Bio-inspired immobilization of gold nanoparticles onto magnetic graphene oxide for catalytic reduction of nitroarenes

Abstract

There is an intense research interest on the development of a bio- inspired strategy for synthesizing magnetic graphene oxide (MGO) composite materials decorated with gold nanoparticles (AuNPs) because of their applications for the catalytic reduction of various nitroarenes. We exploited interesting dopamine chemistry to achieve in situ reduction of Au3+

salt to AuNPs and deposition of AuNPs on the dopamine-MGO surface. The magnetic properties were introduced in the catalyst for easy separation. Graphene oxide as supporting material has high surface area which can enhance the surface capacity by ascribing to the synergistic effect of polydopamine (PDA) with multifunctional groups. Mainly Dopamine coated on the surface of MGO in tris-buffer solution which leads to the formation of MGO-PDA composite where PDA protects AuNPs from aggregation. To compare the catalytical activity of synthesized catalyst MGO-PDA@Au, another noble metal catalyst silver was introduced and synthesized in the same steps involved in gold nanocatalyst synthesis. The resultant catalysts were characterized by employing FESEM, X-ray, EDS, TGA, FTIR and UV-Vis spectroscopy. FESEM study showed that the average size of AuNPs and AgNPs particles is 8 nm and 12 nm, respectively. Dopamine coating and the presence of o ther chemical functional groups were confirmed by FTIR spectroscopy and TGA study showed that the thermal stability of nanocomposites. To study the catalytic activity of MGO-PDA@Au, 4-nitrophenol was selected as model dye as it was UV active. Methylene blue (MB) was taken here to compare the degradation of 4-nitrophenol. In the presence of excess NaBH4, these reactions follow pseudo firstorder reaction kinetics. The reduction of organic dyes using aqueous NaBH4 is thermodynamically favorable, but kinetically not feasible due to the large potential difference between donor and acceptor molecules. The metal NPs accelerates the reaction by facilitating electron relay from the donor BH4-to acceptor dye

molecules thereby overcome the kinetic barrier. After the reaction of catalysis for MGO-PDA@Au catalysts degrade 4-NP and MB almost 96.4% in 7min and 98.9% in 5min respectively. So, MGO-PDA@Au composite materials exhibited good synergistic capabilities of efficient catalytic reduction efficiency along with fast red uction kinetics as tested for both dyes.