N掺杂TiO_2纳米粒子表面光生电荷特性与光催化活性

以尿素为氮源,采用水热法制备了不同N掺杂量的TiO2(N-TiO2)光催化剂.利用X射线衍射(XRD),紫外-可见漫反射光谱(UV-Vis DRS),X射线光电子能谱(XPS)及荧光(PL)光谱等技术对其进行了系统的表征.以罗丹明B(RhB)和甲基橙(MO)溶液的脱色降解为模型反应,分别考察了N-TiO2光催化剂在紫外和可见光区的光催化活性.利用表面光伏(SPV)和瞬态光伏(TPV)技术研究了N-TiO2纳米粒子表面光生电荷的产生和传输机制,并探讨了光生电荷与光催化活性之间的关系.结果显示,随着N含量的增大,TiO2表面光伏响应阈值红移,可见光部分光电压响应强度逐渐增强,瞬态光伏响应达到最大值的时间亦有着不同程度的延迟.这表明适量的N掺杂能够提高TiO2纳米粒子中光生载流子的分离效率,相应地延长载流子的传输时间,增加光生电荷的寿命,从而促进其光催化活性;而过量的N掺杂则增加了TiO2纳米粒子中光生载流子的复合中心,抑制其光催化活性.

Photoinduced Charge Carrier Properties and Photocatalytic Activity of N-Doped TiO2 Nanocatalysts

Nitrogen-doped TiO₂ (N-TiO₂) photocatalysts with different amounts of N doping were successfully synthesized by the hydrothermal method using urea as the nitrogen source. The samples were characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (UV -Vis DRS),X -ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. The photodegradation of rhodamineB (RhB) and methyl orange (MO) solutions was used to evaluate the photocatalytic activity of the catalysts under UV and visible light irradiation. Surface photovoltage (SPV) and transient photovoltage (TPV) techniques were used to investigate the separation and transport mechanism of the photogenerated charge carriers of the N-doped TiO₂ nanoparticles. The relationship between the photogenerated charge carriers and photocatalytic activity was also discussed. The results showed that the SPV threshold values shifted to the visible region and a stronger photovoltaic response in the visible region was observed with an increase in N doping. We also found that the maximum TPV response time was different for N-TiO₂. These results indicate that with an appropriate amount of N doping, the photoinduced charge carriers separate efficiently, the transmission time increases, and the lifetime of the photoinduced charge carriers increases. Therefore, the photocatalytic activity is enhanced. However, excessive N acts as recombination centers for photoinduced electrons and holes, which reduces their photocatalytic activity.