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首页> 外文期刊>Applied Catalysis, B. Environmental: An International Journal Devoted to Catalytic Science and Its Applications >otocatalytic activity of N-doped and N-F co-doped TiO2 and reduction of chromium(VI) in aqueous solution: An EPR study
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otocatalytic activity of N-doped and N-F co-doped TiO2 and reduction of chromium(VI) in aqueous solution: An EPR study

机译：N掺杂和N-F共掺杂的TiO2的光催化活性和水溶液中铬（VI）的还原：EPR研究

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N-doped and N-F co-doped TiO2 catalysts were prepared via a sol-gel method using NH4C1 and NH4F as N and N-F dopant precursors, respectively, having Ti:N and/or F molar ratios of 1:1,1:2 and 1:3.The catalysts were tested for the photocatalytic reduction of Cr(VI) in the presence of oxalate ions. XRD analysis showed the formation of TiO2 anatase phase in all cases. UV-vis DRS spectra showed that both N-F and N-doping resulted in a decrease in the band gap energy (E_g), at the values of 2.81 eV and 3.01 eV, respectively. Thus, N-F doped TiO2 showed enhanced absorption at visible wavelengths. The structure and photodynamics of the TiO2 catalysts was investigated in detail by electron paramagnetic resonance (EPR) spectroscopy. The EPR data showed that: [i] NO centers, Nb~· and O2~(-·) radicals were formed. In addition, lattice Ti~(3+) ions were detected in N-F co-doped solids; [ii] the Nb~· and Ti~(3+) species were photoactive, while the NO species were non-photoactive. The photocatalytic efficiency for Cr(VI) reduction in the presence of oxalate ions, followed the trend TNF1 >TN1 >TNF2>TN3 >TN2>TNF3. Importantly, an apparent correlation between the catalytic efficiency and the concentration of Nb~· species was revealed by EPR. The location of Nb~· in the crystal lattice of TiO2 has been assessed also by measuring their microwave saturation parameters P_(1/2). Electron capturing by O2 and subsequent generation of O2~(-·) was favored for N-doped catalysts. In contrast, in N-F co-doped catalysts, O2 could not compete efficiently with Cr(VI) for the photogenerated electrons in energy states below the conduction band of TiO2, resulting in higher reduction efficiency for these catalysts.
机译：通过溶胶-凝胶法分别使用Ti：N和/或F摩尔比为1：1、1：2和Ti的NH4Cl和NH4F分别作为N和NF掺杂剂前体制备N掺杂和NF共掺杂的TiO2催化剂。 1：3在草酸盐离子存在下测试了催化剂对Cr（VI）的光催化还原。 XRD分析表明在所有情况下都形成了TiO 2锐钛矿相。 UV-vis DRS光谱显示，N-F和N掺杂均导致带隙能量（E_g）降低，分别为2.81 eV和3.01 eV。因此，N-F掺杂的TiO2在可见波长处显示出增强的吸收。 TiO2催化剂的结构和光动力学通过电子顺磁共振（EPR）光谱进行了详细研究。 EPR数据表明：[i]形成了NO中心，形成了Nb〜·和O2〜（-·）自由基。另外，在N-F共掺杂固体中检测到晶格Ti〜（3+）离子。 [ii] Nb〜·和Ti〜（3+）具有光活性，而NO具有非光活性。在草酸根离子存在下，Cr（VI）还原的光催化效率遵循TNF1> TN1> TNF2> TN3> TN2> TNF3的趋势。重要的是，EPR揭示了催化效率与Nb〜·的浓度之间存在明显的相关性。还通过测量其微波饱和度参数P_（1/2）来评估Nb〜·在TiO2晶格中的位置。氮掺杂的催化剂有利于通过O2捕获电子并随后生成O2〜（-·）。相反，在N-F共掺杂催化剂中，O2不能与Cr（VI）有效竞争低于TiO2导带的能态的光生电子，从而导致这些催化剂的还原效率更高。

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