# Synthesis of Au, Ag, and Au–Ag Bimetallic Nanoparticles Using Pulicaria undulata Extract and Their Catalytic Activity for the Reduction of 4-Nitrophenol

## TL;DR

This paper describes a green method to synthesize gold, silver, and bimetallic nanoparticles using a plant extract and shows their catalytic activity in reducing 4-nitrophenol.

## Contribution

A novel green synthesis method for Au, Ag, and Au–Ag bimetallic nanoparticles using Pulicaria undulata extract is presented.

## Key findings

- Low extract concentration produced irregular-shaped nanoparticles, while high concentration yielded spherical ones.
- Bimetallic Au–Ag alloy nanoparticles showed the highest catalytic activity for 4-nitrophenol reduction.
- Nanoparticle morphology and composition significantly influenced catalytic performance.

## Abstract

Plant extract of Pulicaria undulata (L.) was used as both reducing agent and stabilizing ligand for the rapid and green synthesis of gold (Au), silver (Ag), and gold–silver (Au–Ag) bimetallic (phase segregated/alloy) nanoparticles (NPs). These nanoparticles with different morphologies were prepared in two hours by stirring corresponding metal precursors in the aqueous solution of the plant extracts at ambient temperature. To infer the role of concentration of plant extract on the composition and morphology of NPs, we designed two different sets of experiments, namely (i) low concentration (LC) and (ii) high concentration (HC) of plant extract. In the case of using low concentration of the plant extract, irregular shaped Au, Ag, or phase segregated Au–Ag bimetallic NPs were obtained, whereas the use of higher concentrations of the plant extract resulted in the formation of spherical Au, Ag, and Au–Ag alloy NPs. The as-prepared Au, Ag, and Au–Ag bimetallic NPs showed morphology and composition dependent catalytic activity for the reduction of 4-nitrophenol (4-NPh) to 4-aminophenol (4-APh) in the presence of NaBH4. The bimetallic Au–Ag alloy NPs showed the highest catalytic activity compared to all other NPs.