掺氮TiO2可见光降解有机污染物的比较研究

用溶胶-凝胶法制备了不同掺杂量的N/TiO₂复合纳米粉末, 采用X射线衍射(XRD)、扫描透镜(TEM)、紫外-可见反射吸收光谱(UV-vis)对催化剂进行了初步表征. 通过X射线光电子能谱(XPS)、元素分析仪(EA)测定其含氮量. XPS分析结果显示TiO₂晶格中的氧被氮原子取代, N/TiO₂表面存在Ti^3＋离子; 紫外-可见反射吸收光谱测得不同掺杂量的N/TiO₂的禁带宽度(E_g), 推测在TiO₂价带上方生成了由N诱导产生的中间带, 当氮、钛摩尔比为0.0880时N/TiO₂的E_g最小, 为2.50 eV. 在可见光下, 以酸性桃红(SRB)和无色小分子对氯苯酚(4-CP)作为可见光活性实验的探针反应, 确定了最佳掺杂比为n_N/n_Ti＝0.0880. 结果表明, 最佳掺杂量下N/TiO₂能显著降解SRB和4-CP, 通过测定ESR, IR, TOC, COD, 重点比较了TiO₂在掺杂N前后在降解SRB和4-CP时的差异, 包括氧化物种、矿化率、最终产物等, 证明在可见光下, N/TiO₂的降解机理为电子从独立的N 2p轨道激发到Ti 3d轨道, 产生羟基自由基等氧化物种, 达到降解有机物的目的.

Comparative Research on Degradation of Organic Pollutants with Nitrogen-Doped TiO2 Photocatalyst under Visible Light

TiO₂ nanoparticles doped with different content of nitrogen were prepared by sol-gel method, and preliminarily characterized by means of XRD, TEM and UV-vis spectra. The concentration of nitrogen of N/TiO₂ was detected using XPS and elemental analyzer method (EA). It was confirmed by XPS that oxygen sites were substituted by nitrogen atoms and Ti^3＋ species was formed on the surface of the nitrogen-doped titania; UV-visible reflectance spectra measured the band gap (E_g) of nitrogen-doped titania in different content, which indicated that an N-induced midgap level was formed from above the valence band (O 2p). The E_g of N/TiO₂ could be estimated to be 2.50 eV when the molar ratio of N to Ti was 0.0880, which was narrowest. The photocatalytic degradation of sulforhodamine-B (SRB) and 4-chlorophenol (4-CP) in aqueous solution was used as probe reactions to evaluate their photocatalytic activity with different doped content. It indicated that the N/TiO₂ powder with molar ratio n_N/n_Ti＝0.0880 exhibited highly catalytic activity for degradation of SRB under visible light irradiation. The formed oxidation species, total organic carbon (TOC), chemical oxygen demand (COD_Cr) and infrared spectrophotometry (IR) assays showed that the mechanism of photocatalytic degradation involved the excitation of electrons from the isolated N 2p orbitals to the Ti 3d orbitals, generating •OH for degradation of organic compounds.