New insights into how Pd nanoparticles influence the photocatalytic oxidation and reduction ability of g-C3N4 nanosheets

g-C3N4 nanosheets decorated with Pd nanoparticles (C3N4-Pd) were prepared via a facile method. The visible light photocatalytic performance of C3N4-Pd is demonstrated from both oxidability and reducibility aspects. It is amazing to observe the different photocatalytic behavior of C3N4-Pd in the oxidation and reduction reaction. C3N4-Pd displayed highly enhanced photocatalytic activity in oxidation removal of NO as Pd nanoparticles (NPs) could shuttle the electrons photoexcited from g-C3N4 and the Schottky barrier formed between g-C3N4 and Pd NPs could prevent the reverse electron flow from Pd to g-C3N4. While the photooxidation of NO was greatly improved, the photocatalytic reduction of CO2 was significantly inhibited, which could be ascribed to the decreased reducibility of the electrons in g-C3N4 caused by the transfer of photogenerated electrons from g-C3N4 to Pd NPs. The present work shows that the Pd metal played totally distinctive roles in photocatalytic oxidation and reduction, which could provide new perspectives in the design of noble metal modified photocatalysts for different photocatalytic redox reactions.