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2surprise铜虫 (小有名气)
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[交流]
【请教】PbS纳米晶体的吸收光谱
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我合成的PbS纳米晶体尺寸为10纳米左右（以油胺作为表面活性剂）（见附件一），能很好的分散在 甲苯，四氯化碳，氯仿中。 最近想测一下该纳米晶体的吸收光谱，主要是近红外区的（其在紫外可见区没有吸收峰）。可是做出来就是跟文献给的不一致，请大家指教指教。。。我用的仪器是lambda 900 Uv-Vis-NIR 分光光度计，室温下，以对应的溶剂做参比。。将我合成的PbS纳米晶体分散在甲苯 四氯化碳 氯仿 各做了一次。。。虽然在1400nm 1900nm处有吸收。。不过老板说峰太尖锐，不大像PbS的吸收峰（见附件二）与文献Ozin的不一致。。（附件三）他做的前面一段很平，然后有一个吸收，接着一直上升。。不知道是不是PbS纳米晶体表面的活性剂为除干净所致。。不知道大家在做紫外可见吸光谱的时候有没有碰到类似的问题，望不吝赐教！谢谢！！ [search]PbS纳米晶体 吸收光谱[/search] [ Last edited by caosw2001 on 2008-7-28 at 09:12 ] |
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7楼2008-07-28 08:54:45
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2楼2008-07-25 19:33:48
ytiyuiop
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3楼2008-07-26 07:05:32
2surprise
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这是Ludovico给我的回信
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thanks for writing me about your experiments. I am always looking forward for ways to help fellow chemists. Thanks also for the kind words. I have a couple of observations 1) from the absorption spectra you have you can see that there is no peak and that you have a gradually increasing background absorption so: a) the absorption you see might come from scattering (dust, excess PbCl2 which you haven't precipitated or aggregates of nanocrystals) - proposed solution: try to centrifuge the dispersions for at least 10 minutes just before measuring absorption and check if you see any difference b) the absence of the peak might come from very large polydispersity (poor quality of the sample) - proposed solution: use different batches and sources of oleylemine (I always used oleylamine from the 100G package from Aldrich) - other oleylamines give worse results. Maybe you can send me a TEM image of your sample. c)the fact you don't see the peak can also come from the fact that you are measuring in the wrong range of frequencies: you say that your nanocrystals are 10 nm (they are VERY BIG - it is very hard to get PbS nanocrystals of that size with my reaction). Try to get smaller nanocrystals (shorter growth times) and measure their absorbance d) chloroform and chlorurated solvents are BAD for PbS (use toluene, hexane or THF if you can) e) the quality can be bad also because you use too much ethanol to precipitate the nanocrystals - proposed solution: use acetone which is way better - acetone allows you to completely precipitate all of excess PbCl2 immediately, without having to wait for weeks f) the solutions you prepare might be far too concentrated. when you measure absorbance you should be able to see through the 1 cm cuvette g) poor quality material can also come from excessive cleaning cycles - limit yourself to two cleaning cycles This is what I can think of right now. If you can, you should send me some more information so that I can help you better (a representative TEM image and a very detailed list of the synthesis and purification procedure you use would help me identify the problem) Keep me posted Cheers Ludovico |
5楼2008-07-27 19:59:33
