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).

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The changes of magnetic properties in magnetite nanoparticles during two different stabilization processes were investigated. Magnetic nanoparticles (MNPs) were obtained by electrochemical synthesis from two kinds of salts: (CH3)4NCl and NaCl. After that, two methods-steric and electrostatic-were used to stabilize MNPs with oleic acid (OA) and sodium hydroxide (NaOH), respectively. As a consequence, aqueous and organic dispersions were obtained after surface modification. The coated nanoparticles were characterized by TEM, zeta potential, thermogravimetry analysis (TGA), cyclic voltammetry (CV), magnetization measurements, and infrared and Mössbauer spectroscopy. The results showed that the particles were between 8 and 13 nm in size. In addition, the MNPs were coated with negative charge layers from NaOH by physisorption and coated with carboxylate groups from OA by the chemisorption process, and hence, they exhibited different reactivity and behavior depending on the nature of the electrolyte used in the electrochemical synthesis. Furthermore, the uncoated and coated MNPs had a narrow size distribution. Additionally, the saturation magnetization values showed dependence on the magnetite synthesis conditions and surface modifiers.

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The formation of magnetite nanoparticles (Fe 3 O 4 -NPs) by electro-oxidation process was studied by in situ and ex situ techniques in chloride electrolytes with and without ethanol. The electrochemical synthesis is characterized by the application of a current disturbance that promotes the oxidation of a low carbon steel electrode in solution to an oxidized state (Fe 2+ ) which is subsequently transformed into magnetite by reactions in solution. The electrochemical synthesis results in a final product of pure and crystalline magnetite nanoparticles (20-40 nm). The presence of ethanol in the electrolyte does not modify the mechanism of magnetite formation but it extends the lifetime of some precursors during electrosynthesis and promotes the formation of low size magnetite nanoparticles. In situ Raman spectroscopy measurements were used in order to identify the precursor species formed prior to the formation of magnetite nanoparticles during the electro-oxidation of the low carbon steel in electrolyte containing chloride and ethanol. It was corroborated that the electrochemical synthesis of magnetite follows the sequence: Fe(OH) 2 → GR(Cl − ) → γ-FeOOH → Fe 3 O 4 , with a redox interaction between Fe(OH) 2 and γ-FeOOH precursors.

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