Enhanced photocatalytic nitrogen fixation on oxygen doped high specific surface area g-C3N4 under simulated sunlight

Oxygen doped high specific surface area g-C3N4 photocatalysts were synthesized by secondary calcination and microwave hydrothermal method. The photocatalytic properties of the catalysts were evaluated by photocatalytic nitrogen fixation under simulated sunlight. The results indicated that the ammonia producing rate of photocatalyst OCN-10 (treated with 10 vol% hydrogen peroxide solution) reached the maximum (3980 μmol·g−1·h−1), which was 6.24 times that of bulk g-C3N4 (BCN, 638 μmol·g−1·h−1) and 2.46 times that of non-doped catalyst (OCN-0, 1620 μmol·g−1·h−1). Obviously, secondary calcination and oxygen doping led to the enhanced photocatalytic nitrogen fixation performance of OCN-10. To be specific, secondary calcination increased the specific surface area of g-C3N4 and the porous structure provided more nitrogen adsorption sites; Oxygen doping promoted the utilization of visible light, thus leading to a great increment in photoelectrons participating in nitrogen reduction reaction. The outcome of DFT calculation revealed an augmented N2 adsorption energy of −97.31 kJ·mol−1 for oxygen doped g-C3N4 in contrast to an initial adsorption energy of −72.59 kJ·mol−1 for g-C3N4. Stronger adsorption bond facilitated subsequent electron transfer and nitrogen reduction. The as-synthesized highly-efficient photocatalyst can serve as a superior option for clean nitrogen fixation.