In this paper, a green microwave-assisted combustion approach to synthesize ZnO-NPs using zinc nitrate and Citrullus colocynthis (L.) Schrad (fruit, seed and pulp) extracts as bio-fuels is reported. The structure, optical, and colloidal properties of the synthesized ZnO-NP samples were studied. Results illustrate that the morphology and particle size of the ZnO samples are different and depend on the bio-fuel. The XRD results revealed that hexagonal wurtzite ZnO-NPs with mean particle size of 27–85 nm were produced by different bio-fuels. The optical band gap was increased from 3.25 to 3.40 eV with the decreasing of particle size. FTIR results showed some differences in the surface structures of the as-synthesized ZnO-NP samples. This led to differences in the zeta potential, hydrodynamic size, and more significantly, antioxidant activity through scavenging of 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) free radicals. In in vitro cytotoxicity studies on 3T3 cells, a dose dependent toxicity with non-toxic effect of concentration below 0.26 mg/mL was shown for ZnO-NP samples. Furthermore, the as-synthesized ZnO-NPs inhibited the growth of medically significant pathogenic gram-positive (Bacillus subtilis and Methicillin-resistant Staphylococcus aurous) and gram-negative (Peseudomonas aeruginosa and Escherichia coli) bacteria. This study provides a simple, green and efficient approach to produce ZnO nanoparticles for various applications.

In the present study, ZnO nanoparticles (NPs) were synthesized in zerumbone solution by a green approach and appraised for their ability to absorb Pb(II) ions from aqueous solution. The formation of as-synthesized NPs was established by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), and UV–visible studies. The XRD and TEM analyses revealed high purity and wurtzite hexagonal structure of ZnO NPs with a mean size of 10.01 ± 2.6 nm. Batch experiments were performed to investigate the impact of process parameters viz. Pb(II) concentration, pH of solution, adsorbent mass, solution temperature, and contact time variations on the removal efficiency of Pb(II). The adsorption isotherm data provided that the adsorption process was mainly monolayer on ZnO NPs. The adsorption process follows pseudo-second-order reaction kinetic. The maximum removal efficiencies were 93% at pH 5. Thermodynamic parameters such as enthalpy change (ΔH0), free energy change (ΔG0), and entropy change (ΔS0) were calculated; the adsorption process was spontaneous and endothermic. The good efficiency of the as-synthesized NPs makes them attractive for applications in water treatment, for removal of heavy metals from aqueous system.

Among nanoparticles used for medical applications, palladium nanoparticles (PdNPs) are among the least investigated. This study was undertaken to develop PdNPs by green synthesis using white tea (W.tea; Camellia sinensis ) extract to produce the Pd@W.tea NPs. The Pd@W.tea NPs were characterized by UV–vis spectroscopy and X-ray diffractometry, and evaluated with transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The Pd@W.tea NPs were spherical (size 6–18 nm) and contained phenols and flavonoids acquired from the W.tea extract. Pd@W.tea NPs has good 1-diphenyl-2-picrylhydrazyl (DPPH), OH, and NO-scavenging properties as well as antibacterial effects toward Staphylococcus epidermidis and Escherichia coli . MTT assay showed that Pd@W.tea NPs (IC 50 =0.006 μM) were more antiproliferative toward the human leukemia (MOLT-4) cells than the W.tea extract (IC 50 =0.894 μM), doxorubicin (IC 50 =2.133 μM), or cisplatin (IC 50 =0.013 μM), whereas they were relatively innocuous for normal human fibroblast (HDF-a) cells. The anticancer cell effects of Pd@W.tea NPs are mediated through the induction of apoptosis and G2/M cell-cycle arrest.

Green chemistry, which aims at the development of efficient methods for the synthesis of nanoparticles, is a relatively new emerging field of nanotechnology, which has economic and environment‐friendly benefits over chemical and physical processes. The present work was carried out to develop silver nanoparticles (Ag‐NPs) using the plant (Achillea millefolium or yarrow) aqueous extract as both a reducing and capping agent under the green synthesis method. Characterization of synthesized Ag‐NPs was done using IR spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction (XRD), and ultraviolet–visible (UV–vis). The UV–vis spectrum showed the maximum absorbance at around 440–470 nm, which suggested the formation of green synthesized Ag‐NPs. The morphological study demonstrated that the Ag‐NPs were spherical in shape with an average size of 22.4 ± 7.4 nm. The antimicrobial activities of Ag‐NPs against Fusarium and Aspergillus niger species of fungal and Escherichia coli species of bacteria were investigated through the disc diffusion and well‐diffusion method using their zone of inhibition. The cytotoxicity effect of Ag‐NPs on cell lines MOLT‐4 was evaluated by using MTT assay. These nanoparticles showed remarkable antimicrobial activity against bacterias and fungus in low concentration. The cytotoxicity studies showed that IC50 of green synthesized Ag‐NPs was 0.011 µm in comparison to 1.8 for Cisplatin which more active than anticancer drug for MOLT‐4 cell line. The results showed that the green synthesized Ag‐NPs are expected to have notable applications and can be potentially useful in pharmaceutical and biomedical applications.

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