Size dependency of nanocrystalline TiO2 on its optical property and photocatalytic reactivity exemplified by 2-chlorophenol
Size dependency of nanocrystalline TiO2 on its optical property and photocatalytic reactivity exemplified by 2-chlorophenol
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DOI：
10.1016/j.apcatb.2006.07.018
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发表时间：
2006-10-26
影响因子：
22.1
通讯作者：
Tseng, Yao-Hsuan
中科院分区：
文献类型：
--
作者：
Lin, H.;Huang, C. P.;Tseng, Yao-Hsuan
采用金属-有机化学气相沉积法(MOCVD)成功制备了锐钛矿型二氧化钛纳米晶(17-29 nm)。适度控制MOCVD系统参数可以控制颗粒大小。研究了合成的纳米二氧化钛的电光和光催化性能，以及几种商用的超细二氧化钛颗粒(如3.8-5.7 nm)。根据Kubelka-Munk理论，利用变换漫反射技术测定了TiO2光晶体的带隙。结果表明，当粒径从29 nm减小到17 nm时，二氧化钛的禁带宽度从3.239 eV单调减小到3.173 eV，当粒径从17 nm减小到3.8nm时，禁带宽度从3.173 eV增加到3.289 eV。禁带宽度随颗粒尺寸变化的结果与Brus方程，即有效质量模型的预测结果吻合较好。而对2-氯苯酚(2-CP)的光催化氧化结果表明，颗粒越小，降解速度越快。这部分归因于相对于光源光谱的带隙变化和光催化剂的比表面积(或颗粒大小)的综合效应。由于颗粒大小引起的带隙变化仅代表相对于光源的总光谱的一个小的光学吸收窗口，即从380 nm到400 nm，而不是280 nm。因此，较大颗粒的光学性质的增益因其比表面积的减少而严重受损。我们的结果清楚地表明了比表面积在控制光催化剂的光催化活性中的重要性。结果还表明，二次粒子尺寸随时间增长，主要是由于粒子的聚集。光催化速率常数随一次粒子尺寸的增大呈指数下降。光催化性能与光催化剂的光电性质密切相关，光催化剂的初级颗粒大小本身就能预测光催化速率。(C)2006年，爱思唯尔出版。
Anatase TiO2 nanocrystallines (17-29 nm) were successfully synthesized by the metal-organic chemical vapor deposition method (MOCVD). Moderate manipulation of system parameters of MOCVD can control the particle size. The electro-optical and photocatalytic properties of the synthesized TiO2 nanoparticles were studied along with several commercially available ultra-fine TiO2 particles (e.g., 3.8-5.7 nm). The band gap of the TiO2 crystallines was determined using the transformed diffuse reflectance technique according to the Kubelka-Munk theory. Results showed that the band gap of TiO2 monotonically decreased from 3.239 to 3.173 eV when the particle size decreased from 29 to 17 nm and then increased from 3.173 to 3.289 eV as the particle size decreased from 17 to 3.8 nm. The results of band gap change as a function of particle size agreed well with what was predicted by the Brus' equation, i.e., the effective mass model (EMM). However, results of the photocatalytic oxidation of 2-chlorophenol (2-CP), showed that the smaller the particle size, the faster the degradation rate. This is attributed in part to the combined effect of band gap change relative to the spectrum of the light source and the specific surface area (or particle size) of the photocatalysts. The change of band gap due to particle size represents only a small optical absorption window with respect to the total spectrum of the light source, i.e., from 380 to 400 nm versus > 280 nm. Consequently, the gain in optical property of the larger particles was severely compromised by their decrease in specific surface area. Our results clearly indicated the importance of specific surface area in controlling the photocatalytic reactivity of photocatalysts. Results also showed that the secondary particle size grew with time due mainly to particle aggregation. The photocatalytic rate constants decreased exponentially with increase in primary particle size. Primary particle size alone is able to predict the photocatalytic rate as it is closely related to the electro-optical properties of photocatalysts. (c) 2006 Published by Elsevier B.V.