Tuning the nanoarchitectonics of NaNbO ₃ for overall photocatalytic nitrogen fixation: insights into defect engineering and heteroatom doping

Over the past few years, defect engineering has emerged as a powerful method to enhance the photocatalytic activities of semiconductor materials. This approach has been utilized to provide an enhanced number of active sites on the catalyst surface. Vacancy engineering and heteroatom doping are the most common methods used to generate defects in semiconductors. However, these methods have never been compared in terms of their effect on the photocatalytic activity of semiconductors. In this work, we have compared the nitrogen fixation activity of oxygen-vacancy-rich NaNbO₃ and V-doped NaNbO₃ photocatalysts. Both oxygen-vacancy-rich and V-doped NaNbO₃ photocatalysts performed better than their pristine counterpart (bare NaNbO₃). The overall highest activity was observed for V-doped NaNbO₃ (NVNO0.25) having an ammonia generation rate of 36 µmol g^-1 h^-1 as compared to the best oxygen-vacancy-rich NaNbO₃ sample (DNNO2), wherein the ammonia generation rate was 26 µmol g^-1 h^-1 under visible light irradiation. Furthermore, the light to chemical conversion efficiency and turnover frequency for NVNO0.25 were found to be 0.052% and 0.095 h^-1, respectively, under visible light irradiation. Besides, the nitrogen fixation activity of the photocatalysts was also explored under direct sunlight irradiation. In addition to ammonia, the formed nitrate and nitrite species were also quantified. Thus, this work provides a one-on-one comparison of the nitrogen fixation activity of two types of NaNbO₃ photocatalysts. The insights provided by this work can help researchers to design and develop efficient materials for photocatalytic nitrogen fixation.