Fe掺杂TiO2催化剂制备及其光催化脱汞机理

采用溶胶-凝胶法制备Fe-TiO₂(Fe掺杂纳米二氧化钛)催化剂,通过XRD(X射线衍射仪)、SEM(扫描电镜)、EDX(能量色散X射线光谱仪)和UV-Vis谱对其形态、结构、组成和性质进行表征. 采用Fe-TiO₂催化剂脱除气态Hg0(元素汞),研究了该催化剂在紫外光和可见光下的脱汞效果,并考察了Fe3+的最佳掺杂比. 结果表明:在Fe-TiO₂光催化剂中,TiO₂以锐钛矿相形态存在,当Fe3+掺杂浓度〔以n(Fe)/n(Ti)计〕达到0.010时,所制备的Fe-TiO₂在紫外光和可见光下的脱汞率均达到最大,分别为54.76%和18.92%. 提出了Fe-TiO₂光催化脱汞的可能机制:Fe3+掺入TiO₂结构中,使TiO₂的导带与Fe3+的d轨道发生重叠,导致TiO₂能带变窄,从而扩展了可见光的响应范围；Fe3+在TiO₂中作为一个浅俘获阱,当其俘获光生电子以后,光生空穴能够继续扩散到TiO₂表面发生表面化学反应,生成具有强氧化性的超氧自由基O₂-和·OH,对Hg0进行氧化；当Fe3+掺杂浓度大于0.010时,由于过多的Fe3+成为了光生电子和光生空穴的俘获位,从而使俘获的电子-空穴对通过量子隧道效应复合的概率增加,同时,活性氧化物种O₂-和·OH相互消耗,抑制了光催化效率. 

Preparation of Fe-Doped Titania by Sol-Gel Method and Photocatalytic Removal of Gaseous Mercury

Fe-doped titanium dioxide (Fe-TiO₂) nanoparticle catalysts were prepared by the sol-gel method, and their morphological structures, compositions and properties were characterized by XRD(X-ray diffraction), SEM(scanning electronic microscopy), EDX(energy dispersive X-ray spectroscopy) and UV-Vis spectrophotometry. Fe-TiO₂ nanoparticles were used to remove gaseous elemental mercury under UV light and visible light respectively, and the optimum doping content of Fe3+ was determined. The results showed that Fe-TiO₂ nanoparticles are an anatase, and that when the doping mole ratio of Fe/Ti was 0.010, the Fe-TiO₂ catalyst had the highest Hg0 removal ability under both UV light (removal efficiency 54.76%) and visible light (removal efficiency 18.92%). The probable mechanism by which Fe-TiO₂ nanoparticles remove gaseous elemental mercury was proposed:Fe3+ ions doped into the TiO₂ structure may overlap the conduction bands of TiO₂ and the d orbital of Fe3+, which results in the narrowing of the band gap and the extension of the visible light response. Fe3+ in TiO₂ was a shallow trap, so after Fe3+ captured the photo-generated electrons, the photo-generated holes could continue to spread to the surface of TiO₂ and accomplish surface chemical reactions, which produced reactive oxidative radicals O₂- and ·OH for the oxidation of Hg0. When Fe3+ doping molar concentration exceeded 0.010, the excessive Fe3+ became the trapping position of photo-generated electrons and photo-generated holes, increasing the probability of recombination of trapped electron-hole pairs via the quantum tunneling effect. Accompanied with the self-consumption of excessive reactive oxidative radicals O₂- and ·OH, the photocatalytic efficiency was accordingly reduced. This is the mechanism by which there existed an optimum Fe/Ti doping molar ratio. The results provide some help for exploring ion modified method of TiO₂ and its application in the visible light photocatalytic field.