Efficient photocatalytic CO2 reduction by P–O linked g-C3N4/TiO2-nanotubes Z-scheme composites

Abstract

P–O linked g-C3N4/TiO2-nanotubes (TNTs) Z-scheme composites were fabricated using a solid sublimation and conversion means, followed by an impregnation method for the first time, and they were characterized by scanning electrons microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV–visible diffuse reflection spectroscopy. The photocatalytic activity was investigated by CO2 reduction and the charge separation was investigated by surface photovoltage spectroscopy and produced OH radicals. Results showed that CO2 reduction products of acetic, methanol and formic acids with yields of 46.9 ± 0.76 mg L−1 h−1, 38.2 ± 0.69 mg L−1 h−1 and 28.8 ± 0.64 mg L−1 h−1 were obtained using the optimized sample, which were 3.3, 3.5 and 3.8 times of bare TNTs. The optimized sample also showed a transient photocurrent of 0.85 mA cm−2. The enhanced performance was due to the synergistic effect of g-C3N4 and P–O links. The modified g-C3N4 enhanced visible light absorption and charge separation. The P–O links between g-C3N4 and TNTs were benefit for charge transfer. This work contributes to help us comprehend the mechanism of charge transfer and separation in Z-scheme composites, and presents a workable approach for preparing efficient TNTs-based photocatalysts for energy production.