Catalytic reduction of nitroarenes by Mukia maderaspatana leaves extract mediated silver nanoparticles

In this work, we have reported a simple and ecofriendly green method for the synthesis of silver nanoparticles (Ag NPs) using Mukia maderaspatana leaves extract. The phytoconstituents such as alkaloids, flavonoids, carbohydrates, saponins and tannins present in the leaves extract act as reducing and stabilizing agents [1]. The synthesized nanoparticles were characterized by UV-Visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transition electron microscopy (TEM) with energy dispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopy (XPS), and Zeta potential. The absorption peak at 442 nm was attributed to the surface plasmon resonance of Ag NPs. FTIR peaks confirmed that the reducing and capping potential of Mukia maderaspatana leaves extract for the synthesis of Ag NPs. The XRD result showed that the synthesized Ag NPs are crystalline and the size is calculated to be 31.57 nm [2]. The TEM image indicated that the synthesized Ag NPs are spherical in shape and the average particle size is found to be 15.85 nm. The EDAX analysis showed a strong signal at 3 KeV for Ag and the weak signals for C, O, Na and Mg confirmed the green synthesis of Ag NPs [3]. XPS confirmed the Ag0 [4]. The zeta potential value was found to be -17.6mV which indicated the higher stability of Ag NPs and the presence of phytoconstituents [5]. The catalytic efficacy of the Ag NPs was monitored for the reduction of different substituted nitro aromatic compounds such as 4-nitrophenol (4-NP), 3-nitrophenol (3-NP), 2-nitrophenol (2-NP), 4-nitroaniline (4-NA), 3-nitroaniline (3-NA), 2-nitroaniline (2-NA), 2,4-dinitrophenol (2,4-DNP), and 2,4,6-trinitrophenol (2,4,6-TNP) using sodium borohydride (NaBH4)  as a reducing agent and the rate constant k was calculated. The reduction reactions followed pseudo-first-order kinetics. The kinetic studies were also carried out by varying the concentration of nitroaromatic compounds [0.5 × 10-4M to 1.5 × 10-4M], NaBH4 [1 × 10-3M to 10 × 10-3M], and synthesized Ag NPs catalyst [5mg to 25mg]. The reduction product of 4-NP was separated from an aqueous medium using ethyl acetate. The obtained product was analyzed by UV-Vis, FTIR, and 1HNMR spectroscopy. The 1HNMR spectrum showed a peak at δ 8.33 (s, 1H of -OH), δ 6.48-6.40 (dd, 4H of aromatic -H), and δ 4.39 (s, 2H of -NH2) which evidenced the formation of 4-aminophenol (4-AP). Further, the recyclability of the Ag NPs was also determined. The catalytic efficiency of the Ag NPs was retained even after the 5th cycle of reduction reactions and the stability was also confirmed by XRD analysis. From the results, it was inferred that the Mukia maderaspatana leaves mediated Ag NPs which can be an excellent and efficient catalyst for the reduction of toxic environmental pollutants.