Date Published: February 6, 2019
Publisher: Public Library of Science
Author(s): Vesna Antunović, Marija Ilić, Rada Baošić, Dijana Jelić, Aleksandar Lolić, Yogendra Kumar Mishra.
The porous spinel oxide nanoparticles, MnCo2O4, were synthesized by citrate gel combustion technique. Morphology, crystallinity and Co/Mn content of modified electrode was characterized and determined by Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction pattern analysis (XRD), simultaneous thermogravimetry and differential thermal analysis (TG/DTA). Nanoparticles were used for modification of glassy carbon electrode (GCE) and new sensor was applied for simultaneous determination of Pb(II) and Cd(II) ions in water samples with the linear sweep anodic stripping voltammetry (LSASV).The factors such as pH, deposition potential and deposition time are optimized. Under optimal conditions the wide linear concentration range from 0.05 to 40 μmol/dm3was obtained for Pb(II), with limit of detection (LOD) of 8.06 nmol/dm3 and two linear concentration ranges were obtained for Cd(II), from 0.05 to 1.6 μmol/dm3 and from 1.6 to 40 μmol/dm3, with calculated LOD of 7.02 nmol/dm3. The selectivity of the new sensor was investigated in the presence of interfering ions. The sensor is stable and it gave reproducible results. The new sensor was succesfully applied on determination of heavy metals in natural waters.
Spinel structures with general formula AB2O4 are well known materials in the field of catalysis, especially in the area of neutralizing the harmful components from environment, such as heavy metals [1,2]. Contamination of heavy metal ions is one of the most serious environmental issues, since heavy metal ions are not biodegradable and they accumulate in living organisms, tracking the heavy metal concentration in environment is of utmost importance. Heavy metal content is often quantified by well-known analytical methods, such as atomic absorption spectrometry (AAS) [3,4] inductively coupled plasma-mass spectrometry (ICP-MS) [5,6], inductively coupled plasma-optical emission spectrometry (ICP-OES) [7,8]and X-ray fluorescence spectrometry (XRF) . Besides numbered techniques, electrochemical methods are also often used in analysis of heavy metals, mostly due to their high sensitivity, easy operation and transferability [10–12]. Modification of electrode surface by nanostructures such as carbon nanotubes (CNT), graphene or nanoparticles is one of the strategies for surface modification. Numerous papers reported electrode modification such as Cu-CeO2 coated with multiwall carbon nanotubes for determination of guanine and adenine  or Fe3O4/RGO nanoparticles for glassy carbon electrode modification for detection of Cd(II) ions . Determination of various ions such as Zn(II), Cd(II), Pb(II), Cu(II) and Ag(I) using electrode modified with chromium oxide were reported .ZnO are often used as sensing devices in chemical, pharmaceutical and/or agricultural applications [15,16], the group of authors investigated the application of graphene nanoparticles on environmental pollutants and detection of Al(III) ions [17,18].
Porous MnCo2O4 spinel oxide was successfully synthesized by citrate-gel combustion technique. It was an interesting finding that this method of synthesis enabled simultaneous determination of two very toxic metals, lead and cadmium. The GCE-MnCo2O4NPs has shown excellent electrochemical properties such as fast current response, low detection limit and good selectivity due to unique structure. Under optimized conditions, the peak currents were increased with concentrations of metal ions linearly within two range 0.05–40 μmol/dm3 of Pb(II) and 0.05–1.6 and 1.6–40 μmol/dm3 of Cd(II). The detection limits for Pb(II) and Cd(II) were 1.67 and 0.79 μg/dm3, respectively. Additional advantages of this method for determination of cadmium and lead are easily, green and inexpensive synthesis of porous MnCo2O4 spinel and very simple fabrication of modified GC electrode. The sensor was successfully validated on real water samples, therefore, it can be easily used as portable field device for onsite control of heavy metal concentration.