摘要
TiO_2光催化剂在污水和空气净化方面的应用得到越来越多的重视。但由于其能带较宽(3.2 eV),只能被波长小于387 nm的紫外光激发。由于上述波段的光能量只占太阳光中能量的3～5%左右,因此为了更有效地利用太阳光中的可见光能量,开发对可见光响应的、高活性TiO_2光催化剂显得十分必要。
本文以葡萄糖和无定型TiO_2为前驱物在低温条件下制备出了具有可见光活性的碳掺杂TiO_2光催化剂。与先前文献报道的高温合成碳掺杂TiO_2的方法不同,本研究在160℃水热反应的条件下成功低温制备出碳掺杂TiO_2光催化剂,并对产物催化剂进行了XRD,XPS,TEM,N_2吸附-脱附和UV-vis漫反射光谱表征。结果表明碳掺杂TiO_2具有平均孔径大小为8nm的介孔结构以及高达126 m~2/g的比表面积。与非掺杂的光催化剂相比较,碳掺杂TiO_2在400-600 nm光谱范围内表现出较好的可见光吸收特性。在可见光的照射条件下(λ＞420 nm),碳掺杂TiO_2在水溶液降解RhB过程中表现出比非掺杂的TiO_2以及P25更高的光催化活性。
根据所得产物的X-射线光电子能谱表征结果,我们推测碳酸根可能存在于我们所制得的碳掺杂二氧化钛中。为了找出产物的可见光活性原因以及产物中碳的存在形式,我们用红外光谱仪和核磁共振光谱仪对产物进行了更进一步的表征。结果表明在碳掺杂二氧化钛中存在HCO_3~-,CO_3~(2-)以及葡萄糖分解产物的中间体,这些均可作为光敏剂,成为产物具有较高光催化活性的原因。另外,我们发现用本文采用的水热法来制备碳掺杂二氧化钛时,无定形的二氧化钛作为二氧化钛的原料要优于P25作为二氧化钛的原料,这可能是由于无定形的二氧化钛由于其较高的比表面和比较多的-OH键,从而更有利于葡萄糖分解产物中间体与之结合形成碳掺杂TiO_2。
The application of titanium dioxide as a heterogeneous photocatalyst is attracting considerable attention for water and air purification and remediation.Unfortunately, because of its large band gap of 3.2 eV,it can be activated only under UV light irradiation of wavelength＜387 nm,which constitutes only a small fraction(about 3-5%)of the solar spectrum.So it will have a positive effect for improving the photocatalytic efficiency of TiO_2 by shifting its optical response to the visible light.
A visible-light-active carbon-doped TiO_2 photocatalyst was prepared by using glucose as carbon source and amorphous TiO_2 as titanium source,respectively.Different from the previous carbon doped TiO_2 prepared at high temperature,our preparation was performed by a hydrothermal method at temperature as low as 160℃.The resulting photocatalyst was characterized by XRD,XPS,TEM,nitrogen adsorption,and UV-vis diffuse reflectance spectroscopy.The characterizations revealed that the photocatalyst possessed a homogeneous pore diameter about 8 nm and a high surface area of 126 m~2/g. Comparing to undoped TiO_2,the carbon doped TiO_2 shows obvious absorption in the 400-450 nm range with a red shift in the band gap transition.It is found that the resulting carbon doped TiO_2 exhibits significantly higher photocatalytic activity than the counterpart undoped TiO_2 and Degussa P25 on the degradation of rhodamine B(RhB)in water under visible light irradiation(γ＞420 nm).
In order to find out the origin of visible light photocatalytic activity and the nature of carbonaceous species in the carbon doped TiO_2,we treated the photocatalyst with different methods and evaluated the photocatalytic activities of the resulting new catalysts.Through FT-IR spectrum and solid state C~(13)-NMR spectroscopy characterization,we found that HCO_3~-,CO_3~(2-)ions and intermediate product of reduction of glucose coexisted in the catalysts.These carbonaceous species may be embedded within the TiO_2 matrixes to form Ti-O-C structures and act as photosensitizer,resulting in the high photocatalytic activity of our carbon doped TiO_2.
引文
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