Ru-doped Aurivillius phase perovskites Bi4Ti3O12 for boosting photo-redox of N2 in photocatalytic nitrogen fixation

Abstract

In this study, we prepared layered Aurivillius phase bismuth titanate perovskite oxide (Bi4Ti3O12, BT) using the sol–gel method and doped them with various amounts of Ru (BT-Rux, x = 0.05, 0.1, 0.25, and 0.5 % w/w) for photocatalytic nitrogen fixation in the absence of a sacrificial reagent. Among the prepared photocatalysts, BT-Ru0.25 showed the highest NH4+ formation rate of 119 μmolgcat−1 h−1, which is a 3.21-fold higher than BT. The Rietveld refinement X-ray diffraction results suggest that the expansion of the a and b lattice parameters of BT occurs with adding Ru, which correlates with the photocatalytic NH4+ production performance. This is because the expansion of a and b lattices of BT via Ru doping contributed to the increase in oxygen vacancies and the altered surface charge density in the Bi and Ti of BT, creating an asymmetric coordination environment that could induce the polarization of N2. Photoluminescence and Time-resolved photoluminescence analyses showed that the doping of Ru on BT reduced the recombination efficiency of the photogenerated electron-hole pairs and prolonged the electron decay time. In linear sweep voltammetry and Tafel analyses showed that Ru doping of BT suppressed the HER and photocorrosion. In-situ surfaced enhanced Raman spectroscopy (SERS) analysis revealed that the doping of Ru in BT improved the N2 interaction on the Bi-O bonds, accelerating the surface nitrogen oxidation reaction (NOR) to form NO3– and further undergoing a nitrate reduction reaction (NORR) for NH4+ production. This study highlights the importance of incorporating Ru into perovskite oxides to improve the separation of photogenerated carriers in photocatalytic NH4+ production without sacrificial reagents.