Green synthesis of Ag/Fe3O4 nanocomposite using Citrus sinensis peel extract and its catalytic activity for the reduction of organic dyes

Iron oxide magnetic nanoparticles have been widely used in many fields, which are attributed to their unusual magnetic, physical and surface chemical and catalytic properties, high stability and ease of recovery with an external magnet. Recently, the dopping of noble metals to iron oxide nanoparticles has been attracted widelybecause of unique multifunctional applications of hybrid nanostructures. Morever, the iron oxide nanoparticles can act as an effective support to prevent the agglomerationof metals nanoparticles [1]. For the past few years, green synthesis of nanoparticles has been widely attracted. This method has several advantages over chemical and physical synthetic methods, such as facility, safety, elimination of toxic materials and cost effectiveness [2]. Herein, this context outlines the simple and eco-friendly route for the synthesis of Ag/Fe3O4 nanocomposite using Citrus sinensis peel extract without stabilizers or surfactants. The as-synthesized nanocomposite was characterized by UV-Vis, FT-IR, XRD and FE-SEM techniques. The catalytic efficiency of Ag/Fe3O4 nanocomposite was examined for the catalytic reduction process of methylene blue (MB), methylgreen (MG) and methyl orange (MO) in water at room temperature in the presence of sodium borohydride as reducing agent. The concentration of MB, MG and MO wasused 3.1 × 10−5 M, 3 × 10−5 M and 3 × 10−5 M, respectively. The concentration of NaBH4 for the reduction process of MB, MG and MO was used 5.3 × 10−3 M, 2.6 × 10−4 M and 3.7 × 10−2 M, respectively. In a typical experiment, 25 ml of NaBH4 solution was added to 25 ml of dyes solution and the result was that the reduction of MB and MO was not occured after 24 h, and the reduction of MG was performed in 1 h. In the presence of catalyst and NaBH4, the catalytic reduction of MB, MG and MO was completed in 127, 56 and 131 seconds, respectively. The decrease of reaction time shows the performance of nanocomposite clearly. The catalytic reduction occurs at the surface of catalyst. There were two steps of dyes reduction; (i) diffusion and adsorption of dyes to the catalyst surfaces via π-π stacking interactions and (ii) electron transfer mediated by the catalyst surfaces from BH4 − to dyes. Ag NPs supported on the Fe3O4 NPs can function as the electron mediator between oxidant and reductant, and the electron transfer occurs via the Ag NPs. It suggested that the Fe3O4 NPs as support may play an active part in the catalysis, yielding a synergistic effect [3]. The progress of reactions was monitored using UV–Vis spectroscopy