**1. Introduction**

Silver is known as strong antimicrobial agen<sup>t</sup> due to its toxicity against most microorganisms including bacteria, fungi, and viruses [1]. As compared to the silver element in bulk state, silver nanoparticles (Ag NPs) exhibit unusual physico-chemical and antimicrobial properties due to their lower particle size (less than 100 nm) and higher surface area to volume ratio, which increase the proportion of high-energy surface atoms [1–3]. Because of the marvelous antimicrobial properties of Ag NPs, they have been widely utilized in numerous fields such as medicine, electronics, biotechnology, water disinfection, air treatment, and packaging [3].

Green chemistry is the use of chemistry principles to reduce or eliminate the use of toxic reagents, leading to lower amounts of undesirable residues, which in turn are harmful to human health or the environment [4,5]. Incorporation of green chemistry and nanotechnology is of grea<sup>t</sup> interest and has gained much attention over the past decade. Green synthesis of Ag NPs, using plants and their

derivative extracts as an alternative method for the conventional physical and chemical NP fabrication methods, has attracted considerable attention in recent years [1,6]. In fact, various metabolites existing in the plants including sugars, alkaloids, phenolic acids, terpenoids, polyphenols, and proteins play an important role in the bioreduction of silver ions to Ag NPs and their stabilization [7]. Several studies have been completed on green synthesis of Ag NPs using *Aloe vera* and *Pelargonium zonali* leaf extract and chitosan [8–10].

Walnut belongs to *Juglandaceae* family and has the scientific name *Juglans regia* (*J. regia*). Numerous health benefits of walnut for human have been reported, some of which are related to the existence of its main bioactive compounds including polyphenolic compounds, flavonoids, proteins, carotenoids, lipids, and alkaloids. Leaf of walnut contains malic acid, sucrose, α-tocopherol, 3- *O*-caffeoylquinic acids, and quercetin *O*-pentoside as the most abundant organic acids, disaccharide, tocopherol isomer and phenolic compounds, respectively [11–13].

The present work focuses on (i) the potential of walnut leaf extract in the fabrication of Ag NPs; (ii) Ag NPs synthesized parameter optimization using microwave irradiation to achieve Ag NPs with more desirable physico-chemical properties and (iii) an antibacterial activity assessment of the produced Ag NPs.
