One-pot green synthesis of Au-Ag bimetallic nanoparticles from Lawsonia inermis seed extract and its catalytic reduction of environmental polluted methyl orange and 4-nitrophenol

Highlights

• Ultrasound-assisted green synthesis of Au-Ag BNPs using aqueous fraction of Lawsonia inermis seed extract.

• BNPs were characterized by UV-vis, FT-IR, XRD, TEM, and SAED technique.

• The morphology of synthesized Au-Ag BNPs shows polygonal, spherical and irregular shaped and sizes range at 15-35 nm.

• Au-Ag nanocatalyst exhibits potential photocatalytic activity against 4-NP and MO.

Abstract

Background

Bimetallic nanoparticles (BNPs) are used in attractive applications in the medicinal, green catalyst, optics, electrochemical and so on. Apart from the catalytic activity, the chemical synthesized BNPs is less energy and environmentally highly toxic. Hence, Au-Ag BNPs prepared by the green synthesis method is suggested to be eco-friendly and have a potential catalytic reduction/degradation activity against environmentally polluted organic dyes.

Materials and method

In this present work, Ultrasound-Assisted green synthesis of Gold-Silver Bimetallic Nanoparticles (Au-Ag BNPs) was synthesized from Lawsonia inermis seed extract aqueous fraction. The effects of the extract volume, metal ions concentration, pH, and temperature were investigated to determine the optimum conditions of the synthesis of Au-Ag BNPs.

Results and discussion

UV-vis absorbance of the surface Plasmon resonance centre at 537 nm was confirmed the product of Au-Ag BNPs. FT-IR spectroscopy to determine the phytochemicals groups of the plant extract and Au-Ag BNPs. High-resolution transmission electron microscopy image of Au-Ag BNPs shows polygonal, spherical and irregular shaped with particle sizes 15-35 nm. Under UV-vis the light source, the obtained BNPs had a strong photocatalytic reduction/degradation activity against 4-nitrophenol and methyl orange dye in the presence of NaBH₄.

Introduction

Metal nanoparticles (MNPs) have occupied the centre of scientific attention due to their fascinating chemical, optical, and electronic properties [1]. The synthesis of MNPs under the environmentally benign condition is of greater importance to address growing concerns for medicinal and biotechnological applications [2]. Physico-Chemical approaches are the most popular methods for the synthesis of MNPs but most of these methods cannot keep away from the use of toxic chemicals [3]. Biological synthesis of MNPs is vouched based on the fulfilment of the necessity to develop a clean, non-toxic, and efficient method compared to other techniques [4,5]. Recently, phytochemicals based green synthesized MNPs have been used in various potential applications [6,7]. Most of the researchers focus on the several plants/plant parts extract for the synthesis of MNPs and use it for a variety of potential applications. Particularly gold, silver, platinum, and palladium NPs are widely used in our daily life using materials like cosmetic products, toothpaste, pharmacological carrier substances, paints, clothes, etc. The MNPs is also used for medical and pharmaceutical products, catalysis, sensors, electronics, and environmental remediation [8,9].

Comparing both monometallic and bimetallic NPs (BNPs), the BNPs have great attention due to bi-functional properties generated from each metal constituent or enhanced properties or even new properties with high potential applications [10]. Specifically, the Au-Ag BNPs have drawn attention due to their unique properties [11,12]. The BNPs used as nanocatalyst in the removal of dyes and other organic pollutants from the environment and wastewater is gaining significant interest [13]. The stability of the NPs has more important and also should not have any agglomeration during their formation. To achieve greater stability, maximum yield, and aggregation of particles with controlled size, it is imperative to optimize the different parameters used in the green synthesis of NPs [14]. Green synthesis of Au-Ag BNPs using various plants such as Chinese wolfberry [11], Stigmaphyllon ovatum [15], Trapa [16], and Guazuma ulmifolia [17] extract has been previously reported.

Lawsonia inermis (L.inermis) commonly called henna (family: Lythraceae) is world widely used over the centuries for medical and cosmetic purposes. Henna extracts exhibit various pharmaceutical properties such as antioxidant, antidiabetic, anticancer, antimicrobial, hypoglycemic, and hepatoprotective activity [18,19]. To the best of our knowledge, this is the first investigation to develop a polygonal, spherical and irregular shaped Au-Ag BNPs was synthesized using the aqueous fraction of L.inermis seed extract (AF-LSE) by the ultrasound-assisted method. We have studied the optimum conditions on the effects of various reaction parameters on the green synthesis of Au-Ag BNPs. Further, the synthesized Au-Ag BNPs were characterized by various spectral instrumental techniques. Moreover, we had evaluated the efficiency of prepared Au-Ag BNPs using a green catalyst in the reduction/degradation reaction of 4-nitrophenol (4-NP) and methyl orange (MO) dye polluting the environment in the presence of NaBH₄ using UV-Vis light source.