Synthetic Tuning of Co(II)-Doped Silica Nanoarchitecture Towards Electrochemical Sensing Ability

The present work introduces both synthesis of silica nanoparticles doped with Co(II) ions by means of differently modified microemulsion water-in-oil (w/o) and Stöber techniques and characterization of the hybrid nanoparticles (Co(II)@SiO(2)) by TEM, DLS, XRD, ICP-EOS, SAXS, UV-Vis, and UV-Vis/DR spectroscopy and electrochemical methods. The results reveal the lack of nanocrystalline dopants inside the hybrid nanoparticles, as well as no ligands, when Co(II) ions are added to the synthetic mixtures as Co(II)(bpy)(3) complexes, thus pointing to coordination of Co(II) ions with Si-O(-) groups as main driving force of the doping. The UV-Vis/DR spectra of Co(II)@SiO(2) in the range of d-d transitions indicate that Stöber synthesis in greater extent than the w/o one stabilizes tetrahedral Co(II) ions versus the octahedral ions. Both cobalt content and homogeneity of the Co(II) distribution within Co(II)@SiO(2) are greatly influenced by the synthetic technique. The electrochemical behavior of Co(II)@SiO(2) is manifested by one oxidation and two reduction steps, which provide the basis for electrochemical response on glyphosate and HP(O)(OEt)(2) with the LOD = 0.1 μM and the linearity within 0.1–80 μM. The Stöber Co(II)@SiO(2) are able to discriminate glyphosate from HP(O)(OEt)(2), while the w/o nanoparticles are more efficient but nonselective sensors on the toxicants.