Green synthesis of silver nanoparticles using Terminalia cuneata and its catalytic action in reduction of direct yellow-12 dye

https://doi.org/10.1016/j.saa.2016.02.044Get rights and content

Highlights

  • Synthesis of silver nanoparticles using Terminalia cuneata bark is reported.

  • The size of the silver nanoparticles is in the range of 20–50 nm.

  • The catalytic reduction of direct yellow-12 was achieved using NaBH4.

Abstract

Facile green synthesis of silver nanoparticles (AgNPs) using aqueous bark extract of Terminalia cuneata has been reported in this article. The effects of concentration of the extract, reaction time and pH were studied by UV–Vis spectroscopy. Appearance of yellow color with λmax around ~ 420 nm suggested the formation of AgNPs. The stable AgNPs were further characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS) with zeta potential and high resolution transmission electron microscopy (HR-TEM) with energy dispersive X-ray spectroscopy (EDS) analysis. The synthesized AgNPs were in the size range of 25–50 nm with a distorted spherical shape identified from HR-TEM analysis. The catalytic activity of AgNPs on the reduction of direct yellow-12 using NaBH4 was analyzed using a UV–Vis spectrophotometer. This study showed the efficacy of biogenic AgNPs in catalyzing the reduction of direct yellow-12.

Introduction

Nanoscience has blossomed in the recent decades owing to its immense contribution in diverse fields like sensors, catalysts and medicine [1]. The electronic, optical and chemical properties of nanoparticles are entirely different from those of bulk of the same materials [2]. Among the nanoparticles, silver nanoparticles are of great interest to researchers due to its applications toward medical, catalysis, optics and energy fields. Generally colloidal metal nanoparticles are synthesized by chemical reduction of metal ions by reducing and capping agents. The principal advantage of the reduction method is the facile fabrication of nanoparticles with various sizes and shapes viz., nanorods, nanowires, nanoprisms and nanoplates [3]. Polymers and surfactants served as capping agents that protect the metal nanoparticles from aggregation. Some of the reducing and capping agents are toxic to human beings and the environment. To overcome this problem, researchers have started to synthesize nanoparticles using bio-sources such as microorganisms, fungi and plant extracts [4], [5], [6], [7], [8], [9]. This method is very easy, environmentally benign and cost effective. Moreover, different sizes and shapes of nanoparticles can also be synthesized [10].

Direct yellow-12, an anionic azo dye, is readily soluble in polar solvents viz., water, methanol and ethanol, and utilized in different processes including silk, wool, leather, jute, cotton dyeing and paper printing. Direct yellow-12 dye must be present in the effluents of these industries [11]. Direct yellow-12 dye is quite toxic to humans and all aquatic organisms, the reduction of direct yellow-12 are industrially and environmentally important.

In the present work, AgNPs were synthesized using aqueous bark extract of Terminalia cuneata. It is otherwise known as Arjun tree (Fig. 1) belonging to the Combretaceae family. The major phytoconstituents present in the bark are tannins, triterpenoid saponins (arjunic acid, arjunolic acid and arjungenin), flavonoids, gallic acid, ellagic acid and phytosterols [12], [13].

The formation of AgNPs and effect of concentration, reaction time, and pH of the reaction medium on AgNP formation were analyzed by UV–Vis spectroscopy. The stable AgNPs were further characterized by FT-IR, XRD, DLS with zeta potential and HR-TEM with EDS analysis.

The stable AgNPs were utilized as a catalyst for the reduction of carcinogenic direct yellow-12 dye using NaBH4 as a reducing agent. The catalytic activity of AgNPs was analyzed by a decrease in absorbance intensity of the dye at different time intervals using a UV–Vis spectrophotometer.

Section snippets

Preparation of T. cuneata bark extract

T. cuneata barks were collected from the Gandhigram Rural Institute campus, dried and powdered. 0.50 g of the powdered bark was extracted with 100 ml of distilled water at 80 °C for 15 min. The extract was filtered using a Whatman No. 2 filter paper. Further, the filtrate was used as a reducing source for the synthesis of AgNPs.

Synthesis of AgNPs using T. cuneata

The synthesis of AgNPs was carried out by taking different concentrations of T. cuneata extract viz., 0.50, 1.00, 1.75, 2.00 and 2.50 ml and adding those to 24.50, 24.00,

UV–Vis spectroscopy

AgNPs have optical properties and are sensitive to size, shape, concentration, agglomeration state and refractive index near the nanoparticle surface, which makes UV–Vis spectroscopy a valuable tool for identifying, characterizing and studying these AgNPs [14]. After addition of different concentrations of the bark extract of T. cuneata to Ag+ solution, a visible color change (appearance of yellow color) was noticed. This indicates the formation of AgNPs [15]. The intensity of the color

Conclusions

The study has demonstrated that AgNPs could be prepared instantly by making use of aqueous bark extract of T. cuneata. The phytoconstituents (mostly tannins and polyphenols) present in the extracts of T. cuneata act as reducing agents as well as capping agents providing stability to AgNPs as evident from the FT-IR study. The phytosynthesized AgNPs were found to have a crystalline structure with a face centered cubic geometry oriented in the (111) plane as studied by the XRD method. The

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