Metal salts Nanorods

The seeds are then added to a growth solution that consists of fresh metal salt, and a surfactant, cetyltrimethylammonium bromide, CTAB, that directs the growth of nanopartides into nanorods and nanowires. Growth is initiated by the addition... 

Fig. 9.2. Cartoon showing the seed-mediated growth approach to the synthesis of metallic nanorods of controllable aspect ratio. In the first step, metal salts are reduced with sodium borohydride, a strong reducing agent, to metal nanospheres ( seeds ) that are 3-4 nm in diameter. In the subsequent growth steps.

In the standard chemical preparation methods, the properties, especially the size and size distribution of the nanoparticles, are defined by the choice of the reaction conditions, reactant concentrations, etc. The use of electrochemical techniques to generate nuclei has the advantage that the supersaturation is determined by the applied potential or current density. Thus, the size of the particles can be controlled by electrochemical instrumentation rather than by changing the experimental conditions. Reetz and Helbig [115] demonstrated how electrochemical methods can be used to produce metal colloids of nanometer size and more importantly how particle size can be controlled in a simple manner by adjusting the current density [159]. First, a sacrificial anode was used as the source of the metal ions, which were then reduced at the cathode. Later, a more general approach was introduced, where metal salts were used as the starting material [160]. The particles were stabilized by alkylammonium or betaine salts. With a suitable choice of surfactants, the electrochemical method can be applied in the preparation of different shapes of particles, e.g., nanorods [161]. 

The Hydrothermal process has been a well-known procedure for material synthesis since the 1970s. It begins with an aqueous mixture of soluble metal salt (metal and/or metal-organic) precursors, then the solution is placed in an autoclave at a high temperature (between 100°C and 300°C) and under relatively high pressure (> 1 atm) conditions. ZnO nanorods, - CuO, ceria, titania and Mn02 have been prepared by using wet-chemical hydrothermal approaches. 

ZnO nanoflower morphologies usually include nanowires, nanorods, nanorings, nanoneedles, etc. The synthetic techniques of nanomaterials include oxidation of elemental metals, reduction of metal salts, thermal decomposition of relatively unstable compounds, or electrochemical route. Various other metal nanoflowers have also been synthesized by various workers from time to time. 

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