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

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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.