Environmental Research

Background

The advanced oxidation processes such as photocatalysis, radiolysis and sonolysis are useful for degrading undesirable organics from air and water. For example, organic materials such as hydrocarbons, haloaromatics, phenols, halogenated biphenyls, surfactants, textile dyes have been successfully mineralized in TiO2 slurries. In aqueous solutions the photogenerated holes at TiO2 particles are scavenged by surface hydroxyl groups to generate .OH radicals which then oxidize the dissolved organics.
We are currently comparing different oxidative processes inorder to understand the role of .OH radicals. One of the disadvantages of semiconductor slurry based photocatalytic system is the high degree of recombination between photogenerated charge carriers within the individual particles. This is usually overcome by scavenging electrons with a sacrificial electron acceptor such as dissolved oxygen so that the holes can participate in the oxidation of the organics. Therefore scavenging of electrons becomes a limiting factor in controlling the photocatalytic oxidation of organics.
The use of an anodic bias to separate the charge carriers obviates the need for oxygen as an electron scavenger and makes it possible to carry out the photocatalytic reaction in anaerobic conditions. The electrochemically assisted  photocatalysis also provides an unique opportunity to separate the anodic and cathodic processes and thereby isolate the various reactions occurring in photocatalytic systems.

Issuesphotocatalysis

  • To understand the  role of hydroxyl radical in the oxidative transformation of organic compounds that are  considered toxic in the environment
  • To develop new methodologies  (e.g., combining sonolysis and photocatalysis) to improve the rate of degradation and control the fate of reaction pathways leading to mineralization.
  • To develop smart materials that can simulaneously detect and destroy organic contaminants ( e.g. ZnO based smart materials)

 

Our Research Focus

  • Carry out selective hydroxyl radical  and elctron transfer induced oxidation using radiolytic  methods and identify reaction intermediates using pulse radiolysis
  • Iidentify reaction products and computation calculations to establish reaction pathways.
  • Comapre and contrast the merits of photocatalysis, sonolysis and radiolysis  for their effectiveness in the mineralization of organic contaminants and humic substances


Thanks to our collaborators Profs. K. Vinodgopal and Julie Peller; (Indiana Univ. Northwest), Prof. Patricia Morris (Center for Environmental Engineering Science & Technology, Notre Dame), Prof. Kevin O'Shea (Florida International University), Prof. Papa Constantineau (Greece) and Dr. David Kreller (U. Notre Dame), who contribute to the success of our environmental  research.


Progress So Far

  • Demonstrated the effectiveness of Electrochemically Assisted Photocatalysis
  • Introduced the concept of visible light induced degradation of textile azo dyes on titania surface
  • Established the role of hydroxyl radical and direct electron transfer in TiO2 assisted photocatalysts
  • Demonstrated the synergy of combining sonolysis and photocatalysis and minimize the toxic impact of intermediates
  • Introduced the concept of "Sense & Shoot" approach for simultaneous detection and degradtion of organic contaminants using semiconductor nanostructures

 

Important Contributions with  highest citations

  1. Stafford, U., Gray, K. A. and Kamat, P. V., Radiolytic and TiO2 assisted photocatalytic degradation of 4-chlorophenol.  A comparative study. J. Phys. Chem., 1994, 98, 6343-6351.
  2. Vinodgopal, K. and Kamat, P. V., Electrochemically assisted photocatalysis using nanocrystalline semiconductor films. Solar Energy Mater. Solar Cells, 1995, 38, 401-410.
  3. Vinodgopal, K. and Kamat, P. V., Enhanced rates of photocatalytic degradation of an azo dye using SnO2/TiO2 coupled semiconductor thin films. Environ. Sci. Technol., 1995, 29, 841-845.
  4. Vinodgopal, K., Wynkoop, D. and Kamat, P. V., Environmental Photochemistry on semiconductor surfaces: A photosensitization approach for the degradation of a textile azo dye, Acid Orange 7. Environ. Sci. Technol., 1996, 30, 1660-1666.
  5. Peller, J., Wiest, O. and Kamat, P. V., Synergy of  combining sonolysis and photocatalysis in the degradation and mineralization of chlorinated aromatic compounds. Environ. Sci. Technol., 2003, 37, 1926-1932.
  6.  Kamat, P. V., Huehn, R. and Nicolaescu, R., A Sense and Shoot Approach for Photocatalytic Degradation of Organic Contaminants in Water. J. Phys. Chem. B, 2002, 106, 788-794.
  7. Nicolaescu, R., Wiest, O. and Kamat, P. V., Radical induced oxidative transformations of Quinoline. J. Phys. Chem. A, 2003, 107, 427-433.
  8. Peller, J., Wiest, O. and Kamat, P. V., Hydroxyl Radical's Role in the Remediation of a Common Herbicide, 2,4-Dichlorophenoxyacetic acid (2,4-D). J. Phys. Chem. B, 2004, 108, 10925-10933 (Feature Article).

In Popular Press

 Daily InScights: Fighting Toxins With Radiation
Science Daily:Mixing Radiation, Minerals, Toxic Waste could be cleanup boon
sense


Also featuredin Nature Science Update, Scientific American and ALCHEMIST


Cited as one of the major developments of the year 2001 in the National Nanotechnolgy Initiative and its Implementation Plan (see page 29 and 41) submitted by National Science and Technology Council, Committee on Technology Subcommittee on Nanoscale Science, Engineering and Technology. Detailed Technical Report Associated with the Supplemental Report to the President's FY 2003 Budget

jpcacover Featured in December 16, 2004 issue of the Journal of Physical Chemistry A
Peller, J., Wiest, O. and Kamat, P. V., Hydroxyl Radical's Role in the Remediation of a Common Herbicide, 2,4-Dichlorophenoxyacetic acid (2,4-D) -Feature Article. J. Phys. Chem. A, 2004, 108, 10925-10933.
cover pageFeatured in March 31 issue of the The Journal of Physical Chemistry A, 2005, issue 12
Mechanistic Pathways of the Hydroxyl Radical Reactions of Quinoline. 1. Identification, Distribution, and Yields of Hydroxylated Products A. Roxana Nicolaescu, Olaf Wiest, and Prashant V. Kamat J. Phys. Chem. A, 109, 2005, 2822 - 2828
Mechanistic Pathways of the Hydroxyl Radical Reactions of Quinoline. 2. Computational Analysis of Hydroxyl Radical Attack at C Atoms A. Roxana Nicolaescu, Olaf Wiest, and Prashant V. Kamat J. Phys. Chem. A, 109, 2005, 2829 - 2835
 

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