Construction of C3N4/N-doped polycrystalline graphite heterojunction for the degradation of sulfamethoxazole

g-C3N4/N-doped polycrystalline graphite (CN/N2PG) heterojunction photocatalysts were designed and synthesized by a simple calcination method. The structural and optical properties of g-C3N4/N2PG were investigated by a series of characterization techniques. The CN/N2PG-x (x represented N2PG mass) photocatalysts performed much better than pure CN and N2PG, with the CN/N2PG-0.02 sample showing the best photocatalytic performance. Under simulated solar light irradiation, ca. 90% sulfamethoxazole (SMX) could be removed in 120 min. CN/N2PG-0.02 possessed the highest reaction rate constant (0.0187 min−1), which was 3.8 and 12.5 times higher than those of CN and N2PG, respectively. Based on the results of photoluminescence spectroscopy and photoelectrochemical measurements, the enhanced photocatalytic performance of CN/N2PG-0.02 was mainly attributed to the formed Z-scheme heterojunction between CN and N2PG, which improved charge separation and transfer efficiency. Furthermore, the reactive species trapping and EPR experiments showed that h+ and •O2− were the main reactive species for SMX degradation. In combination with LC-MS analysis, possible photocatalytic reaction mechanisms were proposed. This work provides guidance for the construction of high-performance graphite-based heterojunction photocatalysts boosting pollutants treatment.