Photocatalytic And Photoeletrochemical Properties Of Fe Modified TiO₂

The crisis of environment and energy is becoming increasingly severer with world’s economic growth, which may lead to unavoidable conflicts and inestimable costs. As n-type semiconductor with good photocatalytic and photoelectrochemical performance, TiO2 has always been the hot-spot in new energy and environmental fields. Due to its non-toxicity, chemical and thermal stability, TiO2 materials are under intense researches in the fabrication of dye sensitized solar cells, photocatalytic degradation of pollutants and water splitting. However, methods should be taken to overcome its defects for an ideal photoresponsive material to solve environment and energy issues. The relatively large band gap should be narrowed to gain absorbance of visible light, the combination of photoinduced charges should be retarded, etc. Decades of work have been done to improve its properties including doping, composing, sensitizing and so on. Among the above mentioned methods, iron doping was considered as an effective way to modify TiO2, and iron oxide was applied to the synthesizing of TiO2/Fe2O3 composite by various process. In this work, different Fe sources were used to prepare modified TiO2 catalysis and TiO2 nanotube with facile approaches. Materials with enhanced photocatalytic and photoelectrochemical properties were obtained. The results and conclusions are summarized as below.1. A convenient approach of Fe doped carbon incorporated TiO2 was developed by one-step flame-assisted hydrolysis technique. Only a mixture tetrabutyl titanate, anhydrous ethanol, and Fe source was used to synthesis Fe doped photocatalytic material with higher efficiency. The introduction of Fe wouldn’t destroy anatase crystal structure of pristine sample according to XRD patterns. The type of Fe source brought great influence to the morphology of TiO2 particle. Inorganic iron source ruined the homogenous microsphere morphology with a small amount, while organic source didn’t place any impact on the microspheres. It is revealed from XPS spectra that Fe ions entered the crystal lattice of TiO2 by substituting Ti ions. Red shifts and remarkably enhanced absorbance in visible light region for Fe doped samples were illustrated by UV-vis diffuse reflectance spectra. The photocatalytic degradation rate of methylene blue was enhanced by 14% with the introduction of inorganic Fe source under visible light irradiation. A 22% promotion of photocatalytic activity under UV-vis light was observed for samples prepared with organic dopant.2. A simple synchronized method was proposed to modify TiO2 nanotube(titanate nanotube, TNT) film during anodic oxidation step. FeCl3 and Fe(NO3)3 were selected as precursors. The corrosion of Ti substrates was observed when slight amount of FeCl3 was added into the electrolyte. The photocurrent density of TiO2 nanotube film was doubled under UV-vis light irradiation with introduction of 0.01M Fe(NO3)3. The enhancement was up to 50% under visible light. Decreased interface impedances were illustrated by EIS results with adding 0.01M,0.03M Fe(NO3)3. The flat band potential of each film changed more negative then become more positive by increasing the concentration of Fe(NO3)3 in electrolyte, which is demonstrated by the Mott-Schottky plot.3. Due to its large surface area, the particular morphology of TiO2 nanotube facilitates easy attachment of molecules and ions to both inside and outside of the tubes. Immerse-annealing process was proposed to synthesis modified TiO2 nanotube films with dark-blue ink or FeCl3/ethanol solution. Different samples were prepared under 450℃,550℃ thermal treatments with different immersing time(10min,30min, 90min). Decreased photocurrent densities of each modified samples under both UV-vis light and visible light were shown according to the photocurrent density vs. time curves. This phenomenon may be caused by other components in the complex black-blue ink system which is detrimental to the photoelectrochemical activities to TNT film. FeCl3/ethanol solution was used to form Fe2O3/TNT film with immerse-annealing process. Although modified TNT film displayed similar photoelectrochemical response under visible light irradiation, severe decay of photocurrent density was observed under UV-vis light. Compact junction may not be formed during the immerse-annealing process, thus causing negative effects to the charge transfer between semiconductors.