The photocatalytic activity of TiO 2 can be mainly improved from three approaches: (1) enhancing surface energy, (2) increasing availability of visible light and (3) improving the separation efficiency of photo-induced electrons and holes. Here, we report a one-step route to obtain Mo + N codoped TiO 2 sheets with dominant {001} facets by a hydrothermal process using TiN, MoO 3 , HF and HNO 3 as precursor. The XRD patterns confirmed Mo and N doping into the lattice of anatase TiO 2 and the XPS survey spectrum shows nitrogen (N) acting as interstitial N or an O-Ti-N structure and molybdenum (Mo) existed as Mo 6+ in TiO 2 sheets. All Mo + N codoped TiO 2 sheets can absorb visible light, but compared with N-doped TiO 2 sheets, further Mo-doping elevates the conduction band edge and expands the band gap of anatase TiO 2 slightly. The separation efficiencies of photo-induced electrons and holes of Mo + N codoped TiO 2 sheets were enhanced compared with that of N-doped TiO 2 sheets, as confirmed by detecting the production of hydroxyl radicals (_OH), and their photocatalytic activities on decomposition of methylene blue and methyl violet was improved. The Mo + N codoped TiO 2 sheets showed the highest photocatalyst activity when the Mo-doping ratio reached 1%, indicating an appropriate codoping ratio is necessary for synergistic effect between doped metal and nonmetal elements.

No abstract

No abstract

Cu/ZnO/n+-Si structures that show resistive switching behaviour have been successfully fabricated. The influence of ZnO thickness on resistive switching is investigated. As the ZnO thickness is reduced from 100 to 25 nm, Cu/ZnO/n+-Si cells change from forming-necessary ones to forming-free ones. Compared with the forming-necessary cells, the forming-free cells show more stable resistive switching characteristics. The underlying mechanism of the forming-free phenomenon is proposed. We infer that the oxygen vacancies pre-existing in ZnO films play an important role in the realization of forming-free cells.

Compositing TiO2 with metal sulfide to construct heterojunction is an effective approach to improve the carriers’ separation efficiency and photocatalytic activity. However, TiO2 is an N-type semiconductor and most metal sulfide is also N-type semiconductor. It will form n–n heterojunction between TiO2 and metal sulfide. The photoinduced electrons in conduction band of metal sulfide hardly flow into the conduction band of TiO2, which will weaken the improvement of carriers’ separation efficiency. In this work, anatase TiO2 nanosheets with coexposed {101} and {001} facets were composited with porous ZnS to construct a novel n–p–n dual heterojunction. This TiO2/ZnS composite displays 108% improvement of photocatalytic activity compared to that of pristine TiO2 nanosheets. As comparison, P25 with mainly exposed {101} facets/porous ZnS with an n–n single heterojunction only show 2% enhancement of photocatalytic activity than that of P25. The n–p–n dual heterojunction displays an obvious advantage than common TiO2/ZnS n–n heterojunction. In the n–p–n dual heterojunction, first, photoinduced electrons at CB of {001} facets will flow into the CB of {101} facets, while photoinduced holes at VB of {101} facets will flow into the VB of {001} facets; second, photoinduced electrons at CB of ZnS will flow into the CB of {001} facets, while photoinduced holes at VB of {001} facets will flow into the VB of ZnS. In this way, it realizes carriers’ separation in the n–p–n dual heterojunction. This work improves a new strategy to employ crystal facets of photocatalysts to construct n–p–n dual heterojunction with metal sulfide for enhancing the photocatalytic activity.

No abstract

No abstract

Alkaline‐earth metal Ca and N codoped TiO2 sheets with exposed {001} facets were obtained through a one‐step hydrothermal process. The codoped TiO2 appears as microsheets with length of 1–2 μm and thickness of 100–200 nm. The X‐ray diffractometer and X‐ray photoelectron spectroscopy results confirm that Ca and N codoped TiO2 has higher crystallinity than N‐doped TiO2, as well Ca, N atoms were successfully codoped into TiO2 as interstitial Ca and interstitial N or an O–Ti–N structure, respectively. Compared with N monodoped, further alkaline‐earth Ca codoped has little influence on the energy bands of TiO2 except slightly elevating the conduction band edge at a value of 0.02 eV. The hydroxyl radicals (•OH) producing and photocatalytic experiment shows that Ca and N codoped can effectively decrease the generation of recombination centers, and enhance separation efficiency of photo‐induced electrons and holes as well as the photocatalytic activity of TiO2. The codoped photocatalyst has the highest photocatalytic activity when Ca doped ratio reach 0.48%. Excess Ca doped will weaken the crystallization of anatase TiO2, form charge center, produce new recombination centers and finally reduce the photocatalytic activity of TiO2.