A controllable approach to nitrogen-deficient ultrathin graphitic carbon nitride: robust photo-redox properties and mechanistic insights

Abstract

Polymeric graphitic carbon nitride (g-C₃N₄) is an excellent visible-light-driven photocatalyst. However, its photocatalytic efficiency in hydrogen production and organic pollutant degradation is limited by inefficient photogenerated carrier separation and limited redox potential. To overcome the above drawbacks, morphology-controlled and self-modified two-step hydrogen peroxide and cyanuric acid-assisted thermal polycondensation of melamine to fabricate ultrathin nitrogen-deficient g-C₃N₄ (U-g-C₃N₄-n) was innovatively explored. Ultrathin framework and nitrogen vacancy sites were well-controlled through a synergistic interaction between hydrogen peroxide and cyanuric acid. The ideal catalysts showed remarkable nitrogen vacancy and ultrathin framework-dependent photocatalytic redox activity, significantly enhancing hydrogen production and pollutant degradation. The hydrogen production rate and the apparent first-order rate constant for tetracycline (TC) degradation achieved by U-g-C₃N₄-75 were 37.34 and 3.40 times higher, respectively, than those of pristine g-C₃N₄. Comprehensive experimental analyses combined with theoretical calculations confirmed that the precisely engineered nitrogen-deficient sites on the catalyst surface effectively inhibited the recombination of photogenerated charge carriers while accelerating the aggregation of active species at the nitrogen vacancies. The formation of nitrogen vacancies not only resulted in the enrichment of photoinduced electrons but also indirectly facilitated the adsorption of water and pollutant molecules and promoted the desorption of hydrogen.