Tailoring the porous properties of iron containing mixed oxides for As (V) removal from aqueous solutions Gabriela Carja b, * , Ryuichi Nakamura a , Hiroo Niiyama a a Department of Chemical Engineering, Tokyo Institute of Technology 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8550, Japan b Department of Physical Chemistry, Faculty of Industrial Chemistry, Technical University of Iasi, 71 D. Mangeron, Iasi, Romania Received 14 February 2005; received in revised form 29 March 2005; accepted 29 March 2005 Available online 2 June 2005 Abstract Ironcontainingmixedoxideswithtailoredporouspropertiesderivedfromsubstitutedlayereddoublehydroxidesaresynthesized, characterized and tested for the first time in the process of As (V) removal from aqueous solutions. The X-ray diffraction analysis pointsoutthemodificationofthelatticeparameterswhenironisintroducedinthebrucite-likelayer.TheresultsofN 2 adsorption– desorptionprocess,SEMandTEManalysisrevealnewandspecificporousproperties(e.g.,thepresenceofthetensilestrengtheffect phenomena,increasedcontributionofmicroporosity,highervaluesofthesurfaceareaandporevolume)forthesamplessynthesized underhighflow(700ml/min)ofnitrogen.Thespecificporouspropertiesandtheironcontentofthesamplebothcontributeinestab- lishingthehighvaluesofthearsenateremovalcapacityfromtheaqueoussolutionsreachingamaximumvalueequalingto97.7%for cHT 2 Fe. These results can open new perspectives for removing As (V) from aqueous solutions (e.g., contaminated water, contam- inated organisms) by using as precursors cheap and human health friendly materials type iron substituted layered double hydroxides. Ó 2005 Elsevier Inc. All rights reserved. Keywords: As adsorption; Iron mixed oxides; Hydrotalcites; Tailored porosity; TEM analysis 1. Introduction Layered double hydroxides (LDHs) are cheap, human health friendly materials [1] that belong to the classofanionicclaysandcanberepresentedbythegen- eral formula: [M II 1x M III x ðOHÞ 2  xþ [A m x=m  nH 2 O x . They are built up of sheets of edge-sharing metal octahedra, where, by comparison of brucite M(OH) 2 , part of M II isreplacedbyM III metal cations; the excess of the posi- tive charge is counterbalanced by exchangeable anions A m , located as water molecules, in the interlayer space [2]. The incorporation of cations with redox properties in the LDH network and/or the intercalation of a large variety of anions in the interlayer space offer the oppor- tunity to obtain, after the thermal treatment, new bifunctional mixed oxides that are defined not only by a unique combination of acid–base-redox properties but also by a large surface area and tuneable porous characteristics [3]; tailoring the porous properties of these materials is a subject of increasing interest [4,5]. Arsenicisanotoriouslytoxicelement [6];itentersthe environment from anthropogenic sources (e.g., pesti- cides, semiconductors, fertilizer production, and petro- leum refineries) though, usually, the main source of arsenic is geogenic. In aqueous systems arsenic is domi- nated by the As (V) oxyanions, H 2 AsO  4 and HAsO 2 4 , under oxidizing conditions [7]. As a consequence, it has been of high interest in finding low cost but also humanhealthfriendlymaterialspossessinghighadsorp- tion capacities of As (V) from aqueous solutions (not only for contaminated water but also for contaminated 1387-1811/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2005.03.014 * Corresponding author. Tel.: +40 232 277225; fax: +40 232 201160. E-mail address: carja@uaic.ro (G. Carja). www.elsevier.com/locate/micromeso Microporous and Mesoporous Materials 83 (2005) 94–100