Cu and Ag nanostructures electrodeposited onto carbon substrates for glyphosate quantification

AGUIRRE, MARÍA DEL CARMEN; URRETA, SILVIA E.; BERCOFF, PAULA G.; GOMEZ, CESAR G.

Encuentro; XIX Encuentro de superficies y materiales nanoestructurados - NANO2019; 2019

Cu and Ag nanostructures are prepared for electrochemical detection of a widely-usedherbicide, such as glyphosate (Glyp). In the case of Cu0 nanostructures, they areelectrocrystallized onto glassy carbon (GC) surface, at a potential of -0.6 V. It is found that thedeposition process involves a 3D progressive nucleation with a diffusion-controlled growth.At short deposition times, round copper nanoparticles (16 nm), forming islands develops onthe substrate surface. At longer times, agglomerates of about 200 nm, consisting of round andfaceted nanoparticles near 16-50 nm in size, evidencing that nucleation is progressive duringthe deposition process. For Ag0 nanostructures obtained at potentials of +0.2 V and +0.3 Vonto graphite surface (G), a 3D instantaneous nucleation mechanism and diffusion-controlledgrowth is determined from the current-time transients. The morphology of these nanoparticles(dendritic and cubic, of 100 nm) is consistent with the mechanisms proposed.Different electro-active systems are formed by combining the nanostructuressynthesized in background electrolytes of pH 6, containing the metallic ions (Cu2+ or Ag+). Inthese systems (Cu2+-Cu/GC or Ag+- Ag/G), cyclic voltammetry (CV) and differential pulsevoltammetry (DPV) are applied to Glyp determination. Interestingly, during the DPV theelectrode is regenerated in situ in each determination cycle. A remarkable phenomenon isdetected 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 effect is related to the formation of abarrier of adsorbed glyphosate molecules onto copper surface, which prevents Cu2+ ionsdiffusion towards the electrode's surface. The Cu2+-Cu/GC electroactive system allowed a verylow detection limit (LOD) for Glyp of (0.186 ± 0.004) μM (31ppb). Glyp determinations withthe Cu2+-Cu/GC system in presence of cationic interferers, and in drinking water exhibitedsimilar sensitivity and stability that found for the pure system.DPV was also applied to Ag/G electrode in order to quantify Glyp in absence and inpresence of Ag+ ions in a 0.1 M KNO3 solution of pH 6. Optimal herbicide detection propertiesare found at +0.45 V ( vs Ag/AgCl) in connection with the electroactive Ag+-Ag/G system,generated in situ. This sensor yielded a detection limit (LOD) of (0.52 0.02) M (90 ppb)