The improvement of spinach growth by nano-anatase TiO2 treatment is related to nitrogen photoreduction

The improvement of spinach growth is proved to relate to N-2 fixation by nanoanatase TiO2 in this study. The results show that all spinach leaves kept green by nanoanatase TiO2 treatment and all old leaves of control turned yellow white under culture with N-deficient solution. And the fresh weight, dry weight, and contents of total nitrogen, NH4+, chlorophyll, and protein of spinach by nano-anatase TiO2 treatment presented obvious enhancement compared with control. Whereas the improvements of yield of spinach were not as good as nano-anatase TiO2 treatment under N-deficient condition, confirming that nano-anatase TiO2 on exposure to sunlight could chemisorb N-2 directly or reduce N-2 to NH3 in the spinach leaves, transforming into organic nitrogen and improving the growth of spinach. Bulk TiO2 effect, however, was not as significant as nano-anatase TiO2. A possible metabolism of the function of nano-anatase TiO2 reducing N-2 to NH3 was discussed.