Interface-dominated galvanic replacement reactions in the Zn/Cu2+ system

Synthesis of silver nanoparticles by sonogalvanic replacement on aluminium powder in sodium polyacrylate solutions

The process of the formation of silver nanoparticles (AgNPs) via the method of galvanic replacement (GR) of Ag⁺ with aluminum powder in sodium polyacrylate (NaPA) solutions in the ultrasonic (US) field has been studied. It was observed, that the yellow colloidal solutions of stabilized AgNPs with the absorption maximum at ∼ 410 nm were obtained under the application of US power by 20 W and frequency by 20 kHz in the wide range of AgNO₃ and NaPA concentrations (0.1 - 0.5 mM and 0.5 - 5.0 g/L respectively) at 25 ⁰C. It was shown, that the GR process under US field occurs without of the significant induction period. Using the UV-vis spectroscopy the kinetics of AgNPs formation has been studied and it was observed the first order kinetics with respect to Ag⁺ ions both for the nucleation and growth processes. It was found that observable rate constants of nucleation are close for the all experimental conditions but the observable rate constants of growth decreased with increasing of initial concentration of AgNO₃. Based on the obtained kinetic data it was proposed a mechanism of the formation of AgNPs consisted of the following two main stages: 1) the nucleation with the formation of primary nanoclusters (AgNCs) on aluminum surface followed by their ablation from the surface of the sacrificial metal by ultrasound into bulk of solution; 2) the transformation of AgNCs in AgNPs via growth from the Al surface and / or agglomeration of AgNCs. Using TEM it was found that the size of obtained AgNPs does not exceed of 25 nm and slightly depends on the initial concentrations of precursors. High antimicrobial activity of obtained colloidal solutions against gram-negative and gram-positive bacteria as well as against fungi was observed.

Activation of O2 by zero-valent zinc assisted with Cu(II) for organics removal: Performance and mechanism

This study proposes a method to activate O₂ by accelerating the corrosion process for zero-valent zinc (ZVZ) with the assistance of Cu(II), promoting the consecutive production of reactive oxygen species. The mechanisms for reactive oxygen species generation are clarified with metronidazole (MTZ) as the targeted pollutant. The outcome suggests the association of Cu(Ⅱ) and ZVZ presents an apparent cooperative activity, an enhancement of 85% in MTZ removal is attained for the ZVZ/Cu(Ⅱ) system after 10 min compared to that for ZVZ. Analysis of the mechanisms involved indicates that this improvement is due to the addition of Cu(Ⅱ), which can accelerate the corrosion of ZVZ. In addition, quenching experiments and electron paramagnetic resonance (EPR) technology show that superoxide radicals (·O₂^-) result in rapid MTZ degradation. The primary component that is liable for O₂ activation and a certain amount of H₂O₂ generation is verified to be ZVZ. Moreover, Cu(I) is detected in the ZVZ/Cu(Ⅱ) system, which arises from a direct reduction pathway driven by ZVZ and an indirect reduction pathway driven by active hydrogen atoms.

Electrochemical Reduction of CO2 at Coinage Metal Nanodendrites in Aqueous Ethanolamine

Electrocatalytic reduction of CO₂ into usable chemicals is a promising path to address climate change and energy challenges. Herein, we demonstrate the synthesis of unique coinage metal (Cu, Ag, and Au) nanodendrites (NDs) via a facile galvanic replacement reaction (GRR), which can be effective electrocatalysts for the reduction of CO₂ in an ethanolamine (EA) solution. Each metal ND surface was directly grown on glassy-carbon (GC) substrates from a mixture of Zn dust and the respective precursor solution. The electrocatalytic activities of the synthesized ND surfaces were optimized for CO₂ reduction in EA solution by varying their composition. It was determined that a 0.05 mol fraction of EA exhibited the highest catalytic activity for all metal NDs. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques showed that metal-ND electrodes possessed higher current densities, lower onset potentials and lower charge-transfer resistances for CO₂ reduction than their smooth polycrystalline electrode counterparts, indicating improved CO₂ reduction catalytic activity. It was determined, using FTIR and NMR spectroscopy, that formate was produced as a result of the CO₂ reduction.