title: 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.
abstract: 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 degrees C. The results were evaluated in relation to the previously reported surface tension measurements. The presence of curvatures of the van()t Hoff plots suggested the presence of non-zero heat capacities terms (Delta(ads)C(p)). For the yellow dye, it is observed that the values of Delta(ads)H are almost all positive and they decrease in endothermicity, in the absence and in the presence of DBS, from 25 to 55 degrees C. For the red dye, there is an increase in endothermicity in relation to the temperature increase. The negative Delta(ads)G values indicate spontaneous adsorption processes. Almost all adsorption entropy values (Delta(ads)S) were positive. This suggests that entropy is a driving force of adsorption. The adsorption thermodynamic parameters were also evaluated using a new 2(3) 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.
authors.affiliation: Laboratory of Materials and Calorimetry, Departamento de Química/CCET, Universidade Federal de Sergipe, CEP 49100-000, São Cristóvão, Sergipe, Brazil. cestari@ufs.br
authors.forename: Antonio R
authors.initials: AR
authors.lastname: Cestari
authors.forename: Eunice F S
authors.initials: EF
authors.lastname: Vieira
authors.forename: Gláucia S
authors.initials: GS
authors.lastname: Vieira
authors.forename: Luiz P
authors.initials: LP
authors.lastname: da Costa
authors.forename: Andréa M G
authors.initials: AM
authors.lastname: Tavares
authors.forename: Watson
authors.initials: W
authors.lastname: Loh
authors.forename: Claudio
authors.initials: C
authors.lastname: Airoldi
mesh_terms: D000327:Adsorption; D000838:Anions; D004396:Coloring Agents / Q000737:chemistry* / Q000302:isolation & purification*; D015394:Molecular Structure; D016062:Porosity; D012822:Silicon Dioxide / Q000737:chemistry*; D012996:Solutions; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D000838:Anions; D004396:Coloring Agents; D012996:Solutions; D013501:Surface-Active Agents; D012822:Silicon Dioxide