Experimental procedure reduction-precipitation

The results obtained from sorption/desorption edge experiments on Milwhite kaolinite and cadmium are presented in Figure 3.8 as an illustration. The testing parameters of these experiments are tabulated in Table 3.2, and the experimental procedure is detailed in Yeung and Hsu (2005). The low concentration of cadmium in the dissolved phase used in the experiments precludes the formation of cadmium precipitates. Therefore, the reduction in cadmium concentration in the dissolved phase was caused by the sorption of cadmium onto Milwhite kaolinite particle... 

A very reactive form of a finely divided metal is a so-called Rieke powder [79]. These materials are produced as fine powders by chemical precipitation during the reduction of various metal halides ivith potassium metal in refluxing tetrahydrofuran. Obviously this is a potentially hazardous laboratory procedure and ultrasound has provided an alternative method of preparation of these extremely valuable reagents [80]. The sonochemical technique involves the reduction of metal halides with lithium in TH F at room temperature in a cleaning bath and gives rise to metal powders that have reactivities comparable to those of Rieke powders. Thus powders of Zn, Mg, Cr, Cu, Ni, Pd, Co and Pb were obtained in less than 40 min by this ultrasonic method compared with reaction times of 8 h using the experimentally more difScult Rieke method (Tab. 3.1). 

Determination of Branches. Reductive dechlorinations were performed with Bu.SnH as reducing agent. We have modifid the original two-step method given by Starnes et. al. (21) to a one-step method (22). To avoid precipitation, a mixture of tetrahydrofuran and xylene is used as solvent. At high conversion, the concentration of xylene and the temperature is increased. By this procedure, a chlorine content less than 0.1% is obtained in 6 h. The experimental details are as previously given.(22). 

For the preparation of gold nanopartides supported on insoluble solids, the most widely used procedure is the precipitation-deposition method [32-36]. Starting from an aqueous solution of HAuCh, addition of a base leads to precipitation of a mixture of Au(OH)3 and related oxy/hydroxides that adsorbs into the solid and is then reduced to metallic gold by boiling the adsorbed species in methanol or any other alcohol. In this procedure, it has been established that the pH of the precipitation and the other experimental conditions (nature of the alcohol, temperature and time of the reduction, calcination procedure, etc.) can provide a certain control of the particle size of the resulting nanoparticles [3j. Figure 12.2 illustrates the steps required in the formation of supported gold nanoparticles. 

During the last few years, different synthetic procedures have been reported for the synthesis of magnetic nanoparticles. These methods include co-precipitation, thermal decomposition and/or reduction, microemulsion synthesis, and hydrothermal synthesis. Despite poor shape control and quite polydisperse particles, co-precipitation is probably the simplest synthetic route. By contrast, thermal decomposition is experimentally more demanding but affords the best results in... 

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