Morphology-Controlled Synthesis and Characterization of Magnetic Iron Oxide Nanocrystals and Their Potential Applications in Selective Oxidation of Alcohols and Olefins

A protocol for the preparation of iron oxide nanocrystals of two different (nanorods and octahedrons) morphologies has been developed and the synthesized nanocrystals were well characterized by TEM and XRD. These two nanocrystals have been applied for the selectivie oxidation of aryl-methanol and vinyl-arene. Moreover, the magnetic catalysts have easily separated from reaction mixture by a magnet and are reused without appreciable loss of catalytic activity. The oxidation processes avoid the use of toxic catalysts and volatile and hazardous organic solvents. 1. Introduction Selective oxidations of aryl-methanol and vinyl-arene to aryl-aldehyde are synthetically important because of the wide applications of these products in organic reactions and also it is difficult to control the further oxidation to acid. Traditionally, oxidation of benzyl alcohol to benzaldehyde is performed with many oxidizing agents and was used in stoichiometric amount [1–3]. These oxidants are generally expensive in nature and most importantly they generate toxic heavy-metal waste and were performed in hazardous chlorinated solvents. In recent years, the oxidation reactions using hydrogen peroxide (H2O2) as reagent in combination of a catalyst has attracted much attention because H2O2 is very mild in nature, inexpensive, and produce only water as product [4–6]. For this reason, a number of methodologies have been developed for oxidation of alcohols using H2O2 as oxidant and various metal as catalyst [7–18]. Thus, there is a thrust in search for new green catalysts. Very recently, various nano-particles such as NiO2 NPs [19] and metal-oxide-supported nanogold [20] also applied as catalyst for the benzylic oxidation. Iron-based catalysts have been extensively used because they are easily accessible, inexpensive, environmentally benign, and relatively nontoxic in comparison with other transition metals. Different iron (II) [21–23] and iron (III) compounds [24–28] have been used as for the oxidation reactions. Herein, we report the synthesis and characterization of iron oxide nanomaterials of two different morphologies (namely, nanorod and octahedron) and their successful applications in the selective oxidation of aryl-methanol and vinyl-arene with H2O2 under organic solvent-free condition. 2. Results and Discussions At first, we have synthesized both the iron oxide nanorods and octahedrons using hydrogen peroxide by solvothermal technique. In a simple experimental procedure, a mixture of FeCl3 and FeCl2 was used in equimolar ratios as the precursor. Ethylenediamine and water were