High efficiency reduction of 4-nitrophenol on greenly synthesized gold nanoparticles decorated on chitosan matrix (CS-GLA/AuNPs)

An inexpensive bioinspired green approach using Saussurea costus root extract was developed to fabricate CS-GLA/AuNP catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Chitosan beads (CS) supported Au nanoparticles have been modified to improve their mechanical and thermal stability, using Glutaraldehyde (GLA). The modified chitosan beads (CS-GLA) and CS-GLA/AuNPs were investigated using FTIR, SEM, and TEM techniques. The diameter of AuNPs decorated chitosan beads was found to be around 6.0 ± 3 nm. The X-ray diffraction technique confirmed the crystalline nature of (CS-GLA/AuNPs) and AuNPs decorated chitosan beads. The TGA analysis showed that loading of AuNPs on the chitosan matrix increases its thermal stability. The synthesized (CS-GLA/AuNPs) catalysts exhibited excellent activity in reducing 4-nitrophenol to 4-aminophenol, compared to pure AuNPs and chitosan beads (CS-GLA/AuNPs), enabling the conversion of 4-nitrophenol in 30 min with 1 mg of the catalyst. The kinetic study indicated that the reduction of 4-nitrophenol on the CS-GLA/AuNPs catalyst follows the pseudo-first-order model. Moreover, the CS-GLA/AuNPscatalyst could be recycled at least eight times without significant loss of its activity.