| Summary: | 碩士 === 國立清華大學 === 化學系 === 100 === In this study, we have used a simple seed-mediated synthesis method for the preparation of penta-twinned gold nanorods with average lengths from 200 to 4.5 µm. In series I, the gold nanorods can be synthesized from 200 to 400 nm with ~20 nm diameter by tuning the pH of growth solution from 3.0 to 9.1. As the solution pH increases, the length of nanorods becomes shorter but with nanorod yield was much higher. The percentage of nanoplate byproducts decrease substantially as the solution pH increases by comparing the absorbance values of the absorption band of nanoplates to that of the transverse SPR band of nanorods. In Series II, we have systematically extended the lengths of gold nanorods and nanowires from 580 nm to 2850 nm by mainly decreasing the concentrations of tetrachloroauric acid used and raising the amount of nitric acid added to the last growth solution. However, when the pH of the growth solution is very low, the products usually accompanies with lots of nanoplates. In Series III, by lowering the transfer volume of the second growth solution to the third growth solution from 2 mL to 0.2 mL and progressively increasing the amount of nitric acid added only to the third growth solution, ultralong gold nanorods and nanowires with tunable average lengths varying from 700 nm to 4450 nm can be synthesized. The longest nanowires can reach lengths of more than 6 µm. The high uniformity and relatively short lengths of the nanorods synthesized is primarily due to the rapid particle growth rate in a basic solution condition, as evidenced by the fast solution color changes from pink to light purple and then dark purple in less than five minutes. In an acidic condition, the particle growth rate is much slower and the growth progress takes much longer time, allowing the nanorods to grow and extend their lengths. The slow growth rate has been confirmed by examining the intermediate nanorods formed during the particle growth process. HCl was found to be as effective as HNO3 in producing long gold nanorods with similar lengths, showing that the presence nitrate ions is not important to the growth of long gold nanords. These ultralong gold nanorods and nanowires are highly useful materials for a wide range of applications. Their tunable length means that selection of nanorods and nanowires most suitable for a particular situation is possible.
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