This study describes the synthesis and characterization of ethylenediaminetetraacetic acid (EDTA) functionalized magnetic nanoparticles of 20 nm in size – Fe3O4@SiO2‐EDTA – which were used as a novel magnetic adsorbent for Cd(II) and Pb(II) binding in aqueous medium. These nanoparticles were obtained in two‐stage synthesis: covering by tetraethyl orthosilicate and functionalization with EDTA derivatives. Nanoparticles were characterized using TEM, FT‐IR, and XPS methods. Metal ions were detected under optimized experimental conditions using Differential Pulse Anodic Stripping Voltammetry (DPASV) and Hanging Mercury Drop Electrode (HDME) techniques. We compared the ability of Fe3O4@SiO2‐EDTA to bind cadmium and lead in concentration of 553.9 μg L−1 and 647.5 μg L−1, respectively. Obtained results show that the adsorption rate of cadmium binding was very high. The equilibrium for Fe3O4@SiO2‐EDTA‐Cd(II) was reached within 19 min while for the Fe3O4@SiO2‐EDTA‐Pb(II) was reached within 25 minutes. About 2 mg of nanoparticles was enough to bind 87.5 % Cd(II) and 54.1 % Pb(II) content. In the next step the binding capacity of Fe3O4@SiO2‐EDTA nanoparticles was determined. Only 1.265 mg of Fe3O4@SiO2‐EDTA was enough to bind 96.14 % cadmium ions while 5.080 mg of nanoparticles bound 40.83 % lead ions. This phenomenon proves that the studied nanoparticles bind Cd(II) much better than Pb(II). The cadmium ions binding capacity of Fe3O4@SiO2‐EDTA nanoparticles decreased during storage in 0.5 M KCl solution. Two days of Fe3O4@SiO2‐EDTA storage in KCl solution caused the 32 % increase in the amount of nanoparticles required to bind 60 % of cadmium while eight‐days storage caused further increase to 328 %. The performed experiment confirmed that the storage of nanoparticles in solution without any surfactants reduced their binding capacity. The best binding capacity was observed for the nanoparticles prepared directly before the electrochemical measurements.
Two-dimensional phosphorene
has attracted great interest since
its discovery as a result of its extraordinary properties. Two-dimensional
single crystals of phosphorene can be useful for electrochemical (EC)
sensing applications due to their enhanced surface-to-volume ratio.
We proposed to investigate the electrochemical performance of phosphorene
deposited directly on boron-doped diamond (BDD) electrodes. Noncovalent
interaction of phosphorene with BDD was achieved due to van der Waals
interactions. This extends the potential range of EC studies in aqueous
solutions due to the extraordinary wide range of the BDD potential
window (−2 to 2.5 V vs Ag|AgCl|3M KCl). Cyclic voltammetry
studies demonstrated irreversible electrochemical oxidation of the
phosphorene, with peaks observed at different potentials depending
on the sonication power during the liquid exfoliation of black phosphorus
(BP). This indicated the formation of polyphosphoric quasi-oxide layers
with undefined oxidation states of phosphorus. Electrochemical impedance
spectroscopy showed the second time constant for high-power sonicated
BP, which was attributed to P
x
O
y
(OH)
z
formation. The
subsequent film was responsible for limiting the charge transfer rate.
The BDD enabled the EC behavior of phosphorene to be studied at high
anodic potentials.
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