Engineering titania nanostructure to tune and improve its photocatalytic activity
- aDepartment of Chemistry, University of Pennsylvania, Philadelphia, PA 19104;
- bDepartment of Chemical Engineering, Stanford University, Stanford, CA 94305;
- cSUNCAT Center for Interface Science and Catalysis, Stanford University, Stanford, CA 94305;
- dDepartment of Chemical and Pharmaceutical Sciences, Institute of Chemistry of Organometallic Compounds, National Research Council (CNR), National Interuniversity Consortium of Materials Science and Technology (INSTM), University of Trieste, 34127 Trieste, Italy;
- eDepartment of Chemical and Biological Engineering, Drexel University, Philadelphia, PA 19104;
- fLeibniz-Institut für Katalyse e.V., Universität Rostock, 18059 Rostock, Germany;
- gDepartamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, 11510 Puerto Real, Spain;
- hDepartment of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104
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Edited by Alexis T. Bell, University of California, Berkeley, CA, and approved March 1, 2016 (received for review December 16, 2015)

Significance
This work shows that hole−electron recombination can be controlled by engineering the length of brookite nanorods, and that a variety of organic substrates can be efficiently oxidized as the counterreaction to hydrogen evolution. Both are important steps to developing photocatalysis as a sustainable technology. Electron−hole recombination is a major fundamental limitation in any photocatalytic process. By controlling and reducing it with rod length, we can increase the efficiency of photocatalyzed processes. Also, by utilizing demanding substrates in aqueous media, ethanol, glucose, and glycerol, we make a step toward the photoreforming of more plentiful feedstocks such as, or derived from, biomass.
Abstract
Photocatalytic pathways could prove crucial to the sustainable production of fuels and chemicals required for a carbon-neutral society. Electron−hole recombination is a critical problem that has, so far, limited the efficiency of the most promising photocatalytic materials. Here, we show the efficacy of anisotropy in improving charge separation and thereby boosting the activity of a titania (TiO2) photocatalytic system. Specifically, we show that H2 production in uniform, one-dimensional brookite titania nanorods is highly enhanced by engineering their length. By using complimentary characterization techniques to separately probe excited electrons and holes, we link the high observed reaction rates to the anisotropic structure, which favors efficient carrier utilization. Quantum yield values for hydrogen production from ethanol, glycerol, and glucose as high as 65%, 35%, and 6%, respectively, demonstrate the promise and generality of this approach for improving the photoactivity of semiconducting nanostructures for a wide range of reacting systems.
Footnotes
- ↵1To whom correspondence should be addressed. Email: cbmurray{at}sas.upenn.edu.
Author contributions: M.C., T.M., P.F., and C.B.M. designed research; M.C., T.M., S.Y.S., J.B.P., J.J.D.J., V.V.T.D.-N., I.S.M., J.A.S., M.-M.P., T.R.G., and Y.L. performed research; M.C., T.M., S.Y.S., J.B.P., I.S.M., and J.A.S. wrote the paper; J.B.B. supervised the ultrafast spectroscopy part; A.B. supervised the paramagnetic spectroscopy part; and P.F. and C.B.M. supervised the overall project.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1524806113/-/DCSupplemental.