Date of Report: October 15, 2009

EPA Agreement Number: X-83254101-1

Center: Center for Environmental and Energy Research (CEER)

Project Title: Nanoscale Layered Photocatalysts

Investigator: S.T. Misture

Institution of PI: Alfred University

Research Category: Congressionally Mandated Center

Project Period: October 1, 2008 - September 30, 2010

Objective of Research: The Aurivillius phases will host the active Ti and Nb cations and the local environment around these cations can be varied by substitutions onto the perovskite A sites. Therefore, the objectives of the study are threefold. Firstly, the systematic variation of Nb-O and Ti-O bond lengths in Bi₂Sr_2-xA_xNb₂TiO₁₂ (A = Ca, Ba, X = 0, 0.5, 1) and Bi₂Ln₂Ti₃O₁₂ (Ln = lanthanide) will be linked to catalytic activity, then the study will progress to a brief investigation of ferroelectric domain effects on charge recombination. The latter is not yet understood, but holds great promise to improve activity by separating the electron-hole pair using the internal electric field of the ferroelectric domains. Finally, the effects of dilute transition metal doping, which move the band gap into the visible region in TiO₂, will be linked to activity in the Aurivillius phases.

Progress Summary/Accomplishments:

The student who is working on the project, Victoria Knox, started on the project in January 2009. She has thus far studied the following linkages:

• Effects of A-site cations on band gap. Here we have discovered that there exists a substantial shift in band gap (up to ~0.5eV) with the size of the A-site cation.
• Effects of Fe, Nb, Cr on band gap, where we also see a significant shift, presumably as a result of the dilute doping and charge compensation that affects the electron energy structures. These results are unique and we hope to work towards a better understanding of these subtle changes and their effects on the electron energy structures.
• Effects of ion-exchanging the Bi₂O₂ layers with H⁺. Here we have found that two things occur: large shifts in band gap, as might be expected because of the large change in chemistry; and exfoliation of the crystals into sheet-like structures that have substantially increased surface areas. Increased surface area is expected to increase the efficiency because of larger active areas for reaction. We have shown that the surface area can increase by factors of 5 or even 10 times because of the transition from solid grains to the sheet-like structures that resemble a “deck of cards” architecture.
• Synthesized a series of ferroelectric compounds for evaluation of the effects of internal electric field on the catalytic behaviors.

Further, the student has worked towards more accurate means of measuring the photocatalytic activity for two reactions, methylene blue decomposition, and then for water splitting.

Publications/Presentations for this project year:

None to date, however, we have abstracts submitted for the upcoming Materials Science and Technology conference in Pittsburgh, PA, October 2009.

Future Activities:

Future work will center on:

1. Finalizing the catalytic measurements, to allow quantitative linkages of the chemistry to the structures to the activities.
2. Further study of the ion-exchange process to evaluate the final products. In particular, we are interested in understanding the partially disordered crystal structures that are apparent after the ion-exchange process.
3. Capturing the mechanisms and linking each to the catalytic activity. This will likely involve three individual publications that focus on each of the objectives listed above.

Supplemental Key Words: photocatalyst, hydrogen production

Relevant Web Sites: http://ceer.alfred.edu