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The Catalytic Reduction Of Chromium (Vi)
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The Catalytic Reduction Of Chromium (Vi)

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

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

Transcript

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