The removal of reactive dyes from aqueous solutions using chemically modified mesoporous silica in the presence of anionic surfactant-The temperature dependence and a thermodynamic multivariate analysis

The three-parameter Sips adsorption model was successfully employed to modeled equilibrium adsorption data of a yellow and a red dye onto a mesoporous aminopropyl-silica, in the presence of the surfactant sodium dodecylbenzenesulfonate (DBS) from 25 to 55 °C. The results were evaluated in relation to the previously reported surface tension measurements. The presence of curvatures of the vańt Hoff plots suggested the presence of non-zero heat capacities terms (ΔadsCp). For the yellow dye, it is observed that the values of ΔadsH are almost all positive and they decrease in endothermicity, in the absence and in the presence of DBS, from 25 to 55 °C. For the red dye, there is an increase in endothermicity in relation to the temperature increase. The negative ΔadsG values indicate spontaneous adsorption processes. Almost all adsorption entropy values (ΔadsS) were positive. This suggests that entropy is a driving force of adsorption. The adsorption thermodynamic parameters were also evaluated using a new 23 full factorial design analysis. The multivariate polynomial modelings indicated that the thermodynamic parameters are also affected by important interactive effects of the experimental factors and not by the temperature changes alone.