Controlled Synthesis of Surfactant‐Free Water‐Dispersible Colloidal Platinum Nanoparticles by the Co4Cat Process

Abstract

The recently reported Co4Cat process is a synthesis method bearing ecological and economic benefits to prepare precious‐metal nanoparticles (NPs) with optimized catalytic properties. In the Co4Cat process, a metal precursor (e.g., H2PtCl6) is dissolved in an alkaline solution of a low‐boiling‐point solvent (methanol) and reduced to NPs at low temperature (<80 °C) without the use of surfactants. Here, the Co4Cat process to prepare Pt NPs is described in detail. The advantages of this new synthesis method for research and development but also industrial production are highlighted in a comparison with the popular “polyol” synthesis. The reduction of H2PtCl6 from PtIV to PtII and further to Pt0 is followed by UV/Vis and XANES/EXAFS measurements. It is demonstrated how the synthesis can be accelerated, how size control is achieved, and how the colloidal dispersions can be stabilized without the use of surfactants. Despite being surfactant‐free, the Pt NPs exhibit surprisingly long‐term (up to 16 months) stability in water over a wide pH range (4–12) and in aqueous buffer solutions. The Co4Cat process is thus relevant to produce NPs for heterogeneous catalysis, electro‐catalysis, or bio/medical applications.

Monovalent Alkali Cations: Simple and Eco-Friendly Stabilizers for Surfactant-Free Precious Metal Nanoparticle Colloids

“…Alternatively, it may also be related to the decreased formation of CO groups by oxidation of the alcohol leading to lower stabilization of the nanoparticles. 28 The exact mechanism is difficult to prove and was not investigated further in this study. Note, that even the pure alcohol used in the synthesis contains some water; no dried solvents were used since they are not needed to achieve small NP sizes.…”

“…< 80 °C) in an alkaline mono-alcohol like methanol without polymers or surfactants, while the solvent gets oxidized. 28,29 Size control in the range 2-6 nm was achieved by adding substantial amounts of water and the NP size increases with the water content. The latter observation can be ascribed to the lower concentration of the reducing agent (e.g.…”

Ir nanoparticles with ultrahigh dispersion as oxygen evolution reaction (OER) catalysts: synthesis and activity benchmarking

“…We determined a Z-potential as high as 43.0 ± 0.7 mV, typical for a suspension with good stability. [29][30][31] The as-prepared colloidal Ir NP were further characterized by SAXS and HR-TEM, see Fig. 1.…”

“…This is a remarkable achievement for surfactant-free synthesis in line with previous observations for Pt NP produced by the Co4Cat technology. 21,31 3.2 Electrochemical OER performance 3.2.1 Determination of the ECSA. In the literature, different characterization and benchmarking protocols can be found for comparing the catalytic OER performance of Irbased materials.…”

Oxidation of Benzyl Alcohol Compounds in the Presence of Carbon Hybrid Supported Platinum Nanoparticles (Pt@CHs) in Oxygen Atmosphere

“…In terms of green chemistry, functionalizing Pt catalysts for selective alcohol oxidation in the existence of atmospheric oxygen is of great interest. A less expensive and environmentally friendly Pt/C synthesis route is favored for the commercial production of catalysts, and parameters like the size, surface morphology and dispersion status of Pt nanoparticles significantly affect the catalytic efficiency of the Pt/C catalysts [24][25][26][27] .…”