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jasonxmc

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应助: 3 (幼儿园)
金币: 390.6
散金: 236
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帖子: 439
在线: 144.2小时
虫号: 379143
注册: 2007-05-22
性别: GG
专业: 电化学

[交流] 纳米材料——晶体成核问题

有两个问题: 1、为什么要快速成核？作者说 If nucleation is allowed to proceed over an extended period, reactants are unevenly depleted from solution leading to variations in growth rate for seed particles
formed at different reaction times.
2、文中所说的临界浓度应该是金属原子的浓度吧。但是作者说 Fast nucleation is typically achieved by slowly building up the concentration of metal
ions in solution through serial injections of the precursor
materials until nucleation occurs.

文献：small 2008, 4, No. 3, 310 – 325
In homogeneous nucleation, seed formation proceeds
according to the LaMer model (see Figure 4a), where reduction
of metal ions occurs to generate a critical composition
of atomic species in solution. Above this critical concentration,
nucleation results in a rapid depletion of the reactants such that all subsequent growth occurs on the pre-existing
nuclei. As long as the concentration of reactants is kept
below the critical level, further nucleation is discouraged.
This is particularly important for shape control: to obtain a
highly shape-monodisperse yield of nanocrystals, nucleation
must occur rapidly and instantaneously. This is exemplified
by the synthesis of Ag nanocrystalline octahedra, whose reaction
rate can be monitored by UV/vis spectroscopy (see
Figure 4b). In other words, only a single nucleation event
can occur. If nucleation is allowed to proceed over an extended
period, reactants are unevenly depleted from solution
leading to variations in growth rate for seed particles
formed at different reaction times. Fast nucleation is typically
achieved by slowly building up the concentration of metal
ions in solution through serial injections of the precursor
materials until nucleation occurs. However, preventing the
fast reduction of metal ions – especially for colloidal syntheses
carried out at reflux temperatures – is necessary to accumulate
enough reactant species to reach the critical nucleation
concentration. This accumulation may be aided by
modifying the reactivity of the metal precursor. One possible
method is through the formation of metal–surfactant or
metal–polymer complexes in the reaction solution, which hinder the reduction reaction even under highly favorable
conditions.

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