The preparation of semiconductor nanoparticles by PLA in water and the their evaluation as functional materials

采用icp -质谱法测定TiO2单晶PLA在水中形成钛的量。PLA产率与激光通量、水厚度、溶液pH和温度以及酸种类有关。产量主要受前两个因素控制，用两个方程表示。用STM研究了钛颗粒在基体上的大小和行为。在尖端和纳米颗粒之间的偏置电压作用下，纳米颗粒可在衬底表面移动，其尺寸可小至4nm。用漫反射光谱法测得薄膜的带隙为3.87 ~ 4.13eV。这种由量子尺寸效应引起的明显的带隙扩大仅在这些纳米粒子上是非常独特的。这种蓝移不利于TiO2上的光催化反应。然而，薄膜不仅在紫外光和>400nm可见光下对亚甲基蓝具有光活性。这一事实可以用扩大带隙之间形成的杂质水平来解释，例如水中的PTA所涉及的氮。纳米颗粒中高浓度的杂质可能是产生大量可见光氧化活性空穴的重要原因。

The amount of titanium formed by TiO2 single crystal PLA in water was measured by ICP-mass spectrometry. The PLA yield was evaluated as a function of laser fluence, water thickness, pH and temperature in solution, and acid kind. The yield was mainly controlled by the former two factors and was shown by two equations. The size and behavior of titania particles on the substrate were studied with STM. The size of the particles as small as 4nm was detected and they easily moved on the substrate surface by biased voltage between tip and nano-particles. The bandgap of the thin films was measured to be 3.87 to 4.13eV with diffused reflectance spectroscopy. Such clear bandgap enlargement due to quantum-size effect is quite unique only on these nano-particles. Such blue shift is disadvantage for the photo-catalytic reaction on TiO2. However, the thin films were photo-active to methylene blue degradation not only with ultraviolet but also with >400nm visible light. The fact was interpreted by the impurity levels formed in between the enlarged bandgap such as nitrogen involved by PTA in water. Probably high concentration of impurity in nanoparticles play significant role on producing much holes active for photo-oxidation with visible light.