Biosynthesized gold nanoparticles supported on magnetic chitosan matrix as catalyst for reduction of 4-nitrophenol

Abstract

The design and synthesis of environmentally-safe magnetically recoverable solid-supported metal nanoparticles with remarkable stability and catalytic performance has attracted significant interest. In the present study, an inexpensive bioinspired approach for assembling gold nanoparticles (AuNPs) in magnetic chitosan (CS) and carboxylmethylchitosan (CMC) network under green, mild and scalable condition is reported. AuNPs were well loaded on the surface of the magnetic support due to the presence of hydroxyl (-OH) and amino (-NH2) groups in chitosan molecules that provided the driving force for the complexation reaction with the Au(III) ions. Reduction of the Au(III) ion to Au(0) is achieved by using Melicope ptelefolia aqueous leaf extract. The synthesized magnetic chitosan supported biosynthesized Au nanocatalyst was characterized using Fourier transform infrared spectroscopy (FTIR), carbon, hydrogen and nitrogen analysis (CHN), transmission electron microscopy (TEM), X-ray diffraction (XRD) and atomic absorption spectroscopy (AAS). FTIR spectrum of magnetic chitosan showed peaks at 1570 cm- 1 indicative of N-H bending vibration and at 577 cm-1 which designated the Fe-O bond. CHN analytical data further supported the coating of chitosan onto the magnetite. XRD analysis showed six characteristic peaks for magnetite corresponding to lattice planes (220), (311), (400), (422), (511) and (440) in both the magnetite and magnetic chitosan samples (JCPDS file, PDF No. 65-3107). In addition, XRD analysis of the catalyst showed characteristic peaks of AuNPs at 2? (38.21°, 44.38°, 62.2°, 77.32° and 80.76°) which corresponded to (111), (200), (220), (311) and (222) lattice plane (JCPDS file, PDF No.04- 0784). TEM analysis showed an amorphous layer around the magnetite core which supported the coating of chitosan on the magnetite surface and the average particle size of AuNPs calculated was 7.34 ± 2.19 nm. AAS analysis showed the loading of AuNPs as 5.4%. The rate constant achieved for the reduction of 4-nitrophenol to 4-aminophenol in the presence of hydrazine hydrate using 10 mg of catalyst was 0.0046 s-1. The optimum conditions of Fe3O4-CS-AuNPs were 12% of Au loading and 15 mg of catalyst amount. Both the prepared magnetic chitosan supported AuNPs catalysts, Fe3O4-CSAuNPs and Fe3O4-CMC-AuNPs showed good performance as catalyst for the reduction of 4-nitrophenol which gave rate constant of 0.0055 s-1 and 0.0104 s-1, respectively. Fe3O4-CS-AuNPs also gave good recyclability which at least four times without significant loss of activity.