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

The design and environmentally-safe synthesis of magnetically recoverable solid-supported metal nanoparticles with remarkable stability and catalytic performance have significant industrial importance. In the present study, we have developed an inexpensive bioinspired approach for assembling gold nanoparticles (AuNPs) in magnetic chitosan network under green, mild and scalable condition. 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) to Au(0) was is achieved by using Melicope ptelefolia aqueous leaf extract. The synthesized magnetic chitosan supported biosynthesized Au nanocatalyst was characterized using Fourier Transform Infrared (FT-IR), Carbon, Hydrogen and Nitrogen (CHN), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Atomic Absorption Spectroscopy (AAS) analyses. FTIR spectrum of magnetic chitosan showed peaks at 1570 cm-1, which indicate for N-H bending vibration and at 577 cm-1 which designates the Fe-O bond. CHN analytical data further supported the coating of chitosan onto the magnetite. TEM analysis showed an amorphous layer around the magnetite core, proving the coating of chitosan on the magnetite surface and the average particle size of AuNPs calculated was 7.34 ± 2.19 nm. XRD analysis showed six characteristics 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). Meanwhile, XRD analysis of catalyst showed characteristic peaks of AuNPs at 2 (38.21°, 44.38°, 62.2°, 77.32° and 80.76°), which correspond to (111), (200), (220), (311) and (222) lattice planes (JCPDS file, PDF No.04-0784). 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 magnetic chitosan supported AuNPs is effective as catalyst for the reduction of 4-nitrophenol