No abstract

Silver nanoparticles (AgNPs) were synthesized by chemical reduction of Ag + ions (from silver nitrate AgNO 3 ), using aqueous or ethanolic Aloe vera extracts as reducing, stabilizing, and size control agent. The nanoparticles' sizes were between 2 and 7 nm for ethanolic extract and between 3 and 14 nm for aqueous extract, as measured by High-Resolution Transmission Electron Microscope (HRTEM). The antibacterial activity against a mesophilic microorganism, Kocuria varians, a Gram-positive coccus, was measured by counting bacterial colonies in agar plate for both extracts. We found that 4% effective concentration is the lowest concentration that completely inhibited visible growth. Mercury removal was investigated by Atomic Absorption Spectroscopy (AAS) measurements, where it was shown that it is not necessary to use high concentrations of nanoparticles for effective removal of mercury inasmuch as with a 20% V/V concentration of both extracts; the Hg(II) removal percentage was above 95%. These results show that the mercury remaining unremoved from the different essays is below the level allowed by World Health Organization (WHO) and the Environmental Protection Agency (EPA).

No abstract

In this study, magnetic nanoparticles of magnetite were prepared by an eco-friendly method using aqueous leaf extracts of Aloe vera and Kalanchoe daigremontiana. These vegetal extracts have suitable characteristics such as high availability, low cost, and serve as good colloidal stabilizers. Synthetized products were characterized by Transmission Electron Microscopy (TEM), Room Temperature Mossbauer Spectroscopy (RT-MS), and their potential use as adsorbents for Hg (II) removal in natural waters was evaluated by Atomic Absorption Spectroscopy (AAS). Size distribution and morphology of the products obtained by TEM show spherical nanoparticles composites, with sizes between 3 and 10 nm for both extracts. Mossbauer spectra are consistent with superparamagnetic particles for both samples. Moreover, particles from both extracts showed mercury removal efficiencies above 75%.

The synthesis of silver nanoparticles (AgNPs) has been increasingly extended due to its potential applications in fields such as optics, environmental, catalysis, electronics and as an antibacterial agent. In this way it is necessary to develop methods framed in green chemistry to achieve greater stability over time of the AgNPs. The present work aims to show the synthesis of AgNPs using Kalanchoe daigremontiana leaf extract, as a reducing and stabilizing agent. UV–vis and transmission electron microscopy (TEM) were used to characterize AgNPs obtained. The absorbance of solutions was measured, evidencing of the formation of AgNPs due to the existence of plasmon resonance at that λmax ∼ 417 nm. The size distribution and morphology of the AgNPs by TEM shows stable, spherical and nomodispersar nanoparticles with a size between 4 and 12 nm. The measurements were carried out immediately after the synthesis procedure, then the AgNPs solutions were stored at room temperature and darkness by 27 months and it could be corroborated the stabilizing capacity of Kalanchoe daigremontiana leaf extract, since the λmax and the size of particle did not vary significatively in this period of time.