Molecule-Mediated Polymerization for G-C3n4 Photocatalysts Toward Efficient Pollutant Degradation and Hydrogen Evolution

Abstract

Graphitic carbon nitride (g‐C3N4) synthesized via the primitive solid-state polymerization of nitrogen-rich organic precursors unfortunately has a low photocatalytic efficiency due to its small surface area and fast recombination of electron-hole pairs. Herein, g‐C3N4 nanosheets were synthesized by cooperatively mediating the thermal polymerization of melamine and urea using oxalic acid (OA) and water. Compared with single modifications, the combination of oxalate thermolysis and water evaporation resulted in higher specific surface area and more negative conduction band edge. g‐C3N4 nanosheets prepared from the water and oxalic acid co-mediated polymerization exhibited superior photocatalytic activity compared to those prepared using individual mediation manners. The best performing photocatalyst allowed for the high removal of the pollutants including methylene blue (85.9%), methyl orange (97.1%), ciprofloxacin (77.1%), and o-nitroaniline (100%) over 90 min. Radical quenching tests suggested that the consumption of holes led to a promotion of photodegradation. Moreover, such photocatalyst was also competent to the hydrogen evolution from aqueous triethanolamine in the case of metal sulfides as a cocatalyst, achieving a rate value of 703.4 µmol h−1 g−1. The enhancement of catalytic activity can be attributed to favorable energy band structure, the improvement of charge separation efficiency, and more active surface. This work provides a facile approach for tuning the structures and catalytic performance of g-C3N4 based on the molecule-mediated polymerization.

Keywords: Pollutant removal, Hydrogen evolution, Photocatalysis, Carbon nitride, Molecule-mediated polymerization