结晶度,{001}/{101}晶面比和Au负载对热处理TiOF_2制备的锐钛矿TiO_2光催化活性的影响（英文）

TiO_2半导体由于具有清洁、无毒光催化性能优异和热稳定性好等优点,一直是光催化理论及应用研究的一个热点材料,但其较宽的禁带宽度(金红石3.0 eV,锐钛矿3.2 eV)和较快的光生载流子复合速率限制着其进一步应用.在本研究中,我们通过直接煅烧TiOF2前体成功制备出具有截断八面体形貌的锐钛矿TiO_2纳米及亚微米晶体,并采用现代测试方法综合分析了煅烧温度对其结晶度、{001}/{101}晶面比例以及光催化性能的影响,然后以高结晶度的TiO_2样品负载Au,进一步探讨了负载Au对其可见光催化活性的提升.X射线衍射图谱(XRD)和拉曼光谱表征结果表明,未煅烧的样品为TiOF2,在700°C以下煅烧的样品均呈纯锐钛矿相,而800°C煅烧的样品出现了少量金红石相,表明以TiOF2为前体制备的TiO_2锐钛矿相向金红石相的转变温度明显高于常规TiO_2材料.同时, XRD峰强度随煅烧温度升高而增大,表明样品结晶度提高,因而我们认为700与800°C煅烧的样品结晶度较高,而且保持了纯的或大量的锐钛矿物相.根据XRD谱得到的{001}与{101}晶面方向的平均尺寸计算了{001}/{101}晶面比例.结果显示,随着煅烧温度提高,{001}/{101}晶面比例增大.通过场发射扫描电子显微镜观察到煅烧的样品具有较规则的截断八面体双锥形貌,煅烧温度越高,形貌越规则,颗粒尺寸越大.N2吸附-解吸等温线测试结果显示,煅烧后样品的比表面积低于未煅烧的TiOF2,原因是煅烧后的样品团聚现象比较严重.紫外-可见漫反射光谱显示煅烧样品的吸收边相比于未煅烧的TiOF2发生明显红移.不同样品在紫外光下降解甲基蓝与甲醛的性能研究表明, 700°C煅烧的样品具有最高的光催化活性,这可归因于其较高的结晶度及纯的锐钛矿相结构.对于负载Au的高结晶度TiO_2样品(Au-T700和Au-T800),紫外-可见漫反射光谱中在597 nm处出现了Au的等离子吸收峰, X射线光电子能谱中86与83 eV处Au 4f峰的出现也表明Au成功负载在材料表面.丙酮可见光催化降解实验表明,相比于未负载的700和800°C下煅烧TiOF2制备的TiO_2,负载Au的样品的催化活性分别提高了2.6和4.8倍.综上所述,通过升高煅烧温度可提高TiO_2的结晶度、晶粒尺寸和{001}/{101}晶面比例.而结晶度和{001}/{101}晶面比例的提高可以抑制电子和空穴的复合,从而提高TiO_2液相和气相光催化活性.在具有最高结晶度和{001}/{101}晶面比例的TiO_2上负载,后其可见光催化活性进一步提高.

Effects of crystallinity, {001}/{101} ratio,and Au decoration on the photocatalytic activity of anatase TiO2 crystals

Anatase TiO₂ nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF₂ precursors. The as-prepared TiO₂ samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N₂ adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800 °C. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO₂ samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF₂ at 700 and 800 °C.