Research paperWavelength dependence of the efficiency of photocatalytic processes for water treatment

- Novel methodology for evaluation of action spectra using monochromatic LED sources.
- TiO2 and Fe-citrate action spectra for methanol oxidation and E. coli inactivation.
- Quantitative correlation between photonic efficiency and absorption spectrum.
- Higher energy efficiency at 365 nm at for TiO2 and near visible for Fe-citrate.
- Prediction of process efficiency under solar light successfully validated.

The main objective of this work is to present a novel approach to evaluate quantitatively the action spectra and energy efficiency for chemical oxidation and bacterial inactivation of photocatalytic processes using monochromatic LED sources. Two different catalysts with different absorption spectra (TiO2 and iron citrate complex) were used. In all cases, it was confirmed a direct relationship between the absorption spectrum of the catalyst and the spectral dependence of the photonic efficiency. The best alternative for TiO2 processes in terms of energy consumption when using artificial lighting is the use of 365 nm. In contrast, for iron complexes it seems more economically feasible the use of longer wavelengths close to the visible range, because the lower absorption of the complex is counterbalanced by the higher energy efficiency of the LED devices. This can be obviously extrapolated to the use of sunlight, where the use of iron-based photocatalytic processes can harvest a higher fraction of the available light. Predictions of the process efficiency under solar irradiation based on the action spectra determined with LED at laboratory scale have been successfully validated by experimental data. The methodology proposed in this work could be easily extrapolated to other wavelength ranges required by novel catalysts or efficient short wavelength monochromatic LED sources available in the future.

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