Boosting Carbon Nitride Photoactivity by Metal-Free Functionalization for Selective H2O2 Synthesis under Visible Light

Carbon nitride (CN) is a polymer-based material thoroughly studied for different photocatalytic applications due to its optical, electronic, and chemical properties. Its main limitation is fast electron/hole recombination. To overcome this drawback, several functionalization methods have been applied using organic solvents and severe operating conditions. In the present work, a thermally exfoliated CN was functionalized for the first time via a hydrothermal route using glucose (G), perylene (P), and anthraquinone (A) by implementing water as solvent at a mild temperature (120 °C). The materials were tested for the photocatalytic production of hydrogen peroxide (H2O2) in aqueous solutions saturated with dissolved oxygen and in the presence of a sacrificial agent (isopropyl alcohol). Improved evolution rates of H2O2 were confirmed from 9.7 mmol g–1 h–1 for the unmodified CN material, up to 11.1, 14.2, and 25.0 mmol g–1 h–1 for the functionalized photocatalysts CN-G, CN-P, and CN-A, respectively. The surface chemistry studied by XPS, EDX, and FTIR revealed the specific functionalities allowing for improved energy transfer, faster redox reactions, and enhanced photoactivation. The optical and electrochemical characterizations corroborate the photocatalytic results since photoluminescence was severely quenched after functionalization, and the electronic properties were enhanced, both indicating reduced recombination of charge carriers. The band structure was also investigated, proving that the generation of H2O2 was thermodynamically favored for the functionalized materials, while H2O2 decomposition was suppressed.