DETECTION OF BARIUM AND STRONTIUM IONS IN WATER UTILIZING FUNCTIONALIZED SILVER NANOPARTICLES _________________________________________ A Thesis Presented to the Honors Tutorial College Ohio University _________________________________________ In Partial Fulfillment of the Requirements for Graduation from the Honors Tutorial College with the Degree of Bachelor of Science in Chemistry _________________________________________ by Ashley Cobbs May 2020 2 This thesis has been approved by The Honors Tutorial College and the Department of Chemistry and Biochemistry _____________________________ Dr. Anthony S. Stender Assistant Professor, Chemistry & Biochemistry Thesis Advisor _____________________________ Dr. Lauren E. H. McMills Associate Professor, Chemistry & Biochemistry Director of Studies _____________________________ Dr. Donal C. Skinner Dean, Honors Tutorial College 3 Abstract Throughout the world, pollutants in water have become commonplace, largely as the result of human activities. Environmental organizations test waterways all over the United States for a wide array of polluting agents, from organic materials found in pesticides, to harmful bacteria, to heavy metals. The standard instrument used to measure the quantity of metals in water samples is an inductively coupled plasma spectroscopy. This specialized instrument requires extensive training and is expensive to purchase, operate, and maintain. As a result, it places a burden on the testing of water samples and can prohibit water from being tested in a timely manner. Therefore, there is a current need for a faster process to evaluate water samples. The overall objective of this study was to assess the viability of utilizing functionalized silver nanoparticles to economically determine the concentrations of cations, specifically barium and strontium ions, in contaminated water samples. The ligands on the nanoparticles selectively bind the ions, which induce a color change in the nanoparticles that is detectable by a UV-Vis spectrophotometer, a relatively cheap analytical instrument. Significant progress towards the practical application of functionalized nanoparticles with environmental samples was made. After the addition of high concentrations of barium and strontium ions, nanoparticle samples shifted color from yellow to pink, signifying the feasibility of bare- eyed detection. Creating samples with a range of ions from 1 mM to 100 mM, a rough detection range for barium and strontium ions were determined. Regression analysis indicated a strong trend between plasmonic resonance absorbance wavelengths and the concentrations of metal ions in water. With these findings, there are many avenues for future work. To name a few, different nanoparticles could be used, the possibility of interfering factors common in water samples should be investigated, and further data at different concentrations of ions could be collected to produce more precise trend lines. 4 Table of Contents Abstract ............................................................................................................................... 3 List of Figures ..................................................................................................................... 6 List of Tables ...................................................................................................................... 8 List of Abbreviations .......................................................................................................... 9 I. Introduction ............................................................................................................... 10 1.1 Impact on Health ..................................................................................................... 10 1.2 Barium and Strontium ............................................................................................. 11 1.3 Instrumentation........................................................................................................ 12 1.3.1 Instrumentation Comparison ............................................................................ 12 1.3.2 Instrumentation Theory .................................................................................... 13 1.4 Research Objectives ................................................................................................ 19 1.4.1 Research Purpose .............................................................................................. 19 1.4.2 Research Benchmarks ....................................................................................... 20 1.5 Nanoparticles ........................................................................................................... 20 1.5.1 General Background ......................................................................................... 20 1.5.2 Plasmonics ........................................................................................................ 21 1.5.3 Binding to Barium and Strontium .................................................................... 23 II. Experimental Methods ............................................................................................... 25 2.1 Water Quality Comparison...................................................................................... 25 2.1.1 Background ....................................................................................................... 25 2.1.2 Instrumentation & Sample Preparation ............................................................ 26 2.2 Nanoparticle Experiments ....................................................................................... 28 2.2.1 Background ....................................................................................................... 28 2.2.2 Instrumentation & Sample Preparation ............................................................ 30 2.2.3 Methods Development ...................................................................................... 32 2.2.4 Final Method..................................................................................................... 34 III. Results & Discussion ................................................................................................. 36 3.1 ICP Experiment, Water Quality Test....................................................................... 36 3.2 Experiment #4, Tris-HCl Study ............................................................................... 42 3.3 Experiment #5, 10 µM versus 10 mM ..................................................................... 43 3.4 Experiment #6, Barium Concentration Range ........................................................ 45 5 3.5 Experiment #7, Red-Shift Trends ............................................................................ 47 3.5.1 Spectra .............................................................................................................. 47 3.5.2 Trend Analysis .................................................................................................. 51 3.6 Experiment #10, Pink Color Change ...................................................................... 54 3.7 Experiment #14, Citrate versus PVP ...................................................................... 58 IV. Conclusion ................................................................................................................. 62 5.1 Concluding Remarks ............................................................................................... 62 5.2 Future Work ............................................................................................................ 63 V. References ................................................................................................................. 66 6 List of Figures Figure 1: Diagram of ICP plasma torch, adapted from Harris’ textbook.14 ............................ 15 Figure 2: Periodic table listing the theoretical detection limits of samples suspended in solution for ICP-OES (in blue text) and ICP-MS (red text). Using instruments with a MS detector are extremely sensitive. Figure adapted from Evans Analytical Group LLC.15 16 Figure 3: Double-beam UV-Vis spectrophotometer adapted from Harris’ textbook.14 .......... 17 Figure 4: A nanoparticle with a localized surface plasmonic resonance induced by an electric field. Figure adapted from Kelly et al.20 .......................................................................... 21 Figure 5: The variable a is the radius of a gold nanosphere and is equivalent to 60 nm while the variable d is the distance between two gold nanospheres and is the independent variable in this figure. (a) illustrates the red-shifting and formation of multiple peaks as the distance between two nanospheres get closer together. Figure adapted from Romero et al.23 ................................................................................................................................ 22 Figure 6: Diagram of how silver nanoparticles bind to a barium ion via thioglycolic acid ligands. In this case, the nanoparticle is silver and is represented by “Ag”. ................... 24 Figure 7: Experiment #4. First time using 10 nm silver nanoparticles in citrate instead of 50 nm and adding 10 mM barium and strontium solutions instead of 10 µM. Experiment performed on April 9th and 12th, 2019. ........................................................................... 43 Figure 8: Experiment #5. Determining the ability for the UV-vis to differentiate