Green Synthesis of Highly Dispersed Zinc Oxide Nanoparticles Supported on Silica Gel Matrix by Daphne oleoides Extract and their Antibacterial Activity

BACKGROUND: ZnO nanoparticles (ZnO-NPs) are one of the most popular metal oxide nanoparticles, which exhibit significant antibacterial properties against various pathogens. Among nanoparticle synthesis methods, the green synthesis using plant extract is considered as an eco-friendly and cost-effective method for ZnO-NPs production, compared to the chemical procedures. BACKGROUND: This study aimed to evaluate the green synthesis of ZnO-NPs loaded on silica gel matrix (ZnO/SG nanocomposite) by using methanol leaf extract of Daphne oleoides as a new extract and a cost-effective method. Furthermore, the antibacterial activity of the synthesized structure is evaluated against some pathogenic bacteria and the results are compared with unsupported ZnO-NPs. MATERIALS AND METHODS: For ZnO/SG nanocomposite synthesis, a solution of Zn (NO(3))(2) was stirred with silica gel. Then the Daphne oleoides extract was added and stirred continuously until white precipitate was formed. The precipitate was heated at 200 ˚C for calcination, and ZnO/SG nanocomposite was obtained. The phytochemical constituents of leaf extract were then analyzed by gas chromatography–mass spectrometry (GC-MS). Afterwards, the structure of ZnO-NPs on SiO(2) matrix (ZnO/SG nanocomposite) was characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), and Fourier transform infrared spectroscopy (FTIR). Surface area measurement was also determined by Brunauer-Emmett-Teller (BET) techniques. Furthermore, the antibacterial activity of ZnO/SG nanocomposites against pathogenic bacteria was evaluated using agar-based disk diffusion method standardized by clinical and laboratory guidelines. RESULTS: The leaf extract of Daphne oleoides encompassed five major polyphenolic components. The results of the nanocomposite structure showed that ZnO-NPs with an average particle size of 38 nm were obtained and stabilized on the silica gel matrix. The BET surface area measurement of ZnO/SG nanocomposite was compared with unsupported ZnO-NPs, and the results indicated that the surface area of ZnO/SG nanocomposite was increased. Furthermore, the structure showed more powerful antibacterial activity against pathogens than unsupported ZnO-NPs. CONCLUSIONS: Green synthesis of ZnO-NPs supported on the silica gel matrix with the leaf extract of Daphne oleoides is a benign and effective procedure for ZnO/SG nanocomposite synthesis. Embedding ZnO-NPs in silica gel matrix prevents the agglomeration of nanoparticles and prepare homodispersed nanoparticles. This structure revealed great antibacterial activity against many pathogens.