The Catalytic Reduction Of Chromium (Vi)

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Dissertation powerpoint on the catalytic reduction of Chromium (VI) to (III) by palladium nanoparticles.

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  • brittleness and low level of processability constitute major obstacles to its extensive applications Insoluble hindering biological use has a strong tendency to accept electrons
  • has a strong tendency to accept electrons
  • The Catalytic Reduction Of Chromium (Vi)

    1. 1. Catalytic Reduction of Chromium (VI) using Polyamic Acid and Palladium Nanoparticles Vincent Lee CHEM 498 Independent Study Honors
    2. 2. Outline <ul><ul><li>Objectives </li></ul></ul><ul><ul><li>Introduction </li></ul></ul><ul><ul><ul><li>Conducting Polymers </li></ul></ul></ul><ul><ul><ul><ul><li>Polyamic Acid (PAA) </li></ul></ul></ul></ul><ul><ul><ul><li>Palladium Nanoparticles </li></ul></ul></ul><ul><ul><ul><li>Chromium Toxicity </li></ul></ul></ul><ul><ul><ul><li>Environmental Remediation by PAA </li></ul></ul></ul><ul><ul><li>Experimental </li></ul></ul><ul><ul><li>Results and Discussion </li></ul></ul><ul><ul><li>Conclusion </li></ul></ul><ul><ul><li>Future Work </li></ul></ul>
    3. 3. Objectives <ul><li>To examine the reduction of hexavalent chromium (Cr 6+ ) on a Polyamic acid (PAA) gold (Au) electrode in acidic and buffered media. </li></ul><ul><li>To understand the reaction mechanism as well as characterize the analytical applications of the process. </li></ul><ul><li>To examine the electrocatalytic degradation of Cr 6+ by PAA in the presence of Palladium Nanoparticles (PdNPs). </li></ul>
    4. 4. Introduction to Conducting Polymers <ul><li>Electrochemical Properties due to conjugated π electron backbones. </li></ul><ul><ul><li>High Electrical conductivity </li></ul></ul><ul><ul><li>Low Ionization potential </li></ul></ul><ul><ul><li>High Electron Affinities </li></ul></ul><ul><ul><li>Optical properties </li></ul></ul><ul><li>Polypyrrole </li></ul><ul><ul><li>Poor Mechanical properties </li></ul></ul><ul><ul><li>Extreme hydrophobicity </li></ul></ul><ul><ul><li>Purification needed </li></ul></ul><ul><ul><li>Nucleophilic interference with immobilization. </li></ul></ul>
    5. 5. Introduction to Polyamic Acid (PAA) <ul><li>Advantages </li></ul><ul><ul><li>Organic & Inorganic solvents </li></ul></ul><ul><ul><li>Easy Absorption </li></ul></ul><ul><ul><li>Strong Stable interactions with metals. </li></ul></ul><ul><ul><li>Reducing agent </li></ul></ul><ul><ul><li>Electric Insulator </li></ul></ul><ul><li>Redox Polymer </li></ul><ul><ul><li>Dependent on Solvent and Supporting electrolyte </li></ul></ul><ul><li>Materials </li></ul><ul><li>0.01 M 4, 4’-oxydianiline (ODA) </li></ul><ul><li>0.01 M Pyrometallic Dianhydride (PDMA) </li></ul><ul><li>Solvent – Powdered form with Dimethylformamide (DMFA) </li></ul><ul><ul><ul><ul><ul><li>or </li></ul></ul></ul></ul></ul><ul><li>Viscous form with Phosphate Buffer Saline (pH 7.2) </li></ul>
    6. 6. Introduction to Palladium Nanoparticles <ul><li>Forms a good Catalyst </li></ul><ul><ul><li>Electron-Transfer (Redox) </li></ul></ul><ul><ul><li>Hydrogenation </li></ul></ul><ul><ul><li>Dehydrogenation </li></ul></ul><ul><ul><li>Homogenous </li></ul></ul><ul><li>Nanoparticles (Palladium Acetate) </li></ul><ul><ul><li>Stabilize </li></ul></ul><ul><ul><ul><li>Vary Size Distribution </li></ul></ul></ul><ul><ul><ul><li>Problems </li></ul></ul></ul><ul><ul><ul><ul><li>Loss of Catalytic Activity (Change in Redox potential) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Selectivity increases </li></ul></ul></ul></ul>(1) (2) Data from: Marcells A. Omole, Isaac O. K’Owino & Omowunmi A. Sadik, Palladium Nanoparticles for Catalytic Reduction of Cr (VI) using Formic Acid, Applied Catalysis B Environmental , 76, 158-176, 2007
    7. 7. Introduction to Chromium <ul><li>Trivalent form (Cr 3+ ) </li></ul><ul><ul><li>Essential nutrient for humans </li></ul></ul><ul><ul><li>Non-toxic </li></ul></ul><ul><li>Hexavalent form (Cr 6+ ) </li></ul><ul><ul><li>Found in Steel, Chemical, Leather and textile manufacturing. </li></ul></ul><ul><ul><li>Water and soil pollution </li></ul></ul><ul><ul><li>Danger to human health </li></ul></ul><ul><ul><ul><li>Alter genetic material </li></ul></ul></ul><ul><ul><ul><li>Carcinogenic </li></ul></ul></ul><ul><ul><ul><li>Organ damage </li></ul></ul></ul><ul><ul><ul><li>Fatal </li></ul></ul></ul>
    8. 8. Novel Environmental Remediation of Chromium by PAA w/ PdNPs <ul><li>PAA Electrocatalyst </li></ul><ul><li>Complex with PdNPs and Chromium </li></ul><ul><ul><li>Carboxylic Acid Groups </li></ul></ul><ul><ul><li>Amine Groups </li></ul></ul><ul><li>PdNPs will catalyze electron transfer reaction. </li></ul><ul><li>Detection of chromium species with PAA-modified Au-electrode </li></ul>
    9. 9. Experimental: UV-Vis Spectroscopy <ul><li>Monitor change in concentration of Cr 6+ to Cr 3+ </li></ul><ul><ul><ul><li>PAA in different solvents </li></ul></ul></ul><ul><ul><ul><ul><li>Phosphate Buffer Saline (PBS) (pH 7.2) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Dimethylformamide (DMFA) </li></ul></ul></ul></ul><ul><ul><ul><li>60 min. Time based analysis </li></ul></ul></ul><ul><ul><ul><ul><li>Temperature at 85 ºC </li></ul></ul></ul></ul><ul><ul><ul><li>Varying PAA concentration (12 minutes total reaction time) </li></ul></ul></ul><ul><ul><ul><ul><li>Temperature at 45 ºC </li></ul></ul></ul></ul><ul><li>Materials </li></ul><ul><ul><li>5 ml of 10 mM Cr(VI) solution </li></ul></ul><ul><ul><li>100 uL of colloidial PdNPs (4.3 × 10 −2  mg/mL) </li></ul></ul><ul><ul><ul><li>Redissolved in 0.5 mM Acetate buffer pH 5 </li></ul></ul></ul><ul><ul><li>1.68 mL of 0.1 mM Acetate buffer pH 5 (pKa = 4.78) </li></ul></ul><ul><ul><li>3.8 mg/ml of Polyamic Acid in PBS </li></ul></ul><ul><ul><li>or </li></ul></ul><ul><ul><li>3 mg/ml PAA in DMFA </li></ul></ul>
    10. 10. Experimental: Cyclic Voltammetry <ul><li>Measure electrochemical response </li></ul><ul><ul><li>-100 to 1000 mV (scan rate = 50 mV/s, sensitivity = 100 μ A/V) </li></ul></ul><ul><ul><li>1000 μ M Cr(VI) in 0.1 M HCl pH 1 or 0.1 M Acetate Buffer pH 5 </li></ul></ul><ul><ul><ul><li>Au-Electrode vs. PAA-modified Au-electrode </li></ul></ul></ul><ul><ul><li>50 μ M Cr(VI) in 0.1M HCl pH 1 </li></ul></ul><ul><ul><ul><li>Varied Scan Rate (20-400 mV/s) of Au-Electrode vs. PAA-modified Au electrode (Created by adding 6 μL of PAA on Au-electrode then Dried) </li></ul></ul></ul><ul><ul><ul><ul><li>Scan rate 1/2 vs. Peak current </li></ul></ul></ul></ul><ul><li>10 mL 3 of Cr(VI) solution </li></ul>
    11. 11. DATA: Cyclic Voltammetry: Au Electrode vs. PAA-modified Au-Electrode in 1000 μ M Cr(VI) and 0.1 M HCl +537 mV +749 mV
    12. 12. CV: Varying Scan Rates: Au electrode in 50 uM Cr(VI) and 0.1 M HCl +743 mV +539 mV +605 mV
    13. 13. CV: Varying Scan Rates: PAA modified Au-electrode in 50 uM Cr(VI) and 0.1 M HCl +543 mV +467 mV +606 mV
    14. 14. CV: Au Electrode vs. PAA-modified Au-Electrode in 1000 μM Cr(VI) and Acetate buffer +153 mV 208mV +595 mV +684 mV +688 mV
    15. 15. CV: Varying Scan Rates: Au electrode in 50 μ M Cr(VI) and acetate buffer +204 mV +489 mV +680 mV +238 mV +799 mV -102 mV -91 mV
    16. 16. CV: Varying Scan Rates: PAA- modified Au electrode in 50 μ M Cr(VI) and acetate buffer + 215 mV +348 mV +749 mV
    17. 17. CV: Varying Concentrations of Cr(VI) on Au Electrode (50 μ M-1000 μ M)
    18. 18. CV: Vary concentration of Cr(VI) with PAA-modified Au-electrode (50 μ M-1000 μ M) 1000 μM 500 μM 800 μM 200 μM 50 μM Control
    19. 19. UV-Vis Spectroscopy: Varying concentration of PAA in DMFA Cr (VI) Solution w/ PdNPs (350 nm) 350 nm
    20. 20. Varying Concentration of PAA in DMFA: [Cr(VI)] vs. [PAA]
    21. 21. UV-Vis: Time Based analysis of Cr(VI) reduction in PAA in PBS w/ PdNPs (85 ºC) 350 nm
    22. 22. UV-Vis Spectroscopy: Varying PAA in PBS Concentration in Cr (VI) Solution w/ PdNPs (350 nm) 350 nm
    23. 23. Percent Change of Cr(VI) Concentration in presence of PAA
    24. 24. Results <ul><li>PAA detection of chromium w/ Au electrode </li></ul><ul><ul><li>Diffusion Electron Kinetics </li></ul></ul><ul><ul><li>Electrochemically Reversible Reaction </li></ul></ul><ul><li>PAA-enhanced reduction of chromium w/ PdNPs </li></ul><ul><ul><li>PAA in PBS reduces Cr (VI) to Cr (III) by 72.87% at 114 mg/ml in 12 minutes!! </li></ul></ul><ul><li>However, Time based analysis shows discrepancy. </li></ul><ul><ul><li>May be due to the reduction reaction trying to reach equilibrium. </li></ul></ul>
    25. 25. Conclusion <ul><li>PAA has the potential to reduce Chromium (VI) in solution. </li></ul><ul><ul><li>Requires higher concentration for full reduction and more time. </li></ul></ul><ul><li>PAA modified gold electrode may detect Chromium Species in acid media and acetate buffer solution (pH 5). </li></ul><ul><li>Further work needed to confirm. </li></ul>?
    26. 26. Possible Future Work <ul><li>SEM of PAA Stabilized PdNPs. </li></ul><ul><li>Optimization for Temperature, PAA, and Time. </li></ul><ul><li>Test Different PAA Derivatives </li></ul><ul><li>X-ray Photoelectric Spectroscopy </li></ul><ul><ul><li>To find Cr oxidation state </li></ul></ul><ul><li>Electrochemical impedance spectroscopy </li></ul><ul><ul><li>Detect Resistance and confirm PAA-modification </li></ul></ul>
    27. 27. Acknowledgments <ul><li>Marcells Omole </li></ul><ul><li>Committee Members </li></ul><ul><ul><li>Dr. Omowunmi A. Sadik </li></ul></ul><ul><ul><li>Dr. Dennis McGee </li></ul></ul><ul><ul><li>Dr. Nikolay Dimitrov </li></ul></ul><ul><li>Group Members </li></ul><ul><ul><li>Sam M., Sam.K, Rula, Nian, John H., Naumi Ola. </li></ul></ul><ul><li>Audience </li></ul>
    28. 28. References <ul><li>Omole, M.A., K’Owino, I.O., Sadik, O.A. (2007) Palladium nanoparticles for catalytic reduction of Cr(VI) using formic acid, App. Cata. B: Environmental . 76, 158-167. </li></ul><ul><li>Andreescu, D., Wanekaya, A.K, Sadik, O.A., Wang, J. (2005) Nanostructured polyamic acid membranes as novel electrode materials, Langmuir . 21, 6891-6899. </li></ul><ul><li>Ahuja, T., Mir, A.M., Kumar, D., Rajesh. (2007) Biomolecular immobilization on conducting polymers for biosensing applications. Biomaterials. 28, 791-805. </li></ul><ul><li>Welch, C.M., Nekrassova, O., Compton, R.G. (2005) Reduction of hexavalent chromium at solid electrodes in acidic media reaction mechanism and analytical applications. Talanata. 65: 74-80 </li></ul>
    29. 29. Appendix: CV: Oxidation Peak vs. Square root of scan rate w/ Au-electrode (acidic media)
    30. 30. CV: Oxidation Peak vs. Square root of scan rate w/ PAA modified Au-electrode
    31. 31. Square root of Scan Rate of Au-electrode in acetate buffer
    32. 32. Square root of Scan Rate of PAA-modified Au-electrode in acetate buffer
    33. 33. UV-Vis Spectroscopy: Time based Analysis of Cr(VI) Reduction by PAA w/ PdNPs (350 nm) 350 nm
    34. 34. Polyamic Acid-PdNP-Cr complex Free Cr(VI) in Solution Cr Reduction Palladium Nanoparticles Polyamic Acid

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