| Semiconductor photocatalysis is expected as a highly promising strategy for both harvesting solar energy and decomposing unwanted organics in water and air by solar light irradiation. The main problem of TiO2, the most widely studied photocatalyst material by now, is that its band gap is as wide as3.1eV, making it absorb only the UV part of the incident solar irradiation. α-Fe2O3has a proper band gap of about2.1eV which lies in the visible region of solar spectrum and allows utilization of45%of the solar radiation. Together with the environmental compatibility and low cost, α-Fe2O3is considered as a good candidate for visible light photocatalyst.In this study, α-Fe2O3films with nanostructures are fabricated on FTO glasses. To increase the photoelectrochemical performance, films are surface modified with TiO2and surface treated with Ar plasma. In the first part, Fe2O3films are covered with TiO2by reaction magnetron sputtering. In addition, Sn-doped Fe2O3films are prepared and also surface modified with TiO2. In the part of Ar plasma surface treatment, the plasma conditions(Ar pressure, plasma power and processing time) are optimized. Samples are characterized by XRD, SEM and UV-Vis, the photoelectrochemical performance are tested by electrochemical workstation. Some representative samples are studied by HR-SEM and TEM in LEM3CNRS, Metz, France.The main results are as follows:(I) Anatase TiO2can be deposited on the surface of α-Fe2O3films by reaction magnetron sputtering when the temperature is350℃. After TiO2modification, there is a remarkable enhancement of photoelectrochemical performance:after coverd by5nm TiO2, the onset potentials shift negatively by50mV for Fe2O3film and60mV for Sn-doped Fe2O3film; the J0.23v of Fe2O3film increase from0.09mA/cm2to0.30mA/cm2and the J0.23v of Sn-doped Fe2O3increases from0.19mA/cm2to0.30mA/cm2.(II) Two phenomenas caused by TiO2modification attribute to the enhancement of photoelectrochemical performance:1) TiO2modification can reduce the density of surface state, which has a negative influence on the onset potential;2) The cover of TiO2can promote the water oxidation kinetics to enhance the photocurrent. However, when the thickness of TiO2is too thick, the photoelectrochemical property subsides because of the mismatch of band levels of TiO2and Fe2O3. (III) Ar plasma surface treatment could introduce defects into surface of Sn-doped Fe2O3films, and could change the surface appearance. The absorption of light (wavelength>600nm) increase slightly after treatment, which implies that the energy level of defect is between the minimum of conduction band and maximum of valence band. Ar plasma surface treatment could significantly increase the photocurrent of Sn-doped Fe2O3films.(IV) The improvement of photoelectrochemical performance can be attributed to the surface states introduced by Ar plasma treatment. The surface states, on one hand, increase the onset potential by Femi level pinning, however it is not obvious at low power; on the other hand, act as the catalytic center of interfacial reaction, which promote the photocurrent. Nevertheless, as the photoelectrochemical reaction progressing, the unstable surface defects lose their activity slowy and the surface of films appears obvious change. |
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