Enhanced catalytic activity of tannic acid functionalized gold nanorods toward the reduction of 4-nitrophenol

The conversion of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) with sodium borohydride (NaBH4) is the most used chemical reaction for investigating the catalytic activity of various nanomaterials by ultraviolet-visible (UV-Vis) absorption spectroscopy. Herein, a simple approach is reported for the preparation of tannic acid-functionalized gold nanorods (TA-AuNRs), which functioned as catalysts for the reduction of 4-NP with NaBH4. Various processes including UV-Vis absorption spectroscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential, and X-ray photoelectron spectroscopy were employed to characterize the TA-AuNRs. They exhibited good catalytic activity during the conversion of 4NP. Under optimal conditions, the conversion efficiency was up to 79.04% in 20 min. The reduction reaction followed the pseudo-first-order kinetics, and the rate constant was estimated to be 0.0827 min-1. The active species responsible for the conversion efficiency were investigated through scavenger experiments using 1,4-benzoquinone, isopropyl alcohol (IPA), and ammonia oxalate as scavengers. The conversion efficiency decreased to 35.74% in the presence of IPA, indicating that hydroxyl radicals were the main species that degraded 4-NP. Finally, five recycling steps confirmed the reusability and practical application potential of the TA-AuNRs for the catalytic reduction of water samples spiked with 4-NP.