Experimental and Theoretical Research on Photocatalytic Nitrogen Reduction Using MoS₂ Nanosheets with Polysulfide Vacancies

Abstract

MoS 2 nanosheets with different concentrations of S vacancies (V S -MoS 2 ) were synthesized and used for photocatalytic nitrogen reduction reactions (pNRR), and the mechanism of S vacancies enhancing the activity of MoS 2 was explored through DFT calculation. The material characterization confirmed the successful construction of S vacancies at different concentrations on the spherical cluster structure of MoS 2 . The experimental results show that the introduction of S vacancies significantly improves the activity of pNRR, and it increases significantly with the increase of vacancy number, consistent with the trend of photoelectric performance. V S -MoS 2 -3 exhibits the highest pNRR efficiency, which is 3.5 times higher than that of pristine MoS 2 , and after being reused three times, the activity only decreased by about 11%. DFT calculation results indicate that the exposed Mo atoms generated by S vacancies alter the charge layout on the MoS 2 surface while providing abundant Mo active sites. Meanwhile, the band gap structure will narrow with the increase of S vacancies, which is beneficial for the transfer of surface charges. In addition, the increase of S vacancies, on the one hand, strengthens the adsorption of MoS 2 on N 2 , weakens the adsorption of H, improves the selectivity of nitrogen, and is conducive to the progress of NRR. On the other hand, more electrons can be transferred from MoS 2 to the adsorbed N 2 molecules, enhancing the hybridization between them and better activating N 2 .

Experimental and theoretical investigation on facet-dependent MoO2/BiOBr Z-scheme heterojunction photocatalytic nitrogen reduction: modulation of bulk charge separation efficiency by built-in electric field intensity

“…Photocatalytic nitrogen reduction, with the assistance of light, converts nitrogen and water into ammonia, which has significant advantages: 10,11 (1) low energy consumption, as it uses clean solar energy as the energy source; (2) mild reaction conditions, allowing it to be carried out at room temperature and pressure; (3) environmental friendliness, as it replaces non-renewable fossil fuels with water as a hydrogen source, reducing CO 2 gas emissions. 12 The currently researched nitrogen reduction photocatalysts mainly include single atom and cluster catalysts, 13 transition metal oxides (TiO 2 and WO x ), 14,15 nitrides (C x N and BN), 16,17 metal sulfides (MoS 2 and ZnIn 2 S 4 ), 18,19 metal oxygenates (Bi 2 MoO 6 ), 20 and metal–organic frameworks (MOFs). 21 Although there has been some research progress in photocatalytic ammonia synthesis, it still faces difficulties and challenges, mainly due to the low charge separation efficiency of semiconductor catalysts, resulting in low energy conversion efficiency, and the difficulty in activating nitrogen, resulting in a small number of activated molecules participating in the ammonia synthesis reaction.…”