The cobalt nanoparticles (NPs-Co) were synthesized and applied in the removal of Cr(VI). The obtained nanomaterials presented magnetic properties and were characterized by the techniques of Transmission Electron Microscopy and X-ray diffraction. The NPs-Co, with a diameter of less than 50 nm, had a composition based on metallic cobalt and cobalt oxide. The NPs-Co were applied in the removal of Cr(VI) being evaluated different parameters such as time of equilibrium, initial pH, dose of NPs-Co, concentration of Cr(VI), and system temperature. The removal of Cr(VI) was favored at lower pH values, being about 100% at pH 2.0. With the increase of Cr(VI) concentration from 40.0 to 300.0 mg L-1 the removal decreased from 80 to 15%. The NPs-Co dose promoted an increase in removal reaching 90% at a dose of 1.0 g L-1. The removal process was spontaneous and endothermic, and the Langmuir isotherm model fit better to experimental data. The maximum removal capacity was approximately 70.0 mg g-1. The removal kinetics followed the pseudo-second order model. The mechanism of Cr(VI) removal occurred through adsorption by electrostatic interactions between CrO42- anion and Co-NPs, followed by reduction of Cr(VI) to Cr(III) and, lastly, co-precipitation of Cr(III) as Cr(OH)3 on the NPs-Co.

This study investigated the reductive degradation of acetamiprid (5 mg L-1) in aqueous medium (at pH 2.0) induced by zero-valent iron (50 mg). The process was monitored using high-performance liquid chromatography (HPLC) to determine the degradation rate as a function of reaction time, and direct infusion electrospray ionization mass spectrometry (DI-ESI-MS) to search for (and potentially characterize) any possible byproducts formed during degradation. The results obtained via HPLC showed that after 60 min, the degradation of the substrate reached nearly 100% in an acidic medium, whereas the mineralization rate (as determined by total organic carbon measurements) was as low as 3%. Data obtained by DI-ESI-MS showed that byproducts were formed mainly by insertions of hydrogen atoms into the nitrile, imine, and pyridine ring moieties, in addition to the observation of chlorine substitution by hydrogen replacement (hydrodechlorination) reactions.