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

We synthesized Au/FeO microparticles. Initially, citrate-capped FeO 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 FeO 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 FeO was detected at 584 nm, whereas the absorption in the near-infrared region was increased. SEM images has proved that the synthesized Au/FeO composite microparticles has an average diameter of 1.7 micrometers. The results of XRD patterns proved the existence of both crystal phases of FeO 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/FeO 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 s, while the reaction rate constants for the degradation of CR and MB were 9.72×10 s and 14.25×10 s respectively. After 5 cycles, Au/FeO microparticles preserved 99 % of the reaction rate constant, exhibiting considerable recycling efficiency in the reduction of nitro groups.