Elucidating the Synergistic\nPromotional Mechanism\nof Water and Oxygen in the Aerobic C–C Homocoupling Reaction\nCatalyzed by Visible-Light-Derived Core–Shell Pd@A-CQDs Nanostructures

Rational design and precise synthesis of biogenic noble-metal-based\ncatalysts possessing distinctive structure and composition play a\ncrucial role in the chemical industry, enabling sustainable construction\nof an inclusive range of chemical resources. In this study, we have\neffectively fabricated Pd@A-CQDs through a straightforward one-pot\naqueous protocol assisted by visible light employing renewable biomass-derived\namine-rich carbon quantum dots (A-CQDs). The remarkable visible light\nharnessing capability (bandgap, ca. 2.81 eV), high density (35.7 ×\n10<sup>18</sup> cm<sup>–3</sup>), and long lifetime (25 ps)\nof photocharge carriers and amine-rich surface in A-CQDs make them\nideal candidates as both reducing and stabilizing agents, thereby\nfacilitating the in situ construction of metallic Pd(0) nanoparticles.\nComprehensive physicochemical characterizations have provided compelling\nevidence for the spherical morphology of Pd@A-CQDs core–shell\nnanostructures, with ultrathin A-CQDs shells of ca. 1.9 nm and an\naverage diameter of 14 ± 1 nm. The effectiveness of the synthesized\nPd@A-CQDs catalysts was assessed in the ligand- and base-free homocoupling\nreaction of arylboronic acids in water at ambient temperature. The\ncatalytic tests demonstrated the selective production of the homocoupled\ncompound over protodeboronation products with excellent yield and\nhigh catalyst recyclability under ambient conditions. The protocol\nemployed exhibited a high TOF (1.05 × 10<sup>–2</sup> mol\ng<sup>–1</sup> min<sup>–1</sup>) and a low E-factor,\nwith a remarkably low palladium loading. XPS analysis confirmed the\nretention of the metallic nature of the palladium core within the\ncatalysts during the reaction. The catalytic function of the palladium\ncore in conjunction with the A-CQDs shell, along with the promotional\neffects provided by water and oxygen for the formation of nucleophilic\ntetravalent boron, was conclusively recognized by <sup>11</sup>B NMR\nand O<sub>2</sub>-TPD measurements. The obtained experimental results\ndeliver valuable insights into the probable reaction pathway for the\nhomocoupling reaction catalyzed by the Pd@A-CQDs catalysts. Through\na comprehensive and sustainable evaluation, the current methodology\nexhibits superior performance compared to previously documented techniques\nin relation to estimated circularity and adherence to good manufacturing\npractices (GMP).