The application of nanoscale materials and structures, usually ranging from 1 to 100 nanometers (nm), is an emerging area of nanoscience and nanotechnology. Nanomaterials may provide solu- tions to technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine, and water treatment
[1,2]. This increasing demand must be accompanied by “green” synthesis methods. In the global efforts to reduce generated hazardous waste, “green” chemistry and chemical processes are progressively integrating with modern developments in science and industry. Implementation of these sustainable processes should adopt the 12 fundamental principles of green chemistry [3–7]. These principles are geared to guide in minimizing the use of unsafe products and maximizing the efficiency of chemical processes. Hence, any synthetic route or chemical process should address these principles by using environmentally benign solvents and nontoxic chemicals [3]. Nanomaterials often show unique and considerably changed physical, chemical and biological properties compared to their macro scaled counterparts [8]. Synthesis of noble metal nanoparticles for applications such as catalysis, electronics, optics, environmental, and biotechnology is an area of constant interest [9–15]. Gold, silver, and copper have been used mostly for the synthesis of stable dispersions of nanoparticles, which are useful in areas such as photography, catalysis, biological labeling, photonics, optoelectronics and surface-enhanced Raman scattering (SERS) detection [16,17].
Additionally, metal nanoparticles have a surface plasmon resonance absorption in the UV–Visible region. The surface plasmon band arises from the coherent existence of free electrons in the conduction band due to the small particle size [18,19]. The band shift is dependent on the particle size, chemical surrounding, adsorbed species on the surface, and dielectric constant [20]. A unique characteristic of these synthesized metal particles is that a change in the absorbance or wavelength gives a measure of the particle size, shape, and interparticle properties [20,21]. Moreover, functionalized, biocompa- tible and inert nanomaterials have potential applications in cancer diagnosis and therapy [22–26]. The target delivery of anticancer drugs has been done using nanomaterials [22]. With the use of fluorescent and magnetic nanocrystals, the detection and monitoring of tumor biomakers have been demonstrated [24,25]. Generally, metal nanoparticles can be prepared and stabilized by physical and chemical methods; the chemical approach, such as chemical reduction, electrochemical techniques, and photochemical reduction is most widely used [27,28]. Studies have shown that the size, morphology, stability and properties (chemical and physical) of the metal nanoparticles are strongly influenced by the experimental conditions, the kinetics of interaction of metal ions with reducing agents, and adsorption processes of stabilizing agent with metal nanoparticles [21,22]. Hence, the design of a synthesis method in which the size, morphology, stability and properties are controlled has become a major field of interest [29].