Routes to the Synthesis of Nanoparticles

The approach described later on in this chapter builds upon a report in 2002, in which we proposed microfluidic reactors as favourable systems for nanoparticle synthesis, and showed that nanocrystalline cadmium sulfide prepared in such reactors exhibited improved monodispersity compared with particles prepared in conventional bulk-scale vessels (Edel et al., 2002). 

An additional advantage of using microfluidic devices, which we do not have the space to discuss in detail here, is the absence of turbulence (Koo and Kleinstreuer, 2003). In the context of nanoparticle synthesis, turbulence gives rise to unpredictable variations in physical conditions inside the reactor that can influence the nature of the chemical product and in particular affect the size, shape, and chemical composition. In microfluidic devices, turbulence is suppressed (due to the dominance of viscous over inertial forces) and fluid streams mix by diffusion only. This leads to a more reproducible reaction environment that may in principle allow for improved size and shape control. 

In this chapter, we will focus on the automated preparation of CdSe quantum dots (which have been extensively studied and characterized in the scientific literature), but the principles and techniques we describe are general ones that may be applied to a variety of nanomaterials. Indeed, the following paragraphs outline some selected studies which have reported the use of microfluidic reactors for the synthesis of compound semiconductor nano materials. 

A number of elegant studies over the past few years have also addressed the need to minimize particle size distributions through the use of segmented flow microfluidic systems. Such an approach removes the possibility of particle deposition on channels and eliminates the problems of residence time distributions that occur in single phase systems (where drag at the channel walls sets up a velocity distribution inside the channel). For example, Shestopalov et al. reported the two-step synthesis 

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Before we go through the organometalUc or metal organic route to the synthesis of nanoparticles, a brief description of other synthetic methods is given below. 

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