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

通过ICP-质谱法测量由TiO 2单晶PLA在水中形成的钛的量。聚乳酸产量作为激光能量密度，水的厚度，pH值和温度的溶液中，和酸的功能进行了评估。产率主要受前两个因素的控制，可用两个方程表示。利用扫描隧道显微镜（STM）研究了二氧化钛粒子在基底上的尺寸和行为。通过探针与纳米粒子之间的偏压作用，可以很容易地在衬底表面移动，粒子的尺寸可以达到4 nm。用漫反射光谱法测得薄膜的禁带宽度为3.87 ~ 4.13eV。这种明显的带隙扩大由于量子尺寸效应是非常独特的，只有在这些纳米颗粒。这种蓝移不利于TiO 2上的光催化反应。但是，该薄膜不仅在紫外光下而且在> 400 nm可见光下对亚甲基蓝具有光活性。这一事实被解释为在扩大的带隙之间形成的杂质水平，例如水中PTA所涉及的氮。纳米颗粒中高浓度的杂质可能对产生大量的空穴对可见光光氧化活性起重要作用。

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.