Synthesis methods, network selection, catalytic mechanism, and stability challenges of silver, gold, palladium, nickel, and cobalt nanoparticles: A review

This review provides a comparative assessment of the synthesis, better network selection, catalytic applications, and stabilization of silver, gold, palladium, nickel, and cobalt nanoparticles. It focuses particularly on nickel and cobalt, which exhibit high surface energies and tend to aggregate due to van der Waals forces and magnetic dipole–dipole interactions. This aggregation presents a significant challenge for stabilization. Magnetic nickel nanoparticles are particularly susceptible to surface oxidation; therefore, most synthesis protocols utilize organic media and hydrophobic capping agents to prevent agglomeration and oxidation. While cobalt nanoparticles hold promise for magnetic and catalytic applications, they exhibit poor stability against oxidation and hydrolysis, which limits their use in catalytic contexts. The electronic properties also contribute to the stability challenges faced by these five nanoparticles. We review various synthesis methods, including chemical, biological, and green approaches, as well as stabilization strategies such as surfactant capping, confinement within metal-organic frameworks or covalent frameworks, and polymeric gels. Additionally, we summarize advanced characterization techniques and propose a data-driven framework that combines density functional theory, materials databases, and machine learning to predict synthesis parameters and surface modifications. This review highlights that when properly stabilized, nickel and cobalt nanoparticles can serve as cost-effective alternatives to noble metals, providing high catalytic efficiencies in reactions such as the reduction of nitro compounds and the degradation of dyes. By comparing noble and base metal nanoparticles and highlighting the underexplored systems of nickel and cobalt, we provide mechanistic insights and design principles that will facilitate the rational development of durable catalysts for environmental remediation and energy conversion.