Oxygen reduction reaction features in neutral media on glassy carbon electrode functionalized by chemically prepared gold nanoparticles

Gold nanoparticles (AuNPs) were prepared by chemical route using 4 different protocols by varying reducer, stabilizing agent and solvent mixture. The obtained AuNPs were characterized by transmission electronic microscopy (TEM), UV-Visible and zeta potential measurements. From these latter surface charge densities were calculated to evidence the effect of the solvent mixture on AuNPs stability. The AuNPs were then deposited onto glassy carbon (GC) electrodes by drop-casting and the resulting deposits were characterized by cyclic voltammetry (CV) in H2SO4 and field emission gun scanning electron microscopy (FEG-SEM). The electrochemical kinetic parameters of the 4 different modified electrodes towards oxygen reduction reaction (ORR) in neutral NaCl-NaHCO3 media (0.15 M / 0.028 M, pH 7.4) were evaluated by rotating disk electrode voltammetry and subsequent Koutecky-Levich treatment. Contrary to what we previously obtained with electrodeposited AuNPs [Gotti et al., Electrochim. Acta 2014], the highest cathodic transfer coefficients were not obtained on the smallest particles, highlighting the influence of the stabilizing ligand together with the deposits morphology on the ORR kinetics

Oxygen transfer to cassava starch solutions in an aerated, well-mixed bioreactor: Experimental and mass transfer studies

Experimental and mass transfer studies of oxygen transfer to cassava starch solution in an aerated, well-mixed bioreactor of 2 L have been carried out. The volumetric mass transfer coefficient was estimated and parametric studies were performed to study the effect of process variables of stirring rate, aeration rate, concentration of starch and temperature on the volumetric mass transfer coefficient. From the experimental results, it is evident that the first two and the last variables are directly proportional to the volumetric mass transfer coefficient. However, the volumetric mass transfer coefficient is inversely proportional to the concentration of the starch. Also, the saturation dissolved oxygen concentration is greatly affected by temperature and starch solution concentration. Whereas, stirring and aeration rates have neutral impacts on saturation dissolved oxygen concentration. Simulated data generated from obtained volumetric mass transfer coefficient agrees well with the experimental data, which indicates the accuracy of the coefficient