Phosphorus–Oxygen-Codoped Graphitic Carbon Nitride for Enhanced Hydrogen Evolution and Photocatalytic Degradation under Visible Light Irradiation

Phosphorus- and oxygen-codoped g-C3N4 (POCN) with enhanced photocatalytic performance has been fabricated through a facile one-step process, in which ammonium polyphosphate (APP) has been employed as a phosphorus precursor for the first time. The detailed thermal copolymerization process suggests that the presence of hydrogen bonds in melamine/APP complexes and gases generated from the APP molecules during the calcination results in the doping of phosphorus and oxygen atoms into the heterocycles of g-C3N4 and the formation of its nanosized structure. The introduction of APP changes the elementary content and morphology of the obtained POCN. POCN with 3.2% phosphorus and 11.3% oxygen (wt %) exhibits optimal photocatalytic performance and 8 times larger specific surface area than pristine g-C3N4. Compared with pristine g-C3N4, the H2 evolution rate and the apparent degradation rate of rhodamine B catalyzed by the obtained POCN increase by 2- and 5-fold under visible light, respectively. The enhancement of photocatalysis can be mainly attributed to the enlarged surface area, abundant active sites, reduced diffusion distance, and efficient charge separation. The corresponding charge transfer and degradation mechanisms are also proposed.