Template-free synthesis of bubble-like phosphorus-doped carbon nitride with enhanced visible-light photocatalytic activity

A novel photocatalytic material that is phosphorus-doped and graphite-like (carbon nitride (g-C 3 N 4 )) was successfully prepared through direct thermal co-poly-condensation using ammonium dihydrogen orthophosphate as the phosphorus source and melamine as the g-C 3 N 4 precursor. The catalyst was characterized by analyses from multiple tools: X-ray powder diffraction, Fourier transform infrared spectroscopy , scanning electron microscopy, transmission electron microscopy , BET surface area, ultraviolet–visible diffuse reflection spectroscopy , and X-ray photoelectron spectroscopy. The unique bubble-like structure provided the phosphorus-doped g-C 3 N 4 (P-C 3 N 4 ) with a unique property for spatial electron transfer and a large specific surface area (40.89 m 2 g -1 ). The photocatalytic performance of P-C 3 N 4 was determined by assessing rhodamine B (RhB) degradation under visible-light irradiation. The results showed that P-C 3 N 4 exhibited superior photocatalytic performance that is 18 and 4 times higher than pristine bulk g-C 3 N 4 (B-C 3 N 4 ) and modified multi-aperture g-C 3 N 4 (M-C 3 N 4 ), respectively. The enhancement of photocatalytic activity was attributed to the improved light harvesting capacity and the narrowing energy band structure of the copolymer that result from the substitution of phosphorus atoms by carbon atoms in the g-C 3 N 4 framework. The photoelectron emission measurements confirmed that P-C 3 N 4 promoted the separation efficiency of the charge carriers. The bubble-like structured P-C 3 N 4 also possessed superior durability and stability. The radical quenching tests indicated that superoxide radicals ( O 2 − ) and holes (h + ) were the dominant active species for RhB degradation.