Fast Joule heating for transformation of Fe-MIL-125(Ti) to Fe/TiO2 with enhanced photocatalytic activity in N2 fixation

Abstract

It is critical to develop a highly efficient catalyst for the photocatalytic fixation of nitrogen to produce ammonia under ambient conditions. Herein, we reported on a fast Joule heating (FJH) method to synthesize 1.0 wt% Fe-doped TiO2 (JH Fe/TiO2) derived from MIL-125(Ti). For comparison, Fe/TiO2 calcined in a tube furnace was also prepared (TF Fe/TiO2). The photocatalytic production rate of ammonia on JH Fe/TiO2 was increased to 56.87 μmol g−1 h−1, which was 1.5 times higher than that of TF Fe/TiO2. As detected, FJH might lead to the formation of lattice defects with oxygen vacancies (OVs) formation. These OVs and defects had the potential to act as adsorption and reactive sites for N2. Furthermore, in-situ infrared (FT-IR) along with Density Functional Theory (DFT) simulation were applied to study the possible reaction pathways of photocatalytic reduction of N2. As calculated, the substitution of Feδ+ for Ti4+ with the formation of Fe-Ti dual active sites synergistically interacted with the OVs to facilitate the photocatalytic reduction process. Moreover, an alternative pathway was more favorable for the production of NH3. The reasonable design of Fe-doped transition metal oxides and the proposed Fe-Ti dual active sites opened a new approach for highly efficient photocatalytic N2 fixation.