<p>Low surface photogenerated charge concentration is a critical limitation hindering conventional graphitic carbon nitride (CN) from efficiently reducing CO₂ to high-value products. In this work, a pollution-free oxygen oxidation strategy was devised to enhance the surface charge enrichment sites of CN. This approach led to the successful fabrication of a tubular CN photocatalyst functionalized with oxygen-containing groups (C–O–C and C–OH), named O-TCN. The introduction of oxygen functional groups not only effectively widen the light absorption range and narrowed the bandgap but also optimized the surface electronic structure, realizing substantial photogenerated charge accumulation on the O-TCN surface. Photocatalytic performance evaluations revealed that O-TCN achieved exceptional catalytic activity and selectivity in CO₂ reduction, stably converting CO₂ to CO. The average CO yield of O-TCN reaches 49.8 µmol g⁻¹ h⁻¹, representing enhancements of 5.5-fold and 7.7-fold compared to TCN and the classical bulk CN, respectively. This work highlights the potential of surface oxygen functionalization as a powerful strategy to boost the photocatalytic activity of CN-based materials, offering new insights for advancing sustainable energy conversion technologies.</p>