Na and O Co-doped Carbon Nitride for Efficient Photocatalytic Hydrogen Evolution

Elemental doping is an effective strategy for tuning the band structure of graphite carbon nitride (CN) to enhance its photocatalytic performance.In this study, sodium (Na) and oxygen (O) co-doped carbon nitride (Na/O-CN x , x=1.0, 2.0, 3.0, 4.0) was synthesized via solid-phase reaction of sodium citrate (NaCA) and pure CN powder in the Teflon-sealed autoclave under air conditions at 180 .Surface area of Na/O-CN 3.0 is measured to be 18.8 m 2 /g, increasing by 60.7% compared to that of pure CN (11.7 m 2 /g).Bandgap energy of Na/O-CN 3.0 is determined to be 2.68 eV, marginally lower than that of pure CN (2.70 eV), thereby enhancing its capacity for sunlight absorption.Meanwhile, the incorporation of Na and O atoms into Na/O-CN x is found to effectively reduce recombination rates of photogenerated electron-hole pairs.As a result, Na/O-CN x samples exhibit markedly enhanced photocatalytic hydrogen evolution activity under visible light irradiation.Notably, the optimal Na/O-CN 3.0 sample achieves a photocatalytic hydrogen production rate of 103.2 molg -1 h -1 , which is 8.2 times greater than that of pure CN (11.2 molg -1 h -1 ).Furthermore, a series of Na/O-CN x -yO 2 (y=0, 20%, 40%, 60%, 80%, 100%) samples were prepared by modulating the oxygen content within reaction atmosphere.The catalytic performance evaluations reveal that the incorporation of both Na and O atoms in Na/O-CN 3.0 enhances photocatalytic activity.This study also introduces novel methodologies for synthesis of metal atom-doped CN materials at lower temperature, highlighting the synergistic effect of Na and O atoms in photocatalytic hydrogen production of Na/O-CN x samples.