02-09-2013, 03:43 PM
Synthesis of colloidal gold nanoparticles in ethanol using spark-discharge method
Introduction:
To synthesize gold nanoparticles (AuNPs) in ethanol,a green method called pulsed sparkdischarge (PSD) is used. Unlike conventional methods for metal nanoparticles synthesis, the PSD method does not require the addition of chemical surfactants and stabilizers. The gold electrodes discharge in the ethanol, under an intensive electric field and thermal energy, bulk metallic gold and ethanol may produce AuNPs and varieties of chemical derivatives, The analysis results show that there is an oxidation reaction of ethanol occurring during the PSD process to produce ethanol derivatives, such as acetaldehyde, acetic acid, and ethyl acetate, which may modify the surface of AuNPs by coordination of oxygen atoms. However, only acetic acid can form a negative charge by the deprotonation of the carboxylic group of surface in ethanol, resulting in the creation of a repulsion force between the particles to form the stable colloid system. The experimental results indicate that PSD is an alternative green process to synthesize gold nanoparticles suspension in ethanol. Moreover, with a gold rod consumption rate of 15 mg/L, concentrations of gold nanoparticles 9 ppm have been observed; therefore, the net production rate is around 60%. Convetional chemical method can obtain small size gold, and cause AuNPs to be suspended in the solution. However, this technique is slow, difficult to apply, or require post-synthesis separation of unwanted by-products. Here the pulsed spark-discharge (PSD) method, which is called top-down. It prepares colloidal gold in ethanol, which is stable under normal temperatures and atmospheric pressure, without any chemical additives and additional purification step. Therefore, any electric conductive material has the opportunity to be made into nano-material through this method, which is the important advantage of this technique. Moreover, this process is economical and environmentally friendly, and produces uncontaminated nanoparticles which may be useful in numerous applications.
Experimental setup:-
Pulsed spark-discharge method: The pulsed spark-discharge (PSD) method used in this study consists of (1) the servo control system, which controls the gap distance between the two electrodes and continuously maintains the sparkdischarge process, (2) a controller, which provides signals to the servo control system and pulsed generatorpower supply to manipulate the parameters of the process, (3) the pulsed-generator power supply offering a DC electrical energy to the electrodes, and (4) a spark chamber with a dielectric medium (ethanol) used to collect the gold particles sputtered.