Cationic dye adsorption and separation at discrete molecular level: first example of an iron cluster with rapid and selective adsorption of methylene blue from aqueous system

A hexanuclear iron(iii) complex, [Fe-6(III)(mu(3)-O)(edteH)(2)(piv)(6)(N-3)(2)] (1), was prepared by the reaction of FeCl2 center dot 4H(2)O with N,N,N ',N '-tetrakis(2-hydroxyethyl)ethylenediamine (H(4)edte) and pivalic acid (Hpiv) in the presence of NaN3 in MeCN/CH2Cl2. Its X-ray structure determination demonstrated a centrosymmetric complex with two triangular [Fe-3(mu(3)-O)](7+) units. To verify the importance of this material, the adsorption study for 1 was performed. The use of 1 as a possible dye adsorbent was evaluated in an aqueous medium on two model dyes: methylene blue (MB) and methyl orange (MO). The results obtained indicated that 1 showed remarkable adsorption properties for MB (88.60%). This Fe cluster is the first example of a homometallic coordination cluster that presents an exciting adsorption property. The adsorption factor was that free O-H groups in the coordination cluster delivered O-HMIDLINE HORIZONTAL ELLIPSIS pi interactions through the MB dye, which was attributed to enhanced adsorption. The effects of various parameters, such as pH and temperature, were studied. The MB adsorption efficiency by adsorbent was similar to 89% at neutral pH; however, for MO, it was similar to 48% at the same pH. Also, MB adsorption at a higher temperature (40 degrees C) was similar to 96%, whereas similar to 61% for MO. The kinetic data provided a good confirmation of the adsorption pathways, i.e. the pseudo-second-order. Overall, this study disclosed an easy-to-prepare, stable, and reusable iron(iii) cluster as a cost-effective, eco-friendly and efficient adsorbent for hazardous water-soluble aromatic dyes. This type of adsorbents can be fine-tuned further for the desired efficiency and dye selectivity.