## 1 Introduction  
Within the past few years, there have been significant advances in nanotechnology, with various developed methodologies that are being used to synthesize nanoparticles of specific sizes and shapes that serve specific purposes in extremely varied application domains [1]. Considering the development of nanomaterials, metal oxide nanoparticles have shown great promise for use in the biomedical field, particularly for antibacterial, anticancer drug, gene, cell imaging, and bio-sensing applications [2]. One of the most widely studied metal oxides is zinc oxide. This compound is among the most versatile, favorable, and multi-functional inorganic compounds, showing wide application in numerous fields [3, 4]. Zinc oxide nanostructures, available in various forms such as quantum dots,wires, rods, tubes, spheres, belts, and flowers, exhibit a wide range of properties, including semiconductor characteristics with a large band gap, luminescence, photoconductivity, antibacterial activity, high reflectivity in the visible spectrum, strong ultraviolet absorption, catalytic activity, and amphoteric properties. The antimicrobial properties of zinc oxide have been studied at both micro- and nanoscale levels. As the particle size decreases, the electrical, optical, and chemical properties of zinc oxide change, enabling new applications [5]. Zinc oxide nanoparticles demonstrate enhanced antimicrobial properties, particularly at the nanoscale, where they interact with bacterial surfaces and/or cores, leading to various bactericidal mechanisms [6]. Compared to other nanoparticles used to inhibit microorganism growth, zinc oxide offers significant advantages due to its superior photocatalytic efficiency, biocompatibility (better than that of titanium dioxide), and improved selectivity, durability, and heat resistance. These attributes make zinc oxide effective against a broad spectrum of microorganisms, including _Staphylococcus aureus_, _Escherichia coli_, and _Candida albicans_[7]. The antibacterial activity of ZnO depends on both intrinsic and extrinsic factors. Intrinsic factors include size, morphology, specific surface area, crystallinity, and nanoparticle concentration. External factors include the chemical balance of the solution (concentration, pH, chemical composition, temperature) [5]. The intrinsic factors can be controlled by varying the synthesis conditions and thus the antibacterial properties. Various methods for synthesizing zinc oxide nanoparticles are documented in the literature and can be categorized into three main types: chemical, biological, and physical methods. Chemical synthesis can be further divided into liquid-phase and gas-phase synthesis. Liquid-phase synthesis methods include precipitation [8], coprecipitation [9], sol-gel processing [10], water-oil microemulsions [11], hydrothermal synthesis [12], and solvothermal [13], sonochemical [14], and polyol synthesis [15]. Among the various synthesis methods reported for ZnO, the hydrothermal method does not require the use of organic solvents (possibly toxic in contact with living tissue) or additional processing of the product, which makes it a simple and environmentally friendly technique. Synthesis occurs in an autoclave, where the mixture of raw materials is gradually heated to the desired temperature and left for several days. As a result of heating followed by cooling, nucleation centers are initially formed once the ZnO concentration reaches supersaturation because of the dehydration of Zn(OH)\({}_{4}\)\({}^{-2}\), from which crystals then grow [16]. This process has numerous advantages, including low working temperatures and the ability to obtain various morphologies and crystal dimensions. However, its main disadvantage is the prolonged time required for the completion of chemical reactions [17; 18]. This limitation led to the development of a series of new unconventional, hybrid hydrothermal synthesis methods, among which is the hydrothermal method in a microwave field.