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光催化作为一种具有前景的技术,被广泛运用于有机物降解、废水处理、空气净化、抗菌、太阳能电池等领域.在众多的光催化材料中,纳米TiO_2因具有性质稳定、耐腐蚀、廉价和无毒等优点而受到广泛关注.但纳米TiO_2禁带宽度较大(3.2 eV)、只对紫外光有响应及电子-空穴对易复合等特性限制了它的应用.因此,提高纳米TiO_2的可见光响应一直是研究的热点.本文发展了一种在低温下制备棕色纳米TiO_2的改良溶胶-凝胶法.该法以钛酸四丁酯为钛源,无水乙醇为溶剂,形成溶胶后无需陈化和高温高压,在简单温和的条件下即可制备出棕色纳米TiO_2.比较了低温干燥和高温焙烧两种处理方法,结果表明,随着制备温度的升高,样品的粒子尺寸增大,比表面积减小,颜色从白色转变为棕色,在更高的温度又变浅.样品的可见光吸收在180°C时达到最大,随后减弱.在优化温度180°C下制备的TiO_2-180°C纳米粒子不仅具有较小的粒径(5.0 nm),较大的比表面积(213.45 m~2/g),且在整个紫外-可见光区都具有较强的吸收,其禁带宽度低至1.84 eV.X-射线光电子能谱结果表明,TiO_2粒子表面的–OH/H_2O含量随制备温度升高而先增加后下降.Raman光谱中Eg峰的移动和变宽表明TiO_2晶格可能存在缺陷或氧空位,而TiO_2-180°C纳米粒子的电子顺磁共振图谱的g值在2.003左右,对应氧空位中的未成对电子,验证了以上推测.其中TiO_2-180°C纳米粒子呈现为最强的EPR信号,表明其晶格内存在最高浓度的氧空位,这是其具有强可见光吸收的原因.光催化实验结果表明,在可见光照射下,TiO_2-180°C可高效降解亚甲基蓝(MB).当C(MB)=10mg/L,p H=4,催化剂添加量为0.07 g时,TiO_2-180°C催化剂的光催化活性达到最佳,光照1 h后MB降解率达到99.33%,反应速率常数(0.08287 mg/(L×min))约为同条件下P25(0.01342 mg/(L×min))的6倍.同时,TiO_2-180°C催化剂在不同单色光下的光催化活性与它对单色光的光响应大致相符.循环降解实验证明TiO_2-180°C催化剂具有很好的稳定性.光猝灭实验表明,?OH在光催化降解过程占主导作用,而TiO_2-180°C样品表面含有较多的–OH,有利于?OH的产生,乃至光催化反应.研究表明,晶格内高浓度的氧空位导致的强可见光响应,得益于低温制备条件而保留了大量–OH/H_2O的纳米粒子表面以及更大的比表面积,共同促成了TiO_2-180°C优越的光催化活性.所制备的棕色纳米TiO_2经过进一步修饰后有望运用于实际应用中.
As a promising technology, photocatalysis is widely used in the fields of organic degradation, wastewater treatment, air purification, antibacterial, solar cell, etc. Among the many photocatalytic materials, nano-TiO 2 has the advantages of stable properties, corrosion resistance, Non-toxic, etc. However, the wide bandgap (3.2 eV) of nano-TiO 2, its response to ultraviolet light and the easy combination of electron-hole pairs have limited its application. Therefore, Visible light response has always been a hot research topic.In this paper, a modified sol-gel method was developed for the preparation of brown TiO 2 nanoparticles at low temperature.The method uses tetrabutyl titanate as titanium source and anhydrous ethanol as solvent, Aging and high temperature and high pressure, brown nano-TiO 2 can be prepared under simple and mild conditions.Comparing the two methods of low-temperature drying and high-temperature roasting, the results show that with the increase of the preparation temperature, the size of the sample increases, The specific surface area decreases, the color changes from white to brown, and becomes shallower at higher temperatures. The visible light absorption of the sample reaches its maximum at 180 ° C and then decreases. The Ti prepared at an optimized temperature of 180 ° C O_2-180 ° C nanoparticles not only have a smaller particle size (5.0 nm), larger specific surface area (213.45 m 2 / g), but also have strong absorption in the whole UV-Vis range. The band gap The width is as low as 1.84 eV.X-ray photoelectron spectroscopy results show that the content of -OH / H_2O on the surface of TiO_2 increases firstly and then decreases with the increase of preparation temperature.The movement and broadening of Eg peak in Raman spectrum indicate that the TiO_2 lattice may The defect or oxygen vacancies, and TiO_2-180 ° C nanoparticles of the electronic paramagnetic resonance spectroscopy g value of about 2.003, corresponding to unpaired oxygen vacancies in the electron to verify the above speculation that TiO_2 -180 ° C nanoparticles present Is the strongest EPR signal, indicating the highest concentration of oxygen vacancies in the crystal lattice, which is why it has strong visible light absorption.The results of photocatalytic experiments show that under visible light irradiation, TiO 2 -180 ° C can efficiently degrade methylene blue MB) .The photocatalytic activity of TiO_2-180 ° C catalyst reached the best when C (MB) = 10mg / L, p H = 4 and the amount of catalyst added was 0.07g, the MB degradation rate reached 99.33% , The reaction rate constant (0.08287 mg / (L × min)) was about 6 times higher than that of P25 (0.01342 mg / (L × min) -180 ° C under different monochromatic light photocatalytic activity and its light response to monochromatic light broadly consistent with the cycle degradation experiments proved that the catalyst TiO_2-180 ° C has a good stability.Quantum quenching experiments show that, · OH plays a leading role in the photocatalytic degradation process, while the TiO_2-180 ° C sample contains more -OH, which is conducive to the generation of OH and even the photocatalytic reaction.The results show that the high concentration of oxygen vacancies in the crystal lattice Of the strong visible light response, due to low temperature preparation conditions and retained a large number of -OH / H_2O nanoparticle surface and a larger specific surface area, together to promote the superior photocatalytic activity of TiO_2-180 ° C. The prepared brown nano-TiO_2 After further modification is expected to be used in practical applications.