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

The Co4Cat approach is a surfactant-free industry-relevant method to synthesize precious metal nanoparticles with enhanced catalytic properties. Colloidal nanoparticles are obtained by reduction of a metal salt in a monoalcohol such as methanol in the presence of a base. As opposed to alternative surfactant-free syntheses, in the Co4Cat approach, the nature of the alkali cations used strongly influences the most suitable strategy to achieve different nanoparticle size, to  process and to stabilize surfactant-free platinum nanoparticles. The rational selection of the base needed in the Co4Cat process is detailed here. Monovalent alkali cations stabilize the as-synthesized and redispersed nanoparticles in monoalcohols and aqueous solvents with the decreasing order of efficiency: Li⁺> Na⁺ > K⁺ ≈ Cs⁺ which correlates with the decreasing hydration energy of the cation. Li⁺ and Na⁺ cations are shown to serve as simple, eco-friendly, and efficient stabilizers for surfactant-free platinum nanoparticle colloids.