Cu and Ag nanostructures electrodeposited onto carbon substrates for glyphosate quantification

M. DEL C. AGUIRRE; S. E. URRETA; P. G. BERCOFF; C. GOMEZ

Buenos Aires

Encuentro; NANO-2019 (XIX Encuentro de superficies y materiales nanoestructurados); 2019

Cu and Ag nanostructuresare prepared forelectrochemical detection of awidely-used herbicide, such as glyphosate (Glyp). In the case of Cu0nanostructures,they are electrocrystallizedonto glassycarbon (GC) surface, at a potentialof -0.6V. It is found that the depositionprocess involves a3D progressive nucleation with a diffusion-controlled growth.At short deposition times, round copper nanoparticles(~16 nm), forming islands develops on the substratesurface. At longer times, agglomeratesof about 200 nm, consisting of round andfaceted nanoparticles near 16-50 nm in size, evidencing that nucleation isprogressive during the deposition process.For Ag0nanostructuresobtained at potentials of+0.2 V and  +0.3Vonto graphitesurface (G), a3D instantaneous nucleation mechanism and diffusion-controlled growth is determinedfrom the current-time transients. The morphology of these nanoparticles(dendriticand cubic, of ~100 nm)isconsistent with themechanisms proposed.Differentelectro-active systems are formed by combining thenanostructuressynthesized inbackground electrolytes of pH 6, containing the metallic ions (Cu2+or Ag+). In these systems (Cu2+-Cu/GC or Ag+-Ag/G), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) are appliedtoGlyp determination. Interestingly, during the DPV theelectrode is regenerated in situ in each determination cycle.A remarkablephenomenon is detected with Cu/GC electrode immersed in presence of ions Cu2+,when glyphosate is added.For an oxidation potential of -0.015 V (vs Ag/AgCl) of the Cu0/Cu+ couple, the current peak issensitively affected by glyphosate concentration. This effectis related to theformation of a barrier of adsorbed glyphosate molecules onto copper surface,which prevents Cu2+ ions diffusion towards the electrode´s surface.TheCu2+-Cu/GC electroactive systemallowed avery low detection limit (LOD)for Glypof (0.186 ± 0.004) μM (31ppb). Glyp determinations with the Cu2+-Cu/GCsysteminpresence of cationicinterferers,and in drinking water exhibited similarsensitivity and stability that found for the pure system.DPVwas alsoapplied to Ag/G electrodein order to quantifyGlypinabsence and in presence of Ag+ ions ina 0.1M KNO3 solution of pH 6.Optimalherbicide detection properties are found at +0.45 V(vsAg/AgCl)in connection with the electroactive Ag+-Ag/Gsystem, generated in situ.This sensor yielded a detection limit (LOD) of (0.52 ±0.02)mM (90 ppb).