Cu and Ag nanostructures electrodeposited onto carbon substrates for glyphosate quantification

AGUIRRE MARIA DEL CARMEN; GOMEZ CÉSAR G; URRETA SILVIA E; BERCOFF PAULA G

Buenos Aires

Encuentro; XIX Encuentro de Superficies y Materiales Nanoestructurados; 2019

Nanostructures of Cu and Ag are prepared for electrochemical detection of a widely-used herbicide such as glyphosate (Glyp). In the case of Cu0 nanostructures, they are electrocrystallized onto the surface of glassy carbon (GC) using a potential near - 0.6 V. It is found that the deposition process involves a 3D progressive nucleation process while the growth is diffusion-controlled. At short times of deposition, round copper nanoparticles (16 nm) are obtained, forming islands on substrate surface. However, as a longer deposition time is used, agglomerates about 200 nm containing nanoparticles between 16 and 50 nm form, evidencing that under these conditions nucleation is progressive. For Ag0 nanostructures obtained at a potential of +0.2 V and +0.3 V onto graphite (G), a 3D instantaneous nucleation mechanism and diffusion-controlled growth is determined from the current-time transients. The dendritic and cubic morphologies of the synthesized nanoparticles (100 nm) are consistent with the mechanisms proposed for long deposition times.Different electro-active systems are formed by combining the nanostructures synthesized in background electrolytes (Cu2+ or Ag+) at pH 6. In these systems (Cu2+- Cu/GC or Ag+- Ag/G), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) are applied to Glyp determination. Interestingly, during the DPV the electrode is regenerated in situ in each determination cycle. A remarkable phenomenon 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 is sensitively affected by glyphosate concentration. This effect is related to the formation of a barrier of adsorbed glyphosate molecules onto substrate surface, which prevents Cu2+ ions diffusion towards the electrode´s surface. The Cu2+-Cu/GC electroactive system allowed a very low detection limit (LOD) for Glyp of (0.186 ± 0.004) μM (31ppb). Glyp determinations in drinking water with cationic interferers, performed with the Cu2+-Cu/GC system, exhibited similar sensitivity and stability than those found for pure system.DPV was also applied to Ag/G electrode in order to quantify Glyp in absence and in presence of Ag+ ions in a 0.1 M KNO3 solution of pH 6. Optimal herbicide detection properties are 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).