In this work, commercial anatase TiO 2 powders were modified using ultrathin Fe 2 o 3 layer by atomic layer deposition (ALD). The ultrathin Fe 2 o 3 coating having small bandgap of 2.20 eV can increase the visible light absorption of tio 2 supports, at the meantime, Fe 2 o 3 /tio 2 heterojunction can effectively improve the lifetime of photogenerated electron-hole pairs. Results of ALD Fe 2 o 3 modified TiO 2 catalyst, therefore, showed great visible light driven catalytic degradation of methyl orange compared to pristine tio 2. A 400 cycles of ALD Fe 2 o 3 (~ 2.6 nm) coated TiO 2 powders exhibit the highest degradation efficiency of 97.4% in 90 min, much higher than pristine TiO 2 powders of only 12.5%. Moreover, an ultrathin ALD Al 2 o 3 (~ 2 nm) was able to improve the stability of Fe 2 o 3-tio 2 catalyst. These results demonstrate that ALD surface modification with ultrathin coating is an extremely powerful route for the applications in constructing efficient and stable photocatalysts. A rapid industrial development driven by unsustainable technology advances can cause plenty of industrial sewage, spreading chemical hazards into water resources. As a result, water pollution has emerged as one of the most serious environmental issues worldwide 1-4. Photocatalytic oxidation technology has shown great prospects in removing the toxic and harmful contaminants in aqueous environment 5-7. Semiconductors (e.g. TiO 2 , ZnO, SnO 2) have been widely researched for organic pollutant degradation, however, the large band gap hinders their practical applications 8-12. For example, TiO 2 with band gap of 3.2 eV can only absorb the ultraviolet light, accounting for only 4-5% of entire solar spectrum 13. Therefore, various visible light sensitive photocatalysts has also been widely explored, such as g-C 3 N 4 , BiVO 4 , CdSe, Bi 2 WO 6 14-19. On the other hand, TiO 2 is recognized as one of the excellent materials owning to its good inertness, eco-friendly, low cost, strong oxidizing power, and long-term stability against photo and chemical corrosion 9,13,20-22. Thus, plenty of works have been made to extend the absorption spectrum of TiO 2 to visible light so to make a full use of solar spectrum. Several different approaches can be employed, including doping 23-26 and coupling with small band gap semiconductors or metals 27-30. Small band gap semiconductors not only increase the absorption of visible light but also inhibit photogenerated electrons-holes recombination when constructed as a semiconductor/semiconductor heterojunction structure, thus improving the photocatalytic performance dramatically 31. Therefore, various TiO 2 based heterojunction photocatalysts have been proposed for visible light photocatalysis, including NiO/TiO 2 32,33

N-doped ZnO/g-C3N4 composites have been successfully prepared via a facile and cost-effective sol-gel method. The nanocomposites were systematically characterized by XRD, FE-SEM, HRTEM, FT-IR, XPS, and UV-vis DRS. The results indicated that compared with the pure N-doped ZnO, the absorption edge of binary N-doped ZnO/g-C3N4 shifted to a lower energy with increasing the visible-light absorption and improving the charge separation efficiency, which would enhance its photocatalytic activity. Compared with the pure g-C3N4, ZnO, N-doped ZnO and the composite ZnO/g-C3N4, the as-prepared N-doped ZnO/g-C3N4 exhibits a greatly enhanced photocatalytic degradation of methylene blue and phenol under visible-light irradiation. Meanwhile, N-doped ZnO/g-C3N4 possesses a high stability. Finally, a proposed mechanism for N-doped ZnO/g-C3N4 is also discussed. The improved photocatalysis can be attributed to the synergistic effect between N-doped ZnO and g-C3N4, including the energy band structure and enhanced charge separation efficiency.

In this work, TiN film deposited by plasma enhanced atomic layer deposition (PEALD) is adopted to modify the commercial anatase TiO2 powders. A series of analyses indicate that the surface modification of 20, 50 and 100 cycles of TiN by PEALD does not change the morphology, crystal size, lattice parameters, and surface area of TiO2 nano powders, but forms an ultrathin amorphous layer of nitrogen doped TiO2 (TiOxNy) on the powder surfaces. This ultrathin TiOxNy can facilitate the absorption of TiO2 in visible light spectrum. As a result, TiOxNy coated TiO2 powders exhibit excellent photocatalytic degradation towards methyl orange under the visible light with good photocatalytic stability compared to pristine TiO2 powders. TiOxNy (100 cycles PEALD TiN) coated TiO2 powders exhibit the excellent photocatalytic activity with the degradation efficiency of 96.5% in 2 hours, much higher than that of pristine TiO2 powder of only 4.4%. These results clearly demonstrate that only an ultrathin surface modification layer can dramatically improve the visible light photocatalytic activity of commercial TiO2 powders. Therefore, this surface modification using ALD is an extremely promising route to prepare visible light active photocatalysts.

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