Synthesis and characterization of hybrid MCM-41 materials for heavy metal adsorption Kostas Dimos a, * , Panagiota Stathi b , Michael A. Karakassides a , Yiannis Deligiannakis b a Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece b Department of Environmental and Natural Resources Management, University of Ioannina, Seferi 2, Agrinio 30100, Greece article info Article history: Received 20 March 2009 Received in revised form 7 May 2009 Accepted 12 May 2009 Available online 21 May 2009 Keywords: Hybrid MCM-41 Dithiocarbamate Mesoporous Heavy metal adsorption abstract A small dithiocarbamate molecule, N-(2-Aminoethyl)dithiocarbamate, was synthesized, characterized and afterwards used to modify and activate the surfaces of MCM-41 materials. The structure and the sur- face charge properties of the starting and the novel organic–inorganic hybrid mesoporous materials were studied by means of powder X-ray diffraction, Fourier transform infrared spectroscopy, DTA/TG thermal analyses, surface area measurements and potentiometric acid–base titrations. The hybrid materials retained the regular hexagonal arrangement of cylindrical pores which is the characteristic of the MCM-41 solids, while a high content (2.57 mmol/g) of the organic molecules in the final products was achieved. Despite the high concentration of the dithiocarbamate molecules in the pores of the hybrid MCM-41 materials, final solids retained high specific surface areas (632 m 2 /g) indicating a homogenous incorporation of the small organic molecules in the pores. A surface complexation model was developed to explain the results of the potentiometric titrations and to describe the surface charge and H-binding properties of the starting and final hybrid materials. These materials are promising heavy metal adsor- bents due to the presence of the effective dithiocarbamate groups and the low pH value (3.2) of the point of zero charge. Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction The discovery of the mesoporous materials family M41S at Mo- bil’s laboratories in 1992 [1,2] offered a new category of porous materials with many applications as catalysts [3,4], adsorbents [5,6], sensors [7] separators [8], etc. The most interesting M41S member is the MCM-41. The MCM-41 solids exhibit high specific surface areas (1000 m 2 /g), high crystallinity, high thermal stabil- ity, uniformity of hexagonal cylindrical pores, narrow pore distri- bution and regulated pore diameter from 15 to 100 Å. These characteristics render these solids as ideal heavy metal adsorbents [9–11]. The main disadvantage of MCM-41 is the lack of effective binding groups and permanent negative charge as in the case of clays. For this reason, in the last decades huge effort has been taken in the modification of the MCM-41 surface with thiol groups. In most cases, for the modification of mesoporous silicas, mercaptopropyltrimethoxysilane is used as thiol source. The final adsorbents are produced either by co-condensation [12–20] or by post-grafting [8–11,21–27], while the same molecules have been successfully used for the modification of clays [28–30]. Although the modification of porous materials with dithiocarbamate groups is of high importance, these groups are effective chelating agents for metal complexing and there has been an effort in the modifica- tion of clays [31], activated carbon [32] and mesoporous silicas [33–35]. In this aspect we report in this work the synthesis of a novel hybrid mesoporous material based on MCM-41. The MCM-41 material was modified by post-grafting of N-(2-Aminoethyl)dithio- carbamate (AEDTC) molecules on the pores surfaces of the meso- porous solid. The organic molecules of this substance were in a zwitterionic form and thereby their grafting was feasible by the sil- anol groups of the surfaces. AEDTC molecules were chosen in order not to block the MCM-41 pores. The final hybrid adsorbents were characterized with regard to their structural and surface charge properties. 2. Experimental 2.1. Reagents All materials were of reagent or analytical grade and were used as purchased without further purification. Tetraethylorthosilicate (TEOS) 98% was purchased from Sigma-Aldrich (131903), aqueous ammonia solution (NH 3 ) 25%wt. from Fluka (09860), cetyltrimeth- ylammonium bromide (CTAB) 95% from Sigma-Aldrich (855820), 1387-1811/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2009.05.021 * Corresponding author. Tel.: +30 26510 97367; fax: +30 26510 97074. E-mail addresses: kdimos@cc.uoi.gr (K. Dimos), me01791@cc.uoi.gr (P. Stathi), mkarakas@cc.uoi.gr (M.A. Karakassides), ideligia@cc.uoi.gr (Y. Deligiannakis). Microporous and Mesoporous Materials 126 (2009) 65–71 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso