Quaternized POSS modified rGO-supported Pd nanoparticles as a highly efficient catalyst for reduction and Suzuki coupling reactions

Functionalized two-dimensional graphene oxide sheets and their inorganic-organic nanohybrids have aroused great interest because of their excellent synergetic effect on metal-based nanocatalyst PdNPs supported on highly hydrophilic quaternized polyhedral oligomeric silsesquioxane (QPOSS) functionalized reduced graphene oxide (rGO) and were successfully constructed as a nanohybrid catalyst for efficient heterogeneous catalytic reactions. Octaammonium POSS (OAPOSS) was first covalently grafted to carboxylated GO nanosheets through an amidation reaction, and then the OAPOSS decorated on rGO nanosheets was quaternized with glycidyltrimethylammonium chloride (GDTMAC) via an epoxide ring-opening reaction to obtain a highly functional hydrophilic QPOSS@rGO hybrid. Finally, the PdNPs were loaded onto QPOSS@rGO nanosheets through an in situ reduction route. The quaternary ammonium groups on QPOSS@rGO can strongly coordinate with PdNPs, making it particularly advantageous for stabilizing PdNPs and preventing the leaching of Pd metals. Compared to the PdNPs@rGO catalyst without modification with hydrophilic QPOSS, the low-dose PdNPs@QPOSS@rGO nanocatalysts exhibited outstanding catalytic efficiency in the reduction of methylene blue and nitrophenols. In addition, the as-designed nanocatalysts also showed high catalytic activity for the Suzuki coupling reaction when utilizing pure water as a green solvent. It was proved that QPOSS and rGO cacn synergistically catalyze and promote the diffusion of reactants. In particular, the PdNPs@QPOSS@rGO nanohybrid catalyst showed no significant loss of catalytic activity after reusing it five times. Our results demonstrated that highly hydrophilic QPOSS endows the resulting PdNPs@QPOSS@rGO nanohybrid with good dispersibility and stability in water, which remarkably further improves the catalytic activity of the nanocatalyst.