Time and temperature dependent formation of hollow gold nanoparticles via galvanic replacement reaction of As(0) and its catalytic application

Abstract

Abstract

On the Overlooked Critical Role of the pH Value on the Kinetics of the 4-Nitrophenol NaBH4-Reduction Catalyzed by Noble-Metal Nanoparticles (Pt, Pd, and Au)

“…The first detailed kinetic studies by Ballauff and co-workers provided evidence for a Langmuir–Hinshelwood mechanism (Scheme , upper pathway), which was proposed shortly before by Pal et al , An alternative reducing agent to NaBH 4 is molecular hydrogen (Scheme , lower pathway). These are only a few prominent examples out of a few thousand publications on testing catalyst performance using this model reaction, which therefore has become the current gold standard in catalysis with metal NPs. ,− The diversity of catalysts includes metals from groups 8 to 12 (Ni, Rh, Ir, Pd, − Pt, ,, Cu, Ag, , and Au ,,− ) with various morphologies , and even metal-free micelles …”

Impact on the Formation and Catalytic Property of Pt-Based Nanocatalysts by Galvanic Reaction with Co-Reduction Agents

“…(1) The galvanic replacement between Ag and PtCl 4 2‑ (reaction: PtCl 4 2‑ +2Ag → Pt + 2Ag + + 4Cl – ); (2) the reduction of PtCl 4 2– by a reducing agent (reaction: PtCl 4 2‑ + reducing agent → Pt + 4Cl – ); (3) the reduction of produced Ag + by a reducing agent (reaction: Ag + + reducing agent → Ag); and (4) the formation of AgCl precipitate if the concentrations of Ag + and Cl – are high enough (reaction: Ag + + Cl – → AgCl). The galvanic reaction, reaction (1), will lead to the formation of a hollow structure, ,, whereas the reduction by a reducing agent will result in the formation of a spiky branch shell on the AuNDB@Ag@mSiO 2 nanostructure mainly due to the kinetic controlled deposition process. Reactions (2) and (3), the reductions by the reducing agent, compete with reaction (1), the galvanic replacement.…”

“…The as-purified AuNDBs@ SiO 2 (1 mL) was dispersed in an aqueous PVP solution (1 mL, 70.4 mg). Under stirring, various volumes of 0.01 M AgNO 3 (10,20,30,40,50,60, 100, 120, and 200 μL) were added, followed by the addition of HQ (140 μL, 0.01 M) and allowed to stir for 1 h and sat undisturbed for 12 h. The solution was then centrifuged and washed twice in EtOH at 8000 rpm for 8 min before the deposition of Pt shell and characterization. The calculated Au/Ag molar ratio is 15/x, (x = 1, 2, 3, 4, 5, 6, 10, 12, and 20).…”