Layered Crystalline Barium Phosphate Organofunctionalized for Cation Removal Ange´lica M. Lazarin and Claudio Airoldi* Instituto de Quı ´mica, UniVersidade Estadual de Campinas, Caixa Postal 6154, 13084-971 Campinas, SP, Brazil ReceiVed August 26, 2005. ReVised Manuscript ReceiVed December 13, 2005 The available hydroxide groups inside the lamellar cavity of barium phosphate (BaP) were reacted with the silyating agents (RO) 3 Si(CH 2 ) 3 L x (L 1 ) NH 2 ,L 2 ) NH(CH 2 ) 2 NH 2 , and L 3 ) NH(CH 2 ) 2 NH- (CH 2 ) 2 NH 2 ), to yield organofunctionalized nanomaterials BaPSiL 1 , BaPSiL 2 , and BaPSiL 3 . The amount of organofunctional groups covalently attached to the inorganic layer was 1.24, 1.46, and 1.23 mmol g -1 , respectively. The basic nitrogen center atoms attached to the pendant organic chains adsorb FeCl 3 , CuCl 2 , and ZnCl 2 from ethanol solutions to give well-established isotherms at 298 ( 1 K. The results obtained in flow experiments showed a retention and recovery of ca. 100% of the metal ion with packed BaPSiL x columns from solution containing a mixture of these cations. The energetic effect caused by iron, copper, and zinc ion interactions was determined through calorimetric titration at the solid-liquid interface and gave a net thermal effect that enabled the calculation of the exothermic enthalpic values and the equilibrium constants. The complete thermodynamic data showed that the system has favorable enthalpic, Gibbs free energy, and entropic values. The cation removal properties were used with packed columns to successfully determine these cations in ethanol used as fuel sources. Introduction The self-organized molecular assembly producing a desired organic species on an inorganic solid surface is a methodol- ogy applied to synthesize inorganic-organic hybrids. 1 A material designed using mild experimental reaction condi- tions through soft-chemical routes is, instead of other procedures, a promising strategy since the resulting layered inorganic-organic hybrid may have, in a unique nanostruc- ture, properties strongly controlled by host-guest interac- tions. A wide variety of such classes of hybrids have been prepared by intercalation reactions and their properties have been investigated. 2 Among well-established intercalation reactions, lamellar compounds can potentially use the avail- able silanol groups disposed in the interlamellar layer to immobilize organic units, by exploring the versatile attributes of silyating agents. 3 From this process, the final material may have merit in practical applications due to the thermal and chemical stabilities of the hybrid. The silylation layer aggregates the chosen component to the original nanoma- terial, enabling organic functional attachments to produce novel hybrids, by adding activities such as film-forming abilities 4 and adsorptive properties. 5 The silylating reaction is characterized by the displacement of active hydrogen atoms originally attached to silanol groups by organosilyl derivatives of silane coupling agents having the general formula (R′O) 3 SiR. 6,7 This organic molecule contains the moiety R in which functional centers are attached to the organic chain while the alkoxy R′O groups are normally derived from common alcohols. These latter groups are easily hydrolyzed when dispersed in water or simply by the water of hydration that exists on the substrate surface during the chemical process. The selection of a desirable functional group on the R moiety during the immobilization depends on the subject of each application. 6,8 Thus, the R groups are chosen to exploit, for instance, wettability, corrosion, resistance, interfacial electrical resis- tance, and adhesive functions or cation adsorption. 6,8 The application of such immobilization methods can yield grafted surfaces, where defined coupling agents are co- valently bonded onto the inorganic supports. The final products of the anchored surfaces have great utility in many areas such as chemically bonded phases in chromatography, 9 preconcentration and extraction of cations from solutions, 10 use in catalytic processes, 11 and biomaterial immobilization. 12 Among a variety of matrixes, such as oxides, glasses, and clay minerals, which contain available OH-end groups bonded on the respective surfaces, silica gel has been * To whom correspondence should be addressed. E-mail: airoldi@ iqm.unicamp.br. 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Mater. 2006, 18, 2226-2232 10.1021/cm0519333 CCC: $33.50 © 2006 American Chemical Society Published on Web 03/29/2006