Tuning Reactive Species Production of Graphitic Carbon Nitride via Oxygen Doping

In this work, we demonstrate the ability to manipulate the generation of reactive species (RS) in graphitic carbon nitride (g-C3N4) using oxygen doping. g-C3N4 is a catalyst used in photocatalytic applications, and the RS produced through light activation underlies diverse utility ranging from hydrogen production to microbial disinfection. Oxygen was chosen as the dopant due to its lone pair of p-orbital electrons, enabling efficient electron exchange within the g-C3N4 framework. Systematic changes in oxygen doping modulate g-C3N4’s optical, structural, and chemical properties. We show that doping at 3.59% oxygen increased RS production nearly 10-fold compared with undoped g-C3N4 when exposed to light spectrum excluding UV light (390 ± 10–800 nm). Producing high levels of RS without the need for energy-intensive UV light further advances resource efficient applications of g-C3N4. Comprehensive characterization of our O-doped g-C3N4 reveals properties that govern the observed RS enhancement. Specifically, we correlate a predominance of carbonyl moieties (C═O) and a reduction in the ether-type moieties (C–O) with enhanced RS production. Further, the optical bandgap narrows by 35% (2.81 to 1.82) with increasing absorption in the visible region (quantified as the area under the Kubelka–Munk absorbance spectra), which ranges from 624.06 au to 814.19 au. Finally, the size of pores in the g-C3N4 framework increases with increasing O-doping; the average pore size of the highest-doped sample is 2.40× that of the undoped g-C3N4. Collectively, our findings provide valuable insights into the properties and chemistry of oxygen-doped g-C3N4 that drive RS generation, showcasing its potential as an efficient and sustainable visible-light photocatalyst.