The purpose of this experiment was to observe the effects of reduction rates on gold nanoparticles using UV/Vis. The primary topic of this experiment was nanochemistry. Nanochemistry is simply the combination of chemistry and nanoscience. It deals with the formation of building blocks which depend on size, surface, shape and defect properties. This topic is widely used in chemical, physical and materials science, engineering and biological and medical applications.
Reactions involving nanoparticles tend to have a greater effect since nanoparticles have high surface area to volume ratio compared to larger particles. In addition, the rate of the reaction is also faster and therefore can act as catalysts. In this lab gold particles were used because of their interaction with light and its absorbency. Usually, small particles absorb green and blue light, which reflect red. Therefore, turning the reaction red. This solution which contains gold nanoparticles are called colloid solutions. It is simply defined as a mixture in which substances are regularly suspended in a fluid. For a good colloid solution, it is key that the particles remain suspended and not settled into the mixture for a long period of time.
In this experiment, two different reducing agents were used in order to compare sodium citrate and sodium borohydride. Reducing agents are used for reduction reactions and synthesis of metal nanoparticles such as gold, silver or platinum. The expectation was that the reducing agents; sodium citrate and borohydride, would form gold nanoparticles. However, the two reducing agents work very differently. Borohydride was used in a cool environment, while sodium citrate was used in a high temperate environment.
Aggregation refers to the process of several things grouped together and considered as a whole. In this experiment, after the gold particles were formed in colloid solutions, they went through aggregation processes in sodium chloride and ethanol. This process is very common and is used for the destabilization of colloid solutions. Aggregation helps find the intensity and wavelength in the UV-Vis spectrometer in different peaks from the spectra. However, before the aggregated solution is run through the UV-Vis spectrometer, it is let to sit for about 15 minutes. This settling time is done to maximize aggregation process. This process is known as the Ostwald ripening and is observed in solid or liquid solutions that describe the change of an inhomogeneous structure over time. In this experiment, this effect causes smaller particles to dissolve and redeposit onto larger particles causing the nanoparticles to become more stable.
Ultraviolet-visible spectroscopy refers to absorption or reflection spectroscopy in the UV-Visible spectra region. This was used to retrieve the wavelengths of the solution that consists of gold nanoparticles. In this method the size and concentration of a mixture in a solution can be determined. It provides a report displaying the wavelength of peaks measured in nanometers (nm) and intensity of the peaks in arbitrary unit (a.u.). UV-Vis spectra are then read by the Plasmon peaks shown on the graphs. Usually the graphs represent many peaks, however only the highest intensity peaks are taken into account for accuracy.