TiO2/SrTiO3/g-C3N4 ternary heterojunction nanofibers: gradient energy band, cascade charge transfer, enhanced photocatalytic hydrogen evolution, and nitrogen fixation

TiO2/SrTiO3/g-C3N4 ternary heterojunction nanofibers with a cascade energy band alignment were designed and then fabricated by a combination of electrospinning technology and gas-solid reaction. Their photocurrent responses were 1.4 and 1.8 times higher while their transient photoluminescence lifetime were about 0.75 and 0.79 times shorter than those of TiO2/g-C3N4 nanofibers and SrTiO3/g-C3N4 nanofibers, respectively. The enhanced photocurrent response, decreased lifetime, and their dramatically decreased photoluminescence intensity clearly indicated that highly efficient cascade charge transfer and separation were achieved in the ternary nanofibers with the gradient energy band alignment compared with the corresponding traditional binary nanofibers noted above. When tested in photocatalytic reduction reactions of H-2 evolution and nitrogen fixation, the corresponding reaction rates under simulated sunlight irradiation values of 1304 mu mol g(-1) h(-1) and 2192 mu mol g(-1) h(-1) L-1 were 2.1 and 1.9 times better than those of TiO2/g-C3N4 nanofibers and 4.2 and 3.3 times better than those of SrTiO3/g-C3N4 nanofibers, respectively. Furthermore, the photocatalytic activities of the TiO2/SrTiO3/g-C3N4 nanofibers had no significant decrease after several cycles, indicating that they possessed good structural stability properties. This work provides a new route to design and fabricate an efficient photocatalyst for photocatalytic reduction reactions.