes remain scarce. This paper describes the thermodynamics of the interactions between the Ponceau 4R (PR), Congo Red (CR), and Allura Red (AR) dyes and multi-walled carbon nanotubes (MWCNTs). The interactions between the dyes and activated carbon (AC) were also evaluated for comparison. The investigation used a combination of adsorption isotherms and isothermal titration nanocalorimetry (ITC) measurements, and a thermodynamic approach provided full characterization of the adsorption process. For both MWCNT and AC, the amount of adsorbed dye ( Γ D ) increased in the order Γ D (PR) < Γ D (AR) < Γ D (CR), and the adsorption capacity normalized by the adsorbent specific area was up to 5.6 times higher for MWCNT. The maximum amount adsorbed ( Γ D,max ) reached values of up to 2.00 μmol m −2 for CR adsorption on MWCNT. For both adsorbents, the process of dye adsorption was enthalpically driven and entropically unfavorable. All the thermodynamic parameters depended on the surface coverage and the structures of both dye and adsorbent. The adsorption enthalpy change (Δ ads H ) and entropy change (TΔ ads S ref ) values were higher than −137.0 kJ mol −1 and −114.2 kJ mol −1 , respectively. In addition to the structural differences between MWCNT and AC, the ITC data suggested that the adsorption sites are heterogeneous and that the dyes preferentially adsorb on the more hydrophilic sites on the adsorbent surfaces. [ABSTRACT FROM AUTHOR]

• Aggregation of SDBS is studied in imidazolium IL aqueous solution. • SDBS aggregation process involves two stages. • The SDBS aggregate stability is determined by the IL structure. • The IL changes the size of the SDBS aggregates. Ionic liquids (ILs) can modify cooperative process in aqueous solutions to a large extent, including anionic surfactant aggregation. Here, the micellization of sodium dodecylbenzene sulfonate (SDBS) was evaluated in low concentrations of 1-alkyl-3-methylimidazolium chloride (C n mimCl, n = 0, 2, and 4) aqueous solutions through fluorescence spectroscopy, isothermal titration calorimetry, dynamic light scattering, and conductometry. The thermodynamic stability of SDBS aggregates strongly depended on the IL structure and concentration, following the order C 4 mim+ > C 0 mim+ ≈ C 2 mim+. At 1.0 mmol L−1 of the ILs, the increase of the hydrophobicity of the imidazolium cation decreased the enthalpic favorableness, changing Δ H m i c o from −3.75 ± 0.07 kJ mol−1, for C 0 mim+, to −2.69 ± 0.01 kJ mol−1, for C 4 mim+. On the other hand, the entropic feasibility showed an opposite trend, i.e., the higher hydrophobicity of C 4 mim+ overcame the kosmotropic effect of IL cations in the bulks. We suggested that the imidazolium cations interact with the SDBS monomers on the micellar surface, mainly through hydrophobic, π-π, and electrostatic interactions for C 4 mim+ and C 2 mim+, and through electrostatic interactions and hydrogen bonds for C 0 mim+. [ABSTRACT FROM AUTHOR]

Preferential solvation participate in various supramolecular self-assembly processes, whose thermodynamic properties can be modulated by the addition of ionic liquids (ILs). However, the effects of these liquids on the thermodynamics of the host-guest complexation process remain unexplored. In this study, the thermodynamic properties of the complexation between 1-dodecylpyridinium cations (C 12 Py+) and β-cyclodextrin (βCD) species in aqueous solutions with different concentrations of 1-alkyl-3-methylimidazolium halides (C n mimX) were investigated by isothermal titration calorimetry. In water, C 12 Py+ and βCD form a 1:1 inclusion complex, which is enthalpically (Δ H i c o = −9.2 ± 0.1 kJ mol−1) and entropically (T Δ S i c o = 16.1 ± 0.2 kJ mol−1) favorable. However, in IL aqueous solutions, all the βCD―C 12 Py+ thermodynamic parameters of the complexation change and this IL effect is dependent on the carbon chain length of C n mim+ cations. ILs with shorter alkyl chains (C n mim+, n ≤ 4) decreases the system entropy, while ILs with longer alkyl chains (C n mim+, n ≥ 6) reduce the enthalpy values. These effects are attributed to i) preferential solvation of surfactant tails by ILs; ii) ability of the ILs to modify the 3D water structure and iii) inclusion of IL molecules into the inner cavities of βCD. [ABSTRACT FROM AUTHOR]