Green and chemical synthesis of zinc oxide nanoparticles and size evaluation by UV–vis spectroscopy

Extremely small nanomaterials with dimensions roughly less than 100 nanometers (nm), can demonstrate atom-like behaviors resulting from higher surface energy because of their large surface area and broad band gap between valence and conduction band when nanomaterials are divided into near atomic size.1 ZnO nanopowders are basic metal oxide particles with interesting properties and wide applications in several fields. We chose ZnO–NPs as they are promising candidates for various applications such as chemical sensors,2 nano generators,3 catalysis,4 anti-microbial and anti-corrosive5 and piezoelectric devices.6 ZnO nanoparticles, based on its unique properties such as: low toxicity, high selectivity and biocompatibility, have shown that they are inherently selective cytotoxicity against carcinogenic cells compared with other nanoparticles. Therefore, they can be regarded as a promising anti-cancer agent. Zinc, as the co–factor of more than hundreds of enzymes, plays an important role in cellular processes, including: DNA replication, DNA repair, cell cycle progression and it has the exclusive ability to induce oxidative stress in cancer cells, as one of the mechanisms of its cytotoxicity towards tumor cells. Thus, the potential use of nano ZnO in biomedicine is important in the medical societies.7 ZnO nanomaterials possesses exclusive semiconducting, optical, and piezoelectric properties hence has been examined for biomedicine applications, such as biomedical imaging includes fluorescence, magnetic resonance, tomography, drug delivery, and biosensing of a wide range of molecules.8 ZnO due to a wide band gap semiconductor and high exciton binding energy is an efficient excitonic blue and near-UV emitter so, owing to its stability and inherent capability to absorb UV irradiation, ZnO nanoparticles widely used in sunscreens.8 According to the literatures, many other different synthesis methods have been developed for ZnO nanoparticles including mechanochemical processing and selfassembling,9 microwave method,10 direct precipitation,11 reversed micelle,12 RF plasma synthesis.13 Usually these methods have disadvantages, such as, they do not have a uniform distribution of particle size or particle size is coarse. To resolve this problem, according to a new research which was offered on the basis of colloid chemistry, there was a surface coating surrounding the particles. In these processes, some materials added to the solution, which affects the surface tension and prevents it from agglomeration. Plant extracts contain factors that inhibit the aggregation of particles and result in produced smaller–sized particles. The use of plants for synthesis of nanoparticles due to the use of a nontoxic agent is one of the environmentally friendly methods. Green synthesis of ZnO–NPs is an increasingly interesting topic.