title: Designed pendant chain covalently bonded to analogue of heulandite for removal of divalent toxic metals from aqueous solution: thermodynamic and equilibrium study.
abstract: An analogue of heulandite was synthesized by using inorganic salts as a source for silicon and aluminum in the hydrothermal synthesis of the material. The resulting solid was modified by organofunctionalization with 1,4-bis(3-aminopropyl)piperazine and subsequent reaction with methylacrylate in a heterogeneous route. The original (HEU) and modified silicate (HEU(APPMA)) samples were characterized by textural analysis, SEM, and nuclear magnetic nuclei of (29)Si and (13)C. The chemically modified silicate sample showed modification of its physical-chemical properties including specific area 459.0-978.8 m(2) g(-1). The ability of this material to remove nickel(II), cobalt(II), and copper(II) from aqueous solutions was followed by a series of adsorption isotherms adjusted to a Sips equation. The quick adsorption process reached the equilibrium before 10, 15, and 20 min for Cu(II), Ni(II), and Co(II), respectively, with maximum adsorptions at pH 4.0. Based on the capacity of adsorption of HEU(APPMA) to interact with metal ions, the following results were obtained 12.9, 9.8, and 7.5 mmol g(-1) for Cu(II), Ni(II), and Co(II), respectively, reflecting a maximum adsorption order of Cu(II)>Ni(II)>Co(II). The energetic effects caused by metal cation adsorption were determined through calorimetric titrations.
authors.affiliation: Chemistry Institute, State University of Campinas, P.O. Box 6154, 13084-971 Campinas, São Paulo, Brazil. dlguerra@iqm.unicamp.br
authors.forename: Denis L
authors.initials: DL
authors.lastname: Guerra
authors.forename: Rúbia R
authors.initials: RR
authors.lastname: Viana
authors.forename: Claudio
authors.initials: C
authors.lastname: Airoldi