Boosting CO production from visible-light CO2 photoreduction via defects-induced electronic-structure tuning and reaction-energy optimization on ultrathin carbon nitride

Polymeric carbon nitride is a promising photocatalyst for CO2 reduction; however, its efficiency is limited by the rapid recombination of photogenerated charges and weak CO2 activation ability. In this study, we present the synthesis of g-C3N4 with carbon vacancy and oxygen doping (Vc-OCN) through a facile formaldehyde-assisted thermal polycondensation of molten urea. Comprehensive investigations were carried out and established that the oxygen doping site substituted the 2-coordinated nitrogen site while a carbon vacancy (Vc) was formed at the position of C-3N in the heptazine structure. The incorporation of Vc and oxygen doping could efficiently modify the band structure and electronic structure, leading to enhanced optical absorption and charge separation. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and DFT calculations demonstrated that the Vc-OCN reduced the energy of the rate-determining step of CO2 conversion, with the Vc serving as the active site for CO2 activation. Combining thermodynamics and kinetics optimization, Vc-OCN achieved a high CO generation rate of 13.7 mu mol g(-1) h(-1) under visible-light irradiation without the help of any cocatalysts or sacrificial agents, displaying a 7.6-fold improvement over GCN. This study provides a deep understanding of the synergistic effect of doping and vacancies on CO2 photoreduction and provides novel insights into the design of high-efficiency polymer semiconductors obtained through defects engineering.

Automated summary

The synthesis of g-C3N4 with carbon vacancy and oxygen doping (Vc-OCN) was successfully achieved through a facile method. The incorporation of Vc and oxygen doping led to enhanced optical absorption and charge separation, resulting in improved CO2 reduction efficiency.