Comparative Study of Catalytic Activity of Recyclable Au/Fe3O4 Microparticles for Reduction Of 2,4-Dinitrophenol and Anionic, Cationic Azo Dyes.

Abstract

We synthesized Au/Fe3O4 microparticles. Initially, citrate-capped Fe3O4 micro-sized particles were synthesized by the co-precipitation method with an excess amount of trisodium citrate. Gold ions were reduced on the surface of citrate-capped Fe3O4 and grew as gold sub-microparticles with an average diameter of 210 nm on the surface. The characteristic SPR peak of gold nanoparticles on the surface of Fe3O4 was detected at 584 nm, whereas the absorption in the near-infrared region was increased. SEM images has proved that the synthesized Au/Fe3O4 composite microparticles has an average diameter of 1.7 micrometers. The results of XRD patterns proved the existence of both crystal phases of Fe3O4 and Au particles. To investigate the catalytic activity, the reaction rate constant of reduction of 2,4-dinitrophenol (2,4-DNP) and degradation of Congo red (CR), and methylene blue (MB) with NaBH4 in the presence of Au/Fe3O4 catalyst was monitored by UV-Vis spectroscopy. The initial reaction rate constant calculated from the change in characteristic peak absorptions of 2,4-dinitrophenol was 3.97×10-3 s-1, while the reaction rate constants for the degradation of CR and MB were 9.72×10-3 s-1 and 14.25×10-3 s-1 respectively. After 5 cycles, Au/Fe3O4 microparticles preserved 99 % of the reaction rate constant, exhibiting considerable recycling efficiency in the reduction of nitro groups.