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lxdstrong

金虫 (小有名气)

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虫号: 2041221
注册: 2012-10-03
专业: 电化学

[求助] 求大神：反相微乳液法合成Pt@SiO2无法完成包覆的问题已有3人参与

采用油胺油酸十八烯还原Pt(acac)2来制备出约2nm pt纳米粒子，分散度也较好（下图1），但是在得到粒子进行Igepal-环己烷-氨水-TEOS包覆的时候，出现较大的问题无法进行正常包覆
   包覆比例开始参照文献Langmuir 2010, 26(21), 16469–16473
   Cyclohexane(25 mL) was mixed with igepal CO-630 (8.0 mL) and NH4OH solution (1.0 mL), and the mixture was stirred for 10 min. A NiPt particle dispersion in cyclohexane (25 mL, 10 mM with respect to the precursor concentration) was added into the mixture. After 30 s, TMOS (1.0 mL) was injected, and the resulting mixture was stirred for 60 min at room temperature. The NiPt@SiO2 particles were precipitated by adding methanol (10 mL) and were purified by a repetitive dispersion/precipitation cycle in ethanol.
其中TMOS改为了TEOS，考虑到TEOS水解较慢，这里把反应时间增大到12h，最终得到的结果如下图2所示，粒子根本无法进行包覆，粒子仍然聚在一个区域。
   考虑到是否粒子过小而造成这种现象，仅采用油胺还原乙酰丙酮铂得到大小约7nm纳米粒子，分散度比之前2nm的更好，之前在小木虫查到有人说TEOS滴加过快也会造成无法包覆，所以这次试验TEOS一分钟加一次，每次加25微升。滴加完毕后搅拌48h后加入甲醇，出现明显的分层，但是下层只有极少数的黑色沉淀，照电镜后发现也没有包覆成功，水解的二氧化硅球倒是特别均匀，如图3所示。
   后来考虑到是不是这个微乳液的配比不太符合，有参考了文献 J. Phys. Chem. C 2010, 114, 2512–2518
In a 250 mL Erlenmeyer flask, 3 mL of Igepal CO-520 was added to 100 mL of cyclohexane, and the mixture wasstirred at room temperature for 5 min. Nine milligrams of Fe-Pt nanocrystals redispersed in 9 mL of cyclohexane was added to the stirring Igepal solution. After stirring for 5 min, 0.65 mL of 30% aqueous NH4OH solution was added dropwise to the mixture, followed by immediate addition of TEOS; 0.375-1.0 mL of TEOS was added, depending on the desired silica shell thickness, which could be increased from 3 to 13 nm by increasing the amount of TEOS. The mixture was stirred for 48 h, and then the SiO2-coated Fe-Pt nanocrystals were extracted from the cyclohexane phase by adding 50 mL of methanol. The cyclohexane phase was discarded. The nanoparticle dispersion was collected in a 100 mL, round-bottom flask and placed on a rotary evaporator to concentrate the dispersion down to a volume of 10 mL.
采用之前制备的粒子烘干后取9mg参照这种方法进行包覆，TEOS滴加量为0.5ml，反应48h后加入甲醇分层后，甲醇相内并没有出现沉淀，也就是说根本没有包覆成功的粒子出现，不知道实验过程中出现了什么问题，请教一下各位做这个方面的同学怎么解决这种现象。

图1.png