Nanowires solution-phase synthesis

Wen XG, Zhang WX, Yang SH (2002) Solution phase synthesis of Cu(OH)2 nanoribbons by coordination self-assembly using Cu2S nanowires as precursors. Nano Lett 2(12) 1397—1401... 

A templating approach can be important for preparing low-dimensional platinum nanostructures, as the platinum metal has a fee cubic symmetry. In template-free solution-phase synthesis, the introduction of defects can serve as a useful strategy. Some examples of nanorods, nanowires and nanotubes of platinum prepared using different methods, with and without templates, are shown in Figure 10.8. Notably, when the diameter of nanowires becomes very small, they can exhibit excellent flexibUity and form interconnected networks. 

The approaches used for preparation of inorganic nanomaterials can be divided into two broad categories solution-phase colloidal synthesis and gas-phase synthesis. Metal and semiconductor nanoparticles are usually synthesized via solution-phase colloidal techniques,4,913 whereas high-temperature gas-phase processes like chemical vapor deposition (CVD), pulsed laser deposition (PLD), and vapor transfer are widely used for synthesis of high-quality semiconductor nanowires and carbon nanotubes.6,7 Such division reflects only the current research bias, as promising routes to metallic nanoparticles are also available based on vapor condensation14 and colloidal syntheses of high-quality semiconductor nanowires.15... 

Nickel sulfide nanoparticles synthesized by Guo et al. also showed efficient photocatalytic activity in the degradation of Congo Red under visible-light irradiation. The NiS nanoparticles were by a hydrothermal method. A solution of nickel salt, sodium hydroxide and thioacetamide was sealed in a Teflon lined reactor and heated in an oven for 160 °C for 24 hr. After cooling the product was filtered and washed with water and ethanol. CdS nanowires have been used as ID nanoscale substrates for the growth of NiS nanoparticles by a solution phase method.The step involves the synthesis of the CdS nanowires by a solvothermal route. The as-prepared CdS nanowires and NiCla HaO were dissolved in ethanol and loaded into a Telfon autoclave. 

Synthesis mefliods of NWs basically include both vapor phase and solution techniques. Compared to physical methods such as nanohthography and other patterning techniques, chemical methods have been more versatile and effective in the synthesis of these nanowires. The chemical synthesis includes various methods thermal evaporation, chemical vapor-phase deposition, metal-organic chemical... 

The solution-phase nanowire synthesis was developed by the Kaner group using aqueous/organic phase interfacial polymerization. This method is suitable for bulk synthesis of CP NWs and can produce 30-50 run diameter and 500 nm to several microns long NWs having a yield of 6-10 % 57,io2,io3... 

The sol-gel method is a low temperature synthesis route for complex oxides [42]. It can be used to make complex functional oxide nanowires inside the pores of templates. In addition to the sol-gel method precursor-based solution deposition routes can also be used for nanostructure formation [43]. In both cases a postdeposition high temperature anneal (>500-600 °C) is needed to form the required stoichiometric phase. Due to the requirement of a high temperature anneal, alumina templates are used as the polycarbonate membranes decompose at a much lower temperature. For chemical solution deposition the membrane is dipped directly into the precursor solution. For sol-gel growth generally the required sol is prepared and the template is put into the sol for a required period (e.g. 0.5-1 h). After removing the membrane from the sol it is dried and then annealed at higher temperature before the required phase is formed. A schematic of the sol-gel route is shown in Figure 21.10. 

Recently, synthesis of semiconductor nanorods (nanowires or nanoflbers) and investigation of their properties have aroused much interest. Ge et al. (2002) showed that irradiation technique can be very useful in this regard as well. Cadmium sulfide (CdS) nanorods were successfully prepared by y-irradiation at room temperature and ambient pressure using urea as the template. X-ray diffraction (XRD) pattern showed that the phase of the product was hexagonal. The mean diameter of the nanorods was about 40 nm and the length was up to about 100 nm. The ratio between the length and the width is as high as 5 2. More importantly, they demonstrated that the successful obtainment of nanorods was determined by not only the presence of urea in the system but also the crystallization rate of urea from the solution. 

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