Abstract Peroxide gel method, utilizing titanyl sulfate as a titanium source, is employed to synthesize TiO2 nanocrystals. The nanoparticles are further annealed at different temperatures of 300, 500, 700, and 900 °C. XRD analysis reveals a phase pure anatase structure for the as-prepared sample and anatase-rutile mixed-phase for annealed TiO2 nanocrystals. UV–visible diffuse reflectance and Fourier transform infrared spectroscopic measurements also confirm the formation of anatase-rutile mixed phase for annealed samples. Micro-Raman spectra recorded for three different excitation wavelengths suggest the formation of rutile phase in the interior of the anatase nanoparticles upon annealing. Photocatalytic efficiencies of the TiO2 nanocrystals are evaluated by choosing methyl orange as a model dye under UV and simulated solar irradiations. Presence of defect states, mainly oxygen vacancies, that form subband states extending from shallow to the deep levels in TiO2 bandgap are confirmed from photoluminescence measurements. Among the TiO2 samples, the nanocrystals annealed at 300 °C shows the maximum photocatalytic activity. The observed variation in the photocatalytic activities of the TiO2 nanocrystals is explained as per the difference in the intensity ratio of the emission peaks corresponding to those of shallow and deep traps in the bandgap of the TiO2 nanocrystals.

中文翻译：

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锐钛矿-金红石相变和光催化过氧化物凝胶途径制备的 TiO2 纳米晶体：缺陷态的作用

摘要 采用过氧化物凝胶法，以硫酸氧钛为钛源，合成了TiO2纳米晶。纳米颗粒在 300、500、700 和 900 °C 的不同温度下进一步退火。XRD 分析揭示了所制备样品的纯锐钛矿结构和退火的 TiO2 纳米晶体的锐钛矿-金红石混合相。紫外-可见漫反射和傅里叶变换红外光谱测量也证实了退火样品的锐钛矿-金红石混合相的形成。对三种不同激发波长记录的微拉曼光谱表明，退火后锐钛矿纳米颗粒内部形成了金红石相。通过选择甲基橙作为紫外线和模拟太阳照射下的模型染料来评估 TiO2 纳米晶体的光催化效率。光致发光测量证实了缺陷态的存在，主要是氧空位，形成从浅层到深层 TiO2 带隙的子带态。在 TiO2 样品中，在 300 °C 下退火的纳米晶体显示出最大的光催化活性。观察到的 TiO2 纳米晶体光催化活性的变化是根据对应于 TiO2 纳米晶体带隙中浅陷阱和深陷阱的发射峰强度比的差异来解释的。