以棒状纳米微晶纤维素(Nanocrystalline cellulose, NCC)为形貌诱导剂, TiCl4为原料, 采用水解法在70℃的温度下反应4~6 h, 制备了TiO2花状纳米晶体. 采用TEM、HRTEM、XRD和FTIR对不同条件下制得的TiO2晶体的微观形貌、晶粒尺寸和晶相组成进行了表征, 探讨了TiCl4的用量及反应时间对晶体形貌和晶型的影响, 并对其形成机理进行分析. 纳米微晶纤维素表面富含大量羟基, 可与TiO2之间形成氢键连接, 促使TiO2在其表面的异质成核和生长, 同时纳米微晶纤维素在TiO2 表面的吸附作用, 改变了各晶面的表面能和生长速度, 使TiO2沿着[110] 方向优先生长形成一维针状物, 针状物再进一步聚集形成花状聚集体. 以甲基橙为目标污染物, 测试了所得TiO2纳米花状晶体的光催化性能. 结果表明, 随着TiCl4用量的增多及反应时间的延长, 所制得的TiO2纳米晶体中金红石含量增多, 形貌逐渐复杂化, 光催化性能下降.
Flower-like titania nanocrystals were synthesized by hydrolysis of titanium (IV) chloride at a low temperature of 70℃ in 4–6 h, employing nanocrystal cellulose (NCC) as a morphology controlling agent. The obtained nanocrystals were characterized by transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) and FTIR. TEM and HRTEM investigations reveal that the morphologies of the nancrystals are flower-like, and each flower is composed of several nanoneedles with a diameter of 15–20 nm and a length of 100–200 nm. The XRD results show that the crystalline phase of the nanocrystals have a strong dependence on the mole ratio of TiCl4 to H2O and the reaction time. FTIR result shows that a chemical bond is formed between NCC and TiO2. A possible growth mechanism is proposed based on the characteristic results. The NCC whose surface is full of hydrophilic groups can establish hydrogen bonding with TiO2 to promote the nucleation and crystal growth of TiO2 at low temperature. Moreover, the selective adsorption of NCC molecules on the crystal face of TiO2 varies the growth rate of different crystal planes, and the anisotropic crystal growth leads to the formation of nanoneedles. Then these nanoneedles aggregate together to assemble into a flower-like secondary structure. TiO2 prepared at low temperature exhibites high activity in the photocatalytic degradation of methyl orange in aqueous solution under metal halide lamp.
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