Characterization of chromium (III)-glycine complexes in an acidic medium by UV-visible spectrophotometry and capillary electrophoresis

Ag NPs-coated polyurethane sponge as a water filter for removal of toxic metal ions at high concentrations

Heavy metal ions are toxic to humans, plants, and marine life, making it crucial to eliminate them from water. This study reports the development of a new nanocomposite material (Alg@Ag/PU) that involves modifying silver nanoparticles (Ag NPs) with alginate (Alg) and coating them onto a polyurethane sponge (PU) for removing heavy metal ions. The successful coating of Alg@Ag NPs onto PU due to their strong chemical binding was confirmed by morphology and size characterization. Batch experiments were conducted to evaluate the removal efficiency of heavy metal ions at high concentrations (∼100 mg/L). The maximum adsorption amount was achieved within 6 h, and the highest removal efficiency was obtained at pH values between 6 and 7. Furthermore, the Alg@Ag/PU nanocomposite demonstrated excellent recyclability for metal ion removal even after 5 cycles. In summary, this work developed a simple and cost-effective method for producing an environmentally-friendly nanocomposite material for the efficient removal of heavy metal ions.

Nuclear magnetic resonance relaxometry to monitor chromium (VI) reduction by hydrogen peroxide, ascorbic acid, and aluminum powder

The reduction of K₂ Cr₂ O₇ solutions by H₂ O₂ was studied by nuclear magnetic resonance (NMR) relaxometry and UV-vis spectroscopy in HCl/KCl buffer (pH 2), NaCl/glycine/HCl buffer (pH 3), and sodium acetate/acetic acid buffer (pH 4). Because of Cr(III) paramagnetism, 1/T₁ and 1/T₂ of the solutions increase during the reduction of diamagnetic Cr(VI). This increase is proportional to the produced Cr(III) concentration. Using different initial H₂ O₂ concentrations, partially reduced Cr(VI) samples were prepared and studied by T₁ and T₂ relaxometry and by UV-vis spectroscopy. The correlation between the relaxation rates and the concentration of Cr(VI) remaining in the sample, measured by spectroscopy, was excellent. It was possible, thanks to the measurement of T₂ , to study the kinetics of the reduction of K₂ Cr₂ O₇ by H₂ O₂ in the pH 3 and pH 4 buffers. The reduction of Cr(VI) by ascorbic acid was successfully monitored by NMR relaxometry in the pH 2 buffer. The presence of complexing molecules/ions was shown to drastically influence the nuclear magnetic relaxation dispersion profiles of reduced K₂ Cr₂ O₇ solutions: Both relaxation rates are divided by ~5 when citrate or acetate ions are present and by ~3 in the presence of ascorbic acid. Therefore, the comparison of relaxation results obtained in different reaction mixtures must be done carefully. When all the solutions are set to pH 0, which prevents any complexation, the longitudinal and transverse relaxation rates of all samples become comparable. Finally, as a proof of concept for a turbid solution, the kinetics of the reduction of a K₂ Cr₂ O₇ solution by aluminum powder in the pH 2 buffer was successfully monitored.