Abstract
This paper reports the development of a new family of highly active Pd nanoparticle catalysts supported on partially reduced graphene oxide nanosheets for carbon–carbon cross-coupling reactions. We report, for the first time, the synthesis of Pd nanoparticle catalysts supported on partially reduced graphene nanosheets (Pd/PRGO) by pulsed laser irradiation of aqueous solutions of graphene oxide and palladium ions without the use of chemical reducing or capping agents. The redox reactions initiated by the photoexcitation of GO using two 532 nm photons in different reducing environments of appropriate protic solvents (water, methanol, and ethanol) result in the formation of Pd nanoparticles with different sizes supported on the PRGO nanosheets. The laser irradiation process leads to the formation of multiple defect sites on the surface of the PRGO nanosheets which provide an excellent environment for anchoring the Pd nanoparticles, thus impeding the particles’ migration and increasing the catalyst–support interaction. This consequently contributes to the enhanced catalytic performance and recyclability of the catalyst. The Pd/PRGO catalyst generated in water demonstrates excellent catalytic activity for Suzuki, Heck, and Sonogashira cross coupling reactions, with good recyclability for Suzuki coupling with a turn over number (TON) of 7800 and a remarkable turnover frequency (TOF) of 230,000 h–1 at 120 °C under microwave heating. The results indicate that the defect sites generated on the PRGO nanosheets by the laser photochemical process play a major role in imparting the exceptional catalytic properties to these catalysts.