Heat-up method

BP = benzophenone, MM = methyl myristate, DBS = dibutyl sebacate, TOA = trioctylamine, chbt = cyclohexylbutyrate, OAm = oleylamine, Et20 = diethylether. fcHI = hot injection method HU = heating-up method. 

Figure 6.1 Transmission electron microscopy (TEM) images of monodisperse nanocrystals. They are iron oxide nanocrystals synthesized by the heat-up method introduced in Section 6.5. The scale bar in the left picture is 2 p.m and the ones on the right are 10 nm.

In the following two sections, we will discuss the kinetics of two representative synthetic procedures for monodisperse spherical nanocrystals, which are the hot injection and heat-up methods. Although there are other synthetic methods for monodisperse nanocrystals, their formation kinetics have not been clearly elucidated yet (11-13). 

Heat-up is a simple but effective method of synthesizing highly uniform nanocrystals, which yields a degree of size uniformity comparable to that of the best result from the hot injection method. This method is adopted mainly for the synthesis of metal oxide nanocrystals. In this section, we describe the synthetic procedure of iron oxide nanocrystals via the heat-up method as a representative example (23-25). 

The precursors used for the iron oxide nanocrystal synthesis via the heat-up method are various iron carboxylatc complexes, including the most widely used iron-oleate complex. Generally, when heated, metal carboxylatc complexes thermally decompose at temperatures near 300°C or higher to produce metal oxide nanocrystals along with some byproducts, such as CO, CO2, H2, water, ketones, esters, and various hydrocarbons. It is thought that the decomposition reaction proceeds via the formation of thermal See radicals liom metal carboxylatc (26, 27) ... 

The most attractive characteristics of the heat-up method are its simplicity and reliability. The synthetic procedure can be easily scaled up to yield nanocrystals in quantities as high as several tens of grams (24). In the following section, we will discuss how this very simple heat-up method can produce monodisperse nanocrystals. 

Figure 6.17 Schematic of the size distribution control mechanism of the hot injection and heat-up methods. In the left boxes, the monomer supply modes are shown as the plots of supersaturation vs. time. In the right boxes, the resulting time evolutions of the nucleation rate, the mean size, and the relative standard deviation are shown. The injection time and the start of the heat procedure are set as t = 0 in the hot injection and the heat-up processes, respectively.

The solvothermal method is more efficient and permits wide range of reaction temperature due to high boiling point of the organic solvents. The most common method rmder solvothermal is hot-injection method compared to heating-up method used for colloidal synthesis of nanocrystals. 

HI = hot-injection method, HU = heating-up method, RT = room temperature, CdMe = dimethyl cadmium, ZnEt = diethylzinc, TMS = trimethlsilyl, (BDMSj Te = his tert-butyldimethylsilyljteUuride, TDPA = tetradecylphosphonic acid, ODPA = octadecy-Iphosphonic acid, SA = stearic acid, LA = lauric acid, MA = myristic acid, OA = oleic acid, ac = acetate, acac = acetylacetonate, st = stearate, hdx = hexadecylxanthate, ex = ethylxanthate, dx = decylxanthate, TOPO = trioctylphosphine, HDA = hexadecylamine, DDA = dodecylamine, ODA = octadecylamine, TOP = trioctylphosphine, TBP = tribu-tylphosphine, ODE = 1-octadecene, HH = hexadecylhexadecanoate, BP = benzophenone, TOA = trioctylamine, OAm = oleylamine, DPE = diphenylether, TAA = thioacetamide TEA = triethanolamine, DDT = dodecanethiol, dedc= diethyldithiocarbamate. 

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