Sonochemical Synthesis of Cu@Pt Bimetallic Nanoparticles

Precipitation of Pt, Pd, Rh, and Ru Nanoparticles with Non-Precious Metals from Model and Real Multicomponent Solutions

This article presents studies on the precipitation of Pt, Pd, Rh, and Ru nanoparticles (NPs) from model and real multicomponent solutions using sodium borohydride, ascorbic acid, sodium formate, and formic acid as reducing agents and polyvinylpyrrolidone as a stabilizing agent. As was expected, apart from PGMs, non-precious metals were coprecipitated. The influence of the addition of non-precious metal ions into the feed solution on the precipitation yield and catalytic properties of the obtained precipitates was studied. A strong reducing agent, NaBH₄ precipitates Pt, Pd, Rh, Fe and Cu NPs in most cases with an efficiency greater than 80% from three- and four-component model solutions. The morphology of the PGMs nanoparticles was analyzed via SEM-EDS and TEM. The size of a single nanoparticle of each precipitated metal was not larger than 5 nm. The catalytic properties of the obtained nanomaterials were confirmed via the reaction of the reduction of 4-nitrophenol (NPh) to 4-aminophenol (NAf). Nanocatalysts containing Pt/Pd/Fe NPs obtained from a real solution (produced as a result of the leaching of spent automotive catalysts) showed high catalytic activity (86% NPh conversion after 30 min of reaction at pH 11 with 3 mg of the nanocatalyst).

Radiolysis-Assisted Direct Growth of Gold-Based Electrocatalysts for Glycerol Oxidation

The electrocatalytic oxidation of glycerol by metal electrocatalysts is an effective method of low-energy-input hydrogen production in membrane reactors in alkaline conditions. The aim of the present study is to examine the proof of concept for the gamma-radiolysis-assisted direct growth of monometallic gold and bimetallic gold-silver nanostructured particles. We revised the gamma radiolysis procedure to generate free-standing Au and Au-Ag nano- and micro-structured particles onto a gas diffusion electrode by the immersion of the substrate in the reaction mixture. The metal particles were synthesized by radiolysis on a flat carbon paper in the presence of capping agents. We have integrated different methods (SEM, EDX, XPS, XRD, ICP-OES, CV, and EIS) to examine in detail the as-synthesized materials and interrogate their electrocatalytic efficiency for glycerol oxidation under baseline conditions to establish a structure-performance relationship. The developed strategy can be easily extended to the synthesis by radiolysis of other types of ready-to-use metal electrocatalysts as advanced electrode materials for heterogeneous catalysis.

The Reducing Agents in Sonochemical Reactions without Any Additives

It has been experimentally reported that not only oxidation reactions but also reduction reactions occur in aqueous solutions under ultrasound without any additives. According to the numerical simulations of chemical reactions inside an air or argon bubble in water without any additives under ultrasound, reducing agents produced from the bubbles are H, H2, HO2 (which becomes superoxide anion (O2-) in liquid water), NO, and HNO2 (which becomes NO2- in liquid water). In addition, H2O2 sometimes works as a reducing agent. As the reduction potentials of H and H2 (in strongly alkaline solutions for H2) are higher than those of RCHOH radicals, which are usually used to reduce metal ions, H and H2 generated from cavitation bubbles are expected to reduce metal ions to produce metal nanoparticles (in strongly alkaline solutions for H2 to work). It is possible that the superoxide anion (O2-) also plays some role in the sonochemical reduction of some solutes. In strongly alkaline solutions, hydrated electrons (e-aq) formed from H atoms in liquid water may play an important role in the sonochemical reduction of solutes because the reduction potential is extremely high. The influence of ultrasonic frequency on the amount of H atoms produced from a cavitation bubble is also discussed.

Optimum scavenger concentrations for sonochemical nanoparticle synthesis

Maintaining nanoparticle properties when scaling up a chemical synthesis is challenging due to the complex interplay between reducing agents and precursors. A sonochemical synthesis route does not require the addition of reducing agents as they are instead being continuously generated in-situ by ultrasonic cavitation throughout the reactor volume. To optimize the sonochemical synthesis of nanoparticles, understanding the role of radical scavengers is paramount. In this work we demonstrate that optimum scavenger concentrations exist at which the rate of Ag-nanoparticle formation is maximized. Titanyl dosimetry experiments were used in conjunction with Ag-nanoparticle formation rates to determine these optimum scavenger concentrations. It was found that more hydrophobic scavengers require lower optimum concentrations with 1-butanol < 2-propanol < ethanol < methanol < ethylene glycol. However, the optimum concentration is shifted by an order of magnitude towards higher concentrations when pyrolytic decomposition products contribute to the reduction. The reduction rate is also enhanced considerably.