Architecting Nitrogen Functionalities on Graphene Oxide Photocatalysts for Boosting Hydrogen Production in Water Decomposition Process

This study elucidates how nitrogen functionalities influence the transition and transfer of photogenerated electrons in graphene-based materials. Graphene oxide dots (GODs) and Nitrogen-doped GODs (NGODs) are synthesized by thermally treating graphene oxide (GO) sheets in argon and ammonia, respectively, and then ultrasonically exfoliating the sheets in nitric acid. The nitrogen functionalities of NGODs are mainly quaternary/pyridinic/pyrrolic, and the nitrogen atoms in these functionalities are planar to the GO sheets and repair the vacancy defects on the sheets. Hydrothermal treatment of NGODs in ammonia yields ammonia-treated NGODs (A-NGODs), with some pyridinic/pyrrolic groups being converted to amino/amide groups. The nitrogen atoms in the amino/amide groups are not planar to the GO sheets and are prone to donate their lone pair electrons to resonantly conjugate with the aromatic electrons. The promoted conjugation facilitates the relaxation of photogenerated electrons to the triplet states and prolongs the electron lifetime. When deposited with Pt as the co-catalyst, the samples catalyze H-2 production from an aqueous triethanolamine solution under 420 nm monochromatic irradiation at quantum yields of 7.3% (GODs), 9.7% (NGODs), and 21% (A-NGODs). The high activity of A-NGODs demonstrates that architecting nitrogen functionalities effectively mediate charge motion in carbon-based materials for application to photoenergy conversion.