Anku+Madan's+Proposal

 Silver nanoparticles are small structures usually suspended in some solvent. This system is called a suspension. The formation of a nanoparticle suspension is possible because the interaction between the particle surface and the solvent is strong enough to overcome the density difference between the nanoparticles and the molecules of the solvent. This density difference is what normally causes most such materials to sink or float in a liquid.  Nanoparticles are very similar to ultrafine articles in that their diameter is between 1 and 100 nanometers, just as ultrafine particles have. However, the dimensions of nanoparticles can be restricted to just two dimensions, while those of ultrafine particles cannot. Not enough is known as of yet about the size-related properties that nanoparticles exhibit, and how they differ from those of fine particles or bulk materials.  Recently, there has been much interest in nanoparticles because of the transitional nature that they have for science. The physical properties of bulk materials should be constant regardless of size, but this is not always true with nanoparticles. As the size of these nanoparticles approaches that of the nano-scale, their structural and surface properties change. Silver nanoparticles also happen to have a very large aggregation potential, which leads to difficulties when they travel in suspensions through a porous medium such as soil. The current mobility of silver nanoparticles in the soil is measured in centimeters, much less than the distance needed for silver nanoparticles to be efficiently used as is being considered. For maximum efficiency, a mobility of at least several meters has to be achieved.  Silver nanoparticles are currently being considered as a groundwater treatment option because of their antimicrobial properties, which could theoretically make it possible for microbes in buried aquifers in the water table to be killed, purifying the water directly, making this treatment a desirable alternative to the current pump-and-treat option. However, when injected into the soil through an injection well, silver nanoparticles tend to travel a short distance and then proceed to aggregate, increasing their size and making it increasingly difficult to travel through the small pores in soil. We decided to use a substitute in the place of soil in order to mimic as accurately as possible yet keeping a constant media in place during our experimentation. The substitute that we have decided to use in place of soil is a form of glass bead covered in an iron oxide coating. Iron oxide and silicon dioxide are two of the most prevalent compounds found in the soil, making this experiment quite realistic.    How can we improve the mobility of silver nanoparticle suspension when traveling through a porous media coated with iron oxide?    Reducing the aggregation potential by mixing the nanoparticle suspension with an electrolyte is a conceivable way of increasing the mobility, as the silver nanoparticles would take longer to aggregate with each other and could then travel over a longer distance, perhaps in meters instead of centimeters, which is the current mobility. The addition of this electrolyte would introduce both positively and negatively charged ions, of which the oppositely charged ions would be attracted to the surfaces of each individual silver nanoparticle. This would reduce the overall electrostatic repulsion that exists between each particle, making it more likely that they aggregate with each other instead of with other environmental factors, increasing the overall mobility. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">I will be working at Dr. Mark Wiesner’s lab, which is currently conducting research in many different fields at this time, primarily in membrane science, environmental nanotechnology, and surface chemistry/particle transport. I will be focusing, along with two other graduate students, Shihong Lin and Yohan Bobcombe, on the mobility of silver nanoparticles in an iron oxide coated media. There are several processes involved in the investigation of this property, and chief among these is the use of Ultraviolet/Visible Spectroscopy, as this measures adsorption, when electrons move from their ground state to an excited state, as well as use of the Dynamic Light Scattering process. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">DLS- <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">The procedure for using the dynamic light scattering device is relatively simple. What DLS actually does is determine the average hydrodynamic diameter of a suspension of particles, and refers to how a particle diffuses within a fluid. The diameter obtained using this process is that of a sphere that has the same translational diffusion coefficient as the particle being measured. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">The TDC depends on both the size of the particle “core,” but also on any surface structure, as well as the concentration and type of ions in the medium. This means that the size may be larger than actual measurements through electron microscopy may indicate, because the particle is removed from its native environment. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">The reason that this process even works is because of Brownian motion of particles, emulsions, or molecules in a suspension. If these particles were to be illuminated by a powerful laser, the light would be scattered, and the intensity of the light that was scattered changes at a rate that depends on the size of the particles due to the collisions between the solvent particles and the solute particles. Measuring the change in intensity allows one to calculate the velocity of Brownian motion and also the particle size using the Stokes-Einstein relationship. This is what DLS will be used for primarily. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">Using the DLS just requires some basic knowledge of the ALV program that offers a visual GUI that simplifies the usage of the machine. Users are just required to write a script detailing the number of runs, the length of each run, and also the angle at which they want the sensor to be oriented from the light source. After doing this, one can assign the script to the program, which will then automatically carry the process out. One can then come back after a preset period of time and fit a correlation function to the collected data that can quantify the final size of the average particle in the suspension. Trends can be viewed by copying the data from the data viewer in ALV to Microsoft Office Excel and then inserting charts with the aforementioned variables. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">While in the lab, I will be wearing nitrile gloves, a lab coat, and closed-toe shoes at all times. Also, at times when it is necessary, I will be wearing goggles or mittens in order to insulate myself from heat when inserting glass beads into the oven for iron oxide coating. Materials used will be disposed of properly in bins and waste storage containers meant for that purpose. Any dangerous chemicals will be used under a fume hood or with any other appropriate safety cautions that may be required. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">The process of mass titration in order to find the limiting pH, and through that, the point of zero charge (PZC) of the suspension of solid “powder” in an aqueous medium will be done by first placing 20g of both HNO3 treated iron oxide coated glass beads as well as regular, water stirred iron oxide coated glass beads in 200 mL of deionized water. Initially, .4 mL of 1.0 M HCl will be added. Then, at intervals of 15, 30, and 60 minutes, the pH of the mixture will be measured. After this initial procedure, ever decreasing volumes of 1.0 M NaOH will be added, with pH being measured at intervals of 15 and 30 minutes. The pH curve is then plotted, and the equivalence point determined. This point is the point of zero charge, which can be used to determine some properties of the porous media, and we can create ways to increase the mobility of silver nanoparticle suspension through the media. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">Bibliography <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> Zalac, Kallay, N (1991). Application of mass titration to the point of zero charge determination. // Journal of Colloid and Interface Science //,   // 149 // , 233- 240. Song, Elimelech, M (1992). Dynamics of colloid deposition in porous media: modeling the role of retained particles. // Colloids Surfaces A: Physiochem. Eng Aspects //,   // 73 // , 49-63. Lecoanet, H. I., Bottero, J., & Wiesner, M. R. (2008). Laboratory assessment of the mobility of nanomaterials in porous media.//Environmental Sci. Technology//,   // 38 //, 5164-5169. Kim, J. S., Kuk, E., Yu, K. N., Kim, J., Park, S. J., Lee, H. J., et al. (2007). Antimicrobial effects of silver nanoparticles. //Nanomedicine: Nanotechnology, Biology and Medicine//, //3//(1), 95-101. doi: 10.1016/j.nano.2006.12.001. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";"> Elimelech, Menachem, & O, Charles R. (1990). Kinetics of deposition of colloidal particles in porous media. // Environmental Science Technology //,   // 24 // , 1528-1536. <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">
 * <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">A Characterization of Silver Nanoparticles **
 * <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">Question Being Addressed **
 * <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">Hypothesis/Problem/Engineering Goals **
 * <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">Method/Procedure/Materials **
 * <span style="font-size: 12.0pt; font-family: "Times New Roman","serif";">Safety **