Enhanced photocatalytic hydrogen evolution and ammonia sensitivity of double-heterojunction g-C 3 N 4 /TiO 2 /CuO.

The performance of semiconductor photocatalysts has been limited by rapid electron-hole recombination. One strategy to overcome this problem is to construct a heterojunction structure to improve the survival rate of electrons. In this context, a novel g-C 3 N 4 /TiO 2 /CuO double-heterojunction photocatalyst was developed and characterized. Its photocatalytic activity for hydrogen production from water-methanol photocatalytic reforming was explored. Methanol is always used to eliminate semiconductor holes. The g-C 3 N 4 /TiO 2 /CuO double-heterojunction photocatalyst with a narrow bandgap of ∼1.38 eV presented excellent photocatalytic activity for hydrogen evolution (97.48 μmol (g h) -1 ) under visible light irradiation. Compared with g-C 3 N 4 /TiO 2 and CuO/TiO 2 , the photocatalytic activity of g-C 3 N 4 /TiO 2 /CuO for hydrogen production was increased approximately 7.6 times and 1.8 times, respectively. Below 240 °C, the sensitivity of g-C 3 N 4 /TiO 2 /CuO to ammonia was approximately 90% and 46% higher than that of g-C 3 N 4 /TiO 2 and CuO/TiO 2 , respectively. The enhancement of the photocatalytic activity and gas sensing properties of the g-C 3 N 4 /TiO 2 /CuO composite resulted from the close interface contact established by the double heterostructure. The trajectory of electrons in the double heterojunction conformed to the S-scheme. UV-vis, PL, and transient photocurrent characterization showed that the double heterostructure effectively inhibited the recombination of e - /h + pairs and enhanced the migration of photogenerated electrons.