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Photocatalytic Conversion of Cellulosic Biomass into Gaseous Fuels

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<>Project Goals

The goal of this project is to test and develop novel materials for photocatalytic conversion of cellulosic biomass into gaseous fuels. This reaction converts abundant photochemical energy (sunlight) and residues from the forest and food industries (wheat straw and wood chips) into usable fuels, incl. hydrogen, and potentially methane and ethane. <>Impact of Research

Work Tasks Completed:  Cuprous oxide (Cu₂O) nanocrystals, cupric oxide (CuO) nanocrystals, vanadium oxide (V₂O₅) nanoribbons, and copper selenide (CuSe) nanocrystals were synthesized and tested for photocatalytic activity, using methanol as a cellulose model.

Results:  1. Neither Cu₂O nanocrystals or CuO nanocrystals were found to have photocatalytic activity for methanol conversion.  2. Visible illumination (l>400 nm) in aqueous methanol solution photoconverts a red V₂O₅ gel into a green VO₂ gel. The process is accompanied by a shift of the absorption onset from 612 nm (Eg=2.03eV) to 486 nm (Eg=2.55eV), consistent with the bandgaps of the two materials. High resolution TEMs and selective area electron diffraction (SAED) data show that the crystalline structure of the V₂O₅ gel is retained upon reduction. Under visible irradiation (l>400 nm) VO₂ produces small quantities of hydrogen from aqueous solutions of glucose.  After attachment of colloidal Pt nanoparticles, H₂ evolution proceeds catalytically with a quantum efficiency of 1.00-1.69% (at 440 nm). The higher activity of VO₂-Pt is due to the reduction of the H₂ evolution overpotential from -1.064V to -0.979V. From the photocurrent onset potential, the VO₂ conduction band edge is located at –0.12 V (NHE) at pH=3, just below the proton reduction potential. One manuscript is in preparation.  3. CuSe nanocrystals were found to evolve H₂ from aqueous methanol when irradiated with UV light. The potential of this material is being evaluated. <>Impact on Career

1. I presented the results on VO₂ at the Fall 2010 ACS meeting in Boston, as part of a talk entitled: Making Fuel from Sunshine: Inorganic Nanomaterials for Photocatalytic Hydrogen Production.  2. I am currently being evaluated for promotion to full professor.  No publication has resulted from this grant yet. <>Impact on Students

1. The work on V₂O₅/VO₂ is part of a dissertation for F. Andrew Frame, who will graduate later this year with a Ph.D. in chemistry.  2. The work on Cu₂Se will be integrated into the M.S. thesis of Sarah Gee, who will graduate early next year with a M.S. degree in chemistry.