Constructing oxygen vacancies and linker defects in MIL-125 @TiO2 for efficient photocatalytic nitrogen fixation

Abstract

With the emergence of issues such as global warming and glaciers melting, reducing carbon emissions cannot be ignored. Ammonia can participate in the N element cycle in nature and has a huge market demand. In modern industry, the preparation of ammonia mainly relies on the Haber-Bosch process with huge energy consumption. Using clean photocatalytic method to prepare ammonia can alleviate the above problems. Here, the core-shell structure of MIL-125 @TiO2 was prepared by post solvothermal method for photocatalytic nitrogen fixation. Linker defects can appear as active sites in the residual MIL-125, which forms an obvious mesoporous structure that accelerates the exchange of electron/mass and promotes the activation of N2. The shell structure constructed by thin TiO2 nanosheets possesses a large specific surface area. And the oxygen vacancies active sites could be highly exposed for nitrogen adsorption and activation, so as to promote the occurrence of the photocatalytic reaction. The O−Ti−N covalent bond is established between the titanium-oxygen clusters in the peripheral of TiO2 and the linker in MIL-125, which improves the effective separation of electron-hole pairs. The ammonia formation rate of MIL-125 @TiO2-2 h is 102.7 µmol g−1 h−1 under simulated sunlight, which is 8 times higher than that of MIL-125. This work provides a novel idea for the preparation of photocatalytic nitrogen fixation materials with controllable structure and multiple active sites.