Electron transfer bridge inducing polarization of nitrogen molecules for enhanced photocatalytic nitrogen fixation.

Ammonia (NH3) plays a crucial role in the production of fertilizers, medicines, fibers, etc., which are closely relevant to the development of human society. However, the inert and nonpolar properties of NN seriously hinder artificial nitrogen fixation under mild conditions. Herein, we introduce a novel strategy to enhance the photocatalytic efficiency of N2 fixation through the directional polarization of N2 by rare earth metal atoms, which act as a local "electron transfer bridge." This bridge facilitates the transfer of delocalized electrons to the distal N atom and redirects the polarization of adsorbed N2 molecules. Taking cerium doped BiOCl (Ce-BiOCl) as an example, our results reveal that the electrons transfer to the distal N atom through the cerium atom, resulting in absorbed nitrogen molecular polarization. Consequently, the polarized nitrogen molecules exhibit an easier trend for NN cleavage and the subsequent hydrogenation process, and exhibit a greatly enhanced photocatalytic ammonia production rate of 46.7 µmol g-1 h-1 in cerium doped BiOCl, nearly 4 times higher than that of pure BiOCl. The original concept of directional polarization of N2 presented in this work not only deepens our understanding of the N2 molecular activation mechanism but also broadens our horizons for designing highly efficient catalysts for N2 fixation.

[Safety toxicological evaluation of Wen Radix Codonopsis].

OBJECTIVE: To evaluate the toxicological safety of Wen Radix Codonopsis. METHODS: According to the national standards of food safety(GB 15193.3-2014, GB 15193.4-2014, GB 15193.5-2014, GB 15193.8-2014, GB 15193.13-2015), acute oral toxicity test, three genetic toxicity tests(including bacterial recovery mutation test, mammalian erythrocyte micronucleus test and mouse spermatocyte chromosome aberration test) and subchronic toxicity test were conducted in this study. RESULTS: The LD_(50) of Wen Radix Codonopsis to KM mouse was more than 38.72 g/kg, which was actually non-toxic according to the acute toxicity grading standard of mouse. The results of three genetic toxicity tests were negative and no obvious genotoxicity was observed. 90-day oral toxicity test showed that the overall growth condition of the rats in each group was good, and the test index result of each test group showed no statistical significance compared with the negative control group, and all of them were within the normal range in our laboratory. No abnormality was observed in gross anatomy, and no histopathological changes and specific lesions associated with the test substances were found. CONCLUSION: No obvious acute oral toxicity, genetic toxicity and subchronic toxicity were observed in Wen Radix Codonopsis under the present conditions.