Increasing electron density through an n-type semiconductor to accelerate hot electrons from plasmonic Au nanospheres for artificial photosynthesis and cross-coupling reactions

Here, we report the synthesis of an n-type wide band gap semiconductor (SnO₂) and gold nanosphere (GNSs)-based core-satellite heterostructures (GNSs@SnO₂) composed of GNSs as core and ultra-small SnO₂ nanodots as a satellite with multiple thicknesses, which were then utilized for artificial photosynthesis and the Suzuki-Miyaura coupling reaction. SnO₂ nanodot coating thickness on GNSs was maintained as 3-4 nm (GNSs@SnO₂-US), 6-7 nm (GNSs@SnO₂-SS), and 14-15 nm (GNSs@SnO₂-TS) and the prepared nanostructures were used for visible light-induced artificial photosynthesis and the Suzuki-Miyaura coupling reactions. The higher electron density in GNSs@SnO₂-SS led to more light absorption, which generated high-energy hot charge carriers, resulting in a highly active photocatalyst for CO₂ conversion to HCOOH (quantum yield = 2.15%, chemical yield = 3.69%) with high selectivity (96%) and achieving a biphenyl yield of 99.15% in the cross-coupling of phenylboronic acid and iodobenzene. The apparent quantum efficiency for CO₂ photoreduction at 550 nm monochromatic wavelength was observed as 0.799%. GNSs@SnO₂-SS showed robust structure and excellent colloidal stability with excellent reusability for at least 10 reaction cycles without losing catalytic activity and a high shelf life of 1 year. The prepared GNSs@SnO₂-SS nanoparticles also displayed high photocatalytic activity in NIR and sunlight-induced CO₂ reduction and coupling reactions. The controlled coating of 6-7 nm SnO₂ nanodots on GNSs was found to be the optimized satellite thickness, which enhanced the electron density due to the wide band gap of SnO₂. The increased electron density led to greater light absorption to generate high-energy hot electrons and hot holes. This led to high photocatalytic efficiency of GNSs@SnO₂-SS for CO₂ reduction and cross-coupling reactions.