Oyster shell powder-gold nanoparticle composites as a reactive, recyclable, and green catalyst

Abstract

Oyster shell waste can be utilized as a colloidal solid support to anchor abundant gold nanoparticles (AuNPs) for use as a highly selective, reactive, and recyclable catalyst in C-C bond forming reactions under base-free green reaction conditions. A deposition precipitation method is utilized to effectively incorporate sub-10 nm AuNPs onto the ground oyster shell powder (OSP). Although the loaded AuNPs mainly possess bare surfaces without any capping agents, the resulting composite particles exhibited great dispersity and stability in various solvents, including EtOH and water. After examining their structural and compositional properties, the composite particles are tested as a catalyst in C-C bond forming reactions. These composite particles reveal an unexpectedly high reactivity and selectivity in the homocoupling of arylboronic acid without using any additives, including necessary inorganic bases. This is presumably because the abundant carbonate groups around the OSP surfaces can effectively play a role as a base, while the bare surfaces of the incorporated AuNPs act as catalytically reactive sites. In addition to these synergistic features of the composite particles, establishing reliable reaction conditions requiring only reactants in a green EtOH solvent results in the easy isolation of the product and catalyst, yielding great recyclability. The utilization of marine wastes along with biocompatible and catalytically active metal nanoparticles will lead to the development of economical multi-purpose catalysts that are extremely practical and recyclable in eco-friendly reaction conditions.