Construct electron transport path through NH2-MIL-125 modified Fe-doped W18O49 nanowires to enhance photocatalytic nitrogen fixation performance

Abstract

Ammonia has important application value in agriculture and industry as a raw material for producing nitrogen fertilizers and organic chemicals. The Haber-Bosch method is generally utilized to synthesize ammonia through N2 and H2 as raw materials in industry, but the process generates serious energy consumption and pollution. In the paper, a heterojunction catalyst is constructed that adopts NH2-MIL-125 and Fe-doped W18O49 (Fe-W18O49) for photocatalytic nitrogen fixation. Fe-W18O49 is a nanowire containing oxygen vacancies (OVs). OVs can provide active sites for the adsorption and activation of nitrogen gas. The 3D plate-like morphology of NH2-MIL-125 can observably reduce the occurrence of nanowires aggregation. This phenomenon can be attributed to NH2-MIL-125 playing a supporting role in the fixation of nanowires. New mesoporous are formed between NH2-MIL-125 and Fe-W18O49 in the constructed compound catalyst, which can realize efficient mass transfer between the inside and outside of the catalyst. EPR characterization discovers that Fe-W18O49/NH2-MIL-125 cannot produce •O2˗ and •OH radicals. The type II heterojunction forms between Fe-W18O49 and NH2-MIL-125. The heterojunction improves the carrier migration path, and the photocurrent intensity is significantly increased. Under simulated sunlight, Fe-W18O49/NH2-MIL-125–2 emerges the best catalytic performance with an ammonia formation rate of 128.2 µmol g−1 h−1. The yield of ammonia is boosted in comparing with NH2-MIL-125 (13 times) and Fe-W18O49 (1.7 times). After several cycles, Fe-W18O49/NH2-MIL-125 remain maintains good stability during the catalytic process. This paper provides a possibility for constructing low-cost heterojunction catalysts in the territory of photocatalytic nitrogen fixation.