Mechanism of heavy metal uptake by a hybrid MCM-41 material: Surface complexation and EPR spectroscopic study

A novel hybrid MCM-41-based material was synthesized by incorporation of AEDTC [N-(2-aminoethyl)dithiocarbamate] in the MCM-41 pores. The derived MCM-41 circle times AEDTC material possesses high AEDTC loading 35% [w:w], and a well-defined array of regular mesopores with a specific surface area of 632 m(2)/g. Heavy metal, Cd, Pb, Cu, and Zn, uptake was studied in detail at physiological pH values 6-8, by a combination of analytical and electron paramagnetic resonance (EPR) spectroscopic techniques. The analytical data show a significant improvement, i.e., 200-500%, for Pb, Cu, and Zu uptake by the MCM-41 circle times AEDTC hybrid vs the unmodified MCM-41. In contrast, Cd shows an exceptional behavior: (a) Cd Uptake by MCM-41 circle times AEDTC is very low. (b) Competitive metal uptake experiments reveal that Cd ions cause a characteristic inhibition Of Cu Or Pb Uptake by the MCM-41 circle times AEDTC while Cd binding itself always remained low. The present findings are analyzed by a combination of surface complexation modeling and EPR spectroscopy. Accordingly, in the MCM-41 circle times AEDTC the sulfur atoms of AEDTC provide strong binding sites for metal binding, with a stoichiometry [S-AEDTC]:[Metal] = 1:1. Cd inhibits accessibility of Cu or Pb ions in the AEDTC sites. (c) 2009 Elsevier Inc. All rights reserved.