Formation of Nano-particle Titanic Fibers with High Photocatalytic Activity

TiO_2光催化剂的各种应用，特别是在环境方面的应用正在不断发展。为了使其应用，优化其形态和光催化活性是重要的。如果有可能获得纤维钛，由于其易于处理和压力损失小，因此被认为有广泛的应用可能。本文研究了纤维状二氧化钛的合成及表征。将单分散TiO_2颗粒悬浮液在78 ~ 100℃下干燥，制得宽度为50 ~ 250 μm，长度为几~ 10cm的均匀TiO_2纤维。纤维宽度随悬浮液浓度的增大、粒径的增大和干燥温度的降低而增大。纤维呈矩形片状，TiO_2颗粒密集均匀堆积形成纤维。研究了热处理对纤维结晶度、晶体类型、斑点表面积和孔径的影响。经400℃热处理的TiO_2纤维具有高达180m^2/g的高比表面积，同时具有颗粒内孔形成的微孔（0.57nm）和颗粒间孔形成的均匀介孔（30nm）。根据制备条件，即使在1000℃加热后，晶体类型仍保持锐钛矿。TiO_2溶胶（D=7nm）制备的钛纤维在400 ~ 800℃的温度范围内经过热处理后，其光催化活性有所提高，对NOx的分解率高达98%。结晶度也影响光催化活性。采用TiO_2溶胶（D=6nm）和SiO_2溶胶（D=8 ~ 11nm）制备TiO_2-SiO_2纤维。SiO_2的加入提高了钛的光催化活性，对SiO_2含量为0wt%的纤维的NOx分解率为76%，对SiO_2含量为40wt%的纤维的NOx分解率为93%，并通过特征处理和SiO_2的加入提高了TiO_2纤维的强度。

Various applications, especially those for environmental, are developing for TiO_2 photocatalyst. For its application, optimization of the morphology and photocatalytic activity are the important. If it is possible to obtain a fibrous titanic, a wide range of applications are considered to be possible, because of its easiness in handling and low pressure loss. In this study, the synthesis and characterization of fibrous TiO_2 was investigated.Homogeneous fibrous TiO_2 with 50 to 250 μm of width and a few to 10cm of length was prepared by drying the suspension of the monodispersed TiO_2 particles at 78〜100℃. The fiber width increased with increasing concentration of suspension, particle diameter, or with decreasing drying temperature. The fibers had a rectangular plate-like shape and TiO_2 particles were densely and homogeneously packed to form the fibers.The effects of a heat treatment on crystallinity, crystal type, speck surface area and pore size of the fibers were investigated. The TiO_2 fiber heat-treated at 400℃ had a high specific surface area as 180m^2/g and had both of micropore (0.57nm) caused by infra-particle pore and homogeneous mesopore (30nm) caused by inter-particle pore. The crystal type maintains anatase after heating even at 1000℃ depending on preparation conditions.The photocatalytic activity of the titanic fibers formed from TiO_2 sol (D=7nm) increased by heat-treatments between 400〜800℃ and showed such a very high activity as 98% of NOx decomposition. The crystallinity also affects the photocatalytic activity.The TiO_2-SiO_2 fibers were developed by using TiO_2 sol (D=6nm) and SiO_2 sol (D=8〜11nm). The photocatalytic activity of titanic increased by the addition of SiO_2 with the adsorptive action, i.e., 76% of NOx decomposition for 0wt% of SiO_2 content fibers and 93% of NOx decomposition for 40wt% of SiO_2 content fibers, and the strength of TiO_2 fibers were also increased by feat-treatments and the addition of SiO_2.